Effect of melatonin on pain sensitivity. II. The role of melatonin in the development of hyperalgesia.:The role of melatonin in the develoment of hyperalgesia

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Experiments were made to clarify the mechanism of melatonin-induced hyperalgesia and the following results were obtained: 1) Intracerebroventricular (i.c.v.) administration of melatonin (2-20μmouse) elicited hyperalgesic action does-dependently. 2) Hyperalgesia was also induced by chronic administration of melatonin, when melatonin was administered 96μday for 7days by subcutaneous implantation of mini-osmotic pump capsel. 3) Pretreatment of tetrabenazine (50mg/kg, s.c.), α-methyldopa (100mg/kg, s.c.), haloperidol (0.5mg/kg, s.c.), tolazoline (10mg/kg, s.c.), phentolamine (5mg/kg, s.c.) and propranolol (0.5mg/kg, s.c.) prevented the hyperalgesic action of melatonin. And brain contents of dopamine and noradrenaline increased by i.c.v. injection of melatonin. So it is suggested that the dopaminergic mechanism in the CNS may play an important role in melatonin-induced hyperalgsia. 4) Marked change by pretreatment of p-chlorphenylalanine was not observed on melatonininduced hyperalgesia, so that serotonin may not be concerned in development of melatonin hyperelgesia. 5) Melatonin potentiated morphine analgesia significantly, and morphine analgesia disappeared in pinealectomized animals. 6) From the fact that naloxone reversed melatonin-induced hyperalgesia, this hyperalgesic effect may be involved the endogenous opiate system.
歯科基礎医学会の論文