Partial rescue of taste responses of alpha-gustducin null mice by transgenic expression of alpha-transducin

The transduction of responses to bitter and sweet compounds utilizes guanine nucleotide binding proteins (G proteins) and their coupled receptors. Alpha-gustducin, a transducin-like G protein alpha-subunit, and rod alpha-transducin are expressed in taste receptor cells. Alpha-gustducin knockout mice have profoundly diminished behavioral and electrophysiological responses to many bitter and sweet compounds, although these mice retain residual responses to these compounds. Alpha-gustducin and rod alpha-transducin are biochemically indistinguishable in their in vitro interactions with retinal phosphodiesterase, rhodopsin and G protein betagamma-subunits. To determine if alpha-transducin can function in taste receptor cells and to compare the function of alpha-gustducin versus alpha-transducin in taste transduction in vivo, we generated transgenic mice that express alpha-transducin under the control of the alpha-gustducin promoter in the alpha-gustducin null background. Immunohistochemistry showed that the alpha-transducin transgene was expressed in about two-thirds of the alpha-gustducin lineage of taste receptor cells. Two-bottle preference tests showed that transgenic expression of rod alpha-transducin partly rescued responses to denatonium benzoate, sucrose and the artificial sweetener SC45647, but not to quinine sulfate. Gustatory nerve recordings showed a partial rescue by the transgene of the response to sucrose, SC45647 and quinine, but not to denatonium. These results demonstrate that alpha-transducin can function in taste receptor cells and transduce some taste cell responses. Our results also suggest that alpha-transducin and alpha-gustducin may differ, at least in part, in their function in these cells, although this conclusion must be qualified because of the limited fidelity of the transgene expression.

Behavioral analysis of the saccharin deprivation effect in rats

The deprivation effect (DE)--an increase in the level of free-choice consumption of alcohol after a period of forced abstinence--may reflect relapselike drinking and be relevant for modeling alcohol abuse. However, the behavioral mechanisms of the DE are unclear. In these experiments, rats had unlimited free-choice access to water and saccharin-containing solutions and underwent repeated episodes of saccharin deprivation. It was found that DE magnitude correlates positively with the deprivation phase duration, expression of the DE is highly context dependent, and the DE can be prevented by extinguishing response to the saccharin-associated stimuli. Thus, DE procedures may be useful for studying the effects of continued exposure to stimuli associated with various primary reinforcers such as drugs of abuse.

Isolation of an antifungal thaumatin-like protein from kiwi fruits

A single-chain 21 kDa protein exhibiting antifungal activity against Botrytis cinerea and some suppressive effects on Mycosphaerella arachidicola and Coprinus comatus was isolated from kiwi fruits. The protein, designated kiwi fruit thaumatin-like protein, did not inhibit translation in the cell-free rabbit reticulocyte lysate system but inhibited HIV-1 reverse transcriptase. It was purified to apparent homogeneity using a procedure involving saline extraction, (NH(4))(2)SO(4) precipitation, ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, ion exchange chromatography on SP-Sepharose and gel filtration on Superdex 75, respectively.

Conditioned saccharin aversion induced by self-administered cocaine negatively correlates with the rate of cocaine self-administration in rats

Previous studies showed that the degree of saccharin aversion induced by a self-administered drug correlated with the amount of drug taken. The present paradigm evaluated the relationship between conditioned saccharin (0.15% w/w) aversion and cocaine self-administration (0.15 mg/kg per injection) when drug intake was limited to 1 mg/kg per session over five taste-drug pairings. The low dose of self-administered cocaine induced a significant decrease in saccharin intake as a result of the conditioning pairings. In addition, conditioned saccharin intake was significantly correlated with the rate of cocaine self-administration (r=-0.54; P<0.05). A second experiment was designed to control for the effect of cocaine concentration in blood per unit of time. Saccharin was paired with one of three doses of non-contingent IV cocaine (0, 1, 3, 5 mg/kg) over five taste-drug pairings. Although, 3 or 5 mg/kg of non-contingent IV cocaine induced a dose-dependent decrease in saccharin intake after five taste-drug pairings, the low dose of 1 mg/kg was not effective in inducing the effect. Taken together, these results suggest that 1 mg/kg per session of cocaine was effective in inducing saccharin aversion only in rats that self-administered the drug at a high rate. It is suggested that a Pavlovian effect such as conditioned saccharin aversion induced by a self-administered drug may be an alternative tool to investigate the anticipation of addictive drugs.

