Some factors affecting the PTA staining of synaptic junctions

Summary An analysis has been made of the staining properties of phosphotungstic acid (PTA) on non-osmicated, glutaraldehyde fixed brain tissue, with regard to differences arising from the commercial source of the PTA, its water content, methanol as opposed to ethanol dehydration, and perfusion as contrasted with immersion fixation. The quality of the micrographs varied depending on the source of the PTA, the principal component of the synaptic junctions to be affected being the cleft material. Variation in the water content of the PTA solution was also reflected in the appearance of the cleft material, tissues stained with high hydration PTA resulting in cleft material with considerably less electronopacity than the corresponding dense projections and postsynaptic thickening. Low hydration PTA produced the typical picture of cleft densities. Methanol dehydration was unsuccessful in this series of experiments, while immersion and perfusion fixation yielded comparable results.Synaptic junctions from cerebral cortex, cerebellar cortex, thalamus, hippocampus and spinal cord of the rat were examined. In addition to the typical paramembranous densities, subjunctional bodies are present in cerebellar and hippocampal junctions, and subsynaptic profiles in some spinal cord ones. The spinal cord junctions are characterized by a prominent synaptic plate and by a postsynaptic thickening which in places appears to be separated from the underlying postsynaptic membrane.This work was supported in part by a grant from the Australian Research Grants Committee. I would like to thank Mr. R.F. Brearley for his excellent technical assistance, and Mr. D. Stuart and Mrs. Z. Gobby for their help with the photography.