Lateral hypothalamic and peripheral cardiovascular afferent inputs to ventrolateral medullary neurons

Experiments were done in chloralose anesthetized, paralyzed and artificially ventilated cats to identify single units in ventrolateral medulla (VLM) projecting directly to the intermediate gray (IG) region of the upper thoracic cord and responding to inputs from pressor sites in the anterior lateral hypothalamus (Hla) and carotid sinus (CSN) and aortic depressor (ADN) nerves. Forty-eight units were antidromically activated in VLM to stimulation of the IG at the level of T2. Of these 48 units, 15 (31%) were orthodromically excited by stimulation of the Hla with a mean latency of 15.8 +/- 2.1 ms. In addition, 8 of the 15 units responding to Hla stimulation were also excited orthodromically by stimulation of either the CSN or ADN or both. Of the remaining 33 units, 15 responded to stimulation of only the buffer nerves and 18 were unresponsive to the tested inputs. These results provide electrophysiological evidence for the existence of neurons in VLM which receive hypothalamic and buffer nerve inputs and suggest that the VLM plays a role in integrating and relaying cardiovascular afferent information from peripheral baroreceptors and chemoreceptors and from supramedullary centers to provide effector signals to spinal autonomic neurons involved in the control of the circulation.