Abstract
Species differ strongly in their sociality. Highly social species show strong group cohesion and social affiliations, whereas more asocial species show few social interactions and weak affiliation patterns. Two nonapeptide superfamilies have been linked to the regulation of social behaviour in particular. The first, the oxytocin superfamily, includes oxytocin in
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mammals and isotocin in teleost fish. The second includes the vasopressin and its non-mammalian homolog vasotocin. These nonapeptide lineages are highly evolutionary conserved in structure and are present in all vertebrates. The function of the nonapeptides also appears to have been highly conserved. This suggests that these nonapeptide systems form part of a mechanism underlying the regulation of social behaviour, a system that is possibly conserved across all vertebrates. Taken broadly, research findings suggest that oxytocin stimulates pro-social behaviour (e.g. affiliation) whereas vasopressin stimulates anti-social behaviour (e.g. aggression). To study the neural underpinnings of social behaviour and its evolution we examined the zebrafish (Danio rerio) and the Norway rat (Rattus norvegicus). Three categories of social behaviour were studied to investigate sociality and its neural correlates: social learning, social memory and social affiliation (shoaling). First, we demonstrated that naïve zebrafish socially learned a novel escape task from knowledgeable conspecifics. Second, our findings suggested that social memory formation based on familiarity is not an important aspect of adult zebrafish grouping behaviour. Third, we show that the vasotocin system regulates anti-social behaviour in a shoaling context in zebrafish. This finding provides evidence that nonapeptides play a role in the regulation of sociality in zebrafish and adds to the evidence suggesting that this is a highly conserved neural mechanism that underlies social behaviour across vertebrates. To investigate both the effects of social experiences early in life and oxytocin on the propensity to use social information when adult, we used the maternal care system in Norway rats. Extensive research has established that mothers vary in the intensity of licking and grooming of their pups. These maternal care phenotypes have been linked to neuro-endocrine differences in the offspring. Here, we demonstrate for the first time that early social experiences predict the propensity to use social information later in life. The findings presented in this thesis contribute to our understanding of social behaviour and its underlying neural systems. By investigating functional and developmental aspects of social behaviour and the role of the nonapeptide systems we may gain insight into the neural mechanisms underlying vertebrate sociality and the evolution of these mechanisms. Knowledge on how social experiences early in development affect sociality later in life could be used to increase our understanding of the development of human diseases related to social deficits, for instance autism, or social phobias. Translating findings from non-human studies on the neural mechanisms underlying sociality is a promising avenue of research that potentially could result in an effective medical treatment that reduces social deficits or anxiety related behaviours in the future
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