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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., (© 2024. The Author(s).)

Objective: Neonatal encephalopathy (NE) is an important cause of mortality and disability worldwide. Therapeutic hypothermia (HT) is an effective therapy, however not all babies benefit. Novel agents are urgently needed to improve outcomes. Melatonin in preclinical studies has promising neuroprotective properties. This meta-analysis assessed the efficacy of melatonin in term animal models of NE on cerebral infarct size, neurobehavioural tests and cell death., Methods: A literature search was carried out using Embase, MEDLINE and Web of Science (31 May 2021). We identified 14 studies and performed a meta-analysis with a random effects model using standardised mean difference (SMD) as the effect size. The risk of bias was assessed using the Systematic Review Centre for Laboratory animal Experimentation tool and publication bias was assessed with funnel plots, and adjusted using trim and fill analysis. Subgroup and meta-regression analyses were performed to assess the effects of study design variables., Results: We observed significant reduction in brain infarct size (SMD -2.05, 95% CI [-2.93, -1.16]), improved neurobehavioural outcomes (SMD -0.86, 95% CI [-1.23, -0.53]) and reduction in cell death (SMD -0.60, 95% CI [-1.06, -0.14]) favouring treatment with melatonin. Neuroprotection was evident as a single therapy and combined with HT. Subgroup analysis showed greater efficacy with melatonin given before or immediately after injury and with ethanol excipients. The overall effect size remained robust even after adjustment for publication bias., Interpretation: These studies demonstrate a significant neuroprotective efficacy of melatonin in term neonatal models of hypoxia-ischaemia, and suggest melatonin is a strong candidate for translation to clinical trials in babies with moderate-severe NE., (© 2022 The Authors. Annals of Clinical and Translational Neurology published by Wiley Periodicals LLC on behalf of American Neurological Association.)

Therapeutic hypothermia (TH) is standard care in high-resource birth settings for infants with neonatal encephalopathy. TH is partially effective and adjuvant therapies are needed. Here, we examined whether the antioxidant melatonin (MLT) provides additive benefit with TH, compared to TH alone or MLT alone, to improve recovery from acute encephalopathy in newborn lambs. Immediately before cesarean section delivery, we induced asphyxia in fetal sheep via umbilical cord occlusion until mean arterial blood pressure fell from 55 ± 3 mm Hg in sham controls to 18-20 mm Hg (10.1 ± 1.5 minutes). Lambs were delivered and randomized to control, control + MLT (60 mg iv, from 30 minutes to 24 hours), asphyxia, asphyxia + TH (whole-body cooling to 35.1 ± 0.8°C vs. 38.3 ± 0.17°C in sham controls, from 4-28 hours), asphyxia + MLT, and asphyxia + TH + MLT. At 72 hours, magnetic resonance spectroscopy (MRS) was undertaken, and then brains were collected for neuropathology assessment. Asphyxia induced abnormal brain metabolism on MRS with increased Lactate:NAA (P = .003) and reduced NAA:Choline (P = .005), induced apoptotic and necrotic cell death across gray and white matter brain regions (P < .05), and increased neuroinflammation and oxidative stress (P < .05). TH and MLT were independently associated with region-specific reductions in oxidative stress, inflammation, and cell death, compared to asphyxia alone. There was an interaction between TH and MLT such that the NAA:Choline ratio was not significantly different after asphyxia + TH + MLT compared to sham controls but had a greater overall reduction in neuropathology than either treatment alone. This study demonstrates that, in newborn lambs, combined TH + MLT for neonatal encephalopathy provides significantly greater neuroprotection than either alone. These results will guide the development of further trials for neonatal encephalopathy., (© 2021 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Introduction: Fetal growth restriction (FGR) is a serious pregnancy complication, associated with increased rates of perinatal death and morbidity among survivors. Most commonly FGR results from placental insufficiency, where the placenta fails to deliver the oxygen and nutrients required for normal fetal growth. This leads to fetal oxidative stress, resulting in organ damage through lipid peroxidation. The early developing brain is particularly susceptible, such that FGR is associated with poorer neurodevelopment, witnessed as cognitive and behavioural dysfunction, and cerebral palsy. Promisingly, melatonin, a lipid soluble antioxidant is neuroprotective in animal models of FGR. We present a protocol outlining a randomised, placebo-controlled trial to explore whether antenatal maternal melatonin supplementation in pregnancies with severe, early-onset FGR can improve neurodevelopment among survivors at 2 years of age., Methods and