An improved EPTA staining method for synapses in rat cerebral cortex cultures.

Ethanolic phosphotungstic acid (EPTA) staining has proved to be a useful tool in electron microscopic studies on synapse formation and maturation in the developing brain. However, the available staining procedures did not give satisfactory contrast between synaptic structures and background in reaggregated cerebral cortex tissue grown in vitro. Such contrast is a prerequisite for reliable quantitative studies. We therefore varied several steps of the staining procedure and have succeeded in obtaining a modification which gives the required contrast. A short rinsing time after EPTA staining turned out especially to be very crucial.