Mechanisms for quick and variable responses.

Dominant and subordinate males produce neuroendocrine stress responses during aggressive social interaction. In addition, stress responsiveness has both acute and chronic temporal components. A neurochemical marker that distinguishes social status and aggression by temporal and regional differentiation is the activity of serotonergic nuclei and terminals. A unique model for distinguishing the relationships among the neuroendocrine machinery of stress, social status and behavior is the lizard Anolis carolinensis. Dominant males exhibit more aggression and have temporally advanced serotonergic responses. Chronic serotonergic activity is associated with subordinate social status and reduced aggression. Acute and chronic serotonergic responses occur in both dominant and subordinate males, and are distinguished temporally. This provides a fundamental question that may elucidate basic differences in behavior: What causes temporally advanced serotonergic activity in response to stress in dominant males? Secondarily, what is the neural basis for the acute and chronic responses? The neural mechanisms for transduction of the relevant behavioral signals are very plastic. Behavioral experience and visual stimuli can produce very rapid responses. Faster and greater responsiveness may be stimulated by restraint stress, social stress and the absence of social sign stimuli (e.g. eyespots of the lizard Anolis carolinensis). Stress response machinery provides regulatory factors necessary to modify social behavior, and to adapt it for specific contexts. Serotonergic activity is rapidly modified by glucocorticoids and GABA, and also by CRF under conditions of previous stress or in combination with AVP. Advancing acute elevation of serotonergic activity may be a distinguishing characteristic of dominant males. Social events add contextual conditioning to brain transmitter activity, with social information processed in a distributed fashion. Medial amygdala manifests delayed serotonergic response compared to hippocampus and nucleus accumbens, and is therefore a good candidate to mediate chronic stress responsiveness. Limiting or delaying acute effects, in addition to chronic serotonergic activity, may be the distinguishing characteristics of subordinate males. Monoamines, glucocorticoids, testosterone, CRF, AVP, AVT, play neuromodulatory roles producing context appropriate behavior. Copyright 2001 S. Karger AG, Basel