Postsynaptic actin filaments at the giant mossy fiber-unipolar brush cell synapse.
The unipolar brush cell (UBC), a small interneuron occurring at high density in the granular layer of the mammalian vestibulocerebellum, receives a giant glutamatergic synapse from a single mossy fiber (MF) rosette, usually on a brush of dendritic branchlets. MF stimulation produces a current in the UBC several orders of magnitude greater in duration than at other glutamatergic synapses. We assumed that the cytoskeleton would have a special role in plasticity of the MF-UBC synapse. Neurofilaments and microtubules are enriched in the UBC somatodendritic compartment but are conspicuously absent in close proximity to the giant synapse, where standard electron microscopy reveals a granulo-flocculent material. Because osmium tetroxide fixation during sample preparation for standard electron microscopy destabilizes actin filaments, we hypothesized that this subsynaptic granulo-flocculent material is actin-based. After actin stabilization, we observed prominent, but loosely organized, bundles of microfilaments at the subsynaptic region of the MF-UBC synapse that linked the postsynaptic density with the cytoskeletal core of the dendritic branchlets. Confocal fluorescence microscopy and pre- and postembedding immunogold labeling with phalloidin and actin antibodies showed that these microfilaments consist of f-actin and contain little beta-actin. This extraordinary postsynaptic actin apparatus is ideally situated to form a dynamic framework for glutamate receptors and other postsynaptic molecules, and to mediate activity-dependent plastic rearrangements of the giant synapse.
Diño
M R
MR
Northwestern University Institute for Neuroscience, Chicago, Illinois 60611, USA.
Mugnaini
E
E
D008841:Actin Cytoskeleton / Q000502:physiology* / Q000648:ultrastructure; D000818:Animals; D002531:Cerebellum / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D007395:Interneurons / Q000502:physiology* / Q000648:ultrastructure; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D016253:Microscopy, Immunoelectron; D015879:Myosin Subfragments; D009412:Nerve Fibers / Q000502:physiology* / Q000648:ultrastructure; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D013569:Synapses / Q000502:physiology* / Q000648:ultrastructure; D014726:Vestibular Nuclei / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure
D015879:Myosin Subfragments