Iontophoretic application of bitter taste stimuli in hamsters

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Abstract
Recent electrophysiological studies on the iontophoretic application of taste stimuli by weak electric currents using rodents and frogs have produced stimuli which appear to mimic the action of salty, sour and sweet solutions. However, there has been no report of an ionic stimulus which might serve as a bitter iontophoretic probe. Many common bitter stimuli are either uncharged (e.g. quinine, urea) or have mixed quality sensations (e.g. the bitter salts KCl, MgCl2) and therefore are unsuitable. This report investigates the use of four organic anions, all of which are bitter to humans, which may serve as potential bitter stimuli for iontophoretic application to the tongue of the hamster while recording electrophysiologically from its chorda tympani nerve. These anions are m-nitrobenzene sulfonate (NBSA), picrate, cholate and m-nitrobenzoate (NBA). The electrophysiological responses to cathodal polarization via these four anions plus saccharin, an effective cathodal stimulus in the hamster, form the same efficacy series as chemical (i.e. normal sapid) presentations of sodium salts of these anions, i.e. saccharin > NBSA > picrate > NBA > cholate. Behavioral evidence suggests that NBSA is sweet to hamsters while the latter three anions, picrate, NBA and cholate, are bitter. Electrophyiological observations, based on magnitude of response, appear to support these behavioral findings. It was concluded that picrate, NBA and cholate may serve as useful bitter stimulus probes for ionto-phoretic application in the hamster.

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