Autoradiographic study of phenobarbital's effect on development of the central nervous system

Pregnant Sabra mice received 3 g phenobarbital (PhB)/kg milled food from gestation days 9 to 18 as their only food source; control female mice received milled food. All animals were divided into three groups and injected i.p. with a single dose of [H³]thymidine on gestation days (GD) 13, 15, or 17. The offspring survived until 50 days of age when they were anesthetized and perfused with 10% neurtral Formalin and the brains were removed and prepared for autoradiography. Matching sagittal sections of different offspring were selected for the study of the cerebellum, hippocampus, or cortex. The number of labeled Purkinje cells of the cerebellum was reduced 75% (P < 0.001) on GD 13 in experimental female, but not male offspring. The number of labeled cerebellar granule cells per section did not differ between groups. The hippocampus showed a 67% reduction in female offspring (P < 0.01) and a 51% reduction in male offspring. (P < 0.01) of labeled pyramidal cells per section on GD 13 after prenatal treatment of phenobarbital. As in the cerebellum, no deficits occurred in the hippocampal granule cells. In the cortex the drug decreased cell labeling 52% in female (P < 0.05) and 30% in male offspring (P < 0.05) per square millimeter on GD 13. Control groups demonstrated a gender difference in the prenatal labeling of cortical cells: male offspring had 46% more labeled cells per section (P < 0.01) on GD 13. A breakdown of the cortex into different regions showed that the greatest gender difference occurred in the deep strata (close to the corpus callosum) on GD 13. A 58% reduction in treated female (P < 0.001) and 43% reduction in treated male offspring (P < 0.001) was noted. The results suggest that phenobarbital induced alterations in the times of origin of neurons or in necrosis of recently formed neurons.