Requirement of NMDA receptor reactivation for consolidation and storage of nondeclarative taste memory revealed by inducible NR1 knockout

We employed an inducible, reversible and region-specific gene knockout technique to investigate the requirements for cortical NMDA receptors (NMDAR) during the various stages (acquisition, consolidation and storage, and retrieval) of nondeclarative, hippocampal-independent memory in mice using a conditioned taste aversion memory paradigm. Here we show that temporary knockout of the cortical NMDAR during either the learning or postlearning consolidation stage, but not during the retrieval stage, causes severe performance deficits in the 1-month taste memory retention tests. More importantly, we found that the consolidation and storage of the long-term nondeclarative taste memories requires cortical NMDAR reactivation. Thus, the dynamic engagement of the NMDAR during the postlearning stage leads us to postulate that NMDAR reactivation-mediated synaptic re-entry reinforcement is crucial for overcoming the destabilizing effects intrinsic to synaptic protein turnover and for achieving consolidation and storage of nondeclarative memories in the brain.

Effect of xylitol-containing chewing gums on interdental plaque-pH in habitual xylitol consumers

OBJECTIVE

The aim was to investigate the effect of high and low amounts of xylitol on the interdental plaque-pH, directly and after sucrose challenge, in schoolchildren with habitual consumption.

MATERIAL AND METHODS

The study group consisted of 11 healthy children (10-15 years) with low caries risk and the experiment had a single-blind crossover (Latin square) design. After a 2-week run-in period with a daily 4.0 g xylitol intake, the children were subjected to single-dose exposures of chewing gums with (i) paraffin (CTR; no xylitol), (ii) low-dose xylitol (LX; 2.0 g xylitol), and (iii) high-dose xylitol (HX; 6.0 g xylitol) in a randomized order separated by a washout period of 1 week. Samples of chewing-stimulated whole saliva were collected prior to and after the experimental period for determination of bacterial counts. The outcome measures were in situ plaque-pH (micro-touch method) and area under the pH curve (AUC).

RESULTS

The AUC was significantly greater (p < 0.05) in the HX group compared to the LX and control groups during the first 5 min after chewing. After a 10% sucrose rinse, the interdental plaque-pH dropped in all groups but the HX regimen displayed significantly less reduction 0-5 min after chewing (p < 0.05). No significant alterations of the total viable counts or mutans streptococci levels in saliva were disclosed during the 4-week experimental period.

CONCLUSIONS

The present results suggested that a high single dose of xylitol had a short and limited beneficial effect on interdental plaque-pH in habitual xylitol consumers, while a low single dose, resembling normal chewing gum use, did not differ from the control.

Les polyols en odontologie pédiatrique : intérêt du xylitol

Sugars ingested outside of meals play an important role in the etiology of caries. In this respect, sugar substitutes present a very interesting alternative. In addition to the recommendations and usual care to their patients, dental surgeons also have to inform them on a dietetic level. Chewing sugar-free chewing gum after any light meal when it is not followed by a brushing presents a real interest. The authors describe the different polyols and their respective uses. Polyols are widely found in foodstuffs (sweets, chewing-gum, biscuits, cooked meals for diabetic), pharmaceutical products (syrups, pastilles to be sucked, various medicines), non-pharmaceutical chemists (toothpastes, mouth-washes...). By the light of the most recent published works, the particular properties of xylitol are described. Polyols are more particularly indicated for sugar-eater or sick children (syrups), and for those carrying a hight risk of developing caries (progressive polycaries, hyposialie...). Therefore polyols are not only a means of stabilizing some pathologies (diabetes, obesity) but also a weapon in the prevention of dental caries.

