Abdominal vagal afferents excite A1 area neurons antidromically activated from the region of the supraoptic nucleus in the rabbit.

We made extracellular recordings from 113 spontaneously active neurons in the A1 area, after identifying the cells by antidromically activating them from the region of the supraoptic nucleus in urethane-anesthetized rabbits. We tested the response of these neurons to inputs from abdominal vagal, renal and somatic nerves. Electrical stimulation of the abdominal vagus nerve activated 64/85 neurons tested (75%), and had no effect on the remaining 25%. Latency was 195 +/- 25 ms, (conduction velocity 0.7 m/s). Stimulation of renal afferents had no effect on the discharge rate of 4 neurons tested. Stimulation of branches of the sciatic nerve inhibited 7/17 A1 area neurons tested, excited 4 and had no effect on 6 neurons. Stimulation of the central ear nerve inhibited 4/17 neurons tested, excited 6 and had no effect on 7 neurons. Gastric distension had no effect on 20/24 neurons tested. Lightly touching the animals back and legs had no effect on the discharge of 45/49 neurons tested. Similarly, painful stimuli failed to affect 44/49 neurons tested. Our results indicate that A1 area neurons, with projections to the region of the supraoptic nucleus, receive excitatory inputs from the abdominal vagus nerve. The visceral information transmitted to A1 cells by these abdominal vagal afferents is not yet determined, but acute gastric distention does not appear to be a physiological stimulus. A1 area neurons seem not to be involved in transmitting somatic information to the hypothalamus.