Search

The intestinal hormones CCK and PYY3-36 inhibit gastric emptying and food intake via vagal afferent neurons. Here we report that CCK regulates the expression of Y2R, at which PYY3-36 acts. In nodose ganglia from rats fasted up to 48 h, there was a fivefold decrease of Y2R mRNA compared with rats fed ad libitum; Y2R mRNA in fasted rats was increased by administration of CCK, and by refeeding through a mechanism sensitive to the CCK1R antagonist lorglumide. Antibodies to Y2R revealed expression in both neurons and satellite cells; most of the former (89 +/- 4%) also expressed CCK1R. With fasting there was loss of Y2R immunoreactivity in CCK1R-expressing neurons many of which projected to the stomach, but not in satellite cells or neurons projecting to the ileum or proximal colon. Expression of a Y2R promoter-luciferase reporter (Y2R-luc) in cultured vagal afferent neurons was increased in response to CCK by 12.3 +/- 0.1-fold and by phorbol ester (16.2 +/- 0.4-fold); the response to both was abolished by the protein kinase C inhibitor Ro-32,0432. PYY3-36 stimulated CREB phosphorylation in rat nodose neurons after priming with CCK; in wild-type mice PYY3-36 increased Fos labeling in brainstem neurons but in mice null for CCK1R this response was abolished. Thus Y2R is expressed by functionally distinct subsets of nodose ganglion neurons projecting to the stomach and ileum/colon; in the former expression is dependent on stimulation by CCK, and there is evidence that PYY3-36 effects on vagal afferent neurons are CCK dependent.

Cholecystokinin (CCK), acting at CCK1 receptors (CCK1Rs) on intestinal vagal afferent terminals, has been implicated in the control of gastrointestinal function and food intake. Using CCK1R(-/-) mice, we tested the hypothesis that lipid-induced activation of the vagal afferent pathway and intestinal feedback of gastric function is CCK1R dependent. In anesthetized CCK1R(+/+) ("wild type") mice, meal-stimulated gastric acid secretion was inhibited by intestinal lipid infusion; this was abolished in CCK1R(-/-) mice. Gastric emptying of whole egg, measured by nuclear scintigraphy in awake mice, was significantly faster in CCK1R(-/-) than CCK1R(+/+) mice. Gastric emptying of chow was significantly slowed in response to administration of CCK-8 (22 pmol) in CCK1R(+/+) but not CCK1R(-/-) mice. Activation of the vagal afferent pathway was measured by immunohistochemical localization of Fos protein in the nucleus of the solitary tract (NTS; a region where vagal afferents terminate). CCK-8 (22 pmol ip) increased neuronal Fos expression in the NTS of fasted CCK1R(+/+) mice; CCK-induced Fos expression was reduced by 97% in CCK1R(-/-) compared with CCK1R(+/+) mice. Intralipid (0.2 ml of 20% Intralipid and 0.04 g lipid), but not saline, gavage increased Fos expression in the NTS of fasted CCK1R(+/+) mice; lipid-induced Fos expression was decreased by 47% in CCK1R(-/-) compared with CCK1R(+/+)mice. We conclude that intestinal lipid activates the vagal afferent pathway, decreases gastric acid secretion, and delays gastric emptying via a CCK1R-dependent mechanism. Thus, despite a relatively normal phenotype, intestinal feedback in response to lipid is severely impaired in these mice.

