Zur Kurzanzeige

Resolving the Ultrastructural Organization of Synaptic Vesicle Pools at Hippocampal Mossy Fiber and Schaffer Collateral Synapses

dc.contributor.advisorBrose, Nils Prof. Dr.
dc.contributor.authorMaus, Lydia Susann
dc.date.accessioned2021-02-18T10:47:09Z
dc.date.available2021-02-18T10:47:09Z
dc.date.issued2021-02-18
dc.identifier.urihttp://dx.doi.org/10.53846/goediss-1
dc.language.isoengde
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/4.0/
dc.subject.ddc570de
dc.titleResolving the Ultrastructural Organization of Synaptic Vesicle Pools at Hippocampal Mossy Fiber and Schaffer Collateral Synapsesde
dc.typedoctoralThesisde
dc.contributor.refereeBrose, Nils Prof. Dr.
dc.date.examination2020-09-14
dc.description.abstractengThe synapse is the functional unit of chemical communication between neurons in the brain. In order to relay information with spatiotemporal precision, the presynaptic compartment utilizes a specialized molecular machinery to organize synaptic vesicles at the presynaptic membrane so that upon the arrival of an action potential in the presynaptic terminal, synaptic vesicles can fuse with the plasma membrane and release their neurotransmitter contents into the synaptic cleft. Although many molecular components of this machinery are highly conserved, the functional transmitter release properties and plasticity characteristics can differ greatly between distinct neuron types, and even from synapse to synapse within the same cell. While critical for higher order cognitive processes, the underlying mechanisms of plastic changes in synaptic transmission remain poorly understood. Whether the fine ultrastructural organization of vesicles at presynaptic active zone release sites contributes to synaptic functional heterogeneity or to distinct plasticity states therefore remains an open question of considerable importance. The aim of this study was to investigate whether the availability of docked and primed synaptic vesicles contributes to differences in release probability at two functionally well-characterized synapses, namely hippocampal Schaffer collateral and mossy fiber synapses. To address this question, I combined hippocampal slice culture, high-pressure freezing, automated freeze substitution, and electron tomography to accurately resolve the organization of vesicles at presynaptic active zones. Complementary electrophysiological analyses verified that hippocampal mossy fiber synapses exhibited a lower release probability and stronger short-term facilitation than Schaffer collateral synapses in our slice culture system. My ultrastructural analyses revealed that mossy fiber active zones harbored fewer docked synaptic vesicles and a prominent pool of putatively tethered synaptic vesicles. These data support the notion that the availability of docked and primed synaptic vesicles co-determines initial release probability at Schaffer collateral and mossy fiber synapses. I postulate that the abundance of membrane-proximal vesicles, ideally positioned to rapidly dock and prime at the plasma membrane during periods of increased synaptic activity, likely contributes to the facilitation characteristics of hippocampal mossy fiber synapses. Moreover, I hypothesize that the ratio of docked and tethered synaptic vesicles serves as a possible structural predictor of synaptic short-term plasticity characteristics. I discovered that three morphologically distinct types of vesicles docked at mossy fiber active zones: synaptic vesicles, giant vesicles (clear-core vesicles with a diameter exceeding 60 nm), and dense-core vesicles (DCVs). All vesicle types required Munc13 priming molecules to dock at mossy fiber active zones. My data indicate that giant vesicles likely contain neurotransmitters and contribute to glutamatergic signaling at the mossy fiber-cornu ammonis area 3 synapse. I performed a quantitative morphometric analysis of respective vesicle pools at mossy fiber active zones and compared my data with published functional estimates of the readily releasable pool to demonstrate considerable overlap between the total numbers of morphologically docked and functionally primed and fusion-competent synaptic vesicles. Having systematically quantified the ultrastructural profiles of mossy fiber active zones in synapses at rest, I examined whether changes in synaptic release probability induced by acute pharmacological manipulations of presynaptic cyclic adenosine monophosphate (cAMP) would trigger corresponding changes in vesicle organization. Interestingly, my data demonstrate that DCV, but not synaptic vesicle, docking is particularly sensitive to changes in presynaptic cAMP. These findings support a view in which mechanisms mediating cAMP-dependent potentiation of glutamatergic transmission operate downstream of synaptic vesicle docking, and highlight the potential modulatory role of DCV-mediated neuropeptide release in mossy fiber plasticity processes. In conclusion, my work demonstrates that initial release probability is co-determined by the availability of docked and primed vesicles and that the structural organization of vesicles at active zone release sites can indeed provide significant insight into key presynaptic functional properties. Moreover, it emphasizes that systematic and stringent high-resolution ultrastructural analyses are useful to reveal novel insight into ultrastructure-function relationships in other synapse types in the brain.de
dc.contributor.coRefereeMoser, Tobias Prof. Dr.
dc.subject.engMossy Fiberde
dc.subject.engSchaffer Collateralde
dc.subject.engSynapsede
dc.subject.engSynaptic Vesiclede
dc.subject.engActive Zonede
dc.subject.engDockingde
dc.subject.engMunc13de
dc.subject.engUltrastructurede
dc.subject.engHigh-pressure Freezingde
dc.subject.engElectron Microscopyde
dc.subject.engElectron Tomographyde
dc.identifier.urnurn:nbn:de:gbv:7-21.11130/00-1735-0000-0005-1572-3-5
dc.affiliation.instituteBiologische Fakultät für Biologie und Psychologiede
dc.subject.gokfullBiologie (PPN619462639)de
dc.identifier.ppn1748662244
dc.creator.birthnameBickfordde


Dateien

Thumbnail

Das Dokument erscheint in:

Zur Kurzanzeige