The rate of human brain growth is greatest in mid-to-late fetal gestation, corresponding to peak neuronal dendritogenesis. In pregnancies complicated by fetal growth restriction (FGR) caused by placental dysfunction, brain development is adversely impacted, with evidence of reduced total and hippocampal brain volume in childhood and cognitive deficits. The cellular basis for hippocampal maldevelopment and dysfunction in FGR is unknown. In this study we employed complementary preclinical and clinical investigations of hippocampal developmental trajectory in growth restricted neonates to address this knowledge gap. In the preclinical study (FGR n=18, control n=19), FGR was induced in fetal sheep via surgical induction of placental insufficiency at 89 days gestational age (dGA, term is 148dGA), and after near-term birth (136dGA), postnatal memory function was measured over four weeks. Neuronal dendritogenesis (dendrite length, branching, complexity) was assessed using Golgi-Cox staining of individual hippocampal Cornu Ammonis (CA)1 neurons at two neonatal timepoints, newborn age at 24 hours after birth and 4-weeks of age, to compare the trajectory of hippocampal neuron development in FGR and control lambs. Results show that, in control lambs, total dendrite length and branching of CA1 hippocampal neurons significantly increased between newborn age and 4-weeks. In FGR lamb brains, neither dendrite length or branching increased over this period, and dendrite deficits were worse in FGR lambs at 4-weeks, corresponding to reduced hippocampal area. In 4-week-old lambs, we observed a significant correlation between total dendrite length of CA1 neurons and memory function. Hippocampal growth trajectory and function deficits were corroborated in small for gestational age (SGA) infants born very preterm. Magnetic resonance imaging (MRI) was performed in very preterm infants in early life, and repeated at term equivalent age, showing that the trajectory of anterior hippocampal growth was significantly reduced in SGA infants (n=20) compared to appropriate for gestational age (AGA; n=139) infants. Within the SGA infant cohort, reduced anterior hippocampal volume was significantly associated with lower Bayley Cognitive Composite scores at 18 months corrected age, controlling for gestational age at birth and infant sex. Together, these findings demonstrate that the trajectory of hippocampal growth is significantly impaired in SGA/FGR infants, caused by disturbed neuronal dendritogenesis that is programmed by an adverse fetal environment and persists, or worsens, after birth. Results in the clinical cohort provide the critical link between programming of reduced dendritogenesis, hippocampal volume deficit and cognitive dysfunction in SGA infants.

The last pregnancy trimester is critical for fetal brain development but is a vulnerable period if the pregnancy is compromised by fetal growth restriction (FGR). The impact of FGR on the maturational development of neuronal morphology is not known, however, studies in fetal sheep allow longitudinal analysis in a long gestation species. Here we compared hippocampal neuron dendritogenesis in FGR and control fetal sheep at three timepoints equivalent to the third trimester of pregnancy, complemented by magnetic resonance image for brain volume, and electrophysiology for synaptic function. We hypothesized that the trajectory of hippocampal neuronal dendrite outgrowth would be decreased in the growth-restricted fetus, with implications for hippocampal volume, connectivity, and function. In control animals, total dendrite length increased with advancing gestation, but not in FGR, resulting in a significantly reduced trajectory of dendrite outgrowth in FGR fetuses for total length, branching, and complexity. Ex vivo electrophysiology analysis shows that paired-pulse facilitation was reduced in FGR compared to controls for cornu ammonis 1 hippocampal outputs, reflecting synaptic dysfunction. Hippocampal brain-derived neurotrophic factor density decreased over late gestation in FGR fetuses but not in controls. This study reveals that FGR is associated with a significant deviation in the trajectory of dendrite outgrowth of hippocampal neurons. Where dendrite length significantly increased over the third trimester of pregnancy in control brains, there was no corresponding increase over time in FGR brains, and the trajectory of dendrite outgrowth in FGR offspring was significantly reduced compared to controls. Reduced hippocampal dendritogenesis in FGR offspring has severe implications for the development of hippocampal connectivity and long-term function.

