AJP - Regulatory, Integrative and Comparative Physiology, Vol 250, Issue 6 1065-R1073, Copyright © 1986 by American Physiological Society
Lack of involvement of GABA in baroreceptor-mediated sympathoinhibition
R. B. McCall
The purpose of the present investigation was to determine if
gamma-aminobutyric acid (GABA) mediates the baroreceptor-induced inhibition
of sympathetic nerve discharge (SND) in dialurethan-anesthetized cats. The
GABA antagonists picrotoxin and bicuculline produced marked elevations in
arterial blood pressure and inferior cardiac SND. The inhibition of SND
observed during pressor responses was occasionally slightly depressed after
picrotoxin or bicuculline. Midcollicullar transection blocked or reversed
the increase in blood pressure and SND produced by GABA antagonists. Under
these conditions, baroreceptor inhibition of SND was not affected by
picrotoxin. Microinjections of picrotoxin into the rostral ventrolateral
medulla produced increases in arterial blood pressure and SND but failed to
affect baroreceptor-induced sympathoinhibition. GABA antagonists given
intravenously also failed to affect the baroreceptor-induced inhibition of
sympathetically related neurons recorded in the rostral ventrolateral
medulla. However, intravenous picrotoxin did antagonize the inhibitory
affect of microiontophoretically applied GABA on these neurons. These data
provide no evidence to support the contention that GABA mediates the
baroreceptor-induced inhibition of SND. The role of GABA in regulating SND
is discussed.
