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Prenatal exposure to phenytoin in rats, even at safe doses, caused lasting behavioral changes. These findings highlight phenytoin as a potent behavioral teratogen, potentially explaining CNS dysfunction in fetal hydantoin syndrome.
Area of Science:
- Neuroscience
- Developmental Toxicology
- Pharmacology
Background:
- Phenytoin is a widely used anticonvulsant medication.
- The fetal hydantoin syndrome is associated with prenatal exposure to phenytoin.
- Potential neurodevelopmental effects of phenytoin require further investigation.
Purpose of the Study:
- To investigate the behavioral teratogenicity of phenytoin in a rat model.
- To determine if phenytoin administration during gestation induces lasting behavioral abnormalities in offspring.
- To correlate drug dosage and developmental stage with observed behavioral effects.
Main Methods:
- Rats were administered phenytoin at non-embryotoxic and non-teratogenic doses during gestation.
- Offspring behavior was assessed using locomotion tests (pivoting, ambulation, rearing) and a complex water maze.
- Plasma drug concentrations in dams were measured to ensure therapeutic relevance.
Main Results:
- Prenatal phenytoin exposure resulted in significant and enduring behavioral abnormalities in offspring, including hyperactivity.
- Adult offspring showed impaired performance in a complex water maze but not in simple swimming tasks.
- The observed effects were dose-dependent, stage-dependent (most vulnerable during organogenesis), and highly replicable.
Conclusions:
- Phenytoin acts as a potent behavioral teratogen in rats.
- The study findings support the hypothesis that CNS dysfunction is a key feature of fetal hydantoin syndrome.
- Prenatal phenytoin exposure can lead to long-term neurodevelopmental deficits.
Abstract:
In a series of experiments, prenatal administration of phenytoin to rats at non-embryotoxic and non-teratogenic doses produced offspring exhibiting large and enduring abnormalities in behavior. Plasma drug concentrations on the last day of exposure in the dams were within the human therapeutic range for anticonvulsant efficacy. The behavioral abnormalities in the offspring were hyperactivity on tests of locomotion (increased pivoting behavior and figure-8 ambulation), but decreased figure-8 rearing. As adults, the phenytoin rats exhibited no impairment in swimming ability in a straight channel, but when placed in a complex water maze showed large increases in errors compared to controls. The effects of prenatal phenytoin on these behaviors were highly replicable, dose-dependent and stage-dependent. The stage of greatest vulnerability was during organogenesis. The data demonstrate that phenytoin is a potent behavioral teratogen in rats. The data also support clinical descriptions implicating CNS dysfunction as a major feature of the fetal hydantoin syndrome.