The Pathological and Molecular Basis of Anxiety-like Behaviour in the Experimental Autoimmune Encephalomyelitis (EAE) Model of Multiple Sclerosis (MS)

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Department of Psychology and Counselling, School of Psychological Science and Public Health, College of Science, Health and Engineering, La Trobe University, Victoria, Australia.

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system with a neurodegenerative component, affecting principally young adults. Recent evidence has identified emotional and cognitive deficits as primary disease symptoms of MS, rather than psychological consequences of living with a debilitating condition. It is therefore essential to elucidate mechanisms underlying these symptoms, to evaluate the capacity of available treatments to address these disease manifestations or develop novel drugs. Concurrently, over the last decade, the role of platelets as drivers of inflammation has emerged. A key role for platelets in neuroinflammation was previously demonstrated by our laboratory in murine experimental autoimmune encephalomyelitis (EAE), the most accepted MS model. In this thesis, the hypothesis that platelets play an early and critical role in the development of anxiety-like behaviour was investigated. Experimentation was based on the elevated plus maze (EPM) test, a validated test of mouse anxiety-like behavior, in EAE and evaluation of platelet-related inflammatory changes in the hippocampus, a region associated with emotion, cognition and memory. Firstly, optimization of mouse strain and route of drug delivery was performed. Second, early platelet invasion of the hippocampus was identified and platelet depletion was demonstrated to be effective in reducing anxiety-like behavior in EAE. This was confirmed by molecular, and quantitative confocal microscopic analyses. Third, it was shown that immunomodulation has no beneficial effect on anxiety-like behavior, despite effective reduction of the inflammatory environment in the hippocampus. This was also confirmed by molecular and confocal microscopic analyses. These data reveal the contrasting effects of platelet targeting versus targeting of autoreactive T cells in autoimmunity. Therefore, these studies provide proof-of-concept for a direct role for platelets in hippocampal damage and platelet targeting as a novel therapeutic approach for emotional and cognitive deficits in MS.