BioMed Research International
Volume 2015 (2015), Article ID 257139, 14 pages
http://dx.doi.org/10.1155/2015/257139

Review Article

Neuroprotection in Preterm Infants

R. Berger and S. Söder

Marienhaus Klinikum St. Elisabeth, Department of Obstetrics and Gynecology, 56564 Neuwied, Germany

Received 14 October 2014; Accepted 22 December 2014

Academic Editor: Stefan Rimbach

Copyright © 2015 R. Berger and S. Söder. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Preterm infants born before the 30th week of pregnancy are especially at risk of perinatal brain damage which is usually a result of cerebral ischemia or an ascending intrauterine infection. Prevention of preterm birth and early intervention given signs of imminent intrauterine infection can reduce the incidence of perinatal cerebral injury. It has been shown that administering magnesium intravenously to women at imminent risk of a preterm birth leads to a significant reduction in the likelihood of the infant developing cerebral palsy and motor skill dysfunction. It has also been demonstrated that delayed clamping of the umbilical cord after birth reduces the rate of brain hemorrhage among preterm infants by up to 50%. In addition, mesenchymal stem cells seem to have significant neuroprotective potential in animal experiments, as they increase the rate of regeneration of the damaged cerebral area. Clinical tests of these types of therapeutic intervention measures appear to be imminent. In the last trimester of pregnancy, the serum concentrations of estradiol and progesterone increase significantly. Preterm infants are removed abruptly from this estradiol and progesterone rich environment. It has been demonstrated in animal experiments that estradiol and progesterone protect the immature brain from hypoxic-ischemic lesions. However, this neuroprotective strategy has unfortunately not yet been subject to sufficient clinical investigation.

1. Introduction

The prevention of preterm birth represents one of the most significant challenges to the field of obstetrics in the 21st century. Preterm infants born before the 30th week of pregnancy are especially at risk of prenatal mortality and morbidity [1]. Damage to the immature brain is one of the central concerns. Typical lesions include peri-/intraventricular hemorrhages (PIVH) and periventricular leukomalacia (PVL). Both of these complications specifically affect the pyramidal tracts of the lower extremities. The resulting damage leads to spastic cerebral palsy of the legs [2].

2. Peri-Intraventricular Hemorrhage and Periventricular Leukomalacia

PIVH originates in the vascular bed of the germinal matrix, an area of the brain that almost completely disappears as the fetus matures [3–5] (Figure 1). Blood vessels in this area of the brain burst very easily [6, 7]. Pre- and postpartal fluctuations of the cerebral blood flow can thus lead to the rupture of these blood vessels and induce PIVH [8–12]. The extent of the hemorrhage can be increased by an alteration in the thrombocyte aggregation and the coagulation system [13–15]. Such hemorrhages have been shown to lead to the destruction of the germinal matrix, periventricular hemorrhagic infarction of the white brain matter, and hydrocephalus [2].

Figure 1: Germinal matrix, the predilection site for peri-intraventricular brain hemorrhage among immature fetuses [2].

PVL most commonly leads to damage of the radiatio occipitalis on the trigonum of the lateral cerebral ventricles and the white matter around the foramen of Monroe [16, 17] (Figure 2). This involves axons and oligodendrocytes, especially those that are in the early stage of development. Activated microglia then enter the lesion and strip away the necrotic tissue. Subsequently, small cysts form, which can then be identified sonographically [18–20]. The lack of myelinisation as a result of damaged oligodendrocytes and an expansion of the lateral cerebral ventricle are then the consequence [21–24].

Figure 2: The left arrow marks an intraventricular hemorrhage (PIVH). The right arrow marks an area of periventricular leukomalacia (PVL) [25].

PVL can be caused by both cerebral ischemia and infection. During the genesis and the development of the cerebral vascular bed, vascular watersheds develop in the radiatio occipitalis on the trigonum of the lateral cerebral ventricles and the white matter around the foramen of Monroe [26–28]. The vasodilatation capacity and thus the ability to increase blood circulation during and after arterial hypotension appear to be very restricted in these areas of the brain [29]. After the 32nd week of pregnancy, the vascularisation of these predilection sites increases significantly and the likelihood of PVL decreases.

Ascending intrauterine infections can also induce PVL [30–32]. An ascending infection causes a so-called “fetal inflammatory response syndrome” [33]. The release of endotoxins associated with this syndrome leads to serious impediment of the fetal cardiovascular system regulation, resulting in a reduction in cerebral blood circulation and thus in ischemic lesions in the white brain matter [34, 35]. Cytokines, glutamate, and free radicals are also able to directly damage oligodendrocytes in the early stages of development and thus also disrupt the subsequent myelinisation process, which can significantly affect the development of an infant’s motor skills [36–38] (Figure 3).

(a)

(b)

Figure 3: (a) Oligodendrocyte precursor cells between the 3rd and 9th day in culture (d3–d9). The y-axis shows the number of cells per field of vision. The administration of INF- (100 U/mL) and TNF- (100 ng/mL) severely reduced the number of surviving cells (). Western blot was conducted for MBP, MAG, and CNP. On the 12th day in culture pronounced expression of MBP, MAG, and CNP was observed, indicating the differentiation of the oligodendrocyte precursor into the mature cell type. The administration of IFN- and TNF- almost completely inhibits the expression of these proteins [38]. IFN- = interferon gamma; TNF- = tumor necrosis factor-alpha; MBP = myelin-basic protein; MAG = myelin associated protein; CNP = 2′,3′-cyclic nucleotide 3′-phosphodiesterase.

In 2000, Wu and Colford published a meta-analysis of 26 studies on the correlation between chorioamnionitis and infantile cerebral palsy [39]. Their analysis showed a significant correlation with a relative risk of 1.9 (95% CI 1.4–2.5). This data was confirmed by another meta-analysis published in 2010 [40] (Figure 4). Unfortunately, it was shown that the incidence of cerebral palsy could not be reduced by applying antibiotics as soon as chorioamnionitis had been diagnosed. Obviously the pathophysiological processes which led to the damage of the fetal brain were too advanced to be halted by means of therapeutic intervention. More efforts should therefore be undertaken in detecting ascending intrauterine infection very early in pregnancy. Hence, treatment of urinary tract infection by antibiotics has been shown to reduce the rate of preterm delivery [41]. Unfortunately, this effect could not be demonstrated for bacterial vaginosis [42, 43].

Figure 4: Meta-analysis of the association between clinical chorioamnionitis and cerebral palsy [40].

3. Prevention of Preterm Birth and Ascending Intrauterine Infections

Due to the fact that PIVH and PVL are complications which especially affect extreme preterm infants, both can be avoided by preventing the baby from being born preterm. Much evidence has shown that patients who have previously experienced a preterm birth or who develop shortening of the cervix to less than 25 mm before the 24th week of pregnancy benefit from the prescription of progesterone [44–48]. The latter group of patients should receive 200 mg of progesterone daily by vaginal suppositories, whereas women with a history of preterm birth can be treated either with a weekly intramuscular application of 250 mg 17-hydroxyprogesterone caproate or by means of a daily dose of 200 mg progesterone administered vaginally or 100 mg administered orally [44–49]. The use of a cervical cerclage in patients who have previously experienced a preterm birth and develop shortening of the cervix under 25 mm before the 24th week of pregnancy can also significantly reduce the likelihood of preterm birth [50, 51]. Interestingly, the outcome of these patients does not differ no matter whether they got a history indicated or a secondary cerclage. However, the latter procedure can help to avoid unnecessary surgical interventions [52].

Ascending intrauterine infections, which are often observed in patients at risk of preterm birth, seem to significantly increase the risk of fetal brain damage [30]. Bacterial vaginal infections should therefore be consistently treated during pregnancy to prevent the ascension of the infection to the unborn child. With this in mind, it is very interesting to note that progesterone has anti-inflammatory properties. Animal experiments have demonstrated a modulating influence on the gene-activation of COX-2, Connexin-43, TNF-a and IL-1 beta, and Toll-link receptors 2 and 4. The proteins associated with these receptors play a central role in the induction of preterm birth [53, 54]. If the infection has reached the intrauterine environment, it is necessary to consider inducing delivery immediately to prevent any further damage to the infant [39]. Unfortunately we are still lacking sound clinical parameters with which to make adequate medical decisions in this challenging situation.

4. Magnesium

If a preterm birth seems imminent, the infant’s brain should be protected by means of the intravenous application of magnesium [55–57]. Within the last years many experimental studies have been published on the neuroprotective effects of magnesium. During acute cerebral ischemia large amounts of excitotoxic amino acids such as glutamate are released presynaptically. These neurotransmitters activate neuronal NMDA-receptors that operate calcium channels. As a consequence large amounts of calcium ions flow through these channels down an extreme extra-/intracellular concentration gradient, into the cell. Excessive increase in intracellular levels of calcium, so-called calcium overload, leads to cell damage through the activation of proteases, lipases, and endonucleases [58]. Magnesium ion gates the NMDA channels in a voltage-dependent manner and protects the brain from NMDA receptor-mediated injury [59, 60]. Moreover, magnesium suppresses cerebral convulsions and is a well known vasodilator [61, 62]. Both effects are known to be neuroprotective. Finally, magnesium has also been shown to decrease the release of nitric oxide and therefore reduce the postischemic production of oxygen radicals [63].

