Vasoactive intestinal peptide increases intracellular calcium in astroglia: synergism with alpha-adrenergic receptors.

In type I astrocytes from rat cerebral cortex, vasoactive intestinal peptide (VIP) at concentrations below 1 nM evoked an increase in intracellular calcium ion concentration. This response, however, was observed in only 18% of the astrocytes examined. alpha-Adrenergic stimulation with phenylephrine or norepinephrine also resulted in an intracellular calcium response in these cells and the threshold sensitivity of astrocytes to phenylephrine was vastly different from cell to cell. Treatment of these astrocytes with VIP (0.1 nM) together with phenylephrine at subthreshold concentrations produced large increases in intracellular Ca2+ concentration ([Ca2+]i) and oscillations. The continued occupation of the alpha-adrenergic receptor was required for sustained synergism. Both alpha-receptor stimulation and stimulation with the mixture of agonists induced the cellular calcium response by triggering release of calcium from cellular stores, since the response persisted in the absence of extracellular calcium. Furthermore, thapsigargin pretreatment, which depletes intracellular stores, abolished the agonist-induced [Ca2+]i response. VIP (0.1 nM) and phenylephrine were found to increase cellular levels of inositol phosphates; however, there was no apparent additivity in this response when the agonists were added together. These observations suggest a calcium-mediated second messenger system for the high-affinity VIP receptor in astrocytes and that alpha-adrenergic receptors act synergistically with the VIP receptor to augment an intracellular calcium signal. The synergism between diverse receptor types may constitute an important mode of cellular signaling in astroglia.

Adrenalectomy decreases vasoactive intestinal peptide mRNA levels in the rat suprachiasmatic nucleus.

Vasoactive intestinal peptide (VIP) concentrations were shown to be regulated by adrenal steroids. Therefore, we investigated whether adrenal steroids affect VIP mRNA levels, which would suggest an effect on VIP mRNA expression. Adrenalectomy performed on adult male rats resulted in a significant decrease in VIP mRNA in the hypothalamus (from 10.6 +/- 0.3 to 3.5 +/- 0.2 arbitrary units). In situ hybridization experiments revealed that a major site of VIP mRNA expression in the hypothalamus is the suprachiasmatic nucleus. Indeed, adrenalectomy resulted in an approximate decrease by half in VIP transcripts in this nucleus. However, this decrease was not reversed by replacement treatment with corticosterone or the glucocorticoid agonist, RU28362. Thus, VIP mRNA may be regulated by indirect mechanisms, influenced by the adrenal gland.

A decomposition product of a contaminant implicated in L-tryptophan eosinophilia myalgia syndrome affects spinal cord neuronal cell death and survival through stereospecific, maturation and partly interleukin-1-dependent mechanisms.

The L-tryptophan eosinophilia myalgia syndrome (L-TRP-EMS), an inflammatory syndrome characterized by eosinophilia, myalgias, perimyositis, fasciitis and neuropathies, occurred in epidemic proportions in the United States in the summer and fall of 1989. The neuropathic clinical features in L-TRP EMS are complex and mixed. In the present study, one of the impurities most highly associated with development of L-TRP EMS, 1,1'-ethylidenebis[L-tryptophan] (EBT), and two of its diastereoisomeric breakdown products, were compared for evidence of neurotoxicity in vitro. In 1-month-old spinal cord cultures derived from fetal mice, synthetic (-)-(1S,3S)-1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (1S-beta-C) produced a 30 to 35% loss in numbers of neurons. Toxicity was not apparent after treatment with the R-isomer of the same compound or with the parent compound, EBT. Cotreatment of cultures with 1S-beta-C and neutralizing antiserum to interleukin-1 alpha (IL-1 alpha), or with 1S-beta-C and neutralizing antiserum against the murine IL-1 receptor, prevented neuronal cell death associated with 1S-beta-C. Recombinant IL-1 alpha also produced neuronal killing that was not additive to that observed with the 1S-beta-C treatment. In contrast, in immature spinal cord neuronal cultures, the 1S-beta-C, but not the 1R-beta-C or EBT, prevented the 30% cell death which normally occurs in these cultures. Neither neutralizing anti-IL-1 antibody, nor anti-IL-1 receptor antibody blocked the neuronal survival effect, suggesting that 1S-beta-C induces neuronal survival through a receptor-mediated mechanism independent of IL-1.(ABSTRACT TRUNCATED AT 250 WORDS)

HIV envelope protein-induced neuronal damage and retardation of behavioral development in rat neonates.

