Gustatory Cues Research Articles

Habituation of Facial Muscle Responses to Repeated Food Stimuli

We have shown in a series of studies that the human salivary response habituates to repeated presentation of gustatory cues. Parallel animal research has shown that mouthing and food acceptance also habituate. Facial expressions represent a complex response pattern in animals and humans that may provide an objective measurement of motivation to eat. The current study assessed whether facial muscles (orbicularis oris region, risorius region, and zygomaticus region) that regulate mouthing habituate to repeated presentations of a small amount (3 kcal) of a pleasant tasting food stimulus. Participants were randomly assigned to groups that received ten presentations of the same or changing taste stimuli. Following these trials all subjects were presented a novel dishabituating stimulus followed by the habituating stimulus. Integrated facial electromyography EMG responses over each region were measured for a 50 second period following the taste stimulus. Results showed differential habituation rates across the two groups, with participants in the repeated taste group showing decreases in contrast to the changing taste group who did not decrease. The participants in the repeated taste group showed dishabituation of these responses. These results systematically replicate basic animal research, and extend the number of responses related to eating in humans that habituate to repeated food presentations.

Nearly Optimal Foraging in Patches Under Nutrient Constraints.

Three feeding strategies with different rules for prey selectivity were evaluated by Monte Carlo computer simulation. The predator must obtain a minimum quantity of each of three different nutrients, and it sequentially encounters one of three kinds of prey that differ in both their nutrient compositions and their relative abundances. Within patches, prey may be randomly dispersed or aggregated with Markovian transition probabilities. Overall cost is the sum of search time plus consumption cost plus emigration (between-patch traverses) risk. The predator will emigrate if it is unsuccessful in acquiring a minimum of {Gamma} units of any needed nutrient within the T most recent prey encounters. The three strategies are (1) no discrimination-with potentially high consumption costs, (2) minimal consumption-with potentially very prolonged search times, and (3) a hybrid strategy that requires a physiological monitoring of net nutrient acquisition (or the bookkeeping of highly correlated gustatory cues). Each strategy has its characteristic dynamics and optima, but collectively these simulations show that no one strategy is superior and that over a large portion of the parameter space the differences in overall cost are relatively small.

Effect of Protein and Birch-Bark Powder on Selection of Food by Root Voles (Microtus oeconomus)

We tested the effect of levels of protein and birch-bark powder on selection of food by root voles ( Microtus oeconomus ). In the first set of cafeteria trials we offered voles pellets containing 3, 6, or 12% protein. Voles having no previous experience with this type of food did not show a preference among levels of protein during the first two trials, but strongly preferred the highest (12%) level of protein in the two subsequent trials. This suggests a learning process based on a physiological feedback mechanism. In the second set of trials, addition of 10% birch-bark powder to the protein pellets did not change the pattern of selection among the three protein levels. In the third cafeteria experiment, voles were offered pellets containing 6% protein and different concentrations (0, 2, 5, 10, and 20%) of birch-bark powder. The higher the concentration of birch-bark powder, the less the pellets were eaten. The highest concentration (20% birch-bark powder) was hardly touched by voles. This suggests the presence of olfactory or gustatory cues, immediate physiological discomfort elicited by the secondary compounds in birch-bark powder, or both.

Fatty acid modulation of K+ channels in taste receptor cells: gustatory cues for dietary fat.

In an attempt to determine the chemosensory cues, if any, provided by fats in the oral cavity, we have performed patch-clamp recordings on isolated rat taste receptor cells during application of free fatty acids. Cis-polyunsaturated fatty acids, when applied extracellularly, inhibit delayed-rectifying K+ channels. In a subset of cells, these fatty acids also enhance inwardly rectifying K+ currents. Saturated, monounsaturated, and trans-polyunsaturated fatty acids have no significant effect on K+ currents. These effects do not involve activation of G protein-mediated pathways, including protein kinase C and protein kinase A, lipoxygenase pathways, cyclooxygenase pathways, or cytochrome P-450 pathways, consistent with direct effects on these ion channels or closely associated proteins. The net effect of fatty acids is to prolong stimulus-induced depolarizations of taste receptor cells, and we propose the effects on K+ channels represent the mechanism by which fats are detected by receptor cells in the oral cavity.

