Ph.D Thesis

Ph.D StudentLavie Arava
SubjectLong Term Stability of Presynaptic Properties
DepartmentDepartment of Medicine
Supervisor PROF. Noam Ziv
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Synaptic molecules are continuously interchanged among nearby synapses at very significant rates. These dynamics and the lack of obvious barriers confining synaptic molecules to specific synapses might be expected to challenge the ability of individual synapses to maintain constant molecular contents, and by extension, constant functional properties over time. Here we used rat and mouse neuronsin primary culture and imaging-based approaches to examine the ability of individual presynaptic boutons to maintain their molecular and presynaptic vesicle (SV) contents over time and examine the degree to which quantitative relationships between these are conserved. We found that although SV contents of individual boutons did become more stable during development,spontaneous and continuous changes were still observed in mature presynaptic compartments when these were followed for several hours. Extensive electrical stimulation accelerated the redistribution of SVs among neighboring synapses, however careful analysis revealed the presence of “forces" that acted to conserve synapse-specific “set points”. We hypothesized that synaptic scaffolding molecules might play instrumental roles in determining such set points. Indeed, redistribution dynamics of the active-zone molecule Bassoon were not accelerated by the same stimulation schemes. Using pairs of fluorescently-tagged synaptic molecules, we found that relationships between SV and Bassoon contents and between the active-zone molecule Munc-13 and the key postsynaptic scaffold molecule PSD-95 were well conserved in spite of significant fluctuations in their respective contents.Interestingly, we also noted that whereas quantitative relationships between Bassoon and SV content were relatively tight, quantitative relationships between Munc-13 and PSD-95 varied significantly among individual synapses.These findings support the hypothesis that core (pre)synaptic scaffolds serve collectively to conserve synaptic SV and molecular contents. Yet they also suggest that such contents fluctuate significantly and in a coordinated manner over longer time scales, suggesting that on the whole, the tenacity of individual synapses is inherently limited.