Analyses: We will recruit 336 women with a singleton pregnancy complicated by FGR between 23+0 and 31+6 weeks gestation. Participants will be randomised, stratified by gestational age, to either 30 mg melatonin per day or a visually identical placebo, continued until birth. Measures of maternal and fetal health will be collected until birth. Timing of birth will be determined by the treating clinical team in discussion with the woman. Neonatal and infant neurodevelopmental assessments will be undertaken, consisting of brain MRI at term corrected age, general movements assessment at term and 3 months' corrected age, and Bayley Scales of Infant & Toddler Development-III and Infant Toddler Social Emotional Assessment at 2.5 years corrected age. Analyses will be on intention to treat. The primary outcome is a difference of 5 points in the cognitive domain of the Bayley-III. Secondary outcomes address maternal and fetal safety., Ethics and Dissemination: This trial has Monash Health Human Research and Ethics committee approval (17-0000-583A). Findings will be disseminated through peer-reviewed publications, conference presentations and to participants., Trial Registration Number: ACTRN12617001515381; Pre-results., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Preeclampsia remains a leading cause of maternal and perinatal morbidity and mortality. There have been no material advances in the treatment of preeclampsia for nearly 50 years. Combining in vitro studies and a clinical trial, we aimed to determine whether melatonin could be a useful adjuvant therapy. In a xanthine/xanthine oxidase (X/XO) placental explant model, melatonin reduced oxidative stress (8-isoprostane) and enhanced antioxidant markers (Nrf2 translocation, HO-1), but did not affect explant production of anti-angiogenic factors (sFlt, sEng, activin A). In cultured HUVECs, melatonin mitigated TNFα-induced vascular cell adhesion molecule expression and rescued the subsequent disruption to endothelial monolayer integrity but did not affect other markers for endothelial activation and dysfunction. In a phase I trial of melatonin in 20 women with preeclampsia, we assessed the safety and efficacy of melatonin on (i) preeclampsia progression, (ii) clinical outcomes, and (iii) oxidative stress, matching outcomes with recent historical controls receiving similar care. Melatonin therapy was safe for mothers and their fetuses. Compared to controls, melatonin administration extended the mean ± SEM diagnosis to delivery interval by 6 ± 2.3 days reduced the need for increasing antihypertensive medication on days 3-4 (13% vs 71%), days 6-7 (8% vs 51%), and at delivery (26% vs 75%). All other clinical and biochemical measures of disease severity were unaffected by melatonin. We have shown that melatonin has the potential to mitigate maternal endothelial pro-oxidant injury and could therefore provide effective adjuvant therapy to extend pregnancy duration to deliver improved clinical outcomes for women with severe preeclampsia., (© 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Perinatal asphyxia remains a principal cause of infant mortality and long-term neurological morbidity, particularly in low-resource countries. No neuroprotective interventions are currently available. Melatonin (MLT), a potent antioxidant, anti-inflammatory and antiapoptotic agent, offers promise as an intravenous (IV) or transdermal therapy to protect the brain. We aimed to determine the effect of melatonin (IV or transdermal patch) on neuropathology in a lamb model of perinatal asphyxia. Asphyxia was induced in newborn lambs via umbilical cord occlusion at birth. Animals were randomly allocated to melatonin commencing 30 minutes after birth (60 mg in 24 hours; IV or transdermal patch). Brain magnetic resonance spectroscopy (MRS) was undertaken at 12 and 72 hours. Animals (control n = 9; control+MLT n = 6; asphyxia n = 16; asphyxia+MLT [IV n = 14; patch n = 4]) were euthanised at 72 hours, and cerebrospinal fluid (CSF) and brains were collected for analysis. Asphyxia resulted in severe acidosis (pH 6.9 ± 0.0; lactate 9 ± 2 mmol/L) and altered determinants of encephalopathy. MRS lactate:N-acetyl aspartate ratio was 2.5-fold higher in asphyxia lambs compared with controls at 12 hours and 3-fold higher at 72 hours (P < .05). Melatonin prevented this rise (3.5-fold reduced vs asphyxia; P = .02). Asphyxia significantly increased brain white and grey matter apoptotic cell death (activated caspase-3), lipid peroxidation (4HNE) and neuroinflammation (IBA-1). These changes were significantly mitigated by both IV and patch melatonin. Systemic or transdermal neonatal melatonin administration significantly reduces the neuropathology and encephalopathy signs associated with perinatal asphyxia. A simple melatonin patch, administered soon after birth, may improve outcome in infants affected by asphyxia, especially in low-resource settings., (© 2018 The Authors. Journal of Pineal Research Published by John Wiley & Sons Ltd.)