Magnesium is a substance which has been used for decades in the field of obstetrics as a prophylaxis for eclamptic seizures and tocolysis. In a case-control study which included infants weighing less than 1500 grams whose mothers were treated with magnesium [64] the authors established that children suffering from infantile cerebral palsy were less likely to have been exposed to magnesium sulfate than their healthy matched pairs and deduced from these findings that magnesium sulfate has a positive effect on very-low-birthweight infants. Several subsequent observational studies reported similar findings [65–74]. To address this open question, a series of controlled, randomized studies was initiated which included mothers who had been treated with MgSO₄ for the purposes of fetal neuroprotection [75–78].

In August 2008, Rouse and colleagues published the results of the BEAM (Beneficial Effects of Antenatal Magnesium Sulfate) study, conducted by the Maternal-Fetal Medicine Units Network [79]. The primary outcome of this high quality study on the incidence of infantile cerebral palsy among children whose mothers had been treated with MgSO₄ was the combined occurrence of infantile cerebral palsy (of serious or medium severity) or death. No significant difference in the combined risk levels was identified between the therapy and control groups. When the combined results were disaggregated, given similar mortality rates, a significantly lower rate of infantile cerebral palsy was identified among children whose mothers had been treated with magnesium sulfate (1.9 versus 3.5%). Rouse and colleagues concluded from these results that the application of MgSO₄ leads to a reduction in the incidence of cerebral palsy among very preterm infants [79].

In 2009, a Cochrane Review was published on the topic [55]. The five prospective-randomized studies it covered, which were published between 2002 and 2008, included a total of 6145 children. The effect of magnesium sulfate as a neuroprotective agent was tested on patients at risk of preterm birth before the end of the 37th week of pregnancy. The studies found a significant reduction in the incidence of infantile cerebral palsy (relative risk 0.68; 95% confidence interval 0.54 to 0.87), as well as in the incidence of gross motor skill dysfunction (relative risk 0.61; 95% confidence interval 0.44 to 0.85) among children whose mothers had been treated with magnesium sulfate (Table 1). Doyle and coworkers reevaluated the children from the ACTOMgSO₄ trial, one of the five above mentioned prospective studies, at school age. The effects of magnesium on the rate of cerebral palsy and abnormal motor function were no longer evident at this time. Possibly, additional therapeutic interventions in the control group may have improved the health status of these children [80].

Table 1: Magnesium sulfate for neuroprotection.

Magnesium ()
Control ()
RR, 95% CI

Cerebral palsy
104/3052
154/3093
0.68 (0.54–0.87),

Gross motor skill dysfunction
57/2967
94/3013
0.61 (0.44–0.85),

Infant mortality
443/3052
430/3093
1.04 (0.92–1.17)

Antenatal administration of magnesium sulfate significantly reduced the rate of cerebral palsy and gross motor skill dysfunction among preterm infants. The infant mortality rate remained unchanged [55].

The number of women at risk of preterm birth who need to be treated with MgSO₄ to prevent one case of infantile cerebral palsy (number needed to treat (NNT)) is dependent on the week of pregnancy in which the birth occurs; it is 52 before the 34th week of pregnancy [81] and 29 before the 28th week of pregnancy [82]. In the USA around 2000 cases of infantile cerebral palsy are reported annually. If all women who gave birth before the 34th week of pregnancy were treated with magnesium sulfate, around 660 children per year could be spared from infantile cerebral palsy. The cost of preventing these cases would amount to around $10,291 USD annually [81].

The most commonly reported maternal side-effects of systematic magnesium therapy include thrush, sweating, nausea, vomiting, or skin irritation at the injection site. In addition, a 50% increase in the risk of hypotension and tachycardia was reported (number needed to harm (NNH): 28–30). A higher rate of serious complications such as maternal mortality, cardiac or respiratory arrest, pulmonary edema, respiratory depression, serious postpartal hemorrhage, or increased rate of cesarean sections was not identified.

In the various studies, differing amounts of magnesium were given to patients. The levels ranged from 4 g to almost 50 g of MgSO₄. A statistically significant effect was first apparent above a moderate dosage of 4 g magnesium sulfate. There was no significant difference between the placebo group and children whose mothers received a lower dosage [81]. The total dosage of magnesium administered should be taken into consideration, as controversial results reported by the Mittendorf study are likely to be explained by the high magnesium dosages administered (up to 500 g) [83].

The treatment should begin with a bolus injection of 4–6 g within 30 minutes, followed by maintenance doses of 1-2 g/h for 12 hours. The aim of this procedure is to double the magnesium level in the mother’s serum. If birth does not occur within 12 hours, the administration of magnesium can be restarted at a later point in time if preterm birth again appears imminent.

In an Australian perinatal center, Ow and colleagues investigated the rate of women which can be administered magnesium intravenously under clinical conditions for the purpose of neuroprotection in the event of an imminent preterm birth [84]. Out of 330 women at risk of preterm birth, 132 were given magnesium (132/330, 40%). A total of 74% of all women (142/191) were administered magnesium prior to a preterm birth before the 32nd week of pregnancy.

The administration of high dosages of magnesium in the event of an imminent preterm birth leads to a reduction in the rate of infantile cerebral palsy and gross motor skill dysfunction [56, 85].

5. Delayed Clamping of the Umbilical Cord

An infant’s blood volume at birth can be significantly influenced by the time at which the umbilical cord is clamped [86]. In 1988 Hofmeyr and colleagues published a randomized study investigating the outcome among preterm infants dependent upon the time blood flow in the umbilical cord was interrupted [87]. When the umbilical cord was clamped one minute after birth, the brain hemorrhage rate was 35%, compared to 77% when it was clamped immediately [87]. This effect is believed to be caused by the reduced risk of hypoperfusion and improved oxygen delivery to the brain [88]. Delayed clamping of the umbilical cord could also lead to an increase in the concentration of coagulation factors and in the number of stem cells, which have been shown to have neuroprotective effects in animal experiments [89, 90].

Several studies published since 1980 have shown that delayed clamping of the umbilical cord can reduce the need for blood and fluid transfusion, as well as the rate of brain hemorrhages and sepsis among preterm infants [87, 91–94]. However, delayed clamping of the umbilical cord has also been associated with polycythaemia, hyperbilirubinemia, and an increased need for phototherapy [91–94]. To clarify these issues, a prospective randomized study was initiated in 2006. Seventy-two women who experienced a preterm birth before the 32nd week of pregnancy were divided into two groups in which the umbilical cord was clamped either early or late (30–45 s after birth). A significant reduction in the rate of brain hemorrhages and sepsis among the infants whose umbilical cords were clamped later was observed. Other variables including bilirubin and the amount of blood transfused were not affected [94] (Table 2). On the basis of this data, the ACOG recommends delayed clamping of the umbilical cord among all preterm infants born before the 32nd week of pregnancy [95]. The infant should remain at the level of the placenta during this time. The incidence of brain hemorrhage can thus be reduced by up to 50%. It is likely that repeated milking the umbilical cord (four times) leads to similar results [96].

Table 2: Neuroprotection by delayed clamping of the umbilical cord.

ICC (), (%)
DCC (), (%)

Odds ratio
95% CI

IVH

    Total
13 (36)
5 (14)
0.03
3.5
1.1–11

    Grade 1
4 (11)
3 (8)

    Grade 2
8 (22)
2 (6)

    Grade 4
1 (3)
0 (0)

Sepsis
8 (22)
1 (3)
0.03
0.1
0.01–0.84

Among infants born before the 32nd week of pregnancy, delayed clamping of the umbilical cord (DCC: delayed cord clamping 30–45 s) reduced the rate of intraventricular brain hemorrhage (IHV) and neonatal sepsis significantly when compared to immediate severance of the cord (ICC: immediate cord clamping 5–10 s) [94].

6. Experimental Approaches

In order to understand the effect of several other treatment measures which have been predominantly tested in animal experiments, it is important to comprehend the pathophysiological processes occurring during and after an injury. The initial damage caused by an injury is normally the result of insufficient metabolic supply. This leads to a loss of membrane potential, a massive release of excitatory neurotransmitters, and a very strong influx of calcium, which in turn activates proteases, endonucleases, and lipase and thus induces successive cell death [58]. However, significant cell damage can also occur in the early recovery phase, although oxidative phosphorylation has increased [97]. Electroencephalogram is normally suppressed and the cerebral blood flow is reduced in this phase, but oxygenation of the brain usually remains within physiological limits [98, 99]. After approximately 6–15 hours, seizures occur, along with a renewed alteration of the mitochondrial metabolism, cell edema, and subsequent secondary cerebral lesions [97, 98, 100]. Impairment of subsequent neurologic development is strongly affected by this phase [101]. Such secondary damage is often followed by a phase involving tertiary damage as a result of a lack of growth factors, synaptic input, and immigrating neuronal and glial stem cells [102–105].