Fetal growth restriction (FGR) increases the risk of cardiovascular disease. FGR is linked to placental insufficiency and fetal hypoxemia, leading to oxidative stress and inflammation, which collectively influence the developmental programming of cardiovascular disease. This study assessed whether melatonin (MLT), a potent antioxidant and anti-inflammatory agent, could prevent cardiovascular deficits associated with FGR. Placental insufficiency was induced in ewes at 89 days of gestational age (dGA, term 148 dGA). Ewes were randomly allocated to control, FGR or FGR+MLT (i.v., 15 mg day-1, from 95 dGA to birth) groups. Lambs were delivered preterm at 136 dGA and assessed as newborn (24 h) and 4-week-old lambs. Vascular function was determined in femoral arteries using in vitro wire myography and vascular morphology as assessed in carotid and femoral arteries. Newborn FGR lambs were ∼30% smaller than control lambs with an increased brain-to-body weight ratio, indicative of brain sparing. Femoral endothelial function declined between ∼24 h after birth and 4 weeks in FGR lambs. By contrast, femoral arteries from newborn FGR+MLT lambs displayed transient endothelial dysfunction that improved by 4 weeks. However, these arteries showed elevated levels of oxidative stress and inflammation. Despite improving endothelial function, melatonin also disrupted the brain-sparing response in FGR lambs. Furthermore, by 4 weeks of age, melatonin treatment led to heightened oxidative stress and inflammatory markers in the peripheral vasculature, suggesting a potential trade-off between vascular benefits and systemic maladaptation. These findings highlight the complexity of melatonin's effects on the cardiovascular system and underscore the need for careful evaluation of its long-term safety and efficacy before clinical translation. KEY POINTS: Fetal growth restriction (FGR) significantly increases the lifelong risk of cardiovascular disease, and there are currently no targeted treatments to mitigate these risks. This study follows growth-restricted lambs from birth to 4 weeks of age (comparable to a 1-year-old human in terms of cardiovascular function) to characterise how FGR affects vascular development over time. FGR lambs exhibited progressive endothelial dysfunction in the femoral artery, but antenatal melatonin treatment restored endothelial function long-term despite the presence of vascular oxidative stress and inflammation. The brain-sparing response is a key adaptive mechanism for fetal survival, yet melatonin appears to dampen this response, highlighting the need for further investigation into its broader physiological effects.

BACKGROUND:Preterm brain injury involves persistent inflammation, making it a potential therapeutic target. Current large animal models focus on short-term outcomes, limiting understanding of long-term effects. We developed an ovine model of inflammation-induced preterm brain injury to assess long-term neuropathology at an age equivalent to early cerebral palsy diagnosis in human infants. METHODS:Fetal sheep were instrumented at gestational day (d) 90-91 (term is 148d): one group received lipopolysaccharide (LPS 200 ng; n = 9) on 96d, 97d, and 98d (0.65 gestation, ∼25-26 weeks human brain development), and a control group received saline (n = 8). Birth was induced on 138d, and lambs were euthanised within 24 h of birth. Brains were evaluated for white matter injury, microglial/macrophage activation and astrogliosis in the subcortical (SCWM), periventricular (PVWM), and cortical (CWM) white matter, subventricular zone (SVZ), and corpus callosum (CC). RESULTS:Antenatal LPS administration was associated with significant persistent microglial/macrophage activation in the PVWM (P = 0.04), SCWM (P = 0.01), and CWM (P = 0.006). Furthermore, LPS exposure was associated with reduced oligodendrocyte cell number in the PVWM (P = 0.02), SCWM (P = 0.001), and CWM (P = 0.0001), and reduced myelination in CWM (CNPase, P < 0.0001 and MBP, P = 0.04) and SVZ (MBP, P = 0.05). No difference in astrogliosis or microhaemorrhages was observed. CONCLUSION:We demonstrated that in a large animal model of inflammation-induced intrauterine preterm brain injury, long-term persistent inflammation occurs, along with significant white matter injury, including loss of oligodendrocytes and reduced myelination in multiple white matter regions. This model paves the way for long-term evaluation of promising therapeutics and behavioral assessment in this clinically relevant model of persistent preterm brain injury.