Oxidative stress arising from suboptimal placental function contributes to a multitude of pathologies in infants compromised by fetal growth restriction (FGR). FGR infants are at high risk for respiratory dysfunction after birth and poor long-term lung function. Our objective was to investigate the contribution of oxidative stress to adverse lung development and the effects of melatonin administration, a powerful antioxidant, on lung structure in FGR lambs. Placental insufficiency and FGR was surgically induced in 13 fetal sheep at ∼105 days of gestation by ligation of a single umbilical artery. Maternal intravenous melatonin infusion was commenced in seven of the ewes 4 h after surgery and continued until birth. Lambs delivered normally at term and lungs were collected 24 h after birth for histological assessment of lung structure and injury and compared with appropriately grown control lambs ( n = 8). FGR fetuses were hypoxic and had lower glucose during gestation compared with controls. Melatonin administration prevented chronic hypoxia. Within the lung, FGR caused reduced secondary septal crest density and altered elastin deposition compared with controls. Melatonin administration had no effect on the changes to lung structure induced by FGR. We conclude that chronic FGR disrupts septation of the developing alveoli, which is not altered by melatonin administration. These findings suggest that oxidative stress is not the mechanism driving altered lung structure in FGR neonates. Melatonin administration did not prevent disrupted airway development but also had no apparent adverse effects on fetal lung development. NEW & NOTEWORTHY Fetal growth restriction (FGR) results in poor respiratory outcomes, which may be caused by oxidation in utero. We investigated the contribution of oxidative stress to adverse lung development and the effects of melatonin administration, a powerful antioxidant, on lung structure in FGR lambs. FGR disrupted septation of the developing alveoli, which is not altered by melatonin administration. Oxidative stress may not be the mechanism driving altered lung structure in FGR neonates., (Copyright © 2017 the American Physiological Society.)

Chronic moderate hypoxia, such as occurs in fetal growth restriction (FGR) during gestation, compromises the blood-brain barrier (BBB) and results in structural abnormalities of the cerebral vasculature. We have previously determined the neuroprotective and antioxidant effects of maternal administration of melatonin (MLT) on growth-restricted newborn lambs. The potential of maternal MLT therapy for the treatment of cerebrovascular dysfunction-associated developmental hypoxia has also been demonstrated in newborn lambs. We assessed whether MLT had an effect on the previously reported structural and cerebral vascular abnormalities in chronically hypoxic FGR lambs. Single umbilical-artery ligation surgery was performed in fetuses at approximately 105 days of gestation (term: 147 days) to induce placental insufficiency and FGR, and treatment with either saline or an MLT infusion (0.1 mg/kg) was started 4 h after surgery. Ewes delivered naturally at term and lambs were euthanased 24 h later. We found a significant reduction in the number of laminin-positive blood vessels within the subcortical and periventricular white matter (SCWM and PVWM) and the subventricular zone (SVZ) in FGR (p < 0.0005) and FGR + MLT brains (p < 0.0005 vs. controls), with no difference found between FGR and FGR + MLT animals. This was associated with a significant decrease in VEGF immunoreactivity in FGR and FGR + MLT brains versus controls (p < 0.0005; SCWM and PVWM) and in the SVZ in FGR brains versus controls (p < 0.005) and also with significantly lower levels of proliferating blood vessels versus controls (p < 0.0005). Glucose transporter-1 immunoreactivity (vascular endothelium) was decreased in FGR versus control lambs (p < 0.0005) in SCWM, PVWM, and the SVZ; it was significantly increased in FGR + MLT lambs compared with FGR lambs in SCWM and PVWM (p < 0.005) and even more markedly in the SVZ (p < 0.0005). FGR brains showed a 72% reduction in pericyte coverage versus control lambs and 68% versus FGR + MLT