Melatoninergic neuroprotection of the murine periventricular white matter against neonatal excitotoxic challenge

Chronic mild stress during gestation worsens neonatal brain lesions in mice

Cerebral palsy remains a public health priority. Recognition of factors of susceptibility to perinatal brain lesions is key for the prevention of cerebral palsy. In most cases, the pathophysiology of these lesions is thought to involve prior exposure to predisposing factors that make the developing brain more vulnerable to perinatal events. The present study tested the hypothesis that exposure to chronic minimal stress throughout gestation would sensitize the offspring to neonatal excitotoxic brain lesions, which mimic lesions observed in cerebral palsy. Pregnant mice were exposed to chronic, ultramild stress, applied throughout gestation. Neonatal brain lesions were induced by intracerebral injection of glutamate analogs. Excitotoxic lesions were significantly worsened in pups exposed to gestational stress. Stress induced a significant rise of circulating corticosterone levels both in pregnant mothers and in newborn pups. The deleterious effects of stress on excitotoxicity were totally suppressed in mice with reduced levels of glucocorticoid receptors. Stress induced a significant increase of neopallial NMDA binding sites in the offspring. At adulthood, animals exposed to stress and neonatal excitotoxic challenge showed a significant impairment in the Morris water maze test when compared with animals exposed to the excitotoxic challenge but not the gestational stress. These findings suggest that stress during gestation, which may mimic low-level stress in human pregnancy, could be a novel risk factor for cerebral palsy.

N-acetylcysteine reduces lipopolysaccharide-sensitized hypoxic-ischemic brain injury

OBJECTIVE

Maternal inflammation/infection alone or in combination with birth asphyxia increases the risk for perinatal brain injury. Free radicals are implicated as major mediators of inflammation and hypoxia-ischemia (HI)-induced perinatal brain injury. This study evaluated the neuroprotective efficacy of a scavenging agent, N-acetylcysteine (NAC), in a clinically relevant model.

METHODS

Lipopolysaccharide (LPS)-sensitized HI brain injury was induced in 8-day-old neonatal rats. NAC was administered in multiple doses, and brain injury was evaluated at 7 days after HI.

RESULTS

NAC (200mg/kg) provided marked neuroprotection with up to 78% reduction of brain injury in the pre+post-HI treatment group and 41% in the early (0 hour) post-HI treatment group, which was much more pronounced protection than another free radical scavenger, melatonin. Protection by NAC was associated with the following factors: (1) reduced isoprostane activation and nitrotyrosine formation; (2) increased levels of the antioxidants glutathione, thioredoxin-2, and (3) inhibition of caspase-3, calpain, and caspase-1 activation.

INTERPRETATION

NAC provides substantial neuroprotection against brain injury in a model that combines infection/inflammation and HI. Protection by NAC was associated with improvement of the redox state and inhibition of apoptosis, suggesting that these events play critical roles in the development of lipopolysaccharide-sensitized HI brain injury.

Neonatal hypoxic preconditioning involves vascular endothelial growth factor

We studied hypoxic preconditioning (HxP) in the murine developing brain, focusing on the role for vascular endothelial growth factor (VEGF). Newborn mice were used as follows: (1) HxP (or normoxia) then intracerebral (i.c.) NMDA or AMPA-kainate agonist; (2) HxP then intraperitoneal (i.p.) anti-VEGFR2/Flk1 or anti-VEGFR1/Flt1 monoclonal blocking antibody (mAb) then i.c. NMDA/AMPA-kainate agonist; (3) i.p. VEGF then i.c. NMDA/AMPA-kainate agonist; and (4) in mutants lacking the hypoxia-responsive element (HRE) of the VEGF-A gene (VEGF( partial differential/ partial differential)) and their wild-type littermates (VEGF(+/+)), HxP followed by i.c. NMDA agonist. HxP reduced the size of NMDA-related cortical and AMPA-kainate-related cortical and white matter excitotoxic lesions. Anti-VEGFR2/Flk1 mAb prevented HxP-induced neuroprotection. VEGF produced dose-dependent reduction in cortical lesions. HxP did not prevent, but instead exacerbated, brain lesions in VEGF( partial differential/ partial differential) mutants. Thus, exogenous as well as endogenous VEGF reduces excitotoxic brain lesions in the developing mouse. The VEGF/VEGFR2/Flk1 pathway is involved in the neuroprotective response to HxP.

Cyclooxygenase-2 mediates the sensitizing effects of systemic IL-1-beta on excitotoxic brain lesions in newborn mice

Epidemiological and experimental data implicate maternal-fetal infection and an associated increase in circulating cytokines in the etiology of cerebral palsy. We have previously shown that pretreatment of newborn mice with systemic interleukin-1-beta exacerbates ibotenate-induced excitotoxic brain lesions. Such lesions are consistent with those observed in cerebral palsy. The present study builds on this murine model to assess the role of cyclooxygenase in interleukin-1-beta-induced brain toxicity. Pups pretreated with interleukin-1-beta developed greater ibotenate-induced brain damage than controls, an effect blocked by the co-administration of nimesulide (cyclooxygenase-2 inhibitor) or indomethacin (cyclooxygenase-1 and -2 inhibitor). Cyclooxygenase inhibitor administration prevented the interleukin-1-beta-induced increase in the production of brain prostaglandin E(2) (a cyclooxygenase metabolite) and changes in the expression of brain interleukin-6, interleukin-18, tumor necrosis factor-alpha, and brain-derived neurotrophic factor. It also stimulated the expression of brain interleukin-10. Our data suggest that the sensitizing effects of circulating inflammatory cytokines on the brain are mediated by the inducible isoform cyclooxygenase-2, which generates excess prostaglandin E(2). Some of these deleterious effects could involve an autocrine/paracrine loop leading to a disruption of the balance between pro- and anti-inflammatory cytokines in the brain.

Melatonin reduces inflammation and cell death in white matter in the mid-gestation fetal sheep following umbilical cord occlusion

The premature infant is at increased risk of cerebral white matter injury. Melatonin is neuroprotective in adult models of focal cerebral ischemia and attenuates ibotenate-induced white matter cysts in neonatal mice. Clinically, melatonin has been used to treat sleep disorders in children without major side effects. The aim of this study was to investigate the protective and anti-inflammatory effects of melatonin in the immature brain following intrauterine asphyxia. Fetal sheep at 90 d of gestation were subjected to umbilical cord occlusion. Melatonin (20 mg/kg, n = 9) or vehicle (n = 10) was administered IV to the fetus, starting 10 min after the start of reperfusion and continued for 6 h. Melatonin treatment resulted in a slower recovery of fetal blood pressure following umbilical cord occlusion, but without changes in fetal heart rate, acid base status or mortality. The production of 8-isoprostanes following umbilical cord occlusion was attenuated and there was a reduction in the number of activated microglia cells and TUNEL-positive cells in melatonin treated fetuses, suggesting a protective effect of melatonin. In conclusion, this study shows that melatonin attenuates cell death in the fetal brain in association with a reduced inflammatory response in the blood and the brain following intrauterine asphyxia in mid-gestation fetal sheep.

