Adolescent behavior : Links to early-life stress and alcohol in male and female rats

Adolescence is an important developmental phase with large changes in behavior, physiology and neurobiology, which transform an individual from immature child to independent adult. Due to these changes, adolescence is a sensitive period for exposure to environmental factors such as stress and drug exposure; it is also a common age of onset for alcohol consumption as well as several psychiatric disorders. Despite these factors, less is known about this developmental period than regarding adult individuals. Behavior is regulated by the central nervous system and can be used as a lens to study these processes as well as for examination of associations between individual differences, early-life stress and alcohol. The aim of this thesis was to experimentally examine adolescent behavior and its links to early-life stress and alcohol in adolescent male and female rats. Different behavioral tests were used to profile adolescent animals together with animal models of early-life stress, voluntary alcohol consumption and alcohol exposure. In addition, stress responsiveness after early-life stress and the impact of alcohol exposure on endogenous opioid peptide levels as well as blood alcohol concentrations were examined. The adolescent behavioral profile in the multivariate concentric square field™ (MCSF) was characterized and validated against the elevated plus maze and open field tests. The main finding was subgroups based on individual variation that revealed three distinct behavioral types: Explorers, Shelter seekers and Main type animals. This pattern was replicated in an additional, independent cohort. Early-life stress, modelled by prolonged maternal separation, showed small effects on behavior in the MCSF and on social play behavior. However, an effect on stress responsiveness in males but not females subjected to prolonged maternal separation was discovered. Predisposition for high alcohol consumption did not have a shared behavioral profile among selectively bred rat lines. However, a subgroup of high drinking individuals in an outbred cohort showed behavioral similarities to one of the selectively bred lines. Alcohol exposure showed small, but sex-dependent, effects on behavior and endogenous opioid peptide levels. Together, these studies provide new information about adolescent behavior and associations to early-life stress and alcohol in males and females, relationships not extensively studied in adolescence