Sympathetic-related activity of brain stem neurons in baroreceptor-denervated cats

A search was initiated in baroreceptor-denervated cats for brain stem neurons with activity patterns related to inferior cardiac sympathetic nerve discharge (SND). Neurons whose spontaneous discharges were followed by increases or decreases in SND fell into two categories. S unit discharges were related to SND but not electroencephalogram (EEG) activity. The activity of SE units was related to SND and EEG activity. The anatomic distribution of S and SE units was similar to that previously reported [Barman and Gebber, Am J. Physiol. 240 (Regulatory Integrative Comp. Physiol. 9): R335-R347, 1981] for units with activity patterns related to SND in baroreceptor-innervated cats. Autocorrelograms of S unit discharges and SND contained the same rhythm (2-6 cycles/s). This rhythm was different from that contained in SE unit discharges and EEG activity in experiments in which SND and cortical activity were not related. In other experiments, sympathetic nerve and cortical rhythms were locked to each other. SE units but no S neurons were located in these cats, and the rhythm contained within the autocorrelograms of their discharges was the same as that observed in SND and EEG activity. A model of brain stem networks, which govern the discharges of sympathetic nerve, is presented on the basis of these data.