Plasma ghrelin and pancreatic polypeptide concentrations increase with sham feeding. This suggests a vagal efferent pathway mediating ghrelin release. In contrast to pancreatic polypeptide which rises with actual meal ingestion, ghrelin levels did not change.

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The aims of these experiments were to determine in vitro whether colonic distension releases acetylcholine, vasoactive intestinal polypeptide (VIP), and substance P in the guinea pig inferior mesenteric ganglia (IMG) and whether cholinergic and peptidergic mechanosensory nerves projecting from the colon to the IMG receive cholinergic input from other enteric neurons. Colonic distension significantly increased the release of [3H]-acetylcholine, VIP-like immunoreactivity, and substance P-like immunoreactivity in the IMG. Nicotinic receptor blockade in the colon diminished the increase in [3H]acetylcholine release, abolished the increase in VIP-like immunoreactivity release during distension, but had no effect on the release of substance P-like immunoreactivity. Nicotinic receptor blockade in the colon also decreased fast mechanosensory input and significantly reduced by 54% the slow excitatory postsynaptic potential amplitude evoked by colonic distension. The data suggest that enteric cholinergic and VIP mechanosensory neurons that project from the colon to sympathetic neurons in the IMG receive peripheral cholinergic input from other enteric neurons. There was no evidence for enteric cholinergic input to the mechanosensory substance P pathway.

Fluoxetine affects gastric contractility with regional variability - contracting the fundus more than the antrum or pylorus. The fluoxetine contractile effect is reduced by tetrodotoxin, atropine, phentolamine, and a 5-HT(4) receptor antagonist. These results suggest fluoxetine interacts with muscarinic, alpha-adrenergic, and serotoninergic receptors and/or ongoing reuptake/release of serotonin in the stomach.

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SUMMARY1. GABA receptor-modulating drugs and intracellular recording techniques were used to determine the functional significance of peripheral afferent GABA-containing nerves projecting from the distal colon to sympathetic neurones in the inferior mesenteric ganglion of the guinea-pig.2. GABAA receptor-modulating drugs added selectively to the inferior mesenteric ganglion side of a two-compartment bath had pronounced effects on on-going colonic afferent cholinergic synaptic input. Bicuculline (20 1uM) decreased the amplitude and frequency of fast excitatory postsynaptic potentials (EPSPs) by 40% whereas diazepam (5 ,M) increased cholinergic input by 43 %. Neither drug had any effect on the resting membrane potential or membrane input resistance of ganglion cells.3. Bicuculline (20 /2M) significantly reduced, whereas diazepam (5 /tM) significantly enhanced, distension-induced increases in nicotinic fast EPSPs and action potentials.4. Slow EPSPs evoked by colonic distension were not affected by bicuculline or diazepam.5. Manual voltage clamp of the postsynaptic depolarizing response to exogenous GABA revealed GABA-induced presynaptic facilitation of colonic afferent but not central preganglionic efferent cholinergic synaptic input.6. The data suggest that endogenously released GABA participates in on-going colo-colonic reflex activity by acting on presynaptic GABAA receptors to facilitate release of acetylcholine from colonic mechanosensory nerves.

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