Bitter taste receptors for saccharin and acesulfame K

Weight-conscious subjects and diabetics use the sulfonyl amide sweeteners saccharin and acesulfame K to reduce their calorie and sugar intake. However, the intrinsic bitter aftertaste, which is caused by unknown mechanisms, limits the use of these sweeteners. Here, we show by functional expression experiments in human embryonic kidney cells that saccharin and acesulfame K activate two members of the human TAS2R family (hTAS2R43 and hTAS2R44) at concentrations known to stimulate bitter taste. These receptors are expressed in tongue taste papillae. Moreover, the sweet inhibitor lactisole did not block the responses of cells transfected with TAS2R43 and TAS2R44, whereas it did block the response of cells expressing the sweet taste receptor heteromer hTAS1R2-hTAS1R3. The two receptors were also activated by nanomolar concentrations of aristolochic acid, a purely bitter-tasting compound. Thus, hTAS2R43 and hTAS2R44 function as cognate bitter taste receptors and do not contribute to the sweet taste of saccharin and acesulfame K. Consistent with the in vitro data, cross-adaptation studies in human subjects also support the existence of common receptors for both sulfonyl amide sweeteners.

Mouse Strain Differences in Gurmarin-sensitivity of Sweet Taste Responses Are Not Associated with Polymorphisms of the Sweet Receptor Gene, Tas1r3

Gurmarin (Gur) is a peptide that selectively inhibits responses of the chorda tympani (CT) nerve to sweet compounds in rodents. In mice, the sweet-suppressing effect of Gur differs among strains. The inhibitory effect of Gur is clearly observed in C57BL/6 mice, but only slightly, if at all, in BALB/c mice. These two mouse strains possess different alleles of the sweet receptor gene, Sac (Tas1r3) (taster genotype for C57BL/6 and non-taster genotype for BALB/c mice), suggesting that polymorphisms in the gene may account for differential sensitivity to Gur. To investigate this possibility, we examined the effect of Gur in another Tas1r3 non-taster strain, 129 X 1/Sv mice. The results indicated that unlike non-taster BALB/c mice but similar to taster C57BL/6 mice, 129 X 1/Sv mice exhibited significant inhibition of CT responses to various sweet compounds by Gur. This suggests that the mouse strain difference in the Gur inhibition of sweet responses of the CT nerve may not be associated with polymorphisms of Tas1r3.

Possible analgesic and anti-inflammatory interactions of aspartame with opioids and NSAIDs

The purpose of the present study was to investigate analgesic and anti-inflammatory properties of aspartame, an artificial sweetner and its combination with various opioids and NSAIDs for a possible synergistic response. The oral administration of aspartame (2-16mg/kg, po) significantly increased the pain threshold against acetic acid-induced writhes in mice. Co-administration of aspartame (2mg/kg, po) with nimesulide (2 mg/kg, po) and naproxen (5 mg/kg, po) significantly reduced acetic acid-induced writhes as compared to effects per se of individual drugs. Similarly when morphine (1 mg/kg, po) or pentazocine (1 mg/kg, po) was co-administered with aspartame it reduced the number of writhes as compared to their effects per se. Aspartame (4,8,16 mg/kg, po) significantly decreased carrageenan-induced increase in paw volume and also reversed the hyperalgesic effects in rats in combination with nimesulide (2 mg/kg, po). The study indicated that aspartame exerted analgesic and anti-inflammatory effects on its own and have a synergistic analgesic response with conventional analgesics of opioid and non-opioid type, respectively.

Appetite regulation and energy balance

The decision to begin eating or to stop eating is a complex process. Hunger is primarily driven by hunger signals, like ghrelin and neuropeptide Y, originating from the gastrointestinal tract and from the hypothalamus. The hunger signals stimulate the seeking of food and the eating, being activating for the body and mind. Thirty minutes after the start of eating, satiety signals arise from the intestinal tract and, in between meals, from the adipose tissue and liver. Satiety signals are sedative and arrest the processing of food in the intestine, hence leading to termination of eating. One problem with overeating today is the ready access to palatable food, such as sucrose and fat. The palatable food works by weakening the satiety signals and activating the hunger signals. The reward system with endogenous opiates may also be activated.

CONCLUSIONS

Food and drinks rich in sucrose and fat should be given in a restricted way to children, since there is no biological control feedback to regulate the intake of such products.

