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Title: Exocytosis and endocytosis in a retinal neurone
Author: Holt, M. G.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2002
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The synaptic vesicle cycle in the nerve terminal consists of exocytosis and neurotransmitter release, endocytosis and vesicle regeneration. However, the exact mechanisms which underlie this cycle are still largely unknown. This dissertation describes the use of fluorescence microscopy to study aspects of vesicle cycling in the synaptic terminal of retinal depolarizing bipolar cells isolated from goldfish retina. Endocytosis at the synapse may proceed via one of two pathways: through the direct reformation of small vesicles, or through the formation of large cisternae. However, the mechanisms responsible for forming these larger compartments are unclear. In chapter 3, it is shown that following exocytosis membrane is retrieved via small vesicles and large vacuoles in bipolar cells. Vacuoles were heterogeneous in size and their formation was dependent on P1 3-kinase and F-actin, whereas formation of small synaptic vesicles was not. Vacuoles were also transported away from the plasma membrane by an actin-dependent mechanism, stimulated by calcium influx. Bulk membrane retrieval in the bipolar cell therefore exhibits the properties of macropinocytosis observed in non-neuronal cells. The bipolar cell can maintain high levels of neurotransmitter release over periods of many minutes, in response to sustained stimulation. The bipolar cell also contains high amounts of PKCα. A role for this enzyme in continuous exocytosis was investigated and the results presented in chapter 4. To maintain continuous exocytosis required an elevated free Ca2+ level in the synaptic terminal of approximately 1 μM. Inhibition of PKC led to a reduced Ca2+ level during stimulation, blocking exocytosis. In addition, PKCα may also have other roles in the exocytic process, such as modulating the mobility of synaptic vesicles or regulating the sensitivity of the exocytic machinery to Ca2+. In conclusion to the chapter, experiments are described which could help distinguish between these possible functions of PKCα in the bipolar cell. The mobility of synaptic vesicles is likely to play an important role in the regulation of synaptic transmission. This is especially true in the bipolar cell, because of its ability to support continuous exocytosis.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available