Moderate growth restriction: deleterious and protective effects on white matter damage

The role for growth restriction in the multifactorial pathophysiology of developing white-matter damage remains debated. We studied rat pups with prenatal growth restriction (GR) induced by unilateral ligation of the uterine artery. Pups with severe GR exhibited white-matter damage that persisted to adulthood [Olivier, P., Baud, O., Evrard, P., Gressens, P.,Verney, C., 2005. Prenatal ischemia and white matter damage in rats. J. Neuropathol. Exp. Neurol. 64, 998-1006]. Moderate GR was associated with diffuse white-matter lesions, microglial activation, and astrogliosis. Loss of pre-oligodendrocytes on postnatal day 7 was followed by a delay in myelination. Following a cortical excitotoxic insult on postnatal day 5, the size of the induced white-matter lesion was smaller in pups with moderate GR and larger in pups with severe GR, compared to normal pups. The increased pre-oligodendrocyte proliferation seen in the white matter of pups with moderate GR subjected to this "double-hit" injury may constitute a heretofore-undescribed neuroprotective mechanism of immature white matter.

Neurotransmitter receptors in the life and death of oligodendrocytes

Oligodendrocytes are crucial to the function of the mammalian brain: they increase the action potential conduction speed for a given axon diameter and thus facilitate the rapid flow of information between different brain areas. The proliferation and differentiation of developing oligodendrocytes, and their myelination of axons, are partly controlled by neurotransmitters. In addition, in models of conditions like stroke, periventricular leukomalacia leading to cerebral palsy, spinal cord injury and multiple sclerosis, oligodendrocytes are damaged by glutamate and, contrary to dogma, it has recently been discovered that this damage is mediated in part by N-methyl-D-aspartate receptors. Mutations in oligodendrocyte neurotransmitter receptors or their interacting proteins may cause defects in CNS function. Here we review the roles of neurotransmitter receptors in the normal function, and malfunction in pathological conditions, of oligodendrocytes.

Treatment-induced prevention of learning deficits in newborn mice with brain lesions

Perinatal brain injuries often result in irreversible learning disabilities, which manifest in early childhood. The molecular and cellular mechanisms of these injuries and potential pharmacological treatments are emerging, chiefly from studies in newborn rodents. In newborn mice, experimentally induced lesions can be dramatically reduced by appropriate neuroprotective treatments. However, the early effectiveness of these treatments in preserving cognition remained unknown. Here, we addressed this issue by using intracerebral ibotenate to induce excitotoxic brain lesions in 5-day-old mice (postnatal day 5). On postnatal days 6-7, we tested spontaneous preference for maternal odors, as an index of odor memory, and conditioned preference for an artificial odor previously paired with stroking, as an index of associative learning. Brain-lesioned newborn mice showed normal general status and preference for maternal odors. In contrast, odor conditioning was severely impaired. A previous study showed that fructose 1,6-biphosphate acted as a neuroprotective agent which significantly reduced neocortical lesion size. In the present study, treating the newborn mice with fructose 1,6-biphosphate 15 min before the ibotenate injection reduced neocortical lesion size and restored conditioning. This demonstrates, for the first time, that neuroprotective treatment can protect some features of early cognition.

Endocannabinoids potently protect the newborn brain against AMPA-kainate receptor-mediated excitotoxic damage

Brain lesions induced in newborn mice or rats by the glutamatergic agonists ibotenate (acting on NMDA and metabotropic receptors) or S-bromowillardiine (acting on AMPA-kainate receptors) mimic some aspects of white matter cysts and transcortical necrosis observed in human perinatal brain damage associated with cerebral palsy. Exogenous and endogenous cannabinoids have received increasing attention as potential neuroprotective agents in a number of neurodegenerative disorders of the adult. One recent study showed neuroprotection by the cannabinoid agonist WIN-55212 in a newborn rat model of acute severe asphyxia. The present study was designed to assess the neuroprotective effects of the endogenous cannabinoid anandamide using a well-defined rodent model of neonatal excitotoxic brain lesions. In this model, anandamide provided dose-dependent and long-lasting protection of developing white matter and cortical plate reducing the size of lesions induced by S-bromowillardiine. Anandamide had only marginal neuroprotective effect against ibotenate-induced cortical grey matter lesions. Anandamide-induced neuroprotection against AMPA-kainate receptor-mediated brain lesions were blocked by a CB1 antagonist but not by a CB2 antagonist. Furthermore, anandamide effects were mimicked by a CB1 agonist but not by a CB2 agonist. Real-time PCR confirmed the expression of CB1 receptors, but not CB2 receptors, in the untreated newborn neocortex. Finally, neuroprotective effects of anandamide in white matter involved increased survival of preoligodendrocytes and better preservation of myelination. The present study provides experimental support for the role of endocannabinoids as a candidate therapy for excitotoxic perinatal brain lesions.

Lentiviral-mediated gene transfer of brain-derived neurotrophic factor is neuroprotective in a mouse model of neonatal excitotoxic challenge

Excitotoxicity may be a critical factor in the formation of brain lesions associated with cerebral palsy. When injected into the murine neopallium at postnatal day 5, the glutamatergic analog N-methyl-D-aspartate (NMDA) produces transcortical neuronal death and periventricular white matter cysts, which mimic brain damage observed in human term and preterm neonates at risk for developing cerebral palsy. We previously showed that intracerebral injection of brain-derived neurotrophic factor (BDNF) was neuroprotective in this model. Because BDNF does not easily cross the blood-brain barrier, alternative strategies to avoid repeated intracerebral injections of BDNF should be tested, particularly when the goal of such translational research is ultimately to achieve clinical application. The goal of the present study was to assess the protective role of lentiviral-mediated gene transfer of BDNF against excitotoxic lesions induced by NMDA in newborn mice. We first assessed the biological activity of BDNF gene transfer in vitro and determined the efficiency of gene transfer in our in vivo model. We next administered the BDNF-expressing vector by intracerebral injection in neonatal mice, 3 days before inducing NMDA lesions. When compared with a control green fluorescent protein-expressing lentiviral vector, administration of BDNF-expressing vector induced a significant protection of the periventricular white matter and cortical plate against the NMDA-mediated insult. Intraventricular delivery of the BDNF-expressing lentiviral vector was more efficient in terms of neuroprotection than the intraparenchymal route. Altogether, the present study shows that viral-mediated gene transfer of BDNF to newborn mouse brain is feasible and affords significant neuroprotection against an excitotoxic insult.

