VIP neuroprotection against excitotoxic lesions of the developing mouse brain

Implications of white matter damage in amyotrophic lateral sclerosis (Review)

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease, which involves the progressive degeneration of motor neurons. ALS has long been considered a disease of the grey matter; however, pathological alterations of the white matter (WM), including axonal loss, axonal demyelination and oligodendrocyte death, have been reported in patients with ALS. The present review examined motor neuron death as the primary cause of ALS and evaluated the associated WM damage that is guided by neuronal‑glial interactions. Previous studies have suggested that WM damage may occur prior to the death of motor neurons, and thus may be considered an early indicator for the diagnosis and prognosis of ALS. However, the exact molecular mechanisms underlying early‑onset WM damage in ALS have yet to be elucidated. The present review explored the detailed anatomy of WM and identified several pathological mechanisms that may be implicated in WM damage in ALS. In addition, it associated the pathophysiological alterations of WM, which may contribute to motor neuron death in ALS, with similar mechanisms of WM damage that are involved in multiple sclerosis (MS). Furthermore, the early detection of WM damage in ALS, using neuroimaging techniques, may lead to earlier therapeutic intervention, using immunomodulatory treatment strategies similar to those used in relapsing‑remitting MS, aimed at delaying WM damage in ALS. Early therapeutic approaches may have the potential to delay motor neuron damage and thus prolong the survival of patients with ALS. The therapeutic interventions that are currently available for ALS are only marginally effective. However, early intervention with immunomodulatory drugs may slow the progression of WM damage in the early stages of ALS, thus delaying motor neuron death and increasing the life expectancy of patients with ALS.

Neuropeptides shaping the central nervous system development: Spatiotemporal actions of VIP and PACAP through complementary signaling pathways

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are neuropeptides with wide, complementary, and overlapping distributions in the central and peripheral nervous systems, where they exert important regulatory roles in many physiological processes. VIP and PACAP display a large range of biological cellular targets and functions in the adult nervous system including regulation of neurotransmission and neuroendocrine secretion and neuroprotective and neuroimmune responses. As the main focus of the present review, VIP and PACAP also have been long implicated in nervous system development and maturation through their interaction with the seven transmembrane domain G protein-coupled receptors, PAC1, VPAC1, and VPAC2, initiating multiple signaling pathways. Compared with PAC1, which solely binds PACAP with very high affinity, VPACs exhibit high affinities for both VIP and PACAP but differ from each other because of their pharmacological profile for both natural accessory peptides and synthetic or chimeric molecules, with agonistic and antagonistic properties. Complementary to initial pharmacological studies, transgenic animals lacking these neuropeptides or their receptors have been used to further characterize the neuroanatomical, electrophysiological, and behavioral roles of PACAP and VIP in the developing central nervous system. In this review, we recapitulate the critical steps and processes guiding/driving neurodevelopment in vertebrates and superimposing the potential contribution of PACAP and VIP receptors on the given timeline. We also describe how alterations in VIP/PACAP signaling may contribute to both (neuro)developmental and adult pathologies and suggest that tuning of VIP/PACAP signaling in a spatiotemporal manner may represent a novel avenue for preventive therapies of neurological and psychiatric disorders. © 2016 Wiley Periodicals, Inc.

Protective effects of poly (butyl) cyanoacrylate nanoparticles containing vasoactive intestinal peptide against 6-hydroxydopamine-induced neurotoxicity in vitro

