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 and in the reflex regulation of blood pressure. In this study responses of RVLM "cardiovascular" neurons to somatic and visceral afferent stimulation were investigated. The activity of 34 RVLM neurons was recorded in urethan-anesthetized paralyzed and artificially ventilated rats. These neurons were identified as cardiovascular based on their baroreceptor 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 tested (64%), not affecting the remaining 8 units. Stimulation of splenic nerves inhibited the discharge of 7 of 12 RVLM neurons tested (58%), whereas the remaining 5 units were not affected. All RVLM units responsive to visceral afferent stimulation were also responsive to sciatic nerve stimulation. These results indicate that RVLM cardiovascular neurons receive somatic and visceral inputs, suggesting an involvement of these units in the integration of homeostatic responses to changes in the internal and external environment.