Distribution of MT1 melatonin receptor immunoreactivity in the human hypothalamus and pituitary gland: Colocalization of MT1 with vasopressin, oxytocin, and corticotropin-releasing hormone

Melatonin is implicated in numerous physiological processes, including circadian rhythms, stress, and reproduction, many of which are mediated by the hypothalamus and pituitary. The physiological actions of melatonin are mainly mediated by melatonin receptors. We here describe the distribution of the melatonin receptor MT1 in the human hypothalamus and pituitary by immunocytochemistry. MT1 immunoreactivity showed a widespread pattern in the hypothalamus. In addition to the area of the suprachiasmatic nucleus (SCN), a number of novel sites, including the paraventricular nucleus (PVN), periventricular nucleus, supraoptic nucleus (SON), sexually dimorphic nucleus, the diagonal band of Broca, the nucleus basalis of Meynert, infundibular nucleus, ventromedial and dorsomedial nucleus, tuberomamillary nucleus, mamillary body, and paraventricular thalamic nucleus were observed to have neuronal MT1 receptor expression. No staining was observed in the nucleus tuberalis lateralis and bed nucleus of the stria terminalis. The MT1 receptor was colocalized with some vasopressin (AVP) neurons in the SCN, colocalized with some parvocellular and magnocellular AVP and oxytocine (OXT) neurons in the PVN and SON, and colocalized with some parvocellular corticotropin-releasing hormone (CRH) neurons in the PVN. In the pituitary, strong MT1 expression was observed in the pars tuberalis, while a weak staining was found in the posterior and anterior pituitary. These findings provide a neurobiological basis for the participation of melatonin in the regulation of various hypothalamic and pituitary functions. The colocalization of MT1 and CRH suggests that melatonin might directly modulate the hypothalamus-pituitary-adrenal axis in the PVN, which may have implications for stress conditions such as depression.

Antioxidative protection by melatonin: multiplicity of mechanisms from radical detoxification to radical avoidance

Melatonin has been shown to protect against oxidative stress in various, highly divergent experimental systems. There are many reasons for its remarkable protective potential. Signaling effects comprise the upregulation of antioxidant enzymes, such as superoxide dismutases, peroxidases, and enzymes of glutathione supply, down-regulation of prooxidant enzymes, such as nitric oxide synthases and lipoxygenases, and presumably also the control of quinone reductase 2. Other mechanisms are based on direct interactions with several reactive oxygen and nitrogen species. Among these reactions, the capacity of easily undergoing single-electron transfer reactions is of particular importance. Electron donation by melatonin is not only an aspect of direct radical scavenging, but additionally represents the basis for formation of the protective metabolites AFMK (N1-ace-tyl-N2-formyl-5-methoxykynuramine) and AMK (N1-acetyl-5-methoxykynuramine). Recent investigations on mitochondrial metabolism indicate that melatonin as well as AMK are capable of supporting the electron flux through the respiratory chain, of preventing the breakdown of the mitochondrial membrane potential, and of decreasing electron leakage, thereby reducing the formation of superoxide anions. Radical avoidance is a new line of investigation, which exceeds mitochondrial actions and also comprises antiexcitatory effects and contributions to the maintenance of internal circadian phase relationships.

The effects of AMPA receptor antagonists in models of stroke and neurodegeneration

Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists have been shown to have neuroprotective effects in stroke models and although clinical trials with some agents are still ongoing, published results have not been favourable. We therefore wished to compare the effects of GYKI 52466, GYKI 53405, EGIS-8332 and EGIS-10608, non-competitive AMPA receptor antagonists with homophthalazine chemical structures, in standard animal stroke models with effects in a neurodegenerative model--excitoxicity in newborn mice. All compounds inhibited the S-AMPA-induced spreading depression in the chicken retina, in vitro, and were potent anticonvulsants against maximal electroshock in mice, in vivo. The AMPA receptor antagonists prevented domoate-induced cell death of motoneurons, in vitro, and reduced infarct size in a dose-dependent manner in the permanent middle cerebral artery occlusion model in mice, in vivo. In newborn mice (P5, histopathology at P10), local injection of the AMPA receptor agonist S-bromo-willardiine at day 5 after birth induced cortical damage and white matter damage, which was reduced in a dose-dependent manner by the AMPA receptor antagonists. EGIS 10608 was a very powerful receptor antagonist of white matter damage. In contrast, GYKI 52466 did not antagonize cortical and white matter damage induced by ibotenic acid. These models allow quantification of the effects of AMPA receptor antagonists in vitro and in vivo.

Patterns of excitotoxin-induced brain lesions in the newborn rabbit: a neuropathological and MRI correlation

There is pressing need to employ new advances in structural MR brain imaging to better diagnose brain damage in newborn infants. Timely application of such technology will enable improved therapeutic interventions. Diffusion-weighted sequences are a sensitive marker of very early neuronal injury, the spatial pattern of which provides critical information regarding the underlying pathophysiology. We have modified our murine model of excitotoxic neonatal brain injury to the rabbit, an animal whose brain is larger and where the neuroanatomic organization of the subcortical white matter more closely resembles that of the human. Utilizing this rabbit model, we undertook an MRI/histopathologic correlation. We found that as with the mouse, there is a spatiotemporal selectivity to the pattern of brain injury, and that the period from postnatal day (P) 7 to P9 in rabbits corresponds to the time of maximum vulnerability of the brain to excitotoxic white matter damage, which neuropathologically simulates periventricular leukomalacia (PVL). We additionally noted that diffusion-weighted imaging provided the most sensitive means of detecting such lesions and that this method was sensitive to structural maturational changes accompanying the normal cortical ontogeny. Taken together, our findings suggest that this rabbit model of perinatal excitotoxic brain injury will be a valuable addition to experimental approaches to further our understanding of perinatal brain damage, that diffusion-weighted imaging will be an invaluable adjunct to the diagnosis of such injury, and that therapeutic strategies aimed at interrupting the evolution of PVL should include targeting the pathophysiologic cascade induced by excitotoxic neonatal brain injury.

