| The amygdala plays a critical role in the evaluation of salient and threatening cues from the environment and in the modulation of behavioral, autonomic, and neuroendocrine responses to threats. Much less know of is its potential role on the regulation of the hypothalamic-pituitary-adrenal (HPA) axis basal tone and on the development of emotional and neuroendocrine processes through the lifespan. The current study examined the effects of neonatal amygdala lesions in rhesus monkeys on basal and stress reactive HPA function, as well as emotional reactivity from birth to preadolescence. Neonatal amygdalectomy spared the ability to express emotional behaviors, but altered the modulation of those behaviors based on the contextual information provided by the salience of the threat. Interestingly, the sex of the animal modulated the behavioral effects of neonatal amygdala lesions, leading to different patterns of emotional behaviors depending on the sex and lesion status. Neonatal amygdalectomized animals also had elevated cortisol at 5 and 12 months of age, exaggerated cortisol response to a stressor, and increased corticotropin releasing factor (CRF) in cerebrospinal fluid as compared to controls. Pharmacological challenges used to investigate the neural mechanisms of this exaggerated glucocorticoid secretion revealed blunted response to a corticotropin releasing hormone challenge, suggesting a down-regulation of CRF receptors in the anterior pituitary. Thus, the amygdala plays a critical role in the development of both basal and stress-related HPA axis functions and in the expression of sexually dimorphic behaviors, providing valuable insights into the neural mechanism underlying the symptomatology of many developmental neuropsychiatric disorders. |
