Cardiovascular afferent and fastigial nucleus inputs to paramedian reticulospinal neurons

In chloralose anesthetized, paralyzed and artificially ventilated cats, the region of the paramedian reticular nucleus (PRN) was systematically explored for single units antidromically activated by electrical stimulation of histologically verified sites in the intermediate gray region of the upper thoracic cord (T2). These antidromically identified units were then tested for their orthodromic responses to electrical stimulation of ipsilateral carotid sinus nerve (CSN) and of pressor sites in the contralateral fastigial nucleus (FN). Sixty-two histologically verified single units, located predominantly in the caudal half of the ventral PRN, were antidromically activated with latencies corresponding to a mean conduction velocity of 36.4 +/- 2.1 m/s. Of these units 25 (40%) were excited orthodromically by stimulation of the CSN and/or FN: 5 to stimulation of the CSN only (mean latency, 18.3 +/- 9.9 ms), 6 to stimulation of the FN only (mean latency, 7 +/- 1.7 ms), and 14 to stimulation of both the CSN and FN (mean latencies, 12.3 +/- 2.9 ms and 8.4 +/- 1 ms, respectively). These data provide electrophysiological evidence for the existence of PRN reticulo-spinal neurons that integrate and relay cardiovascular afferent information from the CSN and FN to spinal autonomic neurons.