Organ specificity of autonomic nervous system responses

The rapid, aggressive, and widespread autonomic response required to cope with life-threatening danger was the model on which early views of the sympathetic nervous system as a monolithic, undifferentiated effector were based. With advances in experimental techniques and a greater appreciation for the autonomic influences on the function of noncardiovascular tissues, this preliminary construct has been eclipsed by an organizational model featuring an extensive array of functionally specific output channels, which can be simultaneously activated or inhibited in combinations that result in the patterns of autonomic activity that support behavior, mediate homeostatic reflexes, and cope with injury and disease. With this perspective, the defense response is but one of the many activational states of the central autonomic network. Considerable evidence supports the existence of tissue-specific sympathetic output pathways, which are likely to include distinct populations of premotor neurons whose target specificity could be assessed using the functional fingerprints developed from characterizations of postganglionic efferents to known targets. The organ-specific responses of sympathetic outflows to stimulation of a variety of reflex inputs suggests that the circuits regulating the activity of sympathetic premotor neurons must have parallel access to groups of premotor neurons controlling different functions but that these connections vary in the strength of their influence on different sympathetic outputs. Understanding the structural and physiological substrates antecedent to premotor neurons that mediate the differential control of sympathetic outflows, including those to noncardiovascular targets, represents a challenge to our current technical and analytical approaches.