SOMATIC AND VISCERAL INPUTS TO NEURONS OF THE ROSTRAL VENTROLATERAL MEDULLA

Sympathoexcitatory neurons in the rostral ventrolateral medulla (RVLM) play an essential role in the generation of basal sympathetic tone an d in the reflex regulation of blood pressure. In this study responses of RVLM ''cardiovascular'' neurons to somatic and visceral afferent st imulation were investigated. The activity of 34 RVLM neurons was recor ded in urethan-anesthetized paralyzed and artificially ventilated rats . These neurons were identified as cardiovascular based on their baror eceptor sensitivity and their pulse-synchronous discharge. Electrical stimulation of the sciatic nerve excited 31 of the 34 RVLM units (91%) . Renal nerve stimulation inhibited firing of 14 of 22 RVLM neurons te sted (64%), not affecting the remaining 8 units. Stimulation of spleni c nerves inhibited the discharge of 7 of 12 RVLM neurons tested (58%), whereas the remaining 5 units were not affected. All RVLM units respo nsive to visceral afferent stimulation were also responsive to sciatic nerve stimulation. These results indicate that RVLM cardiovascular ne urons receive somatic and visceral inputs, suggesting an involvement o f these units in the integration of homeostatic responses to changes i n the internal and external environment.