Odor-induced changes in taste perception

We investigated odor-induced changes in taste perception (OICTP), by examining the influence of strawberry and soy sauce odors on perceived sweetness (Experiment 1) and saltiness (Experiment 2). We explored whether taste-smell interactions occur at the central level, by delivering odorants (strawberry, soy sauce, odorless water) and tastants (sucrose, sodium chloride) separately, and whether effects of imagined odors are comparable to those of physically presented odors. We found specific taste-smell interactions: sweetness enhancement induced by strawberry odor and saltiness enhancement induced by soy sauce odor. These interactions were elicited with separate delivery of olfactory and gustatory stimuli. Secondly, we found a similar but rather limited effect with the imagined odors: imagined strawberry enhanced perceived sweetness of water solutions, and imagined soy sauce enhanced perceived saltiness of weak sodium chloride solutions. We concluded that OICTP is a centrally mediated phenomenon, and that imagined odors can to some extent induce changes in perceived taste intensity comparable to those elicited by perceived odors.

Monosodium Glutamate and Sweet Taste: Discrimination between the Tastes of Sweet Stimuli and Glutamate in Rats

Generalization of a conditioned taste aversion (CTA) is based on similarities in taste qualities shared by the aversive substance and another taste substance. CTA experiments with rats have found that an aversion to a variety of sweet stimuli will cross-generalize with monosodium glutamate (MSG) when amiloride, a sodium channel blocker, is added to all solutions to reduce the taste of sodium. These findings suggest that the glutamate anion elicits a sweet taste sensation in rats. CTA experiments, however, generally do not indicate whether two substances have different taste qualities. In this study, discrimination methods in which rats focused on perceptual differences were used to determine if they could distinguish between the tastes of MSG and four sweet substances. As expected, rats readily discriminated between two natural sugars (sucrose, glucose) and two artificial sweeteners (saccharin, SC45647). Rats also easily discriminated between MSG and glucose, saccharin and, to a lesser extent, SC45647 when the taste of the sodium ion of MSG was reduced by the addition of amiloride to all solutions, or the addition of amiloride to all solutions and NaCl to each sweet stimulus to match the concentration of Na+ in the MSG solutions. In contrast, reducing the cue function of the Na+ ion significantly decreased their ability to discriminate between sucrose and MSG. These results suggest that the sweet qualities of glutamate taste is not as dominate a component of glutamate taste as CTA experiments suggest and these qualities are most closely related to the taste qualities of sucrose. The findings of this study, in conjunction with other research, suggest that sweet and umami afferent signaling may converge through a taste receptor with a high affinity for glutamate and sucrose or a downstream transduction mechanism. These data also suggest that rats do not necessarily perceive the tastes of these sweet stimuli as similar and that these sweet stimuli are detected by multiple sweet receptors.

5-HT(3A) receptor subunit is required for 5-HT3 antagonist-induced reductions in alcohol drinking

The ionotropic serotonin subtype-3 (5-HT3) receptor has emerged as a potential therapeutic target in the treatment of alcohol abuse and alcoholism because selective pharmacological antagonists reduce alcohol consumption in preclinical and clinical models. 5-HT binds to the extracellular N-terminus of the 5-HT(3A) receptor subunit but receptor activation is also enhanced by distinct allosteric sites, which indicates the presence of other receptor subunits. It is not known if specific molecular subunits of the 5-HT3 receptor modulate alcohol drinking. To address this issue, we characterized acute locomotor response to alcohol and alcohol consumption in a two-bottle home-cage procedure by congenic C57BL/6J mice with a targeted deletion of the 5-HT(3A) receptor subunit gene. 5-HT(3A)-null mice did not differ from wild-type littermate controls on measures of spontaneous locomotor activity, habituation to a novel environment, or locomotor response to ethanol (0, 0.5, 1, or 2 g/kg). Moreover, null mice did not differ from controls on measures of ethanol (2-10%) intake and preference during or after a two-bottle home-cage sucrose fading procedure. Systemic administration of the 5-HT3 antagonist LY-278,584 (0-10 mg/kg) decreased intake of both sweetened (2% sucrose+10% ethanol) and unsweetened (10% ethanol) ethanol in wild-type mice only. These findings indicate that reduction of alcohol drinking produced by 5-HT3 antagonism is dependent on the presence of 5-HT(3A)-containing receptors.

