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

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.

Spatiotemporal distribution of vasoactive intestinal polypeptide receptor 2 in mouse suprachiasmatic nucleus

Vasoactive intestinal polypeptide (VIP) signaling is critical for circadian rhythms. For example, the expression of VIP and its main receptor, VPAC2R, is necessary for maintaining synchronous daily rhythms among neurons in the suprachiasmatic nucleus (SCN), a master circadian pacemaker in animals. Where and when VPAC2R protein is expressed in the SCN and other brain areas has not been examined. Using immunohistochemistry, we characterized a new antibody and found that VPAC2R was highly enriched in the SCN and detectable at low levels in many brain areas. Within the SCN, VPAC2R was circadian, peaking in the subjective morning, and abundantly expressed from the rostral to caudal margins with more in the dorsomedial than ventrolateral area. VPAC2R was found in nearly all SCN cells including neurons expressing either VIP or vasopressin (AVP). SCN neurons mainly expressed VPAC2R in their somata and dendrites, not axons. Finally, constant light increased VIP and AVP expression, but not VPAC2R. We conclude that the circadian clock, not the ambient light level, regulates VPAC2R protein localization. These results are consistent with VPAC2R playing a role in VIP signaling at all times of day, broadly throughout the brain and in all SCN cells.

Pituitary adenylate cyclase-activating polypeptide and its receptors: 20 years after the discovery

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid C-terminally alpha-amidated peptide that was first isolated 20 years ago from an ovine hypothalamic extract on the basis of its ability to stimulate cAMP formation in anterior pituitary cells (Miyata et al., 1989. PACAP belongs to the vasoactive intestinal polypeptide (VIP)-secretin-growth hormone-releasing hormone-glucagon superfamily. The sequence of PACAP has been remarkably well conserved during evolution from protochordates to mammals, suggesting that PACAP is involved in the regulation of important biological functions. PACAP is widely distributed in the brain and peripheral organs, notably in the endocrine pancreas, gonads, respiratory and urogenital tracts. Characterization of the PACAP precursor has revealed the existence of a PACAP-related peptide, the activity of which remains unknown. Two types of PACAP binding sites have been characterized: type I binding sites exhibit a high affinity for PACAP and a much lower affinity for VIP, whereas type II binding sites have similar affinity for PACAP and VIP. Molecular cloning of PACAP receptors has shown the existence of three distinct receptor subtypes: the PACAP-specific PAC1-R, which is coupled to several transduction systems, and the PACAP/VIP-indifferent VPAC1-R and VPAC2-R, which are primarily coupled to adenylyl cyclase. PAC1-Rs are particularly abundant in the brain, the pituitary and the adrenal gland, whereas VPAC receptors are expressed mainly in lung, liver, and testis. The development of transgenic animal models and specific PACAP receptor ligands has strongly contributed to deciphering the various actions of PACAP. Consistent with the wide distribution of PACAP and its receptors, the peptide has now been shown to exert a large array of pharmacological effects and biological functions. The present report reviews the current knowledge concerning the pleiotropic actions of PACAP and discusses its possible use for future therapeutic applications.

Vasoactive intestinal polypeptide immunoreactivity in the human cerebellum: qualitative and quantitative analyses

Although autoradiographic, reverse transcription-polymerase chain reaction and immunohistochemical studies have demonstrated receptors for vasoactive intestinal polypeptide (VIP) in the cerebellum of various species, immunohistochemistry has never shown immunoreactivity for VIP within cerebellar neuronal bodies and processes. The present study aimed to ascertain whether VIP immunoreactivity really does exist in the human cerebellum by making a systematic analysis of samples removed post-mortem from all of the cerebellar lobes. The study was carried out using light microscopy immunohistochemical techniques based on a set of four different antibodies (three polyclonal and one monoclonal) against VIP, carefully selected on the basis of control tests performed on human colon. All of the antibodies used showed VIP-immunoreactive neuronal bodies and processes distributed in the cerebellar cortex and subjacent white matter of all of the cerebellum lobes, having similar qualitative patterns of distribution. Immunoreactive neurons included subpopulations of the main neuron types of the cortex. Statistical analysis of the quantitative data on the VIP immunoreactivity revealed by the different antibodies in the different cerebellar lobes did not demonstrate any significant differences. In conclusion, using four different anti-VIP antibodies, the first evidence of VIP immunoreactivity is herein supplied in the human post-mortem cerebellum, with similar qualitative/quantitative patterns of distribution among the different cerebellum lobes. Owing to the function performed by VIP as a neurotransmitter/neuromodulator, it is a candidate for a role in intrinsic and extrinsic (projective) circuits of the cerebellum, in agreement with previous demonstrations of receptors for VIP in the cerebellar cortex and nuclei. As VIP signalling pathways are implicated in the regulation of cognitive and psychic functions, cerebral blood flow and metabolism, processes of histomorphogenesis, differentiation and outgrowth of nervous tissues, the results of this study could be applied to clinical neurology and psychiatry, opening new perspectives for the interpretation of neurodevelopment disorders and development of new therapeutic strategies in cerebellar diseases.

VPAC and PAC receptors: From ligands to function

Vasoactive intestinal peptide (VIP) and the pituitary adenylate cyclase activating polypeptides (PACAPs) share 68% identity at the amino acid level and belong to the secretin peptide family. Following the initial discovery of VIP almost four decades ago a substantial amount of knowledge has been presented describing the mechanisms of action, distribution and pleiotropic functions of these related peptides. It is now known that the physiological actions of these widely distributed peptides are produced through activation of three common G-protein coupled receptors (VPAC(1), VPAC(2) and PAC(1)R) which preferentially stimulate adenylate cyclase and increase intracellular cAMP, although stimulation of other intracellular messengers, including calcium and phospholipase D, has been reported. Using a range of in vitro and in vivo approaches, including cell-based functional assays, transgenic animals and rodent models of disease, VPAC/PAC receptor activation has been associated with numerous physiological processes (e.g. control of circadian rhythms) and clinical conditions (e.g. pulmonary hypertension), which underlies on-going research efforts and makes these peptides and their cognate receptors attractive targets for the pharmaceutical industry. However, despite the considerable interest in VPAC/PAC receptors and the processes which they mediate, there is still a paucity of selective and available, non-peptide ligands, which has hindered further advances in this field both at the basic research and clinical level. This review summarises the current knowledge of VIP/PACAP and the VPAC/PAC receptors with regard to their distribution, pharmacology, signalling pathways, splice variants and finally, the utility of animal models in exploring their physiological roles.