in PVWM. In SCWM, we found a 77 and 73% reduction compared with control and FGR + MLT lambs, respectively, while in the SVZ, we observed a 68% reduction versus controls and a 70% reduction in FGR versus FGR + MLT lambs. Astrocyte end-feet coverage in the SCWM showed a significant 24% reduction in FGR versus control levels, a 42% decrease within the PVWM, and a 35% decrease within the SVZ versus controls. MLT normalized astrocyte attachment to blood vessels, with no difference seen between controls and FGR + MLT animals in any of the brain regions examined. We also observed a decrease in albumin extravasation and microhemorrhage in controls and FGR + MLT brains versus FGR lambs. Our results demonstrate that umbilicoplacental insufficiency is associated with FGR-produced vascular changes in the white matter and SVZ of FGR newborn brains and that maternal MLT prevented disruption of the BBB by protecting perivascular cells essential for the maintenance of vascular homeostasis and stability., (© 2017 S. Karger AG, Basel.)

Intrauterine growth restriction (IUGR) complicates 5-10% of pregnancies and is associated with increased risk of preterm birth, mortality and neurodevelopmental delay. The development of sleep and cardiovascular control are closely coupled and IUGR is known to alter this development. In the long-term, IUGR is associated with altered sleep and an increased risk of hypertension in adulthood. Melatonin plays an important role in the sleep-wake cycle. Experimental animal studies have shown that melatonin therapy has neuroprotective and cardioprotective effects in the IUGR fetus. Consequently, clinical trials are currently underway to assess the short and long term effects of antenatal melatonin therapy in IUGR pregnancies. Given melatonin's role in sleep regulation, this hormone could affect the developing infants' sleep-wake cycle and cardiovascular function after birth. In this review, we will 1) examine the role of melatonin as a therapy for IUGR pregnancies and the potential implications on sleep and the cardiovascular system; 2) examine the development of sleep-wake cycle in fetal and neonatal life; 3) discuss the development of cardiovascular control during sleep; 4) discuss the effect of IUGR on sleep and the cardiovascular system and 5) discuss the future implications of melatonin therapy in IUGR pregnancies., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Intrauterine growth restriction (IUGR) is associated with impaired cardiac function in childhood and is linked to short- and long-term morbidities. Placental dysfunction underlies most IUGR, and causes fetal oxidative stress which may impact on cardiac development. Accordingly, we investigated whether antenatal melatonin treatment, which possesses antioxidant properties, may afford cardiovascular protection in these vulnerable fetuses. IUGR was induced in sheep fetuses using single umbilical artery ligation on day 105-110 of pregnancy (term 147). Study 1: melatonin (2 mg h(-1)) was administered i.v. to ewes on days 5 and 6 after surgery. On day 7 fetal heart function was assessed using a Langendorff apparatus. Study 2: a lower dose of melatonin (0.25 mg h(-1)) was administered continuously following IUGR induction and the ewes gave birth normally at term. Lambs were killed when 24 h old and coronary vessels studied. Melatonin significantly improved fetal oxygenation in vivo. Contractile function in the right ventricle and coronary flow were enhanced by melatonin. Ischaemia-reperfusion-induced infarct area was 3-fold greater in IUGR hearts than in controls and this increase was prevented by melatonin. In isolated neonatal coronary arteries, endothelium-dependent nitric oxide (NO) bioavailability was reduced in IUGR, and was rescued by modest melatonin treatment. Melatonin exposure also induced the emergence of an indomethacin-sensitive vasodilation. IUGR caused marked stiffening of the coronary artery and this was prevented by melatonin. Maternal melatonin treatment reduces fetal hypoxaemia, improves heart function and coronary blood flow and rescues cardio-coronary deficit induced by IUGR., (© 2014 The Authors. The Journal of Physiology © 2014 The Physiological Society.)

