Daily rhythms of physiology and behaviour in mammals are orchestrated by a hierarchical network of cellular oscillators. The master pacemaker that defines local and systemic timing across the brain and body are the suprachiasmatic nuclei of the hypothalamus (SCN). Disruption to the timing of sleep and daily behavioural activity can manifest in a range of pathologies including neuropsychiatric disorders. Bipolar disorder (BPD) is once such neurological condition that exhibits profound associations with altered circadian rhythm generation and whose toolkit of pharmacological interventions impact upon circadian rhythm generation. Currently it is unclear exactly how changes to rhythmic physiology contribute to the aetiology and pathology of BPD. In recent years, rodent models possessing lesions within genes that make up the basic cellular oscillator are widely reported to exhibit concomitant changes in affective behaviours, namely mania-like phenotypes. Recently a mouse model possessing a mutation within the neuron-specific Na+/K+-ATPase (NKA) alpha3 subunit, known as Myshkin, was described as a model of the manic phase of BPD. The NKA alpha3 is not reported as a critical element of the circadian oscillator and we used this opportunity to characterise the behavioural and physiological circadian system of these animals. Under wheel-running paradigms Myk/+ animals exhibited a broad array of behavioural deficits including lengthened, low amplitude and labile free-running rhythms, altered phase re-setting and elevated metabolic activity. Physiological characterisation of the SCN revealed deficits in amplitude of electrical output and changes to post-synaptic signalling although the ex vivo molecular pacemaking of the SCN remained intact. Myshkin animals therefore represent a novel model in which changes to central output arise independently of changes to basic molecular pacemaking. Despite this seemingly distinct mechanism Myshkin animals share many mood and circadian phenotypes with other clock gene models of affective behaviours highlighting that changes to pacemaking output of the SCN may be a critical factor across animal models exhibiting circadian and mood deficits. In addition, the impact of the mood stabiliser lithium, commonly prescribed in BPD, on cellular pathways within the SCN was investigated. Lithium consistently lengthens the period of cellular and behavioural rhythms in mammals although the mechanism of this action is yet undefined. Glycogen synthase kinase 3β (GSK3β) and inositol monophosphatase (IMPase) are the major biochemical targets of lithium at therapeutic concentrations. GSK3β is known to shorten rhythms and this study targeted IMPase and inositol phosphate turnover in the period lengthening effects of lithium. We reveal that although inhibition of IMPase dampens SCN molecular rhythms, the period of oscillations remains unchanged and therefore lithium acts upon distinct cellular pathways within the SCN to exert effects on period.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:644509 |
| Date | January 2015 |
| Creators | Timothy, Joseph |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/circadian-rhythms-in-the-neuorbiology-of-bipolar-of-bipolar-disorder(8d7f6f92-b7cd-4835-8e53-d15334c2dfe3).html |
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