Application of the U and gamma' models in binary sweet taste mixtures

The U and Gamma' models of sensory interactions, successfully applied in olfaction for several years, are tested here using data from published studies on sweetness. The models are subsequently tested on new data obtained in studies of binary mixtures of four sodium sulfamates. The U model allows for the estimation of a global interaction, whereas the Gamma' model allows for the distinction between that which is due to an intrinsic interaction in the mixture itself and that which may be due to the power function exponents in the mixture. The models give satisfactory predictions for observed phenomena of sweet taste suppression, synergism or pure additivity. Additionally, they appear to be more suitable than other models recently applied in taste, particularly the equiratio model. Application of the models to the sulfamate mixtures, reveals additivity for sodium cyclohexylsulfamate (cyclamate)/potassium cyclohexylsulfamate and sodium cyclohexylsulfamate/sodium exo-2-norbornylsulfamate, respectively; whereas for sodium cyclohexylsulfamate/sodium 3-bromophenylsulfamate, the models revealed a slight hypo addition which is simply due to the dissimilarity values of the power function exponents of the components.

In vitro testing of xylitol as an anticariogenic agent

A number of studies involving xylitol chewing gum have demonstrated that xylitol is both noncariogenic and anticariogenic. The ability of xylitol to act as an anticariogenic agent most likely is due to its ability to be transported into caries-causing oral bacteria and inhibiting fermentation either by depleting the cell of high-energy phosphate or by poisoning the glycolytic system. In vitro tests were conducted to determine the concentration of xylitol required to inhibit the growth of three strains of oral streptococcus (S. mutans, S. salivarius, and S. sanguis). All three strains were inhibited significantly at xylitol concentrations of 12.5% and higher; however, only S. mutans was inhibited significantly at a xylitol concentration of 1.56%.

Effects of bremazocine on self-administration of smoked cocaine base and orally delivered ethanol, phencyclidine, saccharin, and food in rhesus monkeys: a behavioral economic analysis

There is increasing evidence that kappa-opioid receptor agonists modulate cocaine-maintained behavior, and limited findings implicate the involvement of kappa-opioid receptors in ethanol-maintained behaviors. The purpose of the present study was to investigate the effects of bremazocine, a kappa-opioid agonist, on the self-administration of smoked cocaine base and oral ethanol in rhesus monkeys (Macaca mulatta). To determine the selectivity of bremazocine, the effects of bremazocine pretreatment on the oral self-administration of phencyclidine (PCP), saccharin, and food were also examined. Adult male rhesus monkeys were trained to self-administer oral ethanol, PCP, saccharin (n = 8), food (n = 6), or smoked cocaine base (n = 6) and water during daily sessions. Bremazocine (0.00032-, 0.001-, and 0.0025-mg/kg i.m.) injections were given 15 min before session. The 4 days of stable behavior before pretreatment served as baseline. Demand curves (consumption x fixed ratio; FR) were obtained for smoked cocaine base, ethanol, and PCP by varying the cost (FR) of drug deliveries and measuring consumption (deliveries). Bremazocine (0.001 mg/kg) was administered at each FR value in nonsystematic order. Results indicate that bremazocine dose dependently reduced cocaine, ethanol, PCP, and saccharin intake. Food intake was affected less by bremazocine than the other substances in five of the six monkeys. Generally, bremazocine treatment reduced the demand for cocaine, ethanol, and PCP as well as other measures of response strength. These results extend the findings that kappa-agonists reduce the self-administration of drug and nondrug reinforcers to smoked cocaine base and oral ethanol, PCP, and saccharin in rhesus monkeys.

