Gastric-vagal solitary neurons excited by paraventricular nucleus microstimulation.

Electrophysiological studies were performed to determine whether neurons of the nucleus of the solitary tract (NST) which receive sensory input from the stomach via vagal afferents are activated by microstimulation of the medial parvocellular division of the paraventricular nucleus of the hypothalamus (PVHmp). We found that 37% of the NST neurons orthodromically activated by gastric vagal nerve stimulation are also orthodromically excited by PVHmp microstimulation. Not only do these NST neurons receive convergent input from the PVHmp as well as gastric afferent input (vagal), but this input from the PVHmp may also bias the responsiveness of these NST neurons to incoming afferent information. This PVHmp influence on NST excitability is probably mediated by a direct, monosynaptic projection between these two nuclei. These data support the hypothesis that neurons in the PVHmp can control gastric function by altering the sensitivity of neurons which form the sensory limb of gastric vago-vagal reflexes. This ability of the PVHmp to bias the responsiveness of NST neurons to incoming vagal afferent information is probably mediated by a direct, monosynaptic projection between these two nuclei.