Vagus nerve modulates secretin binding sites in the rat forestomach.
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Secretin is well known for its inhibitory action on gastric motility. It has been reported that secretin in a physiological dose inhibits gastric motility through mediation by the vagal afferent pathway. Secretin also elicited relaxation of carbachol-stimulated rat forestomach muscle strips by binding to its receptors, suggesting a direct action on this peripheral tissue. We hypothesized that vagal input may affect the action of secretin by modulating the level of secretin receptor in the forestomach. Several treatments, including vagal ligation, vagotomy, perivagal application of capsaicin or colchicine, intravenous infusion of tetrodotoxin, and intraperitoneal injection of atropine, were performed to investigate their effects on secretin receptor binding to forestomach membranes. Specific binding of 125I-labeled secretin to forestomach membranes was significantly decreased (45%) by vagal ligation, vagotomy (50%), or perivagal colchicine treatment (40%). On the contrary, specific binding of 125I-secretin was not affected by perivagal capsaicin treatment, intravenous infusion of tetrodotoxin, or intraperitoneal injection of atropine. By Scatchard analysis of the binding data, the capacity of the high-affinity binding sites in forestomach membranes was found to decrease significantly after vagal ligation compared with membranes from the sham-operated group. However, the affinity at the high-affinity binding sites, the binding parameters of the low-affinity binding sites, and binding specificity were not changed. Vagal ligation but not perivagal capsaicin treatment reduced the inhibitory effect of secretin on bethanechol-stimulated contraction of isolated forestomach muscle strips, causing a right shift in the dose-response curve. These results suggest that vagal input through axonal transport plays a significant role on secretin action by modulating the capacity of secretin binding sites (but not affinity or specificity), at least in rat forestomach. (+info)
Hair-cycle-associated remodeling of the peptidergic innervation of murine skin, and hair growth modulation by neuropeptides.
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As the neuropeptide substance P can manipulate murine hair growth in vivo, we here further studied the role of sensory neuropeptides in hair follicle biology by determining the distribution and hair-cycle-dependent remodeling of the sensory innervation in C57BL/6 mouse back skin. Calcitonin-gene-related peptide, substance P, and peptide histidine methionine (employed as vasoactive intestinal peptide marker) were identified by immunohistochemistry. All of these markers immunolocalized to bundles of nerve fibers and to single nerve fibers, with distinct distribution patterns and major hair-cycle-associated changes. In the epidermis and around the distal hair follicle and the arrector pili muscle, only calcitonin-gene-related peptide immunoreactive nerve fibers were visualized, whereas substance P and peptide histidine methionine immunoreactive nerve fibers were largely restricted to the dermis and subcutis. Compared to telogen skin, the number of calcitonin-gene-related peptide, substance P, and peptide histidine methionine immunoreactive single nerve fibers increased significantly (p < 0.01) during anagen, including around the bulge region (the seat of epithelial stem cells). Substance P significantly accelerated anagen progression in murine skin organ culture, whereas calcitonin-gene-related peptide and a substance-P-inhibitory peptide inhibited anagen (p < 0.05). The inhibitory effect of calcitonin-gene-related peptide could be antagonized by coadministrating substance P. In contrast to substance P, calcitonin-gene-related peptide failed to induce anagen when released from subcutaneous implants. This might reflect a differential functional assignment of the neuropeptides calcitonin-gene-related peptide and substance P in hair growth control, and invites the use of neuropeptide receptor agonists and antagonists as novel pharmacologic tools for therapeutic hair growth manipulation. (+info)
The VPAC(2) receptor is essential for circadian function in the mouse suprachiasmatic nuclei.
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The neuropeptides pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are implicated in the photic entrainment of circadian rhythms in the suprachiasmatic nuclei (SCN). We now report that mice carrying a null mutation of the VPAC(2) receptor for VIP and PACAP (Vipr2(-/-)) are incapable of sustaining normal circadian rhythms of rest/activity behavior. These mice also fail to exhibit circadian expression of the core clock genes mPer1, mPer2, and mCry1 and the clock-controlled gene arginine vasopressin (AVP) in the SCN. Moreover, the mutants fail to show acute induction of mPer1 and mPer2 by nocturnal illumination. This study highlights the role of intercellular neuropeptidergic signaling in maintenance of circadian function within the SCN. (+info)
Vasoactive intestinal peptide enhances dopamine accumulation in primary cell culture of rat hypothalamus.
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The effect of vasoactive intestinal peptide (VIP) and PHI-27 on dopamine accumulation in cultured rat hypothalamic cells was investigated. VIP enhanced [3H]dopamine accumulation dose dependently. This effect was significant at 10(-8)-10(-5) M VIP with a concomitant increase in intracellular cyclic AMP (cAMP), and reached its plateau level at 10(-6) M VIP. VIP increased [3H]dopamine accumulation significantly within 15 min. PHI-27 and dibutyryl cAMP ((Bu)2-cAMP) also enhanced [3H]dopamine accumulation. These results suggest that VIP enhances dopamine accumulation in hypothalamic cells by increasing intracellular cAMP. (+info)
Release of vasoactive intestinal polypeptide from the rat gastric fundus.
