N-methyl-D-aspartate antagonist applied to the spinal cord hindlimb enlargement reduces the amplitude of flexion reflex in the turtle.

APV (D(-)-2-amino-5-phosphonovalerate), an NMDA (N-methyl-D-aspartate) antagonist, was applied in situ onto segments of the hindlimb enlargement of the turtle spinal cord. APV reduced the response amplitude of the flexion reflex. In contrast, APV did not alter the responsiveness of the rostral scratch reflex. Afferents for the flexion reflex enter the spinal cord via the dorsal roots of the middle segment of the hindlimb enlargement; afferents for the rostral scratch reflex enter the spinal cord via dorsal roots located anterior to the hindlimb enlargement. The results are consistent with the hypothesis that sensory interneuron NMDA receptors, synaptically activated either directly or indirectly by nearby cutaneous afferent axons, play a role in the spinal cord processing of cutaneous information.