Mathematical modelling of rod photoreceptor metabolism

Kunpasuruang, Wannapa (2009) Mathematical modelling of rod photoreceptor metabolism. MPhil thesis, University of Nottingham.

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Abstract

Rod photoreceptors are cells that sense and receive light. They consist of two major parts, an outer and an inner segment, which are linked by a connecting cilium. Continual growth of the rod outer segment is balanced by shedding of the tip of the outer segment. We start this thesis by developing nonlinear ordinary differential equations to describe the metabolic activity of the rod photoreceptor cells in order to investigate whether changes in metabolic demand during periods of light and dark are responsible for the observed (daily) variation in the length of the outer segment of the rod photoreceptors. Analysis of the rod system is carried out by investigating the steady-state solutions.

Secondly, because the eyes form part of the nervous system, we have also developed an ordinary differential model involving the glutamate-glutamine cycle in the nervous system in order to study how the rates at which glutamate and glutamine are released influence the metabolic demand of the system. We use a combination of numerical simulation and asymptotic techniques to understand the system dynamics. The asymptotic analysis provides insight into processes that control different stages of the glutamate-glutamine cycle.

Although glutamate is the main excitatory neurotransmitter in the mammalian central nervous system, it can be toxic to neuronal cells. Excitotoxicity occurs when there is overactivation of neuronal-glutamate receptors caused by excessive extracellular glutamate levels. This can lead to intracellular calcium overload and neurodegeneration. In the later stages of this thesis we extend our model of the glutamate-glutamine cycle by including an additional equation for intracellular calcium levels in order to study how calcium interacts with the glutamate-glutamine cycle and how it triggers excitotoxicity. Moreover, we find that as the extracellular volume fraction decreases, the concentration of components in the extracellular space increases, resulting in a neuron's responsiveness to a fixed amount of neurotransmitter consistent with clinical evidence.

Item Type:Thesis (MPhil)
Supervisors:Byrne, H.M.
King, J.R.
Uncontrolled Keywords:Mathematical Modelling, Rod Photoreceptor, Glutamate-Glutamine Cycle, Asymptotic Expansion
Faculties/Schools:UK Campuses > Faculty of Science > School of Mathematical Sciences
ID Code:642
Deposited By:Wannapa Kunpasuruang
Deposited On:19 Dec 2008
Last Modified:14 Dec 2009 11:36

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