Stimulation of the gerbil's gustatory receptors by disaccharides

Do Steviol Glycosides Provide Ecological Fitness to Stevia rebaudiana through Impact on Dietary Preference of Plant Pests and Herbivores?

The impact of Stevia rebaudiana leaf on feeding preferences of an insect, a mite, and a mammal was investigated. The grasshopper, Valanga irregularis of the Acrididae family, avoided feeding on S. rebaudiana leaf, as evidenced by a decrease in animal weight. Increased mortality on S. rebaudiana feed was ascribed to feeding avoidance to the point of starvation. The extent of red spider mite ( Tetranychus urticae) damage was not proportional to leaf steviol glycoside (SG) concentration, a result ascribed to a feeding mechanism that avoids chlorenchyma cells that contain SGs. Guinea pigs ( Cavia porcellus) were presented with the choice between a control feed and feed amended to contain 5% sucrose or 0.02%, 4%, or 10% (dry weight) of S. rebaudiana leaf. Feed intake increased (39% above the control) for the diet involving high levels of SG amendment of feed (10% S. rebaudiana leaf). Encouragement of general mammalian herbivory may provide ecological fitness to S. rebaudiana if it is more tolerant of grazing pressure than other plants in its environment. Improvement in feed intake may have commercial implication for use of S. rebaudiana as an additive in stock feeds.

Enhanced responses of the chorda tympani nerve to sugars in the ventromedial hypothalamic obese rat

Sweet taste sensitivity in obese rats with lesions of the ventromedial hypothalamus (VMH) was studied by examining chorda tympani nerve responses to various taste stimuli including sugars. In the early progressive phase of obesity (2 wk after creating VMH lesions), there was no significant difference in the nerve responses to any taste stimulus between sham-operated and VMH-lesioned rats. In contrast, in the late phase of obesity (15-18 wk after VMH lesions), the magnitude of responses to sugars (except for fructose) was prominently greater than that in age-matched controls. High-fat diet-induced obese rats and streptozotocin-diabetic rats also showed greater chorda tympani nerve responses to sugars as was observed in VMH-lesioned obese rats, indicating that VMH lesions might not be specifically related to the enhanced gustatory neural responses to sugars. Although it has been demonstrated that the enhanced responses of the chorda tympani nerve to sugars in genetically diabetic db/db mice is largely attributable to the lack of the direct suppressive effect of leptin on the taste receptor cells, plasma leptin levels were not correlated with the changes in chorda tympani responsiveness to sugars in these models of obesity and diabetes. Accordingly, our results suggest that some chronic factors, including high blood glucose, inefficiency of insulin action, or leptin resistance may be related to the enhancement of chorda tympani nerve responses to sugars.

Effect of tricyclic antidepressants on taste responses in humans and gerbils

One of the side effects of antidepressant pharmacotherapy reported clinically is impairment of the sense of taste. In this study, the taste effects of four tricyclic antidepressant compounds (clomipramine HCl, desipramine HCl, doxepin HCl, and imipramine HCl) were evaluated experimentally by topical application of the drugs to the tongue. Taste detection threshold concentrations for all four medications ranged from 0.1 mM to 0.2 mM in young persons but were elevated by as much as 7.71 times that in elderly individuals who were taking no concurrent medications. Each compound had a predominantly bitter taste with other qualities including metallic, sour, and sharp-pungent. In addition, each tricyclic antidepressant at concentrations from 1 mM to 5 mM blocked responses to a wide range of taste stimuli in both humans and gerbils. The differential suppression of other tastes by tricyclic antidepressants at the level of the taste receptors may contribute to the clinical reports of dysgeusia and hypogeusia.

Noncariogenic intense natural sweeteners

There is a definite relationship between the dietary consumption of sucrose and the incidence of dental caries. Noncaloric sucrose substitutes for use in the sweetening of foods, beverages, and medicines may be either synthetic compounds or natural products. In the United States, four potently sweet artificial sweeteners are approved, namely, saccharin, aspartame, acesulfame potassium, and sucralose. Highly sweet plant constituents are used in Japan and some other countries, including the diterpene glycoside stevioside and the protein thaumatin. Recent progress in a research project oriented towards the discovery and evaluation of novel potentially noncariogenic sweeteners from plants has focused on substances in the sesquiterpenoid, diterpenoid, triterpenoid, steroidal saponin, and proanthocyanidin structural classes. The feasibility of using Mongolian gerbil electrophysiological and behavioral assays to monitor the sweetness of plant extracts, chromatographic fractions, and pure isolates has been investigated. An in vivo cariogenicity study on the commercially available natural sweeteners stevioside and rebaudioside A has been carried out.

