Novel anticonvulsant action of chronic melatonin in gerbils.

Melatonin, a hormone from the pineal gland, was tested for its anticonvulsant effects in male gerbils. Daily administration of melatonin (25 micrograms injection-1, s.c.) for ten weeks reduced the number and severity of seizures (total convulsion score: 7.67 +/- 1.83 in controls vs 2.47 +/- 0.90 in melatonin-injected animals, p < 0.05) associated with the injection of the convulsant, pentylenetetrazol (PTZ, 60 mg kg-1, s.c.). However, neither 12 weeks of short photoperiod exposure (LD 10:14) nor biweekly administration of melatonin pellets altered PTZ-induced convulsions. Overall, melatonin-injected gerbils were better able to survive and respond to seizures than control animals. No melatonin-injected gerbils died during seizure induction (0/31) while 5 out of 33 control gerbils died after PTZ injection. The mechanism for melatonin's anticonvulsant effects could be due to a direct inhibitory action on neural activity or a conversion of melatonin to an anticonvulsant compound that resembles the kynurenines.