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1. Auxotonic responses and release of vasoactive intestinal polypeptide-like immunoreactivity (VIP-LI) induced by electrical field stimulation (EFS) were studied in longitudinal muscle strips from the gastric fundus of reserpinized rats suspended between parallel platinum electrodes in Krebs solution containing atropine (1 microM), 5-hydroxytryptamine (3 microM) and bovine serum albumin (50 mg l-1). 2. EFS (supramaximal voltage, 1 ms, 0.25-32.0 Hz, trains of 2 min) induced frequency-dependent relaxations. 3. EFS at frequencies greater than or equal to 8 Hz also produced significant increases in VIP-LI release. 4. VIP-LI release induced by EFS at 16 Hz no longer occurred in the presence of tetrodotoxin (1 microM) or a Ca(2+)-free medium. 5. Detection of VIP-LI upon activation of inhibitory non-adrenergic, non-cholinergic neurones indicates that VIP meets the 'detectable release' criterion for an inhibitory neurotransmitter in the rat gastric fundus. (+info)
Pituitary adenylate cyclase activating polypeptides, PACAP-27 and PACAP-38: stimulators of electrogenic ion secretion in the rat small intestine.
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1. The effects of pituitary adenylate cyclase activating polypeptide (PACAP)-27 and PACAP-38 were investigated and compared with vasoactive intestinal polypeptide (VIP) responses in voltage clamped preparations of rat jejunum. Under these conditions electrogenic ion secretion was continuously recorded. 2. PACAP-27 is the most potent secretagogue described thus far, exhibiting a concentration-dependent dual secretory action. At low concentrations it stimulated rapid, transient secretory responses (not seen with either PACAP-38 or VIP) and these were inhibited by tetrodotoxin (TTX). At higher nM concentrations of PACAP-27 more prolonged secretory responses predominated which were insensitive to TTX. 3. In the presence of TTX, the concentration-response curve to PACAP-27 gave an EC50 value of 29.4 +/- 5.4 nM (n = 4) compared with 0.8 +/- 0.1 nM (n = 9) for PACAP-27 alone and 30.6 +/- 5.6 nM (n = 5) for PACAP-38. C-terminal fragments of PACAP-38 were not significantly effective. 4. Blockade of muscarinic and nicotinic receptors partially inhibited the low concentration effects of PACAP-27. Substance P desensitization and capsaicin pretreatment were effective at inhibiting the transient secretory PACAP-27 responses. Evidence is presented for selective, high affinity PACAP-27 receptors on submucous neurones innervating the mucosal region of the rat jejunum. (+info)
Cyclic AMP formation in chicken brain: effect of vasoactive intestinal peptide, peptide histidine-isoleucine (PHI), and some PHI-related peptides.
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Vasoactive intestinal peptide (chicken form; chVIP), peptide histidine-isoleucine (porcine and rat forms; pPHI and rPHI), D-Phe(4) derivative of porcine PHI (D-Phe(4)-pPHI), peptide histidine-methionine (PHM; human PHI), and helodermin, were tested for their ability to stimulate cAMP production in [(3)H]adenine-prelabeled slices of chick cerebral cortex (CCx) and hypothalamus (HTh). The chVIP (0.1-3 microM) concentration-dependently and potently stimulated cAMP production in HTh and CCx; the responses observed after 3 microM of chVIP were comparable to those produced by 0.1 microM PACAP38. Helodermin (5 microM) moderately but significantly stimulated cAMP formation in both HTh and CCx, whereas pPHI, rPHI, PHM at 5 microM concentration only weakly affected cAMP production in CCx, and were inactive in HTh; D-Phe(4)-pPHI was inactive in both tissues. These data demonstrate that chVIP, PACAP, and to a lesser extent helodermin were capable of potently stimulating cAMP generation in the avian central nervous system. PHI-related peptides showed only weak or no activity, depending on the tissue. (+info)
VPAC2 receptors mediate vasoactive intestinal peptide-induced neuroprotection against neonatal excitotoxic brain lesions in mice.
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Prepro-vasoactive intestinal peptide (VIP) mRNA codes for two neuropeptides: VIP and peptide histidine isoleucine (PHI). Two VIP receptors, shared with a similar affinity by pituitary adenylate cyclase-activating polypeptide (PACAP), have been cloned: VPAC(1) and VPAC(2). PHI binds to these receptors with a lower affinity. VPAC receptors are classically associated with a cAMP-dependent pathway, although other pathways, including calcium mobilization and protein kinase C activation have been described. We previously showed that intracerebral administration of the glutamate agonist ibotenate to postnatal day 5 mice induces white matter lesions mimicking human periventricular leukomalacia. In this model, coinjection of VIP protects against white matter lesions. This neuroprotection is independent from cAMP and is mediated by protein kinase C. Using this model, this study aimed to determine the receptor involved in VIP-induced neuroprotection. VIP effects were mimicked with a similar potency by VPAC(2) agonists and PHI but not by VPAC(1) agonists, PACAP 27, or PACAP 38. VIP neuroprotective effects were lost in mice lacking VPAC(2) receptor. In situ hybridization confirmed the presence of VPAC(2) mRNA in the postnatal day 5 white matter. When analyzed between embryonic life and adulthood, VIP-specific binding site density peaked at postnatal day 5. These data suggest that, in this model, VIP-induced neuroprotection is mediated by VPAC(2) receptors. The pharmacology of this VPAC(2) receptor seems unconventional because 1) PACAP does not mimic VIP effects, 2) PHI acts with a comparable potency, and 3) PACAP 27 modestly inhibited the VIP-specific binding, whereas for PHI or VIP, inhibition was complete. (+info)