Dietary fructose and gastrointestinal symptoms: a review

It has been proposed that fructose may cause or aggravate symptoms in patients with functional gastrointestinal disorders. Fructose is commonly used to sweeten processed foods, and the prevalence of incomplete fructose absorption (25 g, 10%) in healthy subjects is as high as 50%. The only controlled study that has been performed did not demonstrate a higher prevalence of fructose-induced gastrointestinal symptoms or incomplete fructose absorption in patients with functional gastrointestinal disorders. The amount and concentration of fructose used to evaluate absorption by breath testing has varied among studies. Moreover, dietary sources of fructose usually contain glucose, which increases fructose absorption in healthy subjects. Thus, breath testing with fructose alone may not reflect fructose ingestion under normal circumstances. Given these limitations, we suggest that a practical, empirical approach to testing in patients with suspected incomplete fructose absorption is to restrict fructose ingestion. Additional controlled studies are needed to clarify the relation between incomplete fructose absorption and symptoms, assess the effects of co-ingestion of other sugars on fructose absorption, and evaluate the effects of eliminating sugars from the diet on gastrointestinal symptoms.

Recombinant curculin heterodimer exhibits taste-modifying and sweet-tasting activities

Curculin from Curculigo latifolia is a unique sweet protein that exhibits both sweet-tasting and taste-modifying activities. We isolated a gene that encodes a novel protein highly homologous to curculin. Using cDNAs of the previously known curculin (designated as curculin1) and the novel curculin isoform (curculin2), we produced a panel of homodimeric and heterodimeric recombinant curculins by Escherichia coli expression systems. It was revealed that sweet-tasting and taste-modifying activities were exhibited solely by the heterodimer of curculin1 and curculin2.

Monosodium glutamate and sweet taste: generalization of conditioned taste aversion between glutamate and sweet stimuli in rats

Even though monosodium glutamate (MSG) is a prototypical umami substance, previous studies reported that a conditioned taste aversion (CTA) to MSG, mixed with amiloride to block the taste of sodium, generalizes to sucrose. These findings suggest that the taste of glutamate mimics the taste of sucrose and raise the question of whether glutamate has a broadly tuned sweet taste component. To test this hypothesis, CTA experiments were conducted to test for generalization between MSG and several sweet stimuli: sucrose, glucose, maltose, saccharin and SC-45647. Strong bidirectional generalization was seen between MSG mixed with amiloride and sucrose, glucose, saccharin and SC-45647. Weak generalization was seen between MSG and maltose, and sucrose and maltose. None of the CTAs generalized to NMDA. These findings support the hypothesis that the taste of MSG has broadly tuned, sweet-like characteristics, possibly due to the convergence of afferent signals for MSG, natural sugars and artificial sweeteners.

Saccharin stimulates the "deterrent" cell in the blowfly: behavioral and electrophysiological evidence

In the attempt to gain more information on the mechanisms underlying bitter and/or sweet taste reception, we have investigated the responses of labellar chemosensilla in the blowfly Protophormia terraenovae to Na-saccharin, as compared to sweet stimuli (sucrose or fructose) and bitter stimuli (denatonium benzoate or amiloride). Electrophysiological and behavioral results indicate that the sweetener Na-saccharin inhibits the "sugar" cell in the labellar taste sensilla of the blowfly P. terraenovae. In multichoice preference tests, flies ingested more of the solutions containing sugar to those with sugar+Na-saccharin. This finding is in good agreement with the spike frequency reduction observed for the "sugar" cell activity. Analysis of the spike discharges also shows a positive dose-response for the "deterrent" cell following stimulation with Na-saccharin and denatonium benzoate. Flies drank any of the Na-saccharin solutions, regardless of their concentration, less than water, thus indicating a weak deterring effect on water drinking. The prevailing activation of the "deterrent" cell by stimulation with Na-saccharin is not directly coupled with a coherent behavioral output. Cross adaptation was found to occur between responses to Na-saccharin and denatonium benzoate or amiloride regardless of the order of adapting stimuli. In the case of sweet stimuli, cross adaptation occurred when the adapting stimulus was Na-saccharin, but it did not when the adapting stimuli were sucrose or fructose. Addition of Na-saccharin to both sugars significantly depressed the spike firing frequency, while an increase was observed with denatonium benzoate or amiloride.