INVITATION PAPER: C.P. Alexander Fund: HOST CHOICE BY APHIDIID PARASITOIDS (HYMENOPTERA: APHIDIIDAE): HOST RECOGNITION, HOST QUALITY, AND HOST VALUE

AbstractSpecies in the family Aphidiidae (Hymenoptera) parasitize exclusively ovoviviparous aphids. Females use a variety of information to detect and evaluate suitable hosts. Olfactory cues associated with aphids, or the aphids’ host plant, are important for host location. Visual cues including aphid colour, shape, and movement can be evaluated from a distance without physical contact; aphid movement may act as a releasing stimulus for attack. Contact chemosensory cues (gustatory cues) are evaluated by antennation of the host cuticle and during ovipositor probing. A potential host must conform to the wasp’s response profile and satisfy minimum physiological and dietary requirements for immature development and growth. Host quality is determined in part by attributes specific to each aphid species and in part by each aphid’s individual-specific growth potential. Host quality for male and female progeny may vary as a result of different patterns of resource allocation and sexual size dimorphism. For an encountered aphid to be accepted as a host, its perceived value must exceed the wasp’s response threshold for oviposition. Host value, as opposed to host quality, varies dynamically with parasitoid state variables such as age, egg load, and prior experience. A conceptual model of host choice by aphidiid wasps is presented.

Seasonal alteration in taste detection and recognition threshold in seasonal affective disorder: the proximate source of carbohydrate craving

Increased appetite with associated carbohydrate craving are core symptoms of seasonal affective disorder (SAD) and have been attributed to decreased central serotonergic function. The proximate mechanisms for centrally mediated selective macronutrient consumption are unknown. We questioned whether seasonal alterations in taste sensation could serve as a mediator of dietary intake, as implied by the term “craving”. Specifically, individuals who were seasonally depressed and reported carbohydrate craving would be more sensitive to gustatory cues associated with the presence of carbohydrate than nondepressed subjects. Taste detection and recognition thresholds for the four primary gustatory sensations — sweet, sour, salty, and bitter — were obtained in a group of 25 SAD patients and 23 non-psychiatric subjects during the winter, after 2 weeks of 10 000 lux morning and evening light treatment, and during the summer. Relative to the comparison group, the SAD group was less sensitive to sweet taste during the winter. Sweet taste threshold in the SAD group normalized during the summer; however, 2 weeks of light treatment failed to alter sweet detection thresholds in the SAD group. Moreover, within the SAD group, season exerted significant effects on sweet, sour, and bitter detection, but it did not influence salt-detection thresholds. The findings represent the first demonstration of specific changes in taste perception associated with the self-report of carbohydrate craving in SAD and are discussed in terms of the development of sweet craving and the serotonin hypothesis of SAD.

Salivary responding and the duration of measurement

The Strongin-Hinsie Peck whole-mouth salivation measure (Peck, 1959) is typically collected for a 2-min duration. This study compared saliva collected for 120 sec with saliva collected for shorter durations (30 and 60 sec) over repeated presentation of gustatory cues. Results showed reliable increases in salivation from a water stimulus baseline to the first presentation of lemon juice as a function of measurement duration. Repeated measures analysis of variance showed overall decreases in salivation across each measurement duration, with a greater rate of habituation for the 120-sec interval than for the 30- and 60-sec intervals. These data suggest that shorter measurement intervals can be used to measure salivation in acute and repeated measurement paradigms, but the change in response to repeated stimulus presentations is more pronounced for the longer measurement duration.

Social transmission of food preferences among norway rats by marking of food sites and by gustatory contact

Three experiments were conducted to investigate the social learning and transmission of food preferences by excretory marking among adult male Norway rats. The experiments extend our earlier findings that rats prefer to eat from a food bowl marked by the excretory deposits of conspecifics and that this mechanism can result in the communication and social learning of food preferences (Laland & Plotkin, 1991). Here we investigate whether a tradition of food and food site preferences can become established by these means. Experiment 1 established that the residual cues deposited by rats lose their powers of communication as “markers” of food sites over a 72-h period. Experiment 2 showed that while a socially enhanced preference for one flavored diet could be transmitted from one animal to the next along a chain, it was unstable for an alternative diet. This suggests that social transmission may be more stable when it reinforces a prior preference than when it conflicts with one. In Experiment 3, the stability of socially transmitted food preferences was bolstered by the addition of a second process for the communication of diet preferences-namely, gustatory cues on the demonstrator’s breath. This finding suggests that when a socially transmitted trait is mediated by more than one process, the processes may interact, and the diffusion is likely to be more stable.

