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Interanimal transferability of taste aversion learning for 0.1% saccharin.

Three experiments were performed to assess the interanimal transferability of conditioned taste aversion to 0.1% saccharin. Two experiments used an intracerebrospinal fluid (subdural) route for administering brain extracts and a third used an intraperitoneal (IP) route. As assessed by repeated measurements ANOVA, saccharin consumption was significantly lower during extinction of conditioned aversion for experimental recipients (ER) receiving extracts from aversively conditioned donors, than that of control recipients (CR), receiving extracts from unconditioned donors in one subdural experiment, F(21, 189) = 1.61, p less than 0.05. In the IP experiment the results were in the same direction, though not significant, F(34, 238) = 1.39, p less than 0.1. Results of the other subdural experiment are discussed. It is concluded that these experiments with the conditioned taste aversion paradigm have potential as a model for investigations of behavioral interanimal transfer (BIT) and for neuromolecular research aimed at identification of associated putative neurochemical(s) and the elaboration of their mechanism of action.

Animals↗

Adult-like complexity of the larval antennal lobe of D. melanogaster despite markedly low numbers of odorant receptor neurons.

We provide a detailed analysis of the larval head chemosensory system of Drosophila melanogaster, based on confocal microscopy of cell-specific reporter gene expression in P[GAL4] enhancer trap lines. In particular, we describe the neuronal composition of three external and three pharyngeal chemosensory organs, the nerve tracts chosen by their afferents, and their central target regions. With a total of 21 olfactory and 80 gustatory neurons, the sensory level is numerically much simpler than that of the adult. Moreover, its design is different than in the adult, showing an association between smell and taste sensilla. In contrast, the first-order relay of the olfactory afferents, the larval antennal lobe (LAL), exhibits adult-like features both in terms of structure and cell number. It shows a division into approximately 30 subunits, reminiscent of glomeruli in the adult antennal lobe. Taken together, the design of the larval chemosensory system is a "hybrid," with larval-specific features in the periphery and central characteristics in common with the adult. The largely reduced numbers of afferents and the similar architecture of the LAL and the adult antennal lobe, render the larval chemosensory system of Drosophila a valuable model system, both for studying smell and taste and for examining the development of its adult organization.

Animal Structures↗

The effect of taste adaptation on salivary flow rate and salivary sugar clearance.

To provide an objective measure of the rate of taste adaptation, we measured changes in the flow rate of parotid saliva from 12 subjects while a tastant was infused continuously into their mouths. The tastants employed were sucrose, sodium chloride, and citric acid, each at two different concentrations. With all stimuli, the higher concentration elicited significantly higher initial flow rates, which declined exponentially with time. The half-time for adaptation of flow rate was independent of the nature or concentration of the stimulus and averaged 11.3 sec, which suggests that adaptation follows a single exponential curve. The model of salivary sugar clearance developed by Dawes (1983) predicted that the rate of clearance would be independent of the initial sucrose concentration. However, this model did not take into account the effect of taste adaptation on salivary flow. This process was thus incorporated into the model, which then predicted that the time for clearance would be dependent on the initial sucrose concentration, as found experimentally by Goulet and Brudevold (1984). Hence the process of taste adaptation progressively reduces the stimulated salivary flow rate, which retards the rate of salivary clearance of sugar from the oral cavity.

Adaptation, Physiological↗

Odorant receptor gene expression in catfish taste tissue.

Odorant receptor expression has been reported in a variety of non-olfactory cells and tissues in several animal models. We therefore investigated the possible expression of odorant receptor genes in taste tissue of channel catfish. Multiple odorant receptor transcripts were amplified by PCR from barbel. In situ hybridization showed that receptors amplified from taste tissue, as well as receptors amplified from olfactory neurons, hybridized to taste epithelium with similar patterns. These results show that odorant receptor transcripts are expressed in catfish taste tissue. Taken with previous data, these results suggest that some members of the odorant receptor superfamily may mediate various chemoreceptive roles in non-olfactory cells.

Amino Acid Sequence↗

[Enteral nutrition and changes in taste in diabetic patients: a double-blind prospective study].