Synthesis and properties of N-substituted saccharin derivatives

Four different routes for the synthesis of saccharin containing peptides were studied. While reactions between saccharin sodium and alpha-halogeno acids were limited to two examples, reactions of sulfobenzoic anhydride (4) or saccharin-N-carboxylate (6) with amino acid esters yielded the ring opened products 5 and 7. Finally, we found, that the reaction between the benzoxathiol derivative 8 and amino acid derivatives represents a versatile route to the peptidic compounds 9 and 11. Hydrolysis and hydrogenolysis were studied, and by combination of the different routes the "saccharin tripeptides" 18 were obtained. Structures and stereochemistry were elucidated by spectroscopic and chromatographic methods. Selected compounds were tested as sweeteners or as inhibitors of elastase, but no exiting results were found.

Newborn rats' first suckling experience: taste differentiation and suckling plasticity

The present study examined responsiveness of newborn rats to a surrogate nipple providing fluids with basic tastes (sweet, sour, bitter and salty) and assessed the effects of this first gustatory experience on subsequent responding to the nipple itself (empty nipple) or the nipple providing water. Responsiveness (attachment to and ingestion from a surrogate nipple providing saccharin, saline, quinine or ammonium chloride) was compared with that toward a nipple providing water. Compared to water, saline and quinine significantly reduced attachment to and ingestion from the nipple, while saccharin and milk significantly increased attachment behavior. Ammonium chloride increased attachment but not ingestive behavior. Suckling experience with saline, quinine and ammonium chloride attenuated both attachment and ingestive behaviors when subjects were tested 1 h later with an empty surrogate nipple or a nipple providing water. Experience with saccharin and milk (but not water) increased both measures. The data suggest that in newborn rats, as early as a few hours after birth, mechanisms of gustatory detection have control over suckling behavior. Initial experience with the tastants available from the nipple in the first suckling episode may alter further responsiveness to the nipple itself, mediated perhaps by mechanisms of appetitive and aversive conditioning.

Dental considerations in sucralose use

Sucralose is a new type of non-caloric, high-intensity sweetener recently approved for use by the U.S. FDA. Its availability may expand the number of palatable, low-sugar foods and beverages currently on the market. A series of studies has been conducted to assess whether sucralose has cariogenic potential. These include an examination of oral bacterial metabolism, experimental caries in animal models, and the effect of sucralose-containing solutions on human plaque pH in situ. The sum of these studies demonstrates that sucralose is non-cariogenic. Sucralose-based sweeteners that contain bulking ingredients, which allow them to pour and measure more like sugar, do have cariogenic potential due to the presence of added fermentable carbohydrate; however, the data suggest that both the currently marketed sucralose granular and packet products are less cariogenic than sugar. Thus, when used to replace sugar, both sucralose and the tested sucralose-based sweeteners may be useful in the dietary management of caries.

Effect of a lactose-containing sweetener on root dentine demineralization in situ

Since lactose has been used as an excipient in powdered sweeteners, we evaluated its effect on dentine demineralization, in an in situ crossover study. Twelve adult volunteers wore palatal appliances containing 4 blocks of bovine root dentine, which were submitted 4 times a day to: distilled water (negative control), aqueous solution of powdered sweetener (Zero Cal); experimental group), 1.5% lactose solution (active group), 1.5% sucrose solution (positive control). After 15 days, microhardness was determined on dentine surface (SMH) and on the sectioned blocks (CSMH). All groups presented statistical differences in SMH before and after the treatments; water increased, while sweetener, lactose and sucrose decreased SMH. By CSMH, the only significant difference was observed after sucrose treatment. The data suggest that sweeteners containing lactose as a bulking agent may be cariogenic for root dentine.

[Study of physiological and toxic effects of a sweetening agent stevioside (review of the literature)]

The review consist of modern data of physiologic and toxic effects on organism of sweetening stevioside with low energy value. His sweetening is considered by the most of investigators as not toxic, not mutadenic and not cardinogenic one.

Gustatory responses of pigs to sixty compounds tasting sweet to humans

The gustatory responses of pigs to 60 compounds perceived as sweet by humans were studied via a semi-quantitative behavioural method derived from the Richter two-bottle preference test. Among the 60 compounds tested 35 are effective in pigs, but with an effectiveness much lower in pigs than in humans. Lugduname and carrelame, which are the two most potent sweeteners in humans, are also the most effective compounds in pigs.

