Injection of l-glutamate into medial prefrontal cortex induces cardiovascular responses through NMDA receptor – nitric oxide in rat

We have reported that l-glutamate (l-glu) microinjections into ventral portion of medial prefrontal cortex (vMPFC) caused tachycardia and blood pressure increase in unanesthetized rats. In the present study, we report the subtype of vMPFC glutamatergic receptor mediating the response as well as the possible involvement of nitric oxide (NO) in these cardiovascular responses. Microinjection of 200 nL of l-glu (81 nmol) into the vMPFC of unanesthetized rats caused long-lasting pressor and tachycardic responses which were abolished by pretreatment with 4 nmol of the specific NMDA receptor antagonist AP7. The response was not affected by 4 nmol of the non-NMDA receptor antagonist NBQX. Local pretreatment with 80 nmol of the unspecific nitric oxide synthase (NOS) inhibitor NG-nitro-l-arginine methyl ester (l-NAME) or 0.08 nmol of the specific neuronal NOS (nNOS) inhibitor Nω-Propyl-l-arginine (N-Propyl) blocked l-glu effects. Microinjection of the NO donor sodium nitroprusside (SNP: 3, 9, 27 or 81 nmol) in the vMPFC caused dose-related long-lasting pressor and tachycardic responses in unanesthetized rats, which were similar to those caused by l-glu. These results suggest that cardiovascular responses evoked by local injection of l-glu into the vMPFC of unanesthetized rats are caused by activation of a local NMDA receptor–NO pathway.