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PubMed2006

A TAS1R receptor-based explanation of sweet 'water-taste'.

'Water-tastes' are gustatory after-impressions elicited by water following the removal of a chemical solution from the mouth, akin to colour after-images appearing on 'white' paper after fixation on coloured images. Unlike colour after-images, gustatory after-effects are poorly understood. One theory posits that 'water-tastes' are adaptation phenomena, in which adaptation to one taste solution causes the water presented subsequently to act as a taste stimulus. An alternative hypothesis is that removal of the stimulus upon rinsing generates a receptor-based, positive, off-response in taste-receptor cells, ultimately inducing a gustatory perception. Here we show that a sweet 'water-taste' is elicited when sweet-taste inhibitors are rinsed away. Responses of cultured cells expressing the human sweetener receptor directly parallel the psychophysical responses-water rinses remove the inhibitor from the heteromeric sweetener receptor TAS1R2-TAS1R3, which activates cells and results in the perception of strong sweetness from pure water. This 'rebound' activity occurs when equilibrium forces on the two-state allosteric sweet receptors result in their coordinated shift to the activated state upon being released from inhibition by rinsing.

Adaptation, Physiological↗
PubMed1986

Anxiety and drug taste as predictors of anticipatory nausea in cancer chemotherapy.

Interview data from 192 patients receiving cytotoxic chemotherapy for the first time were analyzed to identify factors predictive of the development of anticipatory nausea. Posttreatment nausea and vomiting (particularly vomiting), tastes of drugs during injections, and anxiety before injections were all associated with an increased probability of anticipatory nausea. An index consisting of those three variables, plus age, was found to have good predictive power, even when the predictor variables were assessed only at the first chemotherapy administration and the index was used to predict the development of anticipatory nausea at any time during the first six chemotherapy cycles.

Adolescent↗
PubMed1983

Operant regulation of feeding: a static analysis.

Cyclic-ratio schedules are a rapid method for studying the operant regulation of feeding rate. The cyclic method produces results comparable to traditional but time-consuming parametric methods. Performance on cyclic-ratio schedules is well described by a linear regulatory model that embodies three quantitative feedback assumptions: (a) that rate of feeding is regulated by the rate of operant behavior, (b) that taste factors have an additive effect on the rate of the operant response, and (c) that regulatory "gain" is inversely related to body weight. This model accurately describes poorer regulatory performance at high body weights and following amphetamine administration, and the effects of altered diet palatability on preferred feeding rates.

Animals↗
PubMed2006

Diverse tastes: Genetics of sweet and bitter perception.

Humans will eat almost anything, from caribou livers to rutabagas, but there are some types of foods, and their associated taste qualities, that are preferred by large groups of people regardless of culture or experience. When many choices are available, humans chose foods that taste good, that is, create pleasing sensations in the mouth. The concept of good taste for most people encompasses both flavor and texture of food, and these sensations merge with taste proper to form the concept of goodness. Although we acknowledge the universality of the goodness (sweet) or badness (bitter) of basic taste qualities, we also find that people differ, sometimes extremely so, in their ability to perceive and enjoy these qualities and, by extension, food and drink. The reasons for these differences among people are not clear but are probably due to a combination of experience beginning at an early age, perhaps in utero; learning, for example, as with conditioned taste aversions; sex and maturity; and perceptual differences that arise from genetic variation. In this review, we focus on individual variations that arise from genetic differences and review two domains of science: recent developments in the molecular biology of taste transduction, with a focus on the genes involved and second, studies that examine biological relatives to determine the heritability of taste perception. Because the receptors for sweet, savory (umami), and bitter have recently been discovered, we summarize what is known about their function by reviewing the effect of naturally occurring and man-made alleles of these receptors, their shape and function based on receptor modeling techniques, and how they differ across animal species that vary in their ability to taste certain qualities. We discuss this literature in the context of how taste genes may differ among people and give rise to individuated taste experience, and what is currently known about the genetic effects on taste perception in humans.

Animals↗
PubMedDate not supplied

Initial acceptance of ethanol: gustatory factors and patterns of alcohol drinking.