Parabrachial nucleus lesions and conditioned taste aversion: evidence supporting an associative deficit.

Three experiments examined the conditioned taste aversion (CTA) deficit that occurs following electrolytic lesions of the parabrachial nucleus (PBN). In Experiment 1, lesioned rats failed to avoid either a gustatory or an olfactory stimulus that had been paired with lithium chloride-induced toxicosis. In Experiment 2, however, all rats learned a conditioned flavor preference. Finally, in Experiment 3, all controls and 7 of the 12 lesioned rats learned a conditioned place aversion. Together, these results demonstrate that the disruption of CTA in lesioned rats cannot be ascribed to an inability to process either gustatory or visceral afferent information per se. Rather, the data suggest that PBN-lesioned rats are unable to form a specific association between gustatory and visceral cues.

Ontogenetic differences in the association of gustatory and tactile cues with lithium chloride and footshock

Using a double dissociation design with 15% sucrose solution and exposure to a heat lamp (34 degrees C) as CSs and 0.3 M LiCl and 1-mA footshock as USs, the present study found 15-day-old rats to show selective associations similar to those found in adults. Five-day-old pups, however, expressed similar sucrose aversions when this solution was paired with either LiCl or footshock, whereas they expressed heat aversions after heat-LiCl but not heat-shock pairings. Results are discussed with respect to previous data on selective associations in pups, current theories on selective associations, and ontogenetic differences in stimulus selection.

Feed aversion in small mammals as a potential source of hazard reduction for environmental chemicals: Agrichemical case studies

Behavioral responses to environmental chemicals take various forms that may influence the hazard associated with chemical exposures in the field. From integrated laboratory-field studies that addressed the wildlife hazard associated with two chemicals—paraquat and carbofuran—commonly applied in various agricultural practices, the role of behavioral responses to environmental toxicants may be illustrated. For small mammals, and in particular the cricetid and murid rodents, olfactory and gustatory cues are prominent in influencing the perception of environmental chemicals and eliciting direct or indirect responses to chemical cues. In laboratory studies, subacute dietary exposures were evaluated using microtine rodents; feed aversion and toxicant avoidance appeared the most significant behaviors elicited by feed tainted with either paraquat or carbofuran. Feed aversion was associated with delays in the time-to-first-breeding in carbofuran-exposed females, while a female-biased sex ratio in offspring of paraquat-exposed breeding pairs was not uncommon in these laboratory feeding exposures. Preliminary field investigations that estimated population-level effects (population size and structure), however, suggested that toxicant avoidance, perhaps mediated through responses like feed aversion, may have ameliorated these indirect toxicant effects. While reproductive function and population-level effects in small mammals were not apparent in these preliminary field studies, the laboratory studies suggested that various subtle responses related to altered reproductive function may become apparent in long-term field studies, especially if routes of exposure and chemical bioavailability were altered and different chemical formulations and chemical mixtures were used.

Alcohol aversion generalization in rats: specific disruption of taste and odor cues with gustatory neocortex or olfactory bulb ablations.

Rats with ablations of the gustatory neocortex (Experiment 1) and rats with olfactory bulb ablations (Experiment 2) were compared with normal rats for aversion generalization to both single taste solutions (sucrose, sodium chloride, quinine hydrochloride, hydrochloric acid) and compound taste solutions (pairs of the four single tastants) following alcohol aversion training. All rats acquired equal and strong alcohol aversions. Control rats showed consistent aversion generalization to both the sucrose + quinine and the sucrose + hydrochloric acid solutions; no significant generalization occurred to the single tastants except a weak generalization to sucrose in Experiment 2. Rats with gustatory neocortical ablations failed to show aversion generalization to any of the taste solutions. Rats with olfactory bulbectomies displayed the same aversion generalization functions as control rats but exhibited significantly faster extinction of the alcohol aversion than did the trained control rats. Results from the present experiments suggest that during alcohol aversion learning, rats lacking gustatory neocortex use odor cues (no taste generalization), whereas rats lacking olfactory bulbs utilize taste cues (normal taste generalization).

