INTRATHECAL INJECTIONS OF GALANIN AND ITS ANTISERUM AFFECT NOCICEPTIVE RESPONSE OF RAT TO MECHANICAL, BUT NOT THERMAL, STIMULI

To ascertain the involvement of galanin in nociceptive transmission in the spinal dorsal horn, we examined the effects of intrathecal injections of porcine galanin and its antiserum on behavioral nociceptive responses of the rat, using the paw-pressure and paw-radiant heat tests. An intrathecal injection of antiserum against porcine galanin reversed the decreased nociceptive threshold for mechanical, but not thermal, stimulation of the carrageenin-treated hind paw of rat, with no effect on the nociceptive threshold of the non-inflamed hind paw. Rat galanin as well as porcine galanin suppressed the binding of [I-125]porcine galanin to the antiserum, a finding suggesting that the antiserum can bind rat galanin. An intrathecal injection of porcine galanin (0.1 and 1 nmol, but not 0.01 nmol) decreased the mechanical nociceptive threshold of the rat hind paw with no effect on thermal nociception. These results suggest that galanin present in the dorsal horn is involved in the facilitation of mechanical, but not thermal, nociceptive transmission.