Labor may perhaps be the most painful a woman might experience, although characterized by large inter-individual variability. The perceived pain during labor is the result of diverse factors, i.e. her previous pain experiences, the analgesia she receives and maybe also her genes. The overall aim of this thesis was to investigate biological and psychological mechanisms underlying inter-individual differences in labor pain related behaviors. The mechanisms that characterize endogenous pain relief during labor are not fully understood, though it is known to be partly explained by the effects of β-endorphin (BE). BE plasma levels were followed longitudinally in a cohort of pregnant women and were found to remain unchanged between early and late pregnancy, although with a nadir in the beginning of the third trimester. Furthermore, women with low levels of BE in plasma at the end of the third trimester, required second line labor analgesia to a significantly higher extent than women with normal levels. In a population-based sample of 814 pregnant women we investigated if inter-individual differences in labor pain related behavior was influenced by the pain-protective single nucleotide polymorphism (SNP) combination of guanosine triphosphate cyclohydrolase (GCH1) and the opioid receptor µ-1 gene (OPRM1) A118G SNP. We identified a possible association between the pain-protective SNP combination of GCH1 and use of second line analgesia. No association was found between the OPRM1 and use of analgesia or labor pain related behavior. The association between self-rated antenatal depressed mood and anxiety in relation to pain behaviors and self-reported pain during labor was investigated. We found that depressed mood during pregnancy is associated with early arrival to the delivery department, whereas antenatal anxiety is associated with increased self-rated pain prior to labor analgesia.  In conclusion, although an increasing number of studies strongly suggest that genetic predisposition plays an important role in pain and pain-related mechanisms, GCH1 and OPRM1 has little to offer in terms of individual counseling on labor analgesia. To enable the future use of genetic variability for pre-labor testing and counseling, a number of different genes reflecting pain mediation pathways, involving biological and psychological mechanisms, need to be analyzed in combination.

The present thesis is based on four studies focusing on alcohol consumption among Swedish adolescents, and therewith related psychosocial and genetic factors. One main objective was to study the reasons for drinking alcohol among different population - representative samples of adolescents in order to identify motives for drinking. Relationships between these drinking motives, alcohol consumption, and alcohol - related problems were also investigated. Three motives emerged from this study: social - enhancement, coping and dominance. The association with alcohol consumption and alcohol - related problems was positive for social - enhancement and coping motives, but negative for the dominance motive. A significant heritability of alcohol use disorders has been demonstrated by family, adoption and twin studies. Environmental influences have also been acknowledged to play an important role in the development of alcohol use disorders. Moreover, the interaction between genetic and environmental factors is likely to influence the risk - resilience for alcohol use disorders. In view of this knowledge, plausible candidate polymorphisms were considered in gene - environment interaction models. An effect of the genetic polymorphisms was only present when a G x E model was considered. A genetic variant of the clock gene Period2, in an interaction with sleep problems, was studied in relation to alcohol consumption among adolescents. High alcohol consumption was associated with the AA genotype of the PER2 SNP10870 polymorphism, in an interaction with several and frequent sleep problems, among adolescent boys. A genetic variant in the opioid µ receptor 1 gene, in an interaction with alcohol consumption, was studied in relation to depressive symptoms. Depressive symptoms were predicted by the G allele of the OPRM1 A118G polymorphism, in an interaction with high alcohol consumption, among adolescent girls. Additionally, the PER2 SNP10870 and the OPRM1 A118G polymorphisms were studied in a sample of severely alcoholic females. Furthermore, alcohol consumption was assessed by using different instruments, such as biomarkers and surveys. Comparisons were carried out to identify the most suitable method to assess alcohol consumption among adolescents. Questionnaire and interview seemed more suitable tools than biomarkers in this regard.The results eventually support the importance of psychosocial and genetic influences, and their interaction effect on alcohol consumption among adolescents.

Autism Spectrum Disorder (ASD) is a diverse disorder, and the heterogenous range of possible presentations hinders our understanding of its aetiology. Recently there has been a surge of genome wide association studies for ASD, while historically psychological theories were relied on to explain the emergence of ASD. These fields continue to provide insights into ASD, but they tend to operate in parallel – genetic studies often lack comprehensive psychological phenotyping and theoretical backing, and psychological studies tend to lack genetic explanations. I propose that moving forward, genotype-phenotype studies should have a strong foundation in both fields and should focus on genes and theories with realworld implications for ASD diagnostics and/or interventions. This approach can be supported by focusing on established, well supported psychological theories, and selected ASD candidate genes that could be implicated in these theories, and ideally the genetic mechanism implicated should be one that can be targeted by existing medications. I therefore selected two prominent psychological theories, the Social Motivation Theory for ASD (Panksepp, 1979) and the ToM Theory for ASD (Baron-Cohen et al., 1985), and selected an ASD candidate gene that was likely implicated in each of these theories, namely the mu-opioid receptor gene (OPRM1) and the serotonin transporter promoter length polymorphism (5-HTTLPR) respectively. For the first study of this protocol, I assessed the possible relationships between social motivation, OPRM1, and the ASD phenotype. For the second study, I assessed possible relationships between ToM deficits, 5-HTTLPR, and the ASD phenotype. These two studies shared a sample of 153 male children 4-16 years old; 51 boys per group (i.e. non-verbal ASD; verbal ASD; neurotypical). All ASD children completed ADOS2 assessment for ASD phenotyping. For the Social Motivation Study, attachment was used as a proxy to assess level of social motivation in all participants, and 76 of the 102 children with ASD provided DNA for OPRM1 genotyping. Comparisons across all three groups showed that the ASD samples had significantly lower social motivation than the neurotypical sample, with the non-verbal ASD group displaying the most severely reduced level of social motivation. Reduced social motivation was associated with ASD-related deficits in the non-verbal ASD sample but not the verbal ASD sample. Finally, I was unable to statistically assess the role of OPRM1 as hypothesized, due to an unprecedentedly high rate of the OPRM1 G allele, which indicated atypical mu-opioid processes. This clearly implicated OPRM1 in ASD and is the first study to show this so convincingly. Overall, this study's findings led me to suggest that Panksepp's (1979) theory could be updated to include a threshold effect such that more severely reduced social motivation in ASD is associated with little-to-no language acquisition, while those with less severely reduced social motivation are able to develop language and this protects against associations between social motivation and ASD-related deficits in childhood. For the Theory of Mind Study, the verbal ASD sample and neurotypical sample completed a developmental ToM Battery (i.e. University of Cape Town Theory of Mind Battery) and WASI assessment to establish verbal intelligence quotient (VIQ) scores, and 70 of the children with ASD were successfully genotyped for 5-HTTLPR. This study found that verbal male children with ASD tended to be one developmental stage behind age-matched neurotypical peers on ToM tasks. ToM deficits were associated with greater impairment in overall ASD severity and in symptoms from the social communication and interaction domain. For the non-verbal ASD sample, the 5-HTTLPR short allele, which is implicated in atypical serotonergic transmission, was associated with greater impairment overall and in the restricted and repetitive behaviours and interests symptom domain. No associations between 5-HTTLPR and ToM, or with ASD-related symptoms, was found for the verbal ASD group. This again suggested that language acquisition is an important consideration in genotypephenotype studies in male children with ASD.