INTRODUCTION:Perinatal stroke causes lasting neurological deficits and there are currently no effective treatment options. Established animal models of perinatal stroke do not always mimic the clinical presentation of neonatal injury or are technically challenging to perform. The photothrombotic (PT) stroke model is a minimally invasive method that replicates focal ischaemic injury. Few studies have applied the PT model in neonatal contexts, and none have examined both short- and long-term effects across varying injury severities. This study aimed to optimize a protocol to create a mild model of perinatal stroke and subsequently characterize injury progression, neuropathological impact, and motor deficits over time. METHODS:On postnatal day 10 we used the PT method to induce perinatal stroke in rat pups. Pups were exposed to various light exposure times (10, 20, or 30 min) to determine the optimal time needed to produce a mild and reproducible cortical stroke injury. Behavioural assessments were conducted on days 4, 10, 20, and 30 post-injury. Brains were collected for analysis on days 3 and 40 post-injury. RESULTS:Three days post-injury, the 20 and 30 min group had significant focal lesions and microbleeds were present in each of the PT groups. All PT groups showed significant neuron loss in the peri-infarct region and the thalamus, and microglia activation in multiple brain regions. As 30 min of light exposure showed extensive cortical tissue loss (>70%), we excluded the 30-min group from long-term assessment. 40 days post-injury, the 10 and 20 min groups demonstrated significant tissue loss and neuronal loss in the peri-infarct region and thalamus, but only the 20 min group showed neuron loss in the hippocampus. The 10 and 20 min groups both demonstrated ongoing motor deficits. CONCLUSION:Our results demonstrate that increasing light exposure time in PT stroke results in a more severe stroke phenotype. 30 min of light exposure resulted in a severe injury at only 3 days post insult, therefore, was not further investigated. 10 and 20 min of light exposure had a similar effect at 3 days, however, after 40 days the 20 min exposure time created a moderate injury phenotype. From this study, we propose that 10 min of light exposure is optimal to create a mild stroke phenotype and is associated with motor deficits and altered neuropathology. This injury phenotype provides a focal and reproducible insult, while still being mild enough to feasibly test therapeutics.

Fetal growth restriction (FGR) arises from chronic hypoxia and increases the risk of cardiovascular dysfunction following perinatal asphyxia, although underlying mechanisms remain unclear. We investigated whether cardiovascular responses to asphyxia are impaired in preterm FGR lambs and whether this arises from α1- and β1-adrenergic receptor dysfunction. Ewes underwent sterile fetal surgery at 89 days’ gestation (d; term=148 d) to induce FGR (single umbilical artery ligation) or sham surgery (control). At 126 d, lambs were delivered, instrumented and randomised to immediate ventilation (ControlVENTn=6; FGRVENTn=6) or asphyxia (ControlASPHYXIAn=12; FGRASPHYXIAn=11) by umbilical cord occlusion until diastolic blood pressure (BP) decreased to 10 mmHg. Lambs were ventilated for 8 hours before baseline ex vivo cardiac function was assessed via Langendorff perfusion to measure left ventricular developed pressure (LVDP), heart rate (HR) and coronary perfusion pressure (CPP). Ex vivo α1- and β1-adrenergic responses were assessed via phenylephrine and dobutamine administration, respectively. FGRASPHYXIA lambs had lower BP during asphyxia and took longer to reach a diastolic BP of 10 mmHg (P<0.05 vs ControlASPHYXIA). FGRASPHYXIA lambs had lower BP in the first 5 minutes after return of spontaneous circulation due to impaired vascular contractility (P<0.05 vs ControlASPHYXIA). Baseline LVDP, HR and CPP were similar between groups. FGRASPHYXIA lambs had increased LVDP responses to phenylephrine and dobutamine (P<0.05 vs FGRVENT and ControlASPHYXIA), without significant changes to HR or CPP. Overall, FGR lambs exhibit impaired vascular contractility and heightened cardiac α1- and β1-adrenergic responsiveness after perinatal asphyxia, consistent with reduced autonomic regulation, potentially increasing susceptibility to cardiovascular dysfunction postnatally.