Immunohistochemical distribution of glucose-dependent insulinotropic polypeptide in the adult rat brain

We have previously demonstrated that glucose-dependent insulinotropic polypeptide (GIP; gastric inhibitory polypeptide) is present in the adult rat hippocampus. This finding leads to the conclusion that all members of the secretin-glucagon family of gastrointestinal regulatory polypeptides can be found in the brain. To investigate the localization of GIP-producing cells, we used immunohistochemistry on sections of the adult rat brain. High levels of GIP immunoreactivity were observed in the olfactory bulb, hippocampus, and Purkinje cells in the cerebellum. Moreover, a moderate but distinct GIP immunoreactivity was observed in the cerebral cortex, amygdala, substantia nigra, and lateral septal nucleus as well as in several nuclei in the thalamus, hypothalamus, and brainstem. GIP immunoreactivity was frequently found to colocalize with the neuronal marker NeuN but never with the glial marker glial fibrillary acidic protein. Thus, GIP appears to be mainly neuronal to its distribution. This widespread distribution of GIP-immunoreactive cells suggests the involvement of GIP in various neuronal functions and suggests that GIP may act as a neurotransmitter or neuromodulator. This is the first characterization of the anatomical distribution of GIP-immunoreactive cells in the rat brain providing an anatomical framework for future investigations regarding the functions of GIP in the central nervous system.

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.

Effects of vasoactive intestinal polypeptide microinjected into the nucleus tractus solitarius on jejunal electrolytes absorption in rats

It has been shown that vasoactive intestinal polypeptide (VIP) injected into the nucleus tractus solitarius inhibits alanine absorption across the jejunum. The aim of the present study was to investigate the effects of VIP injection into the nucleus tractus solitarius on jejunal absorption of electrolytes in the rat. Fifty-three Wistar rats were submitted to midline laparotomy to expose and isolate 20 cm of jejunal loop and to perform a subdiaphragmatic troncular vagotomy. Saline or VIP (10 pg 100 nl(-1)) was injected into the rostral nucleus tractus solitarius using a stereotaxic instrument. Tyrode solution, pH 8, containing twice glucose, sodium and potassium concentration was infused (0.5 ml min(-1)) into the jejunal loop. Samples were taken at 10-min intervals during the 40-min-experiment. Injection of VIP into the nucleus tractus solitarius increased jejunal potassium absorption. Moreover, VIP associated with vagotomy resulted in inhibition of jejunal potassium absorption by VIP alone at 40 min after perfusion (5.99 +/- 0.74 vs. 9.83 +/- 0.57 microM). There was no change in jejunal sodium absorption in any of the experimental groups. VIP had a modulatory action on jejunal potassium absorption when injected into the nucleus tractus solitarius.

Effects of vasoactive intestinal polypeptide microinjected into the nucleus tractus solitarius on jejunal glucose absorption in rats

It has been shown that vasoactive intestinal polypeptide (VIP) injected into the nucleus tractus solitarius and into the dorsal motor nucleus of the vagus inhibits alanine absorption across the jejunum. The aim of the present study was to investigate the effects of VIP injection into the nucleus tractus solitarius on jejunal absorption of glucose in the rat. Forty Wistar rats were submitted to midline laparotomy to expose and isolate 20 cm of jejunal loop and to perform a subdiaphragmatic troncular vagotomy. Saline or VIP (10 pg 100 nl(-1)) was injected into the rostral nucleus tractus solitarius using a stereotaxic instrument. Tyrode solution, pH 8, containing twice glucose, sodium, and potassium concentrations was infused (0.5 ml min(-1)) into the jejunal loop. Samples were taken at 10-min intervals during the 40-min experiment. Injection of VIP into the nucleus tractus solitarius associated with vagotomy resulted in inhibition of jejunal glucose absorption by VIP alone at 10 and 40 min after perfusion (2.75+/-0.19 vs. 3.53+/-0.29 mg). The vagal outflow tract maintained jejunal glucose absorption even when VIP was microinjected into the nucleus tractus solitarius.

Vasoactive intestinal peptide selectively depolarizes thalamic relay neurons and attenuates intrathalamic rhythmic activity

The reciprocal synaptic relationship between the relay thalamus and surrounding thalamic reticular nucleus can lead to the generation of various rhythmic activities that are associated with different levels of behavioral states as well as certain pathophysiological conditions. Intrathalamic rhythmic activities may be attenuated by numerous neuromodulators that arise from a variety of brain stem nuclei. This study focuses on the potential role of a particular neuropeptide, vasoactive intestinal peptide (VIP). VIP and its receptors are localized within the thalamic circuit and thus may serve as an endogenous modulator of the rhythmic activity. Using extracellular multiple-unit recording techniques, we found that VIP strongly attenuated the slow, 2- to 4-Hz intrathalamic rhythm. This rhythm is similar to that observed during slow wave sleep and certain pathophysiological conditions such as generalized absence epilepsy. Using intracellular recording techniques, we found that VIP selectively depolarized relay neurons in the ventrobasal nucleus but had negligible actions on neurons in thalamic reticular nucleus. The VIP-mediated depolarization is produced via an enhancement of the nonselective cation conductance, Ih. The antioscillatory actions of VIP likely occur by shifting the membrane potential to decrease the probability of burst discharge by relay neurons, a requirement to maintain the rhythmic activity. Not only does VIP alter the intrathalamic rhythmic activity, this peptide that is endogenous to the thalamic circuit may also play a significant role in the regulation of information transfer through the thalamocortical circuit.

Conformationally restricted PACAP27 analogues incorporating type II/II' IBTM beta-turn mimetics. Synthesis, NMR structure determination, and binding affinity

To probe the importance of a proposed beta-turn within residues S9-R12 of PACAP for recognition by VIP/PACAP receptors, compounds 1 and 2, two conformationally restricted analogues of PACAP27 incorporating respectively (S)- or (R)-IBTM as type II or II' beta-turn dipeptide mimetic at the Y10-S11 position, were synthesized. According to 1H NMR conformational analyses in aqueous solution and 30% TFE, both PACAP27 and the [S-IBTM(10,11)]PACAP27 analogue 1 adopt similar ordered structures. PACAP27 shows an N-terminal disordered region (residues H1-F6) and an alpha-helical conformation within segment T7-L27. For residues S9-R12, our data seem more compatible with a segment of the alpha-helix than with the beta-turn previously proposed for this fragment. In compound 1 the alpha-helix, also spanning T7-L27 residues, appears slightly distorted at the N-terminus relative to the native peptide. Although this distortion could lead to the marked decrease in binding affinity of this compound at the VIP/PACAP receptors, the lack of the Y10 side chain in analogues 1 and 2 could also significantly affect the binding of these compounds.

