A simple novel approach for detecting blood-brain barrier permeability using GPCR internalization.

AIMS: Impairment of blood-brain barrier (BBB) is involved in numerous neurological diseases from developmental to aging stages. Reliable imaging of increased BBB permeability is therefore crucial for basic research and preclinical studies. Today, the analysis of extravasation of exogenous dyes is the principal method to study BBB leakage. However, these procedures are challenging to apply in pups and embryos and may appear difficult to interpret. Here we introduce a novel approach based on agonist-induced internalization of a neuronal G protein-coupled receptor widely distributed in the mammalian brain, the somatostatin receptor type 2 (SST2). METHODS: The clinically approved SST2 agonist octreotide (1 kDa), when injected intraperitoneally does not cross an intact BBB. At sites of BBB permeability, however, OCT extravasates and induces SST2 internalization from the neuronal membrane into perinuclear compartments. This allows an unambiguous localization of increased BBB permeability by classical immunohistochemical procedures using specific antibodies against the receptor. RESULTS: We first validated our approach in sensory circumventricular organs which display permissive vascular permeability. Through SST2 internalization, we next monitored BBB opening induced by magnetic resonance imaging-guided focused ultrasound in murine cerebral cortex. Finally, we proved that after intraperitoneal agonist injection in pregnant mice, SST2 receptor internalization permits analysis of BBB integrity in embryos during brain development. CONCLUSIONS: This approach provides an alternative and simple manner to assess BBB dysfunction and development in different physiological and pathological conditions.

EFNB2 haploinsufficiency causes a syndromic neurodevelopmental disorder.

Ephrin B2, one of the ligand of the EphB receptors, is involved in a complex signaling pathway regulating the development of the nervous system, neuronal migration, erythropoiesis and vasculogenesis. We report a patient with a de novo variant in EFNB2 and a family in which segregates a 610-kb deletion at chromosome 13q33 encompassing only ARGLU1 and EFNB2 genes. The de novo variant was observed in a patient with anal stenosis, hypoplastic left ventricle and mild developmental delay. The deletion was identified in 2 sibs with congenital heart defect and mild developmental delay. One of the affected sibs further had myoclonic epilepsy and bilateral sensorineural hearing loss. The carrier mother was apparently asymptomatic. Because EFNB2 is located in the subtelomeric region of 13q chromosome, we reviewed the previous reports of terminal 13q deletion. We suggest that haploinsufficiency of the EFNB2 could be at the origin of several clinical features reported in 13qter deletions, including intellectual disability, seizures, congenital heart defects, anorectal malformation and hearing loss.

Dietary omega-3 deficiency exacerbates inflammation and reveals spatial memory deficits in mice exposed to lipopolysaccharide during gestation.

Maternal immune activation (MIA) is a common environmental insult on the developing brain and represents a risk factor for neurodevelopmental disorders. Animal models of in utero inflammation further revealed a causal link between maternal inflammatory activation during pregnancy and behavioural impairment relevant to neurodevelopmental disorders in the offspring. Accumulating evidence point out that proinflammatory cytokines produced both in the maternal and fetal compartments are responsible for social, cognitive and emotional behavioral deficits in the offspring. Polyunsaturated fatty acids (PUFAs) are essential fatty acids with potent immunomodulatory activities. PUFAs and their bioactive derivatives can promote or inhibit many aspects of the immune and inflammatory response. PUFAs of the n-3 series ('n-3 PUFAs', also known as omega-3) exhibit anti-inflammatory/pro-resolution properties and promote immune functions, while PUFAs of the n-6 series ('n-6 PUFAs' or omega-6) favor pro-inflammatory responses. The present study aimed at providing insight into the effects of n-3 PUFAs on the consequences of MIA on brain development. We hypothesized that a reduction in n-3 PUFAs exacerbates both maternal and fetal inflammatory responses to MIA and later-life defects in memory in the offspring. Based on a lipopolysaccharide (LPS) model of MIA (LPS injection at embryonic day 17), we showed that n-3 PUFA deficiency 1) alters fatty acid composition of the fetal and adult offspring brain; 2) exacerbates maternal and fetal inflammatory processes with no significant alteration of microglia phenotype, and 3) induces spatial memory deficits in the adult offspring. We also showed a strong negative correlation between brain content in n-3 PUFA and cytokine production in MIA-exposed fetuses. Overall, our study is the first to address the deleterious effects of n-3 PUFA deficiency on brain lipid composition, inflammation and memory performances in MIA-exposed animals and indicates that it should be considered as a potent environmental risk factor for the apparition of neurodevelopmental disorders.

