Extracranial vasodilatation mediated by vasoactive intestinal polypeptide (VIP)

Pooled antisera to vasoactive intestinal polypeptide were used to block neurogenic extracranial vasodilatation elicited from either brainstem (locus coeruleus) or pterygopalatine ganglion stimulation in the cat. Vasodilatation was not inhibited by sham immune sera, or by antisera to bradykinin or substance P. The efferent pathway for vasodilatation from the locus coeruleus traverses the facial nerve (greater superficial petrosal branch) and the pterygopalatine and otic ganglia. Its blockade demonstrates a novel action of a peptide transmitter in the expression of a central neurogenic response.     

Selective facilitatory effect of vasoactive intestinal polypeptide (VIP) on muscarinic firing in vesical ganglia of the cat

VIP immunoreactivity was identified in nerve fibers and in 10-13% of the neurons in pelvic and bladder ganglia of the cat. Ninety percent of the VIP positive neurons contained acetylcholinesterase. VIP immunoreactivity was not altered in decentralized ganglia 1 week to 8 months after transection of the pelvic and hypogastric nerves indicating that VIP fibers arose from neurons within the peripheral nervous system. The intra-arterial administration of VIP (1-50 micrograms/kg) enhanced the postganglionic discharge elicited by the muscarinic agonist, acetyl-beta-methylcholine, but did not alter the postganglionic firing elicited by the nicotinic agonist, tetramethylammonium or by electrical stimulation of preganglionic axons in the pelvic nerve. VIP did not elicit a postganglionic discharge in untreated ganglia, but did evoke a prolonged discharge in ganglia treated with an irreversible anticholinesterase agent, 217AO. This discharge was not affected by hexamethonium but was blocked by atropine. VIP suppressed the muscarinic inhibition of ganglionic transmission produced by acetyl-beta-methylcholine without altering the response to other inhibitory agents (norepinephrine, leucine-enkephalin and gamma-aminobutyric acid (GABA). VIP (0.1-0.3 micrograms/kg) also had a direct inhibitory effect on bladder smooth muscle. These findings raise the possibility that intraganglionic pathways containing VIP may exert a selective modulatory influence on muscarinic transmission in vesical parasympathetic ganglia.     

The potentiation of sinus arrhythmia by vasoactive intestinal polypeptide (VIP) in the anaesthetized dog

Vasoactive intestinal polypeptide (VIP) is a neuropeptide released from the vagus, which in contrast to acetylcholine has a long-acting positive chronotropic effect on the heart. The aim of this study, in the anaesthetized dog, was to examine the effects of VIP and a VIP antagonist when injected into the sinus node artery of a vagally intact heart in sinus arrhythmia. The response was compared to that produced by noradrenaline (NAD) infusion and stimulation of the sympathetic nerves to the heart. Mean +/- S.D. of 30 R-R intervals was used to describe mean heart rate interval and heart rate variability. VIP, a VIP antagonist, NAD and sympathetic nerve stimulation all caused increases in heart rate without significant increases in blood pressure. However, only VIP caused an increase in heart rate variability; VIP antagonism and NAD caused a decrease and sympathetic nerve stimulation had no effect. These results suggest that VIP and acetylcholine when released from the vagus act synergistically to increase sinus arrhythmia.     

Development of vasoactive intestinal polypeptide (VIP) containing neurones in the rat brain

The development of VIP-containing neurones in the rat CNS and duodenum has been studied using a specific radioimmunoassay and immunohistochemistry. In the brain, VIP immunoreactivity appears entirely postnatally, while VIP in peripheral neurones in the duodenum was present before birth. The developmental changes observed in cerebral cortex appear to represent the maturation of a population of intrinsic cortical interneurones which contain VIP. These neurones develop entirely after birth. They are first seen in deep cortical layers, but later spread out into all cortical layers, particularly layers II--IV. Changes in the intensity of VIP cell body fluorescence can be correlated with changes in VIP content in the cortex measured by radioimmunoassay. Thus VIP forms a unique chemical marker for studying the maturation of a cortical neurone.     