Second-order stimuli do not always increase overall response rates in second-order schedules of reinforcement in the rat

RATIONALE

Second-order schedules of reinforcement have been used extensively to model reward-seeking and drug-seeking behaviour. Second-order stimuli within second-order schedules have been shown to enhance response rates during operant responding for natural reinforcers and drug reinforcers. This has led some to view second-order schedules of drug reinforcement as a model maintained of drug-seeking in addicts by drug-associated stimuli. However, the functional role of the second-order stimulus within second-order schedules is complex.

OBJECTIVE

We investigated the role of second-order stimuli within a second-order schedule of reinforcement [FI 4 min (FR10: S)] maintained by sweetened water reinforcement.

METHODS

Eight rats were trained to press a bar on a second-order schedule of reinforcement and tested in the presence and absence of the second-order stimulus.

RESULTS

In contrast to most previous work, overall bar-pressing rates were significantly increased when the second-order stimulus was omitted (second-order stimulus omission: 0.17 Hz (+/-0.04, 95% CI); second-order stimulus present: 0.13 Hz (+/-0.04, 95% CI)). However, second-order stimuli also changed the pattern of responding whereby rats would make a bout of bar presses prior to the presentation of the second-order stimulus and then pause briefly after the second-order stimulus. In the absence of second-order stimuli, responding was uniformly high. Control measures, such as the ability of the second-order stimulus to evoke checking for the primary reinforcers, indicated that the second-order stimulus was associated with the primary reinforcer.

CONCLUSIONS

These results demonstrated that although second-order stimuli maintained responding and caused the rat to check for primary reinforcement, overall response rates were increased when the second-order stimuli were omitted. This has implications for interpreting the results of studies where overall response rates within second-order schedules have been the only measure used to assess the effects of potential anti-addiction drugs. Future studies could be improved by performing a second-order stimulus omission test analysing both the overall response rates and the temporal organization of responding with respect to the second-order stimulus.

Female Rats show a Bimodal Preference Response to the Artificial Sweetener Sucralose

The preference of female Sprague-Dawley rats for sucralose, a non-nutritive sweetener derived from sucrose, was evaluated in 23 h two-bottle tests with water or saccharin. Overall, the rats displayed weak or no preferences for sucralose (0.25-4 g/l) over water but strong preferences for saccharin (0.5-8 g/l) over water and saccharin (1 g/l) over sucralose (0.5 g/l). The rats also preferred a saccharin + sucrose mixture to sucrose, but sucrose to a sucralose + sucrose mixture. There were marked individual differences in sucralose preferences: about half the rats preferred sucralose to water at some concentrations while most remaining rats avoided sucralose. Both subgroups preferred saccharin to sucralose. Sucralose appears to have an aversive off-taste that reduces its palatability to rats.

Morphine-induced conditioned taste aversions: assessment of sexual dimorphism

Although sex differences in taste aversions have been reported with emetics such as lithium chloride (LiCl), little is known whether such findings generalize to other aversion-inducing drugs, including recreational compounds. One particular class of recreational compounds that induces taste aversions but that has not been examined for sex differences in its aversive properties is the opioids. To assess sex differences in the aversive properties of the opioids, Experiment 1 examined the acquisition and extinction of morphine-induced taste aversions in male and female rats. To determine whether the specific parametric conditions used in Experiment 1 would support sex differences in general, Experiment 2 examined possible sex differences in the acquisition and extinction of LiCl-induced taste aversions, a compound for which sex differences have been previously reported. During acquisition, male and female rats were given 20-min access to a novel saccharin solution and injected with either morphine (0, 10, 18 and 32 mg/kg s.c.; Experiment 1) or LiCl (0, 0.3, 0.6 and 1.2 mEq s.c.; Experiment 2) every fourth day for a total of four conditioning trials. During extinction, subjects were allowed access to saccharin but were not injected (for a total of eight trials). There were no sex differences in acquisition with either morphine or LiCl. There were also no sex differences in extinction with morphine; however, sex differences were found with LiCl, an effect consistent with prior assessments with this drug. The basis for and implications of the differences in the effects of sex on morphine- and LiCl-induced taste aversions were discussed.