The present study investigated brain delivery system of vasoactive intestinal peptide (VIP) adsorbed on poly (butyl cyanoacrylate) nanoparticles coated with polysorbate 80 (P80-poly (butyl) cyanoacrylate (PBCA)-nanoparticles (NPs)) and the neuroprotective effects on the formulation in the model of 6-hydroxydopamine (6-OHDA)-induced Parkinsonian dysfunction in the human neuroblastoma cell line SH-SY5Y. Drug-loaded nanoparticles were prepared by emulsion polymerization method using VIP and PBCA and then stirring with polysorbate 80. The resulting nanoparticles possessed high entrapment efficiency and favorable stability against CaCl2 or fetal bovine serum (FBS)-induced aggregation. Use of fluorescein isothiocyanate (FITC)-conjugated polysorbate 80-PBCA nanoparticles in confocal microscopy revealed that nanoparticles are located inside, while the FITC solution could not penetrate into the cells. The blank nanoparticles showed no significant effects on cell viability, indicating that they had no role in protection; however, polysorbate 80-modified VIP-loading PBCA nanoparticles showed enhanced cell viability compared to free VIP in 6-OHDA-mimic cellular model of Parkinson's disease. In addition, the nanoparticles strikingly increased the anti-apoptosis activity and restored the loss of mitochondrial membrane potential (MMP) significantly after the treatment of 6-OHDA. These results demonstrated that the activity of VIP was enhanced by polysorbate 80-PBCA nanoparticles compared to control solutions, suggesting that PBCA nanoparticles coated with polysorbate 80 could be an effective carrier system for VIP.

Subcellular localization and secretion of activity-dependent neuroprotective protein in astrocytes

Activity-dependent neuroprotective protein (ADNP, approximately 123562.8 Da), is synthesized in astrocytes and expression of ADNP mRNA is regulated by the neuroprotective peptide vasoactive intestinal peptide (VIP). The gene that encodes ADNP is conserved in human, rat and mouse, and contains a homeobox domain profile that includes a nuclear-export signal and a nuclear-localization signal. ADNP is essential for embryonic brain development, and NAP, an eight-amino acid peptide that is derived from ADNP, confers potent neuroprotection. Here, we investigate the subcellular localization of ADNP through cell fractionation, gel electrophoresis, immunoblotting and immunocytochemistry using alpha-CNAP, an antibody directed to the neuroprotective NAP fragment that constitutes part of an N-terminal epitope of ADNP. Recombinant ADNP was used as a competitive ligand to measure antibody specificity. ADNP-like immunoreactivity was found in the nuclear cell fraction of astrocytes and in the cytoplasm. In the cytoplasm, ADNP-like immunoreactivity colocalized with tubulin-like immunoreactivity and with microtubular structures, but not with actin microfilaments. Because microtubules are key components of developing neurons and brain, possible interaction between tubulin and ADNP might indicate a functional correlate to the role of ADNP in the brain. In addition, ADNP-like immunoreactivity in the extracellular milieu of astrocytes increased by approximately 1.4 fold after incubation of the astrocytes with VIP. VIP is known to cause astrocytes to secrete neuroprotective/neurotrophic factors, and we suggest that ADNP constitutes part of this VIP-stimulated protective milieu.

Vasoactive intestinal peptide enhances striatal plasticity and prevents dopaminergic cell loss in Parkinsonian rats

Destruction of the nigrostriatal dopaminergic pathway by the administration of 6-OHDA generates an animal model of Parkinson's disease. The main characteristic of this progressive neurological disorder is the loss of the dopaminergic neurons located in the substantia nigra pars compacta (SNc). Dopaminergic inputs from the SNc innervate the medium spiny neurons of the striatum and modulate the spontaneous activity of the primary output nuclei of the basal ganglia, globus pallidus interna, and substantia nigra pars reticulata. In our previous studies, we showed that systematically administered vasoactive intestinal peptide (VIP) is effective at reversing motor deficits, decreasing neuronal cell death, and repairing the myelin sheet in parkinsonian rats. In the current study, the effects of VIP on the dendritic morphology of the striatal neurons and the number of dopaminergic neurons in the SNc were examined in 6-OHDA-lesioned rats using Golgi-Cox staining and design-based stereological methods, respectively. Adult Sprague-Dawley rats were separated into sham-operated, bilaterally 6-OHDA lesioned and lesioned + i.p. VIP-injected (25 ng/kg) groups. VIP was first injected 1 h after the intrastriatal 6-OHDA microinjection (every 2 days for 15 days). The 6-OHDA significantly decreased the total number of dopaminergic neurons, branching, and spine density of the medium spiny neurons in the striatum. VIP significantly increased the number of neurons immunostained with tyrosine hydroxylase and the density of spines without altering the branching and the total length of dendrites. In conclusion, VIP might display synaptogenetic activity by enhancing the spine density in the striatum of the parkinsonian rats.

