Abstract
Previous reports have described that glutamate ionotropic receptors in the nucleus tractus solitarius (NTS) are involved in the reflex control of heart rate, and that such a control can be inhibited by NTS-5-HT 3 receptor stimulation. In the present study, we examined in urethane anaesthetized rats the effects of intra-NTS microinjection of 1-( m-chlorophenyl)-biguanide (CPBG), a potent and selective 5-HT 3 receptor agonist, on the cardiovascular responses 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 cardiovascular responses to intra-NTS microinjections of AMPA or kainic acid. The reduction by CPBG of the NMDA-evoked cardiac response was blocked by prior intra-NTS microinjection of granisetron, a 5-HT 3 receptor antagonist, as well as bicuculline, a GABA A receptor antagonist. These results suggest that the stimulation of NTS 5-HT 3 receptors specifically reduces, via a GABA-dependent mechanism, the cardiac response to local NMDA administration.
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