Fetal intrauterine growth restriction (IUGR) is a serious pregnancy complication associated with increased rates of perinatal morbidity and mortality, and ultimately with long-term neurodevelopmental impairments. No intervention currently exists that can improve the structure and function of the IUGR brain before birth. Here, we investigated whether maternal antenatal melatonin administration reduced brain injury in ovine IUGR. IUGR was induced in pregnant sheep at 0.7 gestation and a subset of ewes received melatonin via intravenous infusion until term. IUGR, IUGR + melatonin (IUGR + MLT) and control lambs were born naturally, neonatal behavioral assessment was used to examine neurological function and at 24 hr after birth the brain was collected for the examination of neuropathology. Compared to control lambs, IUGR lambs took significantly longer to achieve normal neonatal lamb behaviors, such as standing and suckling. IUGR brains showed widespread cellular and axonal lipid peroxidation, and white matter hypomyelination and axonal damage. Maternal melatonin administration ameliorated oxidative stress, normalized myelination and rescued axonopathy within IUGR lamb brains, and IUGR + MLT lambs demonstrated significant functional improvements including a reduced time taken to attach to and suckle at the udder after birth. Based on these observations, we began a pilot clinical trial of oral melatonin administration to women with an IUGR fetus. Maternal melatonin was not associated with adverse maternal or fetal effects and it significantly reduced oxidative stress, as evidenced by reduced malondialdehyde levels, in the IUGR + MLT placenta compared to IUGR alone. Melatonin should be considered for antenatal neuroprotective therapy in human IUGR., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Melatonin has diverse physiological actions in addition to its well-recognized maintenance roles in circadian and seasonal timing. In particular, melatonin may have a direct protective action on the developing fetal brain. We examined the cellular processes by which melatonin provides protection following an acute late gestation hypoxic insult. 15 fetal sheep at 126 days' gestation were instrumented with a brachial artery catheter and a silastic cuff around the umbilical cord. At ~130 days' gestation, the cuff was inflated for 10 min in 10 fetuses, causing complete umbilical cord occlusion (UCO). 5 UCO fetuses received intravenous melatonin maternally for 2 h, before and after UCO (UCO + melatonin). The remaining 5 fetuses had no UCO performed (sham-operated controls). At 48 h after UCO, the fetal brain was collected from each animal. Compared to controls, UCO caused significant hypoxia, hypercapnia and acidosis in UCO and UCO + melatonin fetuses. In the UCO-alone animals there were significant increases in pyknotic cell death, in the hippocampus (>7-fold) and the cerebellum (3-fold). Maternal melatonin administration ameliorated cellular pyknosis in UCO fetuses. UCO was also associated with astrogliosis, increased albumin uptake, activated microglia and lipid peroxidation. Melatonin prevented these effects. There were no significant differences in the number of brain macrophages or microglia between any of the groups. Following acute severe hypoxia in the late gestation fetus, melatonin reduces neuronal lipid peroxidation and prevents loss of blood-brain barrier integrity and astrogliosis. These are likely key mechanisms underlying the neuroprotective actions of melatonin in the fetal brain., (Copyright © 2013 S. Karger AG, Basel.)

Oxygen free radicals, including the highly toxic hydroxyl radical (*OH), initiate lipid peroxidation and DNA/RNA fragmentation and damage cells. The pineal hormone melatonin is an antioxidant and powerful scavenger of *OH. We hypothesized that maternally administered melatonin could reduce *OH formation, lipid peroxidation, and DNA/RNA damage in the fetal brain in response to asphyxia. In 15 fetal sheep, extracellular *OH was measured by microdialysis in white and gray matter of the parasagittal cortex. In 10 fetuses, asphyxia was induced by umbilical cord occlusion for 10 min using an inflatable cuff - the ewes of these fetuses received either intravenous melatonin (1 mg bolus, then 1 mg/h for 2 h; n = 5) or vehicle (1% ethanol in saline; n = 5), and results were compared to fetuses with sham cord occlusion and vehicle-infused ewes (n = 5). Hypoxemia, acidemia, hypertension and bradycardia produced by cord occlusion was similar in the melatonin- and vehicle-treated groups. In the vehicle-treated group, cord occlusion resulted in a significant increase in *OH in gray matter at 8-9.5 h after occlusion (p < 0.05); in contrast, there was no *OH change in the melatonin-treated group. After cord occlusion, lipid peroxidation (4-hydroxynonenal immunoreactivity) found throughout the brain of vehicle-infused ewes was significantly less in the melatonin-infused group. Melatonin had no significant effect on the distribution of DNA/RNA fragmentation, as shown by 8-hydroxydeoxyguanosine immunoreactivity. Thus, brief asphyxia results in significant and delayed entry of *OH into the extracellular space of cortical gray matter in the fetal sheep brain, and melatonin given to the mother at the time of the insult abrogates this increase. Melatonin, in reducing O2 free radical production, may be an effective neuroprotective treatment for the fetus.