The authors present a prospective double blind test aimed at objectively determining the acceptance of flavoured orally administered enteric diets specific to patients with glucose metabolism alterations (Glucerna and Precitene Diabet), in the light of the taste disorders described in such patients. Sixty-two patients were studied, 32 diabetics and 32 control patients, who were given a sample of each product; the level of acceptance was quantified on a modified wine-tasting scale. The average taste of the diabetics was 12.1 points (SD = 4.34) for Glucerna, and 10.1 (SD = 3.91) for the Precitene Diabet. In the control patients, the scores were 12.7 (SD = 3.78) and 13.2 (SD = 3.23) respectively. Multiple regression analysis did not reveal significant differences in taste according to age, sex or place of origin. Average taste among the diabetic patients as a whole with both products was 11.2 points and, for the nondiabetics, 12.92. The model detected significant differences (p = 0.01) between the two groups. The average taste of the diabetics was less than that of the non-diabetics, irrespective of all the remaining variables examined, including the type of preparation. These results confirm the lower oral acceptance in diabetic patients, possibly associated with disorders in the sense of taste, showing the utility of the modified wine-tasting scale as a test in evaluating the acceptance of enteric diets which must be administered orally.

Adolescent↗

[Bradley-Terry-Luce scale of taste qualities of champagne].

In a paired comparison experiment 783 subjects judged five different brands of champagne (three normal and two alcohol-reduced). Each subject judged only one single pair with respect to which one tasted more fizzy ("spritziger"), dry ("trockener"), prickling ("prickelnder") and better ("besser"). Three extended versions of the Bradley-Terry-Luce model are discussed and used to assess scale values for the criteria as well as for order effects. The results can be summarized into three points: (1) Goodness-of-fit for the simple BTL-model is satisfactory for all criteria--except for the judgement "tastes better than". (2) Using four graded response categories instead of dichotomous responses decreases goodness-of-fit considerably. (3) Alcohol-reduced brands are less "dry", but are quite within the range of the other brands with respect to the remaining criteria. It is argued that the particular scaling method used is especially useful for deciding which criteria are appropriate for measurement on a one-dimensional scale and which are not.

Carbonated Beverages↗

Molecular neurobiology of ingestive behavior.

The concepts and tools of molecular biology may be applied to almost any component of the animal involved in ingestion, but two categories of model system are particularly relevant for molecular analysis: homeostatic regulation of neuropeptide expression in the hypothalamus and neuronal plasticity underlying persistent changes in ingestive behavior. Molecular approaches to these models are reviewed, focusing on our strategy for analyzing conditioned taste aversion learning. Three questions must be answered: Where do the long-term changes occur within the distributed neural network that mediates feeding? This answer reveals the site of neuronal restructuring mediated by gene expression. When does the transition occur from short-term expression to long-term persistence of the change in behavior? This transition reveals the critical time of gene expression. What genes are expressed during the change in behavior? The expression of thousands of genes in discrete subpopulations of cells is likely to be required during critical periods of neuronal restructuring. The identification of these genes is a general challenge for molecular neurobiology. The analysis of ingestive behavior can profit from molecular tools, but ingestion also provides informative models that elucidate the principles of time- and neuron-specific gene expression mediating complex behaviors.

Animals↗

Temporal integration and reaction times in human smell.

A model description of intensity perception in human taste and smell developed earlier has now been verified experimentally to determine parameter values for odorants. The final objective is to quantify and understand odour-odour interaction phenomena in e.g., masking, deo-perfumes and flavour enhancement. Five types of olfactometer experiments were carried out, viz. determination of thresholds, determination of reaction times, scaling of perceived intensity after 5 sec stimulation, scaling of perceived intensity of a fixed concentration at variable duration, and measurement of intensity/time relationships. Four subjects were used and the odorants cineole, geraniol and hexane.

Acyclic Monoterpenes↗

Brain-derived neurotrophic factor-, neurotrophin-3-, and tyrosine kinase receptor-like immunoreactivity in lingual taste bud fields of mature hamster.

The neurotrophins brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), as well as their respective tyrosine kinase (Trk) receptors, TrkB and TrkC, influence peripheral target cell innervation, survival, and proliferation. In the mature taste system the role of neurotrophins and their receptors is not known. The mature hamster is an intriguing model because anterior lingual fungiform, unlike posterior lingual foliate and circumvallate, taste buds survive denervation. In light of this difference, we examined whether the degree of neurotrophin- or neurotrophin receptor-like immunoreactivity (IR) normally differs among lingual gemmal fields. In single- and double-labeled immunofluorescent experiments, 3,209 taste bud sections (profiles) from 13 hamsters were examined for immunopositive gemmal cells or nerve fibers using antibodies to BDNF and NT-3, their respective receptors TrkB and TrkC, and the neural marker ubiquitin c-terminal hydrolase L-1 [protein gene product (PGP) 9.5]. In each gemmal field, more than 75% of taste bud profiles showed immunopositivity to BDNF, NT-3, and TrkB. Across bud fields, BDNF-, TrkB-, and BDNF/TrkB-like IR, as well as PGP 9.5 and PGP 9.5/BDNF-like IR in centrally located, fungiform bud cells was greater (P < 0.0001 to P < 0.002) than in circumvallate or foliate buds. Within bud fields, the number of BDNF-like, labeled bud cells/bud profile was greater than that for NT-3-like IR in fungiform (P < 0.0002) and foliate (P < 0.0001) buds. TrkC was immunonegative in gemmal cells. The average density of TrkB- and TrkC-like fiber IR was more pronounced in fungiform than posterior gemmal-bearing papillae. Thus, fungiform papillae, whose taste buds are least affected by denervation, exhibit specific neurotrophin and receptor enrichment.

