Analgesic activity of a synthetic analogue of eel-calcitonin and its effect on the spontaneous activity of brainstem neurons in the rat.

Intracerebroventricular (i.c.v.) injection of (Asul,7)eel-calcitonin, a synthetic analogue of eel-calcitonin, at doses of 3 or 6 IU/rat, (but not at 1.5 IU/rat) determined analgesic activity, in male rats, as evaluated by the 'hot-plate' test. Also electrophysiological studies carried out on 13 neurons belonging to the nucleus raphe magnus (NRM) showed that i.c.v. administration of the same doses of (Asul,7)eel-calcitonin increased the spontaneous cellular firing rate. No modification of the discharge frequency was observed when 1.5 IU/rat (Asul,7)eel-calcitonin was used. Authors suggest that the analgesic activity induced by i.c.v. injection of (Asul,7)eel-calcitonin is due, at least in part, to mechanisms affecting NRM neurons.