The Role of the Preoptic Area in Social Interaction in Zebrafish

Abstract

The proposed “Social Decision Making Network” (SDMN) is a network of conserved, interconnected brain areas believed to regulate social behaviour across vertebrate taxa. While the role of the SDMN in complex social behaviours is relatively well understood, we know comparatively little about the role of the SDMN in simple grouping and responses to social cues. While the existence of the SDMN in mammals is well supported, its role in social behaviour in other taxa is less well studied. By analysing neuronal activation in the preoptic area (POA), dorsal nucleus of the ventral telencephalic area (Vd), supracommissural nucleus of the ventral telencephalic area (Vs), and ventral nucleus of the ventral telencephalic area (Vv) in zebrafish (Danio rerio) I aimed to determine how these four nodes of the SDMN respond when shoaling and when exposed to different social cues. Combined visual and olfactory exposure to conspecifics significantly increased levels of the phosphorylated ribosome S6 protein (PS6) in the POA, however surprisingly there was no change in POA PS6 levels when fish were allowed to shoal, suggesting the POA may in fact be responding to social cues rather than shoaling itself. Other nodes of the SDMN showed no changes in PS6 levels. Based on these findings I investigated POA regulation of shoaling by analysing expression of isotocin (IT) neurons in the POA of two populations of zebrafish with different shoaling phenotypes. I found that more social fish had more magnocellular IT neurons than less social fish, but there were no differences in parvocellular or gigantocellular IT neuron numbers. My findings provide evidence that the POA is sensitive to social cues but is not necessarily activated by shoaling. Furthermore, my results demonstrate that adult plasticity in magnocellular IT neurons is associated with changes in shoaling tendencies in zebrafish.