Convergence of sensory information from abdominal viscera in the rat brain stem

This study was carried out to establish whether there was convergence of sensory information in the rat brain stem stimulated by physiological activation of gastric mechanoreceptors and hepatic glucoreceptors. Extracellular recordings were made from single neurons in the region of the dorsal vagal nucleus and nucleus of the solitary tract in the medulla. The responses of these neurons to gastric distension, hepatic portal vein perfusion of isotonic D-glucose, and hepatic portal vein infusion of isotonic saline were studied. Fifty-six neurons were studied; it was found that there was no significant difference in the proportion of neurons responding to gastric distension compared with the number responding to either form of hepatic stimulation. In 20 neurons (all 3 types of stimulation were tested on the same neuron), both excitation and inhibition were observed with both forms of visceral stimulation. Of the seven of these neurons that responded to hepatic portal vein infusion, four of them also had an input from gastric mechanoreceptors. Only three of the neurons that responded to hepatic stimulation showed a specific response to hepatic glucose perfusion; in the remainder a component of the response was due to the infusion of the volume itself. The results from these experiments have demonstrated an apparently weak functional synaptic projection carried by hepatic vagal afferents, particularly those responding to changes in portal glucose concentration, which may indicate a rather diffuse and nonspecific sensory system in the liver. These results have also demonstrated the convergence onto neurons in the brain stem of information from gastric and hepatic enteroceptors.(ABSTRACT TRUNCATED AT 250 WORDS)