Allelic variation of the Tas1r3 taste receptor gene selectively affects behavioral and neural taste responses to sweeteners in the F2 hybrids between C57BL/6ByJ and 129P3/J mice

Recent studies have shown that the T1R3 receptor protein encoded by the Tas1r3 gene is involved in transduction of sweet taste. To assess ligand specificity of the T1R3 receptor, we analyzed the association of Tas1r3 allelic variants with taste responses in mice. In the F2 hybrids between the C57BL/6ByJ (B6) and 129P3/J (129) inbred mouse strains, we determined genotypes of markers on chromosome 4, where Tas1r3 resides, measured consumption of taste solutions presented in two-bottle preference tests, and recorded integrated responses of the chorda tympani gustatory nerve to lingual application of taste stimuli. For intakes and preferences, significant linkages to Tas1r3 were found for the sweeteners sucrose, saccharin, and D-phenylalanine but not glycine. For chorda tympani responses, significant linkages to Tas1r3 were found for the sweeteners sucrose, saccharin, D-phenylalanine, D-tryptophan, and SC-45647 but not glycine, L-proline, L-alanine, or L-glutamine. No linkages to distal chromosome 4 were detected for behavioral or neural responses to non-sweet quinine, citric acid, HCl, NaCl, KCl, monosodium glutamate, inosine 5'-monophosphate, or ammonium glutamate. These results demonstrate that allelic variation of the Tas1r3 gene affects gustatory neural and behavioral responses to some, but not all, sweeteners. This study describes the range of ligand sensitivity of the T1R3 receptor using an in vivo approach and, to our knowledge, is the first genetic mapping study of activity in gustatory nerves.

Preabsorptive factors are not the main determinants of intake depression induced by a high-protein diet in the rat

The factors involved in the depression of food intake produced by a high-protein diet are still poorly understood. The aim of this study was to assess the role of several preingestive or preabsorptive factors likely to influence food intake when rats were fed ad libitum. Food intake was measured after modifying the composition of the high-protein diet, i.e., the type of proteins, or carbohydrates. Moreover, correlations between high-protein diet intake and the quantity of fluid ingested or stomach volume were studied. By varying the carbohydrate composition (sucrose/cornstarch) and the protein source (soy or gluten or total milk protein) of high-protein diets, we modified the orosensory properties of these diets. However, no differences in food intake were observed between these groups of rats during the transition phase or after adaptation, except during the first day of soy- or gluten-based diets when the depression of food intake was intensified. The depression of high-protein diet intake was neither the consequence of any delay necessary to increase the fluid intake induced by eating a high-protein diet nor due to a marked increase in stomach volume, which might explain enhanced satiety and decreased food intake through the activation of vagal afferent fibers. Our experiments do not indicate a preponderant role for oropharyngeal or preabsorptive factors in the depression of food intake induced by a high-protein diet.

Lack of effect of sucralose on glucose homeostasis in subjects with type 2 diabetes

OBJECTIVE

To investigate the effect of 3-months' daily administration of high doses of sucralose, a non-nutritive sweetener, on glycemic control in subjects with type 2 diabetes.

DESIGN

A multicenter, double-blind, placebo-controlled, randomized study, consisting of a 6-week screening phase, a 13-week test phase, and a 4-week follow-up phase.

SUBJECTS/SETTING

Subjects with type 2 diabetes (age range 31 to 70 years) entered the test phase of this study; 128 subjects completed the study. The subjects were recruited from 5 medical centers across the United States and were, on average, obese.

INTERVENTION

Subjects were randomly assigned to receive either placebo (cellulose) capsules (n=69) or 667 mg encapsulated sucralose (n=67) daily for the 13-week test phase. All subjects blindly received placebo capsules during the last 4 weeks of the screening phase and for the entire 4-week follow-up phase.

MAIN OUTCOME MEASURES

Glycated hemoglobin (HbA1c), fasting plasma glucose, and fasting serum C-peptide were measured approximately every 2 weeks to evaluate blood glucose homeostasis. Data were analyzed by analysis of variance using repeated measures.

RESULTS

There were no significant differences between the sucralose and placebo groups in HbA1c, fasting plasma glucose, or fasting serum C-peptide changes from baseline. There were no clinically meaningful differences between the groups in any safety measure.