Cariogenic traits in xylitol-resistant and xylitol-sensitive mutans streptococci

Long-term xylitol consumption leads to the emergence of xylitol-resistant (X-R) mutans streptococci. The aim of the present study was to compare cariogenic traits in X-R and xylitol-sensitive (X-S) strains. Six strains of mutans streptococci, three X-R and three X-S strains, were studied. Xylitol resistance and sensitivity were confirmed by growth in xylitol-supplemented media. Acid production from glucose or fructose or uptake of xylitol was initiated by adding (14)C-labelled glucose, fructose or xylitol to bacterial suspensions. The resultant metabolites were identified by HPLC. Lactate was the major metabolite from glucose, whether the bacteria were grown in the presence or the absence of xylitol. Lactate production per colony-forming unit was lower in X-S cells than in X-R cells. Fructose was metabolized by both X-R and X-S cells. Both X-R and X-S cells took up xylitol, but xylitol-5-P was detected in X-S cells only. Total polysaccharides were measured through production of C(14)-labelled ethanol-insoluble polymers from [U(14)-C]-sucrose. No difference in polysaccharide production was found between X-R and X-S cells. The present study thus does not support the contention that X-R are less cariogenic than X-S mutans streptococci.

Investigation into the significance of task difficulty and divided allocation of resources on the glucose memory facilitation effect

RATIONALE

Memory for a list of 20 words can be enhanced by preceding learning with consumption of 25 g glucose rather than an equally sweet aspartame solution. In previous studies, participants performed a secondary hand-movement task during the list-learning phase.

OBJECTIVE

The present placebo-controlled, double-blind study examined whether the additional cognitive load created by a secondary task is a crucial feature of the glucose memory facilitation effect.

METHODS

The effect of glucose administration on word recall performance in healthy young participants was examined under conditions where the primary memory task and a secondary task were competing for cognitive resources (across a range of secondary tasks), and where task difficulty was increased but dual task-mediated competition for cognitive resources did not exist. Measures of non-verbal and working memory performance were also compared under the different glycaemic conditions (glucose versus aspartame drinks).

RESULTS

In the present study, a beneficial effect of glucose on memory was detected after participants encoded a 20-word list while performing a secondary task, but not when participants encoded the list without a secondary task, nor when the 20 target words were intermixed with 20 non-target words (distinguished by gender of speaker). In addition, glucose significantly enhanced performance on spatial and working memory tasks.

CONCLUSION

The data indicate that possible "depletion" of episodic memory capacity and/or glucose-mediated resources in the brain due to performing a concomitant cognitive task might be crucial to the demonstration of a glucose facilitation effect. Possible implications regarding underlying cognitive and physiological mechanisms are discussed in this article.

Ingestional responses to metabolic challenges in rats selectively bred for high and low saccharin intake

Rats selectively bred on the basis of saccharin intake also differ on some measures of emotional reactivity. The present studies were designed to contribute to our understanding of this association. Rats selectively bred for relatively high (HiS) versus low (LoS) saccharin intake were tested in two paradigms useful in assessing the ability to respond adaptively to internal perturbations of metabolic regulation or to external events that may produce metabolic challenges. The first study concerned slow-onset (regular insulin) and rapid-onset (2-deoxy-D-glucose [2-DG], fast-acting insulin) glucoprivation and resultant feeding behavior. LoS and HiS lines did not differ in response to saline or slow-onset challenges, but LoS rats ate less in the first half hour after rapid-onset challenges; the line differences were eliminated by pretreatment with caffeine. The second study revealed significantly higher plasma corticosterone (CORT) among LoS rats relative to HiS rats, both in the light and in the dark. Preliminary assessments after a single stressor and a single dose of dexamethasone showed, respectively, CORT elevation and suppression that was comparable in the two lines. These results add further support to the ideas that voluntary consumption of saccharin is related to the expression of classically defined emotional behaviors, and that responsiveness to diverse metabolic challenges may share a common basis, such as genetic pleiotropism.

