Social complexity during early development has long-term effects on neuroplasticity in the social decision-making network

In social species, early social experience shapes the development of appropriate social behaviours during conspecific interactions referred to as social competence. However, the underlying neuronal mechanisms responsible for the acquisition of social competence are largely unknown. One key candidate to influence social competence is neuroplasticity, which functions to restructure neural networks in response to novel experiences or alterations of the environment. One important mediator of this restructuring is the neurotrophin BDNF, which is well conserved among vertebrates. We studied the highly social fish Neolamprologus pulcher , in which the impact of early social experience on social competence has been previously shown. We investigated experimentally how variation of the early social environment impacts markers of neuroplasticity by analysing the relative expression of the bdnf gene and its receptors p75NTR and TrkB across nodes of the Social Decision-Making Network. In fish raised in larger groups, bdnf and TrkB were upregulated in the anterior tuberal nucleus, compared to fish raised in smaller groups, while TrkB was downregulated and bdnf was upregulated in the lateral part of the dorsal telencephalon. In the preoptic area (POA), all three genes were upregulated in fish raised in large groups, suggesting that early social experiences might lead to changes of the neuronal connectivity in the POA. Our results highlight the importance of the early social experience in programming the constitutive expression of neuroplasticity markers, suggesting that the effects of early social experience on social competence might be due to changes in neuroplasticity.