Sweet taste in the calf: III. Behavioral responses to sweeteners

The hedonic response to the sweeteners acesulfame-K, aspartame, fructose, galactose, glucose, glycine, lactose, maltose, Na-saccharine, sucrose, and xylitol was recorded in five groups of 4-16-week-old calves. The compounds were presented to the calves for 12 or 24 h in two-bottle preference tests with tap water as one choice. Glycine (10 mM and higher), sucrose (20 mM and higher), and fructose concentrations were most preferred. Sodium-saccharine was highly preferred at and above 4 mM concentration, fructose and lactose were preferred above 40 mM, galactose was preferred moderately, acesulfame-K and maltose were preferred inconsistently, and aspartame and xylitol were not preferred at any concentration. The change of preference during the tests was also studied. Three types of consumption changes were observed. 1) Increased preference of the tastant during consumption, seen during sucrose and, to lesser a extent, fructose consumption. 2) Initial high preference for the tastants, diminishing during the test period, observed with fructose, galactose, glucose, glycine, lactose, and maltose. 3) Initial large fluctuations in consumption from the two bottles, but no change in overall preference. This pattern was seen with xylitol and aspartame. This technique seems to offer a method to assess the long-term preference for a compound within one relatively short two-bottle preference session.

Single neuron gustatory responses of the gerbil chorda tympani to a variety of stimuli (recorded by a new method)

In most mammalian studies on gustatory single neuron recordings, the animal's chorda tympani nerve was cut and manipulated. This results in nerve trauma which may have affected the precision of the responses. In this paper, we are presenting a method whereby gustatory recordings were obtained from gerbil single chorda tympani neurons by inserting a microelectrode directly into the uncut nerve. The stimuli included 0.3 M NaCl, 0.3 M KCl, 0.3 M CaCl2, 0.3 M NH4Cl, 0.05 M acetic acid, 0.01 M quinine HCl, 32% Polycose and the sweeteners 0.5 M D-glucose, 0.5 M D-fructose, 0.02 M sodium saccharin and 0.5 M sucrose. While thirty-seven of the sixty seven neurons tested did not respond to any of the eleven gustatory stimuli applied to the gerbil's tongue, thirty positive single neuron responses were obtained to this group of compounds. The thirty positive neuron responses were grouped in two ways: (1) by observationally sorting the data according to maximum responses to four stimuli, sucrose, NH4Cl, NaCl, and acetic acid; and (2) by objectively sorting the data matrix using cluster analysis. The groups resulting from each method were then characterized and compared by discriminant function analysis. By the first grouping method, ten neurons responded best to sodium chloride, seven to acetic acid, four to ammonium chloride, and nine to sucrose. However, canonical discriminant function analysis showed that two of the four groups, acetic acid and ammonium chloride, occupied the same region of discriminant space and should be combined.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory interactions among rodent taste axons

The left side of the tongue of the Mongolian gerbil, Meriones unguiculatus, was experimentally innervated with both chorda tympani nerves. While this dual innervation did not increase the number or volume of fungiform taste buds on the left side, at least half of the taste buds were dually innervated since they could be neurotrophically maintained by either chorda tympani nerve. Impulse discharges occurred simultaneously in the native (left) and foreign (right) chorda tympani nerves when the taste stimulus was restricted to the left side of the tongue. The marked attenuation of the phasic or tonic portions of some taste responses suggested that dual innervation had enhanced inhibition, especially of foreign chorda tympani responses. This was confirmed when electrical stimulation of the native chorda tympani reduced the peak summated action potential discharges of the foreign chorda tympani to NaCl or sucrose by an average of 52 and 41%, respectively. Inhibition began within seconds and continued with an 11.5-min half-life. The inhibition was unaffected by acutely disconnecting either chorda tympani nerve from the brain. We propose that dual chorda tympani innervation accentuated lateral inhibitory connections that may function normally to reduce spurious sensory signals in taste axons.

