Ultrastructure of synapses in the lateral line canal organ.

The ultrastructure of afferent and efferent synapses on hair cells in the lateral line canal organ of hair cells in the lateral line canal organ of the fish Lota lota was studied, utilizing various fixation and staining techniques. New information was obtained about membrane-associated material, such as the presynaptic body and postsynaptic densities, by examining glutaral-dehyde-fixed material not subjected to osmication. Contrast was instead obtained either by section staining with uranyl acetate and lead citrate or by block impregnation with phosphotungstic acid (PTA). PTA-staining enhances the postsynaptic membrane of both the afferent and efferent synapses. It also stains the presynaptic dense projections at the efferent synapse and in a differential fashion, the afferent synaptic body. Secretion staining reveals a substructure in the feed of the afferent synaptic body, faintly seen but masked in osmicated tissue.