CLASSIFICATION OF CAUDAL VENTROLATERAL PONTINE NEURONS WITH SYMPATHETIC NERVE-RELATED ACTIVITY

This study was designed to answer three questions concerning caudal ve ntrolateral pontine (CVLP) neurons whose naturally occurring discharge s are correlated to sympathetic nerve discharge (SND). 1) what are the proportions of CVLP neurons that have activity correlated to both the cardiac-related and 10-Hz rhythms in SND, to only the 10-Hz rhythm, a nd to only the cardiac-related rhythm? 2) Do CVLP neurons with activit y correlated to the cardiac-related and/or IO-Hz rhythm in SND subserv e a sympathoexcitatory or sympathoinhibitory function? 3) Do CVLP neur ons with activity correlated to the cardiac-related and/or 10-Hz rhyth m in SND project to the thoracic spinal cord? To address these issues we recorded from 476 CVLP neurons in 24 urethan-anesthetized cats. Spi ke-triggered averaging, arterial pulse-triggered analysis, and coheren ce analysis revealed that the discharges of 66 of these neurons were c orrelated to inferior cardiac postganglionic SND. For 39 of these neur ons, we were able to determine whether their discharges were correlate d to one or both rhythms. The results showed that the CVLP contained a heterogeneous population of neurons with sympathetic nerve-related ac tivity. The discharges of 21 neurons were correlated to both the 10-Hz and cardiac-related rhythms in SND, 9 neurons had activity correlated to only the 10-Hz rhythm, and 9 neurons had activity correlated to on ly the cardiac-related rhythm. The firing rates of CVLP neurons with a ctivity correlated to both rhythms or to only the 10-Hz rhythm were de creased during the inhibition of SND induced by baroreceptor reflex ac tivation (rapid obstruction of the abdominal aorta). These neurons are presumed to exert sympathoexcitatory actions. The time-controlled col lision test verified that 11 of 12 CVLP neurons with activity correlat ed to both rhythms were antidromically activated by stimulation of the first thoracic segment of the spinal cord. Antidromic mapping at this level showed that the site requiring the least stimulus current to el icit the longest latency response (nearest the terminal) was in the vi cinity of the intermediolateral nucleus (IML). In contrast, only 1 of 13 CVLP neurons with activity correlated to only one of the rhythms in SND could be antidromically activated by spinal stimulation. These da ta demonstrate for the first time that there is a direct pathway from the CVLP to the IML that is comprised almost exclusively of sympathoex citatory neurons whose discharges are correlated to both the 10-Hz and cardiac-related rhythms in SND.