The vagal afferent system is strategically positioned to mediate rapid changes in motility and satiety in response to systemic glucose levels. In the present study we aimed to identify glucose-excited and glucose-inhibited neurons in nodose ganglia and characterize their glucose-sensing properties. Whole-cell patch-clamp recordings in vagal afferent neurons isolated from rat nodose ganglia demonstrated that 31/118 (26%) neurons were depolarized after increasing extracellular glucose from 5 to 15 mm; 19/118 (16%) were hyperpolarized, and 68/118 were non-responsive. A higher incidence of excitatory response to glucose occurred in gastric-than in portal vein-projecting neurons, the latter having a higher incidence of inhibitory response. In glucose-excited neurons, elevated glucose evoked membrane depolarization (11 mV) and an increase in membrane input resistance (361 to 437 M ). Current reversed at −99 mV. In glucose-inhibited neurons, membrane hyperpolarization (−13 mV) was associated with decreased membrane input resistance (383 to 293 M ). Current reversed at −97 mV. Superfusion of tolbutamide, a K ATP channel sulfonylurea receptor blocker, elicited identical glucose-excitatory but not glucose-inhibitory responses. Kir6.2 shRNA transfection abolished glucose-excited but not glucose-inhibited responses. Phosphatidylinositol bisphosphate (PIP 2 ) depletion using wortmannin increased the fraction of glucose-excited neurons from 26% to 80%. These results show that rat nodose ganglia have glucose-excited and glucose-inhibited neurons, differentially distributed among gastric-and portal vein-projecting nodose neurons. In glucose-excited neurons, glucose metabolism leads to K ATP channel closure, triggering membrane depolarization, whereas in glucose-inhibited neurons, the inhibitory effect of elevated glucose is mediated by an ATP-independent K + channel. The results also show that PIP 2 can determine the excitability of glucose-excited neurons.

BACKGROUND AND AIMS: Visceral hypersensitivity is common in patients with irritable bowel syndrome (IBS). We investigated whether inflammatory molecules, such as histamine and proteases, activate prostaglandin-endoperoxide synthase 2 (also called COX2) to increase the synthesis of prostaglandin E 2 (PGE2) by mast cells, which activates the receptor PTGER2 (also called EP2) in the dorsal root ganglia to promote visceral hypersensitivity. METHODS: We used an enzyme-linked immunosorbent assay to measure levels of spontaneous release of molecules from mast cells in colonic mucosa from patients with IBS with diarrhea (IBS-D; 18 women and 5 men; aged 28-60 years), healthy individuals (controls, n ¼ 24), mice, and rats. We measured visceromotor responses to colorectal distension in rodents after intracolonic administration of colon biopsy supernatants, histamine, PGE2, a small interfering RNA against EP2, or an agonist of F2R like trypsin receptor 1 (F2RL1, also called protease-activated receptor 2 [PAR2]). We investigated the role of COX2, produced by mast cells, in mediation of visceral hypersensitivity using mice with the Y385F substitution in Ptgs2 (Ptgs2 Y385F mice), mast celldeficient (W/W V ) mice, and W/W V mice given injections of mast cells derived from wild-type or Ptgs2 Y385F mice. RESULTS: Colon biopsies from patients with IBS-D had increased levels of PGE2, based on enzyme-linked immunosorbent assay, and COX2 messenger RNA and protein, compared with control biopsies. Immunohistochemistry showed that most of the COX2 was in mast cells. Intracolonic infusions of rats with IBS-D biopsy supernatants generated a 3-to 4-fold increase in visceromotor responses to colorectal distension; this was associated with significant increases in PGE2, histamine, and tryptase in the colonic mucosa. These increases were prevented by a mast cell stabilizer, COX2 inhibitor, or knockdown of EP2. Intracolonic administration of supernatants from biopsies of patients with IBS-D failed to induce visceral hypersensitivity or increase the level of PGE2 in W/W V and Ptgs2 Y385F mice. Reconstitution of mast cells in W/W V mice restored the visceral hypersensitivity response. CONCLUSIONS: Abnormal synthesis of PGE2 by colonic mast cells appears to induce visceral hypersensitivity in patients with IBS-D.