Introduction Fetal growth restriction (FGR) arises from chronic hypoxia and increases the risk of cardiovascular dysfunction following perinatal asphyxia, although the underlying mechanisms are unknown. We investigated whether FGR lambs have altered cardiovascular responses to perinatal asphyxia compared to control lambs, and whether impairments in α1 and β1 adrenergic receptor function underlie these responses. Methods Single or twin-bearing ewes underwent sterile fetal surgery at 89 days gestation (dGA; term=148d) to induce FGR (single umbilical artery ligation) or sham surgery (Control). At 126dGA, lambs were delivered via caesarean section, instrumented and randomised to immediate ventilation (ControlVENT n =6; FGRVENT n =6), or asphyxia (ControlASPHYXIA n =12; FGRASPHYXIA n =11) induced by umbilical cord occlusion while withholding resuscitation until diastolic blood pressure (BP) decreased to 10mmHg. Lambs were ventilated for 8 hours before baseline ex vivo cardiac function was assessed via Langendorff perfusion to measure left ventricular developed pressure (LVDP), heart rate (HR) and coronary perfusion pressure (CPP). Ex vivo α1 and β1 adrenergic responses were assessed via phenylephrine (10−5 to 10−2 mmol/L) and dobutamine (10−7 to 10−4) administration, respectively. Results FGRASPHYXIA lambs had lower BP during asphyxia (p<0.05 vs ControlASPHYXIA) and took longer to reach a diastolic BP of 10mmHg (14.5 ± 0.8 min vs. 19.2 ± 1.3 min; p=0.005). FGRASPHYXIA lambs had lower BP in the first 5 minutes after return of spontaneous circulation (p<0.05) due to impaired vascular contractility, with reduced Tau, dP/dtmax and dP/dtmin (p<0.03 vs ControlASPHYXIA). Baseline LVDP, HR and CPP were similar between groups, however FGRASPHYXIA lambs had increased LVDP responses to phenylephrine and dobutamine (p<0.05 vs ControlASPHYXIA), without significant changes to HR or CPP. Conclusion FGR lambs have altered physiological responses to perinatal asphyxia due to impaired vascular contractility and dysregulated cardiac α1 and β1 adrenergic receptor function, which may increase susceptibility to cardiovascular dysfunction in the neonatal period. ### Competing Interest Statement The authors have declared no competing interest.

BACKGROUND:Intraventricular haemorrhage (IVH) is the primary neuropathology in infants born very preterm. IVH describes bleeding into the ventricular space of the newborn brain, originating from the germinal matrix, termed germinal matrix haemorrhage. IVH is diagnosed at a rate of 1 in 5 infants born very preterm (less than 32 weeks' gestation), but the incidence increases with earlier gestation at birth. IVH is graded in severity (I to IV), and the neurological sequelae of IVH in infants born very preterm are significant, with more than 1 in 4 infants with any grade of IVH subsequently diagnosed with a moderate to severe neurodevelopmental deficit, increasing to more than half of infants diagnosed with severe IVH (grade III/IV). SUMMARY:The high susceptibility to IVH in infants born at less than 32 weeks' arises in part to the presence of the germinal matrix. The germinal matrix is a transient brain region that produces neural stem and progenitor cells. The germinal matrix region is rich in angiogenic blood vessels that have a low density of pericyte and astrocyte coverage to provide structural stability, and it is a border zone for vascular endpoints that are highly fragile to haemodynamic instability. In addition to immaturity, antenatal complications may also adversely impact cerebrovascular development, pericyte and astrocyte coverage, and subsequently the structural integrity of the blood-brain barrier that might increase the risk for IVH. KEY MESSAGES:Here, we will report the maturational profile of cerebrovascular development in the extremely preterm neonate, and implications for susceptibility to IVH, the complications that may contribute to the risk of haemorrhage, and neurodevelopmental deficits that primarily arise from IVH. We aimed to elucidate the cellular foundations of IVH to provide insight into neuroprotective targets.

