Effects of Porcine Calcitonin on Behavioral and Electrophysiological Responses Elicited by Electrical Stimulation of the Tooth Pulp in Rabbits

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Abstract
Effects of porcine calcitonin on both behavioral and electrophysiological responses of rabbits to painful stimuli were examined. The behavioral pain response (licking reaction) to electrical stimulation of the tooth pulp was suppressed dose dependently by intracerebroventricular administration of calcitonin, 8 and 17 U/kg, but not by intravenous injection of 7.5–50 U/kg of the peptide. The duration of action of intracerebroventricular calcitonin was over 90 min. The EEG arousal response and the development of the long latency cortical potential evoked by electrical stimulation of the tooth pulp in gallamine-immobilized rabbits, were inhibited by intracerebroventricular calcitonin, 17 U/kg, for the period of over 90 min but not by the intravenous injection of 50 U/kg. Morphine, 2 mg/kg i.v., inhibited all of the responses for 30 min or longer. The EEG arousal response induced by sound stimulation was not affected by calcitonin or morphine. Naloxone (0.5 mg/kg i.v.), an opiate antagonist, showed no influence upon the inhibitory effects of calcitonin in licking reaction, EEG arousal response and evoked potential, though it completely antagonized the effects of morphine. The results suggest that the analgesic effect of intracerebroventricular porcine calcitonin can be attributed to blocking of pain pathways in the central nervous system in a manner distinct from the narcotic analgesic.