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 Al area, after identifying the cells by antidromically activat ing them from the region of the supraoptic nucleus in urethane-anesthe tized rabbits. We tested the response of these neurons to inputs from abdominal vagal, renal and somatic nerves. Electrical stimulation of t he abdominal vagus nerve activated 64/85 neurons tested (75%), and had no effect on the remaining 25%. Latency was 195 +/- 25 ms, (conductio n velocity 0.7 mx/s1). Stimulation of renal afferents had no effect on the discharge rate of 4 neurons tested. Stimulation of branches of th e sciatic nerve inhibited 7/17 Al area neurons tested, excited 4 and h ad no effect on 6 neurons. Stimulation of the central ear nerve inhibi ted 4/17 neurons tested, excited 6 and had no effect on 7 neurons. Gas tric distension had no effect on 20/24 neurons tested. Lightly touchin g the animals back and legs had no effect on the discharge of 45/49 ne urons tested. Similarly, painful stimuli failed to affect 44/49 neuron s tested. Our results indicate that Al area neurons, with projections to the region of the supraoptic nucleus, receive excitatory inputs fro m the abdominal vagus nerve. The visceral information transmitted to A l cells by these abdominal vagal afferents is not yet determined, but acute gastric distention does not appear to be a physiological stimulu s. Al area neurons seem not to be involved in transmitting somatic inf ormation to the hypothalamus.