Effects of long-term ingestion of aspartame on hypothalamic neuropeptide Y, plasma leptin and body weight gain and composition

The aim of this study was to determine the effects of the chronic ingestion of aspartame (ASP) on brain neuropeptide Y (NPY) concentrations, plasma hormones, food intake and body fat. Two groups of male Long-Evans rats, fed on a control (C) well-balanced diet, had to drink either a 0.1% ASP solution or water for a period of 14 weeks starting at weaning. Food intake and body weight were weekly recorded. At the end of the experiment, fat pads were sampled, leptin and insulin were measured in the plasma and NPY in several microdissected brain areas. Substituting ASP for water led to lower body weight (-8%; P<.004) and lower fat depot weight (-20%; P<.01) with no differences in energy intake or plasma insulin concentrations. Plasma leptin was significantly reduced by 34% (P<.05). Leptin concentrations were well-correlated with final body weight (r=.47; P<.025) and fat pad mass (r=.53; P<.01). NPY concentrations were 23% lower (P<.03) in the arcuate nucleus of ASP rats with no differences in other brain areas. The beneficial effects on body composition could be related to the decreased effects of NPY on lipid and energy metabolism, independently of insulin. The reasons for the NPY decrease (regulatory or toxicological) are not obvious. The constitutive amino acids of the ASP molecule might participate in the NPY regulation.

pH changes in dental plaque after using sugar-free pediatric medicine

The aim of this study was to compare the pH changes in the dental plaque after rinsing with sugared- (sucrose) or sugar-free (saccharine, cyclamate and sorbitol) versions of the same pediatric acetaminophen solution (ekosetol) up to one hour. Twenty-nine undergraduate dental students (17 girls and 12 boys) collected plaque for 48 hours by abstaining from oral hygiene, during which period they maintained normal dietary habits. Plaque sampling was done in two subsequent days before and 2, 5, 10, 15, 20, 25, 30, 40, 50 and 60 minutes after rinsing with both solutions. Measurements of pH were done within one hour using a micro pH electrode and a pH meter. All experiments were finished in 6 days by dividing the group to three. Results showed a significant difference between groups in respect to pH values and pH drops after rinsing. Mean pH values were below 5.70 for one hour in sugared solution, whereas no mean pH value was detected below 5.80 for one hour with the sugar-free solution. Minimum pH values (sugar-free: 5.62+/-0.36; sugared: 5.00+/-0.33, p<0.001) and maximum pH drops (sugar-free: -0.57+/-0.26; sugared: -1.16+/-0.44, p<0.001) were also significantly different. No difference was found between genders. We concluded that changing of sucrose to non-acidogenic sweeteners was essential to prevent the cariogenic potential of the pediatric medicines.

Self-administration of ethanol and saccharin in newborn rats: effects on suckling plasticity

Responsiveness to a surrogate nipple providing water, saccharin, 5% ethanol, or 10% ethanol was tested in newborn rats naive to suckling (3-5 hr old) on Postnatal Day (P) 0 and in older neonates with regular suckling experience on P1 or P2. At all ages, pups demonstrated greater nipple attachment for saccharin or 5% ethanol than for water. Intake of saccharin and 5% ethanol was high in newborns, far exceeding that of water. At P1 and P2, pups exhibited a preference for saccharin, but not for 5% ethanol. Preexposure to a nipple providing ethanol or saccharin (but not a nipple alone or fluids alone) increased subsequent responsiveness toward an empty surrogate nipple (no fluid), both 1 hr and 24 hr after preexposure. Although, during preexposure, pups responded most positively to the nipple providing saccharin, the longest time spent on an empty nipple was observed in pups preexposed to 10% ethanol.

Sweetener preference of C57BL/6ByJ and 129P3/J mice

Previous studies have shown large differences in taste responses to several sweeteners between mice of the C57BL/6ByJ (B6) and 129P3/J (129) inbred strains. The goal of this study was to compare behavioral responses of B6 and 129 mice to a wider variety of sweeteners. Seventeen sweeteners were tested using two-bottle preference tests with water. Three main patterns of strain differences were evident. First, sucrose, maltose, saccharin, acesulfame-K, sucralose and SC-45647 were preferred by both strains, but the B6 mice had lower preference thresholds and higher solution intakes. Second, the amino acids D-phenylalanine, D-tryptophan, L-proline and glycine were highly preferred by B6 mice, but not by 129 mice. Third, glycyrrhizic acid, neohesperidin dihydrochalcone, thaumatin and cyclamate did not evoke strong preferences in either strain. Aspartame was neutral to all 129 and some B6 mice, but other B6 mice strongly preferred it. Thus, compared with the 129 mice the B6 mice had higher preferences for sugars, sweet tasting amino acids and several but not all non-caloric sweeteners. Glycyrrhizic acid, neohesperidin, thaumatin and cyclamate are not palatable to B6 or 129 mice.

