Neural Mechanisms of Dominance Behavior

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Dominance hierarchies organize the social behavior of all social animals, and the behaviors that contribute to them are immediately recognizable. Despite the ubiquity and importance of social dominance, little is understood about its neural substrates in any species. Serotonin has been identified as a neurotransmitter that helps mediate social dominance in vertebrates and invertebrates. Although serotonin has many effects and sites of action in the central nervous system, the effects and sites that are relevant to social dominance are largely unknown. One approach to this problem is to examine how serotonin affects neural circuits that help govern specific aspects of behavior, and to determine how these effects change with social dominance status. The well-understood neural circuitry for escape behavior in crayfish provides an opportunity to determine how changes in an animal's social status lead to changes in the effect of serotonin on the excitability of neural circuits for escape. Earlier work has shown that serotonin's effect on the excitability of the lateral giant (LG) command neuron for escape varies from facilitation in socially dominant crayfish to inhibition in subordinate crayfish. Two molecular receptors for serotonin have been identified in crayfish, and their distributions in the crayfish nervous system have been described. This project will test the hypothesis that the differences in serotonin's effects in dominant and subordinate crayfish result from differences in the distribution or the efficacy of serotonin receptors that affect the LG neuron's excitability. Differences in receptor distribution in the LG escape circuit will be determined using fluorescently labeled antibodies to the receptors. Serotonin agonists and antagonists specific to each receptor will be used to determine how its activation contributes to the effect of 5-HT in each social type of animal. This research will show how differences in the distribution and action of serotonin receptors produce differences in nervous system function in dominant and subordinate crayfish. Because the action of serotonin affects social status in many animals, these mechanisms are likely to be widespread in the animal kingdom. This work will provide research training opportunities for a Post-doctoral student and a few undergraduates drawn from GSU and from other members of the Center for Behavioral Neuroscience (CBN). The research will be presented and discussed at the CBN's Aggression and Affiliation Collaboratories, and so contribute to the CBN mission.