The purpose of this study was to evaluate the effects of early life stress on the vulnerability to ethanol consumption in adolescence. To this aim, mice were separated from their mothers for 12 hours/day on postnatal days 8 and 12. Emotional behavior (light-dark box, elevated plus maze and tail suspension tests) and pre-attentional deficit (pre-pulse inhibition) were evaluated in adolescent maternal separated (MS) mice. Alterations of the corticotropin-releasing factor (CRF), glucocorticoid receptor (NR3C1), tyrosine hydroxylase (TH), mu-opioid receptor (MOr), brain-derived neurotrophic factor (BDNF), neuronal nuclei (NeuN), microtubule-associated protein 2 (MAP2) and neurofilament heavy (NF200)-immunoreactive fibers were studied in the paraventricular nucleus of the hypothalamus (PVN), ventral tegmental area (VTA), nucleus accumbens (NAc) or hippocampus (HIP). The effects of maternal separation (alone or in combination with additional stressful stimuli) on ethanol consumption during adolescence were evaluated using the oral ethanol self-administration paradigm. MS mice presented mood-related alterations and pre-attentional deficit. Increased CRF, MOr and TH, and reduced BDNF, NR3C1, NeuN, MAP2 and NF200-immunoreactive fibers were observed in the PVN, NAc and HIP of adolescent MS mice. In the oral ethanol self-administration test, adolescent MS mice presented higher ethanol consumption and motivation. Exposure to additional new stressful stimuli during adolescence significantly increased the vulnerability to ethanol consumption induced by maternal separation. These results clearly demonstrated that exposure to early life stress increased the vulnerability to ethanol consumption, potentiated the effects of stressful stimuli exposure during adolescence on ethanol consumption and modified the expression of key targets involved in the response to stress, ethanol reinforcing properties and cognitive processes.
This study evaluated for the first time the effects of maternal separation with or without additional exposure to other stressful stimuli during adolescence in the consumption, motivation and reinforcing properties of ethanol using the oral ethanol self-administration paradigm. Adolescent MS mice presented higher motivation (increased number of effective response in the active lever) and consumption of ethanol. Interestingly, re-exposure to stressful-like stimuli during adolescence significantly increased the vulnerability to ethanol consumption in MS mice. These results point to the fact that early-life stress increases the vulnerability to later-life stress.