Sf. Morrison, RAPHE PALLIDUS EXCITES A UNIQUE CLASS OF SYMPATHETIC PREGANGLIONIC NEURONS, The American journal of physiology, 265(1), 1993, pp. 180000082-180000089
The responses of splanchnic sympathetic preganglionic neurons (SPNs) t
o stimulation in raphe pallidus and in rostral ventrolateral medulla (
RVLM) were compared to determine the basis for the excitatory response
s evoked in the whole splanchnic preganglionic nerve bundle. Most (88%
) of the SPNs with a short-latency (32 ms) excitatory response to RVLM
stimulation were unaffected by raphe pallidus stimulation, although 1
2% were excited at a long latency (123 ms). Each of the SPNs with long
-latency (114 ms) excitatory responses to RVLM stimulation was also ex
cited by raphe pallidus stimulation at latencies (106 ms) that were 7
ms (P < 0.01) shorter than those evoked from the RVLM. Antidromic acti
vation of raphe pallidus neurons from both the T8 intermediolateral nu
cleus (98 ms) and from the RVLM (18 ms) indicated that their spinally
projecting axons emit collaterals (mean conduction time: 12 ms) into t
he ventrolateral medulla. In conclusion, the short-latency (70 ms) spl
anchnic nerve excitation evoked by RVLM stimulation is mediated primar
ily by SPNs that do not respond to raphe pallidus stimulation. Similar
ly, the long-latency (162 ms) splanchnic excitation evoked from the ra
phe pallidus is mediated primarily by SPNs that do not respond to the
rapidly conducting sympathoexcitatory pathway from the RVLM. The long-
latency (169 ms), RVLM stimulus-evoked excitation of the splanchnic ne
rve may arise from action potentials conducted on the axonal branches
of raphe spinal neurons.