Studies on the antinociceptive effect of intrathecal salmon calcitonin

The involvement of spinal opioid receptors and spinal monoaminergic systems, in the antinociceptive effect of intrathecal (IT) salmon calcitonin, has been evaluated by means of the hot plate test, in the rat. Intrathecal pretreatment with 40 micrograms MR 1452 and 40 micrograms ICI 154,129, purported selective antagonists respectively for kappa and delta opioid receptors did not modify sCT-induced antinociception (2 micrograms IT). A delay in the development of IT sCT-induced antinociception was observed in rats selectively depleted of cord serotonin (25 mg/kg IP desipramine plus 100 micrograms IT 5,7-dihydroxytryptamine), whereas the administration of serotonergic antagonists, methysergide and ketanserin, 30 micrograms IT, did not influence sCT effect. Cord catecholamine depletion (6-OHDA pretreatment) reduced significantly sCT antinociception. A similar reduction was produced by the dopaminergic antagonist haloperidol (15 micrograms IT), but not by the alpha-blocker phentolamine (15 micrograms IT). Findings of this study rule out an involvement of opioid peptidergic system in sCT-induced increase of hot plate latencies at spinal level; a possible involvement of cord dopaminergic receptors is suggested.