Cytochemistry of synapses: selective staining for electron microscopy.

Material at synapses and in some synaptic vesicles becomes selectively stained when glutaraldehyde-fixed rat brain that has not been treated with osmium is stained with phosphotungstic acid. The material stained at synapses is distinct from the adjacent unstained synaptic membranes and has cytochemical properties of protein. The specialized spatial arrangement exhibited by this synaptic material suggests its close involvement in synaptic function.