Regulation of vasoactive intestinal peptide receptor expression in developing nervous systems

Vasoactive intestinal peptide (VIP) is a 28-amino acid peptide that has several functions, including the regulation of water and electrolyte secretion, hormone and cytokine release, bronchodilitation, and neurogenesis. VIP effects are mediated by specific G-protein coupled receptors. Three distinct receptor subtypes, with differing affinity for VIP, have been cloned and characterized as receptors 1 and 2 (VPAC1 and VPAC2) and pituitary adenylate cyclase activating polypeptide receptor (PAC1). Our laboratory has demonstrated that upregulation of VPAC1 in SK-N-SH neuroblastoma cells results in marked shift in cell type to the glial lineage with a corresponding loss of neuronal lineage and suppression of xenograft tumor growth. To understand the molecular mechanisms responsible for regulation of the VPAC1 gene in neuronal lineage, we have cloned and sequenced 2.6-kb of the 5'-flanking sequences of the human VPAC1 gene. Sequence analysis demonstrated that the human VPAC1 promoter sequence contains putative binding sites for several known transcription factors, including Sp1, NFkB, and cETS-1. To study the temporal and spatial expression pattern of human VPAC1 promoter sequences, we have generated transgenic mice expressing the bacterial beta-galactosidase gene under the control of the 2.6-kb 5'-flanking and promoter sequence of the human VPAC1 gene. Transgene expression was detected in brain, spinal cord, and lung in 14-day-old animals. Taken together, these results demonstrate that VPAC1 may play an important role in the nervous system, and suggest a role for VIP in neuronal differentiation.

VIP and PACAP: very important in pain?

Neuropathic pain arising from direct trauma to, or compression injury of, peripheral nerves is a common clinical problem. It is characterized by the development of abnormal pain states (spontaneous pain, hyperalgesia, allodynia), which can persist long after the initial injury has resolved. The underlying mechanisms are poorly understood and, as a consequence, treatment is often unsatisfactory. Some of the main contributing factors are thought to be the morphological and phenotypic changes that occur centrally, including alterations in the expression of neurotransmitters and their associated receptors, both in the dorsal root ganglia and in the spinal dorsal horn. This article focuses on the functional role of the two structurally related peptides VIP and PACAP within the spinal cord, and their possible contribution to the altered transmission of sensory information in neuropathic conditions.

Vasoactive intestinal polypeptide is a potent regulator of bile secretion from rat cholangiocytes

BACKGROUND & AIMS

Vasoactive intestinal polypeptide (VIP) is a neuropeptide with diverse biological functions including stimulatory effects on bile secretion. The effects of VIP on bile secretion and its site of action were examined.

METHODS

Choleretic effects of VIP were examined using isolated perfused livers, hepatocyte couplets, isolated bile duct units, and cholangiocytes from rat liver.

RESULTS

VIP (100 nmol/L) produced a small increase in bile flow and bile salt output in taurocholate-supplemented isolated perfused livers but had no significant effect on bile flow in the absence of bile salt supplements or on fluid secretion in isolated hepatocyte couplets. In addition, VIP significantly increased bile pH, bicarbonate concentration, and output in the isolated perfused livers from both normal and 2 week bile duct-ligated rats, although bile flow increased only in the bile duct-ligated model. VIP also produced a dose-dependent increase in fluid secretion in isolated bile duct units, which was inhibited significantly by VIP antagonist, a specific VIP receptor inhibitor. This VIP-stimulated secretory response in isolated bile duct units was more potent than those produced by bombesin or secretin. Neither somatostatin nor substance P inhibited the VIP response in isolated bile duct units. In contrast to secretin, VIP had no significant effect on adenosine 3', 5'-cyclic monophosphate (cAMP) levels in isolated cholangiocytes.

CONCLUSIONS

VIP is a potent stimulant of fluid and bicarbonate secretion from cholangiocytes via cAMP-independent pathways, suggesting that this neuropeptide plays a major regulatory role in biliary transport and secretion.

Vasoactive intestinal polypeptide excites medial pontine reticular formation neurons in the brainstem rapid eye movement sleep-induction zone

Although it has long been known that microinjection of the cholinergic agonist carbachol into the medial pontine reticular formation (mPRF) induces a state that resembles rapid eye movement (REM) sleep, it is likely that other transmitters contribute to mPRF regulation of behavioral states. A key candidate is the peptide vasoactive intestinal polypeptide (VIP), which innervates the mPRF and induces REM sleep when injected into this region of the brainstem. To begin understanding the cellular mechanisms underlying this phenomenon, we examined the effects of VIP on mPRF cells using whole-cell patch-clamp recordings in the in vitro rat brainstem slice. VIP directly depolarized cells via activation of an inward current; these effects were attenuated and potentiated in low-sodium and low-calcium medium, respectively. The depolarization induced by VIP was slower in onset and longer-lived than that evoked by carbachol. The VIP-induced depolarization was reduced in a dose-dependent manner by a competitive antagonist of VIP receptors. Effects of VIP were attenuated in the presence of guanosine 5'-O-(2-thiodiphosphate, 2'5'dideoxyadenosine, and PKI15-24 and were nonadditive in the presence of 8-bromo-cAMP. We conclude that VIP excites mPRF neurons by activation of a sodium current. This effect is mediated at least in part by G-protein stimulation of adenylyl cyclase, cAMP, and protein kinase A. These data suggest that VIP may play a physiological role in REM induction by its actions on mPRF neurons.

Role of VIP, PACAP, and related peptides in the regulation of the hypothalamo-pituitary-adrenal axis

Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of a family of regulatory peptides that are widely distributed in the body and share numerous biologic actions. The two peptides display a remarkable amino acid-sequence homology, and bind to a class of G protein-coupled receptors, named PACAP/VIP receptors (PVRs), whose signaling mechanism mainly involves the activation of adenylate-cyclase and phospholipase-C cascades. A large body of evidence suggests that VIP and PACAP play a role in the control of the hypothalamo--pituitary-adrenal (HPA) axis, almost exclusively acting in a paracrine manner, since their blood concentration is very low. VIP and PACAP are contained in both nerve fibers and neurons of the hypothalamus, and VIP, but not PACAP, is also synthesized in the pituitary gland. Both peptides are expressed in the adrenal gland, and especially in medullary chromaffin cells. All the components of the HPA axis are provided with PVRs. VIP and PACAP enhance pituitary ACTH secretion, VIP by eliciting the hypothalamic release of CRH and potentiating its secretagogue action, and PACAP by directly stimulating pituitary corticotropes. Through this central mechanism, VIP and PACAP may increase mineralo- and glucocorticoid secretion of the adrenal cortex. VIP but not PACAP also exerts a weak direct secretagogue action on adrenocortical cells by activating both PVRs and probably a subtype of ACTH receptors. VIP and PACAP raise aldosterone production via a paracrine indirect mechanism involving the stimulation of medullary chromaffin cells to release catecholamines, which in turn enhance the secretion of zona glomerulosa cells via a beta-adrenoceptor-mediated mechanism. PACAP appears to be able to evoke a glucocorticoid response through the activation, at least in the rat, of the intramedullary CRH/ACTH system. The relevance of these effects of VIP and PACAP under basal conditions is questionable, although there are indications that endogenous VIP is involved in the maintenance of the normal growth and steroidogenic capacity of rat adrenal cortex. However, indirect evidence suggests that these peptides might play a relevant role under paraphysiological conditions (e.g., in the mediation of HPA axis responses to cold and inflammatory stresses) or may be somehow involved in the pathogenesis of Cushing disease or some case of hyperaldosteronism associated with secreting pheochromocytomas.

