Segmental effect of NMDA block in the dorsal horn on the pressor reflex

Abstract

The purpose of this study was to examine the influence of NMDA receptor blockade in the dorsal horn of adjacent spinal segments as it pertains to the pressor reflex evoked by static contraction and stretch of skeletal muscle. In this preparation, cats were anesthetized and the afferent fibers mediating the pressor reflex entered the spinal cord via the L 7 dorsal root. Blockade of dorsal horn NMDA receptors at L 6 and L 7 attenuated the pressor reflex evoked by static contraction and muscle stretch. However, NMDA block in the L 6 dorsal horn alone failed to alter the peak increase in MAP produced by static contraction and muscle stretch, but the initial pressor response evoked by static contraction was attenuated. These data support the hypothesis that the pressor reflex is partially mediated by activation of NMDA receptors in the dorsal horn, and this occurs at multiple spinal segments. Further, these data suggest that activation of NMDA receptors plays an important role in initiating the rise in arterial pressure produced by static contraction of skeletal muscle.