Effects of exposure period and nutrition on the developmental neurotoxicity of anticonvulsants in rats: short and long-term effects.

The results of three experiments on the functional neuroteratogenicity of anticonvulsants in rats are presented. Two of the experiments have been reported previously and are reviewed here, while the third experiment is presented here for the first time. The first experiment examined prenatal phenytoin (200 mg/kg), trimethadione (250 mg/kg), and phenobarbital (80 mg/kg) for critical period effects by exposing separate groups of rats to the drugs or to vehicle on embryonic (E) days 7-10, 11-14, or 15-18. Phenytoin produced effects in the E11-14 offspring, but few effects in the E15-18 offspring, and almost no effects in the E7-10 offspring. Phenytoin's E11-14 effects in the offspring were increased pivoting, delayed swimming ontogeny, hyperactivity, impaired water maze learning, and impaired passive avoidance retention. The second experiment looked for phenytoin's long-term effects. Phenytoin-exposed offspring administered 200 mg/kg on E7-18 exhibited numerous postnatal dysfunctions, including water maze learning deficits that persisted to beyond 501 days of age. The learning deficits were neither increased nor decreased in severity at this age compared to those seen in littermates tested at 50 days of age. The third experiment assessed the role of manganese in counteracting phenytoin-induced postnatal dysfunction and the possible confounding effects of maternal undernutrition associated with the drug's administration. The typical pattern of phenytoin-induced behavioral effects was observed in rat offspring. The results demonstrated that undernutrition was not a confound, since pair-feeding and pair-watering controls did not diminish the phenytoin-induced dysfunction in the offspring. Also, administration of a manganese supplementation (200 ppm in the drinking water) during gestation did not significantly alter the pattern of phenytoin-induced postnatal effects.