Specific inhibitor for bitter taste: inhibition of frog taste nerve responses and human taste sensation to bitter stimuli

Among various taste stimuli, bitter substances are most abundant and their chemical structures are greatly diverse from each other. It has been known that there are multiple receptor sites and transduction mechanisms. Already in neonates, bitter stimuli elicit rejection responses, indicating strong negative hedonic tone. Bitter taste is decidedly unpleasant when the sensation is strong. The development of a method to mask bitterness has widely been required in pharmaceutical sciences and food sciences. To mask bitterness, a specific bitterness inhibitor would be most useful. Such an inhibitor would also be useful in elucidating the receptor mechanisms of bitter substances. No inhibitor has, however, been available. Recently we found that a lipoprotein, PA-LG made of phosphatidic acid (PA) and beta-lactoglobulin (beta-LG), selectively suppresses the taste responses to bitter substances. In this paper we describe the protocol used for inhibition of the frog taste (glossopharyngeal) nerve responses to bitter stimuli by the lipoprotein. The frog taste system is used because it is sensitive to various bitter substances and surgery of the animal for the electrophysiological recording is rather easy. We also describe the protocol used for inhibition of human taste sensation to bitter stimuli.