Responses of the hamster chorda tympani nerve to binary component taste stimuli: evidence for peripheral gustatory mixture interactions

Abstract

Studies of taste receptor cells, chorda tympani (CT) neurons, and brainstem neurons show stimulus interactions in the form of inhibition or enhancement of the effectiveness of sucrose when mixed with acids or citrate salts, respectively. To investigate further the effects of acids and the trivalent citrate anion on sucrose responses in hamsters (Mesocricetus auratus), we recorded multifiber CT responses to 100 mM sucrose; a concentration series of HCl, citric acid, acetic acid, sodium citrate (with and without amiloride added), potassium citrate, and all binary combinations of acids and salts with 100 mM sucrose. Compared with response additivity, sucrose responses were increasingly suppressed in acid + sucrose mixtures with increases in titratable acidity, but HCl and citric acid were more effective suppressors than acetic acid. Citrate salts suppressed sucrose responses and baseline CT neural activity to a similar degree. Citrate salts also elicited prolonged, concentration-dependent, water-rinse responses. The specific loss in sucrose effectiveness as a CT stimulus with increasing titratable acidity was confirmed; however, no increase in sucrose effectiveness was found with the addition of citrate. Further study is needed to define the chemical basis for effects of acids and salts in taste mixtures.

Cracking taste codes by tapping into sensory neuron impulse traffic

“…A constant component in the oral environment is saliva, which is itself a variable formulation (Schneyer et al ., 1972); and single-stimulus, self-adaptation , or multiple stimulus, cross-adaptation , control our perceptual experiences. Evaluation of peripheral taste information, which contributes to decisions to ingest or reject, adjusts to nutritional needs via receptivity to systemic signals (Contreras and Frank, 1979) and peripheral taste signaling adjusts to dangerous substances present in available sources of food and drink (Formaker and Frank, 1996). Neural activity carried to the brain by gustatory afferent neurons is malleable, reflecting a variable oral milieu, internal needs and nutrient sources.…”

“…And, when the tongue is rinsed with water, hamster CT responses to 30 mM quinine HCl are reduced to zero in mixtures containing 50 mM or more NaCl (Formaker and Frank, 1996). In a saliva adapted context, low concentrations of quinine in water may be detected by a transient inhibition of neural activity (Rehnberg et al .…”

“…Stimulus salience is altered by dampening responses of Na + -specialists, allowing induced salt appetite to reestablish electrolyte homeostasis in rats (Contreras and Frank, 1979; Contreras and Lundy, 2000). Similarly, responses of hamster sucrose-best specialists to sucrose and other sweeteners are muted when stimulus contamination makes ingestion for calories dangerous (Formaker and Frank, 1996; Frank, 2000). Nevertheless, stimulus quality, the Na+-salt and sweet tastes, are retained; in fact S afferent neurons continue with their 1.4 Hz “sweet rhythm” (Frank et al .…”

The taste transduction channel TRPM5 is a locus for bitter‐sweet taste interactions

“…The neural component corresponding to sucrose in the presence of quinine was determined by subtracting CT responses to quinine at different concentrations from the responses to the corresponding sucrose-quinine mixtures (2). This method is supported by the facts that sucrose and quinine responses are generated by different subsets of CT fibers and that sucrose does not affect CT responses to quinine (3,19). As shown in Fig.…”

“…It has been proposed that gustatory mixture interactions may occur through multiple mechanisms: chemical reaction between tastants, competition of the tastants for the receptors, cross-talk between transduction cascades in the taste receptor cells, lateral cell-cell interactions within the taste buds, and interaction between gustatory signals at the levels of the papillae, afferent nerve fibers, central nervous system, and conscious experience (2, 3, 11, 19 -21). However, electro-physiological studies have narrowed the main locus for the suppression of the responses to sweeteners by quinine to the gustatory periphery and, in particular, to the level of taste receptor cells (2,3,19).…”