Glutamate receptors of the A5 region modulate cardiovascular responses evoked from the dorsomedial hypothalamic nucleus and perifornical area.

Abstract

To assess the possible function of glutamate in the interaction between the dorsomedial hypothalamic nucleus-perifornical area (DMH-PeF) and the A5 pontine region (A5), cardiovascular and respiratory changes were studied in response to electrical stimulation of the DMH-PeF (1ms pulses, 30-50μA given at 100Hz for 5s) before and after the microinjection of kynurenic acid (non-specific glutamate receptor antagonist; 50nl, 5nmol), MK-801 (NMDA receptor antagonist; 50nl, 50nmol), CNQX (non-NMDA receptor antagonist; 50nl, 50nmol) or MCPG (metabotropic glutamate receptor antagonist; 50nl, 5nmol) within the A5 region. DMH-PeF electrical stimulation elicited a pressor (p< 0.001) and tachycardic response (p< 0.001) which was accompanied by an inspiratory facilitation characterised by an increase in respiratory rate (p< 0.001) due to a decrease in expiratory time (p< 0.01). Kynurenic acid within the A5 region decreased the tachycardia (p< 0.001) and the intensity of the blood pressure response (p< 0.001) to DMH-PeF stimulation. After the microinjection of MK-801 and CNQX into the A5 region, the magnitude of the tachycardia and the pressor response were decreased (p< 0.05 and p< 0.01; p< 0.001 and p< 0.05, respectively). After MCPG microinjection into the A5 region, a decrease in the tachycardia (p< 0.001) with no changes in the pressor response was observed during DMH-PeF stimulation. The respiratory response elicited by DMH-PeF stimulation was not changed after the microinjection of kynurenic acid, MK-801, CNQX or MCPG within the A5 region. These results suggest that A5 region glutamate receptors play a role in the cardiovascular response elicited from the DMH-PeF. The possible mechanisms involved in these interactions are discussed.