Topiramate prevents excitotoxic damage in the newborn rodent brain

Brain lesions induced in newborn mice by the glutamatergic agonists ibotenate (acting on NMDA and metabotropic receptors) and S-bromowillardiine (acting on AMPA-kainate receptors) mimic some aspects of white matter cysts and transcortical necrosis observed in human perinatal brain damage. Topiramate (TPM), already used in children to manage newly diagnosed and refractory epilepsy, has potential neuroprotective effects that may be useful in human perinatal brain lesions. In the excitotoxic newborn mouse model, TPM provided dose-dependent and long-lasting protection of developing white matter and cortical plate against S-bromowillardiine. TPM had no significant effect on ibotenate-induced brain lesions. TPM-induced neuroprotection potentially involved increased survival of pre-oligodendrocytes, decreased neuronal apoptosis, inhibition of microglial activation and astrogliosis, and decreased seizure activity. Diazepam, phenytoin, and carbamazepine had no neuroprotective effect in this model. The present study provides experimental support for the consideration of TPM as a candidate therapy for excitotoxic perinatal brain lesions.

Neuronal TGF-beta1 mediates IL-9/mast cell interaction and exacerbates excitotoxicity in newborn mice

Intraneocortical injection of ibotenate, a glutamate analog, in newborn mice produces damage mimicking lesions observed in human infants with cerebral palsy. Previous research using this model has demonstrated that pretreatment with IL-9, a Th2 cytokine, significantly exacerbated excitotoxic brain lesions. The goal of this study is to identify the underlying pathophysiological mechanism of lesion formation. Pretreatment with TGF-beta1 produced the same effects as IL-9 on ibotenate-induced lesions. IL-9 effects were abolished when a specific TGF-beta1 neutralizing antibody is administered at the same time. Real-time PCR, Western blot, and immunohistochemistry showed that pretreatment with IL-9 increased TGF-beta1 neocortical expression. In vitro studies using real-time PCR and immunocytochemistry demonstrated that neurons were a major contributor in IL-9-induced increase of TGF-beta1. In c-Kit mast cell-deficient mice, TGF-beta1 failed to exacerbate excitotoxic brain lesions, suggesting a key role of mast cells in TGF-beta1 effects. A specific inhibitor of mast cell degranulation and histamine receptor blockers abrogated TGF-beta1 effects on excitotoxic lesions, providing further evidence of mast cell involvement and the role of mast cell-derived histamine. Finally, in vitro studies using a mast cell line showed that TGF-beta1 increased histamine in the supernatant. In aggregate, these data support the notion that neuronal TGF-beta1 plays a key role in the IL-9/mast cell interaction, which leads to an exacerbation of neonatal excitotoxic damage through an increased extracellular histamine concentration. The identification of this pathway, if confirmed in human neonates, might have important implications for understanding and preventing cerebral palsy.

VPAC2 receptors mediate vasoactive intestinal peptide-induced neuroprotection against neonatal excitotoxic brain lesions in mice

Prepro-vasoactive intestinal peptide (VIP) mRNA codes for two neuropeptides: VIP and peptide histidine isoleucine (PHI). Two VIP receptors, shared with a similar affinity by pituitary adenylate cyclase-activating polypeptide (PACAP), have been cloned: VPAC(1) and VPAC(2). PHI binds to these receptors with a lower affinity. VPAC receptors are classically associated with a cAMP-dependent pathway, although other pathways, including calcium mobilization and protein kinase C activation have been described. We previously showed that intracerebral administration of the glutamate agonist ibotenate to postnatal day 5 mice induces white matter lesions mimicking human periventricular leukomalacia. In this model, coinjection of VIP protects against white matter lesions. This neuroprotection is independent from cAMP and is mediated by protein kinase C. Using this model, this study aimed to determine the receptor involved in VIP-induced neuroprotection. VIP effects were mimicked with a similar potency by VPAC(2) agonists and PHI but not by VPAC(1) agonists, PACAP 27, or PACAP 38. VIP neuroprotective effects were lost in mice lacking VPAC(2) receptor. In situ hybridization confirmed the presence of VPAC(2) mRNA in the postnatal day 5 white matter. When analyzed between embryonic life and adulthood, VIP-specific binding site density peaked at postnatal day 5. These data suggest that, in this model, VIP-induced neuroprotection is mediated by VPAC(2) receptors. The pharmacology of this VPAC(2) receptor seems unconventional because 1) PACAP does not mimic VIP effects, 2) PHI acts with a comparable potency, and 3) PACAP 27 modestly inhibited the VIP-specific binding, whereas for PHI or VIP, inhibition was complete.

Ontogenic study of the influence of tissue plasminogen activator (t-PA) in neonatal excitotoxic brain insult and the subsequent microglia/macrophage activation

Intracerebral injections of ibotenic acid in neonatal mice produced white and gray matter lesions that mimic some aspects of the acquired cerebral injuries observed in human newborns (i.e. periventricular leukomalacias in preterm newborns and post-ischemic cortical necrosis in at term infants). We have evaluated the effects of tissue plasminogen activator inactivation (t-PA-/-) on the effects of ibotenic acid (0.01-20 microg), and on F4/80 labeling of microglia/macrophages at different stages. Three ontogenic periods have been identified. In mice injected the day of birth, postnatal (P) day 0, ibotenic acid induced neuronal migration disorders together with low local microglial activation in wild-type and t-PA-/- mice. In P2 and P5 mice, ibotenic acid induced diffuse microglial activation in the whole cortex and subcortical areas; e.g. caudate nucleus and septum. In wild-type mice, cystic lesions of the white matter were consistently observed, surrounded by macrophages. In t-PA-/- mice, noncystic lesions filled of macrophages were more frequent than cysts. Macrophages were virtually absent in the gray matter. White and gray matter lesions were reduced in t-PA-/- mice. The plasmin inhibitor aprotinin reduced white and gray matter lesions only in wild-type mice injected with high ibotenic acid doses (2.5-5 microg). During this period, a transient F4/80 immunoreactive cell population was detected in the cingulum. At P10, the salient lesion characteristic was a large gray matter lesion containing macrophage accumulation. Microglial activation was confined to the injection site in the white matter. t-PA-/- mice showed reduced lesion size under high doses (>5 microg) of ibotenic acid. Similarly, aprotinin diminished the lesion in wild-type animals exposed to 10 microg ibotenic acid. These data demonstrate that t-PA and microglia do not actively participate in the migration disorders induced in P0 mice. Conversely, t-PA was implicated in cyst formation in older (P2-P10) mice, and in their subsequent growth. t-PA was also involved in GM lesions, probably through an inflammatory process involving macrophages.