CONCLUSIONS

This study demonstrated that, similar to cellulose, sucralose consumption for 3 months at doses of 7.5 mg/kg/day, which is approximately three times the estimated maximum intake, had no effect on glucose homeostasis in individuals with type 2 diabetes. Additionally, this study showed that sucralose was as well-tolerated by the study subjects as was the placebo.

The Combination Effect of L-Arginine and NaCl on Bitterness Suppression of Amino Acid Solutions

The purpose of the present study was to quantify the degree of suppression of the bitterness of two amino acids (L-isoleucine (L-Ile), and L-phenylalanine (L-Phe)) which could be achieved by the addition of various test chemicals, and to examine the mechanism of this bitterness suppression. The test chemicals used were two sweeteners (sucrose, aspartame), NaCl, various acidic (L-aspartic acid, L-glutamic acid), or basic (L-histidine, L-lysine and L-arginine) amino acids, tannic acid and phosphatidic acid. The combination of L-arginine (L-Arg) and NaCl together was the most effective in reducing the bitterness of 100 mM L-Ile and L-Phe solutions in human gustatory sensation tests. Even in bitterness of 0.1 mM quinine solution, L-Arg was also successful in reducing the bitterness. This bitterness-suppression effect was specific to L-Arg and not to the other basic amino acids. No comparable taste-masking effect was observed for the acidic amino acids. The artificial taste sensor failed to predict completely the bitterness-suppressing effect of L-Arg. It seems likely that the bitterness-suppressing effect of L-Arg is mediated not only by binding at the receptor site, but also elsewhere in the process of bitterness perception, such as a direct effect on the sodium channel. It is conjectured that the guanidinium group of L-Arg may interact with sodium channels in taste bud membranes.

Influence of repeated consumption of beverages containing sucrose or intense sweeteners on food intake

OBJECTIVE

To investigate the influence of ingestion of beverages with sucrose or with intense sweeteners on food intake (FI) and on hunger ratings in before and after a month of daily consumption of beverages.

DESIGN

Experimental study.

SETTING

Department of Physiology, University Hospital, Dijon, France.

SUBJECTS

In all, 12 men and 12 women, aged 20-25 y.

INTERVENTION

Four beverages contained either sucrose (E+:100 g/l, 1672 kJ) or intense sweeteners (E-: null energy content) and were flavoured with either orange (O) or raspberry (R). FI was measured in the lab during two 2-consecutive-day periods, carried out on 2 successive weeks (session 1). The subjects drank 2 l of either E+ or E- beverages on the first day of both weekly periods, according to a balanced randomised design. E+ was paired with O for 50% of subjects and with R for the other 50%. Subjects were then habituated over a 4-week period to both beverages, consuming 1 l of E+ beverage on odd days and 1 l of E- drink on even days. After this period, the measurements of session 1 were repeated (session 2, weeks 7-8). Finally, FI was measured for two more 2-day periods (weeks 9-10) after the association between flavour and energy content was reversed (session 3).

RESULTS

The E- drinks were less palatable than the E+ drinks. Besides, we observed that FI was not reduced in response to a liquid extra caloric load and there was no change in hunger ratings after the beverages in any of the sessions.

CONCLUSION

Ingestion of caloric beverages induced a positive energy balance and the continuous exposure phase to these beverages over 1 month did not improve FI adaptation in response to the extra energy provided by the beverages.

The reinforcing properties of alcohol are mediated by GABA(A1) receptors in the ventral pallidum