Distribution of vasoactive intestinal polypeptide (VIP) in the rat brain stem nuclei

The distribution of vasoactive intestinal polypeptide (VIP) in the individual nuclei of the rat brain stem was examined. Highest VIP concentrations in brain stem (> 1 ng/mg protein) are confined to dorsal regions, including periaqueductal gray and structures under the fourth ventricle. VIP concentrations are moderately high (0.8–1 ng/mg protein) in gracile nucleus, area postrema, nucleus of the solitary tract, motor nucleus of the XIIth, locus ceruleus and dorsal tegmental nucleus. Cerebellum and pontine nuclei contained only very low levels (< 0.2 ng/mg protein) of VIP.     

Preferential immunohistochemical localization of vasoactive intestinal polypeptide (VIP) in the sacral spinal cord of the cat: light and electron microscopic observations

In the present study we have employed immunoperoxidase techniques to investigate the distribution of vasoactive intestinal polypeptide (VIP)-like immunoreactivity in the spinal cord and sensory ganglia of the cat. The spinal distribution of VIP-containing neuronal processes was also compared with that of substance P (SP), somatostatin (SOM), and cholecystokinin-8 (CCK) at lumbar, sacral, and coccygeal levels. At sacral levels, VIP was found to be contained in small and medium-sized primary sensory neurons and in dorsal rootlets. Deafferentation, by either ganglionectomy or dorsal rhizotomy, resulted in a nearly complete loss of VIP immunoreactivity in the spinal cord. The spinal distribution of VIP fibers and terminals was most dense and extensive in sacral segments. Forming a thin shell around the dorsal horn, collaterals, apparently originating from Lissauer's tract, projected either medially or laterally through lamina I. Laterally, many VIP axons terminated in lateral laminae V to VII. Others projected further through the neck of the dorsal horn to medial lamina V and the gray matter near the central canal. Medially, VIP axons descended through lamina I to expand into terminal fields in the posterior commissure and medial lamina V. At the ultrastructural level, VIP-like immunoreactivity was found in dense core vesicles within axonal enlargements containing both large dense core and smaller clear round vesicles. Synaptic connections were infrequently observed but, when encountered, were of the simple axodendritic type. The spinal distribution of VIP-containing fibers was remarkably similar to that reported for pelvic nerve visceral afferents, both in termination patterns within the spinal gray matter and in localization to the sacral cord. The density of SP-, SOM-, and CCK-containing fibers and terminals was constant at all levels examined (L4 to Co4). In marked contrast, the distribution of VIP fibers, much like that of pelvic nerve afferents, was mostly confined to sacral segments. Thus, although SP, SOM, and CCK may be contained within a population of sacral visceral afferents, they must be common to afferent systems in other segments as well. VIP, however, appears to be preferentially contained within pelvic visceral afferent fibers confined mostly to sacral segments.     

Characterization of the gene and messages for vasoactive intestinal polypeptide (VIP) in rat and mouse.

We have studied the structure and expression of the gene for vasoactive intestinal polypeptide (VIP) in rodents. We used a human cDNA to identify and clone a fragment of the rat VIP gene. This genomic fragment contained two separate exons, one encoding VIP itself and the other encoding a closely related neuropeptide, peptide histidine-isoleucine (PHI-27). Probes containing either exon, or both, hybridized to two messages: a prominent 1700-base (b) mRNA and a rare 1000-b species. These messages are expressed together in a tissue-specific manner, with highest levels in polyadenylated RNA from cerebral cortex and from small intestine, paralleling the reported levels of the neuropeptides themselves in these tissues. Using the rat genomic fragment as a probe, we isolated the mouse VIP gene in its entirety. The mouse gene is similar in organization to its human counterpart, with a total of 7 exons spanning 8 kilobases (kb). The 7th and largest exon, which is transcribed into the bulk of the 3' untranslated region of the messages, bears two potential polyadenylation sites 700 basepairs (bp) apart. S-1 nuclease protection with a fragment of this exon indicated that the two identifiable VIP messages differ in the extent of their 3' untranslated regions. Conversely, we found no evidence for differential splicing to produce messages encoding only one of the neuropeptides. Instead, specific oligonucleotide-directed digestion with RNase H demonstrated that all of the detectable mRNA from this gene contains both VIP and PHI coding sequences.     

