The analgesic activity of calcitonin and the central serotonergic system

The effect of peripherally administered cyproheptadine or reserpine and the administration of 5,7-dihydroxytryptamine (5,7-DHT) in the nucleus raphe dorsalis on the analgesic activity of salmon calcitonin (sCT) injected into the lateral ventricle were investigated in male rats. Cyproheptadine or reserpine, given respectively 30 min or 24 h before the peptide, completely abolished the analgesic activity at all the times studied. However, when reserpine was given before the peptide it increased the effect of sCT at 30 (P less than 0.01), 60 (P less than 0.001), 120 (P less than 0.01) and 180 (P less than 0.01) min. 5,7-DHT injected in the nucleus raphe dorsalis 15 days before the peptide led to complete abolition of the analgesic activity. If neurotoxin was injected 4 days before sCT, the effect of the peptide was significant (P less than 0.05) only at 60 min. The results obtained confirm that the analgesic activity of sCT may involve central serotonergic pathway(s), and that the midbrain raphe nuclei 5-HT content is an important focus for this activity.