Hypothalamic stimulation counteracts sympathetically mediated gastrointestinal inhibition in chloralose-anaesthetised cats

The inhibitory motor effect of the sympathetic gastrointestino-gastrointestinal (GI-GI) reflex was studied in cats with isolated innervated ileal (Thiry-Vella) loops. They were subjected to acute experiments under chloralose-gallamine anaesthesia where gastric volume, arterial blood pressure and heart rate were continuously monitored. The cervical vagi were sectioned and used for efferent stimulation. The hypothalamus was systematically explored by means of stereotaxically guided electrodes. When the abdomen was undisturbed, gastric contractile responses to central stimulation were virtually absent, regardless of whether a vagally induced tone was present or not. Distension of the isolated intestinal loop induced marked inhibition of vagally induced gastric tone, indicating activation of the GI-GI reflex. Under these conditions, about 17% of the hypothalamic points induced gastric excitation, due to withdrawal of sympathetic tone. The GI-GI reflex can thus be inhibited from diencephalic levels. This inhibition is not linked to any distinct cardiovascular 'pattern'.