1. Whole cell recordings from neurons in the rostral, gustatory nucleus of the solitary tract (rNST) were made using the "blind" patch-clamp technique in horizontal brain stem slices of rats. 2. Postsynaptic potentials (PSP) were elicited in 71 rNST neurons by electrical stimulation of the solitary tract (ST). To investigate PSPs evoked by convergent input from the chorda tympani and glossopharyngeal nerves, the ST was stimulated at levels where these two nerves terminate. These are referred to as rostral (rST) and intermediate (iST) ST, respectively. 3. When the rST was stimulated 72% of the PSPs were depolarizing, and 28% were hyperpolarizing (n = 64). Stimulation of the intermediate ST resulted in 75% depolarizing and 25% hyperpolarizing PSPs (n = 56). 4. Application of gamma-aminobuturic acid-A (GABAA) and glutamate receptor blockers revealed that all PSPs recorded in the present study were a composite of summed excitatory and inhibitory PSPs. Application of the GABAA receptor blocker bicuculline, by eliminating the hyperpolarizing component of a PSP, revealed the excitatory postsynaptic potential (EPSP) component of the potential. Bicuculline also increased the amplitude and prolonged the decay time of the depolarizing potentials once the hyperpolarizing potential component had been eliminated. These pure EPSP revealed by GABAA receptor blockade reversed at approximately 0 mV. 5. Application of glutamate ionotropic receptor blockers effectively eliminated the initiation of the synaptic responses evoked by ST stimulation. If the stimulus strength was increased, an inhibitory postsynaptic potential (IPSP) was elicited, presumably by direct activation of interneurons close to the stimulating electrode. These IPSPs had a mean reversal potential of -88 mV. 6. When synaptic responses were initiated by stimulation of the projection areas of both the chorda tympani and glossopharyngeal nerves, all neurons tested (n = 49) responded to stimulation of both sites on the ST. The resulting synaptic potential was a sum of the two individual synaptic potentials. 7. If stimulation of the rostral and intermediate sites both elicited depolarizing potentials, the potential resulting from stimulation of both sites was the arithmetical sum of the two individual PSPs. The EPSPs summed even if the time between stimulation of the rostral and intermediate sites was separated by < or = 100 ms. 8. Inhibitory PSPs evoked by simultaneous stimulation of the rostral and intermediate ST also summed. The summation was not linear and saturated at a mean level of -66 mV. 9. When the PSP at one stimulation site was excitatory but inhibitory at the other site, the PSP wave form resulting from dual stimulation was a complex mixture of the two individual potentials. The inhibitory potential was capable of blocking action potentials resulting from the excitatory PSP. 10. These results indicate that synaptic responses in rNST are complex mixtures of excitatory and inhibitory potentials. The synaptic potentials result from excitatory afferent input m...

Research has shown that the synergistic interaction between vagal cholecystokinin-A receptors (CCKARs) and leptin receptors (LRbs) mediates short term satiety. We hypothesize that this synergistic interaction is mediated by cross-talk between signaling cascades used by CCKARs and LRbs, which, in turn, activates closure of K ؉ channels, leading to membrane depolar- Leptin, the product of the ob gene, is secreted primarily from white adipocyte tissue; its level in the circulation correlates with the degree of adiposity (1, 2). Circulating leptin crosses the blood-brain barrier via a receptor-mediated transport system (3, 4) and acts on the long form of the leptin receptor (LRb) 2 in the medial hypothalamus to regulate feeding behavior and energy balance (5). Leptin is secreted from several other sites, including the gastric mucosa, brown adipocyte tissue, placenta, mammary gland, ovarian follicles, and brain (5, 6). Leptin mRNA and leptin protein have also been detected in human stomach mucosa (7) and rat gastric fundus (8). Leptin levels in the stomach are altered by nutritional state and by cholecystokinin (CCK) administration. CCK is not, however, a stimulus for leptin release from isolated adipocytes (8). Leptin is the key signaling molecule responsible for long term satiety and energy balance; mutations that cause defective leptin secretion or abnormal leptin receptor signaling result in obesity in ob/ob mice (9, 10) and in humans (11). The leptin receptor belongs to the IL-6 receptor family of class 1 cytokine receptors and mediates the biological effects of leptin via the Janus kinase 2-signal transducer and activator of transcription 3 (JAK2/STAT3) pathway (12-14). Several splice variants of the leptin receptor exist; however, the LRb isoform mediates the leptin effect on satiety (4). CCK is an endogenous peptide found in the gastrointestinal tract and the brain. It is released into the circulation after a meal and acts on neurons both centrally and peripherally (15). The satiety action of CCK appears to be mediated by low affinity CCK-A receptors (CCKARs) on vagal afferent neurons (16). Systemic administration of CCK inhibits food intake in several species, including rats and humans (17), giving credence to the hypothesis that peripheral CCK acts as a satiety signal. CCK cannot penetrate the blood-brain barrier; therefore, systemically administered CCK likely acts at a peripheral site to inhibit feeding (18). In contrast to leptin, the effect of CCK on food intake occurs within 15 min after intraperitoneal administration of CCK-8, suggesting that CCK may act as a meal-related short term satiety signal (19,20).Both CCKARs and LRbs are widely distributed in nodose ganglia (NG) and the vagus nerve (21,22). There is evidence that a synergistic interaction between leptin and CCK leads to the reduction of short term food intake (23)(24)(25). In fact, the satiety action of CCK appears to depend on leptin signaling (26). Currently, the intracellular signaling mechanisms responsible for the synergistic interacti...