Cognitive and motor impairment are common symptoms among patients infected with the human immunodeficiency virus (HIV), including children who suffer neurological deficits and are frequently developmentally impaired. The HIV envelope protein, gp120, which has been shown to be toxic to neurons in culture, is shed in abundance by infected cells, and thus may play a significant role in the neuropathology of AIDS. To test this possible mechanism, neonatal rats were injected systemically with purified gp120 and the following consequences were observed: (1) radiolabeled gp120 and toxic fragments thereof were recovered in brain homogenates; (2) dystrophic changes were produced in pyramidal neurons of cerebral cortex; (3) retardation was evident in developmental milestones associated with complex motor behaviors. In parallel studies, co-treatment with peptide T, a gp120-derived peptide having a pentapeptide sequence homologous with vasoactive intestinal peptide, prevented or attenuated the morphological damage and behavioral delays associated with gp120 treatment. These studies suggest that gp120 and gp120-derived toxic fragments may contribute to the neurological and neuropsychiatric impairment related to HIV infection, and that peptide T appears to be effective in preventing gp120-associated neurotoxicity in developing rodents.

VIP-mRNA is increased in hypertensive rats.

Vasoactive intestinal peptide (VIP) is a potent vasodilator. We therefore set out to investigate VIP-gene expression in spontaneous hypertensive rats. By quantitative in situ hybridization histochemistry as well as by RNA blot hybridization experiments we discovered a significant increase in VIP transcripts in the brains of those hypertensive rats. We suggest that the increase in VIP-gene expression may play a compensatory role in these rats where otherwise the rise in blood pressure may have had a much more adverse effect.

Lactation elevates vasoactive intestinal peptide messenger ribonucleic acid in rat suprachiasmatic nucleus.

Vasoactive intestinal peptide (VIP) has been suggested to play a role in lactation; indeed several studies implied that VIP induces the release of PRL in the pituitary. Quantitative RNA studies from our laboratory show an increase in the VIP messenger RNA (mRNA) content in the hypothalamus of lactating rats. The purpose of this investigation is to determine which hypothalamic neurons are increasing the expression of VIP. A sensitive in situ hybridization assay employing synthetic oligodeoxynucleotide probes corresponding to specific exons of the VIP gene was used to study VIP gene expression at the neuronal level. We were able to detect VIP-encoding transcripts in various brain regions including the ventrolateral thalamus, neocortex, pyriform cortex, and hypothalamus with a particularly high concentration in the suprachiasmatic nucleus. When lactating animals were compared to non-lactating animals, a 2-fold increase was observed in VIP transcripts in the suprachiasmatic nucleus. Since the suprachiasmatic nucleus is not directly associated with the physiology of lactation, the response of the VIP gene to lactation may be, in part, indirect. Taken together, our results suggest that lactation and the expression of the VIP gene are interrelated.

Sequential expression in the nervous system of c-myb and VIP genes, located in human chromosomal region 6q24.

Vasoactive intestinal peptide (VIP) is a major neuropeptide involved in multiple functions such as vasodilation, smooth-muscle relaxation, sweat secretion, gastrointestinal peristalsis, pancreatic function, and brain activity. In view of the multiple roles associated with VIP, it is important to understand its gene regulation. We have recently isolated the human VIP gene and determined its structure. By in situ hybridization techniques we have now localized this gene to the long arm of chromosome 6, 6q24, a chromosomal region that has been shown previously to contain the coding sequences for the nuclear protooncogene c-myb. Genes found in close proximity to each other on the chromosome are often functionally related and, as VIP is primarily expressed in the nervous system, we investigated the possible correlation of c-myb to VIP in neuronal tissue. A sharp peak of c-myb mRNA was observed in the hippocampus of 3-day-old rats, preceding the peak of VIP mRNA that occurs in this brain area at 8 days of age. Thus, the protooncogene c-myb may be associated with events in brain development occurring prior to the appearance of elevated concentrations of VIP.

The gene encoding vasoactive intestinal peptide is located on human chromosome 6p21----6qter.

Vasoactive intestinal peptide (VIP) is a regulatory neuropeptide involved in a wide variety of functions, among them vasodilation, smooth muscle relaxation, sweat secretion, gastrointestinal peristalsis, and pancreatic function. A deficient VIP-innervation of sweat glands was recently described as a possible pathogenic factor in sweating of cystic fibrosis (CF) patients. To investigate a possible role for a defective VIP-gene in cystic fibrosis, we have used a panel of rodent-human hybrid cells, retaining defined complements of human chromosomes to localize the VIP-gene to the human chromosome region 6p21----6qter. As the CF gene was recently mapped to chromosome 7, we conclude that the VIP-gene is not the primary gene defect in this disease.