NON-NMDA RECEPTORS IN THE ROSTRAL VENTROLATERAL MEDULLA MEDIATE SOMATOSYMPATHETIC PRESSOR-RESPONSES

The role of excitatory amino acid receptors in the rostral ventrolater al medulla (RVLM) in mediating a somatosympathetic pressor response (S PR) was studied. Rats were anesthetized with urethane, bilaterally vag otomized, paralyzed and respirated. increases in mean arterial pressur e were evoked by 10-s trains of electrical stimulation of sciatic nerv e afferents before and after bilateral microinjections into the RVLM o f the N-methyl-D-aspartic acid (NMDA) receptor antagonist D-2-amino-7- phosphonoheptanoic acid (D-AP7) or the non-NMDA receptor antagonist 6, 7-dinitroquinoxaline-2,3-dione (DNQX). DNQX reversed or markedly atten uated the SPR. In contrast, the SPR was not significantly altered by b lockade of NMDA receptors in the RVLM with D-AP7. However, prior admin istration of D-AP7 prevented reversal of the SPR by DNQX, while admini stration of D-AP7 after DNQX partially restored the SPR. These results indicate that pressor responses evoked by electrical stimulation of s ciatic nerve afferents require synaptic activation of non-NMDA recepto rs in the RVLM. A somatic depressor response, revealed after blockade of non-NMDA receptors within the RVLM, may be mediated by activation o f NMDA receptors in this region of the brainstem.