Despite the clear importance of adolescence in the emergence of a number of disease states and processes, there is surprisingly little known about how the endocrine and metabolic events accompanying puberty in humans impact normal developmental neurobiology. Epidemiologic studies have identified sexual dimorphisms in the prevalence of several neuropsychiatric disorders, including depression, schizophrenia, and substance abuse. Many of these sex differences emerge during or shortly after puberty and are maintained until the 5th-6th decade of life. For example, the two-fold greater risk of unipolar depression in women compared with men does not appear until adolescence, and prior to puberty girls are not at increased risk relative to boys. Puberty is a structured, transitional process that can be influenced by both nutritional factors and environmental stressors; nonetheless, the variability in the timing and duration of puberty is largely determined by oligogenic inheritance. Basic neuroscience research has demonstrated that hormonal events accompanying puberty impact on many of the physiologic systems involved in the regulation of brain function (e.g., the appearance of new neurons in a brain-region specific pattern, neuronal remodeling, and the pruning of cortical connectivity). Additionally, not only does stress during puberty increase the risk of disturbances in affective adaptation during adulthood, but the events accompanying puberty modify stress responsivity (e.g., alterations in the duration and peak response of hypothalamic-pituitary-adrenal \[HPA\] axis hormones to stressors). Moreover, animal work has demonstrated that neural connectivity differs in a brain regional specific manner according to the stage of puberty (i.e., early versus late). In humans, puberty also occurs in stages, and although the endocrinology of puberty, surprisingly, has not been fully characterized with longitudinal data, studies have documented that the physical changes measured by Tanner stages I to V are accompanied by progressive increases in the secretions of both gonadal and adrenal steroids. Nonetheless, there remains considerable variability in the timing and duration of this otherwise highly structured reproductive transition. We propose to perform a longitudinal, naturalistic study examining changes in brain structure and function, behavior, and stress responsivity in boys and girls across the pubertal transition. Because the pubertal transition is defined by a complex series of physiologic events that emerge sequentially over several years and involve changes in multiple endocrine and growth systems, and because there is also considerable variability in the timing of these events reflecting the influence of both genetic and environmental factors, puberty cannot by delineated by age of the participants as has been done in most imaging and other neurobiological studies of adolescence. The present study will formally bridge this gap by defining pubertal events per se in participants. Participants will include healthy boys and girls whose pubertal status will be assessed, and in whom endocrine, metabolic, and brain imaging measures will be evaluated at eight - ten month intervals from age eight years (pre-puberty) until age 17 years (post-puberty). Reproductive endocrine, metabolic, and physical measures will be employed to characterize the stage and duration of pubertal development. Outcome measures will be derived via multimodal neuroimaging techniques, cognitive/behavioral assessments, metabolic measurements, and evaluations of HPA axis function. Additionally, the impact of genetic variation on the developmental trajectory of these parameters (both reproductive and CNS) will be determined. This cross-institute proposal will employ a multidisciplinary approach to evaluating the effects on CNS function of the process of puberty in both boys and girls. This work will not only serve to inform research on the mechanisms by which sexual dimorphisms in neuropsychiatric disorders develop, it will also have important implications for the prevention and treatment of these disorders.