Individual differences related to taste, determined by prior two-bottle tests of quinine and saccharin selection against water, were found to be related to the initial selection of 15% ethanol solution during the first week of access by 60 randomly bred male rats. The 36 rats that drank the least alcohol during the first week (mean +/- SE: 0.49 +/- 0.06 g/kg/day), however, greatly increased their intake during the second and third weeks, to the level of the 24 initially high alcohol drinkers (4.07 +/- 0.39 g/kg/day during 1st week), and the influence of gustatory factors was no longer apparent. Subsequently, the initially low rats drank less alcohol when saccharin was the alternative fluid. The results can be interpreted as showing that initially low rats, that only drank rather large amounts of alcohol after prolonged exposure, resemble Cloninger's Type 1 alcoholics not only in this temporal pattern but also in being high in novelty seeking, and low in harm avoidance and reward dependence, and that the initially high rats that spontaneously drank rather large amounts even in the first week show the opposite characteristics and resemble Type 2 alcoholics. Although these rats are not themselves models for alcoholism, the results nevertheless suggest it might be possible to develop two separate animal models for the two types of alcoholism.

Alcohol Drinking↗
PubMed2001

Determination of saltiness from the laws of thermodynamics--estimating the gas constant from psychophysical experiments.

One can relate the saltiness of a solution of a given substance to the concentration of the solution by means of one of the well-known psychophysical laws. One can also compare the saltiness of solutions of different solutes which have the same concentration, since different substances are intrinsically more salty or less salty. We develop here an equation that relates saltiness both to the concentration of the substance (psychophysical) and to a distinguishing physical property of the salt (intrinsic). For a fixed standard molar entropy of the salt being tasted, the equation simplifies to Fechner's law. When one allows for the intrinsic 'noise' in the chemoreceptor, the equation generalizes to include Stevens's law, with corresponding decrease in the threshold for taste. This threshold reduction exemplifies the principle of stochastic resonance. The theory is validated with reference to experimental data.

Animals↗
PubMed1992

Chromosome mapping of Soa, a gene influencing gustatory sensitivity to sucrose octaacetate in mice.

Strain distribution patterns among recombinant inbred strains suggested that a locus influencing taste sensitivity to sucrose octaacetate was on chromosome 6. A location for Soa was established by linkage analysis of behavioral and electrophoretic data from outbred and congenic strains and from test-cross progeny. Haplotyping of 41 outbred CFW-Cr animals with a cDNA probe showed perfect cosegregation of Soa and Prp, a gene for salivary proline-rich proteins. Five of twelve B6.SW-Soaa strains were found to retain Ldr-1, lactate dehydrogenase regulator-1, on chromosome 6 as an allelic passenger from the SWR/J donor strain (source of the Soaa Taster allele). Centimorgan distance was estimated using the ABP/Le linkage-testing strain (non-Taster, Soab) and the SWR/J strain (Taster, Soaa) in a testcross breeding system. The data are consistent with a position for the Soa locus on mouse chromosome 6, 62 cM from the centromere.

Animals↗
PubMed2006

Taste receptors in the gastrointestinal tract. I. Bitter taste receptors and alpha-gustducin in the mammalian gut.

Molecular sensing by gastrointestinal (GI) cells plays a critical role in the control of multiple fundamental functions in digestion and also initiates hormonal and/or neural pathways leading to the regulation of caloric intake, pancreatic insulin secretion, and metabolism. Molecular sensing in the GI tract is also responsible for the detection of ingested harmful drugs and toxins, thereby initiating responses critical for survival. The initial recognition events and mechanism(s) involved remain incompletely understood. The notion to be discussed in this article is that there are important similarities between the chemosensory machinery elucidated in specialized neuroepithelial taste receptor cells of the lingual epithelium and the molecular transducers localized recently in enteroendocrine open GI cells that sense the chemical composition of the luminal contents of the gut.

Animals↗
PubMed2002

Craving for alcohol in the rat: adjunctive behavior and the lateral hypothalamus.