It has been hypothesized that alcohol addiction is mediated, at least in part, by specific gamma-aminobutyric acid(A) (GABA(A)) receptors within the ventral pallidum (VP). Among the potential GABA(A) receptor isoforms regulating alcohol-seeking behaviors within the VP, the GABA(A) alpha1 receptor subtype (GABA(A1)) appears pre-eminent. In the present study, we developed beta-carboline-3-carboxylate-t-butyl ester (betaCCt), a mixed agonist-antagonist benzodiazepine (BDZ) site ligand, with binding selectivity at the A1 receptor to explore the functional role of VP(A1) receptors in the euphoric properties of alcohol. The in vivo actions of betaCCt were then determined following microinfusion into the VP, a novel alcohol reward substrate that primarily expresses the A1 receptor. In two selectively bred rodent models of chronic alcohol drinking (HAD-1, P rats), bilateral microinfusion of betaCCt (0.5-40 microg) produced marked reductions in alcohol-reinforced behaviors. Further, VP infusions of betaCCt exhibited both neuroanatomical and reinforcer specificity. Thus, no effects on alcohol-reinforced behaviors were observed following infusion in the nucleus accumbens (NACC)/caudate putamen (CPu), or on response maintained by saccharin. Parenteral-administered betaCCt (1-40 mg/kg) was equally effective and selective in reducing alcohol-reinforced behaviors in P and HAD-1 rats. Additional tests of locomotor activity revealed that betaCCt reversed the locomotor sedation produced by both chlordiazepoxide (10 mg/kg) and EtOH (1.25 g/kg), but was devoid of intrinsic effects when given alone. Studies in recombinant receptors expressed in Xenopus oocytes revealed that betaCCt acted as a low-efficacy partial agonist at alpha3beta3gamma2 and alpha4beta3gamma2 receptors and as a low-efficacy inverse agonist at alpha1beta3gamma2, alpha2beta3gamma2, and alpha5beta3gamma2 receptors. The present study indicates that betaCCt is capable of antagonizing the reinforcing and the sedative properties of alcohol. These anti-alcohol properties of betaCCt are primarily mediated via the GABA(A1) receptor. betaCCt may represent a prototype of a pharmacotherapeutic agent to effectively reduce alcohol drinking behavior in human alcoholics.

Some sweet and bitter tastants stimulate inhibitory pathway of adenylyl cyclase via melatonin and alpha 2-adrenergic receptors in Xenopus laevis melanophores

The sweeteners saccharin, D-tryptophan, and neohesperidin dihydrochalcone (NHD) and the bitter tastant cyclo(Leu-Trp) stimulated concentration-dependent pigment aggregation in a Xenopus laevis melanophore cell line similar to melatonin. Like melatonin, these tastants inhibited (by 45-92%) cAMP formation in melanophores; pertussis toxin pretreatment almost completely abolished the tastant-induced cAMP inhibition, suggesting the involvement of the inhibitory pathway (Gi) of adenylyl cyclase. The presence of luzindole (melatonin receptor antagonist) almost completely abolished the inhibition of cAMP formation induced by saccharin, D-tryptophan, and cyclo(Leu-Trp) but only slightly affected the inhibitory effect of NHD. In contrast, the presence of an alpha2-adrenergic receptor antagonist, yohimbine, almost completely abolished the inhibition of cAMP formation induced by NHD but had only a minor effect on that induced by the other tastants. Thus saccharin, D-tryptophan, and cyclo(Leu-Trp) are melatonin receptor agonists whereas NHD is an alpha2-adrenergic receptor agonist, but both pathways lead to the same transduction output and cellular response. Formation of D-myo-inositol 1,4,5-trisphosphate (IP3) in melanophores was reduced (15-58%, no concentration dependence) by saccharin, D-tryptophan, and cyclo(Leu-Trp) stimulation but increased by NHD stimulation. Tastant stimulation did not affect cGMP. Although some of the above tastants were found to be membrane permeant, their direct activation of downstream transduction components in this experimental system is questionable. MT1 and MT2 melatonin receptor mRNAs were identified in rat circumvallate papilla taste buds and nonsensory epithelium, suggesting the occurrence of MT1 and MT2 receptors in these tissues. Melatonin stimulation reduced the cellular content of cAMP in taste cells, which may or may not be related to taste sensation.

