Neuroanatomy of Stress Responses

The autonomic nervous system, especially the sympathetic nervous system, regulates immune responses, while cytokines produced in the immune system also affect neuronal activities. Stress-induced expression of immediate early genes, such as c-Fos in the brain, and the viral transneuronal labeling using pseudorabies virus make it possible to analyze the neurocircuitry of the stress-related central autonomic nervous system. Limbic systems (amygdala, lateral septum, infralimbic, insular, ventromedial temporal cortical regions), and several hypothalamic and brainstem nuclei have been identified as the central sites that regulate stress-induced sympathetic nervous activation. This review focuses on the involvement of the amygdala in the regulation of stress-induced sympathetic nervous responses. All amygdaloid subnuclei receive psychological information from other limbic regions, while the lateral and central subnuclei receive sensory and immune information from parabrachial nucleus and medical geniculate nucleus. Output to the hypothalamus mainly originates from the medial amygdala, while output to the bed nucleus of the stria terminalis originates from the central amygdala and the medial amygdala. Sex steroids such as estrogen and androgen can modulate the sympathetic nervous activity since their receptors are expressed in the medial amygdala.