Melatonin (MLT) is an endogenous hormone that controls circadian cycle. MLT has additional important properties that make it appealing as a neuroprotective agent-- it is a potent anti-oxidant, with anti-apoptotic and anti-inflammatory properties. MLT is safe for administration during pregnancy or to the newborn after birth, and can reduce white matter brain injury under conditions of chronic fetal hypoxia. Accordingly, in the current study, we examined whether an intermediate dose of MLT could restore white matter brain development when administered after an acute hypoxic ischemic (HI) insult in preterm fetal sheep. Fifteen fetal sheep at 95-98 days gestation were instrumented with femoral artery and vein catheters, and a silastic cuff placed around the umbilical cord. At 102 days gestation, the cuff was inflated, causing complete umbilical cord occlusion for 25 min in 10 fetuses, to induce acute severe HI. Five HI fetuses received intravenous MLT for 24 h beginning at 2 h after HI. The remaining five fetuses were administered saline alone. Ten days after HI, the fetal brain was collected from each animal and white and gray matter neuropathology assessed. HI caused a significant increase in apoptotic cell death (TUNELC), activated microglia (Iba-1C), and oxidative stress (8-OHdGC) within the subventricular and subcortical white matter. HI reduced the total number of oligodendrocytes and CNPaseC myelin density. MLT administration following HI decreased apoptosis, inflammation and oxidative stress within the white matter. MLT had intermediate benefits for the developing white matter: it increased oligodendrocyte cell number within the periventricular white matter only, and improved CNPaseC myelin density within the subcortical but not the striatal white matter. MLT administration following HI was also associated with improved neuronal survival within the cortex. Neuropathology in preterm infants is complex and mediated by multiple mechanisms, including inflammation, oxidative stress and apoptotic pathways. Treatment with MLT presents a safe approach to neuroprotective therapy in preterm infants but appears to have brain region-specific benefits within the white matter. [ABSTRACT FROM AUTHOR]

Melatonin has diverse physiological actions in addition to its well-recognized maintenance roles in circadian and seasonal timing. In particular, melatonin may have a direct protective action on the developing fetal brain. We examined the cellular processes by which melatonin provides protection following an acute late gestation hypoxic insult. 15 fetal sheep at 126 days' gestation were instrumented with a brachial artery catheter and a silastic cuff around the umbilical cord. At ∼130 days' gestation, the cuff was inflated for 10 min in 10 fetuses, causing complete umbilical cord occlusion (UCO). 5 UCO fetuses received intravenous melatonin maternally for 2 h, before and after UCO (UCO + melatonin). The remaining 5 fetuses had no UCO performed (sham-operated controls). At 48 h after UCO, the fetal brain was collected from each animal. Compared to controls, UCO caused significant hypoxia, hypercapnia and acidosis in UCO and UCO + melatonin fetuses. In the UCO-alone animals there were significant increases in pyknotic cell death, in the hippocampus (>7-fold) and the cerebellum (3-fold). Maternal melatonin administration ameliorated cellular pyknosis in UCO fetuses. UCO was also associated with astrogliosis, increased albumin uptake, activated microglia and lipid peroxidation. Melatonin prevented these effects. There were no significant differences in the number of brain macrophages or microglia between any of the groups. Following acute severe hypoxia in the late gestation fetus, melatonin reduces neuronal lipid peroxidation and prevents loss of blood-brain barrier integrity and astrogliosis. These are likely key mechanisms underlying the neuroprotective actions of melatonin in the fetal brain. Copyright © 2013 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]