An ethanolic phosphotungstic acid (EPTA) analysis of photoreceptor and synaptic ultrastructure in the guinea pig retina.

Ethanolic phosphotungstic acid (EPTA) has been used to elucidate the structure of certain organelles contained within retinal cells not clearly discernible using conventional preparations. Both synaptic and nonsynaptic components of the guinea pig neural retina have been analyzed. Within the photoreceptor (PR) cell EPTA-stained components include the connecting cilia, their basal bodies, and the root filament system. Cross-striated fibrillar organelles, similar in appearance to the root filaments, are also observed in the nuclear region, the synaptic terminal and other parts of the PR cell. The possible structural continuity and significance of these structures are discussed. Within retinal synapses of both the inner and outer plexiform layers, ribbons and associated paramembranous specializations are stained. The photoreceptor ribbons have a trialaminar structure with filamentous, tufted borders. Synaptic cleft material and postsynaptic densities are also stained. Bipolar cell synapses in the inner plexiform layer contain stained short ribbons as well as closely associated peg-like densities extending towards the presynaptic membrane.