Evidence for roles of vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) receptors in modulating the responses of rat dorsal horn neurons to sensory inputs

The extracellularly recorded electrophysiological activity of single multireceptive dorsal horn neurons was markedly increased by ionophoretic administration of vasoactive intestinal polypeptide (VIP) or pituitary adenylate cyclase activating polypeptide (PACAP)-38. Some cells responded selectively to PACAP-38 (suggesting mediation by a PACAP receptor), whereas others responded to both VIP and PACAP-38 (suggesting a VIP1 and/or VIP2 receptor). Most non-nociceptive cells were unaffected by PACAP-38 and all were unaffected by VIP. The selectivity of VIP/PACAP receptor antagonists was established on cloned rat VIP1, VIP2 and PACAP receptors in vitro before their utilization to indicate the likely involvement of VIP1, and possibly PACAP receptors, in VIP- and PACAP-38-mediated responses of dorsal horn neurons. The VIP/PACAP receptor antagonists inhibited responses of multireceptive cells to sustained innocuous (brush) and noxious (mustard oil) stimuli, with a selectivity suggesting the involvement of VIP1 and PACAP receptors, although the participation by VIP2 receptors cannot be excluded. These data implicate both VIP and PACAP in regulating the basal responsiveness of multireceptive dorsal horn neurons to sensory stimuli.

Peptide T prevents NBM lesion-induced cortical atrophy in aged rats

Because VIP is known to be neurotrophic in vitro, the present study tested whether peptide T (PT), an octapeptide with a pentapeptide sequence homologous to VIP, could prevent nucleus basalis (NBM)-induced degenerative changes in the parietal neocortex of aged rats. Aged (20-21 months old) Sprague-Dawley rats were given bilateral neurotoxic lesions of the NBM, and injected daily with PT (1 mg, IP) or vehicle solution for 5 months. Compared to unoperated controls, vehicle-treated NBM lesioned animals had: 1) a significant 17% decrease in overall cortical thickness, 2) significant decreases of 13-29% in the thickness of cortical layers II-IV, V, and VI, and 3) significant neuronal and glial cell loss in layer V. PT treatment prevented or attenuated these lesion-induced decreases in cortical thickness and attenuated the accompanying loss of large neurons in layer V. These results provide evidence that PT1 perhaps acting via VIP receptor stimulation, is neurotrophic and important for the integrity of brain tissue following denervation.

Anomalous growth hormone response to vasoactive intestinal peptide and peptide histidine methionine in patients with prolactinoma or hypothalamic hyperprolactinemia

We examined a possible GH-releasing activity of vasoactive intestinal peptide (VIP) and its homologous peptide, peptide histidine methionine (PHM), in 22 patients with hyperprolactinemia (HPRL) who comprised 19 cases of prolactinoma (PRLoma) and 3 cases of hypothalamic HPRL. Each patient underwent iv bolus injections of VIP (100 micrograms) and PHM (100 micrograms) on separate days, and plasma levels of GH and PRL were measured. The plasma GH response to VIP and PHM were considered positive (a paradoxical increase) when an increase over baseline of at least 50% occurred. In agreement with previous reports, the PRL-releasing activity of VIP and PHM in our patients with HPRL were subnormal. Thirteen (59%) patients showed a paradoxical rise in GH after VIP, and 4 (18%) patients did so after PHM. It is to be noted that all the 3 patients with hypothalamic HPRL responded to VIP with a significant rise in GH. 3 of the 4 PHM-responders were also responsive to VIP, which suggests that PHM may have activated VIP receptors in the pituitary of the PHM-responders as a partial agonist of the VIP receptor. The responders and nonresponders to VIP or PHM, respectively, had similar results with respect to the mean age, and the mean basal PRL and GH levels in the plasma. Since these paradoxical GH responses were observed in not only the patients with PRLoma but also those with hypothalamic HPRL, it may be that these anomalous GH responses in HPRL were due to the HPRL itself rather than due to the neoplastic lactotrophs.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization and developmental pattern of vasoactive intestinal polypeptide binding sites in the human hypothalamus

Using a quantitative in vitro autoradiographic approach, vasoactive intestinal polypeptide (VIP) binding site densities were compared in the post-mortem hypothalamus of human neonate/infant and adult. The densities were similar during development in most of the hypothalamic nuclei and areas examined underlying the stability of 125I-VIP binding sites in the post-mortem hypothalamus of young and adult individuals. However, the ventral part of the medial preoptic area, the medial, lateral, and supramammillary nuclei were characterized by an increase of 125I-VIP binding with age. In young and adult individuals, the highest densities of hypothalamic 125I-VIP binding sites were detected in the supraoptic and infundibular nuclei; the ependyma; the organum vasculosum of the lamina terminalis; the horizontal limb of the diagonal band of Broca; the ventral part of the medial preoptic area (in adult); the suprachiasmatic, paraventricular, and periventricular nuclei; and the medial and lateral mammillary nuclei in adult. Moderate densities were found in the vertical limb of the diagonal band of Broca, the bed nucleus of the stria terminalis, the ventral part of the medial preoptic area in neonate/infant, the medial and lateral mammillary nuclei in neonate/infant, the supramammillary nucleus in adult, the dorsal hypothalamic area, and the ventromedial nucleus. Low to moderate binding site densities were observed in the other hypothalamic regions of young or adult individuals. The nonspecific binding ranged from 15% of the total binding in the anterior hypothalamus to 20% in the mediobasal and posterior hypothalamic levels. Taken together, these results provide evidence for a large distribution of VIP binding sites in neonate/infant and adult human hypothalamus suggesting the implication of VIP in the development of this brain structure and the maintenance of its various functions.

Vasoactive intestinal polypeptide immunoreactive structures in the mouse barrel field

Immunohistochemistry for vasoactive intestinal polypeptide was carried out in tangentially cut vibratome sections of the barrel cortex in adult mice. Sections through layer IV have revealed an association between the cytoarchitectonically visible modular organization of barrels and the distribution of immunoreactive axon terminals. These terminals are preferentially localized in the side region of a barrel, whereas the hollow shows a relative scarcity of these structures as shown with image analysis. This finding is the first direct demonstration of a modular distribution of vasoactive intestinal polypeptide-containing axon terminals in the neocortex.

