Stimulation of serotonin 3 receptors in the nucleus tractus
solitarius inhibits the cardiac bezold-jarisch reflex response.
S[acute]evoz, Caroline, Anne Nosjean, Joao-Carlos Callera, Benedito
Machado, Michel Hamon, and Raul Laguzzi.
INSERM U.288, C.H.U. Piti[acute]e-Salp[circumflex]etri[grave]ere,
75634 Paris Cedex 13, France and Department of Physiology, School of
Medecine of Ribeirao Preto, U.S.P., 14049-900, Ribeirao Preto, Sao
Paulo, Brazil
APStracts 2:0562H, 1995.
Intra-atrial administration of phenylbiguanide has been shown to
trigger, through the stimulation of vagal afferent C-fibers, reflex
bradycardia, hypotension and sympathoinhibition classically known as
the Bezold-Jarisch (B-J) reflex (Krayer, Naunyn-Schmiedeberg's Arch.
Exp. Pathol. Pharmacol. 240: 361-368, 1961). The effects of
microinjections, into the nucleus tractus solitarius (NTS), of 5-HT
and 1-(m-chlorophenyl)-biguanide (CPBG), a potent 5-HT3 receptor
agonist, on these reflex responses were studied in urethane
-anesthetized rats. 5-HT (600, 900 pmol) and CPBG (10-150 pmol)
produced a dose-dependent inhibition of the atropine-sensitive
bradycardiac component of the B-J reflex. The effect of both agonists
was reversed by prior local microinjection of the 5-HT3 receptor
antagonists zacopride (100 pmol) and ondansetron (100 pmol), but not
by that of the 5-HT2 receptor antagonist ketanserin (10 pmol) or the
mixed 5-HT1/5-HT2 receptor antagonist methysergide (100 pmol). In
contrast, CPBG (150 pmol) did not affect the B-J reflex inhibition of
lumbar sympathetic nerve discharge. These results show that
stimulation of NTS 5-HT3 receptors produced an inhibition of the
cardiovagal component of the B-J reflex without affecting its
sympathetic component. Since the stimulation of these receptors also
inhibits the cardiac component of the baroreflex, the present data
suggest the participation of NTS 5-HT3 receptors in the mechanisms
which modulate cardiac reflex responses elicited by messages from
different vagal afferents.
Received 18 April 1995; accepted in final form 7 December 1995.
APS Manuscript Number H370-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 December 95