Glutamatergic systems in the bed nucleus of the stria terminalis, effects on cardiovascular system.

The bed nucleus of the stria terminalis (BST) is a part of the limbic system. Two studies have shown that microinjection of L: -glutamate in the BST elicited cardiovascular depressive and bradycardic responses, but in one study, both pressor and depressor responses were observed in the chemical stimulation of BST by glutamate in the urethane-anesthetized rats. Also, the roles of glutamate receptor subtypes have not been investigated yet. The aim of this study was to find the effects of glutamate and its receptors on the blood pressure and heart rate in the BST of urethane-anesthetized rats. The drugs (50 nl) were microinjected into the BST of anaesthetized rats. The blood pressure and heart rate were recorded throughout each experiment. The average changes in the mean arterial pressure and heart rate at different intervals were compared both within each case group and between the case and the control groups, using repeated measures ANOVA. Microinjection of L: -glutamate (0.25 M) into the BST resulted in the decrease of the mean arterial pressure (-18.85 +/- 3.84 mmHg) and heart rate (-18 +/- 4 beats/min). Injection of AP5, antagonist of glutamate NMDA receptor (2.5 , 5 mM) and CNQX, antagonist of glutamate AMPA receptor (0.5, 1 mM) had no significant effect on the mean arterial pressure and heart rate. Either Ap5 or CNQX, when co-injected with glutamate, abolished the depressor and bradycardic effects of glutamate, suggesting that simultaneous activation of both glutamate receptors is necessary for the effect of glutamate system to emerge.