The effects of phenytoin on threshold intensities of stimulation were
studied in cortical epileptic afterdischarges (ADs) in 12-day-old and
adult rats with implanted electrodes. Stimulation of the sensorimotor
cortical area induced movements directly related to the stimulation as
well as EEG afterdischarges (ADs) of the spike-and-wave type and of t
he limbic type. Rat pups exhibited lower thresholds for stimulation-bo
und movements and spike-and-wave ADs than adult animals. On the contra
ry, the limbic type of ADs was elicited with lower current intensity i
n adult than in immature rats. Phenytoin increased the threshold for s
timulation-related movements only in adult rats, whereas threshold int
ensities for spike-and-wave ADs were increased and thresholds for limb
ic type of ADs remained uninfluenced in both age groups. The age-depen
dent effect on stimulation-related movements might be due to a maturat
ion of connectivity in the motor system or to developmental changes in
the voltage-gated sodium channels as the main target of phenytoin act
ion.