Social Interaction over Time, Implications for Stress Responsiveness
Cliff H. Summers
Biology & Neuroscience
University of South Dakota
Behavioral interaction during social situations is a continuum of action, response, and reaction to response. The temporal nature of social interaction creates a series of stressful situations, such as aggression, physical threat, displacement from resources, and the persistent psychological threat accompanying social hierarchy. The ebb and flow of neurochemical and endocrine secretions during social stress do not necessarily follow the pattern of individual social stressors, but neuroendocrine stress responsiveness does change over time. In addition to the information derived from measuring temporal patterns of neuroendocrine stress responsiveness, social interaction is a unique tool for understanding individualized responses to stress. This is because when two or more individuals interact, often a social hierarchy ensues. In the case with two males competing for dominance, one secures that social position, and the other is relegated to subordinate status. Each social station is an adaptive response to a stressful social condition, resulting in a unique behavioral repertoire. Aggressive interactions establishing social position are stressful for all, and maintenance of each level of social status is also potentially stressful. The purpose of this paper is to explore what happens to neural and endocrine measures of stress responsiveness in both dominant and subordinate individuals during the course of stressful social interaction. By examining the temporal changes of monoaminergic transmitters in the limbic system, and in plasma glucocorticoids, some semblance of social adaptation appears.
Coping with the stresses from behavioral interaction is an important adaptation for all social animals. In this paper I will use examples of temporal patterns of neuroendocrine response induced by social stress in fish, reptiles and primates. The similarity of social, neural, and endocrine responses are remarkable. Even different specific coping mechanisms point out the similarity of vertebrate stress responses. Much of the work from my lab has focused on the lizard Anolis carolinensis, a useful model to construct these temporal patterns from because of a unique social sign stimulus generated during social stress by the sympathetic nervous system. During social interaction, males that will become dominant have a shorter latency to eyespot darkening than their opponents, and the presence of eyespots inhibit aggressive display and biting. Eyespot coloration can be delayed using the selective serotonin (5-HT) reuptake inhibitor sertraline, with the added consequence that dominant social status in many animals is lost. Reversal of social status via serotonergic activation, appears to mimic chronic serotonergic activity (estimated by the ratio of catabolite to transmitter; 5-HIAA/5HT). The pattern of eyespot darkening, faster in dominant males, is coincident with that for serotonergic activity. The fundamental temporal relationship between dominant and subordinate reactivity in limbic monoaminergic activity over a continuous course of social interaction appears to be a two phase response, temporally specific to brain region, and always faster in dominant individuals.
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