7. Stem Cells

This is the point at which therapy with so-called stem cells becomes relevant. Stem cells can be obtained from many different types of tissue. Depending on their origin, they are referred to as neuronal, mesenchymal, or hematopoietic stem cells, and so forth. Mesenchymal stem cells are currently considered to have the most potential for clinical applications. They can be grown easily from bone marrow and from extraembryonic tissue such as the placenta, Wharton’s jelly, and umbilical cord stroma [106–108].

Originally it was believed that the applied stem cells multiplied in the damaged region, where they differentiated and replaced the destroyed tissue. However, it quickly became clear that this could not be the way the neuroprotective mechanism worked. The low number of stem cells growing and the insufficient rate at which they differentiate in no way explained the significant neuronal improvements observed. Recent animal experiments have shown that the application of stem cells leads to a significantly improved outcome following hypoxic-ischemic damage [109–111]. This neuroprotective effect has recently also been demonstrated in preterm sheep fetuses [112] (Figure 5). The stem cells applied to damaged tissue appear to release numerous factors in the damaged area which induce the formation and migration of neuronal stem cells, encourage the expansion of dendrites and axons, and suppress postischemic inflammation [111, 113] (Figure 6).

Figure 5: Hypoxic-ischemic brain damage was induced in fetal sheep on the 105th day of gestation (term is at 150 days) by occluding the umbilical cord for 25 minutes. One hour after the injury had been inflicted, the animals in study group were given i.v. 3.5 × 10⁶ mesenchymal stem cells (MSCs), whereas those in the control group received saline (SAL). In sham-operated animals (Sham) occlusion was not carried out. (a) Diffusion Tensor Images (DTI) measured using magnetic resonance tomography (MRI) presented as fractional anisotropy (FA). Regions of interest SCWM (subcortical white matter) and hippocampus. (b) Mesenchymal stem cells reduce brain damage in the SCWM, measured as FA. Means ± 95% CI () are depicted. Dots show each measurement per animal. (c) Representative image of an aEEG trace from an animal of the control group with hypoxic-ischemic brain damage. The arrows mark seizures. (d) The administration of MSC significantly reduces the number of seizures () (; ) [112].

Figure 6: Neuroregeneration using mesenchymal stem cells (MSCs) following neonatal hypoxia-ischemia. After transplantation into an ischemically damaged area of the brain mesenchymal stem cells respond to the environment by producing growth and differentiation factors. These factors stimulate proliferation and differentiation of neural stem cells (NPCs) and stimulate repair processes. Upon transplantation of MSCs, microglia are activated and modulate the inflammatory response of the brain contributing to neurorepair [113].

Via transmitters, mesenchymal stem cells modulate numerous signaling cascades during apoptosis, neurogenesis, angiogenesis, and synaptogenesis. Increased expressions of fibroblast growth factor-2, epidermal growth factor, glial cell line-derived neurotrophic factor, and sonic hedgehog have been observed [114]. These factors play a central role in the proliferation of progenitor cells, as well as in neurogenesis and cell differentiation [115–120] (Figure 6). Mesenchymal stem cells stimulate the proliferation of progenitor cells in the dentate gyrus. These progenitor cells move into the damaged area and differentiate under the influence of mesenchymal stem cells into astrocytes, oligodendrocytes, and neurons [110, 121]. Additionally, stem cells induce the formation of neuropilin-1 and 2, neuregulin-1, and EphrinB2, messengers which play an important role in the regulation of axonal growth, synapse formation, and the integration of the neuronal network [114, 122]. Mesenchymal stem cells support the proliferation and differentiation of oligodendrocyte-progenitor cells and thus the myelinisation of the newly formed axons [110, 123, 124]. Additionally, mesenchymal stem cells appear to counteract glial scar formation, which hinders the migration of axons and dendrites [125, 126] (Figure 6).

Postischemic inflammation is most commonly caused by microglia, macrophages of the central nervous system, which originate in bone marrow and migrate to the brain during development, where they then differentiate into microglia. When brain damage occurs, these local microglia are activated, and monocytes from peripheral blood also migrate to the trauma site [127, 128]. These so-called M1 microglia release proinflammatory cytokines, oxygen-based free radicals, and neurotoxins and further damage the altered tissue. There is an alternative pathway for the activation of microglia (M2), which has neuroprotective effects and leads to the release of IL-10, insulin growth factor-1, transforming growth factor-β, and other immunomodulating factors [128–130]. The application of mesenchymal stem cells reduces the number of classically activated microglia (M1) and thus also inhibits the release of proinflammatory cytokines [112, 114, 124]. In contrast, the M2 cascade is activated with synthesis of growth factors supporting the regeneration of damaged tissue [131, 132] (Figure 6).

To what extent effects caused by mesenchymal stem cells can also be instigated by exosomes remains to be seen. Exosomes are small membrane vesicles (70–120 nm) which contain lipids, proteins, and RNA and which are secreted by various types of cells. Exosomes obtained from mesenchymal stem cells have been shown to reduce the extent of myocardial damage following ischemia in experiments with adult mice [133].

8. Estradiol and Progesterone

The steroid hormones estradiol and progesterone play a critical role in the growth, differentiation, and function of the reproductive system. However, the peripheral and central nervous system is also affected by these hormones, as shown by the ubiquitous distribution of the relevant receptors [134–137]. Estradiol induces axonal and dendritic growth and promotes the development of synapses as well as the integration of the cerebral cortex [138].

In the third trimester of pregnancy, the maternal serum concentration of estradiol and progesterone increases significantly and can reach up to 100 times its original level [139, 140]. Preterm infants are removed abruptly from this environment. In animal experiments estradiol has been shown to protect the immature fetal brain from hypoxic-ischemic lesions [141–143] (Figure 7). Progesterone has also been shown to have neuroprotective effects [144]. It therefore makes sense to treat preterm infants with estradiol and progesterone after birth [145]. Unfortunately, there is currently a lack of sufficient clinical data to support such treatment [146].

Figure 7: Neuronal cell damage in the cerebral cortex (A1–A5) and hippocampus (CA 1/2, CA3, DG) in neonatal rats following hypoxia-ischemia. The animals in the study group were treated with estradiol both before and after injury, whereas animals of the control group received NaCl. Neuronal cell damage was significantly reduced in the cerebral cortex as well as in the hippocampus after application of estradiol. Neuronal cell damage was evaluated using a scoring system (1 = 0%–4%; 2 = 5%–49%; 3 = 50%–94%; 4 = 95%–99%; 5 = 100% damaged neurons). Means ± SD (; ) [143].

The neuroprotective effects of estradiol can be imparted receptor-dependent (genomic and nongenomic) or receptor-independent [147–149]. The estrogen-receptor independent effects are the result of the direct antioxidative properties of estradiol and of the interaction with potential binding sites on the neuronal membrane receptors [147]. These membrane receptors can modulate the neurotransmission and excitability of the neuronal membrane [150, 151]. The classic receptor-mediated effects on neuronal gene transcription cause the growth of axons and dendrites, the creation of synapses, the expression of neurotropic factors, and increased acetylcholine synthesis. In the central nervous system, the estrogen receptor subtypes und have been shown to be differently distributed and regulated [134, 135]. Both receptors have the same affinity for estradiol [152], but differing levels of affinity for “estrogen-response-elements,” and have therefore demonstrated partially different gene activation patterns [153]. Two effects of the estradiol receptor- are responsible for the antiapoptotic properties. The activation of the receptor leads to a rapid induction of the insulin-like growth factor 1 (IGF-1) receptor pathway and the associated signal cascade [154]. IGF-1 has been shown to have neuroprotective capacity [155]. In addition, 17β-estradiol inhibits the caspase-pathway which plays a key role in apoptosis [156].

The neuroprotective effects of progesterone are also mediated by various mechanisms. Progesterone reduces postischemic cellular edema by maintaining the integrity of the blood-brain barrier. Increased expressions of claudin5 and occludin1 have been observed in connection with this process, both of which are proteins that play an important role in the creation of tight junctions. In contrast, it has been shown that the expression of MMP-3 and MMP-9 is reduced. The latter is involved in extracellular tissue degradation [157, 158]. Additionally, progesterone inhibits postischemic apoptosis and induces the release of the growth factor BNDF, as has been demonstrated by investigations using the TUNEL assay and caspase 3 [159]. Progesterone suppresses postischemic inflammation by reducing the expression of IL-1β, TNF-α, IL 6, COX-2, and ICAM-1 [146, 149–151]. It also reduces the expression of TGF-β2, VCAM-1, CD68, and Iba1 [160–162], factors which play a role in postischemic inflammation. The inducible form of NO-synthase is inhibited by progesterone [163], while the levels of superoxide dismutase, catalase, and glutathione peroxidase in tissue are increased [164]. The administration of progesterone also leads to the increased release of GAP43 and synaptophysin, both of which are markers for synaptogenesis [165]. However, one study including experiments with rats showed an increase in hypoxic-ischemic brain damage following the administration of progesterone on the 7th and 14th day of life, but not on the 21st day [166].

