| Abstract: | Recent electrophysiological studies on the iontophoretic applicationof taste stimuli by weak electric currents using rodents andfrogs have produced stimuli which appear to mimic the actionof salty, sour and sweet solutions. However, there has beenno report of an ionic stimulus which might serve as a bitteriontophoretic 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. Thisreport investigates the use of four organic anions, all of whichare bitter to humans, which may serve as potential bitter stimulifor iontophoretic application to the tongue of the hamster whilerecording electrophysiologically from its chorda tympani nerve.These anions are m-nitrobenzene sulfonate (NBSA), picrate, cholateand m-nitrobenzoate (NBA). The electrophysiological responsesto cathodal polarization via these four anions plus saccharin,an effective cathodal stimulus in the hamster, form the sameefficacy series as chemical (i.e. normal sapid) presentationsof sodium salts of these anions, i.e. saccharin > NBSA >picrate > NBA > cholate. Behavioral evidence suggeststhat 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 behavioralfindings. It was concluded that picrate, NBA and cholate mayserve as useful bitter stimulus probes for ionto-phoretic applicationin the hamster. |
