Increased alcohol drinking and seizure susceptibility in female humanized ApoE4 knockin rats

Epidemiological analyses suggest that the Ɛ4 allele of apolipoprotein E (ApoE) genes may influence the effects of alcohol on cognitive and executive function and dementia risk compared to the Ɛ3 allele. Here, we investigated this question in female rats given that women are more vulnerable than men to the Ɛ4 genotype effects on various diseases. Experiment 1 examined the effects of alcohol drinking on performance in a Barnes maze and an operant strategy set-shifting (OSS) task during abstinence in wildtype (WT) and homozygous ApoE4 knock-in (E4) rats. Experiment 2 repeated the behavioral assessments to assess the effects of heavy alcohol exposure and explored seizure susceptibility in E4 and homozygous ApoE3 knock-in (E3) rats. The experiments revealed that E4 rats drank significantly higher doses of alcohol than did the WT and E3 rats. However, there was no genotype or alcohol effect on performance in the Barnes maze and the OSS task. Notably, E4 rats had a shorter latency to kainate-induced seizures and maintained worse seizures compared to age-matched E3 rats. These findings suggest that the Ɛ4 allele may confer a higher risk for increased alcohol drinking without significantly exacerbating alcohol-associated decline in cognitive and executive function in females. Given the scarcity and discrepant reports regarding the role of ApoE polymorphism on seizure disorders among human and rodent studies, results of this study also underscore the need for more rigorous clinical and preclinical studies to determine the role of ApoE in sporadic and alcohol withdrawal seizures.