Both highly stress-reactive and novelty-seeking individuals are susceptible to alcohol use disorders. Variation in stress reactivity, exploration, and response to novelty have been attributed to differences in corticotropin-releasing hormone (CRH) system function. As such, CRH gene variation may influence risk for alcohol use and dependence.
To determine whether CRH variation influences relevant intermediate phenotypes, behavior, and alcohol consumption in rhesus macaques.
We sequenced the rhesus macaque CRH locus (rhCRH) and performed cladistic clustering of haplotypes. In silico analysis, gel shift, and in vitro reporter assays were performed to identify functional variants. Cerebrospinal fluid (CSF) and blood samples were obtained, and levels of CRH and corticotropin (ACTH) were measured by radioimmunoassay. Behavioral data were collected from macaques during infancy. Among adolescent/adult animals, we recorded responses to an unfamiliar conspecific and measured levels of ethanol consumption.
National Institutes of Health Animal Center.
Main Outcome Measures
Animals were genotyped for a single-nucleotide polymorphism disrupting a glucocorticoid response element, rhCRH −2232 C>G, and the effects of this allele on CSF levels of CRH, plasma levels of ACTH, behavior, and ethanol consumption were assessed by analysis of variance.
We show that −2232C>G alters DNA×protein interactions and confers decreased sensitivity of the CRH promoter to glucocorticoids in vitro. Consistent with the known effects of glucocorticoids on CRH expression in the brain, carriers of the G allele had lower CSF levels of CRH but higher levels of ACTH. Infants carrying the G allele were more exploratory and bold, and among adolescent and adult male macaques, the G allele was associated with exploratory/bold responding to an unfamiliar male. Adults with the C/G genotype also exhibited increased alcohol consumption in the social group, a model for high-risk alcohol-seeking behavior.
Haplotypes that differ in terms of corticosteroid sensitivity have been identified in humans. Our data may suggest that functionally similar CRH variants could influence risk for externalizing disorders in human subjects.