Pharmacokinetics of dexmedetomidine combined with therapeutic hypothermia in a piglet asphyxia model.

BACKGROUND: The highly selective α2 -adrenoreceptor agonist, dexmedetomidine, exerts neuroprotective, analgesic, anti-inflammatory and sympatholytic properties that may be beneficial for perinatal asphyxia. The optimal safe dose for pre-clinical newborn neuroprotection studies is unknown. METHODS: Following cerebral hypoxia-ischaemia, dexmedetomidine was administered to nine newborn piglets in a de-escalation dose study in combination with hypothermia (whole body cooling to 33.5°C). Dexmedetomidine was administered with a loading dose of 1 µg/kg and maintenance infusion at doses from 10 to 0.6 µg/kg/h. One additional piglet was not subjected to hypoxia-ischaemia. Blood for pharmacokinetic analysis was sampled pre-insult and frequently post-insult. A one-compartment linear disposition model was used to fit data. Population parameter estimates were obtained using non-linear mixed effects modelling. RESULTS: All dexmedetomidine infusion regimens led to plasma concentrations above those associated with sedation in neonates and children (0.4-0.8 µg/l). Seven out of the nine piglets with hypoxia-ischaemia experienced periods of bradycardia, hypotension, hypertension and cardiac arrest; all haemodynamic adverse events occurred in piglets with plasma concentrations greater than 1 µg/l. Dexmedetomidine clearance was 0.126 l/kg/h [coefficient of variation (CV) 46.6.%] and volume of distribution was 3.37 l/kg (CV 191%). Dexmedetomidine clearance was reduced by 32.7% at a temperature of 33.5°C. Dexmedetomidine clearance was reduced by 55.8% following hypoxia-ischaemia. CONCLUSIONS: Dexmedetomidine clearance was reduced almost tenfold compared with adult values in the newborn piglet following hypoxic-ischaemic brain injury and subsequent therapeutic hypothermia. Reduced clearance was related to cumulative effects of both hypothermia and exposure to hypoxia. High plasma levels of dexmedetomidine were associated with major cardiovascular complications.

Neuroinflammatory markers at school age in preterm born children with neurodevelopmental impairments.

Background: Immune system activation in the neonatal period is associated with white matter injury in preterm infants. In animal studies, neonatal priming of the immune system leads to chronic activation of i.e. microglia cells and altered neuroinflammatory responses potentially years after preterm birth. This may contribute further to brain injury and neurodevelopmental impairment. It is unknown to what extend this also occurs in human. Aim: To identify neuro-inflammatory markers at school age that relate to motor, cognitive and behavioral impairments in preterm born children in a pilot case-control study. Methods: We included n = 20 preterm born children (GA < 28 weeks) in this study, of which n = 10 with motor, cognitive and behavorial impairments and n = 10 preterm born controls next to n = 30 healthy adult controls. In the preterm children, at 8-9 years, 39 inflammatory markers were assessed by Luminex assay in blood serum samples. Firstly, the preterm concentrations of these markers were compared to n = 30 adult controls. Then a univariate analysis was performed to determine differences in values between preterm children with and without impairment at school age. Finally, a principal component analysis and hierarchical clustering was performed to identify protein profiles in preterm born children that relate to impairment at school age. Results: Inflammatory proteins in preterm children at school age differed from values of adult controls. Within the group of preterm children, we found significantly higher levels of GM-CSF in preterms with impairment (p < 0.01) and a trend towards significance for Gal1 and TRAIL (p = 0.06 and p = 0.06 respectively) when compared to preterms without impairment. In addition, differences in clustering of proteins between preterm children was observed, however this variance was not explained by presence of neurodevelopmental impairments. Conclusion: The inflammatory profile at school age in preterm children is different from that of adult controls. The immune modulating cytokines GM-CSF, Gal1 and TRAIL were higher in preterm children with impairment than control preterm children, suggesting that immune responses are altered in these children. No specific cluster of inflammatory markers could be identified. Results indicate that even at school age, neuroinflammatory pathways are activated in preterm born children with neurodevelopmental impairments.

Toll-like receptor 3 expression in glia and neurons alters in response to white matter injury in preterm infants.

