AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 2 405-R409, Copyright © 1989 by American Physiological Society
Baroreceptor activation or glutamate coinjection facilitates depressor responses to ANF microinjection into NTS
D. J. McKitrick and F. R. Calaresu
Department of Physiology, University of Western Ontario, London, Canada.
As microinjection of atrial natriuretic factor (ANF) into the nucleus of
the solitary tract (NTS) has been shown to elicit depressor responses [D.
J. McKitrick and F. R. Calaresu. Am. J. Physiol. 255 (Regulatory
Integrative Comp. Physiol. 24): R182-R187, 1988], we investigated the
possibility that these responses might be facilitated either by electrical
stimulation of arterial baroreceptor fibers in the aortic depressor nerve
(ADN) or by simultaneous microinjection of L-glutamate (Glu) into the same
sites in the NTS. Male Wistar rats (n = 51) were anesthetized with urethan
(1.4 g/kg ip), artificially ventilated, and the dorsal medulla was exposed.
The ADN was isolated, cut distally, and the central end was placed on
bipolar stimulating electrodes. Threshold doses of 10(-7) M ANF
microinjected into the NTS were combined with threshold electrical
stimulation of the ADN (n = 37) or threshold doses of 0.13-0.5 M Glu (n =
14) microinjected into the NTS. There was a significant interaction between
ANF microinjection and ADN stimulation in producing changes in mean
arterial pressure (MAP) and heart rate [HR; P less than 0.05; -20.2 +/- 2.3
(SE) mmHg and -30.8 +/- 6.9 (SE) beats/min, respectively; n = 18]. There
was also a significant interaction between ANF and Glu in producing changes
in MAP and HR [P less than 0.05; -16.3 +/- 1.8 (SE) mmHg and -15.0 +/- 3.0
(SE) beats/min, respectively; n = 8]. These results indicate that ANF
influences neurons in the NTS, which are also influenced by activation of
arterial baroreceptors, and ANF and Glu interact in the NTS to produce
facilitated cardiovascular responses.