Effects of vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) on the spontaneous release of acetylcholine from the rat hippocampus by brain microdialysis

Vasoactive intestinal polypeptide (VIP) has been suggested to have a presynaptic effect on cholinergic terminals in the rat hippocampus, which results in an activation of acetylcholine (ACh) synthesis. Recently, a VIP-related novel peptide, pituitary adenylate cyclase activating polypeptide (PACAP) was isolated from the ovine hypothalamus, and we previously demonstrated in the rat that PACAP binding site densities were high in the hippocampus. In the present study, we investigated the effects of VIP and PACAP on the release of ACh from the rat hippocampus. We succeeded in detecting the spontaneous release of ACh from the dorsal hippocampus in the conscious rat using microdialysis and HPLC-ECD. VIP, PACAP38 and PACAP27 were applied through a microinjection cannula placed in a region adjacent to the tip of a microdialysis tube. Injections of VIP, PACAP38 and PACAP27 (12, 120 pmol) resulted in dose-related increases in ACh release. The ability to enhance ACh release was VIP > PACAP38 > PACAP27. The increased release of ACh caused by these peptides was highly calcium-dependent. Tetrodotoxin (10(-6) M) added to the perfusion medium significantly reduced both the release of ACh enhanced by these peptides and the basal release. The present results suggest that VIP, PACAP38 and PACAP27 presynaptically stimulate cholinergic activity in the hippocampus, which may be reflected by an increase in ACh synthesis to maintain releasable terminal stores of ACh.

Neuronal number and volume alterations in the neocortex of HIV infected individuals

Substantial neuronal loss in the superior frontal gyrus in patients who have died of AIDS have been reported previously. This investigation examined the distribution of neuronal loss in three other neocortical areas and, alteration in neuronal volume in four neocortical areas. This was carried out using two stereological probes, the "disector" and the "nucleator". These recently developed methods provide estimations, regardless of size and shape, in real three-dimensional space, and are more efficient than conventional quantitation. The study was performed on 12 HIV infected individuals and nine controls. The HIV group had no neuropathological evidence of opportunistic infections or neoplasms, five had HIV encephalitis and the remaining seven had only minimal pathology. There was significant neuronal loss of 30% (p = 0.018) in the calcarine cortex (primary visual area), and loss of 18% in the superior parietal lobule which just failed to reach significance. This loss was not related to the presence of HIV encephalitis. The mean neuronal volume was increased in the occipital area by 29% (p = 0.028) and the frequency of large neurons (over 2000 microns 3) doubled in the frontal (p < 0.05) and parietal (p < 0.02) areas. The results confirm the hypothesis that HIV infection is associated with neuronal injury and death, and suggest that increase in neuronal size may be a feature of the cytopathology of this condition.

A further study on the stimulatory effect of peptide histidine methionine on growth hormone secretion in acromegaly: a dose-related study and a comparison with vasoactive intestinal peptide

We examined whether the GH-releasing effect of peptide histidine methionine (PHM) in acromegaly may be mediated by activation of pituitary receptors for vasoactive intestinal peptide (VIP), which is structurally similar to but more powerful than PHM in stimulating GH secretion in acromegaly. VIP (50 or 100 micrograms) or PHM (50, 100, or 200 micrograms) was given as an i.v. bolus to 11 patients with active acromegaly, and plasma GH levels were measured before and at intervals up to 120 min after the injection. A paradoxical GH response (> 50% and > 6 micrograms/l above the basal) to 50 or 100 micrograms of VIP was observed in 4 (36%) or 5 (45%) patients, respectively. 2 (18%) patients showed paradoxical GH responses to both 50 and 100 micrograms of PHM, and, interestingly, as many as 5 (45%) patients showed positive GH responses to 200 micrograms of PHM. 3 of these 5 responders to 200 micrograms of PHM were also responders to both doses of VIP. To add to, one of the responders to 100 micrograms of VIP did not show a positive GH response to even 200 micrograms of PHM. These results may suggest that in at least some acromegalics the PHM stimulation of GH secretion is mediated by activation of pituitary VIP receptors by PHM and/or by PHM binding to its specific receptors which may have appeared concomitantly with VIP receptors. However, the occasional heterogeneity of the VIP- and PHM-induced GH responses may suggest that on some somatotroph adenomas either VIP or PHM receptors may appear independently.

VIP receptor subtypes in mouse cerebral cortex: evidence for a differential localization in astrocytes, microvessels and synaptosomal membranes

The binding characteristics of a monoiodinated form of vasoactive intestinal peptide (M-[125I]VIP) to the membranes of astrocytes, intraparenchymal microvessels and synaptosomes were analyzed in mouse cerebral cortex. Binding to astrocytes, studied in primary cultures, indicates the presence of a single class of high affinity binding sites with a Kd of 3.3 nM and a Bmax of 565 fmol/mg protein. The structurally related peptide secretin does not compete for sites labeled by M-[125I]VIP. In cultured astrocytes, VIP has been previously shown to promote glycogenolysis. Secretin, despite its lack of interaction with sites labeled by M-[125I]VIP, stimulates glycogenolysis with an EC50 of 0.5 nM, thus demonstrating the presence in astrocytes of functional secretin receptors independent from those for VIP. Trypsinization of the primary astrocyte cultures followed by replating as secondary cultures, reveals a second class of low affinity binding sites, with a Kd of 41.3 nM and a Bmax of 881 fmol/mg protein. Secretin does not compete for this class of low affinity binding sites either. Binding of M-[125I]VIP to intraparenchymal microvessels reveals the presence of two classes of binding sites with Kd of 1.4 and 30.3 nM, and Bmax of 7.1 and 73.8 pmol/mg protein, respectively. Similar to what is observed in primary or secondary astrocyte cultures, secretin does not interact with these sites. In this cell type VIP stimulates cAMP formation with an EC50 of 18 nM, while secretin is ineffective. Finally, in agreement with previous reports in rat and guinea pig cerebral cortex, two classes of binding sites are observed in synaptosomal membranes: a high affinity class with a Kd of 4.9 nM and a Bmax of 316 fmol/mg protein, and a low affinity class with a Kd of 42.8 nM and a Bmax of 1578 fmol/mg protein. In contrast to what is observed in non-neuronal membranes, in synaptosomal membranes, secretin effectively competes for sites labeled by M-[125I]VIP with an EC50 of approximately 150 nM. These results indicate that secretin may represent a useful tool to discriminate between neuronal and non-neuronal VIP binding sites, since it competes with M-[125I]VIP exclusively for the neuronal class of binding sites.

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.

[125I]vasoactive intestinal polypeptide binding sites: quantitative autoradiographic distribution in the rat spinal cord

The quantitative autoradiographic distribution of [125I]vasoactive intestinal polypeptide (VIP) receptor binding sites was investigated in the rat spinal cord. [125I]VIP binding sites are discretely distributed, with a rostro-caudal gradient, along the longitudinal length of the cord; highest densities of sites being observed in its lumbar and sacral segments. In transverse sections, highest levels of [125I]VIP sites are present in laminae I and II, around the central canal, and in the parasympathetic lateral horn of the sacral segment. Moderate densities are seen along the medial border of the dorsal horn and the sympathetic lateral horn of the thoracic cord. Low amounts of labeling are observed in most structures of the ventral horn while white matter areas are apparently devoid of specific [125I]VIP binding. Thus, the distribution of spinal [125I]VIP receptor sites correlates well with that of VIP-like immunoreactive materials and support possible roles for this peptide in sensory neurotransmission and in the control of autonomic functions.

