Antinociception induced in rats by intrathecal administration of antiserum against calcitonin gene-related peptide.

To determine whether or not endogenous calcitonin gene-related peptide (CGRP) participates in pain transmission in the spinal dorsal horn, effects of an intrathecal injection of anti-CGRP antiserum on nociceptive threshold in the paw-pressure test was examined in non-arthritic and adjuvant arthritic rats. An intrathecal injection of the antiserum increased the nociceptive threshold in non-arthritic animals, while 0.9% saline, pre-immune serum and antiserum, previously absorbed by synthetic CGRP, were without effect. Adjuvant arthritic rats showed a hyperalgesia, and improvement occurred with intrathecal injection of the antiserum. Saline and absorbed antiserum were without effect on the hyperalgesia. These results suggest that the endogenous CGRP present in primary afferents probably has a facilitating function in nociceptive transmission in the spinal dorsal horn.