A review of previous results and the new data in this report show clearly that the Falk model of adjunctive behavior is an adequate analogue of human alcoholism and can be applied to induce excessive ethanol consumption. New data on the consumption of sweet flavored ethanol solutions and, especially, sweet alone solutions during brief periods of ethanol withdrawal provide some significant insights concerning the possible physiological basis for cravings in humans. Because voluntary consumption of ethanol is the normal process by which alcoholism develops, a general set of environmental and other experimental conditions that produce behavioral excess; adjunctive behavior, electrical stimulation of the brain, and salt arousal of drinking are discussed in some detail. Neuronal circuits of the lateral hypothalamus are important because some of the cells are chemosensitive and monitor osmolality of the blood and initiate drinking in the normal regulation of body fluids. Alcohol in very small amounts has a direct effect on these cells that also project to lower spinal motor neurons and modulate the level of excitability in spinal reflexes and thereby reactivity to environmental stimulation. Taste and other sensory information from the mouth arrives in presynaptic endings on these same cells by a multitude of indirect multisynaptic pathways. A theoretical model is developed to explain how tactile and taste sensory information and what is initially a nonspecific general state of motor arousal interact together to produce an excessive consumption or craving for ethanol.

Alcohol Drinking↗
PubMed1994

Mechanisms of alcohol abuse and alcoholism in adolescents: a case for developing animal models.

This paper reviews the ontogeny of neurotransmitter systems and neuropharmacological challenge within transmitter systems and discusses the actions of alcohol on such systems during the juvenile through adolescent periods. To place the animal research within the context of human development, an attempt is made to first examine some fundamental principles of developmental research as they relate to the adolescent period. Evidence presented from animal studies indicates that unique neurochemical and behavioral changes are occurring during postnatal development, including adolescence, that could mediate the response to alcohol. The limited number of studies on the neurochemical and behavioral response to alcohol during adolescence has employed rats and has been restricted by the relatively brief adolescent period in that species. While one alternative is to use primates, it is suggested that innovative behavioral paradigms be developed for adolescent animals in other species to study behaviors such as alcohol self-administration or alcohol stimulus discrimination. It is also suggested that existing behavioral models that are more easily adapted to younger age ranges (e.g., conditioned place preference, conditioned taste aversion, thermal response to ethanol) be extended to make ontogenetic comparisons through adolescence and adulthood. This may further our understanding of alcohol's immediate consequences during each maturational stage and, more important, the contribution of early alcohol exposure to excessive drinking and abnormal cognitive and social functioning during subsequent stages of development.

Adolescent↗
PubMed2004

Nerve regeneration-induced recovery of quinine avoidance after complete gustatory deafferentation of the tongue.

The concentration-dependent decrease in quinine licking by rats is substantially attenuated by combined bilateral transection of the chorda tympani (CT) and glossopharyngeal (GL) nerves, but transection of either nerve alone produces marginal impairments at most. Here we tested whether regeneration of one or both of these nerves after combined transection would result in recovery of taste avoidance. Water-restricted rats were presented with a series of brief-access (5 s) taste trials (water and 0.003-3.0 mM quinine-HCl) in a 5-day test block of 40-min sessions both before nerve transection and starting 75-77 days after transection. Licking avoidance returned to presurgical levels when both nerves were allowed to regenerate. When only the GL was allowed to regenerate, performance did not differ from that of sham-transected animals. This suggests that even after considerable gustatory deafferentation, regeneration has the capacity to restore normal taste-guided behavior. Surprisingly, when only the CT was allowed to regenerate, avoidance behavior was severely impaired and was not different from that of rats in which regeneration of both nerves was prevented. Taking into account prior findings, it appears that the absence of the GL in the presence of an intact CT is fundamentally different from the absence of the GL in the presence of a regenerated CT with respect to some taste functions. This represents the first reported instance to our knowledge in which the capacity of a regenerated nerve to maintain taste-guided behavior was distinctly different from that of an intact nerve in a rodent model.