Background & Aims: Two distinct receptors, cholecystokinin (CCK)-A and CCK-B, mediate CCK effects in the digestive system. The aim of this study was to elucidate the cellular sites of expression of CCK-A receptor in the rat stomach and small intestine., Methods: We developed and characterized an antibody to the N-terminal region (LDQPQPSKEWQSA) of rat CCK-A receptor and used it for localization studies with immunohistochemistry., Results: Specificity of the antiserum was demonstrated by (1) detection of a broad band at 85-95 kilodaltons in Western blots of membranes from CCK-A receptor CHO-transfected cells; (2) cell surface staining of CCK-A receptor-transfected cells, (3) translocation of CCK-A receptor immunostaining in CCK-A receptor-transfected cells after exposure to CCK; and (4) abolition of tissue immunostaining by preadsorbtion of the antibody with the peptide used for immunization. CCK-A receptor immunoreactivity was localized to myenteric neurons and to fibers in the muscle and mucosa. In the stomach, myenteric neurons and mucosal fibers were abundant. Many CCK-A receptor myenteric neurons contained the inhibitory transmitter vasoactive intestinal polypeptide, and some were immunoreactive for the excitatory transmitter substance P. Subdiaphragmatic vagotomy reduced the density of CCK-A receptor fibers in the gastric mucosa by approximately 50%, whereas celiac/superior mesenteric ganglionectomy had no detectable effect on fiber density., Conclusions: CCK-A receptor is expressed in functionally distinct neurons of the gastrointestinal tract. CCK-A receptor may mediate reflexes stimulated by CCK through the release of other transmitters from neurons bearing the receptor.

The ability of nutrients in the intestinal lumen to exert feedback control over the proximal gastrointestinal tract function is well recognized, yet the control mechanisms are poorly defined. There is evidence that extrinsic sensory pathways from the intestine are required to initiate this regulatory process. Furthermore, CCK appears to be involved in the gastric response to several intestinal stimuli, such as fat, carbohydrate and protein. Our hypothesis is that nutrients release CCK from the intestine, which then stimulates intestinal mucosal afferents to signal reflex changes in gastric motor function and thus inhibit gastric emptying.

Cholecystokinin (CCK) stimulates vagal afferent fiber discharge, both gastric and intestinal, which seems to result in reflex decrease in gastric motility, gastric acid secretion, and stimulation of pancreatic protein secretion. Endogenous release of CCK by fat or soybean trypsin inhibitor also alters function by way of a capsaicin-sensitive pathway. We suggest that CCK is released locally from the intestine and acts locally or systemically to stimulate vagal afferent fiber discharge to alter proximal gastrointestinal function (Fig. 14). In this way, in addition to its effect on food intake, CCK and the neural pathway integrate function in the proximal gastrointestinal tract, regulating the entry of food into the duodenum to ensure effective digestion and absorption.

Objective: The object of this study was to investigate the mechanisms of postoperative gastric ileus in an experimental model of abdominal surgery in anesthetized rats., Summary Background Data: Sensory neurons partly mediate postoperative gastric ileus. Among other neuropeptides, sensory neurons contain calcitonin gene-related peptide (CGRP) and release CGRP in response to noxious stimulation. Because CGRP inhibits gastric motility, it was hypothesized that abdominal surgery stimulates sensory neurons, which then releases CGRP, thereby inhibiting gastric motility., Methods: Postoperative ileus was induced by abdominal surgery. Gastric corpus motility was measured by an intragastric catheter. CGRP action was blocked by CGRP immunoneutralization or by a CGRP receptor antagonist. Spinal sensory neurons were ablated by application of a sensory neurotoxin (capsaicin) to the celiac and superior mesenteric ganglia., Results: Abdominal surgery decreased gastric corpus motility in the first 5 minutes after abdominal surgery by 59 +/- 5% and by 24 +/- 4% during the 1st postoperative hour. Capsaicin pretreatment of the celiac and superior mesenteric ganglia, CGRP immunoneutralization, or CGRP receptor antagonism reversed the postoperative decrease in gastric corpus motility during the 1st postoperative hour by 50%, 100%, and 59%, respectively., Conclusions: These data indicate that spinal sensory neurons and CGRP partly mediate postoperative gastric ileus. CGRP may be released from spinal sensory neuron terminals in the celiac and superior mesenteric ganglia as part of an extraspinal intestinogastric inhibitory reflex activated by abdominal surgery.