Many more neuroprotective strategies have been investigated in animal experiments. However, a detailed discussion of all of these strategies is outside the scope of this review. We would like to invite interested readers to refer to the relevant literature.

Condensation

Clinical and experimental strategies to protect the immature brain from ischemic and/or infectious injury are reviewed.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

References

Neonatal data from the German federal states (BQS Bundesauswertung 2008, Datensatzversion 16/1 2008 11.0. Datenbankstand 15.03.2009. 658.200 Datensätze)

J. J. Volpe, Neurology of the Newborn, WB Saunders, 1995.

G. Hambleton and J. S. Wigglesworth, “Origin of intraventricular haemorrhage in the preterm infant,” Archives of Disease in Childhood, vol. 51, no. 9, pp. 651–659, 1976.

D. M. Moody, W. R. Brown, V. R. Challa, and S. M. Block, “Alkaline phosphatase histochemical staining in the study of germinal matrix hemorrhage and brain vascular morphology in a very-low-birth-weight neonate,” Pediatric Research, vol. 35, no. 4, pp. 424–430, 1994.

Y. Nakamura, T. Okudera, S. Fukuda, and T. Hashimoto, “Germinal matrix hemorrhage of venous origin in preterm neonates,” Human Pathology, vol. 21, no. 10, pp. 1059–1062, 1990.

K. C. K. Kuban and F. H. Gilles, “Human telencephalic angiogenesis,” Annals of Neurology, vol. 17, no. 6, pp. 539–548, 1985.

K. E. Pape and Wigglesworth, Haemorrhage, Ischemia and the Perinatal Brain, J. B. Lippincott, Philadelphia, Pa, USA, 1979.

M. Funato, H. Tamai, K. Noma et al., “Clinical events in association with timing of intraventricular hemorrhage in preterm infants,” The Journal of Pediatrics, vol. 121, no. 4, pp. 614–619, 1992.

R. N. Goldberg, D. Chung, S. L. Goldman, and E. Bancalari, “The association of rapid volume expansion and intraventricular hemorrhage in the preterm infant,” The Journal of Pediatrics, vol. 96, no. 6, pp. 1060–1063, 1980.

A. Jensen, V. Klingmuller, W. Kunzel, and S. Sefkow, “The risk of brain haemorrhage in preterms- and in mature newborns-infants,” Geburtshilfe und Frauenheilkunde, vol. 52, no. 1, pp. 6–20, 1992.

D. W. A. Milligan, “Failure of autoregulation and intraventricular haemorrhage in preterm infants,” The Lancet, vol. 1, no. 8174, pp. 896–898, 1980.

R. Berger, S. Bender, S. Sefkow, V. Klingmüller, W. Künzel, and A. Jensen, “Peri/intraventricular haemorrhage: a cranial ultrasound study on 5286 neonates,” European Journal of Obstetrics Gynecology and Reproductive Biology, vol. 75, no. 2, pp. 191–203, 1997.

M. Amato, J. C. Fauchere, and U. Hermann Jr., “Coagulation abnormalities in low birth weight infants with peri-intraventricular hemorrhage,” Neuropediatrics, vol. 19, no. 3, pp. 154–157, 1988.

B. A. Lupton, A. Hill, M. F. Whitfield, C. J. Carter, L. D. Wadsworth, and E. H. Roland, “Reduced platelet count as a risk factor for intraventricular hemorrhage,” The American Journal of Diseases of Children, vol. 142, no. 11, pp. 1222–1224, 1988.

A. Shirahata, T. Nakamura, M. Shimono, M. Kaneko, and S. Tanaka, “Blood coagulation findings and the efficacy of factor XIII concentrate in premature infants with intracranial hemorrhages,” Thrombosis Research, vol. 57, no. 5, pp. 755–763, 1990.

J. C. Larroche, Developmental Pathology of the Neonate, Excerpta Medica, New York, NY, USA, 1997.

M. G. Norman, “Perinatal brain damage,” Perspectives in Pediatric Pathology, vol. 4, pp. 41–92, 1978.

L. S. de Vries, J. S. Wigglesworth, R. Regev, and L. M. S. Dubowitz, “Evolution of periventricular leukomalacia during the neonatal period and infancy: correlation of imaging and postmortem findings,” Early Human Development, vol. 17, no. 2-3, pp. 205–219, 1988.

P. L. Hope, S. J. Gould, S. Howard, P. A. Hamilton, A. M. L. Costello, and E. O. R. Reynolds, “Precision of ultrasound diagnosis of pathologically verified lesions in the brains of very preterm infants,” Developmental Medicine & Child Neurology, vol. 30, no. 4, pp. 457–471, 1988.

N. Paneth, R. Rudelli, W. Monte et al., “White matter necrosis in very low birth weight infants: neuropathologic and ultrasonographic findings in infants surviving six days or longer,” The Journal of Pediatrics, vol. 116, no. 6, pp. 975–984, 1990.

M. Dambska, M. Laure-Kamionowska, and B. Schmidt-Sidor, “Early and late neuropathological changes in perinatal white matter damage,” Journal of Child Neurology, vol. 4, no. 4, pp. 291–298, 1989.

S. M. De la Monte, F. I. Hsu, E. T. Hedley-Whyte, and W. Kupsky, “Morphometric analysis of the human infant brain: effects of intraventricular hemorrhage and periventricular leukomalacia,” Journal of Child Neurology, vol. 5, no. 2, pp. 101–110, 1990.

F. H. Gilles and S. F. Murphy, “Perinatal telencephalic leucoencephalopathy,” Journal of Neurology Neurosurgery and Psychiatry, vol. 32, no. 5, pp. 404–413, 1969.

F. H. Gilles, A. Leviton, and E. C. Dooling, The Developing Human Brain: Growth and Epidemiologic Neuropathology, John Wright PSG, Boston, Mass, USA, 1983.

A. Quasebarth, Periventrikuläre Leukomalazie und Perinatale Telenzephale Leukoenzephalopathie. Ein und dieselbe Krankheit? Eine neuropathologische Studie anhand von 10 Falldarstellungen, Goethe University Frankfurt, Frankfurt, Germany, 2001.

J. L. De Reuck, “Cerebral angioarchitecture and perinatal brain lesions in premature and full-term infants,” Acta Neurologica Scandinavica, vol. 70, no. 6, pp. 391–395, 1984.

L. B. Rorke, “Anatomical features of the developing brain implicated in pathogenesis of hypoxic-ischemic injury,” Brain Pathology, vol. 2, no. 3, pp. 211–221, 1992.

S. Takashima, D. L. Armstrong, and L. E. Becker, “Subcortical leukomalacia. Relationship to development of the cerebral sulcus and its vascular supply,” Archives of Neurology, vol. 35, no. 7, pp. 470–472, 1978.

W. Szymonowicz, A. M. Walker, V. Y. H. Yu, M. L. Stewart, J. Cannata, and L. Cussen, “Regional cerebral blood flow after hemorrhagic hypotension in the preterm, near-term, and newborn lamb,” Pediatric Research, vol. 28, no. 4, pp. 361–366, 1990.

O. Dammann and A. Leviton, “Maternal intrauterine infection, cytokines, and brain damage in the preterm newborn,” Pediatric Research, vol. 42, no. 1, pp. 1–8, 1997.

S. K. Sinha, J. M. Davies, D. G. Sims, and M. L. Chiswick, “Relation between periventricular haemorrhage and ischaemic brain lesions diagnosed by ultrasound in very pre-term infants,” The Lancet, vol. 2, no. 8465, pp. 1154–1156, 1985.

U. Verma, N. Tejani, S. Klein et al., “Obstetric antecedents of intraventricular hemorrhage periventricular leukomalacia in the low-birth-weight neonate,” The American Journal of Obstetrics and Gynecology, vol. 176, no. 2, pp. 275–281, 1997.

R. Romero, Z. A. Savasan, T. Chaiworapongsa et al., “Hematologic profile of the fetus with systemic inflammatory response syndrome,” Journal of Perinatal Medicine, vol. 40, no. 1, pp. 19–32, 2011.

Y. Garnier, A. Coumans, R. Berger, A. Jensen, and T. H. M. Hasaart, “Endotoxemia severely affects circulation during normoxia and asphyxia in immature fetal sheep,” Journal of the Society for Gynecologic Investigation, vol. 8, no. 3, pp. 134–142, 2001.

Y. Garnier, A. B. C. Coumans, A. Jensen, T. H. M. Hasaart, and R. Berger, “Infection-related perinatal brain injury: the pathogenic role of impaired fetal cardiovascular control,” Journal of the Society for Gynecologic Investigation, vol. 10, no. 8, pp. 450–459, 2003.

