Animal model of autism using GSTM1 knockout mice and early post-natal sodium valproate treatment

Abstract

Autism is a heterogeneous, behaviorally defined developmental disorder with unknown etiology but thought to be the result of environmental insult acting upon the developing brain of a genetically susceptible individual. Approximately 30% of individuals with autism have normal development up to the age of about 30 months after which they experience behavioral regression and lose previously acquired motor, cognitive and social skills. Early post-natal toxicant administration to mice has been used to model autistic regression. To test the hypothesis that genetically altered mice might be more sensitive to toxicant exposure early in life, mice with a deletion of glutathione-S-transferaseM1 (GSTM1; a gene associated with increased risk of autism that codes for an enzyme involved in the management of toxicant-induced oxidative stress) and wild-type controls were exposed to valproic acid (VPA; a toxicant known to cause autism-like behavioral deficits that, in part, are mediated through oxidative stress) on post-natal day 14. VPA treatment caused significant increases in apoptosis in granule cells of the hippocampus and cerebellum. There was a genotype by treatment by sex interaction with wild-type females exhibiting significantly fewer apoptotic cells in these regions compared to all other groups. VPA treatment also resulted in long-lasting deficits in social behaviors and significant alterations in brain chemistry. VPA-treated GSTM1 knockout animals performed significantly fewer crawl-under behaviors compared to saline-treated knockout animals as well as wild-type controls receiving either treatment. Collectively, these studies indicate that VPA-treatment causes cerebellar and hippocampal apoptosis and that having the wild-type GSTM1 genotype may confer protection against VPA-induced neuronal death in female mice.