Central analgesic action of calcitonin and its relationship with central monoamine transmitters

The analgesic action of calcitonin (0.25 MRC units.kg-1) injected into lateral cerebral ventricle was investigated in rats. The pain threshold was evaluated by the tail-flick test. The influences of icv naloxone 5 micrograms/rat, a blocker of opiate receptor, on the analgesic action of calcitonin were observed. The results showed that icv calcitonin produced a significant analgesic action, which was reversed by naloxone. While the pain threshold was raised by calcitonin, the contents of central monoamines (5-HT, NE, DA) in brain (diencephalon, brain stem) were examined by fluorophotometry, which were increased remarkably. It is suggested that calcitonin-induced analgesia is related to the opiate receptors and the contents of 5-HT, NE, and DA in CNS.