ADOLESCENCE: A SENSITIVE PERIOD FOR SHAPING THE ADULT SOCIAL BRAIN

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The importance of environmental experiences in the early years of life in shaping brain development and function is well known. In comparison, there has been little focus on the adolescent period, a period in which there is ongoing brain development, and a time of life that is different from adulthood in terms of social behaviour and many aspects of physiology. My research has shown in rats that social relationships in adolescence shape social behaviour in adulthood, using a manipulation of social experiences (social instability) that seems to have no lasting effect on behaviour when experienced in adulthood. In this grant, we propose to investigate the neural underpinnings of the social instability-induced changes in social behaviour of adolescents. Objective 1: We will test the hypothesis that social experiences in adolescence alter the development of regions of the brain (eg., the medial amygdala). Objective 2: We will investigate whether the atypical social behaviour exhibited by rats that underwent social instability in adolescence involves differences in the social regulation of motivational systems and social learning. The dopaminergic mesocorticolimbic system plays a crucial role in highly motivated behaviours and undergoes significant change in adolescence. There is much evidence that social interactions carry greater reward value in adolescence than in adulthood in rats, but is this true after social instability? Objective 3: Most of our studies of social behaviour have involved male rats only; this objective addresses this disparity. We will investigate the effects of social instability on social behaviour in females, because many sex differences emerge in adolescence and the effects of social instability likely differ for males and females. Objective 4 is based in part on our evidence that the experience of social instability results in a different pattern of neuroendocrine responding in adolescents and adults. These neuroendocrine differences may be a basis for the age-specific effects of social experiences. Further, we have preliminary evidence that relationships between neuroendocrine systems are different for post-pubertal adolescents than for adults; whereas testosterone typically dampens the release of adrenal hormones in response to environmental challenges, in adolescents we found testosterone heightened adrenal hormone release. Thus, experiments are proposed to investigate the mechanisms underlying these age differences the relationships between these hormonal systems. The experiments of my research program are important steps in addressing gaps in our knowledge of the adolescent period of life, which will contribute to the understanding the developmental mechanisms and social experiences that build the social brain. Further, the research program will provide excellent research training and transferrable skills for undergrad and graduate students.