Abstract
Ageing is associated with cognitive decline, attributed to a decreased ability of neurons to transmit and sense signals. Despite this, little work has explored how ageing affects neurotransmitter release. This study explored how increasing age affected vesicular neurotransmitter content and release from the cerebral giant cell (CGC), a key neuron involved in long-term memory formation in the pond snail L. stagnalis.Micro and nano-tip carbon-fibre electrodes in combination with single cell amperometry (SCA) and intracellular vesicle impact electrochemical cytometry (IVIEC) were used to monitor somatic vesicular 5-hydroxytryptamine (5-HT) release and intracellular vesicle content of the CGCs. Gaussian mixture clustering algorithm was applied to the collected data to identify different population of vesicles with different modes of release. CGCs of young and old snails were capable of spontaneous vesicular 5-HT release. The Ca2+ ionophore ionomycin was able to trigger release from the young CGCs but was less successful in the old. No significant differences were observed between spontaneous or ionomycin-evoked release events. Ageing significantly increased the number of serotonin molecules released per vesicle from the CGCs, due to increases in the width, rise and fall time of the events, but did not change their amplitude. The proportion of transmitter released by the CGCs increased from 46% in the young to 78% in the old. Cluster analysis suggested the existence of two different pools of intracellular vesicles releasing in two different modes with the number of molecules released increasing with age for both modes. The observed age-related differences in the kinetics of the release events and quantity of serotonin release from the CGCs could be due to changes in the lipids composing the neuronal membranes. Therefore, high-performance liquid chromatography-mass spectrometry was used to determine the effect of age on the lipids of the central nervous system. Age significantly increased the total concentration of sphingomyelin, cholesteryl esters, phosphatidylcholine, lyso-phosphatidylcholine and phosphatidylglycerol, but decreased the phosphatidylinositol. These findings suggest the age-related changes in the lipid composition may underly the changes in neurotransmitter release.
In conclusion, this thesis has shown for the first time that the natural ageing process not only increases the amount of serotonin release but that this occurs due to an increase in the proportion of serotonin released from an individual vesicle. These effects appear to be consistent for both pools of vesicle identified using cluster analysis and strongly suggest that plasticity at the level of the individual vesicle is reduced with increasing age.
| Date of Award | Mar 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Mark Yeoman (Supervisor), Marcus Dymond (Supervisor) & Bhavik Patel (Supervisor) |