The role of the vagal and spinal afferent innervation in the inhibition of gastric emptying induced by duodenal perfusion with a disaccharide (maltose 300 mM) was investigated in awake rats fitted with gastric and duodenal cannulas. Perfusion of the duodenum with maltose inhibited gastric emptying by 44%. Maltose-induced inhibition of gastric emptying was reversed by 46% and 100% by functional ablation of the vagal or spinal capsaicin-sensitive afferent innervation, respectively. Pretreatment with the specific CCK 'A' receptor antagonist, MK329, completely abolished the effects of maltose on gastric emptying. These results suggest that disaccharides inhibit gastric emptying via activation of capsaicin-sensitive afferents in the duodenal mucosa via a mechanism involving an action of CCK at type 'A' receptors, possibly located on afferent fibers.

The role of corticotropin-releasing factor (CRF) in the paraventricular nucleus of the hypothalamus (PVN) in the control of gastric emptying of a nonnutrient meal and colonic transit was investigated in conscious fasted rats chronically implanted with hypothalamic cannulas and catheters in both the stomach and proximal colon. CRF (0.06-0.6 nmol) microinfused unilaterally into the PVN resulted in a dose-dependent inhibition of gastric emptying (0-51%) and stimulation of colonic transit (0-93%). CRF (0.6 nmol)-induced delay in gastric emptying was inhibited by 50% by subdiaphragmatic vagotomy or atropine methyl nitrate (1 mg/kg ip), whereas the stimulation of colonic transit was completely abolished by atropine methyl nitrate and reduced by 19% by vagotomy. Microinfusion of CRF (0.6 nmol) into the lateral hypothalamus or central amygdala had no effect. Restraint exposure for 1 h delayed gastric emptying and stimulated colonic transit by 28 and 78%, respectively. Bilateral microinfusion of the CRF antagonist alpha-helical CRF-(9-41) (13 nmol) into the PVN before restraint abolished stress-induced alterations of gastric and colonic transit. The CRF antagonist did not alter basal gastric and colonic transit under basal conditions. These data indicate that the PVN is a specific responsive site for central CRF-induced alterations of gastric and colonic transit and suggest that endogenous CRF in the PVN plays a role in mediating restraint stress-related alterations of gastrointestinal transit.

In this article, we have presented evidence that vagal capsaicin-sensitive afferent fibers are involved in the regulation of gastric mucosal and motor function. Gastric acid secretion stimulated by gastric distension, histamine and central injection of TRH analog are all partly dependent on vagal capsaicin-sensitive afferent mechanisms. It is possible that as vagal efferent activity releases histamine, the common final pathway is the reduction in the response to histamine. At present, it is unclear as to the mechanism by which capsaicin-sensitive afferents are involved in the secretory response to histamine. With regard to the gastric acid and mucosal blood flow responses to TRH, it is not clear whether the sensory neurons represent a component of the efferent pathway that is activated by TRH or whether their role is to set the sensitivity of, or exert feedback control on this efferent pathway. As perineural capsaicin application decreases peptide content in the peripheral terminal fields of sensory neurons and these peptides may produce local effector functions within the tissue, it is possible that alterations in the gastric responses to TRH result from a decrease in the local effector functions of vagal neurons. From the experiments on electrical stimulation of the vagus nerve, it is evident that antidromic stimulation of vagal afferents can stimulate gastric mucosal blood flow, although under these experimental conditions there was no evidence for a capsaicin-sensitive stimulation of gastric acid secretion. The physiological relevance of this stimulation of gastric mucosal blood flow is at present unclear, but it is possible that physiological stimuli, such as distension or nutrients, may stimulate afferents and signal for an increase in gastric mucosal blood flow. In addition, pathophysiological or noxious stimulation of vagal afferents may also signal for an increase in gastric mucosal blood flow and may play a role in the response of the mucosa to injury.

