Fine structure of the afferent synapse of the hair cells in the saccular macula of the goldfish, with special reference to the anastomosing tubules.

The fine structure of the afferent synapse has been studied in the hair cells of the goldfish saccular macula. A spherical dense body which is surrounded by synaptic vesicles is observed in association with the presynaptic membrane. An alternating, parallel arrangement of dense bars and of rows of synaptic vesicles is observed on the presynaptic membrane beneath the dense body. Each row consists of five to six immediately available synaptic vesicles, and five to six such rows of vesicles are observed per synapse. Sometimes anastomosing tubules are found around the dense body. The tubules are formed by direct infolding of the plasma membrane. Many coated vesicles are found at the periphery of the anastomosing tubules. A possible role of the anastomosing tubules in the turnover of the synaptic vesicle membrane is discussed.