Possible involvement of descending serotonergic systems in antinociceptionby centrally administered elcatonin in mice

To elucidate the mechanisms of analgesic action of elcatonin, a synthetic a nalog of eel calcitonin, the effect of centrally injected elcatonin on acet ic acid-induced writhing behavior was examined in mice. Intracisternal or i ntracerebroventricular injection of elcatonin significantly inhibited aceti c acid-induced writhing behavior, while the intrathecal injection of elcato nin did not inhibit it. The inhibitory effect of intracisternal elcatonin w as significantly attenuated by subcutaneous pretreatment with methysergide and (+/-)-propranolol or by intrathecal pretreatment with methysergide, (+/ -)-propranolol, 1-(2-methoxyphenyl)-4-[4-(2-phthalimido) butyl]-piperazine hydrobromide (NAN-190) and granisetron, but not with (+/-)-atenolol or buto xamine. Further, the depletion of spinal 5-hydroxytryptamine (5-HT, seroton in) by pretreatment with 5,7-dihydroxytryptamine (5,7-DHT) significantly at tenuated the inhibitory effect of intracisternally injected elcatonin on ac etic acid-induced writhing behavior. These results suggest that the inhibit ory descending serotonergic systems may be involved, through 5HT(1A) and 5- HT3 receptors, in the production of an antinociceptive effect by centrally injected elcatonin.