The objective of the research described in this thesis was to demonstrate the role of gene-environment interactions in the emergence of individual differences in cocaine use. For this purpose we... Show moreThe objective of the research described in this thesis was to demonstrate the role of gene-environment interactions in the emergence of individual differences in cocaine use. For this purpose we used two inbred mouse strains, the C57Bl/6 (C57) and DBA/2 (DBA), which are known to differ in drug-intake and to be differentially sensitive to several stressors. We studied the impact of early life experiences (long-term influence) as well as a later life psychosocial stressor (short-term influence) on adult drug intake behavior in these two mouse strains. To study the impact of the early life environment, we manipulated the maternal environment of the mice by fostering them with non-related mother strains showing either high or low pup-oriented behaviour. The late life experience consisted of a short-lasting period of group housing in adulthood. Cocaine self-administration in mice with a C57 background was not affected by either changes in postnatal maternal environment or a short group housing experience in adulthood, while these same experiences did affect mice with a DBA background. As a first step towards the biological mechanisms underlying this gene-environment interaction we found that vasopressin was differentially regulated in the extended amygdala of the DBA mice. Show less
This thesis addressed the physiological impact of fear in 4- and 7-year-old children, induced by media and social fear-inducing tasks (the Trier Social Stress Test for Children). The main question... Show moreThis thesis addressed the physiological impact of fear in 4- and 7-year-old children, induced by media and social fear-inducing tasks (the Trier Social Stress Test for Children). The main question pertained to individual differences in physiological reactivity to fear-inducing stimuli. The possibly relevant factors of attachment security, the child’s temperamental fearfulness, and variations in the serotonin transporter gene (5-HTTLPR; long vs. short allele) were taken into account. Results showed that temperament, attachment, and genetic influences play significant and interactive roles in the expression of fear reactivity. A secure relationship affected the reactivity to media-induced fear stimuli in temperamentally more fearful children but not in less fearful children irrespective of children’s ages. This finding adds to the growing literature showing that children high in negative emotion are more susceptible to positive as well as negative rearing influences. Furthermore, we found evidence that reactivity to the social fear-inducing task was explained by a combination of variations in the serotonin transporter gene and attachment security. Children with a secure attachment representation and two long 5-HTT alleles showed the lowest levels of fear reactivity, indicating that physiological reactivity to a social fear-inducing task is a product of the child’s biology and environment. Show less
The Adult Attachment Interview (AAI) was developed in the early 1980s to measure an adult’s attachment representation. Since then, it has been applied in more than 100 studies. This thesis aimed to... Show moreThe Adult Attachment Interview (AAI) was developed in the early 1980s to measure an adult’s attachment representation. Since then, it has been applied in more than 100 studies. This thesis aimed to shed light on some of the potentials and limitations of the AAI. We found that coherence, which is an important concept in attachment interviews, is not defined similarly by attachment experts, linguists, and non-experts. Therefore, it seems that a measure for coherence cannot make the AAI more easily accessible for non-attachment experts. Secondly, we showed that the attachment representations of adopted adolescents were related (1) to their own autonomy behaviors and mothers’ relatedness behaviors during a discussion task, (2) to the adolescents’ emotional investment in others, and (3) to the adolescents’ perceived support from others. Intelligence and perceived temperament were not associated with the adolescents’ attachment representation. These results support the validity of the AAI when assessed with (adopted) adolescents. Finally, we revealed that the AAI differentiates between adolescents with divergent physiological responses (interbeat interval reactivity) to attachment relevant situations: dismissing adolescents showed less physiological reactivity during the AAI than secure adolescents, while they appeared to be more stressed during a discussion task with their mothers. Show less
