Vesicle-free transition zones, dense core vesicles, and vesicle pool redistribution contribute to synapse growth


Vesicle-free transition zones, dense core vesicles, and vesicle pool redistribution contribute to synapse growth

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dc.contributor.advisor Harris, Kristen M.
dc.creator Bell, Maria Elizabeth 2012-07-13T18:48:50Z 2012-07-13T18:48:50Z 2012-05 2012-07-13 May 2012
dc.description.abstract Long-term potentiation (LTP) is a widely studied cellular mechanism of learning and memory. LTP occurs at excitatory synapses on dendritic spines. Two hours after LTP induction in mature rat hippocampal slices, a reduction in spine number that is perfectly balanced by enlargement of the remaining synapses was previously observed. The sequence of events by which mature synapses enlarge is not well understood, but potential pre- and postsynaptic ultrastructural correlates of synapse growth have been identified. Vesicle-free transition zones (VFTZs) are postsynaptic thickenings contiguous with the PSD that have no apposing presynaptic vesicles perpendicular to the presynaptic membrane. VFTZs could be regions where synapses have expanded postsynaptically, but to which presynaptic vesicles have not yet been recruited. Presynaptic 80-nm dense core vesicles (DCVs) transport active zone proteins to the synapse during synaptogenesis, and may perform the same function during synaptic plasticity. 3-D reconstructions from ssTEM were used to investigate changes in VFTZs, DCVs, and presynaptic vesicles following LTP induction. By 30 minutes, VFTZ area and docked vesicle counts decreased, suggesting mobilization of additional vesicles to the synapse and enhanced release or delayed recycling. By two hours, VFTZs enlarged, suggesting VFTZ assembly contributes to synapse enlargement. DCV counts at 2 hours decreased relative to that at 30 minutes in both control and LTP conditions, suggesting DCVs were inserted at existing synapses to enlarge potentiated synapses in the LTP condition and to support ongoing spinogenesis in the control condition. The overall vesicle count in presynaptic boutons decreased at 2 hours following LTP induction, but docked vesicle count did not. Docked vesicle count was elevated at 2 hours relative to 30 minutes, suggesting that the depletion of docked vesicles observed at 30 minutes was followed by a replenishment and enhancement by 2 hours supplied by the non-docked vesicle pool. That the largest spines had more and larger VFTZs and recruited more DCVs and docked vesicles, and that the ratio of the sum of VFTZ area to the sum of PSD area is constant, provide further evidence that dendritic segments serve as functional units that manage resources in a coordinated and homeostatic way.
dc.format.mimetype application/pdf
dc.language.iso eng
dc.subject Synapse
dc.subject EM
dc.subject LTP
dc.subject Plasticity
dc.title Vesicle-free transition zones, dense core vesicles, and vesicle pool redistribution contribute to synapse growth 2012-07-13T18:49:00Z
dc.identifier.slug 2152/ETD-UT-2012-05-5561
dc.contributor.committeeMember Aldrich, Richard
dc.contributor.committeeMember Benson, Deanna
dc.contributor.committeeMember Jones, Theresa
dc.contributor.committeeMember Nishiyama, Hiroshi
dc.description.department Neuroscience
dc.type.genre thesis
dc.type.material text Neuroscience Neuroscience University of Texas at Austin Doctoral Doctor of Philosophy

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