Non-NMDA receptors in the rostral ventrolateral medulla mediate somatosympathetic pressor responses

The role of excitatory amino acid receptors in the rostral ventrolateral medulla (RVLM) in mediating a somatosympathetic pressor response (SPR) was studied. Rats were anesthetized with urethane, bilaterally vagotomized, paralyzed and respirated. Increases in mean arterial pressure were evoked by 10-s trains of electrical stimulation of sciatic nerve afferents before and after bilateral microinjections into the RVLM of the N-methyl-D-aspartic acid (NMDA) receptor antagonist D-2-amino-7-phosphono-heptanoic acid (D-AP7) or the non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX). DNQX reversed or markedly attenuated the SPR. In contrast, the SPR was not significantly altered by blockade of NMDA receptors in the RVLM with D-AP7. However, prior administration of D-AP7 prevented reversal of the SPR by DNQX, while administration of D-AP7 after DNQX partially restored the SPR. These results indicate that pressor responses evoked by electrical stimulation of sciatic nerve afferents require synaptic activation of non-NMDA receptors in the RVLM. A somatic depressor response, revealed after blockade of non-NMDA receptors within the RVLM, may be mediated by activation of NMDA receptors in this region of the brainstem.