title: Structural plasticity of hippocampal mossy fiber synapses as revealed by high-pressure freezing.
abstract: Despite recent progress in fluorescence microscopy techniques, electron microscopy (EM) is still superior in the simultaneous analysis of all tissue components at high resolution. However, it is unclear to what extent conventional fixation for EM using aldehydes results in tissue alteration. Here we made an attempt to minimize tissue alteration by using rapid high-pressure freezing (HPF) of hippocampal slice cultures. We used this approach to monitor fine-structural changes at hippocampal mossy fiber synapses associated with chemically induced long-term potentiation (LTP). Synaptic plasticity in LTP has been known to involve structural changes at synapses including reorganization of the actin cytoskeleton and de novo formation of spines. While LTP-induced formation and growth of postsynaptic spines have been reported, little is known about associated structural changes in presynaptic boutons. Mossy fiber synapses are assumed to exhibit presynaptic LTP expression and are easily identified by EM. In slice cultures from wildtype mice, we found that chemical LTP increased the length of the presynaptic membrane of mossy fiber boutons, associated with a de novo formation of small spines and an increase in the number of active zones. Of note, these changes were not observed in slice cultures from Munc13-1 knockout mutants exhibiting defective vesicle priming. These findings show that activation of hippocampal mossy fibers induces pre- and postsynaptic structural changes at mossy fiber synapses that can be monitored by EM.
authors.affiliation: Department for Structural Neurobiology, Center for Molecular Neurobiology Hamburg-ZMNH, University of Hamburg, D-20246 Hamburg, Germany.
authors.forename: Shanting
authors.initials: S
authors.lastname: Zhao
authors.forename: Daniel
authors.initials: D
authors.lastname: Studer
authors.forename: Xuejun
authors.initials: X
authors.lastname: Chai
authors.forename: Werner
authors.initials: W
authors.lastname: Graber
authors.forename: Nils
authors.initials: N
authors.lastname: Brose
authors.forename: Sigrun
authors.initials: S
authors.lastname: Nestel
authors.forename: Christina
authors.initials: C
authors.lastname: Young
authors.forename: E Patricia
authors.initials: EP
authors.lastname: Rodriguez
authors.forename: Kurt
authors.initials: K
authors.lastname: Saetzler
authors.forename: Michael
authors.initials: M
authors.lastname: Frotscher
mesh_terms: D000818:Animals; D056654:CA3 Region, Hippocampal / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure*; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D066298:In Vitro Techniques; D017774:Long-Term Potentiation / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D019599:Mossy Fibers, Hippocampal / Q000378:metabolism / Q000648:ultrastructure*; D009412:Nerve Fibers / Q000378:metabolism / Q000648:ultrastructure*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000378:metabolism / Q000648:ultrastructure*; D013569:Synapses / Q000378:metabolism / Q000648:ultrastructure*; D013572:Synaptic Vesicles / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D009419:Nerve Tissue Proteins; C503321:Unc13a protein, mouse