Nur(R1)turing a notion on the etiopathogenesis of Parkinson's disease

The canonical histopathological feature of Parkinson's disease (PD) is the loss of dopaminergic neurons in the ventral midbrain. Although the common sporadic/idiopathic form of PD most often presents clinically at around 60 years of age when the levels of striatal dopamine and numbers of ventral dopaminergic neurons are posited to have declined by 80 and 60%, respectively, the temporal pattern of injury to these vulnerable cells is unknown. The conventional view is that PD results from an accelerated age-related loss of dopamine neurons. However, an alternative hypothesis is that dopamine neuron loss is a developmental phenomenon. What evidence might support this alternative view? Apart from the rare familial forms, wherein loss or gain of function mutations in single genes convey highly penetrant PD, sporadic disease is genetically complex and may have other contributory non-genetic components. Epidemiologic and twin studies have strongly implicated gene-environmental interaction as a pathogenic dyad in the etiology of PD. Among the most attractive candidates that may connect the environment to inherited vulnerability is the nuclear receptor, Nurr1. Encoding an orphan transcription factor that is expressed at high levels within discrete regions of the developing and adult mammalian brain, Nurr1 is essential for the formation of ventral midbrain dopamine neurons. Given the absence of a known lipophilic small molecule regulator and established transcriptional role in the formation of the definitive dopaminergic phenotype, Nurr1 represents an intriguing molecule to explore in the context of sporadic PD as a developmental disorder. The study described herein addresses two features of Nurr1 biology that provide plausibility for this hypothesis. First is the description of Nurr1 regulation of a potent dopaminergic neuronal trophic factor, vasoactive intestinal peptide (VIP), and second is the identification of a protein, termed Nurr1 interacting protein (NuIP) that appears to link upstream signaling pathways in the regulation of Nurr1 transcriptional activity.

Peptidergic agonists of activity-dependent neurotrophic factor protect against prenatal alcohol-induced neural tube defects and serotonin neuron loss

INTRODUCTION

Prenatal alcohol exposure via maternal liquid diet consumption by C57BL/6 (B6) mice causes conspicuous midline neural tube deficit (dysraphia) and disruption of genesis and development of serotonin (5-HT) neurons in the raphe nuclei, together with brain growth retardation. The current study tested the hypothesis that concurrent treatment with either an activity-dependent neurotrophic factor (ADNF) agonist peptide [SALLRSIPA, (SAL)] or an activity-dependent neurotrophic protein (ADNP) agonist peptide [NAPVSIPQ, (NAP)] would protect against these alcohol-induced deficits in brain development.

METHODS

Timed-pregnant B6 dams consumed alcohol from embryonic day 7 (E7, before the onset of neurulation) until E15. Fetuses were obtained on E15 and brain sections processed for 5-HT immunocytochemistry, for evaluation of morphologic development of the brainstem raphe and its 5-HT neurons. Additional groups were treated either with SAL or NAP daily from E7 to E15 to assess the potential protective effects of these peptides. Measures of incomplete occlusion of the ventral canal and the frequency and extent of the openings in the rhombencephalon were obtained to assess fetal dysraphia. Counts of 5-HT-immunostained neurons were also obtained in the rostral and caudal raphe.

RESULTS

Prenatal alcohol exposure resulted in abnormal openings along the midline and delayed closure of ventral canal in the brainstem. This dysraphia was associated with reductions in the number of 5-HT neurons both in the rostral raphe nuclei (that gives rise to ascending 5-HT projections) and in the caudal raphe (that gives rise to the descending 5-HT projections). Concurrent treatment of the alcohol-consuming dams with SAL prevented dysraphia and protected against the alcohol-induced reductions in 5-HT neurons in both the rostral and caudal raphe. NAP was less effective in protecting against dysraphia and did not protect against 5-HT loss in the rostral raphe, but did protect against loss in the caudal raphe.