Toll-like receptors (TLRs) are members of the pattern recognition receptor family that detect components of foreign pathogens or endogenous molecules released in response to injury. Recent studies demonstrate that TLRs also have a functional role in regulating neuronal proliferation in the developing brain. This study investigated cellular expression of TLR3 using immunohistochemistry on human brain tissue. The tissue sections analysed contained anterior and lateral periventricular white matter from the frontal and parietal lobes in post-mortem neonatal cases with a postmenstrual age range of 23.6-31.4 weeks. In addition to preterm brains without overt pathology (control), preterm pathology cases with evidence of white matter injuries (WMI) were also examined. In order to identify TLR-positive cells, we utilized standard double-labelling immunofluorescence co-labelling techniques and confocal microscopy to compare co-expression of TLR3 with a neuronal marker (NeuN) or with glial markers (GFAP for astrocytes, Iba-1 for microglia and Olig2 for oligodendrocytes). We observed an increase in the neuronal (28 vs. 17%) and astroglial (38 vs. 21%) populations in the WMI group compared to controls in the anterior regions of the periventricular white matter in the frontal lobe. The increase in neurons and astrocytes in the WMI cases was associated with an increase in TLR3 immunoreactivity. This expression was significantly increased in the astroglia. The morphology of the TLR3 signal in the control cases was globular and restricted to the perinuclear region of the neurons and astrocytes, whilst in the cases of WMI, both neuronal, axonal and astroglial TLR3 expression was more diffuse (i.e., a different intracellular distribution) and could be detected along the extensions of the processes. This study demonstrates for the first time that neurons and glial cells in human neonatal periventricular white matter express TLR3 during development. The patterns of TLR3 expression were altered in the presence of WMI, which might influence normal developmental processes within the immature brain. Identifying changes in TLR3 expression during fetal development may be key to understanding the reduced volumes of grey matter and impaired cortical development seen in preterm infants.

A mouse model for Zellweger syndrome.

The cerebro-hepato-renal syndrome of Zellweger is a fatal inherited disease caused by deficient import of peroxisomal matrix proteins. The pathogenic mechanisms leading to extreme hypotonia, severe mental retardation and early death are unknown. We generated a Zellweger animal model through inactivation of the murine Pxr1 gene (formally known as Pex5) that encodes the import receptor for most peroxisomal matrix proteins. Pxr1-/- mice lacked morphologically identifiable peroxisomes and exhibited the typical biochemical abnormalities of Zellweger patients. They displayed intrauterine growth retardation, were severely hypotonic at birth and died within 72 hours. Analysis of the neocortex revealed impaired neuronal migration and maturation and extensive apoptotic death of neurons.

Deletion of the hypoxia-response element in the vascular endothelial growth factor promoter causes motor neuron degeneration.

Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons.

Potential antiviral effects of pantethine against SARS-CoV-2.

SARS-CoV-2 interacts with cellular cholesterol during many stages of its replication cycle. Pantethine was reported to reduce total cholesterol levels and fatty acid synthesis and potentially alter different processes that might be involved in the SARS-CoV-2 replication cycle. Here, we explored the potential antiviral effects of pantethine in two in vitro experimental models of SARS-CoV-2 infection, in Vero E6 cells and in Calu-3a cells. Pantethine reduced the infection of cells by SARS-CoV-2 in both preinfection and postinfection treatment regimens. Accordingly, cellular expression of the viral spike and nucleocapsid proteins was substantially reduced, and we observed a significant reduction in viral copy numbers in the supernatant of cells treated with pantethine. In addition, pantethine inhibited the infection-induced increase in TMPRSS2 and HECT E3 ligase expression in infected cells as well as the increase in antiviral interferon-beta response and inflammatory gene expression in Calu-3a cells. Our results demonstrate that pantethine, which is well tolerated in humans, was very effective in controlling SARS-CoV-2 infection and might represent a new therapeutic drug that can be repurposed for the prevention or treatment of COVID-19 and long COVID syndrome.

Maternal dietary omega-3 deficiency worsens the deleterious effects of prenatal inflammation on the gut-brain axis in the offspring across lifetime.

Maternal immune activation (MIA) and poor maternal nutritional habits are risk factors for the occurrence of neurodevelopmental disorders (NDD). Human studies show the deleterious impact of prenatal inflammation and low n-3 polyunsaturated fatty acid (PUFA) intake on neurodevelopment with long-lasting consequences on behavior. However, the mechanisms linking maternal nutritional status to MIA are still unclear, despite their relevance to the etiology of NDD. We demonstrate here that low maternal n-3 PUFA intake worsens MIA-induced early gut dysfunction, including modification of gut microbiota composition and higher local inflammatory reactivity. These deficits correlate with alterations of microglia-neuron crosstalk pathways and have long-lasting effects, both at transcriptional and behavioral levels. This work highlights the perinatal period as a critical time window, especially regarding the role of the gut-brain axis in neurodevelopment, elucidating the link between MIA, poor nutritional habits, and NDD.

