Pattern- and age-dependency of the antiepileptic effects induced by valproic acid in the rat hippocampus

The effects induced by the antiepileptic drug valproic acid were studied in the CA3 subfield of in vitro hippocampal slices obtained from young (16- to 27-day-old) and adult (over 60-day-old) rats. Spontaneous epileptiform discharges were induced by the addition of the convulsant 4-aminopyridine to the medium. Valproic acid (0.5 mM) selectively blocked the ictal epileptiform discharges in slices obtained from young rats. Interictal epileptiform discharges disappeared during perfusion with higher doses of valproic acid (2 mM). This blockade of interictal epileptiform activity was not observed when valproic acid (0.5-5 mM) was tested in hippocampal slices from adult rats. Thus, in the hippocampus of young rats, 4-aminopyridine-induced ictal activity is more sensitive to valproic acid than are interictal discharges. Moreover, valproic acid is effective in controlling interictal discharges in the young, but not in the adult rat hippocampus.