Animals↗

The role of innervation in induction and differentiation of taste organs: introduction and background.

To establish lingual receptive fields that are the basic unit of taste function, ganglion cells must extend neurites of peripheral and central targets and form connections. This symposium concerns developmental interactions between the geniculate, trigeminal and petrosal ganglia and peripheral taste organs, the gustatory papillae and resident taste buds. Investigators present data from organ and tissue culture, from mice with targeted gene deletions and from grafting experiments, in pursuit of principles that direct early innervation of the taste system. The lingual ganglia and the taste papillae initially develop independently, but then become reciprocally dependent as ganglia drive neurotrophin support from gustatory papillae and the papillae require sensory innervation for growth and morphogenesis. The issue of subsequent taste bud induction is discussed with results from amphibian and mammalian models, yielding conclusions that are not yet totally convergent. However, an essential role for sensory innervation in mammalian taste bud differentiation and acquisition of appropriate quantitative relations between ganglion cells and target organs is clearly demonstrated. A working outline is presented for periods of ganglion cell/target organ independence and interdependence during early innervation of the peripheral taste system.

Animals↗

Anion size of sodium salts and simple taste reaction times.

Simple taste reaction times (RT) and taste intensities were measured in adult humans for 100-mM aqueous solutions of sodium chloride, acetate, glutamate, ascorbate, and gluconate flowed over the anterodorsal tongue with a closed liquid delivery system. Results from 12 subjects showed a significant increase in RT with molecular weight of the tastant, and a correlation of 0.941 between RT and the square roots of anionic weights. A multiple regression analysis controlling for perceived taste intensity indicated that RT increased linearly with the square root of the anionic weight. These findings support a model that includes both the permeability of ions through the tight junctions between the taste receptor cells of fungiform papillae taste buds and the effects of ions at apical portions of the receptor cells. They also suggest that gustatory transduction of sodium salts in humans normally involves intercellular spaces of taste buds as part of the functional sensory structures, in addition to individual taste receptor cells.

Adolescent↗

Taste recognition: food for thought.

The ability to identify food that is nutrient-rich and avoid toxic substances is essential for an animal's survival. Although olfaction and vision contribute to food detection, the gustatory system acts as a final checkpoint control for food acceptance or rejection behavior. Recent studies with model organisms such as mice and Drosophila have identified candidate taste receptors and examined the logic of taste coding in the periphery. Despite differences in terms of gustatory anatomy and taste-receptor families, these gustatory systems share a basic organization that is different from other sensory systems. This review will summarize our current understanding of taste recognition in mammals and Drosophila, highlighting similarities and raising several as yet unanswered questions.

Animals↗

Possible prediction of taste quality using a liquid membrane.

Oscillations of electric potential across a liquid membrane consisting of picric acid in nitrobenzene between two aqueous layers were studied. When fully described the oscillations were found to be characteristic of the structural class of a tastant present in the RHS of the liquid membrane. Smaller variations were observed in the pattern of oscillations and were apparently related to variations in the taste qualities within that class.

Humans↗

Ultrastructure of taste cells and synapses in the mudpuppy Necturus maculosus.

Taste buds in the mudpuppy Necturus maculosus were examined with electron microscopy. Three cell types (dark, light, and basal) were identified and reconstructed from serial thick sections. Dark and light cells extend from the basal lamina to the surface of the tongue. The apical process of the dark cells was usually quite lamellar when viewed in cross section, in contrast to light cells, whose apical process appeared more cylindrical. Basal cells are situated at the base of the bud and do not extend processes to the surface of the tongue. The cytoplasm of basal cells contains numerous clear and dense-cored vesicles. Small, spinelike processes (2-3 microns in length) project outward from the basal cells into the cytoplasm of the surrounding tast receptor cells. Morphologically, basal cells in mudpuppy taste buds resemble Merkel cells. Unmyelinated afferent nerve fibers enter the taste bud at the base and course through the lower portion of the bud. Synapses were found between taste receptor cells and nerve fibers, between basal cells and nerve fibers, and between basal cells and taste receptor cells. Over 65% of the synapses observed in the mudpuppy taste bud involved the basal cell. These findings suggest that basal cells play some role in chemosensory signal processing or integration of the taste response.

Animals↗