Effect of CCK pretreatment on the CCK sensitivity of rat polymodal gastric vagal afferent in vitro.
ABSTRACT To prevent the blood-borne interference and reflex actions via neighboring organs and the central nervous system, the study was conducted in an in vitro isolated stomach-gastric vagus nerve preparation obtained from overnight-fasted, urethan-anesthetized rats. Afferent unit action potentials were recorded from the gastric branch of the vagus nerve. The left gastric artery was catheterized for intra-arterial injection. In vitro we found that 1) 55/70 gastric vagal afferents (GVAs) were polymodal, responding to CCK-8 and mechanical stimuli, 13 were mechanoreceptive, and 2 were CCK-responsive; 2) sequential or randomized intra-arterial injections of CCK-8 (0.1-200 pmol) dose-dependently increased firing rate and reached the peak rate at 100 pmol; 3) the action was suppressed by CCK-A (Devazepide) but not by CCK-B (L-365,260) receptor antagonist; 4) neither antagonist blocked the mechanosensitivity of GVA fibers. These results are consistent with corresponding in vivo well-documented findings. Histological data indicate that the layered structure of the stomach wall was preserved in vitro for 6-8 h. Based on these results, it seems reasonable to use the in vitro preparation for conducting a study that is usually difficult to be performed in vivo. For instance, because there was no blood supply in vitro, the composition of the interstitial fluid, i.e., the ambient nerve terminals, can be better controlled and influenced by intra-arterial injection of a defined solution. Here we report that acutely changing the ambient CCK level by a conditioning stimulus (a preceding intra-arterial injection of increasing doses of CCK-8) reduced the CCK sensitivity of GVA terminals to a subsequent test stimulus (a constant dose of CCK-8 intra-arterial injection).
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ABSTRACT: Noxious stimuli inhibit inflammation by activating neuroendocrine stress axes, an effect that is potently attenuated by ongoing activity in subdiaphragmatic vagal afferents. Because this vagal afferent activity is carried in the coeliac and coeliac accessory branches of the subdiaphragmatic vagus, we tested the hypothesis that the activity arises from vagal afferents that innervate a proximal segment of the gastrointestinal tract. Surgical removal of the duodenum, but not the stomach, produces a marked (six orders of magnitude) leftward shift in the dose-response curve for intraplantar capsaicin-induced inhibition of synovial plasma extravasation induced by the potent inflammatory mediator bradykinin, in the knee joint; this is similar in magnitude to the inhibition produced by subdiaphragmatic or by coeliac plus coeliac accessory branch vagotomy. Fasting, to unload mechanically sensitive polymodal afferents in the proximal gastrointestinal tract, produces a similar leftward shift in the dose-response curve for the inhibitory effect of capsaicin, an effect that is reversed by balloon distension in the duodenum in fasted rats, while balloon distension postvagotomy had no effect. These results suggest that activation of mechanically sensitive vagal afferents in the duodenum contributes vagal afferent activity that modulates neuroendocrine control of the inflammatory response.The Journal of Physiology 02/2004; 554(Pt 1):227-35. · 4.38 Impact Factor
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ABSTRACT: The management of pancreatic pain is a significant clinical problem so understanding of how sensory signals are generated in pancreatic tissue is fundamental. We aimed to characterize mechanosensitive and chemosensitive properties of pancreatic spinal and vagal afferents in vitro. Spinal and vagal afferent preparations from Sprague-Dawley rats were established incorporating the left splanchnic nerve or vagus nerves respectively. The common bile duct was cannulated for distension of the pancreatic duct with fluid. Nerve discharge evoked by blunt probing, duct distension or electrical stimulation was obtained from teased nerve bundles using standard extra-cellular recording. Discharge from 197 spinal afferent bundles was recorded, of which 57% displayed spontaneous activity. Blunt probing revealed 61 mechanosensitive receptive fields which were associated primarily with arteries/blood vessels (33/61) and the parenchyma (22/61). All mechanosensitive responses were slowly adapting, with 33% continuing to discharge after termination of the stimulus and 60% displaying a response threshold <10 g. Application of chemical mediators (bradykinin, histamine, 5-hydroxytryptamine, cholecystokinin octapeptide) evoked a response from 31/57 units, with 33% excitatory and 23% inhibitory. Spontaneous discharge was recorded from 72% of 135 vagal bundles. Mechanosensitive receptive fields were not identified in the pancreas but were evident in adjacent organs. No spinal or vagal afferent response to duct distension was obtained. In conclusion, pancreatic mechanosensitive spinal afferents are common, in contrast to pancreatic mechanosensitive vagal afferents indicating that pancreatic sensory innervation is predominantly spinal. Chemosensitive spinal afferent nerve endings are present in the pancreas and respond to a variety of inflammatory and physiological mediators.Neurogastroenterology and Motility 06/2008; 20(9):1060-9. · 2.94 Impact Factor
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ABSTRACT: Glucosensing nodose ganglia neurons mediate the effects of hyperglycemia on gastrointestinal motility. We hypothesized that the glucose-sensing mechanisms in the nodose ganglia are similar to those of hypothalamic glucose excited neurons, which sense glucose through glycolysis. Glucose metabolism leads to ATP-sensitive potassium channel (K(ATP)) channel closure and membrane depolarization. We identified glucosensing elements in the form of glucose transporters (GLUTs), glucokinase (GK), and K(ATP) channels in rat nodose ganglia and evaluated their physiological significance. In vitro stomach-vagus nerve preparations demonstrated the gastric vagal afferent response to elevated glucose. Western blots and RT-PCR revealed the presence of GLUT1, GLUT3, GLUT4, GK, and Kir6.2 in nodose ganglia neurons and gastric branches of the vagus nerve. Immunocytochemistry confirmed the expression of GLUT3, GK, and Kir6.2 in nodose ganglia neurons (46.3 ± 3%). Patch-clamp studies detected glucose excitation in 30% (25 of 83) of gastric-projecting nodose ganglia neurons, which was abolished by GLUT3 or GK short hairpin RNA transfections. Silencing GLUT1 or GLUT4 in nodose ganglia neurons did not prevent the excitatory response to glucose. Elevated glucose elicited a response from 43% of in vitro nerve preparations. A dose-dependent response was observed, reaching maximum at a glucose level of 250 mg/dl. The gastric vagal afferent responses to glucose were inhibited by diazoxide, a K(ATP) channel opener. In conclusion, a subset of neurons in the nodose ganglia and gastric vagal afferents are glucoresponsive. Glucosensing requires a GLUT, GK, and K(ATP) channels. These elements are transported axonally to the gastric vagal afferents, which can be activated by elevated glucose through modulation of K(ATP) channels.Endocrinology 12/2012; · 4.72 Impact Factor