AREA POSTREMA EXCITES AND INHIBITS SYMPATHETIC-RELATED NEURONS IN ROSTRAL VENTROLATERAL MEDULLA IN RABBIT

This study investigated the effects of area postrema stimulation on the activity of cardiovascular-related neurons in the rostral ventrolateral medulla and determined whether the effects were mediated by cell bodies. Results are based on recordings of extracellular spikes from 113 neurons in 37 alpha-chloralose- or pentobarbital sodium-anesthetized rabbits. Single sequential stimuli evoked an excitation (onset, 22 +/- 8 ms; duration, 20 +/- 14 ms) followed by an inhibition (onset, 53 +/- 21 ms; duration, 127 +/- 82 ms) in 1) 58 neurons with discharge patterns that were correlated with sympathetic nerve activity (determined by spike-triggered averaging) and with the cardiac cycle (determined by post-R wave-triggered histograms) and that were inhibited by increasing arterial pressure and 2) 27 neurons that exhibited a cardiac rhythm but not a sympathetic rhythm. Area postrema-evoked excitation and inhibition were markedly attenuated by kainic acid injections in area postrema, suggesting that both inputs were derived from cell bodies. The results suggest that area postrema neurons may modulate the activity of medullary neurons in the baroreflex-sympathetic are as well. as neurons in other networks that share baroreceptor input but may not be related to sympathetic nerve activity.