H. N. Liu, B. I. Giasson, W. E. Mushynski, and G. Almazan, “AMPA receptor-mediated toxicity in oligodendrocyte progenitors involves free radical generation and activation of JNK, calpain and caspase 3,” Journal of Neurochemistry, vol. 82, no. 2, pp. 398–409, 2002.

A. B. C. Coumans, J. Middelanis, Y. Garnier et al., “Intracisternal application of endotoxin enhances the susceptibility to subsequent hypoxic-ischemic brain damage in neonatal rats,” Pediatric Research, vol. 53, no. 5, pp. 770–775, 2003.

B. Feldhaus, I. D. Dietzel, R. Heumann, and R. Berger, “Effects of interferon-γ and tumor necrosis factor-α on survival and differentiation of oligodendrocyte progenitors,” Journal of the Society for Gynecologic Investigation, vol. 11, no. 2, pp. 89–96, 2004.

Y. W. Wu and J. M. Colford, “Chorioamnionitis as a risk factor for cerebral palsy: a meta-analysis,” Journal of the American Medical Association, vol. 284, no. 11, pp. 1417–1424, 2000.

J. G. Shatrov, S. C. Birch, L. T. Lam, J. A. Quinlivan, S. McIntyre, and G. L. Mendz, “Chorioamnionitis and cerebral palsy: a meta-analysis,” Obstetrics & Gynecology, vol. 116, no. 2, part 1, pp. 387–392, 2010.

V. T. Guinto, B. De Guia, M. R. Festin, and T. Dowswell, “Different antibiotic regimens for treating asymptomatic bacteriuria in pregnancy,” Cochrane Database of Aystematic Reviews, vol. 9, Article ID CD007855, 2010.

P. Brocklehurst, A. Gordon, E. Heatley, and S. J. Milan, “Antibiotics for treating bacterial vaginosis in pregnancy,” Cochrane Database of Systematic Reviews, Article ID CD000262, 2013.

D. Subtil, G. Brabant, E. Tilloy et al., “Early clindamycin for bacterial vaginosis in low-risk pregnancy: the PREMEVA1 randomized, multicenter, double-blind, placebo-controlled trial,” American Journal of Obstetrics & Gynecology, vol. 210, no. 1, supplement, p. S3, 2014.

E. B. Da Fonseca, R. E. Bittar, M. H. B. Carvalho, and M. Zugaib, “Prophylactic administration of progesterone by vaginal suppository to reduce the incidence of spontaneous preterm birth in women at increased risk: a randomized placebo-controlled double-blind study,” American Journal of Obstetrics and Gynecology, vol. 188, no. 2, pp. 419–424, 2003.

P. J. Meis, M. Klebanoff, E. Thom et al., “Prevention of recurrent preterm delivery by 17 α-hydroxyprogesterone caproate,” The New England Journal of Medicine, vol. 348, no. 24, pp. 2379–2385, 2003.

P. J. Meis, M. Klebanoff, E. Thom et al., “Correction: Prevention of recurrent preterm delivery by 17 α-hydroxyprogesterone caproate,” The New England Journal of Medicine, vol. 349, no. 13, p. 1299, 2003.

E. B. Fonseca, E. Celik, M. Parra, M. Singh, K. H. Nicolaides, and Fetal Medicine Foundation Second Trimester Screening Group, “Progesterone and the risk of preterm birth among women with a short cervix,” The New England Journal of Medicine, vol. 357, no. 5, pp. 462–469, 2007.

S. S. Hassan, R. Romero, D. Vidyadhari et al., “Vaginal progesterone reduces the rate of preterm birth in women with a sonographic short cervix: a multicenter, randomized, double-blind, placebo-controlled trial,” Ultrasound in Obstetrics and Gynecology, vol. 38, no. 1, pp. 18–31, 2011.

P. Rai, S. Rajaram, N. Goel, R. Ayalur Gopalakrishnan, R. Agarwal, and S. Mehta, “Oral micronized progesterone for prevention of preterm birth,” International Journal of Gynecology and Obstetrics, vol. 104, no. 1, pp. 40–43, 2009.

J. Owen, G. Hankins, J. D. Iams et al., “Multicenter randomized trial of cerclage for preterm birth prevention in high-risk women with shortened midtrimester cervical length,” American Journal of Obstetrics & Gynecology, vol. 201, no. 4, pp. 375.e1–375.e8, 2009.

V. Berghella, T. J. Rafael, J. M. Szychowski, O. A. Rust, and J. Owen, “Cerclage for short cervix on ultrasonography in women with singleton gestations and previous preterm birth: a meta-analysis,” Obstetrics and Gynecology, vol. 117, no. 3, pp. 663–671, 2011.

V. Berghella and A. D. MacKeen, “Cervical length screening with ultrasound-indicated cerclage compared with history-indicated cerclage for prevention of preterm birth: a meta-analysis,” Obstetrics and Gynecology, vol. 118, no. 1, pp. 148–155, 2011.

M. Elovitz and Z. Wang, “Medroxyprogesterone acetate, but not progesterone, protects against inflammation-induced parturition and intrauterine fetal demise,” American Journal of Obstetrics and Gynecology, vol. 190, no. 3, pp. 693–701, 2004.

M. A. Elovitz and C. Mrinalini, “Can medroxyprogesterone acetate alter Toll-like receptor expression in a mouse model of intrauterine inflammation?” The American Journal of Obstetrics and Gynecology, vol. 193, no. 3, part 2, pp. 1149–1155, 2005.

L. W. Doyle, C. A. Crowther, P. Middleton, S. Marret, and D. Rouse, “Magnesium sulphate for women at risk of preterm birth for neuroprotection of the fetus,” Cochrane Database of Systematic Reviews, no. 1, Article ID CD004661, 2009.

American College of Obstetricians and Gynecologists Committee on Obstetric Practice Society for Maternal-Fetal Medicine, “Committee Opinion No. 573: magnesium sulfate use in obstetrics,” Obstetrics and Gynecology, vol. 122, no. 3, pp. 727–728, 2013.

C. T. J. van Velthoven, A. Kavelaars, F. van Bel, and C. J. Heijnen, “Mesenchymal stem cell transplantation changes the gene expression profile of the neonatal ischemic brain,” Brain, Behavior, and Immunity, vol. 25, no. 7, pp. 1342–1348, 2011.

R. Berger and Y. Garnier, “Pathophysiology of perinatal brain damage,” Brain Research Reviews, vol. 30, no. 2, pp. 107–134, 1999.

L. Nowak, P. Bregestovski, P. Ascher, A. Herbet, and A. Prochiantz, “Magnesium gates glutamate-activated channels in mouse central neurones,” Nature, vol. 307, no. 5950, pp. 462–465, 1984.

M. Hallak, J. W. Hotra, and W. J. Kupsky, “Magnesium sulfate protection of fetal rat brain from severe maternal hypoxia,” Obstetrics and Gynecology, vol. 96, no. 1, pp. 124–128, 2000.

A. G. Euser and M. J. Cipolla, “Magnesium sulfate for the treatment of eclampsia: a brief review,” Stroke, vol. 40, no. 4, pp. 1169–1175, 2009.

M. Faragó, C. Szabó, E. Dóra, I. Horváth, and A. G. B. Kovách, “Contractile and endothelium-dependent dilatory responses of cerebral arteries at various extracellular magnesium concentrations,” Journal of Cerebral Blood Flow and Metabolism, vol. 11, no. 1, pp. 161–164, 1991.

Y. Garnier, J. Middelanis, A. Jensen, and R. Berger, “Neuroprotective effects of magnesium on metabolic disturbances in fetal hippocampal slices after oxygen-glucose deprivation: mediation by nitric oxide system,” Journal of the Society for Gynecologic Investigation, vol. 9, no. 2, pp. 86–92, 2002.

K. B. Nelson and J. K. Grether, “Can magnesium sulfate reduce the risk of cerebral palsy in very low birthweight infants?” Pediatrics, vol. 95, no. 2, pp. 263–269, 1995.

J. C. Hauth, R. L. Goldenberg, K. G. Nelson, M. B. DuBard, M. A. Peralta, and F. L. Gaudier, “Reduction of cerebral palsy with maternal MgSO₄ treatment in newborns weighing 500–1000 g,” American Journal of Obstetrics & Gynecology, vol. 172, p. 419, 1995.

D. E. Schendel, C. J. Berg, M. Yeargin-Allsopp, C. A. Boyle, and P. Decoufle, “Prenatal magnesium sulfate exposure and the risk for cerebral palsy or mental retardation among very low-birth-weight children aged 3 to 5 years,” Journal of the American Medical Association, vol. 276, no. 22, pp. 1805–1810, 1996.

T. E. Wiswell, L. J. Graziani, J. L. Caddell, N. Vecchione, C. Stanley, and A. R. Spitzer, “Maternally administered magnesium sulphate protects against early brain injury and long-term adverse neurodevelopmental outcomes in preterm infants: a prospective study,” Pediatric Research, vol. 39, p. 253, 1996.

