MELATONIN REDUCES LOW-MG2+ EPILEPTIFORM ACTIVITY IN HUMAN TEMPORAL SLICES

Seizure susceptibility waxes and wanes in an apparently circadian mann er in many epileptic patients. Fluctuations of melatonin concentration with highest levels during the night and lowest levels in the early m orning could be involved in this phenomenon. Therefore, the action of melatonin on epileptic activity was tested. The experiments were carri ed out on human temporal neocortical slices cut from tissue resected f or surgical treatment of epilepsy. Autoradiographic studies were perfo rmed on parallel slices with 100-120 pmol 2-[I-125]iodomelatonin/l in the absence or presence of unlabelled melatonin. High-affinity binding sites of melatonin could be demonstrated in layers II-V of the tempor al cortex. The binding was saturable, specific and occurred with low c apacity. In electrophysiological studies, epileptiform field potential s were elicited by omission of Mg2+ from the superfu sate and recorded from layers II-V. The frequency of occurrence of epileptiform field p otentials was reduced to 0.5 of the initial value with application of melatonin (10 and 100 nmol/l) in each case. This effect was reversible upon washing. The findings favour the hypothesis that melatonin depre sses epileptiform neuronal activity through specific neocortical recep tors.