title: Differential covariation in taste responsiveness to bitter stimuli in rats.
abstract: Variation exists in the sensitivity of individual rodents and humans to different bitter tastants. An absence of uniform correlation in responsiveness to different bitter substances across individuals within a species suggests heterogeneity in the mechanisms underlying stimulus processing within this taste modality. Here, we examined taste responsiveness of individual rats to three bitter compounds (quinine hydrochloride, denatonium benzoate, and cycloheximide) in short-term lick tests to determine the magnitude of covariation among responses to these stimuli and infer commonalities in their receptor and neural mechanisms. Rats were tested with a given pair of bitter stimuli during three sessions comprising randomized trial blocks of six concentrations of each stimulus + deionized water. Psychophysical functions were generated for individual rats for respective stimulus pairs, and concentrations of each stimulus that produced equivalent lick suppression relative to water were correlated across animals. Behavioral taste responsiveness to quinine hydrochloride strongly covaried with responsiveness to denatonium benzoate (r = +0.82). Lick responsiveness to quinine was less robustly correlated with that to cycloheximide (r = +0.44), and denatonium and cycloheximide responses failed to correlate. These results imply substantial overlap in the bitter taste coding mechanisms for quinine and denatonium but some degree of independence in the mechanisms responsible for gustatory processing of cycloheximide. More generally, these data reinforce the notion that bitter taste processing is not a homogeneous event.
authors.affiliation: Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, 855 Monroe Avenue, Memphis, TN 38163, USA. sbrasser@utmem.edu
authors.forename: Susan M
authors.initials: SM
authors.lastname: Brasser
authors.forename: Khyobeni
authors.initials: K
authors.lastname: Mozhui
authors.forename: David V
authors.initials: DV
authors.lastname: Smith
mesh_terms: D000818:Animals; D001362:Avoidance Learning; D001522:Behavior, Animal; D001835:Body Weight; D003216:Conditioning, Operant; D003513:Cycloheximide / Q000737:chemistry; D004193:Discrimination Learning; D004192:Discrimination, Psychological; D004305:Dose-Response Relationship, Drug; D008297:Male; D011601:Psychophysics / Q000379:methods; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D011803:Quinine / Q000737:chemistry; D051381:Rats; D017207:Rats, Sprague-Dawley; D011984:Sensory Receptor Cells; D013268:Stimulation, Chemical; D013649:Taste; D013650:Taste Buds; D013652:Taste Threshold; D013997:Time Factors; D014059:Tongue
chemical_list: D000644:Quaternary Ammonium Compounds; C043414:denatonium; D003513:Cycloheximide; D011803:Quinine