Cariogenic potential of lactosylfructoside as determined by acidogenicity of oral streptococci in vitro and human dental plaque in situ

The cariogenic potential of lactosylfructoside [O-beta-D-galactopyranosyl-(1-->4)-O-alpha-D-glucopyranosyl-(1<-->2)-beta-D-fructofuranoside] was estimated by experiments on oral streptococci in vitro and human dental plaque in situ. Lactosylfructoside was unable to support growth of the strains of Streptococcus mutans and S. sobrinus used in this study. However, it was able to support growth of strains of S. sanguis, S. mitis and S. oralis. Acid was produced rapidly by cell suspensions of S. oralis ATCC 10557 incubated with lactosylfructoside. Application of 5% w/v solution decreased the pH of human dental plaque. The minimum pH value was below 5.3. The results suggest that lactosylfructoside is as acidogenic as lactose and could be cariogenic if it is consumed frequently and retained for a long period in the mouth.

Whole nerve chorda tympani responses to sweeteners in C57BL/6ByJ and 129P3/J mice

The C57BL/6ByJ (B6) strain of mice exhibits higher preferences than does the 129P3/J (129) strain for a variety of sweet tasting compounds. We measured gustatory afferent responses of the whole chorda tympani nerve in these two strains using a broad array of sweeteners and other taste stimuli. Neural responses were greater in B6 than in 129 mice to the sugars sucrose and maltose, the polyol D-sorbitol and the non-caloric sweeteners Na saccharin, acesulfame-K, SC-45647 and sucralose. Lower neural response thresholds were also observed in the B6 strain for most of these stimuli. The strains did not differ in their neural responses to amino acids that are thought to taste sweet to mice, with the exception of L-proline, which evoked larger responses in the B6 strain. Aspartame and thaumatin, which taste sweet to humans but are not strongly preferred by B6 or 129 mice, did not evoke neural responses that exceeded threshold in either strain. The strains generally did not differ in their neural responses to NaCl, quinine and HCl. Thus, variation between the B6 and 129 strains in the peripheral gustatory system may contribute to differences in their consumption of many sweeteners.

Effect of aronia berry honey syrup used for sweetening jams on their quality

The effects of sweetening agents on the quality of low sweetened jams were compared with respect to blackcurrant, raspberry, sour cherry, strawberry, and bilberry jams. The sweetening agents were sucrose, aronia berry honey syrup, and sucrose + honey syrup at a ratio of 1:1. The level of physicochemical indices, especially the content of vitamin C and anthocyanins determined directly after production and after 3- and 6-month storage, was used as the quality criterion for the evaluation of jams. Moreover, after 6-month storage the products were subjected to sensorial analysis. According to the accepted method of the investigation the produced jams were characterized by a 32-33% content of extract. During the production and 6-month storage the content of acids slightly and that of pectin considerably (from 26 to 46%) decreased, although the consistency of the jams was not affected thereby. In the case of vitamin C, its pronounced losses concerned raspberry (62-67% of the initial value), strawberry (57-61%), and sour cherry (57-58%), being distinctly smaller in blackcurrant (13-16%) and bilberry (15-35%) jams. With respect to anthocyanins a similar regularity was observed, the losses reaching 49-63% in strawberry jam, 40-56% in raspberry, 33-39% in sour cherry, 30-36% in blackcurrant, and 28-36% in bilberries. In almost all the products the losses of vitamin C and anthocyanins were higher when sweetening agent was aronia berry honey syrup. The organoleptic evaluation showed that the addition of aronia berry honey syrup to raspberry and strawberry jams slightly spoiled their colour but improved the aroma and taste. In the final score the significant differentiation in favour of the addition of aronia berry honey syrup concerned only blackcurrant, sour cherry, and bilberry jams.