Antagonism of the gerbil's sweetener and Polycose gustatory responses by copper chloride

Antagonism of the gerbil's whole chorda tympani nerve taste responses by CuCl2 was studied. A 30 min pretreatment of 0.1 mM CuCl2 suppressed responses to single concentrations of the following sweeteners: L-alanine, L-proline, D-tryptophan, 6-chloro-D-tryptophan, L-valine, glycine, sucrose, maltose, lactose, tetrachloro-galacto-sucrose, glucose, fructose, methyl alpha-D-glucopyranoside, glycerol, sorbitol, sodium saccharin, L-4'-cyano-3'-(2-2-2-trifluoro acetamido)succinanilic acid, phenethyurea, and stevioside. The responses to L-serine and the starch hydrolysate, Polycose were depressed to a lesser degree. The responses to glycine HCl and NaCl were slightly suppressed by CuCl2. The 0.1 mM CuCl2 had no effect on the shape of the sucrose concentration-response curve or its 1/2 maximal response (CR50), but did suppress the maximum response (Rmax), characteristic of non-competitive antagonism. Our work suggests the presence of 2 separate receptor sites on the gerbil's taste receptor cell membrane, one of which interacts with sugar sweeteners and most other non-sugar sweeteners and the other with Polycose.

The sweet taste in the calf. I. Chorda tympani proper nerve responses to taste stimulation of the tongue

Electrophysiological recordings were obtained from the chorda tympani nerve in calves during stimulation with NaCl, quinine hydrochloride, citric acid, acesulfan-K, aspartame, fructose, galactose, glucose, glycine, lactose, maltose, monellin, Na-saccharin, sucrose, thaumatin, and xylitol. In cattle the chorda tympani innervates the posterior third of the tongue as well as the anterior part. It was found that the posterior receptive field generally responded better to sweet substances than the anterior. Glycine and Na-saccharin followed by xylitol were the most effective sweet stimuli. The monosaccharides elicited larger responses than the disaccharides. Aspartame gave a weak nerve response in 5 of 13 calves. Monellin and thaumatin elicited no change in chorda tympani nerve activity and did not crossadapt with any sweetener. No effects on citric acid responses were observed after application of miraculin.

Cross-adapted sugar responses in the mouse taste cell

1. Intracellular recordings of mouse taste cell responses were made using a glass micro-electrode filled with Procion yellow dye solution. 2. Six sugars (sucrose, maltose, lactose, glucose, galactose and fructose) produced the depolarization responses. 3. Gustatory cross adaptation between sugars was determined. When the taste cell was pre-adapted with one of the six sugars, the other five sugars, cross adapted, produced depolarization, hyperpolarization or null responses. 4. From these observations, it is suggested that there are multiple sugar receptor sites on the receptor membrane of the mouse taste cell.

The gerbil: a unique model for research on aging

The Mongolian gerbil (Meriones unguicultatus) is suggested as a model for aging research because of its unique physiological attributes, ease of handling, and because of data previously collected. Factors that demonstrate the gerbils' suitability in fulfulling practical and scientific considerations important in determining a model for aging research are listed. Additionally, several unique physiological attributes of gerbils are described. Based on these attributes and on review of research in gerbils, it is suggested that gerbils can serve as animal models for behavioral and biological processes, and for normative and pathological aspects for aging.

Qualitative discrimination of gustatory stimuli in three different strains of mice

Qualitative similarities and differences among various taste stimuli were examined by comparing the generalization patterns of a conditioned aversion from single chemicals to other compounds in 3 different strains of mice (BALB, C3H and C57BL mice). It was observed as a common characteristic in all 3 strains of mice that generalization gradients among sugars and saccharin Na appeared in the order sucrose--saccharin Na--fructose--glucose--maltose, in which the closer stimuli generalized more strongly to each other. Strain differences were found in sensitivities to D-phenylalanine and L-proline, which generalized to sugars and saccharin Na in C57BL mice, but not in BALB and C3H mice. These strain differences correspond quite well to those previously observed in the responses of single chorda tympani fibers to these amino acids in the 3 strains of mice. A hierarchical cluster analysis and a multidimensional scaling analysis showed that 15 compounds including the 4 basic taste stimuli (sucrose, NaCl, HCl and quinine-HCl) were classified into 7 different groups according to their behavioral similarities and some amino acids were not grouped with any of the 4 basic taste stimuli in the 3 strains of mice. These results suggest the possibility that mice perceive tastes of these amino acids in a way different from human taste primaries.

Methyl 4,6-dichloro-4,6-dideoxy-alpha-D-galactopyranoside: an inhibitor of sweet taste responses in gerbils

The sugar methyl 4,6-dichloro-4,6-dideoxy-alpha-D-galactopyranoside (DiCl-gal) is a new type of inhibitor of the gerbil's electrophysiological taste response to sucrose or saccharin. Saturated solutions of this compound alone barely stimulate the gerbil's taste nerve. But, when mixed with sucrose or saccharin, DiCl-gal suppresses the gerbil's taste response to these two sweeteners. In contrast, when mixed with sodium chloride or hydrochloric acid, DiCl-gal does not affect the taste responses to these compounds. However, unlike other inhibitors of sweet taste, the DiCl-gal taste suppression is short-lived and occurs only when the inhibitor is combined with the sweetener.

