Oral sensory papillae, chemo- and mechano-receptors, in the snake, Elaphe quadrivirgata. A light and electron microscopic study

The oral sensory papillae of the snake (Elaphe quadrivirgata), comprising a compound sensory system located along the tooth rows, were studied by ligh t microscopy, immunohistochemistry for neuron specific enolase and S 100 pr otein, and scanning and transmission electron microscopy. Each sensory papi lla exhibited a single taste bud and free nerve endings in the epithelium, and Meissner-like corpuscles, branched coiled terminals, and lamellated cor puscles in the connective tissue. The taste buds consisted of four types of cells; the type III cells, exclusively synapsing onto intragemmal nerves, were identified as gustatory in function. The gustatory cells included dens e-cored and clear vesicles in the cytoplasm. These vesicles were accumulate d both in the presynaptic and infranuclear regions, suggesting dual functio ns: the synaptocrine and paracrine/endocrine release of signal substances, The free nerve endings constantly contained mitochondria and frequent clear vesicles. The Meissner-like corpuscles were located in the uppermost zone of the connective tissue. These corpuscles consisted of nerve fibers and la mellar cells. The nerve fibers, rich in mitochondria, were folded and layer ed on each other, The branched coiled terminals were localized in the conne ctive tissue along the side wall of the papillae, Nerve fibers, free from a Schwann-cell covering, swelled up to make terminals which accumulated mito chondria and glycogen particles. The lamellated corpuscles were associated with the nerve-fiber bundles in the connective tissue, Consisting of a cent ral nerve axon and lamellar cells encircling it, these corpuscles resembled mammalian Vater-Pacini corpuscles, except that they lacked a capsule. Thes e findings demonstrated that the snake sensory papilla represents one of th e most specialized, compound sensory systems among vertebrates, which may p lay an important role in receiving chemical and mechanical information on p rey.