ACTION OF ENDOTHELIN-1 ON VASOMOTOR NEURONS IN RAT ROSTRAL VENTROLATERAL MEDULLA

Intracisternal administration of endothelin-1 (ET-1) elicits sympathet ically mediated cardiovascular responses by acting on the ventral surf ace of the medulla oblongata (VSM) subjacent to the rostral ventrolate ral medulla (RVLM). We examined, in urethane-anesthetized rats, whethe r intracisternal ET-I affected activity of vasomotor neurons (VMNs) in the RVLM, by acting either directly on the VMNs or indirectly via the VSM. VMNs were identified electrophysiologically. Intracisternal admi nistration of ET-1 altered activity of all the 13 VMNs tested. At a do se of 0.1 pmol, ET-1 invariably caused transient excitation-in six VMN s examined, whereas at a dose of 1 pmol in separate experiments all th e seven VMNs tested were inhibited with (n = 6) or without (n = 1) pre ceding excitation. Similarly, topical application of ET-1 (0.1-1 pmol) to the VSM caused inhibition with (n = 3) or without (n = 2) precedin g excitation in all the five VMNs tested. Direct iontophoretic applica tion of ET-1 to the VMNs caused excitation in four of seven VMNs exami ned but did not affect the other three neurons. These results support the view that intracisternally administered ET-I alters activity of VM Ns in the RVLM, by acting directly on neurons themselves and indirectl y via the VSM.