Ultrastructure of symmetric interneuronal junctions after staining with ethanolic phosphotungstic acid.

1. The symmetric interneuronal junctions (attachment plaques) of large axon terminals in the dorsal lateral geniculate body of the rat were studied, applying besides the conventional staining the block staining method with ethanolic phosphotungstic acid (E-PTA). 2. After staining these contact zones with E-PTA 3 main components become visible: the interior presynaptic layer, the intermembranous material and the postsynaptic layer. 3. As opposed to the asymmetric synaptic junctions the interior presynaptic layer is not divided into dense projections. 4. The intermembranous material consists of 2 median situated intracleft lines, which are more or less fused with each other. 5. The staining intensity of the paramembranous material of the symmetric junctions stained with E-PTA corresponds to the intensity of the material of the asymmetric synaptic junctions.