AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 1 48-R56, Copyright © 1995 by American Physiological Society
Cardiovascular effects of serotonin in the nucleus of the solitary tract
P. D. Feldman and F. J. Galiano
Department of Pharmacology and Experimental Therapeutics, Louisiana State University Medical Center, New Orleans 70112-1393, USA.
The cardiovascular regulatory role of serotonin [5-hydroxytryptamine
(5-HT)] in the solitary tract nucleus (NTS) was investigated in
urethan-anesthetized Wistar rats. Unilateral microinjection of 5-HT (5 nmol
in 50 nl) into the NTS evoked depressions of both arterial pressure (-20
+/- 1 mmHg) and heart rate (-43 +/- 6 beats/min). Induction of bradycardia
and hypotension was repeatable and consistently obtained with injections
into the NTS but not into neighboring structures. Microinjection of the
nonselective 5-HT receptor antagonist methiothepin or the 5-HT1A/5-HT1B
antagonist pindolol prevented any cardiovascular change by subsequent
microinjection of 5-HT into the NTS. In contrast, microinjection of the
5-HT2-selective antagonist ketanserin or the 5-HT1A antagonist spiroxatrine
had no effect on the subsequent effects of 5-HT. Bilateral vagal
denervation prevented the bradycardia induced by 5-HT, whereas the
vasodepression remained intact. These data provide evidence that 5-HT in
the NTS evokes vagal chronotropic cardioinhibition and sympathetic
withdrawal and suggest that this action is mediated by 5-HT1 serotonergic
receptors, possibly of the 5-HT1B subtype.