Microglial MyD88 signaling regulates acute neuronal toxicity of LPS-stimulated microglia in vitro.

Although the role of microglial activation in neural injury remains controversial, there is increasing evidence for a detrimental effect in the immature brain, which may occur in response to release of neurotoxic substances including pro-inflammatory cytokines. However, the signaling mechanisms involved in microglial-induced neuronal cell death are unclear. Microglia isolated from the brains of wild-type (WT) or MyD88 knockout (KO) mice were exposed to PBS or the TLR4-ligand LPS (100 ng/mL) for 2, 6, 14, or 24 h, and the microglia-conditioned medium (MCM) collected. Detection of multiple inflammatory molecules in MCM was performed using a mouse 22-plex cytokine microbead array kit. Primary neuronal cultures were supplemented with the 14 or 24 h MCM, and the degree of neuronal apoptosis examined after exposure for 24 h. Results showed a rapid and sustained elevation in multiple inflammatory mediators in the MCM of WT microglia exposed to LPS, which was largely inhibited in MyD88 KO microglia. There was a significant increase in apoptotic death measured at 24 h in cultured neurons exposed to CM from either 14 or 24 h LPS-stimulated WT microglia (p<.05 vs. WT control). By contrast, there was no increase in apoptotic death in cultured neurons exposed to CM from 14 or 24 h LPS-stimulated MyD88 KO microglia (p=.15 vs. MyD88 KO control). These data suggest that MyD88-dependent activation of microglia by LPS causes release of factors directly toxic to neurons.

Essential omega-3 fatty acids tune microglial phagocytosis of synaptic elements in the mouse developing brain.

Omega-3 fatty acids (n-3 PUFAs) are essential for the functional maturation of the brain. Westernization of dietary habits in both developed and developing countries is accompanied by a progressive reduction in dietary intake of n-3 PUFAs. Low maternal intake of n-3 PUFAs has been linked to neurodevelopmental diseases in Humans. However, the n-3 PUFAs deficiency-mediated mechanisms affecting the development of the central nervous system are poorly understood. Active microglial engulfment of synapses regulates brain development. Impaired synaptic pruning is associated with several neurodevelopmental disorders. Here, we identify a molecular mechanism for detrimental effects of low maternal n-3 PUFA intake on hippocampal development in mice. Our results show that maternal dietary n-3 PUFA deficiency increases microglia-mediated phagocytosis of synaptic elements in the rodent developing hippocampus, partly through the activation of 12/15-lipoxygenase (LOX)/12-HETE signaling, altering neuronal morphology and affecting cognitive performance of the offspring. These findings provide a mechanistic insight into neurodevelopmental defects caused by maternal n-3 PUFAs dietary deficiency.

IL-9/IL-9 receptor signaling selectively protects cortical neurons against developmental apoptosis.

In mammals, programmed cell death (PCD) is a central event during brain development. Trophic factors have been shown to prevent PCD in postmitotic neurons. Similarly, cytokines have neurotrophic effects involving regulation of neuronal survival. Nevertheless, neuronal PCD is only partially understood and host determinants are incompletely defined. The present study provides evidence that the cytokine interleukin-9 (IL-9) and its receptor specifically control PCD of neurons in the murine newborn neocortex. IL-9 antiapoptotic action appeared to be time-restricted to early postnatal stages as both ligand and receptor transcripts were mostly expressed in neocortex between postnatal days 0 and 10. This period corresponds to the physiological peak of apoptosis for postmitotic neurons in mouse neocortex. In vivo studies showed that IL-9/IL-9 receptor pathway inhibits apoptosis in the newborn neocortex. Furthermore, in vitro studies demonstrated that IL-9 and its receptor are mainly expressed in neurons. IL-9 effects were mediated by the activation of the JAK/STAT (janus kinase/signal transducer and activator of transcription) pathway, whereas nuclear factor-kappaB (NF-kappaB) or Erk pathways were not involved in mediating IL-9-induced inhibition of cell death. Finally, IL-9 reduced the expression of the mitochondrial pro-apoptotic factor Bax whereas Bcl-2 level was not significantly affected. Together, these data suggest that IL-9/IL-9 receptor signaling pathway represents a novel endogenous antiapoptotic mechanism for cortical neurons by controlling JAK/STAT and Bax levels.

