Time-dependent anticonvulsant activity of melatonin in hamsters.

The objective of the present study was to assess whether the anticonvulsant activity of melatonin displays diurnal variability in hamsters. Convulsions were induced by administering 3-mercaptopropionic acid (3-MP). There was a significant diurnal variation in 3-MP-induced convulsions, hamsters being more prone to exhibit seizures during the night than during the day. Melatonin (50 mg/kg i.p.) had a maximal anticonvulsive effect in the early evening (20:00 h). The administration at 20:00 h of the central-type benzodiazepine antagonist, Ro 15-1788, although unable by itself to modify seizure threshold, blunted the anticonvulsant response to melatonin. The results indicate that the time-dependent anticonvulsant activity of melatonin is sensitive to central-type benzodiazepine antagonism.