CONCLUSIONS

These findings further support the potential usefulness of these peptides for therapeutic interventions in pregnancies at risk for alcohol-induced developmental deficits. Notably, the ascending 5-HT projections of the rostral raphe have profound effects in regulating forebrain development and function, and the descending 5-HT projections of the caudal raphe are critical for regulating respiration. Protection of the rostral 5-HT-system may help prevent structural and functional deficits linked to abnormal forebrain development, and protection of the caudal systems may also reduce the increased risk for sudden infant death syndrome associated with prenatal alcohol exposure.

Neuroprotection: a comparative view of vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide

The neuroprotective properties of vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) place these peptides in a special category of ligands that have implications for our understanding of pathological conditions as well as a potential basis for therapeutic intervention. It is remarkable that these peptides have a protective impact against such a wide variety of clinical relevant toxic substances. This protective diversity is consistent with the multiple pathways that are activated or inhibited by the action of these peptides. Although knowledge is emerging on the neuroprotective mechanisms of VIP and PACAP, it is already evident that these two peptides are not identical in their action and each peptide has multiple mechanisms that allow for neuroprotective diversity. The multiple intracellular signaling pathways and differing extracellular mediators of neuroprotection contribute to this diversity of action. In this review, examples of neuroprotective actions will be presented that serve to demonstrate the remarkable breadth of neuroprotective processes produced by VIP and PACAP.

Signaling involved in pituitary adenylate cyclase-activating polypeptide-stimulated ADNP expression

Activity-dependent neurotrophic protein (ADNP) was discovered as a novel response gene for VIP and has neuroprotective potential. When the VIP paralog, PACAP38 was added to mouse neuron-glia co-cultures, it induced ADNP mRNA expression in a bimodal fashion at subpico- and nanomolar concentrations with greater response at subpicomolar level. The response was attenuated by a PAC1-R antagonist at both concentrations and by a VPAC1-R antagonist at nanomolar concentration only. An IP3/PLC inhibitor attenuated the response at both concentrations of PACAP38, but a MAPK inhibitor had no effect. A PKA inhibitor suppressed the response at nanomolar concentration only. These findings suggest that ADNP expression is mediated through multiple receptors and signaling pathways that are regulated by different concentrations of PACAP.

Prevention of alcohol-induced learning deficits in fetal alcohol syndrome mediated through NMDA and GABA receptors

OBJECTIVE

Vasoactive intestinal peptide (VIP)-related peptides prevented the learning deficit in the offspring in a model for fetal alcohol syndrome. We evaluated whether the mechanism of the peptide protection included NR2B, NR2A, and GABAAalpha5.

STUDY DESIGN

Timed, pregnant C57BL6/J mice were injected on gestational day 8 with alcohol (0.03 mL/kg), placebo, or alcohol plus peptides. Embryos were harvested after 6 hours, 24 hours, and on gestational day 18. Some of the litters were allowed to deliver, and the adult brains harvested after the offspring were tested for learning. Calibrator-normalized relative real-time polymerase chain reaction (PCR) was performed using primers for NR2B, NR2A, and GABAAalpha5 with GAPDH standardization. Statistic: analysis of variance (ANOVA) and Fisher PLSD, P < .05 was considered significant.

RESULTS

In the embryo, the peptides prevented NR2B rise (P < .001) at 6 hours, NR2B down-regulation (P = .002), and GABAAalpha5 decrease (P < .01) on gestational day 18. In the adult, the peptides prevented NR2B down-regulation (P = .01) and NR2A up-regulation (P < .001).

CONCLUSION

VIP-related peptides prevented alcohol-induced changes in NR2B, NR2A, and GABAAalpha5. This may explain, at least in part, the peptides' prevention of alcohol-induced learning deficits.

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.

