Glutamate N-methyl-D-aspartate (NMDA) and non-NMDA receptor antagonists administered into the brain stem depress the renal sympathetic reflex discharges evoked by single shock of somatic afferents in anesthetized rats

The involvement of glutamate receptors in the central transmission of somatosympathetic reflexes was studied by examining, in anesthetized rats, the effects of MK-801, an N-methyl-D-aspartate (NMDA) receptor antagonist, and CNQX, a non-NMDA receptor antagonist, on two reflex components, the A- and C-reflexes evoked in the left sympathetic renal nerve by a single shock to the left tibial nerve. The A-reflex elicited by myelinated A fiber stimulation and the C-reflex elicited by unmyelinated C fiber stimulation were depressed, in a dose-dependent manner, following administration of either MK-801 or CNQX into the cisterna magna (i.c.m.). Intrathecal (i.t.) administration of MK-801 did not have any effect on either A- or C-reflexes, while i.t. administration of CNQX had a slight effect on the A-reflex (significantly on the A-reflex only when treated with the highest dose of 100 ng) and the C-reflex. These results indicate that both NMDA and non-NMDA receptors, stimulated by glutamate released possibly as a neurotransmitter, are involved in the central transmission pathways of somatosympathetic reflexes at the level of the brain stem, but not the spinal cord.