Neuronal deficits in mice following phenobarbital exposure during various periods in fetal development.

Four groups of pregnant mice were fed milled food containing 3 g/kg phenobarbital, acid form, and water as their only nutritional source during various periods during pregnancy (days 9-18, 9-13, 13-16 or 16-18). Control females received milled food and water. The brains of control and phenobarbital-treated male offspring were removed at age 50 days, fixed, cut and stained with HE. Matching sagittal sections were sections were selected for the study of the cerebellar Purkinje cells and th hippocampal pyramidal cells. Previous findings were confirmed in that prenatal phenobarbital exposure during the last two trimesters of pregnancy (days 9-18) resulted in a long-lasting deficit in the number of the Purkinje (23%) and pyramidal cells 9% (P < 0.01). Phenobarbital administration during only part of this period (days 9-13, 13-16 or 16-18) had the same effect as administration during the entire period. The cell deficit did not correlate with the time of appearance of the neurons, thus, suggesting that phenobarbital may possibly act even on neurons which are already formed.