Naloxone decreases ethanol consumption within a free choice paradigm in rats

The effect of subcutaneous naloxone administration on the consumption of a weak ethanol solution in rats on the three consecutive days (testing days) was investigated using a behavioral paradigm which includes a first forced ethanol exposure (conditioning day) followed by a two-bottle ethanol/water choice procedure. Besides reducing fluid intake, naloxone treatment prior to forced ethanol exposure interferes with the acquisition of ethanol preference. Post-conditioning naloxone administration fails to affect ethanol preference. Administration of naloxone prior to the first testing session induces a reduction on total fluid intake, at the day of treatment; a decrease on ethanol preference throughout the three consecutive testing days is also observed with the higher dose of the antagonist (5 mg/kg). An involvement of endogenous opioids in ethanol consumption is suggested through the modulation of alcohol reinforcement or the affective quality of the gustatory cue.

Molecular parameters involved in bee-plant relationships: a biological and chemical approach

Honeybee-plant relationships are based on a conditioning process in which olfactory (plant aroma) and gustatory cues (mainly nectars) are closely linked, leading to a selective foraging behaviour. Among crops dependent upon entomophilous cross-pollination, the sunflower has recently undergone extensive expansion due to hybrid variety selection. Sunflower hybrid seed production is strictly dependent upon pollinating insects, mainly the honeybees, but foragers may have preferences among the parental lines, leading to a lack of pollen carriage and consequently to a decrease of hybrid seed yield. In order to define the role of plant chemicals (aromas, nectars) involved in the pollination process, we set up a study combining behavioural and chemical assays. It appears that even though volatile chemical blends are much more complex compared to glucidic blends, for both kinds of cues only a ‘limited chemical pattern’ is responsible for foragers' choices. Therefore, it is henceforth possible to take these molecular criteria into account for plant improvement.

Importance of tactile and olfactory cues to the inhibition of the grasshopper mouse's attack through toxicosis

This study examined the effect that toxicosis paired with the presence of a distinctive texture had on the inhibition of the grasshopper mouse's predatory attack. The first experiment measured the context in which tactile cues would be most effective by presenting prey with various combinations of added stimuli. The combination of distinctive tactile, olfactory, and gustatory cues produced the longest lasting inhibition. Because certain manipulations also had an unintended weak odor associated with them, the second experiment measured the importance of a weak or strong odor to inhibition of a mouse's attack. A combination of strong odor and distinctive texture paired with toxicosis inhibited an attack more effectively than a weak odor and a similar texture. In a third experiment, toxicosis was paired with an acraea moth caterpillar which has a highly distinctive texture. This produced the longest lasting inhibition of mouse's attack observed thus far. The ecological significance of a combination of a distinctive texture and odor to the inhibition of the grasshopper mouse's attack is discussed.

Conditioning of aversion to alcohol orosensory cues in 5- and 10-day rats: subsequent reduction in alcohol ingestion.

Two experiments examined in 5- and 10-day-old rat pups the impact of alcohol olfactory aversions upon subsequent alcohol intake. In Experiment 1 it was observed that at both ages, animals given a single pairing of alcohol odor and LiCl subsequently consumed less alcohol than those in any of 4 control conditions (alcohol odor unpaired with LiCl, alcohol odor exposure, lemon odor paired with LiCl, and untreated animals). In Experiment 2, pups of both age groups were given LiCl following exposure to alcohol odor, the infusion of an alcohol solution or both stimuli simultaneously. Rats given explicitly unpaired presentations of the different conditioned stimuli and internal malaise served as controls. It was observed that equivalent aversions to alcohol ingestion were expressed whether the infants had experienced the alcohol odor, the alcohol infusion, or both, paired with toxicosis. These experiments extend the ontogenetic spectrum of circumstances in which olfactory experiences affect subsequent ethanol ingestion and also may indicate an early nondifferentiated processing of odorant and gustatory cues arising from an ethanol stimulus.

