IMMUNOHISTOCHEMICAL LOCALIZATION OF DELTA-OPIOID AND MU-OPIOID RECEPTORS IN PRIMATE SPINAL-CORD

IMMUNOFLUORESCENT techniques were used to examine the distribution of delta- and mu-opioid receptor-like immunoreactivity (ir) in primate sp inal cord. At every segmental level examined, opioid receptor-ir forme d a dense plexus of small profiles within the superficial dorsal horn. delta-Opioid receptor-ir was found in laminae I and II, whereas mu-op ioid receptor-ir was confined mostly to lamina II. The distribution of opioid receptors within the superficial dorsal horn is appropriate fo r a localization to the central terminals of thinly myelinated and unm yelinated sensory neurons. Differences in the distribution of the delt a- and mu-opioid receptors may reflect the presence of these two opioi d receptor types on different functional classes of afferent neurons, or they may relate to differences in presynaptic and postsynaptic loca lization within the spinal gray matter.