Within 24 h of birth, growth-restricted (FGR) newborn lambs exhibited altered lipid and serotonin metabolites, suggesting disrupted postnatal cardiac metabolic adaptation. Despite upregulation of the fatty acid transporter gene SLC27A6, with other fatty acid oxidation genes remaining largely unchanged, reductions in lipid and carnitine metabolites indicate potential impairments in fatty acid utilization. Decreased serotonin bioavailability further suggests metabolic reprogramming in FGR hearts, highlighting the need for future studies on the implications for postnatal cardiac function.

BACKGROUND: Intraventricular hemorrhage (IVH) most commonly occurs in infants born very preterm (<32 weeks' gestation). There are mixed findings on whether infants small for gestational age (SGA) or with suspected fetal growth restriction (FGR) are at higher risk for IVH. Understanding the relationship between SGA or FGR and IVH is critical to inform clinical care. OBJECTIVE: The primary aim was to determine the rates of IVH in very preterm newborns, with SGA or suspected FGR, and to stratify for severity of both FGR and IVH. The secondary aim was to identify risk factors for IVH in a large contemporary cohort. STUDY DESIGN: A population-based retrospective cohort study using data from the Australian and New Zealand Neonatal Network. Participants were babies born before 32 weeks' gestation (22-31 weeks + 6 days gestation) between 2014 and 2019 inclusive. The primary outcomes were IVH and severity of IVH. Small babies were classified as being SGA (SGA; birth weight <10th percentile), suspected FGR (birth weight <10th and >= 3rd birth weight percentile and abnormal antenatal ultrasound), or severe FGR (birth weight <3rd percentile). Multivariate regression was then performed, adjusting for potential maternal and fetal confounders to determine the association between FGR and IVH. RESULTS: 20,551 very preterm newborns were included in the study with a median gestational age (25th, 75th) of 29 (27, 30) weeks gestation and birth weight of 1201 (383.9) grams. The incidence of any IVH was 20.02% (n=4115) and increased with decreasing gestation at birth (10% of infants born at 31 weeks had IVH compared with 70% of infants born at 22 weeks). The rate of severe IVH (Grade 3 or 4) was 3.23%. In this cohort, 7.7% were SGA (n=1583) and 6.23% (n=1281) of babies had suspected early-onset FGR. The incidence of SGA was reduced in babies with IVH (6.0% vs 8.1%, respectively, aOR, 0.82; 95% CI 0.68-0.97). Similarly, suspected FGR was significantly lower in infants with IVH (any grade) compared to those without (2.5% vs 4.6%, respectively, adjusted odds ratio (aOR), 0.69; 95% CI 0.54-0.89). Further, there was a negative association between SGA (aOR, 0.80; 95% CI 0.67-0.95) and FGR (aOR 0.69; 95% CI 0.54-0.88) and the severity of IVH. Severe FGR (<3rd birth weight percentile) was not associated with either the presence (1.9% with IVH, vs 2.1% without IVH, aOR, 0.86; 95% CI 0.64-1.16) or severity of VH (aOR, 0.85; 95% CI 0.63-1.14). CONCLUSION: This large retrospective cohort study identified that in very preterm infants born with a median gestational age at birth of 29 weeks and who survive to the neonatal unit, the presence of SGA or suspected FGR is associated with a reduced rate of IVH, compared to infants without SGA/FGR. Future studies should directly assess whether placental insufficiency prevents the development of IVH, so that novel neuroprotective strategies for the very preterm infant can be implemented.