Combined effects of tumor promoters and serum on proliferin mRNA induction: a biomarker sensitive to saccharin, 2,3,7,8-TCDD, and other compounds at minimal concentrations promoting C3H/10T1/2 cell transformation

Increases in proliferin (PLF) gene family mRNA abundance and promotional effects in cell transformation assays are paired responses that follow exposures to diverse chemical and physical agents in the C3H/10T1/2 in vitro model of multi-stage carcinogenesis. This study measured PLF mRNA abundance changes over 1 to 3 d in response to several types of promoters that were previously unassessed for this effect. Saccharin is a known promoter of cell transformation in C3H/10T1/2 cell cultures, but unlike 12-O-tetradecanoylphorbol 13-acetate (TPA) or mezerein, PLF mRNA abundance increases were inconsistently detected following simple addition of saccharin to the culture medium. Consistent effects occurred when pretreatments with promoting concentrations of saccharin or sodium saccharin (1-13 mM) were combined with subsequent additions of serum or complete medium changes. When added at or near their lowest observed effect levels (LOELs) for transformation, other promoters of 10T1/2 cells such as formaldehyde (50-100 microM), diethylstilbesterol (DES) (0.5-30 microM), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) (4-40 pM) were shown to be inducers of both basal and serum-induced PLF mRNA levels. Acetaldehyde (300-900 microM) was comparable to formaldehyde as an inducer. In contrast to these various promoters, pretreatment with phenobarbital or methanol, both non-promoters in these cells, did not affect serum-induced PLF mRNA levels at concentrations up to 3 mM and 2 M, respectively. The published values for the LOELs of 17 promoters of cell transformation and the LOELs determined to date for PLF mRNA induction were highly correlated over a 1 billion - fold concentration range. The response of PLF mRNA is a short-term marker sensitive to the active concentration ranges of diverse chemical agents with promotional activity in C3H/10T1/2 cell transformation system.

Xylitol Inhibition of Acid Production and Growth of Mutans Streptococci in the Presence of Various Dietary Sugars under Strictly Anaerobic Conditions

The aim of this study was to investigate the inhibitory effect of xylitol on the growth of and acid production by mutans streptococci in the presence of various dietary sugars, and the relationship between the inhibition and the accumulation of xylitol 5-phosphate (X5P) under strictly anaerobic conditions like those in the deep layers of dental plaque. Xylitol retarded the growth of mutans streptococci in the presence of glucose (G), galactose (Gal), maltose (M), lactose (L) or sucrose (S) as an energy source, though the inhibition of growth on fructose (Fr) was small. Xylitol inhibited acid production by washed cells of Streptococci mutans from G, Gal, M, L or S (12-83% inhibition). S. mutans accumulated X5P intracellularly through activity of the phosphoenolpyruvate-xylitol phosphotransferase system (PEP-xylitol PTS) when they fermented these sugars in the presence of xylitol. However, in the presence of Fr, no inhibition of acid production was observed. In addition, the amounts of X5P during the fermentation of Fr were smaller than those of other sugars in spite of the presence of PEP-xylitol PTS activity. These results suggest that along with the intracellular accumulation of X5P, xylitol decreases the growth and acid production of mutans streptococci in the presence of various dietary sugars except Fr.

Effects of a non-drug reinforcer, saccharin, on oral self-administration of phencyclidine in male and female rhesus monkeys

RATIONALE

Previous research with male subjects has demonstrated that alternative non-drug reinforcers reduce self-administration of drugs of abuse under a wide variety of conditions. Recent findings indicate sex differences in drug self-administration, and females may be more responsive to the suppressive effects of pharmacological treatment strategies than males; however, it is not known whether or not there are similar sex differences in the effect of behavioral interventions, such as non-drug reinforcers, on drug self-administration.

OBJECTIVES

The goal of this research was to determine whether the suppressive effects of non-drug reinforcers vary as a function of sex using behavioral economic measures in rhesus monkeys.

METHODS

During daily 3-h sessions, seven male and seven female adult rhesus monkeys orally self-administered concurrently available phencyclidine (PCP) and water, PCP and saccharin, or saccharin and water, from two separate spouts, under a series of fixed-ratio (FR) values. The FR value was varied from 4 to 8, 16, 32, 64, and 128, and the demand (consumption x FR) for PCP was measured in order to determine the effect of concurrent access to saccharin (versus water).

RESULTS

The availability of saccharin resulted in reduced PCP self-administration compared with the condition when water was available in both males and females. Consumption of PCP and saccharin was similar between the sexes under the two conditions when water was concurrently available. When saccharin was available with PCP, PCP responses and deliveries were reduced in both sexes at low to intermediate FR values, but the amount of PCP consumed (mg/kg) was reduced significantly more in females than in males only at FR 32.