Avian Predation on Heteroptera: Experiments on the European Blackbird Turdus m. merula L.

AbstractHeteroptera are often preyed upon by birds in spite of their noxious scent‐gland secretions. Consequently, the question is raised as to whether or not birds possess physiological immunity to the secretions, simply tolerate any discomfort, or use special prey‐handling techniques.This study reports the responses of 12 European blackbirds, ranging in age from 45 days to 8 years, to 583 adult Heteroptera from 8 species (Coreidae, Pyrrhocoridae, Pentatomidae). The main results are:(1) The non‐aposematic bugs were eaten (63.1%) far more often than the aposematic ones (16.3%). Palomena prasina and Coreus marginatus had the highest edibility rank; Eurydema ornatum, the lowest. The highest rate of predation took place in the youngest birds.(2) The metathoracic secretion of 4 of the pentatomid species functioned as a topical contactirritant of the buccal cavity, head and eyes; the other test species provoked little or no discomfort. Some birds showed little sensitivity to the secretions. Among the behaviors induced were head‐shaking, dirt‐eating, respiratory difficulties, head‐scratching, and eye‐blinking. One bird engaged in “anting” with Graphosoma lineatum. No intoxication resulted from ingestion of the bugs.(3) Several prey‐handling techniques were used: seize, mandibulate, peck, shake, and wipe. The last three are probably correlated with the distinct physical properties of the Heteroptera. In general, the bugs were handled more during the first trials than during the last. The blackbirds learned to modify their handling techniques in such ways as to avoid or minimize exposure to the insects' secretions.(4) The caustic action of the scent‐gland secretion did not constitute an effective deterrent. Rejection of the Heteroptera was primarily based on gustatory cues.

On the nature of processes governing defensive burying of aversive flavors and odors in rats

Four experiments are reported which investigated the processes which contribute to the failure of rats to bury fluids that have acquired aversive properties through pairings with lithium chloride toxicosis. Fluids that failed to provide strong olfactory stimulation were avoided but not buried. These solutions, however, produced higher order conditioning of odor-bearing solutions which were buried readily. Various control experiments indicated that these effects depended upon the odorous qualities of the stimulus and not upon simple novelty effects or changes in gustatory stimulation. These data indicate that the inability of aversive gustatory cues to produce burying reflects a constraint on motivational or S-R learning processes.

Food-finding behavior of selected aquatic detritivores: Direct or indirect behavioral mechanism?

In feeding tests, the aquatic detritivores Pycnopsyche guttifer and Pteronarcys pictetii consumed microbially colonized leaves more readily than uncolonized leaves. Videotape analysis of insect movements in bioassay arenas where colonized and uncolonized leaves were presented in both still and flowing water revealed no evidence for movement directed toward food resources (i.e., attraction). We suggest that gustatory cues sensed after random contact with food items are responsible for the differential arrestment and feeding on colonized versus uncolonized leaves. This is supported by the observation of well-developed gustatory receptors on P. pictetii and P. guttifer. Olfactory receptors of these detritivores resembled those of terrestrial arthropods and their effectiveness in the aquatic medium remains unknown.

Taste aversion learning: simulation of interference with the gustatory cue during conditioning

Rats were taught an aversion to a sucrose taste cue of varying strengths. The concentration of the sucrose solution was either, 10, 7.5, 5, 2.5, 1, 0.5, or 0.25% which the animals drank for 5 min. Thirty minutes later they were poisoned with lithium chloride. On the test day all animals had access to a 10% sucrose solution regardless of the concentration they had drunk on the conditioning day. Animals conditioned with a 10, 7.5, or 5% sucrose cue subsequently displayed an identically strong aversion to the 10% cue. Only those animals conditioned with a sucrose cue which was 1% or less displayed a significantly weaker aversion to the 10% cue. The results are discussed in terms of the theory that interference with taste aversion learning by such agents as pentylenetetrazol and electroconvulsive shock may have their effect by disrupting the gustatory engram. If this assumption is correct then it suggests that the memory of the gustatory cue may be stored, at least prior to poisoning, in a quite labile state and an apparently limited disruption of taste aversion learning may in fact represent a substantial amnesic effect.