Abstract

Exposure to mild stress is known to activate dopamine (DA), serotonin (5-HT), and norepinephrine (NE) metabolism in the anteromedial prefrontal cortex (m-PFC). Neuroanatomical site(s) providing afferent control of the stress activation of the m-PFC monoaminergic systems is at present unknown. The present study used a conditioned stress model in which rats were trained to fear a substartle-threshold tone paired previously with footshock and assessed for behavioral, neuroendocrine, and neurochemical stress responses. Bilateral NMDA-induced excitotoxic lesioning of the basolateral and central nuclei of the amygdala was performed before or after training. Pretraining amygdala lesions blocked stress-induced freezing behavior, ultrasonic vocalizations, adrenocortical activation, and dopaminergic metabolic activation in the m-PFC. Post-training amygdala lesions blocked stress-induced m-PFC DA, 5-HT, and NE metabolic activation. Post-training amygdala lesions also blocked stress-induced freezing and defecation, and greatly attenuated adrenocortical activation. These data provide evidence of amygdalar control of stress-induced metabolic activation of the monoaminergic systems in the m-PFC, as well as amygdalar integration of behavioral and neuroendocrine components of the rat stress response. These results are discussed in terms of possible relevance to stress-induced exacerbation of schizophrenic symptoms and the pathophysiology of post-traumatic stress disorder.