Socially induced plasticity of the posterior tuberculum and motor behavior in zebrafish (Danio rerio).

Social dominance is prevalent throughout the animal kingdom. It facilitates the stabilization of social relationships and allows animals to divide resources according to social rank. Zebrafish form stable dominance relationships that consist of dominants and subordinates. Although social-status-dependent differences in behavior must arise due to neural plasticity, mechanisms of how neural circuits are reconfigured to cope with social dominance are poorly described. Here, we describe how the posterior tuberculum nucleus (PT), which integrates sensory social information to modulate spinal motor circuits, is morphologically and functionally influenced by social status. We combined non-invasive behavioral monitoring of motor activity (startle escape and swim) and histological approaches to investigate how social dominance affects the morphological structure, axosomatic synaptic connectivity, and functional activity of the PT in relation to changes in motor behavior. We show that dopaminergic cell number significantly increases in dominants compared to subordinates, while PT synaptic interconnectivity, demonstrated with PSD-95 expression, is higher in subordinates compared to dominants. Secondly, these socially induced morphological differences emerge after one week of dominance formation and correlate with differences in cellular activities illustrated with higher phosphor-S6 ribosomal protein expression in dominants compared to subordinates. Thirdly, these morphological differences are reversible as the social environment evolves and correlates with adaptations in startle escape and swim behaviors. Our results provide new insights of the neural bases of social behavior that may be applicable to other social species with similar structural and functional organization.