Brain mast cells and therapeutic potential of vasoactive intestinal peptide in a Parkinson's disease model in rats: brain microdialysis, behavior, and microscopy

In the present study, the effect of systemically administered vasoactive intestinal peptide (VIP) (25 ng/kg i.p.) was investigated on drug-induced rotational behavior, extra-cellular dopamine levels and histology of corpus striatum in a 6-hydroxydopamine (6-OHDA)-induced rat model of Parkinson's disease. After 15 days of 6-OHDA lesion, apomorphine-induced (0.05 mg/kg s.c.) rotational behavior of the animals significantly increased and extra-cellular dopamine levels of corpus striatum were significantly reduced. VIP reversed the rotational deficits but did not alter the decrease in striatal dopamine levels. On the other hand, histological data indicate that VIP significantly reduced neuronal death and demyelination. Electron microscopic appearance of mast cells showed ultra-structural variety between VIP-treated and 6-OHDA lesioned groups. VIP activates mast cells without any evidence of typical exocytosis, and possibly mast cells could participate in neuroprotection. Our results suggest that systemically administered VIP can attenuate the motor response changes, neuronal cell death, and myelin sheet loss characteristically associated with 12 microg 6-OHDA administration into the rat striatum. Brain mast cells seem to participate in neuronal protection. Possibly, protective cues could be produced by brain mast cells.

Estrogen neuroprotection against the neurotoxic effects of ethanol withdrawal: potential mechanisms

Ethanol withdrawal (EW) produces substantial neurotoxic effects, whereas estrogen is neuroprotective. Given observations that both human and nonhuman female subjects often show less impairment following EW, it is reasonable to hypothesize that estrogens may protect females from the neurotoxic effects of ethanol. This article is based on the assumption that the behavioral deficits seen following EW are produced in part by neuronal death triggered by oxidative insults produced by EW. The EW leads to activation of protein kinase C, especially PKCepsilon, which subsequently triggers apoptotic downstream events such as phosphorylation of nuclear factor-kappaB (NFkappaB) complex. On phosphorylation, active NFkappaB translocates to the nucleus, binds to DNA, and activates caspases, which trigger DNA fragmentation and apoptosis. In contrast, estrogens are antioxidant, inhibit overexpression of PKCepsilon, and suppress expression of NFkappaB and caspases. Estrogen treatment reduces the behavioral deficits seen during EW and attenuates molecular signals of apoptosis. The effects of ethanol and estrogen on each step in the signaling cascade from ethanol exposure to apoptosis are reviewed, and potential mechanisms by which estrogen could produce neuronal protection against the neurotoxicity produced by EW are identified. These studies serve as a guide for continuing research into the mechanisms of the neuroprotective effects of estrogen during EW and for the development of potential estrogen-based treatments for male and female alcoholics.

The significance of vasoactive intestinal peptide in immunomodulation

First identified by Said and Mutt some 30 years ago, the vasoactive intestinal peptide (VIP) was originally isolated as a vasodilator peptide. Subsequently, its biochemistry was elucidated, and within the 1st decade, their signature features as a neuropeptide became consolidated. It did not take long for these insights to permeate the field of immunology, out of which surprising new attributes for VIP were found in the last years. VIP is rapidly transforming into something more than a mere hormone. In evolving scientifically from a hormone to a novel agent for modifying immune function and possibly a cytokine-like molecule, VIP research has engaged many physiologists, molecular biologists, biochemists, endocrinologists, and pharmacologists and it is a paradigm to explore mutual interactions between neural and neuroendocrine links in health and disease. The aim of this review is firstly to update our knowledge of the cellular and molecular events relevant to VIP function on the immune system and secondly to gather together recent data that support its role as a type 2 cytokine. Recognition of the central functions VIP plays in cellular processes is focusing our attention on this "very important peptide" as exciting new candidates for therapeutic intervention and drug development.

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.

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.