Pathophysiology of neonatal brain lesions: lessons from animal models of excitotoxicity

AIM

The pathophysiology of perinatal brain lesions is probably complex and multifactorial. The development and characterization of distinct yet complementary animal models should help to unravel the cellular and molecular mechanisms underlying perinatal brain lesions. This paper reviews experimental data obtained in animal models of neonatal excitotoxic brain lesions that closely mimic some of the lesions found in human cerebral palsy.

CONCLUSION

Available data point to a key role for brain macrophages and oligodendrocytes in neonatal rodent excitotoxic brain lesions and underline the impact of cytokines on these lesions.

Novel 2-Alkylamino-1,4-benzoxazine Derivatives as Potent Neuroprotective Agents: Structure−Activity Relationship Studies

2-Alkylamino-substituted-1,4-benzoxazine derivatives, a new class of potential neuroprotective agents, were synthesized and examined for their intrinsic cytotoxicity and their capacity to inhibit oxidative stress-mediated neuronal degeneration in vitro. Through structure-activity relationship studies, the 3,3-diphenyl-substituted-1,4-benzoxazine derivative 3l was identified as the optimal candidate, owing to its potent neuroprotective activity, without the manifestation of intrinsic cytotoxicity. Accordingly, 3l proved to be effective in an animal model of excitotoxic lesions in newborn mice.

Melatonin attenuates gray and white matter damage in a mouse model of transient focal cerebral ischemia

We have previously shown that melatonin reduces infarct volumes and enhances neurobehavioral and electrophysiological recoveries following transient middle cerebral artery (MCA) occlusion in rats. In the study, we examined whether melatonin would display neuroprotection against neuronal, axonal and oligodendrocyte pathology after 24 hr of reperfusion following 1 hr of MCA occlusion in mice. Melatonin (5 mg/kg) or vehicle was given intraperitoneally at the commencement of reperfusion. Neurological deficits were assessed 24 hr after ischemia. Gray matter damage was evaluated by quantitative histopathology. Axonal damage was determined with amyloid precursor protein and microtubule-associated protein tau-1 immunohistochemistry to identify postischemic disrupted axonal flow and oligodendrocyte pathology, respectively. Oxidative damage was assessed by 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 4-hydroxynonenal (4-HNE) immunohistochemistry. Relative to controls, melatonin-treated animals not only had a significantly reduced volume of gray matter infarction by 42% (P<0.001), but also exhibited a decreased score of axonal damage by 42% (P<0.001) and a reduction in the volume of oligodendrocyte pathology by 58% (P<0.005). Melatonin-treated animals also had significantly reduced immunopositive reactions for 8-OHdG and 4-HNE by 53% (P<0.001) and 49% (P<0.001), respectively. In addition, melatonin improved sensory and motor neurobehavioral outcomes by 47 and 30%, respectively (P<0.01). Thus, delayed (1 hr) treatment with melatonin reduced both gray and white matter damage and improved neurobehavioral outcomes following transient focal cerebral ischemia in mice. The finding of reduced oxidative damage observed with melatonin suggests that its major mechanisms of action are mediated through its antioxidant and radical scavenging activity.

Emerging concepts in periventricular white matter injury

Approximately 10% of newborns are born prematurely. Of these children, more than 10% will sustain neurological injuries leading to significant learning disabilities, cerebral palsy, or mental retardation, with very low birth weight infants having an even higher incidence of brain injury. Whereas intraventricular hemorrhage was the most common form of serious neurological injury a decade ago, periventricular white matter injury (PWMI) is now the most common cause of brain injury in preterm infants. The spectrum of chronic PWMI includes focal cystic necrotic lesions (periventricular leukomalacia; PVL) and diffuse myelination disturbances. Recent neuroimaging studies support that the incidence of PVL is declining, whereas diffuse cerebral white matter injury is emerging as the predominant lesion. Factors that predispose to PVL include prematurity, hypoxia, ischemia, and inflammation. It is believed that injury to oligodendrocyte (OL) progenitors contributes to the pathogenesis of myelination disturbances in PWMI by disrupting the maturation of myelin-myelin-forming oligodendrocytes. Other potential mechanisms of injury include activation of microglia and axonal damage. Chemical mediators that may contribute to white matter injury include reactive oxygen (ROS) and nitrogen species (RNS), glutamate, cytokines, and adenosine. As our understanding of the pathogenesis of PWMI improves, it is anticipated that new strategies for directly preventing brain injury in premature infants will evolve.

Animal models of shaken baby syndrome: revisiting the pathophysiology of this devastating injury

To better understand outcomes after early brain injuries, studies must address multiple variables including age at injury, the mechanisms and severity of injury, environmental factors (before and after injury) and developmental factors. Animal models are helpful for elucidating these different aspects. First, this paper describes a new model of shaken baby syndrome (SBS) in mice, without impact or hypoxia. Mortality was 27%; 75% of survivors had focal brain lesions consisting of haemorrhagic or cystic lesions of the white matter, corpus callosum and cerebellum. All shaken animals, with and without focal lesions, showed delayed white matter atrophy. White matter damage and atrophy were reduced by pre-treatment with an NMDA receptor antagonist, indicating that excess glutamate release contributed to the pathophysiology of the lesions. Secondly, it discusses data on neuroprotection after early brain injuries; drugs targeting the NMDA receptors cannot be used in clinical practice but indirect neuroprotection strategies including anti-NO, anti-free radicals and trophic factors hold promise for limiting the excitotoxic white matter damage induced by early injury, in particular caused by shaking, during brain development. Thirdly, it describes two experimental models in which SBS outcomes are determined when the trauma is combined with environmental influences, namely medications during the acute phase, most notably anti-epileptic drugs and rearing conditions.