Algorithms↗
PubMed2001

Effects of energy density and sweetness of gruels on Burkinabe infant energy intakes in free living conditions.

In free living conditions, 24 breastfed infants, aged 6 to 10 months, were given successively five experimental gruels to study the effect of energy density (ED) and sweetness (sweet taste) on energy intakes (EI). Four gruels (G0, G1, G9 and G20) were prepared with experimental flours which were composed of the same local ingredients and which contained different levels of sucrose. The fifth gruel (GC) was prepared with an industrial flour. G0 had an average ED of 45 kcal/100 g (189 kJ/100 g) and the other gruels an average ED of 110 kcal/100 g (461 kJ/100 g). Although the sugar contents of the flours were 1% for G1, 9% for G0 and G9 and 20% for G20, because of flour composition and gruel dry matter content, the gruel G1 had the same sweetness as G0, G20 the same sweetness as GC and G9 a sweetness between that of G1 and G20. The results show that the amounts of G0 consumed were significantly higher than those of high ED gruels (7.84 for G0 vs 6.12, 5.63, 4.46, 4.72 g/kg body weight/meal, respectively for G20, G9, G1 and GC, P < 0.05). However, EI from high ED gruels were significantly (P < 0.001) higher than those from G0 (6.65, 6.10, 4.86, 4.83 kcal/kg/meal, respectively for G20, G9, G1 and GC vs 3.46 for G0). Energy intakes from G9 and G20 gruels were not significantly different but were significantly higher than those from GC and G1 (P < 0.001). So, consumption of sweet gruels with high ED and composed of local ingredients increased, at least by 76%, the EI from gruels in comparison with those from low ED gruels, but the amounts consumed by the infants remained too low to cover more than 15% of their daily total energy needs.

Analysis of Variance↗
PubMed1979

Biochemical studies of taste sensation. VII. Enhancement of taste stimulus binding to a catfish taste receptor preparation by prior exposure to the stimulus.

The taste receptor membrane fraction (Fraction P2) was prepared from a homogenate of the taste tissue of the channel catfish Ictalurus punctatus. This included the rostral, dorsal, and dorsolateral surfaces of the catfish in addition to those of the barbels. The yield of Fraction P2 is 4-7 mg protein from an individual fish, with a purification averaging 8- to 15-fold over that of the crude whole homogenate and essentially quantitative recovery of binding activity in Fraction P2. Treatment of Fraction P2 in vitro with a high concentration of the taste stimulus molecule L-alanine led to a several-fold enhancement of binding activity. Enhancement of the binding of 3H L-alanine was observed after treatment with unlabeled 10 mM L-alanine and removal of the L-alanine by washing. Enhancement occurred whether the preparation was stored frozen (-65 degrees C) for an extended period in the presence of the L-alanine, or merely exposed to it in the cold without freezing. D-Alanine enhanced the binding activity of 3H L-alanine to about 60% of the level induced by L-alanine. Nonspecific binding of 3H L-alanine was unaffected by the treatment. Scatchard analyses of saturation curves for binding of 3H L-alanine to freshly prepared Fraction P2 and to L-alanine-treated Fraction P2 revealed no change in the KD value, but a several-fold increase occurred in the amount bound. Binding activity is operationally defined. Because the enhancement observed here is reminiscent of an increase in transport due to a countertransport effect, further studies were carried out to examine whether the phenomenon reflects transport or true binding. The measured binding was not increased in the presence of Na+, indicating that it is not due to an Na+-coupled transport of L-alanine. When Fraction P2 was preloaded with L-alanine (10(-6)--10(-2) M) prior to assay, no stimulation of binding was observed; instead, binding decreased. This result is consistent with a true binding phenomenon but not with a carrier-mediated transport process to explain the enhancement phenomenon. Binding assays carried out over a range of osmolarities revealed decreased binding at high osmotic strengths, suggesting that a significant portion of the ligand might be contained in vesicles. It is postulated that "hidden" or "buried" receptor sites exist in the Fraction P2 as isolated, and that these are exposed upon perturbation of the membrane structure by a high ligand concentration.

Alanine↗