Excessive release of neurotransmitter is a characteristic of epileptogenic cells.
A number of lines of evidence implicate defects in the synaptic vesicle cycle as a
cause of this excessive release. Synaptic vesicles are retrieved by more than one
route in central nerve terminals. During mild stimulation the dominant synaptic
vesicle retrieval pathway is classical clathrin mediated endocytosis. During elevated
neuronal activity retrieval of synaptic vesicle membrane by bulk endocytosis is the
predominant retrieval method. As it is triggered by strong stimulation, bulk
endocytosis may be of importance in retrieval during epilepsy, however little is
currently known about this pathway. In order to investigate the role of bulk
endocytosis, we sought to establish a cell culture model of epilepsy, to develop an
assay to distinguish retrieval by bulk endocytosis, and to use these tools to look at the
molecular players controlling this form of endocytosis.
Characterisation of bulk endocytosis through the development of tailored
assay systems has revealed that bulk endocytosis is a fast event that is triggered
during strong stimulation. Bulk endocytosis provides the nerve terminal with an
appropriate mechanism to meet the demands of synaptic vesicle retrieval during
periods of intense synaptic vesicle exocytosis. Inhibition of a dephosphorylation
specific dynamin I-syndapin I interaction by competitive peptides inhibits activity
dependent bulk endocytosis, implicating this interaction in a role in this method of
synaptic vesicle retrieval. Having characterised the strength of stimulation needed to
activate bulk endocytosis, and the speed at which it occurs, we also investigated the
effects of known anti-epileptogenic drugs on bulk endocytosis in our central nerve
terminal model system