ACUTE AND CHRONIC EFFECTS OF MELATONIN AS AN ANTICONVULSANT IN MALE GERBILS

Melatonin, a hormone produced in the pineal gland and released into th e general circulation on a diurnal basis, has been implicated in many behavioral processes, where it has been shown to have anxiolytic, seda tive, and anticonvulsant effects. Male gerbils (Meriones unguiculatus) injected daily with melatonin (25 mu g, s,c.) exhibited a reduced sei zure response to pentylenetetrazol (PTZ, 60 mg/kg, s.c.). The present studies determined 1) whether melatonin's effect was related to the ti me of day that it was administered and 2) whether a single acute injec tion of melatonin at various doses could produce anticonvulsant activi ty. Gerbils provided with 13 weeks of daily melatonin injections (25 m u g, s.c,) exhibited fewer convulsions after PTZ treatment irrespectiv e of the time of day melatonin was injected. In addition, the melatoni n-treated gerbils had lower mortality rates (1/12) than the untreated or vehicle-injected gerbils (5/12). On the other hand, single acute in jections of melatonin (0.1-10 mg/kg, i.p,) produced no anticonvulsant activity. It appears that the anticonvulsant effects of melatonin occu r only after the animals are chronically exposed to the indole. In add ition, melatonin's anticonvulsant ability may utilize a different mech anism than those involved in its endocrine effects, since no diurnal d ifference in melatonin's anticonvulsant activity was observed.