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The aim of the present study was to investigate electrophysiologically the effect of systemic cholecystokinin (CCK) on the discharge of vagal gastric mechanoreceptors. Twenty-two single vagal afferent fibers were selected for the investigation of responses to intravenous CCK octapeptide (CCK-8) on the basis of a positive response to gastric distension. Resting discharge in these afferent fibers was 1.3 +/- 0.3 impulses.s-1 and increased to 9.2 +/- 0.9 impulses.s-1 during distension (P < 0.0001), CCK (20-100 pmol iv) caused a gastric relaxation of 2.1 +/- 0.2 cmH2O and inhibition of phasic motility. The discharge of 20/22 of vagal tension receptors closely followed the magnitude and time course of the fall in pressure. Mean discharge before and after CCK (50 pmol) was 7 +/- 0.9 and 3.9 +/- 0.8 impulses.s-1, respectively (P < 0.001, n = 22). Both the pressure response and the concomitant changes in afferent discharge were abolished by L-364,718 (1.2 mg/kg iv). Only two afferent units failed to show a decrease in firing following CCK (50 pmol), and at 500 pmol the discharge of these units was augmented. In conclusion, CCK (50 pmol) has predominantly indirect effects on gastric mechanoreceptors, which decrease their firing in association with gastric relaxation.

This observation supports the hypothesis that, during sleep, the cerebral cortex switches from processing of exteroceptive and proprioceptive information to processing of interoceptive information.

The aim of this study was to map areas within the rat insular cortex from which respiratory responses originate and compare those sites with gastrointestinal control regions. The insular cortex was systematically microstimulated and histological location of responsive sites determined. Increased inspiratory airflow and decreased respiratory cycle duration were considered to be respiratory excitatory responses. The responses were localized in dysgranular and agranular insular cortex at levels caudal to the joining of the anterior commissure. More rostrally, respiratory inhibitory responses were elicited: these were manifested as a decrease in inspiratory airflow without a significant alteration in respiratory cycle duration. Respiratory inhibitory responses were usually accompanied by changes in gastric motility. These results suggest that the respiratory area in the rat insular cortex consist of two distinct zones which overlap a region modulating the gastrointestinal activity.