Different types of nutritional deficiencies affect different domains of spatial memory function checked in a radial arm maze.

Several studies using animal models have suggested that the effects of nutritional insult on the developing brain are long-lasting and lead to permanent deficits in learning and behavior. Malnutrition can refer to the availability of all the nutrients but in insufficient quantities or it may imply that one or more of essential nutrients is either missing or is present, but in the wrong proportions in the diet. The hypothesis addressed in this study is that different domains of cognitive functioning can be affected by malnutrition and this can be related to the type of nutritional deficiency that the brain has been exposed to during development. To study the effect of nutritional deprivation during brain development, a paradigm of maternal malnutrition during the period of gestation and lactation was used and its effects were studied on the F1 offspring using Swiss albino mice. Three different types of malnutrition were used, that involve, caloric restriction, inadequate amount of protein in the diet and condition of low iron content. Our results show that the domain of spatial memory affected in the F1 generation depended on the kind of malnutrition that the mother was subjected to. Further our study shows that although hippocampal volume was reduced in all F1 pups, hippocampal subregions of the F1 animals were differentially vulnerable depending on type of malnutrition that the mother was subjected to. These results highlight the importance of qualifying the kind of malnutrition that is suffered by the mother during the period of gestation and lactation as it has consequences for the cognitive domain affected in the offspring. Awareness of this should inform prevention strategies in trying to reverse the effects of adverse maternal nutrition during critical periods in brain development.

[Neuroprotection with hypothermia for hypoxic ischemic encephalopathy in term newborn: review of the learning]. / Neuroprotection par hypothermie lors des encéphalopathies anoxo-ischémiques du nouveau-né à terme: état des connaissances.

The hypothermia treatment for neonatal hypoxic ischemic encephalopathy is a concept revisited for more than 10 years. With this strategy, animal studies have shown an 80% reduction of brain damage. Conditions for the practice of hypothermia, to obtain neuroprotection, have been described in these studies: rapidity of the onset of cooling after the hypoxic ischemic event, prolonged duration during several hours, ability to obtain neuroprotection with two methods of cooling, selective head cooling or whole body hypothermia. Pilot studies in human newborns have demonstrated the feasibility of these strategies without immediate adverse effects. Two large randomised trials have been conducted in 2005 to test the efficacy. Only with the strategy of whole body cooling, the incidence of poor outcome at 18 months (death or severe disability) was statistically decreased (44% versus 66% in the control group). This reduction seems especially significant in the sub group of intermediate severity (48% versus 66%), whereas severe forms (Grade III in the Sarnat and Sarnat classification) were probably not ameliorated with this treatment. Now, the major problem is to determine the best indications for hypothermia with an early and precise assessment of the grade of the encephalopathy.

[Distal spinal-muscular atrophy 1 (DSMA1 or SMARD1)]. / L'amyotrophie spinale distale de type 1 (DSMA1 ou SMARD1).

In this article, we review the clinical, neuropathological and genetic aspects of distal spinal-muscular atrophy 1 (DSMA1; MIM#604320), formerly designated as autosomal recessive spinal muscular atrophy with respiratory distress type 1 (SMARD1) and also known as distal hereditary-motor neuropathy type 6 (dHMN6 or HMN6).

Severe microcephaly induced by blockade of vasoactive intestinal peptide function in the primitive neuroepithelium of the mouse.

Vasoactive intestinal peptide (VIP) has potent growth-related actions that influence cell mitosis, neuronal survival, and neurodifferentiation in cell culture. VIP can also produce dramatic growth in postimplantation mouse embryos in vitro, characterized by large increases in cell number. The goal of the present study was to assess the role of VIP on early nervous system development in vivo. Pregnant mice were treated with a specific antagonist to VIP. Prenatal administration of the antagonist early in development (E9-E11) produced severe microcephaly characterized by decreased embryonic brain weight with reduced DNA and protein content. The retardation of growth was disproportionally manifested in the brain compared with the body and was prevented by co-treatment with VIP. Identical treatment with the antagonist later in gestation had no detectable effect on embryonic growth. VIP receptors, which were restricted to the central nervous system during this stage of embryonic development, were increased in the neuroepithelium of antagonist-treated embryos while the number of cells in S-phase was significantly decreased. Thus, VIP regulates brain growth in vivo and inhibition of its action provides new insight into a molecular mechanism for microcephaly.