Y. Matsuda, S. Kouno, Y. Hiroyama et al., “Intrauterine infection, magnesium sulfate exposure and cerebral palsy in infants born between 26 and 30 weeks of gestation,” European Journal of Obstetrics Gynecology and Reproductive Biology, vol. 91, no. 2, pp. 159–164, 2000.

N. Paneth, J. Jetton, J. Pinto-Martin, and M. Susser, “Magnesium sulfate in labor and risk of neonatal brain lesions and cerebral palsy in low birth weight infants. The Neonatal Brain Hemorrhage Study Analysis Group,” Pediatrics, vol. 99, no. 5, p. E1, 1997.

T. M. O'Shea, K. L. Klinepeter, and R. G. Dillard, “Prenatal events and the risk of cerebral palsy in very low birth weight infants,” American Journal of Epidemiology, vol. 147, no. 4, pp. 362–369, 1998.

D. Wilson-Costello, E. Borawski, H. Friedman, R. Redline, A. A. Fanaroff, and M. Hack, “Perinatal correlates of cerebral palsy and other neurologic impairment among very low birth weight children,” Pediatrics, vol. 102, no. 2, pp. 315–322, 1998.

C. A. Boyle, M. Yeargin-Allsopp, D. E. Schendel, P. Holmgreen, and G. P. Oakley, “Tocolytic magnesium sulfate exposure and risk of cerebral palsy among children with birth weights less than 1,750 grams,” American Journal of Epidemiology, vol. 152, no. 2, pp. 120–124, 2000.

J. K. Grether, J. Hoogstrate, E. Walsh-Greene, and K. B. Nelson, “Magnesium sulfate for tocolysis and risk of spastic cerebral palsy in premature children born to women without preeclampsia,” American Journal of Obstetrics and Gynecology, vol. 183, no. 3, pp. 717–725, 2000.

M. M. Costantine, H. Y. How, K. Coppage, R. A. Maxwell, and B. M. Sibai, “Does peripartum infection increase the incidence of cerebral palsy in extremely low birthweight infants?” American Journal of Obstetrics and Gynecology, vol. 196, no. 5, pp. e8–e8, 2007.

R. Mittendorf, J. Dambrosia, P. G. Pryde et al., “Association between the use of antenatal magnesium sulfate in preterm labor and adverse health outcomes in infants,” The American Journal of Obstetrics and Gynecology, vol. 186, no. 6, pp. 1111–1118, 2002.

C. A. Crowther, J. E. Hiller, L. W. Doyle, R. R. Haslam, and Australasian Collaborative Trial of Magnesium Sulphate (ACTOMg SO4) Collaborative Group, “Effect of magnesium sulfate given for neuroprotection before preterm birth: a randomized controlled trial,” The Journal of the American Medical Association, vol. 290, no. 20, pp. 2669–2676, 2003.

Magpie Trial Follow-Up Study Collaborative Group, “The Magpie Trial: a randomised trial comparing magnesium sulphate with placebo for pre-eclampsia. Outcome for children at 18 months,” BJOG: An International Journal of Obstetrics & Gynaecology, vol. 114, no. 3, pp. 289–299, 2007.

S. Marret, L. Marpeau, C. Follet-Bouhamed et al., “Effect of magnesium sulphate on mortality and neurologic morbidity of the very-preterm newborn with two-year neurological outcome: results of the prospective PREMAG trial,” Gynecologie Obstetrique Fertilite, vol. 36, no. 3, pp. 278–288, 2008.

D. J. Rouse, D. G. Hirtz, and E. Thom, “Eunice kennedy shriver NICHD maternal-fetal medicine units network. A randomized, controlled trial of magnesium sulfate for the prevention of cerebral palsy,” The New England Journal of Medicine, vol. 359, no. 9, pp. 895–905, 2008.

L. W. Doyle, P. J. Anderson, R. Haslam, K. J. Lee, C. Crowther, and Australasian Collaborative Trial of Magnesium Sulphate (ACTOMgSO4) Study Group, “School-age outcomes of very preterm infants after antenatal treatment with magnesium sulfate vs placebo,” The Journal of the American Medical Association, vol. 312, no. 11, pp. 1105–1113, 2014.

A. Conde-Agudelo and R. Romero, “Antenatal magnesium sulfate for the prevention of cerebral palsy in preterm infants less than 34 weeks' gestation: a systematic review and metaanalysis,” American Journal of Obstetrics & Gynecology, vol. 200, no. 6, pp. 595–609, 2009.

A. G. Cahill and A. B. Caughey, “Magnesium for neuroprophylaxis: fact or fiction?” The American Journal of Obstetrics and Gynecology, vol. 200, no. 6, pp. 590–594, 2009.

R. Mittendorf, J. Dambrosia, P. G. Pryde et al., “Association between the use of antenatal magnesium sulfate in preterm labor and adverse health outcomes in infants,” American Journal of Obstetrics and Gynecology, vol. 186, no. 6, pp. 1111–1118, 2002.

L. L. Ow, A. Kennedy, E. A. McCarthy, and S. P. Walker, “Feasibility of implementing magnesium sulphate for neuroprotection in a tertiary obstetric unit,” Australian and New Zealand Journal of Obstetrics and Gynaecology, vol. 52, no. 4, pp. 356–360, 2012.

“X4PB. Prädiktion und Prävention der Frühgeb urt,” Der Frauenarzt, vol. 54, pp. 1060–1071, 2013.

A. C. Yao and J. Lind, “Blood flow in the umbilical vessels during the third stage of labor,” Biology of the Neonate, vol. 25, no. 3-4, pp. 186–193, 1974.

G. J. Hofmeyr, K. D. Bolton, D. C. Bowen, and J. J. Govan, “Periventricular/intraventricular haemorrhage and umbilical cord clampings. Findings and hypothesis,” South African Medical Journal, vol. 73, no. 2, pp. 104–106, 1988.

O. Baenziger, F. Stolkin, M. Keel et al., “The influence of the timing of cord clamping on postnatal cerebral oxygenation in preterm neonates: a randomized, controlled trial,” Pediatrics, vol. 119, no. 3, pp. 455–459, 2007.

J. Bonnar, G. P. McNicol, and A. S. Douglas, “The blood coagulation and fibrinolytic systems the newborn and the mother at birth,” Journal of Obstetrics and Gynaecology of the British Commonwealth, vol. 78, no. 4, pp. 355–360, 1971.

D.-H. Park, C. V. Borlongan, A. E. Willing et al., “Human umbilical cord blood cell grafts for brain ischemia,” Cell Transplantation, vol. 18, no. 9, pp. 985–998, 2009.

H. Rabe, A. Wacker, G. Hülskamp et al., “A randomised controlled trial of delayed cord clamping in very low birth weight preterm infants,” European Journal of Pediatrics, vol. 159, no. 10, pp. 775–777, 2000.

M. McDonnell and D. J. Henderson-Smart, “Delayed umbilical cord clamping in preterm infants: a feasibility study,” Journal of Paediatrics and Child Health, vol. 33, no. 4, pp. 308–310, 1997.

S. Kinmond, T. C. Aitchison, B. M. Holland, J. G. Jones, T. L. Turner, and C. A. J. Wardrop, “Umbilical cord clamping and preterm infants: a randomised trial,” British Medical Journal, vol. 306, no. 6871, pp. 172–175, 1993.

J. S. Mercer, B. R. Vohr, M. M. McGrath, J. F. Padbury, M. Wallach, and W. Oh, “Delayed cord clamping in very preterm infants reduces the incidence of intraventricular hemorrhage and late-onset sepsis: a randomized, controlled trial,” Pediatrics, vol. 117, no. 4, pp. 1235–1242, 2006.

American College of Obstetricians and Gynecologists, “Committee Opinion No.543: timing of umbilical cord clamping after birth,” Obstetrics & Gynecology, vol. 120, no. 6, pp. 1522–1526, 2012.

H. Rabe, A. Jewison, R. Fernandez Alvarez et al., “Milking compared with delayed cord clamping to increase placental transfusion in preterm neonates: a randomized controlled trial,” Obstetrics and Gynecology, vol. 117, no. 2, pp. 205–211, 2011.

L. Bennet, V. Roelfsema, P. Pathipati, J. S. Quaedackers, and A. J. Gunn, “Relationship between evolving epileptiform activity and delayed loss of mitochondrial activity after asphyxia measured by near-infrared spectroscopy in preterm fetal sheep,” Journal of Physiology, vol. 572, no. 1, pp. 141–154, 2006.

A. J. Gunn, T. R. Gunn, H. H. de Haan, C. E. Williams, and P. D. Gluckman, “Dramatic neuronal rescue with prolonged selective head cooling after ischemia in fetal lambs,” The Journal of Clinical Investigation, vol. 99, no. 2, pp. 248–256, 1997.

E. C. Jensen, L. Bennet, C. J. Hunter, G. C. Power, and A. J. Gunn, “Post-hypoxic hypoperfusion is associated with suppression of cerebral metabolism and increased tissue oxygenation in near-term fetal sheep,” Journal of Physiology, vol. 572, no. 1, pp. 131–139, 2006.