Taste aversion to sugars by the gerbil

Some conditioned taste aversion experiments were undertaken to determine how the gerbil responds to disaccharides, monosaccharides and polyols. We observed the following: animals taught an aversion to 0.1 M sucrose generalized the avoidance to most sugars, the exception being galactitol; animals taught to avoid 0.01 M hydrochloric acid generalized the avoidance towards lactose, cellobiose, maltitol, methyl alpha-D-galactopyranoside, methyl alpha-D-mannopyranoside, methyl beta-D-glucopyranoside, and glycerol; animals taught to avoid 0.001 M quinine . HCl generalized the avoidance towards methyl alpha-D-glucopyranoside, methyl-beta-D-glucopyranoside, glycerol, ethylene glycol and erythritol. In no case did animals taught to avoid 0.1 M sodium chloride avoid any of the sugars. Moreover, it was observed that the gerbil's behavior with most reducing sugars was different than with equivalent methyl glycosides. For example, animals that were taught to avoid sucrose generalized the avoidance towards reducing sugars, such as, D-galactose, D-glucose, and D-mannose. However, the methyl glycosides, such as methyl alpha-D-glucopyranoside, methyl beta-D-glucopyranoside, methyl alpha-D-galactopyranoside and methyl alpha-D-mannopyranoside, in addition to being avoided by animals taught to avoid sucrose, were also avoided by animals taught to avoid quinine . HCl or hydrochloric acid. In addition, we have observed that the control animals consumed differing amounts of sugars and have concluded, therefore, that the sugars were not equally pleasant despite our attempt to use concentrations which produced equally intense neural responses in the gerbil's chorda tympani nerve.

Stimulation of the gerbil's gustatory receptors by artificial sweeteners

Some electrophysiological and behavioral taste experiments have been undertaken to determine how the Mongolian gerbil responds to artificial sweeteners. In the electrophysiological experiment only fourteen of twenty-one sweeteners produced neural responses. The most potent compound was L-4'-cyano-3-(2,2,2-trifluoroacetamido)succinanilic acid. Halogenated derivatives were more potent stimuli than non-halogenated ones. D-Tryptophan was stimulatory while L-tryptophan was not. The electrophysiological responses to sucrose were not inhibited by the presence of non-stimulating sweeteners nor were the responses to D-tryptophan inhibited by L-tryptophan. All the compounds that were stimulatory electrophysiologically were used in the behavior experiment. Using conditioned taste aversion, the gerbils responded to 5 of the compounds as sweet, one as sweet-salty, two as sweet-bitter, one as sour and one as bitter. In addition, 3 compounds were drunk equally by all groups suggesting that they were tasteless or possessed some unknown taste quality. A correlation was found between the efficacy (Kd) of the sweet-tasting compounds (pure sweet or mixed sweet) and the sweetness ranking by humans.

Determination of odour affinities based on the dose-response relationships of the frog's electro-olfactogram

Electro-olfactograms (EOG's) recorded from the frog's olfactory epithelium for 11 substances were used to calculate dissociation constants which in turn serve as an index for the affinity between odorant and receptor site. These constants were calculated with and without a correction for the odour partition between water and air. For a homologous series of 7 n-alcohols these values decrease up to 1-heptanol. The dose-response relationships were based on the peaks of the EOG's since the peak/plateau-ratio was concentration-dependent for some of the substances.

Stimulation of the gerbil's gustatory receptors by monosaccharides

The gustatory responses of the Mongolian gerbil were tested with a large number of monosaccharides. Electrophysiological methods were used to record from the chorda tympani nerve. Methyl glycosides which have structural features in common with sucrose are the most effective monosaccharides for eliciting a neural response. Among the monosaccharides tested, efficacy appears to be highest in D-pyranosides having equatorial substituents at the C-2 and C-4 positions and axial substituents at the C-1 position. A C-5 hydroxymethyl group is not required. Similarities in the structural requirements for taste response in the fly and gerbil are discussed.

Stimulation of the gerbil's gustatory receptors by polyols

The gustatory responses of the Mongolian gerbil were tested with 12 sugar alcohols. The electrophysiological effectiveness of the linear polyols as gustatory stimulants increased as the length of the carbon chain increased from 2 to 5. Six and 7 carbon acyclic polyols were no more effective than the pentitols. By comparison myoinositol, a cyclic polyol, was more effective in evoking a response. Responses to mixtures of D-sorbitol and sucrose suggest that these sugars compete for a common receptor site. A sucrose receptor site and a model of it is proposed.