Evidence that vasoactive intestinal polypeptide (VIP) mediates neurogenic vasodilation of feline cerebral arteries

In this study the magnitude of non-sympathetic, non-cholinergic neurogenic vasodilation of feline cerebral arteries in vitro was correlated with the extent of innervation by VIP-immunoreactive nerves. Well-innervated arteries underwent nerve-mediated relaxation whereas those that are not supplied with VIP-containing axons did not relax to transmural nerve stimulation. The relaxation of cerebral arteries that are well endowed with VIP-immunoreactive nerves was selectively and reversibly inhibited by VIP-specific antiserum. Substance P-specific antiserum did not affect the dilator responses. We conclude that VIP is a functional neurodilator transmitter in the cerebral circulation.     

No evidence for a diurnal vasoactive intestinal polypeptide (VIP) rhythm in the human suprachiasmatic nucleus

The mammalian suprachiasmatic nucleus (SCN) is implicated in the temporal organization of circadian rhythms in a variety of physiological, endocrine and behavioral processes. Since the environmental light-dark cycle is the main zeitgeber for many of these rhythms, photic information may have a synchronizing effect on the endogenous clock of the SCN by inducing periodic changes in the activity of certain groups of neurons. The present study was performed to investigate the diurnal profile of the vasoactive intestinal polypeptide (VIP)-producing neurons in the SCN of humans. No significant diurnal variations were found in the volume of the VIP subdivision of the SCN nor in the number of VIP-producing neurons. In contrast with the VIP cell population, the subdivision of the human SCN containing vasopressin-producing neurons has previously been reported to exhibit a distinct diurnal rhythm, with low values during the night and peak values during the early morning. These findings suggest that the expression of vasopressin, but not that of VIP, in the human SCN exhibits an endogenous circadian rhythm.     

The regional distribution of receptors for vasoactive intestinal polypeptide (VIP) in the rat central nervous system

The regional distribution of receptors for vasoactive intestinal polypeptide (VIP) was studied in the rat central nervous system (CNS). The specific binding was highest in cerebral cortex, limbic forebrain and cerebellum, whereas moderate to low binding was found in hypothalamus, thalamus, brainstem and pituitary. The lowest binding was observed in pons and spinal cord. Scratchard analysis showed curvilinear plots with upward concavity, which was interpreted as two classes of binding sites. The K_d values were similar in all regions and calculated as 2.4 and 62 nmol/liter, respectively. The variations of specific [¹²⁵I]VIP binding were due to differences in the total amount of receptors and were in the range of 1.7–8.6 pmol per mg protein. The regional distribution of VIP receptors was parallel with the occurence of VIP-containing nerve terminals with exceptions of cerebellum, olfactory areas and nucleus caudatus, where a greater number of receptors than expected from the VIP content was found. In these regions, VIP may interact with receptors for a different, but homologous neuropeptide. In conclusion, the regional distribution of VIP receptors in CNS gives further evidence for the role of VIP as a central neurotransmitter.     

Behavioral actions of vasoactive intestinal peptide (VIP)

The effect of vasoactive intestinal peptide (VIP) was studied on fear-motivated behaviours, exploration of a novel environment and on novelty and ACTH-induced grooming. VIP was administered via a plastic cannula into the lateral ventricle. Retention of a step-through passive avoidance task was inhibited by 10 and 30 ng VIP injected 1 hour before the retention test. Extinction of pole-jumping active avoidance behaviour was facilitated by 10 and 100 ng VIP. Mild effects were observed in an open field test on exploration and grooming activity. In conclusion, VIP produces inhibitory effects on fear-motivated behaviours.     

