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    An investigation into the interaction of the microbiome-gut-brain axis with stress : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Science at Massey University, Manawatū, New Zealand
    (Massey University, 2023) Bear, Tracey
    This thesis aimed to investigate whether changes in the gut microbiota and associated biomarkers were associated with stress-induced anxiety-like and depressive-like behaviour. Two studies used the unpredictable chronic mild stress (UCMS) over 4 or 6 weeks (vs no UCMS, control) in Sprague-Dawley rats. Depressive-like behaviour was measured in female rats using the sucrose preference test, and the Porsolt swim test. Anxiety-like behaviour was measured with the light-dark box test. Faecal corticosterone, caecal microbiota (composition and organic acids), serum gut permeability (lipopolysaccharide-binding protein, LBP) and plasma inflammation (12 cytokines) markers were measured. Atypical behaviours were observed in female rats following UCMS and no depressive-like behaviours were observed. The circulating concentration of cytokines, but not plasma LBP or caecal organic acids, was higher in UCMS-exposed female rats. Relative abundance of taxa from the Clostridiales order and Desulfovibrionaceae family correlated with anxiety-like behaviours and plasma cytokine concentrations, regardless of UCMS. Studies of these atypical behaviours in female rats confirmed expected patterns of sucrose intake in the sucrose preference test and no decreased depressive-like behaviours in the Porsolt swim test with antidepressant citalopram and imipramine drugs. A further study also showed differences in baseline behaviour in male versus female rats, leading the second UCMS study to be in male rats. Increased faecal corticosterone and anxiety-like behaviours were observed in male UCMS-exposed and control rats at week 4 of UCMS compared to baseline. Plasma cytokine concentrations were higher in the UCMS group but higher faecal corticosterone concentrations and anxiety behaviours in control rats suggest that they were more stressed than treated rats. Caecal neurotransmitter concentrations did not differ between treatments nor correlate with serum neurotransmitter, cytokines or LBP concentrations or behaviour. The findings showed an association between the gut microbiota and anxiety-like behaviours, which was not stress dependent. No measured biomarkers explained the observed anxiety-like behaviours. Caecal digesta neurotransmitter profiles were dissimilar to serum profiles indicating it may not be an important influence on serum levels. Despite the atypical behavioural results following the interventions, the results still provided useful and unique information which contributes to the body of Microbiome Gut Brain Axis research.
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    Rigidity : a cognitive style conceptualization of depression : a thesis presented in partial fulfilment of the requirements for the degree of Master of Arts in Psychology at Massey University
    (Massey University, 1975) McDonald, Craig Westley
    The traditional ideas of depression as an affective illness are examined and evidence is presented that contrary to the view presented in many texts, depression is also associated with thought disorders as severe as those experienced in other psychopathological illnesses. A model of depression as a single entity is proposed that suggests that the various manifestations of the disorder are due to a single underlying mechanism. This mechanism is conceived of in terms of cognitive style and cognitive control theory and evidence is presented that this is an adaptive mechanism for the individual and consists of selective blocking of incoming stimuli or in more general terms, 'rigidity'. Twelve depressed patients were examined using a battery of tests which yielded 22 measures including level of depression, rigidity, anxiety, field-dependence and various scales of personality. These measures were then correlated using Pearsons Product-Moment correlation coefficients and were then subjected to cluster analysis using Tryons modification of Holzinger and Harmon's B-coefficient technique. This gave four meaningful clusters of which three matched the components of Becks primary triad, with the important addition that this analysis reveals the importance of rigidity as a factor in Beck's second component-negative self-concept.