| When a primary taste afferent, the chorda tympani nerve, is sectioned, the nerve and associated receptor cells become non-functional. After a period of time, the chorda tympani regenerates and receptor cells again exhibit physiological taste responses. While sodium restriction alone, or chorda tympani sectioning alone did not after gustatory function in adult rats, combination of the two resulted in profound changes in neural responses to sodium stimuli. Responses from regenerated taste receptors in sodium-restricted rats exhibited greatly reduced responses to sodium, just as in developmentally sodium-restricted animals. Surprisingly, the intact chorda tympani nerve demonstrated responses to sodium that are also low immediately following contralateral nerve section, but then increase to a supersensitive level in the following weeks. This study indicates that communication occurs between two distant populations of taste receptors that do not share neural connections in the peripheral gustatory system.; Further work showed that the time course of sensitivity to the sodium-restricted diet was different for the regenerated and intact chorda tympani nerves, which indicates that separate mechanisms may underlie functional changes. Immunohistochemical studies demonstrated that sodium-restriction does not alter the number of receptor organs, or taste buds, that remain after degeneration during the corresponding functional sensitive period. Thus, gross structural differences as a result of the dietary manipulation cannot account for the profound functional changes that occur after nerve sectioning.; In the final set of experiments, the role of the immune system in the function of the denervated gustatory system was examined. Stimulation of immune function in sodium-restricted rats, proposed to be immunosuppressed, induced recovery of normal gustatory responses in the intact nerve soon after contralateral nerve section. It is suggested that the immune system is the source of soluble factors that communicate between receptors on the two sides of the tongue and also serves to maintain normal taste function. Importantly, this is the first indication of an interaction between the gustatory and immune systems. |