Intrinsic vasoactive intestinal polypeptide (VIP)-containing neurons in the baroreceptor nucleus of the solitary tract in rat

Vasoactive intestinal polypeptide (VIP)-immunoreactive cell bodies, dendrites and nerve terminals in the nucleus of the solitary tract have been identified with electron microscopic immunocytochemistry in rats. The relatively high concentration of VIP in this nucleus, which corresponds to the primary baroreceptor center, was depleted only insignificantly by uni- or bilateral transection of the solitary tract, which eliminates peripheral neuronal (via glossopharyngeal and vagal nerves) input to the nucleus. Both immunocytochemical and biochemical data suggest that the majority of VIP in the nucleus of the solitary tract is present in intrinsic neurons.     

Neuronal localization of pancreatic polypeptide (PP) and vasoactive intestinal peptide (VIP) immunoreactivity in the earthworm (Lumbricus terrestris)

Nerve fibres and cell bodies displaying vasoactive intestinal polypeptide (VIP) or pancreatic polypeptide (PP) immunoreactivity were demonstrated in ganglia of the earthworm (Lumbricus terrestris). VIP cell bodies were found in the most anterior ganglion of the ventral nerve cord, the subpharyngeal ganglion. Immunoreactive nerves were seen running in the center of the cord until about the 10th segment. PP cell bodies were found in the cerebral ganglion where VIP was lacking, in the subpharyngeal ganglion and in more posteriorly located ganglia of the ventral nerve cord. PP nerve fibres could be followed below the 10th segment of the cord.     

Vasoactive intestinal polypeptide (VIP) immunohistochemistry in the rabbit retina

A commercially obtained antiserum to vasoactive intestinal polypeptide (VIP) was used with the avidin-biotin-peroxidase immunohistochemical method to localize VIP-like immunoreactivity in the adult rabbit retina. A population of cell bodies in the inner nuclear layer is specifically stained. The cells are most dense in the central retina (40-50 cells/mm2), and least numerous in the superior periphery (15-20 cells/mm2). The dendritic fields overlap extensively; cells in the periphery have dendritic fields up to 1 mm in diameter. The processes of the cells are in the inner plexiform layer, where they tend to form a tristratified pattern in sublayers 1, 3 and 5. This pattern of lamination is similar to that described by other laboratories for dopaminergic amacrine cells and provides further evidence for an interaction between these two neuromodulators.     

Electron immunocytochemistry in vasoactive intestinal peptide (VIP) in the rat brain

In order to clearly identify the cellular elements as well as the organelles containing vasoactive intestinal peptide (VIP), an immunocytochemical localization of this peptide was performed in the rat brain. Ultrastructural localization studies involving use of both pre- and post-embeding staining techniques clearly demonstrated that VIP immunoreactivity was associated with dentrites and axonal processes. In dendrites, the labeling was rather diffuse throughout the cytoplasm whereas in terminals, it was observed in large dense core vesicles and not within the small clear vesicles. About 50% of ositive endings were observed forming typical synaptic contact. These results support the hypothesis that VIP can act as a neurotransmitter.     