Properties and distribution of receptors for pituitary adenylate cyclase activating peptide (PACAP) in rat brain and spinal cord

A high density (in the pmol/mg protein range) of specific functional receptors for PACAP (pituitary adenylate cyclase activating polypeptide) was observed in membranes from rat brain cortex, olfactory bulb, hypothalamus, hippocampus, striatum, cerebellum, pons and cervico-dorsal spinal cord, using [125I]PACAP-27 (PACAP 1-27). The tracer bound rapidly, specifically and reversibly. Competition binding curves were compatible with the coexistence, in the eight central nervous areas explored, of high and low affinity binding sites for PACAP-27 (Kd of 0.2 nM and 3.0 nM, respectively), and of only one class of binding sites for PACAP-38 (PACAP (1-38), Kd 0.2-0.9 nM). VIP inhibited only partially the binding of [125I]PACAP-27, and PHI, GRF(1-29)NH2 and secretin were ineffective at 1 microM. Chemical [125I]PACAP-27 cross-linking revealed a single specific 64 kDa protein species. In rat brain cortical membranes, saturation and competition experiments, using [125I]PACAP-38 as radioligand, indicated the presence of both high (Kd 0.13 nM) and low (Kd 8-10 nM) affinity binding sites for PACAP-38 and of low affinity (Kd 30 nM) binding sites for PACAP-27. These data taken collectively suggest the coexistence of PACAP-A receptors with a slight preference for PACAP-27 over PACAP-38 and of PACAP-B receptors that recognize PACAP-38 with a high affinity and PACAP-27 with low affinity. Both PACAP-27 and PACAP-38 stimulated adenylate cyclase with similar potency and efficacy. VIP was markedly less potent in this respect and also less efficient, except on cerebellar membranes.

Vasoactive intestinal peptide binding sites and fibers in the brain of the pigeon Columba livia: an autoradiographic and immunohistochemical study

The distribution of vasoactive intestinal peptide (VIP) binding sites in the pigeon brain was examined by in vitro autoradiography on slide-mounted sections. A fully characterized monoiodinated form of VIP, which maintains the biological activity of the native peptide, was used throughout this study. The highest densities of binding sites were observed in the hyperstriatum dorsale, archistriatum, auditory field L of neostriatum, area corticoidea dorsolateralis and temporo-parieto-occipitalis, area parahippocampalis, tectum opticum, nucleus dorsomedialis anterior thalami, and in the periventricular area of the hypothalamus. Lower densities of specific binding occurred in the neostriatum, hyperstriatum ventrale and nucleus septi lateralis, dorsolateral area of the thalamus, and lateral and posteromedial hypothalamus. Very low to background levels of VIP binding were detected in the ectostriatum, paleostriatum primitivum, paleostriatum augmentatum, lobus parolfactorius, nucleus accumbens, most of the brainstem, and the cerebellum. The distribution of VIP-containing fibers and terminals was examined by indirect immunofluorescence using a polyclonal antibody against porcine VIP. Fibers and terminals were observed in the area corticoidea dorsolateralis, area parahippocampalis, hippocampus, hyperstriatum accessorium, hyperstriatum dorsale, archistriatum, tuberculum olfactorium, nuclei dorsolateralis and dorsomedialis of the thalamus, and throughout the hypothalamus and the median eminence. Long projecting fibers were visualized in the tractus septohippocampalis. In the brainstem VIP immunoreactive fibers and terminals were observed mainly in the substantia grisea centralis, fasciculus longitudinalis medialis, lemniscus lateralis, and in the area surrounding the nuclei of the 7th, 9th, and 10th cranial nerves. The correlation between the distribution of VIP binding sites and immunoreactive fibers and terminals was assessed in a restricted number of regions. A qualitatively good matching was found in the area corticoidea dorsolateralis, hyperstriatum dorsale, hyperstriatum accessorium, nucleus septi lateralis, nuclei dorsomedialis and dorsolateralis thalami, and in some hypothalamic areas. A striking mismatch occurred in the hyperstriatum ventrale, neostriatum, tectum opticum (high to moderate density of binding sites but only few immunoreactive profiles), and in the tuberculum olfactorium, median eminence, and spinal cord (lower density of binding sites but abundant immunoreactive profiles). The paleostriatum, lobus parolfactorius, and ectostriatum were virtually devoid of both binding sites and immunoreactive profiles. The results are discussed in relation to the known actions of VIP in the rodent and avian brain and are compared with previous observations on the distribution of VIP binding sites in the central nervous system of other vertebrates.

Intraventricular injection of vasoactive intestinal polypeptide facilitates the development of amygdaloid kindling

To determine the involvement of vasoactive intestinal polypeptide (VIP) in the development of kindling in rats, VIP or antibody to VIP (anti-VIP) was injected into the third ventricle after the daily stimulation of the basolateral amygdala. The number of stimulations required to reach full amygdaloid kindling was significantly smaller in rats treated with VIP than rats treated with saline, whereas it increased significantly in rats treated with anti-VIP compared to that in the rats treated with either saline or normal rabbit serum. The results suggest that VIP participates in the development of amygdaloid kindling as a facilitatory factor.

Autoradiographic analysis of the distribution of vasoactive intestinal peptide binding sites in the vertebrate central nervous system: a phylogenetic study

The distribution of vasoactive intestinal peptide (VIP) binding sites in the brain of several vertebrate species was examined by in vitro autoradiography on slide-mounted sections. This study included fish, frog, snake, pigeon, rat, mouse, guinea pig, cat and monkey brain. A fully characterized, monoiodinated form of vasoactive intestinal peptide (M-125I-VIP), which maintains the biological activity of the native peptide in the central nervous system (CNS), was used throughout the study. Among the lower vertebrate species, no significant specific binding was found in the fish brain, whereas in the frog and snake brain, specific VIP binding sites were observed, mainly in the telencephalon. In the pigeon brain, high densities of VIP binding sites were localized in the hyperstriatum, neostriatum, archistriatum, hippocampal area, dorsolateral cortical area and in the optic tectum. Ectostriatum and paleostriatum augmentatum displayed lower densities of specific binding. In mammals, the highest concentrations of VIP binding sites were observed in the rodent brain. In the rat, mouse and guinea pig brain, high densities were detected in the olfactory bulb, external layers of the cerebral cortex, dentate gyrus, midline thalamic nuclei, geniculate nuclei, some hypothalamic nuclei, superior colliculus and locus coeruleus. Intermediate densities were found in amygdala, caudate-putamen, septum and nucleus accumbens, CA1-CA3 fields of the hippocampus and central gray. The cerebellum of these species presented high densities of VIP binding sites, with species to species differences in their localization. The non-specific binding was, however, increased in the rodent cerebellum. Lower densities of VIP binding sites were observed in the cat and monkey CNS. In these two species, the non-specific binding was considerably higher than in the lower mammals brain. In the cat and monkey brain, as in the lower mammals, the highest densities were revealed in the neocortex, dentate gyrus, thalamic nuclei and some midbrain structures including substantia nigra and locus coeruleus. In all the species studied, the white matter was never labeled with M-125I-VIP. This study suggests that VIP binding sites appear relatively early in the evolution of the vertebrate CNS. The most important densities of specific VIP binding sites are observed in the pigeon and rodent brain, whereas the cat and monkey present a marked increase in non-specific binding. It is interesting to note that the distribution of VIP binding sites as revealed by autoradiography is quite conservative in terms of evolution and indicates an association, although non-exclusive, of VIP receptors with brain regions involved in the processing of specific sensory inputs.

