Cytoplasmic organization in cerebellar dendritic spines.

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Abstract
Three sets of filamentous structures were found associated with synaptic junctions in slices of mouse cerebellar tissue prepared by rapid-freezing and freeze-etch techniques. The electron-dense fuzz subjacent to postsynaptic membranes correponds to a web of 4- to 6-nm-diameter filaments that were clearly visualized in rapid-frozen, freeze-etched preparations. Purkinje cell dendritic spines are filled with a meshwork of 5- to 7-nm filaments that contact the spine membrane everywhere at the synaptic junction and extend through the neck of the spine into the parent dendrite. In addition, 8- to 10-nm microfilaments, possibly actin, were associated with the postsynaptic web and extended into the body and neck of the spine. The arrangements and attachments of the filamentous elements in the Purkinje cell dendritic spine may account for its shape.