The pathway by which cholecystokinin octapeptide (CCK-8) inhibits motility of the proximal stomach and the role of this pathway in the CCK-induced delay in gastric emptying of a liquid meal has been studied in rats by selective destruction of vagal afferent C-fibers using bilateral perineural application of the sensory neurotoxin, capsaicin, 3 or 4 days prior to the experiment. The capsaicin treatment significantly attenuated the decrease in intragastric pressure in urethan-anesthetized rats in response to CCK-8 (0.1-100 pmol iv) compared with vehicle-treated controls. Removal of the celiac-superior mesenteric ganglion completely abolished the inhibitory action of CCK-8 on gastric motility in these rats. In contrast, only celiac ganglionectomy in combination with vagotomy abolished the CCK-8 effect in vehicle-treated controls. Intravenous injection of CCK-8 (300 pmol) 5 min before intragastric administration of a methylcellulose solution decreased gastric emptying by 55% in conscious control or vehicle-treated rats. Perivagal capsaicin treatment abolished the delay in gastric emptying induced by CCK-8. In addition, capsaicin treatment alone significantly increased gastric emptying. These results demonstrate that CCK-8 decreases gastric motility in the gastric corpus and delays gastric emptying by a capsaicin-sensitive vagal afferent pathway. These same afferent fibers may also play a physiological role in the gastric emptying of liquids.

The actions of intravenous sulfated cholecystokinin octapeptide (CCK-8) on intraluminal pressure in the body of the stomach were studied in urethan-anesthetized rats. There was a dose-related decrease in pressure in response to CCK-8 over the range 0.3-33 pmol. Bilateral cervical vagotomy alone reduced the response to CCK-8 and together with splanchnic section abolished it. Hexamethonium also reduced the response. Vagotomy did not change the response to CCK-8 in hexamethonium-treated rats, but celiac ganglionectomy abolished it. Guanethidine and phentolamine, but not propranolol, significantly decreased the response to CCK-8; subsequent vagotomy abolished the response. Similarly, depletion of tissue catecholamines by pretreatment with 6-OH dopamine, reserpine, or celiac ganglionectomy together with vagal section abolished the effect of CCK-8. It concluded that CCK-8 decreases mean intragastric pressure in the rat by pathways involving both vagal and splanchnic nerves. The splanchnic pathway involves an alpha-adrenergic mechanism but is hexamethonium resistant. The vagal pathway is hexamethonium sensitive and nonadrenergic. Similar pathways may mediate the effect of CCK on gastric emptying.

The importance of the dorsal vagal complex (DVC) in the control of gastric motor activity has been previously established by electrical and chemical stimulation of this region. We have further evaluated excitatory and inhibitory influences on motor activity of the gastric corpus by microinjection of L-glutamic acid (GLU) and thyrotropin-releasing hormone (TRH) into the DVC. GLU and TRH were ejected by pressure (20-30 psi) in 1-10 nl vol. from multibarreled micropipettes and intraluminal pressure in the gastric corpus was measured using a manometric catheter placed into the stomach through the pylorus of urethane-chloralose anesthetized rats. Gastric motor activity was monitored while micropipettes were advanced from the surface of the dorsomedial medulla to a depth of 1 mm in 100 micron increments. Microinjections of GLU (1-10 pmol) at depths of 200-600 microns below the surface of the brainstem caused a decrease in tonic intraluminal pressure and amplitude of phasic contractions of the gastric corpus. Injection of TRH (1-10 pmol) at depths of 200-800 microns increased both tonic intraluminal pressure and amplitude of phasic contractions. The responses to GLU (10 pmol) and TRH (10 pmol) were abolished by hexamethonium and vagotomy; atropine abolished the effect of TRH and attenuated that of GLU. It is concluded that GLU evokes only vagally mediated inhibitory effects on tonic and phasic gastric motor activity when microinjected into the DVC. In contrast, injection of TRH at the same loci causes only vagal cholinergic increases in motor activity. Subpopulations of neurons in the DVC may, therefore, be activated by specific neurotransmitters having opposite effects on gastric motor activity.

Cholecystokinin octapeptide (CCK8) given i.v. or i.p. produces a variety of behavioural and CNS effects; these actions are probably exerted at a peripheral site but the neuronal pathways involved are uncertain. We show here that i.v. CCK8 acts on neurones in the n. tractus solitarius with an input from the stomach; cells are either excited or depressed by CCK8 and gastric distension, and responses to the two stimuli are always in the same direction. The responses to close arterial injection of CCK8 indicate a site of action within the splanchnic bed, and most probably a direct action on the vagal afferents mediating gastric mechanoreceptor discharge.