Introduction: Diabetes is strongly linked to human depression and induces depressive behaviours in animal models. The psycho-immune-neuroendocrine (PINE) network, a theoretical framework of interrelatedness of our key non-communicable diseases, posits a role of sickness and self-care behaviours in the progression of metabolic conditions. Periodontal disease (gingivitis and periodontitis) may be a common precursor to both metabolic and mood disorders; periodontal disease unequivocally and reciprocally influences metabolic disorders and may be a direct complication of Type II diabetes (T2DM). Congruent with a role for periodontal disease to promote widespread metabolic and mood disorders, a causative relationship has not been proven. The imbalances instigated by metabolic and mood conditions reportedly cause reduced infarct tolerance and responsiveness to cardioprotection. It remains unclear how a combined disease status challenges this. The work presented in this thesis assesses the functional outcomes associated with behavioural and cardiovascular impacts of chronic Type II diabetes (T2D), periodontal disease (PD), and chronic stress (ST). This thesis aims to delineate alterations in behaviours in response to disease comorbidities, the effects of these comorbidities on heart function via echocardiography, and their impact on post-ischaemic heart function.

Methods: Ninety-six male C57Bl/6 mice were assigned to eight distinct experimental groups (n = 12). Mice were stratified into control (n = 48) and Type II diabetes (T2D) (n = 48) and monitored over 20 weeks. T2D cohort was subject to streptozotocin injection (75mg/kg) and maintained on WD diet regimen. At Week 14, PD was induced utilising ligature method (n = 48), and restraint stress was introduced to specific subsets during the final two weeks of study (n = 48). Behavioural assessments were conducted at baseline, pre-periodontal intervention, and post-stress intervention (Week 0, 14, 20), utilising the open field test (OFT) and elevated plus maze (EPM) to quantify anxiety-like and depressive-like behaviours. At the same time, echocardiography was performed on a subset of mice (n = 8) per group. After sacrifice, Langendorff Isolated Heart Perfusions were executed on a subset of mice (n = 8) per group to evaluate post-ischaemic myocardial functional responses.

Results: This research investigated the impact of T2D, ST, and PD on various physiological parameters in a murine model, scrutinising their multifaceted physiological and behavioural ramifications. Robust metabolic assessments revealed significant findings associated with body weight changes, metabolic assessments, locomotory behavioural analyses, cardiac structural parameters, ventricular performance, and recoveries during reperfusion following ischaemia. Significant increases in T2D mice body mass were concomitant with significant metabolic dysregulation characterised with elevated fasting blood glucose and impaired glucose tolerance. Whilst insulin levels exhibited no marked variation between the groups, introduction of periodontitis and stress exerted discernible influences on insulin levels and the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR score) where intricate regulatory interactions may be modulated by these factors. The concurrent presence of stress and periodontal disease did not exacerbate these metabolic perturbations, underscoring the nuanced dynamics at play. Behavioural analyses unveiled alterations in locomotion and exploratory behaviours, evidenced with changes in line crossings indicative of depressive-like or anxiogenic tendencies associated with T2D and stress. These behavioural phenotypes remained relatively stable across temporal assessments. The study highlighted significant differences in line crossings and centre square entries at different time points for different treatment groups, isolating age as a factor of developing depressive-like behaviours in addition to T2D induced hypoactivity. Evaluation of cardiac structural and functional parameters showed subtle and discernible differences between CTRL and T2D cohorts; notable variations in fractional shortening and diastolic dysfunction. Cardiac output, stroke volume, and ejection fraction remained largely unaffected, distinct alterations in heart size normalised to body mass were apparent that suggests relative preservation of cardiac geometry despite metabolic challenges. Ischaemic contracture analysis unveiled disparities in myocardial responses to ischaemic insult - implicating differential recoveries of left ventricular developed pressure post-ischaemia between CTRL and T2D groups

Conclusion: Consequently, the findings delineate and elucidate the physiological landscape and functional outcome underlying T2D, ST, and PD, on metabolic, behavioural, cardiac parameters, and ischaemic responses in murine models. It is shown that T2D with a WD can elicit changes in cardiometabolic parameters and heart function. Comorbid PD may not cause synergistic worsening, and ST may attenuate certain cardiometabolic parameters. Behavioural function does not appear to be sensitive to disease conditions where age is deemed to have a greater impact on developing anxiogenic and depressive-like behaviours. The mechanisms that govern these changes are unclear and require further investigation.