Abstract
Application of bitter substances and some salts to the tongue elicits phasic taste responses in the frog glossopharyngeal nerve. However, it is not known whether there are multiple taste receptor sites in the phasic components. In the present study, cross-adaptation was carried out by varying concentrations of bitter substances (quinine-HCl, caffeine, theophylline and denatonium) and salts (NaCl and choline Cl) in a wide range. The peak magnitude of the integrated responses of the glossopharyngeal nerve to taste stimuli in the frog (Rana catesbeiana) were measured. The response to caffeine after quinine was decreased with increasing concentrations of quinine applied first and reached the spontaneous level, while that to theophylline and denatonium after quinine was decreased to 60-70% of the original level. Responses to NaCl and choline Cl were scarcely affected after adaptation of quinine. The results obtained suggest that quinine and caffeine stimulate the same receptor site and that theophylline and denatonium stimulate receptor sites that are different from the receptor site responsible for quinine response although there exist receptor sites stimulated commonly by bitter substances. It is also suggested that quinine and salts such as NaCl and choline Cl stimulate different receptor sites. [J Physiol Sci. 2006;56 Suppl:S182]
