Abstracts

Rationale: When given in a therapeutic concentrations, certain antiepileptic drugs (AEDs) such as phenobarbital (PB) and phenytoin (PHE) induce neuronal apoptosis in the developing rat brain, while other AEDs such as carbamazepine (CBZ) do not. This effect has been well documented in cortex, striatum and thalamus, with relatively little attention focused on limbic system regions. Therefore, we examined cell death in amygdala, nucleus accumbens, septum, and regions of piriform cortex following acute treatment with AEDs at postnatal day (P) 7. P7 in the rat previously has been shown to be the timepoint of greatest sensitivity to the proapoptotic action of AEDs; this falls within the "brain growth spurt" (third-trimester to early infancy in humans), a period of rapid brain growth and synaptogenesis. Methods: Sprague-Dawley rat pups were treated with one of the following drugs on P7: PB (75mg/kg, ip), PHE (50mg/kg, ip), CBZ (25mg/kg, ip), and sacrificed after 24 hrs. Brain sections were processed using the TUNEL method to detect apoptotic cells. Regions of interest were analyzed in a treatment blind manner. A separate cohort of animals were treated with PHE and allowed to survive until P80, when they were tested in the elevated plus maze in order to evaluate emotionality. Time spent in open and closed arms, as well as total arm entries were recorded using video tracking software (AnyMaze, Stoelting Co). Results: PHE and PB exposure both caused a 20-fold increase in neuronal cell death in the amygdala. PB also increased neuronal cell death in the nucleus accumbens, septum, and anterior deep prepiriform cortex. CBZ exposure did not cause an increase in cell death in any of the brain regions examined. PHE-exposed male, but not female, rats displayed a significant reduction in time spent in the open arms of the elevated plus maze when tested as adults. In addition, the PHE-exposed males exhibited a significant decrease in the percentage of total entries into the open arms. Total arm entries were not different between PHE-treated rats and controls. Conclusions: The PHE and PB-induced cell death that we observed in the neonatal amygdala, and the PB-induced cell death observed in several additional limbic regions, raises the possibility that exposure to these drugs during late gestation or early infancy may have long-term impact on mood and affective behavior. In particular, the cell death in the neonatal amygdala may contribute to a sex-dependent increase in anxiety, as suggested by our results with the elevated plus maze in adult rats exposed to PHE as neonates. Other limbic-mediated behaviors are currently under investigation, as is the possibility that this long-term adverse outcome may be avoided by using AEDs that do not induce cell death in the neonatal amygdala. Support: T32DA007291, R01NS020576, and Glaxo-Smith-Klein