Neurobiological Consequences of Social Conditions and Alcohol Exposure in Adolescent rats

Abstract: Adolescence represents a time of extensive reorganisation and maturation of brain circuits involved in emotions, motivation and cognition and it is a period particular sensitive for external stimuli. External stimuli can be both socio-environmental factors and exposure to exogenous compounds such as drugs of abuse (e.g. alcohol). If these stimuli are of an adverse nature the probability of develop neuropsychiatric diseases or addiction is increased. To study the neurobiological consequences of adverse events during adolescence animal models are crucial since they give the opportunity of providing an environment where the exposure of the stimuli is controlled and also enable a detailed analysis of the effects in the brain. The overall aim of in this thesis was to investigate how environmental factors, social conditions or alcohol exposure, during adolescence affect the brain and/or drug-taking in rats. Rats are very sensitive for dis- turbances in their social conditions and to induce an adverse social environment, early adolescent rats where single-housed for either a short or prolonged time. A short period of single housing induced an acute stress response and increased levels of nociceptin/orphanin FQ in brain areas associated with stress. Prolonged single housing reduced the levels of Met-enkephalin-Arg6Phe7 in several brain areas. Rats exposed to alcohol during adolescence had an altered dopamine response in dorsal striatum after an am- phetamine challenge but displayed similar amphetamine intake-behaviour as water controls. However, animals exposed to a combination of adolescent alcohol exposure and subsequent amphetamine intake had a more efficient removal of dopamine in dorsal striatum after an amphetamine challenge. This thesis demonstrates how two different environmental stimuli are able to alter the neurobiology in adolescent rats. The results further support the notion that environmental conditions are of importance for normal brain maturation and provide new evidence that endogenous opioids are severely affected by social dis- turbances during adolescence. Furthermore, additional information is provided to the existing literature of how alcohol exposure during adolescence affects dopamine dynamics and drug-taking behaviour. In the literature, the majority of the studies of adolescent alcohol exposure have focused on the nucleus accum- bens, a brain area important in the processing of rewards. The results herein provide evidence that dorsal striatum, a brain area involved in the transition into habitual drug use is also affected by adolescent alco- hol exposure. An altered drug response in dorsal striatum may affect habit formation and contribute to a heightened susceptibility for high drug consumption later in life.