A possibility of efferent innervation of the gustatory cell in the rat circumvallate taste bud.

A transmission-electron microscope study of the rat circumvallate taste bud revealed that occasionally one and the same gustatory or Type III cell received innervation associated with subsurface cisterns as the Type II cell did, in addition to the ordinary afferent synapse. The subsurface cistern a flattened, smooth-surfaced saccular membrane system, hugged the plasma membrane of the gustatory cell along the boundary against the nerve terminal. The nerve terminal attaching to the cell was occupied with mitochondria and synaptic type vesicles. As these structural features resemble those of efferent synapses in certain other sensory cells including the inner ear hair cells, the gustatory cells dually innervated as demonstrated in the present study are presumably involved not only in the afferent but also in the efferent projection of nerves.