A morphological analysis of vasoactive intestinal polypeptide (VIP)-like immunoreactive neurons in the area dentata of the rat brain

The general distribution and morphology of vasoactive intestinal polypeptide-like immunoreactive (VIP-LI) neurons in the area dentata (AD) have been studied using immunohistochemical methods on thick (70-120 micron) sections from the rat brain. The long (greater than or equal to 72 hours) incubation of free-floating sections in combination with a sensitive immunoperoxidase method resulted in extensive labeling of VIP-positive cell bodies, along with their dendritic and axonal processes in the hippocampal formation, including the area dentata. The VIP-positive cells are found in all parts of the area dentata, and plots of the distribution of individual cells showed that there is a preferential clustering of these neurons within, or in close proximity to, the granule cell layer, while the deep zones in the hilus are almost completely devoid of VIP-LI immunoreactive neurons. Throughout the long axis of the AD the number and relative position of the VIP-LI neurons remains rather constant. Analysis of the size and shape of the VIP-positive neurons in the AD shows a remarkable morphological heterogeneity, with the soma ranging from small (long axis: approximately 10 micron) ovoid or round, to large (long axis: approximately 25 micron) stellate or multipolar; of these the small to medium sized cells predominate. Comparisons between the morphology of neurons visualized with the VIP antibody and sections stained by the rapid Golgi method allow a rather conclusive classification of some of the VIP-stained neurons, while the classification of a majority of the VIP neurons remains tentative, perhaps because of the selective visualization by the rapid Golgi method of only certain cell types in the AD. On the basis of this comparison, several displaced granule cells in the molecular layer, as well as granule cells, small ovoid cells, and pyramidal basket cells in the granule cell layer have been identified as VIP-positive as determined by their somatic shape, dendritic branching pattern, and axonal projections. In addition, several VIP-positive neurons have been identified with less certainty. These include the dentate basket cell of Cajal, certain small cells in the molecular layer, and fusiform cells in the polymorph layer. Taken together the present results demonstrate the usefulness of "Golgi-like" immunoperoxidase staining for detailed classification of chemically defined neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Co-existence of vasoactive intestinal polypeptide (VIP)- and cholecystokinin (CCK)-like immunoreactivities in thalamocortical neuron in the ventrolateral nucleus of the rat

Cholecystokinin (CCK)- and/or vasoactive intestinal polypeptide (VIP)-like immunoreactivity (LI) was seen in many thalamocortical VL neurons which were retrogradely labeled with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injected into the frontal cortex of the rat. VIP- or CCK-LI was observed in 70-80% or 50-60% of thalamocortical VL neurons, respectively. Almost all of thalamocortical VL neurons with CCK-LI exhibited VIP-LI.     

Binding sites for pituitary adenylate cyclase activating polypeptide (PACAP): comparison with vasoactive intestinal polypeptide (VIP) binding site localization in rat brain sections.

Pituitary adenylate cyclase activating polypeptide (PACAP) is structurally similar to vasoactive intestinal polypeptide (VIP). We investigated the characteristics and topographical distribution of [125I]PACAP binding sites compared with those of [125I]VIP binding sites in the rat brain. Radiolabeled PACAP and VIP showed highly specific binding to sections at the level of the dorsal hippocampus. The specific binding of [125I]PACAP was 10 times higher than that of [125I]VIP in hippocampal sections. [125I]PACAP binding was scarcely displaced by unlabeled VIP, while [125I]VIP binding was effectively displaced by unlabeled PACAP. Therefore, PACAP binding sites may reflect both PACAP specific binding sites and VIP/PACAP binding sites. However, the amount of VIP/PACAP binding sites was negligibly low. Autoradiography revealed that [125I]PACAP binding sites were dense in the piriform cortex, diagonal band, accumbens nucleus, anterior part of the striatum, hippocampal formation, habenular nucleus, lateral hypothalamic area, superior colliculus and dorsal raphe nucleus. Moderate to high labeling was observed in the medial septal nucleus, olfactory tubercle, caudal part of the striatum, most parts of the thalamus, supraoptic and periventricular hypothalamic nuclei, central gray, substantia nigra pars compacta, locus coeruleus, pontine reticular nucleus and cerebellum. Distribution pattern was remarkably different from that of [125I]VIP binding sites in the hippocampal formation, lateral hypothalamic area, substantia nigra pars compacta, pontine reticular nucleus and cerebellum. The present results suggest that PACAP may have a physiological role in the regulation of the central nervous system.