NMDA RECEPTOR BLOCKADE IN CAT DORSAL HORN BLUNTS REFLEX PRESSOR-RESPONSE TO MUSCLE-CONTRACTION AND STRETCH

The role of N-methyl-D-aspartate (NMDA) receptors in the reflex presse r response to static muscle contraction and passive stretch was examin ed by microdialyzing the NMDA receptor antagonist DL-2-amino-5-phospho novalerate (AP-5) into the L(7) or L(6) and S-1 levels of the dorsal h orn of anesthetized cats. Contraction, elicited by electrical stimulat ion of the cut L(7) and S-1 ventral roots, increased mean arterial pre ssure (MAP) and heart rate (HR). Passive stretch at tensions similar t o those generated by contraction also increased these variables. These cardiovascular changes were unaffected by dialyzing AP-5 (10 mM) into the dorsal horn at L(7) Increasing the syringe concentration of AP-5 to 100 mM attenuated the presser and HR responses from 62 +/- 8 to 31 +/- 6 mmHg and 18 +/- 4 to 12 +/- 4 beats/min, respectively. AP-5 blun ted the increase in MAP (59 +/- 10 vs. 41 +/- 10 mmHg) evoked by muscl e stretch. Simultaneously microdialyzing AP-5 (10 or 100 mM) into the dorsal horn at the L(6) and S-1 spinal levels also blunted the MAP and HR responses to contraction and stretch. These results suggest that N MDA receptors play a role in mediating the MAP and HR responses to sta tic muscle contraction at the spinal level of the central nervous syst em. Furthermore, these data demonstrate that collaterals from muscle a fferents partially mediate the reflex cardiovascular responses evoked by muscle contraction and stretch.