Abstract: (14235 Views)
Introduction: We previously shown that microinjection of glutamate into the hDB of rat
elicited cardiovascular depressive responses. Microinjection of AP5 (an NMDA receptor
antagonist, 2.5 mM, 50 nl) and CNQX (an AMPA receptor antagonist, 1 mM, 50 nl) caused
no significant changes in the blood pressure and heart rate. Microinjection of bicuculline
(BMI: a GABAA receptor antagonist, 1 mM, 50 nl) resulted in the increased blood pressure
and heart rate. In this study we investigated the possible interaction of GABAergic and
glutaminergic systems by coinjection of the antagonists of both systems.
Methods: Experiments were performed on 27 urethane anesthetized rats. Drugs were
microinjected into the hDB using micropipettes. The arterial pressure and heart rate were
continuously recorded and repeated measures ANOVA was used for data analysis.
Results: Our results showed that coinjection of 50 nl of BMI (1mM ) and AP5 (2.5 mM)
significantly (P < 0. 01) decreased the presser effects of BMI. Also, coinjection of 50 nl of
BMI (1 mM) and CNQX (1 mM) significantly (P < 0.01) decreased the presser effects of
BMI. Microinjection of the doses of BMI and two glutamate receptor antagonists produced
the same results.
Conclusion: These findings suggest that the cardiovascular effects of the blockade of
GABAergic system depend on the activation of local NMDA and AMPA receptors. A
possible explanation for the results is that, GABAergic system tonically inhibits the
glutaminergic neurons.