The role of stress, sex and early-life environment in shaping alcohol vulnerability

Background: Genetically-selected Marchigian Sardinian alcohol-preferring (msP) rats represent a unique animal model of excessive alcohol drinking and anxiety disorder. They show innate upregulation of the corticotropin-releasing factor receptor 1 (CRF1) which correlates with heightened ethanol consumption and stress sensitivity. Stress, dysregulation of the hypothalamic-pituitary-adrenal axis (HPA) and alterations in glucocorticoid receptor (GR) function have been linked to transition from recreational alcohol use to dependence and GR is considered to play an essential role in modulating stress-associated behaviors Here, we investigated the effect of pharmacological blockade of GR on alcohol self-administration (SA) using male and female msP and Wistar rats. Furthermore, we evaluated if GR antagonism might decrease innate symptoms of anxiety in msPs. Methods: Animals were trained to self-administer 10% (v/v) alcohol. Once stable alcohol SA baseline was reached, we tested the effect of the GR antagonists mifepristone (0.0, 10, 30 and 60 mg/kg) and CORT113176 (0.0, 10, 30 and 60 mg/kg) on alcohol SA. To evaluate whether the effects of the two compounds were specific for alcohol, the two drugs were tested on a similar saccharin SA regimen. Basal blood corticosterone (CORT) levels before and after alcohol SA were determined. Finally, we evaluated the effect of mifepristone injection (0.0 and 60 mg/kg) on novelty-induced hypophagia (NIH) assay, comprehensive lab monitoring system (CLAMS) and stress sensitivity using acoustic startle measures. Results: Systemic injection with mifepristone dose-dependently reduced alcohol SA in male and female Wistars but not in msPs. Administration of CORT113176 decreased alcohol SA in male and female Wistars as well as in female msPs but not in male msP rats. At the highest dose, mifepristone also reduced saccharin SA in male Wistars and female msPs, suggesting the occurrence of some nonspecific effects at 60 mg/kg of the drug. Similarly, the highest dose of CORT113176 (60 mg/kg) decreased saccharin intake in male Wistars. Analysis of CORT levels revealed that females of both rat lines had higher blood levels of CORT compared to males. Additionally, we found that male and female msPs display greater anxiety-like behaviors as well as enhanced acoustic startle responses compared to Wistar counterparts. Importantly, the enhanced anxiety-like behavior and startle responses were not ameliorated by mifepristone administration. Conclusions: Overall, these findings indicate that selective blockade of GR selectively reduces alcohol SA and genetically selected msP rats are less sensitive to this pharmacological manipulation compared to heterogeneous Wistars. Results also suggest sex differences in the ability of alcohol to regulate GR transmission. Moreover, the increased expression of stress- related behaviors in msPs are not mediated by activation of GR system.