A. Lorek, Y. Takei, E. B. Cady et al., “Delayed ('secondary') cerebral energy failure after acute hypoxia-ischemia in the newborn piglet: continuous 48-hour studies by phosphorus magnetic resonance spectroscopy,” Pediatric Research, vol. 36, no. 6, pp. 699–706, 1994.

S. C. Roth, J. Baudin, E. Cady et al., “Relation of deranged neonatal cerebral oxidative metabolism with neurodevelopmental outcome and head circumference at 4 years,” Developmental Medicine and Child Neurology, vol. 39, no. 11, pp. 718–725, 1997.

F. Colbourne and D. Corbett, “Delayed postischemic hypothermia: a six month survival study using behavioral and histological assessments of neuroprotection,” Journal of Neuroscience, vol. 15, no. 11, pp. 7250–7260, 1995.

R. Geddes, R. C. Vannucci, and S. J. Vannucci, “Delayed cerebral atrophy following moderate hypoxia-ischemia in the immature rat,” Developmental Neuroscience, vol. 23, no. 3, pp. 180–185, 2001.

B. S. Stone, J. Zhang, D. W. Mack, S. Mori, L. J. Martin, and F. J. Northington, “Delayed neural network degeneration after neonatal hypoxia-ischemia,” Annals of Neurology, vol. 64, no. 5, pp. 535–546, 2008.

R. D. Barrett, L. Bennet, J. Davidson et al., “Destruction and reconstruction: hypoxia and the developing brain,” Birth Defects Research Part C: Embryo Today: Reviews, vol. 81, no. 3, pp. 163–176, 2007.

A. J. Friedenstein, R. K. Chailakhyan, N. V. Latsinik, A. F. Panasyuk, and I. V. Keiliss-Borok, “Stromal cells responsible for transferring the microenvironment of the hemopoietic tissues. Cloning in vitro and retransplantation in vivo,” Transplantation, vol. 17, no. 4, pp. 331–340, 1974.

M. Najar, G. Raicevic, H. I. Boufker et al., “Adipose-tissue-derived and Wharton's jelly-derived mesenchymal stromal cells suppress lymphocyte responses by secreting leukemia inhibitory factor,” Tissue Engineering Part A, vol. 16, no. 11, pp. 3537–3546, 2010.

S. Yust-Katz, Y. Fisher-Shoval, Y. Barhum et al., “Placental mesenchymal stromal cells induced into neurotrophic factor-producing cells protect neuronal cells from hypoxia and oxidative stress,” Cytotherapy, vol. 14, no. 1, pp. 45–55, 2012.

C. Meier, J. Middelanis, B. Wasielewski et al., “Spastic paresis after perinatal brain damage in rats is reduced by human cord blood mononuclear cells,” Pediatric Research, vol. 59, no. 2, pp. 244–249, 2006.

C. T. J. van Velthoven, A. Kavelaars, F. van Bel, and C. J. Heijnen, “Mesenchymal stem cell treatment after neonatal hypoxic-ischemic brain injury improves behavioral outcome and induces neuronal and oligodendrocyte regeneration,” Brain, Behavior, and Immunity, vol. 24, no. 3, pp. 387–393, 2010.

J. A. Lee, B. I. Kim, C. H. Jo et al., “Mesenchymal stem-cell transplantation for hypoxic-ischemic brain injury in neonatal rat model,” Pediatric Research, vol. 67, no. 1, pp. 42–46, 2010.

R. K. Jellema, T. G. A. M. Wolfs, V. Lima Passos et al., “Mesenchymal stem cells induce T-cell tolerance and protect the preterm brain after global hypoxia-ischemia,” PLoS ONE, vol. 8, no. 8, Article ID e73031, 2013.

C. T. J. van Velthoven, A. Kavelaars, and C. J. Heijnen, “Mesenchymal stem cells as a treatment for neonatal ischemic brain damage,” Pediatric Research, vol. 71, no. 4, part 2, pp. 474–481, 2012.

C. T. J. vn Velthoven, A. Kavelaars, F. van Bel, and C. J. Heijnen, “Mesenchymal stem cell transplantation changes the gene expression profile of the neonatal ischemic brain,” Brain, Behavior, and Immunity, vol. 25, no. 7, pp. 1342–1348, 2011.

A. Gritti, P. Frölichsthal-Schoeller, R. Galli et al., “Epidermal and fibroblast growth factors behave as mitogenic regulators for a single multipotent stem cell-like population from the subventricular region of the adult mouse forebrain,” The Journal of Neuroscience, vol. 19, no. 9, pp. 3287–3297, 1999.

B. A. Reynolds and S. Weiss, “Generation of neurons and astrocytes from isolated cells of the adult mammalian central nervous system,” Science, vol. 255, no. 5052, pp. 1707–1710, 1992.

T. Kobayashi, H. Ahlenius, P. Thored, R. Kobayashi, Z. Kokaia, and O. Lindvall, “Intracerebral infusion of glial cell line-derived neurotrophic factor promotes striatal neurogenesis after stroke in adult rats,” Stroke, vol. 37, no. 9, pp. 2361–2367, 2006.

L. H. Shen, Y. Li, and M. Chopp, “Astrocytic endogenous glial cell derived neurotrophic factor production is enhanced by bone marrow stromal cell transplantation in the ischemic boundary zone after stroke in adult rats,” GLIA, vol. 58, no. 9, pp. 1074–1081, 2010.

K. Lai, B. K. Kaspar, F. H. Gage, and D. V. Schaffer, “Sonic hedgehog regulates adult neural progenitor proliferation in vitro and in vivo,” Nature Neuroscience, vol. 6, no. 1, pp. 21–27, 2003.

K. Lai, B. K. Kaspar, F. H. Gage, and D. V. Schaffer, “Sonic hedgehog regulates adult neural progenitor proliferation in vitro and in vivo,” Nature Neuroscience, vol. 6, pp. 21–27, 2003.

R. J. Felling, M. J. Snyder, M. J. Romanko et al., “Neural stem/progenitor cells participate in the regenerative response to perinatal hypoxia/ischemia,” The Journal of Neuroscience, vol. 26, no. 16, pp. 4359–4369, 2006.

S. T. Carmichael, “Cellular and molecular mechanisms of neural repair after stroke: making waves,” Annals of Neurology, vol. 59, no. 5, pp. 735–742, 2006.

F. J. Rivera, M. Kandasamy, S. Couillard-Despres et al., “Oligodendrogenesis of adult neural progenitors: differential effects of ciliary neurotrophic factor and mesenchymal stem cell derived factors,” Journal of Neurochemistry, vol. 107, no. 3, pp. 832–843, 2008.

C. T. J. van Velthoven, A. Kavelaars, F. van Bel, and C. J. Heijnen, “Repeated mesenchymal stem cell treatment after neonatal hypoxia-ischemia has distinct effects on formation and maturation of new neurons and oligodendrocytes leading to restoration of damage, corticospinal motor tract activity, and sensorimotor function,” The Journal of Neuroscience, vol. 30, no. 28, pp. 9603–9611, 2010.

Y. Li, J. Chen, C. L. Zhang et al., “Gliosis and brain remodeling after treatment of stroke in rats with marrow stromal cells,” GLIA, vol. 49, no. 3, pp. 407–417, 2005.

L. H. Shen, Y. Li, Q. Gao, S. Savant-Bhonsale, and M. Chopp, “Down-regulation of neurocan expression in reactive astrocytes promotes axonal regeneration and facilitates the neurorestorative effects of bone marrow stromal cells in the ischemic rat brain,” GLIA, vol. 56, no. 16, pp. 1747–1754, 2008.

C. T. Ekdahl, Z. Kokaia, and O. Lindvall, “Brain inflammation and adult neurogenesis: the dual role of microglia,” Neuroscience, vol. 158, no. 3, pp. 1021–1029, 2009.

M. Czeh, P. Gressens, and A. M. Kaindl, “The yin and yang of microglia,” Developmental Neuroscience, vol. 33, no. 3-4, pp. 199–209, 2011.

U.-K. Hanisch and H. Kettenmann, “Microglia: active sensor and versatile effector cells in the normal and pathologic brain,” Nature Neuroscience, vol. 10, no. 11, pp. 1387–1394, 2007.

M. Schwartz, O. Butovsky, W. Brück, and U.-K. Hanisch, “Microglial phenotype: is the commitment reversible?” Trends in Neurosciences, vol. 29, no. 2, pp. 68–74, 2006.

J. Aarum, K. Sandberg, S. L. B. Haeberlein, and M. A. A. Persson, “Migration and differentiation of neural precursor cells can be directed by microglia,” Proceedings of the National Academy of Sciences of the United States of America, vol. 100, no. 26, pp. 15983–15988, 2003.

P. Thored, U. Heldmann, W. Gomes-Leal et al., “Long-term accumulation of microglia with proneurogenic phenotype concomitant with persistent neurogenesis in adult subventricular zone after stroke,” GLIA, vol. 57, no. 8, pp. 835–849, 2009.