Role of tissue-derived plasminogen activator (t-PA) in an excitotoxic mouse model of neonatal white matter lesions

White matter (WM) lesions in preterm newborns may lead to cerebral palsy. To study WM lesions in a mouse model, we used intrapallial stereotactic injections of ibotenic acid, an N-methyl-D-aspartate receptor agonist. Previous studies support a contribution of tissue-type plasminogen activator (t-PA) to the brain lesions seen in various adult excitotoxic models. Therefore, we studied both 5-day-old (P5) wild-type mice and t-PA knock-out (t-PA-/-) mice. The ibotenic acid doses required to induce WM cysts were lower in the wild-type mice (EC50 < 0.01 microg/animal) than in the t-PA-/- mice (EC50 = 2.5 microg/animal) (p < 0.01), indicating the existence of t-PA-dependent and t-PA-independent mechanisms. Dose-dependent prolonged cyst growth occurred in the wild-type mice only. Early microglial activation and astrogliosis were similar in the wild-type and t-PA-/- mice. In adult mice (P45), demyelination occurred at the injection site in both groups but the astroglial scar was denser in the wild-type than in the t-PA-/- mice. These data support involvement of t-PA at several stages of WM lesion formation. Inactivation of t-PA might confer protection by prolonged hemostasis. The role of t-PA in cyst expansion suggests a new approach to the development of neuroprotective strategies in infants with developing WM lesions.

Melatonin stimulates cell proliferation in zebrafish embryo and accelerates its development

All vertebrates show a dramatic circadian rhythm in circulating melatonin with high levels at night and very low levels during daytime. In adults, melatonin is thought to synchronize other circadian rhythms and regulate seasonal rhythms in photoperiodic animals by acting on specific G-protein coupled receptors. The role of melatonin in development is unknown, even though melatonin receptors appear to be more highly expressed in developing embryos and neonates than in adults. In this study on zebrafish embryos, we describe a role for melatonin in increasing cell proliferation and accelerating development. We propose that melatonin has a role in extending the safe limit of proliferation rate at night to allow more rapid development when potentially damaging ultraviolet light is absent.

Early microglial activation following neonatal excitotoxic brain damage in mice: a potential target for neuroprotection

Previous studies in a mouse model of neonatal excitotoxic brain damage mimicking the brain lesions in human cerebral palsy showed microglial activation within 24 h after intracerebral injection of the glutamatergic analog ibotenate. Using this model, we studied the expression of CD-45 antigen, a marker of blood-derived cells, by these activated microglial cells labeled by Griffonia simplicifolia I isolectin B4. Immunohistochemistry performed during early development of excitotoxic lesions showed that most cells labeled with the isolectin B4 were CD-45-negative, suggesting that these early activated microglial cells were deriving chiefly from resident microglia and not from circulating monocytes. We also directly tested the hypothesis that activated resident microglia and/or blood-derived monocytes play a role in the pathophysiology of excitotoxic brain damage. Repeated i.p. administrations of chloroquine, chloroquine+colchicine, minocycline, or an anti-MAC1 antibody coupled to the toxin saporin before and/or after ibotenate injection induced a significant reduction in the density of isolectin B4-positive cells. This inhibition of resident microglial and/or blood-derived monocytes activation was accompanied by a significant reduction in the severity of ibotenate-induced brain lesions (up to 79% lesion size reduction with the highest minocycline dose) as well as of ibotenate-induced cortical caspase-3 activation (49% reduction).

Methylphenidate and MK-801, an N-methyl-d-aspartate receptor antagonist: shared biological properties

Methylphenidate (MPH), a dopamine reuptake inhibitor, is used increasingly to treat attention deficit and hyperactivity disorders in children. Given that dopaminergic mechanisms, contribute to the structural and functional maturation of brain circuitry, consideration of the potential influence of MPH in disrupting such processes seems warranted. Following a similar logic regarding the relevance of glutamate neurotransmission in mediating aspects of brain maturation, we and others have previously utilized in vivo and in vitro studies of the developing rodent brain to establish that MK-801, an N-methyl-d-aspartate (NMDA) receptor antagonist has both neuroprotective and pro-apoptotic actions. In this study we used a neonatal murine model of excitotoxin-induced cortical injury to compare such actions between MPH and MK-801, and found that MPH shared some biological properties with MK-801. Specifically, both drugs were neuroprotective against excitotoxic challenge resulting in neonatal brain lesions and in vitro neuronal death, but both drugs also exacerbated programmed neural cell death. However, this profile of action was not shared by the dopamine reuptake blocker GBR-12783, a molecule which like MPH binds to and blocks the dopamine transporter, but which is structurally dissimilar to MPH, suggesting that inhibition of dopamine reuptake alone cannot explain the results from our MPH studies. The implications of our findings are that when studied in our developmental mouse model both drugs demonstrate similar capacities to be either neuroprotective or pro-apoptotic, depending on the specific biologic setting in which they act. Additional studies to identify some potential positive as well as negative consequences of exposure to these drugs during brain development in clinical settings are warranted.

Potent mammalian cerebroprotection and neuronal cell death inhibition are afforded by a synthetic antioxidant analogue of marine invertebrate cell protectant ovothiols

Implicit strategies for neuroprotection in the adult brain include GABAA receptor activation, N-methyl-d-aspartate receptor and sodium voltage-gated channel inhibition. Ironically, these same targets may be harmful to the immature or developing brain. Protection has been demonstrated for both immature and mature brain with the use of a synthetic ovothiol analogue. The following beneficial effects have been demonstrated in mice: protection against audiogenic seizures, brain structures with clear-cut delineation of ibotenate-challenged white and grey matter lesions along with exceptional early and delayed protections, and potent cerebral cell death inhibition. The compound lacks both GABAergic activity and sodium channel blocker properties, which may help explain the lack of toxicity normally expressed in an immature brain utilizing these agents [J.W. Olney (2002) Neurotoxicology, 93, 1-10]. The oxidized form of the compound is virtually devoid of antioxidant activity. In vivo it exhibits cerebroprotective properties similar to those of reduced compounds endowed with antioxidant properties. This unexpected finding has prompted an extensive in vitro exploration of underlying molecular mechanisms that have led to the identification of several recycling mechanisms consistent with non rate-limiting conversion of oxidized to reduced compound forms. Taken as a whole, this work offers an unique combined in vitro and in vivo support that: (i). antioxidant therapy, here engineered from marine invertebrate egg protectants, may be a valuable strategy in protecting both mammalian adult and developing brain; and (ii). recycling (thiol-disulphide exchange) properties of the oxidized form of an antioxidant compound are as important as the antioxidant potential exhibited by a bioactive reduced antioxidant in certain neuroprotective processes.

