Interactions of gastric vagal and peripheral nerves on single neurons of lateral hypothalamus in the cat.

Extracellularly recorded unitary responses in the lateral hypothalamus were evaluated in anesthetized cats during electrical stimulation of the gastric branches of the ventral and dorsal vagal trunks, the T9 intercostal nerve, and the common peroneal nerve (L6-S2). These nerves were stimulated with single or paired (10-ms interval) pulses of 300-500 microA for 0.3 ms at a frequency of 0.5 Hz. The latency of the evoked lateral hypothalamic responses after stimulation of the gastric vagal branches (373 +/- 39.8 ms; means +/- SD) was significantly longer than the latencies after intercostal nerve (62 +/- 17.0 ms) or common peroneal nerve (109 +/- 29.3 ms) stimulation. Convergence of gastric vagal input from the proximal stomach and peripheral nerves (PNs) on single neurons in the lateral hypothalamus was observed. Ninety-two percent of the lateral hypothalamic neurons tested that responded to gastric vagal stimulation also received inputs from the T9 intercostal nerve. Seventy-seven percent of the lateral hypothalamic gastric vagally evoked unitary responses received convergent inputs from the intercostal nerve and the common peroneal nerve. A condition-test paradigm was applied to determine the time course of convergent gastric and PN input on single lateral hypothalamic neurons. The test revealed that stimulation of the T9 intercostal nerve had a more pronounced effect than common peroneal nerve stimulation on the lateral hypothalamic neurons that receive gastric vagal input. The results demonstrated that gastric vagal afferent and PN inputs converge onto single lateral hypothalamic neurons and suggested that the central processing of visceral input from the stomach can be substantially affected by peripheral nerve stimulation.