Early-onset fetal growth restriction (FGR) is associated with prolonged fetoplacental hypoxia and altered brain development, including deficits in hippocampal structure and function. Neuroprotective actions of lactoferrin have been described, mediated via anti-inflammatory and antioxidant properties. Here, we investigated whether the antenatal administration of lactoferrin (1) improves hippocampal structure, (2) promotes neuronal growth, and (3) mitigates neuroinflammation in the hippocampus of fetal sheep with FGR. Early-onset FGR was induced by performing single umbilical artery ligation surgery on ovine fetuses at ~89 days gestational age (dGA; term ~148 dGA), compared with appropriate for gestational age (AGA) controls. Lactoferrin supplementation to the ewe commenced at 95 dGA (oral, 36 g/day) and continued until 127 dGA (fetal group) or birth (newborn group). Experimental fetal groups included control appropriate for gestational age (AGA; n = 8), FGR (n = 5), control + lactoferrin (AGA + Lacto; n = 6), and FGR + lactoferrin (FGR + Lacto; n = 6). In the fetal group, results showed that neither FGR nor lactoferrin altered hippocampal structure at 127 dGA. Lactoferrin exposure significantly increased neuronal abundance but also altered neuronal morphology. Lactoferrin increased the neurotrophic factor, brain-derived neurotrophic factor (BDNF) in the hippocampus. Lactoferrin exerted region-specific anti-inflammatory effects, with reduced total microglial cell count and resting microglia count in the Cornu Ammonis (CA)3 region only. In the newborn cohort, we observed increased circulating haematocrit concentration in early life. These findings support that antenatal lactoferrin has an anti-inflammatory effect in the fetal brain and increases fetal brain neurotrophic factor BDNF. Still, prolonged exposure during pregnancy may yield mixed effects on fetal brain development and haematological balance.

Neonatal hypoxia ischemia (HI) causes injury to the blood brain barrier (BBB), which in turn is associated with widespread cell loss. Cell therapies are currently being investigated for use in perinatal neuroprotection and umbilical cord blood (UCB) endothelial progenitor cells (EPCs; CD133+) have been previously shown to reduce gross neuropathology associated with HI; however, no study has investigated the effect of EPC treatment on the vulnerable BBB. Therefore, in this study, we investigated the effect of EPC treatment on BBB integrity in a neonatal rat model of HI. HI brain injury was induced in postnatal day (PND) 7 rat pups via permanent ligation of the left carotid artery, followed by a 180-minute hypoxic challenge at 8

IntroductionFetal growth restriction (FGR) is a common pregnancy complication, caused by placental insufficiency, with serious adverse consequences for development in utero and postnatal wellbeing. There are no antenatal treatments to improve growth or organ development in FGR, and animal models are essential to mimic the physiological adaptations in FGR and to assess potential interventions. This study aimed to identify the temporal nature of reduced developmental trajectory in fetuses with FGR, and to examine the effects of common factors that may mediate differential growth such as glucocorticoid treatment. We hypothesised that the trajectory of growth would be adversely impacted by FGR.MethodsFGR was induced via surgical placental insufficiency in fetal sheep (89 days gestation/0.6 gestation; n=135) and compared to age-matched controls over the last third of gestation and into neonatal life (n=153).ResultsBody weight of FGR fetuses/lambs was significantly reduced compared to controls (p<0.0001) from 127 days of gestation (term is 148 days), with increased brain:body weight ratio (p<0.0001) indicative of brain sparing. All biometric measures of body size were reduced in the FGR group with the exception of biparietal (head) diameter. The trajectory of body growth in the last trimester of sheep pregnancy was significantly reduced in the FGR group compared to controls, and stillbirth rate increased with longer gestation.DiscussionThis work provides a well characterised FGR animal model that mimics the known physiological adaptations in human pregnancy and can be used to determine the efficacy of potential interventions.

