An electron microscopic study on the innervation in the taste buds of the mouse circumvallate papillae

Taste buds of the mouse circumvallate papillae were studied by electron microscopy to elucidate the innervation involving the adrenergic nerve supply. Typical afferent synaptic contacts, with increased density of the membranes and aggregations of synaptic vesicles in the cytoplasm adjacent to the nerve endings, were demonstrated between the type III cells and the nerve endings. Along the regions of contact between the type II cells and the nerve endings, cisternae of endoplasmic reticulum were often seen beneath the cell membrane, and the nerve endings contained relatively many synaptic-sized vesicles. Such an innervation seems to be efferent in nature. For the detection of the adrenergic nerve supply, 5-hydroxydopamine (5-OH-DA) was injected after pretreatment with L-DOPA and nialamide. The mice showed numerous adrenergic nerve fibers in the connective tissue underlying the taste buds. On very few occasions, the adrenergic nerves penetrated the basal lamina of the taste buds and came into contact with the bud cells. Some adrenergic nerves were distributed among the epithelial cells around the taste buds. The reaction product from acetylcholine esterase activity was found around the adrenergic nerve fibers labeled with 5-OH-DA.