Initiation site of gustatory neural impulse in frog tongue.

Abstract

The taste organ in the frog tongue is situated at the summit of the fungiform papilla. Morphologically, the frog taste organ is usually called the taste disk rather than taste bud. It comprises many taste cells which respond to various taste stimuli with depolarizing receptor potentials. There are many axon terminals at the base of the taste cell layer in the frog, and it has been found that there exists a chemical synapse between a frog taste cell and a gustatory axon terminal. It is considered that a depolarizing receptor potential in a taste cell elicited by a taste stimulus may release a transmitter from the cell, and then the postsynaptic potential in the axon terminal membrane evoked by the transmitter may trigger an initiation of gustatory neural impulses.Although it has been supposed that gustatory neural impulses may be initiated at the first node of Ranvier on the gustatory nerve fiber, obvious evidence has not been obtained until recently. In order to clarify the initiation site of gustatory neural impulse, it is important to examine the course of single gustatory nerve fibers within the fungiform papilla as giving attention to the spatial position of nodes of Ranvier.The purpose of the present experiment was to examine histologically the sensory innervation of the frog taste disk and to determine electrophysiologically the initiation site of gustatory neural impulses.