Vasoactive intestinal peptide prevents excitotoxic cell death in the murine developing brain.

Excitotoxic damage may be a critical factor in the formation of brain lesions associated with cerebral palsy. When injected at birth, the glutamatergic analog ibotenate induces mouse brain lesions that strikingly mimic human microgyria. When ibotenate is injected at postnatal day 5, it produces transcortical necrosis and white matter cysts that mimic human perinatal hypoxic-like lesions. Vasoactive intestinal peptide (VIP) has potent growth-related actions and neuroprotective properties that influence mitosis and neuronal survival in culture. The goal of this study was to assess the protective role of VIP against excitotoxic lesions induced by ibotenate in developing mouse brain. VIP cotreatment reduced ibotenate-induced microgyric-like cortical lesions and white matter cysts by up to 77 and 85%, respectively. VIP protective effects were reproduced by a peptide derived from activity-dependent neurotrophic factor (ADNF), a trophic factor released by VIP-stimulated astrocytes, and by stearyl norleucine VIP, a specific VIP agonist that does not activate adenylate cyclase. Neither forskolin, an adenylate cyclase activator, nor pituitary adenylate cyclase-activating peptide, provided VIP-like protection. VIP and neurotrophic analogs, acting through a cAMP-independent mechanism and inducing ADNF release, could represent new avenues in the understanding and prevention of human cerebral palsy.

Nociceptin/orphanin FQ exacerbates excitotoxic white-matter lesions in the murine neonatal brain.

Intracerebral administration of the excitotoxin ibotenate to newborn mice induces white-matter lesions, mimicking brain lesions that occur in human preterm infants. Nociceptin (NC), also called orphanin FQ, is the endogenous ligand of the opioid receptor-like 1 (ORL1) receptor and does not bind classical high-affinity opioid receptors. In the present study, administration of NC exacerbated ibotenate-induced white-matter lesions while coadministration of ibotenate with either of two NC antagonists reduced excitotoxic white-matter lesions by up to 64%. Neither ibotenate plus endomorphin I (a selective mu receptor agonist), nor ibotenate plus naloxone (a classical opioid receptor antagonist) modulated the excitotoxic lesion. Pretreatment with antisense oligonucleotides targeting the NC precursor peptide mRNA significantly reduced ibotenate-induced white-matter damage. Finally, high doses of fentanyl, which stimulates both classical mu-opioid receptors and ORL1, exacerbated excitotoxic white-matter lesion. This toxic effect was blocked by inhibiting ORL1 but not classical opioid receptors. Together, these findings show that endogenous or exogenous stimulation of the ORL1 receptor can be neurotoxic and that blocking NC signaling protects the white matter against excitotoxic challenge. These data point to potential new avenues for neuroprotection in human preterm infants at high risk of brain lesions.

Melatonin prevents learning disorders in brain-lesioned newborn mice.

Perinatal brain injuries often result in irreversible learning disabilities, which manifest in early childhood. These injuries are chiefly ascribable to marked susceptibility of the immature brain to glutamate-induced excitotoxicity. No treatments are available. One well-characterized model of perinatal brain injuries consists in injecting the glutamate analog ibotenate into the brain of 5-day-old mice. The resulting excitotoxic lesions resemble the hypoxic-ischemic gray-matter lesions seen in full-term and near-term newborns, as well as the white-matter lesions of preterm newborns. We previously reported that these lesions disrupted odor preference conditioning in newborn mice. The aim of this study was to assess the effectiveness of the neuroprotector melatonin in preventing learning disabilities in newborn mice with ibotenate-induced brain injury. In postnatal day (P) 6-P7 pups, we tested psychomotor reflexes, spontaneous preference for maternal odors as an index of memory, ultrasonic vocalization responses to stroking as an index of sensitivity to tactile stimuli, and conditioned preference for an odor previously paired with stroking as an index of learning abilities. Without melatonin, conditioning was abolished, whereas spontaneous odor preference, psychomotor reflexes, and sensitivity to tactile stimuli were normal. Thus, abolition of conditioning was not associated with sensorimotor impairments. Histological analysis confirmed the efficacy of melatonin in reducing white-matter lesions induced by ibotenate. Furthermore, treatment with melatonin protected the ability to develop conditioning. Thus, melatonin, which easily crosses the blood-brain barrier and has been proven safe in children, may be effective in preventing learning disabilities caused by perinatal brain injuries in human preterm infants.