Investigating the fronto-limbic and hypothalamic-pituitary-adrena axis systems in conduct disorder

Abstract

In this thesis, I report studies investigating the neurobiology of conduct disorder (CD) – a disorder diagnosed in children and adolescents who display a persistent pattern of disruptive and aggressive behaviour. My particular focus is on the role of frontal, limbic and hypothalamic-pituitary-adrenal (HPA) axis systems, and especially whether CD-related alterations in these systems differ between males and females. A range of different imaging techniques were applied to data from the Neurobiological and Treatment of Adolescent Female Conduct Disorder study (Fem-NAT-CD). In study 1 (Chapter 4), we employed surface-based morphometry techniques to assess frontal and limbic (cortical and subcortical) brain structures. Similar patterns of CD-related related reductions in cortical volume, thickness, and surface area in the superior frontal gyrus were seen in both sexes. The second study (Chapter 5) assessed the shape of subcortical limbic structures. Youths with CD exhibited shape deformations (i.e., inward) in the shell of the nucleus accumbens compared to controls, independent of sex. The third study (Chapter 6) used spherical deconvolution basedtractography and virtually dissected key fronto-limbic white matter tracts, namely: the uncinate fasciculus, fornix, and the subgenual, retrosplenial and parahippocampal bundles of the cingulum. We observed reduced fractional anisotropy in the retrosplenial cingulum in the CD group relative to healthy controls. However, this result was moderated by sex: males with CD showed reduced, while females with CD showed increased fractional anisotropy compared to sex-matched healthy controls. Finally, we investigated sex differences in HPA axis function (Chapter 7) by measuring cortisol response during the Trier Social Stress Test for Children. Both males and females with CD showed blunted cortisol response to stress, and such effects were not explained by low levels of self-rated fear or anxiety. In a small, proof of concept analysis we observed a positive correlation between cortical volume of the superior frontal gyrus and cortisol reactivity. I conclude that the neurobiological basis of CD is relatively similar in males and females. Thus, previous findings in males with CD may also apply for females with CD. Suggestions for future research are presented and clinical implications are discussed.

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ORCID for Graeme Fairchild: orcid.org/0000-0001-7814-9938

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