Quantitative analysis of perinatal rodent oligodendrocyte lineage progression and its correlation with human

The development of a rodent model in the perinatal rat or mouse that reproduces the principal features of human perinatal white matter injury (periventricular leukomalacia) has been hampered by uncertainty about the developmental window in the rodent that coincides temporally with cerebral white matter development in the premature infant. We recently determined oligodendrocyte (OL) lineage progression in human cerebral white matter and found that the late OL progenitor (preOL) predominates throughout the high-risk period for periventricular leukomalacia [J. Neurosci. 21(2001), 1302-1312]. Here, we determined in the perinatal rat and mouse when each species displays a distribution of OL stages that is similar to the premature human cerebral white matter. PreOLs are abundant in the rat and mouse at P2. By P7, extensive OL maturation occurs in both species and coincides with the onset of early myelination. PreOLs and immature OLs mature in the P2 white matter along a medial to lateral gradient. This may provide an explanation for regional variation in the susceptibility of perinatal white matter to injury. We propose that the sequence of OL lineage progression is a useful means to estimate developmental windows of white matter maturation in perinatal rodents that coincide with those of developing human cerebral white matter. These studies support that the vulnerable period for white matter injury in the rodent is centered around P2 and should decline thereafter, coincident with the onset of myelination.

Neuroprotective properties of tianeptine: interactions with cytokines

Tianeptine is an antidepressant with proven clinical efficacy and effects on hippocampal plasticity. Hypoxia increased lactate dehydrogenase (LDH) release from cortical neuronal cultures, and tianeptine (1, 10 and 100 microM) inhibited LDH release as efficiently as the N-methyl-D-aspartate (NMDA) antagonist, MK-801. However, tianeptine did not block apoptosis in cultured cortical neurones caused by NMDA, but reduced apoptosis when interleukin-1beta (IL-1beta) was included with NMDA. In 5-day old mice, intracerebral injection of ibotenate induced reproducible lesions in cortex and white matter. Lesion size was markedly reduced by co-administration of MK-801 (1 mg/kg i.p.) but neither by tianeptine or its enantiomers administered acutely (1, 3 or 10 mg/kg i.p.) nor by tianeptine administered chronically (10 mg/kg i.p. for 5 days). Chronic administration of IL-1beta (10 ng/kg i.p. for 5 days) prior to ibotenate injection exacerbated lesion size in cortex and white matter, and this exacerbation was prevented by chronic pre-treatment with tianeptine (10 mg/kg i.p.) or by acute administration of tianeptine (10 mg/kg i.p.) concomitantly with ibotenate. Thus tianeptine has neuroprotective effects against hypoxia in tissue culture and against the deleterious effects of cytokines in cortex and white matter, but not against NMDA receptor-mediated excitotoxicity.

Positive allosteric modulators of AMPA receptors are neuroprotective against lesions induced by an NMDA agonist in neonatal mouse brain

Four positive modulators of AMPA-type glutamate receptors (cyclothiazide, CX614, LY404187 and S18986-1) given in acute or chronic manner exerted a neuroprotective effect in lesions induced in postnatal day 5 (P5) mice by intracerebral injection of ibotenate, an NMDA agonist. The neuroprotective effects were mediated via the MAPK pathway since coinjection of the MEK inhibitor, PD98059, blocked the neuroprotective effects. Administration of CX614 to neonatal mice was followed by upregulation of hippocampal and cortical BDNF expression.

Melatonin protects SHSY5Y neuronal cells but not cultured astrocytes from ischemia due to oxygen and glucose deprivation

As a potent free radical scavenger and antioxidant, melatonin protects brain tissue against ischemia-reperfusion injury, partly via suppression of ischemia-induced production of nitric oxide, when given before ischemia-reperfusion or within 2 hr of onset of ischemia. In this study, we examined the neuroprotective effect of melatonin in an in vitro model of ischemia. Primary cultured astrocytes were subjected to 4 or 8 hr of oxygen-glucose deprivation (OGD), and cultured SHSY5Y human neuronal cells were exposed to 1 hr of OGD. Melatonin was added to the medium at the commencement of OGD to achieve different final concentrations, and cell death was quantified using the measurement of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) at 24 hr after reversion of OGD. Treatment with melatonin did not affect the astrocytic cell death following 4 or 8 hr of OGD. The relative MTT values of the neuronal cells were (as mean +/- S.E.M.) 59.1 +/- 2.4% in the vehicle-treated OGD group and 80.1 +/- 2.7%, 82.5 +/- 2.9%, 74.1 +/- 2.3%, 64.2 +/- 2.3%, 62.7 +/- 2.8%, and 61.0 +/- 3.9% in the OGD groups treated with melatonin at 10(-3), 10(-4), 10(-5), 10(-6), 10(-7), and 10(-8) m, respectively. Reduction in cell death was significant following treatment with melatonin at 10(-3), 10(-4), or 10(-5) m. Reverse transcription-polymerase chain reaction showed that human mt1 and MT2 membrane receptors were not expressed in the cultured neuronal cells. Our results show that melatonin co-treatment protects cultured neuronal cells but not astrocytes against OGD-induced cell death in a dose-dependent manner and that the neuroprotection is independent of its known membrane receptors.

The utility of melatonin in reducing cerebral damage resulting from ischemia and reperfusion

The brain is highly susceptible to focal or global ischemia. Unless ischemia is promptly reversed, reperfusion produces further cerebral damage. Acute thrombolysis or defibrinogenation is effective only in selective patients with ischemic stroke and carries a significant risk of bleeding complications. Whereas numerous neuroprotectants were shown to be effective in experimental studies, none of them have been shown to work in clinical trials. The major pathogenetic mechanisms of ischemia/reperfusion injury include excitotoxicity, disturbed calcium ion homeostasis, overproduction of nitric oxide and other free radicals, inflammation, and apoptosis. Nitric oxide and other free radicals, the key mediators of excitotoxicity and disturbed calcium ion homeostasis, cause direct injury and also indirectly damage via inflammation and apoptosis. Melatonin is a potent free radical scavenger and an indirect antioxidant. This mini review summarizes the in vivo and in vitro evidence that melatonin protects against ischemia/reperfusion injury. There is convincing evidence from the literature that melatonin treatment is highly effective in different in vivo and in vitro models of excitotoxicity or ischemia/reperfusion in multiple animal species. Melatonin is safe and non-toxic in humans, and its administration via the oral route or intravenous injection is convenient. While more experimental studies should be conducted to further explore the neuroprotective mechanisms and to document any synergistic or additive protection from combining melatonin with thrombolysis, defibrinogenation or other neuroprotectants, interested clinical scientists should consider planning phase II and III studies to confirm the benefit of melatonin as an acute stroke treatment or a preventive measure for stroke patients.