CONCLUSIONS

. Non-drug reinforcers are an effective treatment for drug abuse in females as well as males over a range of PCP FR values. Males show elevated drug-maintained responding compared with females, but when differential body weights are considered (mg/kg) females consume more than males only under limited schedule parameters.

NaCl and sugar release, salivation and taste during mastication of salted chewing gum

Salt perception impacts on food acceptability and nutrition and depends upon salt release from foods that was determined in situ during mastication of chewing gum with up to 10% (1800 mmol/kg) added NaCl. The mechanical action of chewing increased salivation, which was further increased by the presence of salt, particularly above 180 mmol NaCl/kg gum or above 100 mM NaCl in saliva. The average resting salivary flow rate was 1 ml/min, increasing to 4 and 6 ml/min with gums containing low and high salt, respectively. Thus, stimulation of salivation by salt occurred at a concentration well above the taste threshold of 20 mM NaCl. NaCl concentration in nonstimulated saliva was about 10 mM and increased to 500 mM after 30 s chewing of the 10% NaCl gum and returned to near nonstimulated levels after 4 min chewing. Changes in pH of saliva were more gradual, increasing to a maximum at about 2 min and remaining elevated after 4 min. Salty taste was related to the free chloride ion concentration in saliva irrespective of the initial salt concentration in the gum with an indication of adaptation after 3 min chewing. During chewing, salty taste increased ahead of the increase in salivary conductivity and the salt concentration in the sublingual saliva varied in a cyclic fashion about every 20 s. This is consistent with a cyclic swallowing of saliva and replacement with newly secreted saliva of low salt content and mastication releasing further salt from the gum.

Effect of stevioside and steviol on the developing broiler embryos

At day 7 of incubation, fertile broiler eggs were injected with different amounts of stevioside and steviol of 0.08, 0.8, or 4 mg stevioside/egg and 0.025, 0.25, or 1.25 mg steviol/egg. At hatch (day 21) and 1 week later, not any influence of the different treatments could be found on embryonic mortality, body weight of the hatchlings, deformations (e.g., bone, beak, and head malformations, abnormal feathering, open vent), or abnormal development of the gonads. No stevioside or steviol could be detected in the blood of the hatchlings. The hatchlings developed normally. It is concluded that prenatal exposure to stevioside and steviol is not toxic for the chicken embryo.

Anticarcinogenic activity of natural sweeteners, cucurbitane glycosides, from Momordica grosvenori

To search for cancer chemopreventive agents from natural resources, many phytochemicals and food additives have been screened. Consequently, two natural sweeteners, mogroside V and 11-oxo-mogroside V isolated from the fruits of Momordica grosvenori, exhibited strong inhibitory effect on the primary screening test indicated by the induction of Epstein-Barr virus early antigen (EBV-EA) by a tumor promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA). These sweet glycosides, having cucurbitane triterpenoid aglycon, exhibited the significant inhibitory effects on the two-stage carcinogenesis test of mouse skin tumors induced by peroxynitrite (ONOO-) as an initiator and TPA as a promoter. Further, 11-oxo-mogroside V also exhibited the remarkable inhibitory effect on two-stage carcinogenesis test of mouse skin tumor induced by 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and TPA as a promoter.

Monkey electrophysiological and human psychophysical responses to mutants of the sweet protein brazzein: delineating brazzein sweetness

Responses to brazzein, 25 brazzein mutants and two forms of monellin were studied in two types of experiments: electrophysiological recordings from chorda tympani S fibers of the rhesus monkey, Macaca mulatta, and psychophysical experiments. We found that different mutations at position 29 (changing Asp29 to Ala, Lys or Asn) made the molecule significantly sweeter than brazzein, while mutations at positions 30 or 33 (Lys30Asp or Arg33Ala) removed all sweetness. The same pattern occurred again at the beta-turn region, where Glu41Lys gave the highest sweetness score among the mutants tested, whereas a mutation two residues distant (Arg43Ala) abolished the sweetness. The effects of charge and side chain size were examined at two locations, namely positions 29 and 36. The findings indicate that charge is important for eliciting sweetness, whereas the length of the side-chain plays a lesser role. We also found that the N- and C-termini are important for the sweetness of brazzein. The close correlation (r = 0.78) between the results of the above two methods corroborates our hypothesis that S fibers convey sweet taste in primates.