Cardiovascular afferent inputs to neurons in the ventrolateral medulla projecting directly to the central autonomic area of the thoracic cord in the cat.

Experiments were done in chloralosed, paralyzed and artificially ventilated cats to identify single units in the ventrolateral medulla (VLM) projecting directly to the central autonomic area of the thoracic cord (CA) and responding to peripheral and central inputs carrying cardiovascular information. Forty-three single units were antidromically activated in the VLM to stimulation of either ipsilateral or contralateral CA with latencies corresponding to conduction velocities of 27.5 +/- 2.0 m/s. Of these 43 units, only 14 (33%) responded orthodromically to stimulation of either the carotid sinus nerve (CSN) or of pressor sites in the paraventricular nucleus of the hypothalamus (PVH) or both. These experiments have demonstrated a bilateral projection of VLM neurons to the CA and have provided evidence for their role in integrating and mediating cardiovascular information from the CSN and PVH directly to spinal sympathetic centers.