Recombinant peroxiredoxin 5 protects against excitotoxic brain lesions in newborn mice

The pathophysiology of brain lesions associated with cerebral palsy is multifactorial and likely involves excess release of glutamate and excess production of free radicals, among other factors. Theoretically, antioxidants could limit the severity of these brain lesions. Peroxiredoxins are a family of peroxidases widely distributed in eukaryotes and prokaryotes. Peroxiredoxin 5 (PRDX5) is a recently discovered mammalian member of this family of antioxidant enzymes that is able to reduce hydrogen peroxide and alkyl hydroperoxides. The present study was designed to examine the neuroprotective effects of recombinant PRDX5 against neonatal excitotoxic challenge in both in vivo and in vitro experiments. For in vivo experiments, mice (postnatal day 5) were injected intraneopallially with ibotenate acting on NMDA and metabotropic receptors, or S-bromowillardiine acting on AMPA-kainate receptors to produce excitotoxic stress and brain lesions. Systemically administered recombinant PRDX5 provided protection against ibotenate-induced excitotoxic stress. Brain lesions of animals given ibotenate and PRDX5 were up to 63% smaller than that given ibotenate alone. However, PRDX5 provided no prevention from lesions induced with S-bromowillardiine. A mutated recombinant PRDX5 that is devoid of peroxidase activity was also tested and showed no protection against lesions induced by either ibotenate or S-bromowillardiine. Two classical antioxidants, N-acetylcysteine and catalase-PEG, provided the same neuroprotective effect as PRDX5. For in vitro experiments, neocortical neurons were exposed to 300 microM NMDA alone, NMDA plus recombinant PRDX5, or NMDA, recombinant PRDX5 and dithiothreitol, a classical electron donor for peroxiredoxins. Recombinant PRDX5 plus dithiothreitol displayed a synergistic neuroprotective effect on NMDA-induced neuronal death. These findings indicate that reactive oxygen species production participates in the formation of NMDA receptor-mediated brain lesions in newborn mice and that antioxidant compounds, such as PRDX5, provide some neuroprotection in these models.

Effects of interleukin-10 on neonatal excitotoxic brain lesions in mice

Interleukin-10 markedly reduces production of proinflammatory cytokines by activated microglia or macrophages and downregulates the expression of activating molecules on these cells. In studies performed in adults or in cell cultures, interleukin-10 protected against hypoxic-ischemic neuronal death and against lipopolysaccharide-mediated oligodendrocyte cell death. Furthermore, it was recently shown that interleukin-10 counteracts metabolic and microcirculatory effects of hypoxia-ischemia in the perinatal pig brain. Intracerebral injection of the glutamatergic analogue ibotenate to newborn mice induces cortical plate and white matter lesions mimicking the brain damage associated with cerebral palsy, and pretreatment with proinflammatory cytokines such as interleukin-1-beta or with interleukin-9 significantly exacerbates these lesions. The present study evaluated the influence of interleukin-10 on ibotenate-induced brain lesions in newborn mice under basal conditions or after exposure to cytokines. Intraperitoneal injection of interleukin-10 for 3 days following ibotenate significantly reduced the size of excitotoxic brain lesions. Intraperitoneal injection of neutralizing anti-interleukin-10 antibody for 3 days following ibotenate had no detectable effect and no difference in ibotenate-induced brain lesion size was found between wild type pups and pups deleted for the interleukin-10 gene, suggesting that endogenous interleukin-10 in newborn mice may have limited effects. Co-administration of intracerebral ibotenate and interleukin-10 had no detectable effect, arguing against a direct neuroprotective effect of interleukin-10 on neurons. While pretreatment with intraperitoneal interleukin-10 alone had no detectable effect on excitotoxic brain lesions, interleukin-10 given with interleukin-1-beta pretreatment blunted the toxic effects of interleukin-1-beta. On the other hand, combined pretreatment with IL-9 and anti-IL-10 antibody largely reversed the exacerbating effect of IL-9 on excitotoxic brain lesions. Altogether, these data suggest that, in newborn mice, exogenous interleukin-10 can be neuroprotective when acting in an inflammatory context.

Fructose-1,6-biphosphate prevents excitotoxic neuronal cell death in the neonatal mouse brain

The excitotoxic cascade may represent an important pathway leading to brain damage and cerebral palsy. Brain lesions induced in newborn mice by ibotenate (acting on N-methyl-D-aspartate receptors) and by S-bromowillardiine (acting on alpha-3-amino-hydroxy-5-methyl-4-isoxazole propionic acid and kainate receptors) mimic some aspects of white matter cysts and transcortical necrosis observed in human perinatal brain damage. Fructose 1,6-biphosphate (FBP) is a high-energy glycolytic pathway intermediate which, in therapeutic doses, is non-toxic and neuroprotective in hypoxic-ischemic models of brain injury. Mechanisms of action include modulation of intracellular calcium through phospholipase C (PLC) activation. The goal of this study was to determine the neuroprotective effects of FBP in a mouse model of neonatal excitotoxic brain injury. Mice that received intraperitoneal FBP had a significant reduction in size of ibotenate-induced (80% reduction) or S-bromowillardiine-induced (40% reduction) cortical plate lesions when compared with control animals. Studies of fragmented DNA and cleaved caspase 3 confirmed the survival promoting effects of FBP. FBP had no detectable effect on excitotoxic white matter lesions. The effects of FBP were antagonized by co-administration of PLC, protein kinase C or mitogen-associated protein kinase inhibitors but not by protein kinase A inhibitor. A moderate, transient cooling of pups immediately after the insult extended the therapeutic window for FBP, as FBP administered 24 h after ibotenate was still significantly neuroprotective in these pups. This data extends the neuroprotective profile of FBP in neonatal brain injury and identifies gray matter lesions involving N-methyl-D-aspartate receptors as a major target for this promising drug.

Advances in postnatal neuroimaging: relevance to pathogenesis and treatment of brain injury

The human brain is susceptible to a wide variety of insults. The permanent residua of these abnormalities are represented in dysfunction of one or more areas of neurodevelopment. A full understanding of normal brain development, mechanisms of brain injury, and consequences for subsequent brain development is required to determine which infants are at risk for neurodevelopmental handicap, and to monitor the effects of new treatments and management regimens designed to prevent these disabilities. Advanced magnetic resonance techniques, such as quantitative morphometric magnetic resonance techniques, diffusion-weighted magnetic resonance techniques, and magnetic resonance spectroscopy applied to the study of early human brain development have given us a better understanding of the pathophysiologic mechanisms of brain injury and its effects on subsequent brain development. Magnetic resonance imaging has provided an invaluable tool for the study of the fetal and newborn brain in vivo.