Taste responses of bullfrog to pungent stimuli

Taste responses of bullfrogs to various pungent compounds and taste substances were electrophysiologically recorded from glossopharyngeal nerves. The threshold concentrations were ∼ 10 −7 M for piperine, ∼ 10 −6 M for capsaicin and ∼ 10 −4 M for allyl isothiocyanate. At any concentration examined, piperine was more potent than capsaicin. Both piperine and capsaicin elicited desensitizing responses, but the taste receptors recovered from the desensitization within 10 min after washing with deionized water. Cross-adaptation experiments revealed that capsaicin only partially desentizes receptors for piperine, l-leucine, HCl or quinine. Perfusion of the lingual artery with a solution containing no added Ca decreased the responses to capsaicin. Such a solution has been shown to suppress the taste nerve responses by blocking synaptic transmissions between taste cells and taste nerves [8]. These results suggest that the gustatory effects of capsaicin are different from its pharmacological effects on sensory neurons. It is likely that capsaicin and other pungent compounds, when they act as seasonings, stimulate taste cells rather than the free nerve endings of the sensory neurons.