Hypothalamic unitary responses to gastric vagal input from the proximal stomach

Gastric vagally evoked extracellular unitary responses were recorded in the hypothalamus of anesthetized cats. The evoked unitary responses were localized in the paraventricular dorsomedial region, ventromedial nucleus, and lateral hypothalamus. The mean latency of the gastric vagally evoked hypothalamic neuronal responses in these three areas ranged from 368 +/- 39.8 to 371 +/- 45.2 (SD) ms. The majority (82%) of the gastric vagally evoked hypothalamic responses consisted of one to five spikes, while the remaining 18% were tonically active units. The vagal effect was inhibitory in 78% of the tonically active hypothalamic units responding to gastric vagal input. Convergence of gastric vagal input on single hypothalamic units from afferents in the dorsal and ventral vagal trunks was observed. Units were identified in the hypothalamus that responded to activation of mechanoreceptors in the proximal stomach by an intragastric balloon. This study provided new direct evidence of the density, localization, and characteristics of neuronal processing of gastric vagal input from the proximal stomach in the hypothalamus. The reciprocal connections between these areas of the hypothalamus and nucleus tractus solitarius in the caudal brain stem suggest that the hypothalamus may serve an important role in modulating the input of primary vagal afferent input from the proximal stomach.