R. C. Lai, F. Arslan, M. M. Lee et al., “Exosome secreted by MSC reduces myocardial ischemia/reperfusion injury,” Stem Cell Research, vol. 4, no. 3, pp. 214–222, 2010.

P. J. Shughrue, M. V. Lane, and I. Merchenthaler, “Comparative distribution of estrogen receptor-alpha and -beta mRNA in the rat central nervous system,” The Journal of Comparative Neurology, vol. 388, no. 4, pp. 507–525, 1997.

N. Laflamme, R. E. Nappi, G. Drolet, C. Labrie, and S. Rivest, “Expression and neuropeptidergic characterization of estrogen receptors (ERα and ERβ) throughout the rat brain: anatomical evidence of distinct roles of each subtype,” Journal of Neurobiology, vol. 36, no. 3, pp. 357–378, 1998.

A. E. Clipperton-Allen, A. W. Lee, A. Reyes et al., “Oxytocin, vasopressin and estrogen receptor gene expression in relation to social recognition in female mice,” Physiology & Behavior, vol. 105, no. 4, pp. 915–924, 2012.

D. G. Zuloaga, S. L. Yahn, Y. Pang et al., “Distribution and estrogen regulation of membrane progesterone receptor-β in the female rat brain,” Endocrinology, vol. 153, no. 9, pp. 4432–4443, 2012.

S. Haraguchi, K. Sasahara, H. Shikimi, S.-I. Honda, N. Harada, and K. Tsutsui, “Estradiol promotes purkinje dendritic growth, spinogenesis, and synaptogenesis during neonatal life by inducing the expression of BDNF,” Cerebellum, vol. 11, no. 2, pp. 416–417, 2012.

D. Tulchinsky, C. J. Hobel, E. Yeager, and J. R. Marshall, “Plasma estradiol, estriol, and progesterone in human pregnancy. II. Clinical applications in Rh-isoimmunization disease,” The American Journal of Obstetrics and Gynecology, vol. 113, no. 6, pp. 766–770, 1972.

C. E. Wood, “Estrogen/hypothalamus-pituitary-adrenal axis interactions in the fetus: the interplay between placenta and fetal brain,” Journal of the Society for Gynecologic Investigation, vol. 12, no. 2, pp. 67–76, 2005.

J. Nuñez, Z. Yang, Y. Jiang, T. Grandys, I. Mark, and S. W. Levison, “17β-Estradiol protects the neonatal brain from hypoxia-ischemia,” Experimental Neurology, vol. 208, no. 2, pp. 269–276, 2007.

B. Gerstner, J. Lee, T. M. DeSilva, F. E. Jensen, J. J. Volpe, and P. A. Rosenberg, “17β-estradiol protects against hypoxic/ischemic white matter damage in the neonatal rat brain,” Journal of Neuroscience Research, vol. 87, no. 9, pp. 2078–2086, 2009.

M. M. Müller, J. Middelanis, C. Meier, D. Surbek, and R. Berger, “17β-estradiol protects 7-day old rats from acute brain injury and reduces the number of apoptotic cells,” Reproductive Sciences, vol. 20, no. 3, pp. 253–261, 2013.

E. R. Deutsch, T. R. Espinoza, F. Atif, E. Woodall, J. Kaylor, and D. W. Wright, “Progesterone's role in neuroprotection, a review of the evidence,” Brain Research, vol. 1530, pp. 82–105, 2013.

A. Trotter, L. Maier, and F. Pohlandt, “Management of the extremely preterm infant: is the replacement of estradiol and progesterone beneficial?” Paediatric Drugs, vol. 3, no. 9, pp. 629–637, 2001.

R. Hunt, P. G. Davis, and T. Inder, “Replacement of estrogens and progestins to prevent morbidity and mortality in preterm infants,” The Cochrane Database of Systematic Reviews, no. 4, Article ID CD003848, 2004.

C. Behl and F. Holsboer, “The female sex hormone oestrogen as a neuroprotectant,” Trends in Pharmacological Sciences, vol. 20, no. 11, pp. 441–444, 1999.

C. Behl, “Oestrogen as a neuroprotective hormone,” Nature Reviews Neuroscience, vol. 3, no. 6, pp. 433–442, 2002.

S. J. Lee and B. S. McEwen, “Neurotrophic and neuroprotective actions of estrogens and their therapeutic implications,” Annual Review of Pharmacology and Toxicology, vol. 41, pp. 569–591, 2001.

R. J. Bicknell, “Sex-steroid actions on neurotransmission,” Current Opinion in Neurology, vol. 11, no. 6, pp. 667–671, 1998.

Q. Gu, K. S. Korach, and R. L. Moss, “Rapid action of 17β-estradiol on kainate-induced currents in hippocampal neurons lacking intracellular estrogen receptors,” Endocrinology, vol. 140, no. 2, pp. 660–666, 1999.

G. G. J. M. Kuiper, B. Carlsson, K. Grandien et al., “Comparison of the ligand binding specificity and transcript tissue distribution of estrogen receptors and alpha and beta,” Endocrinology, vol. 138, no. 3, pp. 863–870, 1997.

S. M. Hyder, C. Chiappetta, and G. M. Stancel, “Interaction of human estrogen receptors α and β with the same naturally occurring estrogen response elements,” Biochemical Pharmacology, vol. 57, no. 6, pp. 597–601, 1999.

S. Kahlert, S. Nuedling, M. van Eickels, H. Vetter, R. Meyer, and C. Grohé, “Estrogen receptor a rapidly activates the IGF-1 receptor pathway,” The Journal of Biological Chemistry, vol. 275, no. 24, pp. 18447–18453, 2000.

K. G. Brywe, C. Mallard, M. Gustavsson et al., “IGF-I neuroprotection in the immature brain after hypoxia-ischemia, involvement of Akt and GSK3β?” European Journal of Neuroscience, vol. 21, no. 6, pp. 1489–1502, 2005.

Y. Zhang, O. Tounekti, B. Akerman, C. G. Goodyer, and A. LeBlanc, “17-beta-estradiol induces an inhibitor of active caspases,” The Journal of Neuroscience, vol. 21, no. 20, article RC176, 2001.

T. Ishrat, I. Sayeed, F. Atif, F. Hua, and D. G. Stein, “Progesterone and allopregnanolone attenuate blood-brain barrier dysfunction following permanent focal ischemia by regulating the expression of matrix metalloproteinases,” Experimental Neurology, vol. 226, no. 1, pp. 183–190, 2010.

C.-Y. Xu, S. Li, X.-Q. Li, and D.-L. Li, “Effect of progesterone on MMP-3 expression in neonatal rat brain after hypoxic-ischemia,” Zhongguo Ying Yong Sheng Li Xue Za Zhi, vol. 26, no. 3, pp. 370–373, 2010.

T. Ishrat, I. Sayeed, F. Atif, F. Hua, and D. G. Stein, “Progesterone is neuroprotective against ischemic brain injury through its effects on the phosphoinositide 3-kinase/protein kinase B signaling pathway,” Neuroscience, vol. 210, pp. 442–450, 2012.

C. L. Gibson, D. Constantin, M. J. W. Prior, P. M. W. Bath, and S. P. Murphy, “Progesterone suppresses the inflammatory response and nitric oxide synthase-2 expression following cerebral ischemia,” Experimental Neurology, vol. 193, no. 2, pp. 522–530, 2005.

C. Jiang, K. Cui, J. Wang, and Y. He, “Microglia and cyclooxygenase-2: possible therapeutic targets of progesterone for stroke,” International Immunopharmacology, vol. 11, no. 11, pp. 1925–1931, 2011.

J. Wang, Y. Zhao, C. Liu, C. Jiang, C. Zhao, and Z. Zhu, “Progesterone inhibits inflammatory response pathways after permanent middle cerebral artery occlusion in rats,” Molecular Medicine Reports, vol. 4, no. 2, pp. 319–324, 2011.

T. Coughlan, C. Gibson, and S. Murphy, “Modulatory effects of progesterone on inducible nitric oxide synthase expression in vivo and in vitro,” Journal of Neurochemistry, vol. 93, no. 4, pp. 932–942, 2005.

R. Aggarwal, B. Medhi, A. Pathak, V. Dhawan, and A. Chakrabarti, “Neuroprotective effect of progesterone on acute phase changes induced by partial global cerebral ischaemia in mice,” Journal of Pharmacy and Pharmacology, vol. 60, no. 6, pp. 731–737, 2013.

Y. Zhao, J. Wang, C. Liu, C. Jiang, C. Zhao, and Z. Zhu, “Progesterone influences postischemic synaptogenesis in the CA1 region of the hippocampus in rats,” Synapse, vol. 65, no. 9, pp. 880–891, 2011.

M. Tsuji, A. Taguchi, M. Ohshima, Y. Kasahara, and T. Ikeda, “Progesterone and allopregnanolone exacerbate hypoxic-ischemic brain injury in immature rats,” Experimental Neurology, vol. 233, no. 1, pp. 214–220, 2012.