Stimulation of the aortic nerve evokes three different response patterns in neurons of the rostral ventrolateral medulla of the rat. Zagon, Aniko, and K. Michael Spyer. Department of Physiology, Royal Free Hospital School of Medicine, Rowland Hill Street, London NW3 2PF, U.K.
APStracts 3:0236R, 1996.
Since the aortic nerve of the rat is believed to contain only barosensory fibers in a functionally significant number, stimulation of this nerve provides a convenient means to identify barosensitive neurons in the CNS (11, 23, 30). The aim of the present study was to describe the characteristics of responses to stimulation of the aortic nerve in ventrolateral medullary neurons using in vivo intracellular recordings. Data were obtained from 25 neurons that were either spontaneously active and exhibited pulse-synchronous discharge or were silent. Cells, that showed a regular increase in their discharge rate during diastole, responded with either an IPSP (group 1; n=3) or a biphasic, EPSP-IPSP (group 2; n=10) to aortic nerve stimulation. Parameters of the inhibitory response were similar in both groups (27 + 2 and 31+ 2 ms onset latency and 55 + 10 and 67 + 7 ms duration, respectively). In group 2 cells the inhibition was, however, preceded by a brief excitation (14 + 2 ms onset latency and 13 + 1 ms duration). Group 3 neurons that showed a regular increase in their discharge rate during or prior to systole (n=7), responded with an EPSP (20 + 2 ms onset latency and 44 + 5 ms average duration). Group 1 and 3 responses were also encountered in quiescent neurons (n=5). Intracellular labelling revealed that neurons of all three types were localized within the rostral ventrolateral medulla oblongata. The functional significance of these findings is discussed. 

Received 19 September 1995; accepted in final form 15 May 1996.
APS Manuscript Number R587-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96