Demonstration of specific binding sites for pituitary adenylate cyclase activating polypeptide (PACAP) in rat astrocytes

The high and low affinity binding sites for PACAP were identified in rat astrocytes using [125I]PACAP27 as the labeled ligand. Scatchard analysis of displacement of the bound tracer by unlabeled PACAP27 indicated the existence of two classes of binding sites, with the dissociation constant (Kd) = 1.22 +/- 0.4 nM, the binding maximal capacity (Bmax) = 821 +/- 218 fmols/mg protein for the high affinity binding site, and Kd = 0.59 +/- 0.06 microM, Bmax = 563 +/- 12 pmols/mg protein for the low affinity binding site, respectively. The specificity of [125I]PACAP27 binding was tested using PACAP38 and peptides structurally related to PACAP, such as VIP, GHRF, PHI, secretin and glucagon. PACAP38 completely displaced the binding of [125I]PACAP27 and Scatchard analysis also indicated the presence of two classes of binding sites with similar Kd and Bmax to those for PACAP27. VIP and GHRF competed with [125I]PACAP27, but to a much lesser extent than unlabeled PACAP27 in binding. Other peptides tested did not displace the binding of [125I]PACAP27 at 10(-6) M.

Cardioacceleration provoked by intrathecal administration of vasoactive intestinal peptide (VIP): mediation by a non-central nervous system mechanism

Intrathecal administration of VIP to the thoracic spinal cord in the urethane anaesthetized rat provoked a dose-dependent increase in heart rate without any change in arterial pressure. The cardioacceleration observed following administration of 6.5 nmol of VIP at the T9 level (n = 8) occurred within 1-2 min of administration, with a peak effect of 70-85 bpm, 10-30 min after administration. The magnitude of the maximum change when this dose was given at the T2 level (n = 8) was approximately 100 beats per min, 7-8 min after administration. However, the differences between T2 and T9 administration were not statistically significant. Intravenous administration of 6.5 nmol of VIP (n = 6) mimicked the cardioacceleratory effect of intrathecal administration, and also decreased systolic and diastolic arterial pressure by 9-13 mmHg 6-13 min after administration. The cardioacceleration observed following intrathecal administration at T9 was not blocked by prior systemic administration of the autonomic ganglion blocker hexamethonium (5 mg/kg) or by bilateral vagotomy. Nor was the effect blocked by prior intrathecal administration of the local anaesthetic lidocaine (250 micrograms), although lidocaine did block the tachycardia and hypertension resulting from intrathecal administration of substance P. Considered collectively, the findings that the cardioacceleration observed following intrathecal VIP injection is mimicked by i.v. administration, is not reversed by blockade of nicotinic transmission of autonomic ganglia or by bilateral vagotomy, and is not blocked by lidocaine suggest that VIP's tachycardic effect does not result from a direct action on spinal mechanisms mediating autonomic control of the cardiovascular system, but occurs via diffusion to a site of action outside the central nervous system.

Vasoactive intestinal peptide (VIP), a putative neurotransmitter of nonadrenergic, noncholinergic (NANC) inhibitory innervation and its relevance to therapy

Nonadrenergic, noncholinergic (NANC) innervation, the third division of the autonomic nervous system, has both inhibitory and excitatory parts. The excitatory part received only limited attention. Substance P has been suggested to be the neurotransmitter of the excitatory part. The NANC-inhibitory innervation has recently been studied in detail. Although the neurotransmitter has not been conclusively identified, a substantial body of evidence exists to support vasoactive intestinal peptide (VIP) as the neurotransmitter. VIP is widely distributed in the body. Reports show that this innervation in animals and man plays a significant role in both health and disease. Pathological conditions could result from either an increase or decrease in VIP production. An absence of VIP-producing neurons has been identified to be responsible for Hirschsprung's disease in the alimentary system and hyperactive airways in the respiratory system. An increase in VIP production is associated with chronic water diarrhea syndrome in humans. Taking these factors into consideration, various therapeutic measures are suggested with the use of VIP or its antagonists.

Astrocytes from forebrain, cerebellum, and spinal cord differ in their responses to vasoactive intestinal peptide

Astrocytes from cortex, cerebellum, and spinal cord responded to isoproterenol and vasoactive intestinal peptide (VIP) with increases in intracellular cyclic AMP levels. The response to VIP was as great as that to isoproterenol in cortical astrocytes (180-fold and 185-fold, respectively), and the effect of VIP in combination with isoproterenol was partially additive. Spinal cord astrocytes also responded to VIP and isoproterenol with equal potency (seven- to ninefold and eight- to 13-fold, respectively), but the level of response was much smaller than in cortex. Spinal cord astrocytes were synergistic in their response to VIP and isoproterenol. The response to VIP was lowest in cerebellar astrocytes (only threefold), and no additivity was observed when VIP was added together with isoproterenol. A small response to alpha-melanocyte stimulating hormone (alpha-MSH) was also observed in cortex and cerebellum, but not in spinal cord. Somatostatin inhibited the response to isoproterenol in cortex and cerebellum, but had no effect in spinal cord. The results from the above study show that astrocytes obtained from these three regions of the rat CNS express quite different responses to VIP and alpha-MSH and further point to possible astrocyte heterogeneity.

Ramification patterns of vasoactive intestinal polypeptide (VIP)-cells in the rat primary visual cortex. An immunohistochemical study

Vasoactive intestinal polypeptide (VIP)-immunoreactive cells in the primary visual cortex of the rat were classified on the basis of ramification pattern of cell processes. The distribution of cells over cortical layers, and proportions of cell classes relative to total cell numbers were evaluated by means of quantitative methods. Two main types of VIP-positive neurons, the bipolar and the multipolar were distinguished constituting 76% and 24% of the VIP populations, respectively. The axons of vertically oriented bipolars were observed to ramify within a column around the descending dendrite. By contrast, multipolar cells have a non-oriented ramification pattern. The two overlapping axonal systems form the VIP-innervation of the rat visual cortex.

