Effects of melatonin on the photosensitive epilepsy of the baboon, Papio papio

The acute pharmacological effects of melatonin (5-methoxy-N-acetyl-tryptamine) were evaluated on behaviour and electrographic signs in the photosensitive baboon (Papio papio), including visually evoked potentials VEPs). Doses of 5 and 10 mg/kg i.v. had little effect, contrasting with the enhancement of spontaneous paroxysmal activity and latency of clinical signs elicited by intermittent light stimulation (ILS) produced by the 20 and 50 mg/kg doses. Moreover, a modification of the electrographic pattern of discharge during ILS-induced myoclonic responses was observed. These observations indicate a slight decrease of light sensitivity after melatonin. Only frontal VEPs were modified, with increase in amplitude of their late components for all doses tested. These effects lasted for 2-4 h. The participation of serotoninergic mechanisms involved in melatonin effect and in this model of experimental epilepsy are discussed.