The hippocampus is a neuron-rich specialised brain structure that plays a central role in the regulation of emotions, learning and memory, cognition, spatial navigation, and motivational processes. In human fetal development, hippocampal neurogenesis is principally complete by mid-gestation, with subsequent maturation comprising dendritogenesis and synaptogenesis in the third trimester of pregnancy and infancy. Dendritogenesis and synaptogenesis underpin connectivity. Hippocampal development is exquisitely sensitive to perturbations during pregnancy and at birth. Clinical investigations demonstrate that preterm birth, fetal growth restriction (FGR), and acute hypoxic-ischaemic encephalopathy (HIE) are common perinatal complications that alter hippocampal development. In turn, deficits in hippocampal development and structure mediate a range of neurodevelopmental disorders, including cognitive and learning problems, autism, and Attention-Deficit/Hyperactivity Disorder (ADHD). In this review, we summarise the developmental profile of the hippocampus during fetal and neonatal life and examine the hippocampal deficits observed following common human pregnancy complications. Impact The review provides a comprehensive summary of the developmental profile of the hippocampus in normal fetal and neonatal life. We address a significant knowledge gap in paediatric research by providing a comprehensive summary of the relationship between pregnancy complications and subsequent hippocampal damage, shedding new light on this critical aspect of early neurodevelopment.

Blood–brain barrier (BBB) dysfunction and neuroinflammation are key mechanisms of brain injury. We performed a time-course study following neonatal hypoxia–ischemia (HI) to characterize these events. HI brain injury was induced in postnatal day 10 rats by single carotid artery ligation followed by hypoxia (8% oxygen, 90 min). At 6, 12, 24, and 72 h (h) post-HI, brains were collected to assess neuropathology and BBB dysfunction. A significant breakdown of the BBB was observed in the HI injury group compared to the sham group from 6 h in the cortex and hippocampus (p < 0.001), including a significant increase in albumin extravasation (p < 0.0033) and decrease in basal lamina integrity and tight-junction proteins. There was a decrease in resting microglia (p < 0.0001) transitioning to an intermediate state from as early as 6 h post-HI, with the intermediate microglia peaking at 12 h (p < 0.0001), which significantly correlated to the peak of microbleeds. Neonatal HI insult leads to significant brain injury over the first 72 h that is mediated by BBB disruption within 6 h and a transitioning state of the resident microglia. Key BBB events coincide with the appearance of the intermediate microglial state and this relationship warrants further research and may be a key target for therapeutic intervention.

BACKGROUND:Early-onset fetal growth restriction (FGR) is associated with adverse outcomes. We hypothesised that maternal melatonin administration will improve fetal brain structure in FGR. METHODS:Surgery was performed on twin-bearing ewes at 88 days (0.6 gestation), and FGR induced in one twin via single umbilical artery ligation. Melatonin was administered intravenously (6 mg/day) to a group of ewes commencing on day of surgery until 127 days (0.85 gestation), when the ewe/fetuses were euthanized, and fetal brains collected. RESULTS:Study groups were control (n = 5), FGR (n = 5), control+melatonin (control+MLT; n = 6) and FGR+melatonin (FGR + MLT; n = 6). Melatonin administration did not significantly alter fetal body or brain weights. Myelin (CNPase+) fibre density was reduced in FGR vs. control animals in most brain regions examined (p < 0.05) and melatonin treatment restored CNPase fibre density. Similar but less pronounced effect was seen with mature myelin (MBP+) staining. Significant differences in activated microglia (Iba-1) activity were seen between lamb groups (MLT mitigated FGR effect) in periventricular white matter, subventricular zone and external capsule (p < 0.05). Similar effects were seen in astrogliosis (GFAP) in intragyral white matter and cortex. CONCLUSIONS:Maternal melatonin administration in early onset FGR led to improved myelination of white matter brain regions, possibly mediated by decreased inflammation. IMPACT:Maternal melatonin administration might lead to neuroprotection in the growth-restricted fetus, possibly via dampening neuroinflammation and enhancing myelination. This preclinical study adds to the body of work on this topic, and informs clinical translation. Neuroprotection likely to improve long-term outcomes of this vulnerable infant group.