Effect of vasoactive intestinal peptide on dopaminergic system in the rat brain

The present study analyzed the effect of vasoactive intestinal peptide (VIP) on the content of dopamine (DA) and its main metabolite, DOPAC, in the rat brain. Intracerebroventricular administration of VIP increased the DA and DOPAC content, causing a dose-dependent increase in the DOPAC/DA ratio in various regions of the brain. The results suggest that VIP facilitates the DA metabolism in the brain.

Quantitative immunohistochemical analysis of VIP-neurons in the rat visual cortex

A critical appraisal of quantitative immunohistochemistry of neuropeptides is presented defining the main criteria of selecting the type of immune-staining and preparation suitable for these investigations. As an example of meeting the established criteria, the immunohistochemical demonstration of vasoactive intestinal polypeptide (VIP)-containing neurons in the rat brain and the processing of VIP-immunostained preparations for computer-controlled image analysis are described.

Autoradiographic mapping of [mono[125I]iodo-Tyr10, MetO17]vasoactive intestinal peptide binding sites in the rat brain

The distribution of vasoactive intestinal peptide binding sites in the rat brain was examined by in vitro autoradiography on slide-mounted sections. A fully characterized monoiodinated form of vasoactive intestinal peptide (M-[125I]VIP) previously shown to maintain in the central nervous system the full biological activity of native vasoactive intestinal peptide was used for this study. In initial kinetic and pharmacological experiments the binding of M-[125I]vasoactive intestinal peptide to slide-mounted sections was shown to be time-dependent, saturable and reversible. Association of M-[125I]VIP specific binding was maximal within 90-120 minutes. Specific binding, corresponding to approximately 50% of total binding was saturable, of high affinity (Kd of 76.6 pM) and low capacity (fmol/mg prot range). Dissociation of M-[125I]VIP was maximal at 10 minutes. Unlabeled vasoactive intestinal peptide and the two structurally related peptides "peptide-histidine-isoleucine" (PHI) and secretin competed in a concentration-dependent manner for sites labeled by M-[125I]vasoactive intestinal peptide with the following rank order of potencies: vasoactive intestinal peptide greater than PHI greater than secretin. Vasoactive intestinal peptide receptors, as revealed by quantitative autoradiography, are present at various levels of the neuraxis. High densities were observed in olfactory bulb, cerebral cortex (highest in layers I, II, IV and VI), dentate gyrus, subiculum, various thalamic and hypothalamic nuclei, superior colliculus, locus coeruleus, area postrema, subependymal layer and pineal gland. Intermediate densities were found in the amygdala, nucleus accumbens, caudate-putamen, septum, bed nucleus of the stria terminalis, CA1 to CA4 fields of the hippocampus and central gray. No specific binding of M-[125I]vasoactive intestinal peptide was observed in white matter tracts such as corpus callosum, anterior commissure, medial forebrain bundle and fornix. The mapping of M-[125I]vasoactive intestinal peptide binding sites as revealed by autoradiography on slide-mounted sections indicates an association, although not exclusive, of vasoactive intestinal peptide receptors with brain regions involved in the processing of specific sensory inputs.

Characterization and autoradiographic distribution of vasoactive intestinal peptide binding sites in the rat central nervous system

Biochemical characteristics and topographical distribution of mono-[125I )vasoactive intestinal peptide (VIP) binding sites in rat brain were studied on tissue sections and by quantitative autoradiography. Biochemical investigations show two classes of binding sites with a dissociation constant of 1.03 +/- 0.11 nM and 68 +/- 14 nM and a maximal binding capacity of 43.3 +/- 5.1 fmol/mg protein and 713 +/- 117 fmol/mg protein respectively. The order of potency of various peptides to inhibit 125I-VIP binding to brain sections is: VIP greater than PHI greater than secretin greater than VIP greater than hGRF. Autoradiography reveals the highest densities of binding sites in the pineal gland, the dentate gyrus of the hippocampus, the central amygdaloid nucleus and in various thalamic nuclei such as the mediodorsal, lateral posterior, submedius, dorsolateral and medial geniculate nuclei. Similar high densities are observed in the olfactory bulbs as well as in the suprachiasmatic and dorsomedial nuclei of the hypothalamus and in the superior colliculus. These data together with the distribution of the endogenous peptide suggest a physiological role for VIP both in the regulation of CNS activities and pituitary functions.

Neurotransmitters in the cerebral cortex

This article surveys the conventional neurotransmitters and modulatory neuropeptides that are found in the cerebral cortex and attempts to place them into the perspective of both intracortical circuitry and cortical disease. The distribution of these substances is related, where possible, to particular types of cortical neuron or to afferent or efferent fibers. Their physiological actions, where known, on cortical neurons are surveyed, and their potential roles in disease states such as the dementias, epilepsy, and stroke are assessed. Conventional transmitters that occur in afferent fibers to the cortex from brain-stem and basal forebrain sites are: serotonin, noradrenaline, dopamine, and acetylcholine. All of these except dopamine are distributed to all cortical areas: dopamine is distributed to frontal and cingulate areas only. The transmitter in thalamic afferent systems is unknown. Gamma aminobutyric acid (GABA) is the transmitter used by the majority of cortical interneurons and has a profound effect upon the shaping of receptive field properties. The vast majority of the known cortical peptides are found in GABAergic neurons, and the possibility exists that they may act as trophic substances for other neurons. Levels of certain neuropeptides decline in cases of dementia of cortical origin. Acetylcholine is the only other known transmitter of cortical neurons. It, too, is contained in neurons that also contain a neuropeptide. The transmitter(s) used by excitatory cortical interneurons and by the efferent pyramidal cells is unknown, but it may be glutamate or aspartate. It is possible that excitotoxins released in anoxic disease of the cortex may produce damage by acting on receptors for these or related transmitter agents.

Autoradiographic visualization of CNS receptors for vasoactive intestinal peptide

Receptors for VIP were characterized in the rat CNS. 125I-VIP bound with high affinity to rat brain slices. Binding was time dependent and specific. Pharmacology studies indicated that specific 125I-VIP binding was inhibited with high affinity by VIP and low affinity by secretin and PHI. Using in vitro autoradiographic techniques high grain densities were present in the dentate gyrus, pineal gland, supraoptic and suprachiasmatic nuclei, superficial gray layer of the superior colliculus and the area postrema. Moderate grain densities were present in the olfactory bulb and tubercle, cerebral cortex, nucleus accumbens, caudate putamen, interstitial nucleus of the stria terminalis, paraventricular thalamic nucleus, medial amygdaloid nucleus, subiculum and the medial geniculate nucleus. Grains were absent in the corpus callosum and controls treated with 1 microM unlabeled VIP. The discrete regional distribution of VIP receptors suggest that it may function as an important modulator of neural activity in the CNS.