Bradycardic responses to microinjection of N-methyl-D-aspartate into the nucleus tractus solitarius are inhibited by local activation of 5-HT3 receptors
Lgh. Bonagamba et al., Bradycardic responses to microinjection of N-methyl-D-aspartate into the nucleus tractus solitarius are inhibited by local activation of 5-HT3 receptors, NEUROPHARM, 39(12), 2000, pp. 2336-2345
Previous reports have described that glutamate ionotropic receptors in the
nucleus tractus solitarius (NTS) are involved in the reflex control of hear
t rate, and that such a control can be inhibited by NTS-5-HT3 receptor stim
ulation. In the present study, we examined in urethane anaesthetized rats t
he effects of intra-NTS microinjection of 1-(m-chlorophenyl)-biguanide (CPB
G), a potent and selective 5-HT3 receptor agonist, on the cardiovascular re
sponses to local administration of glutamate ionotropic receptor agonists.
Intra-NTS microinjection of CPBG reduced the atropine-sensitive bradycardia
elicited by local microinjection of NMDA without affecting the cardiovascu
lar responses to intra-NTS microinjections of AMPA or kainic acid. The redu
ction by CPBG of the NMDA-evoked cardiac response was blocked by prior intr
a-NTS microinjection of granisetron, a 5-HT3 receptor antagonist, as well a
s bicuculline, a GABA(A) receptor antagonist. These results suggest that th
e stimulation of NTS 5-HT3 receptors specifically reduces, via a GABA-depen
dent mechanism, the cardiac response to local NMDA administration. (C) 2000
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