AGE-DEPENDENT PHENYTOIN EFFECTS ON CORTICAL STIMULATION IN RATS

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.