The amygdala, a sexually differentiated brain structure intimately involved in emotions, cognition, social behavior, and sexuality, is particularly important in monkeys for recognizing and responding to social context and danger. This structure continues to develop postnatally and is sexually differentiated prior to puberty, yet nothing is known about its contribution to sex differences in behavior and cognition, it impact on neuroendocrine function or its role in modulating social signals influencing puberty. Puberty in monkeys and humans is affected by social context and the amygdala may be one of the modulators of the interaction between social context and neuroendocrine function. We will investigate social, emotional, cognitive and neuroendocrine consequences of neonatal and post-pubertal amygdalectomy in male and female rhesus monkeys. Subjects will live in semi-natural complex social groups. A team with expertise in emotional regulation, cognition, neuroendocrine function, and social behavior, will track the development of these systems and relate changes in juvenile function to the pubertal transition and adult social behavior. Forty- eight monkeys, distributed between 8 male and 8 female controls, 8 neonatally amygdalectomized of each sex, and 8 post-pubertally lesioned subjects of each sex, will be created in two annual cohorts of 24. Neonatal gonadal function, anxiety, fear, and maternal attachment will be assessed along with extensive observations of social interactions in the subjects'natal group during the first year of life. Social observations, assessment of emotionality, and stress physiology will continue for the 2nd through 4th years of life. At two years of age, cognitive tasks, using continuously available computer kiosks, will assess object and spatial memory span and object discrimination. Sex differences in social interactions and social integration will be investigated through detailed observations of social behavior. At two years of age females will start intense endocrine sampling to assess pubertal timing as well as pubertal changes in social and sexual behavior. Three year old males will be removed from their natal group to simulate male migration and formed into bachelor groups for investigation of the pubertal transition. It is hypothesized that the different male and female natal social environments, combined with the sexually differentiated nature of amygdala function will result in different magnitudes of effect of amygdala damage, with males likely more severely affected than females. We hypothesize that amygdalectomized females will uniformly show early puberty. Altered amygdala function is found in a number of neurodevelopmental disorders and while amygdalectomy does not serve as a model for any single human mental disorder, understanding its functional effects on a range of behavioral, cognitive and neuroendocrine endpoints will be invaluable for understanding the developmental trajectory of alterations produced by early amygdala dysfunction in human neurodevelopmental disorders.
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