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) as modulators of both innate and adaptive immunity

The structurally related neuropeptides VIP and PACAP are released within the lymphoid organs following antigenic stimulation, and modulate the function of inflammatory cells through specific receptors. In activated macrophages, VIP and PACAP inhibit the production of pro-inflammatory agents (cytokines, chemokines, and nitric oxide), and stimulate the production of the anti-inflammatory cytokine IL-10. These events are mediated through the VIP/PACAP effects on de novo expression or nuclear translocation of several transcription factors, i.e., NFkappaB, CREB, c-Jun, JunB, and IRF-1. The in vivo administration of VIP/PACAP results in a similar pattern of cytokine and chemokine modulation, which presumably mediates the protective effect of VIP/PACAP in septic shock. In addition, VIP/PACAP reduce the expression of the co-stimulatory molecules B7.1/B7.2, and the subsequent stimulatory activity of macrophages for T-helper cells. In T-cells expressing specific VIP/PACAP receptors, VIP and PACAP inhibit the expression of FasL through effects on NFkappaB, NFAT, and Egr2/3. The reduction of FasL expression has several biological consequences: inhibition of antigen-induced cell death in CD4 T-cells, inhibition of the FasL-mediated cytotoxicity of CD8 and CD4 effectors against direct and bystander targets, and promotion of long-term memory Th2 cells, through a positive effect on the survival of Th2, but not Th1, effectors. The various biological effects of VIP and PACAP are discussed within the range of a general anti-inflammatory model.

Neurobiology of hypoxic-ischemic injury in the developing brain

Hypoxic ischemia is a common cause of damage to the fetal and neonatal brain. Although systemic and cerebrovascular physiologic factors play an important role in the initial phases of hypoxic-ischemic injuries, the intrinsic vulnerability of specific cell types and systems in the developing brain may be more important in determining the final pattern of damage and functional disability. Excitotoxicity, a term applied to the death of neurons and certain other cells caused by overstimulation of excitatory, mainly glutamate, neurotransmitter receptors, plays a critical role in these processes. Selected neuronal circuits as well as certain populations of glia such as immature periventricular oligodendroglia may die from excitotoxicity triggered by hypoxic ischemia. These patterns of neuropathologic vulnerability are associated with clinical syndromes of neurologic disability such as the extrapyramidal and spastic diplegia forms of cerebral palsy. The cascade of biochemical and histopathologic events triggered by hypoxic ischemia can extend for days to weeks after the insult is triggered, creating the potential for therapeutic interventions.

Voltage-operated Ca(2+) channels involved in K(+)-evoked release of vasoactive intestinal polypeptide from the rat hypothalamus

Rat brain hypothalami were exposed to various depolarizing stimuli and vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI) release was measured by means of a radioimmunoassay (RIA) procedure. Under conditions of noradrenergic blockade, exposure to high K(+) (40-100 mM) produced dose-dependent increases in the VIP-LI release in a Ca(2+)-dependent manner. Exposure to veratridine (3-100 microM) also induced concentration-dependent increases in VIP-LI release, an effect that was Ca(2+)-dependent and tetrodotoxin (TTX)-sensitive. Specific ligands for the L, N, and P/Q-type voltage-operated Ca(2+) channels (VOCCs) were used to determine which channel subtypes were involved in the K(+)-evoked VIP-LI release. The L-type VOCC ligand, nifedipine (10 microM), had no effect on release. In contrast, the N-type VOCC blocker, omega-conotoxin GVIA (omega-CgTx GVIA) (0.1-100 nM), markedly reduced the K(+)-evoked response, with maximal inhibition of approximately 60+/-8%. omega-Agatoxin IVA (omega-Aga IVA) (1-50 nM), which binds P-type and, at high doses, also Q-type VOCCs, produced dose-dependent inhibition of up to 25+/-3%, while the maximal inhibition observed with the non-selective VOCCs ligand, omega-conotoxin MVIIC (omega-CmTx MVIIC) (1 nM-3 microM), amounted to 85+/-8%. These findings indicate that N and P-type Ca(2+) channels play predominant roles in the high K(+)-evoked release of VIP-LI from the rat hypothalamus.