Substrate dependence of the postischemic cardiomyocyte recovery: Dissociation between functional, metabolic and injury markers

Defining the substrate that influences the most favourably the myocardial post-ischemic recovery is subject of debates, due to dissociation between functional and biochemical benefits. Hence, we studied the effects of either glucose or different fatty acids on the functional and metabolic recovery of post-ischemic cardiomyocytes in a substrate-free hypoxia model of simulated ischemia-reperfusion. Rat cardiomyocytes were submitted to a 2.5 h simulated ischemia followed by a 2 h reoxygenation without substrate (control), or with either glucose, octanoic acid, oleic acid, or elaidic acid. During simulated ischemia, electromechanical function gradually disappeared while the cellular viability and mitochondrial function declined. During control simulated reperfusion, cardiomyocytes recovered near normal function but a significant reduction in the action potential amplitude and rate persisted. The addition of glucose or oleic acid during simulated reperfusion promoted a faster, better and sustain functional recovery. Amongst the fatty acids, the functional recovery was slower with elaidic and octanoic acids as compared with oleic acid. The mitochondrial function was better improved during simulated reperfusion with glucose than with the tested fatty acids, among which elaidic acid was the less unfavourable. Paradoxically, the addition of whichever substrate during simulated reperfusion tended to worsen the cellular viability. Thus, cardiomyocytes recovery strongly relies on the characteristics of the substrate supplied at the onset of simulated reperfusion: glucidic or lipidic nature, chain-length, insaturation degree. Moreover, these data suggest that defining the appropriateness of a given substrate for the post-ischemic cardiomyocyte recovery is closely related to the functional and the biological endpoints in consideration.

Peripheral gustatory processing of sweet stimuli by golden hamsters

Behaviors and taste-nerve responses to bitter stimuli are linked to compounds that bind T2 receptors expressed in one subset of taste-bud receptor cells (TRCs); and behavioral and neural responses to sweet stimuli are linked to chemical compounds that bind a T1 receptor expressed in a different TRC subset. Neural and behavioral responses to bitter-sweet mixtures, however, complicate the ostensible bitter and sweet labeled lines. In the golden hamster, Mesocricetus auratus, quinine hydrochloride, the bitter prototype, suppresses chorda tympani (CT) nerve responses to the sweet prototype: sucrose. This bitter-sweet inhibition was tested with concentration series of sucrose and dulcin, a hydrophobic synthetic sweetener that hamsters behaviorally cross-generalize with sucrose. Dulcin, sucrose and other sweeteners activate one subset of CT fibers: S neurons; whereas, quinine activates a separate subset of CT fibers: E neurons. Whole-nerve and S-neuron CT responses to a sweetener concentration series, mixed with 0, 1, 3 and 10 mM quinine, were measured for 0-2.5 s transient and/or 2.6-10 s steady-state response periods. Ten-sec total single-fiber records, aligned at response onset, were averaged for 100 ms bins to identify response oscillations. Quinine inhibition of dulcin and sucrose responses was identical. Each log molar increment in quinine resulted in equivalent declines in response to either sweetener. Furthermore, sucrose response decrements paralleled response increments in quinine-sensitive CT neurons to the same quinine increases. A 1.43 Hz bursting rhythm to the sweeteners was unchanged by quinine inhibition or decreases in sweetener concentration. Taste-bud processing, possibly between-cell inhibition and within-cell negative feedback, must modify signals initiated by T1 receptors before they are transmitted to the brain.

Green Light Emitting Diode Irradiation Enhances Fibroblast Growth Impaired by High Glucose Level

BACKGROUND AND OBJECTIVE

The chronic metabolic disorder diabetes mellitus is an important cause of morbidity and mortality due to a series of common secondary metabolic complications, such as the development of severe, often slow healing skin lesions. In view of promoting the wound-healing process in diabetic patients, this preliminary in vitro study investigated the efficacy of green light emitting diode (LED) irradiation on fibroblast proliferation and viability under hyperglycemic circumstances.

MATERIALS AND METHODS

To achieve hyperglycemic circumstances, embryonic chicken fibroblasts were cultured in Hanks' culture medium supplemented with 30 g/L glucose. LED irradiation was performed on 3 consecutive days with a probe emitting green light (570 nm) and a power output of 10 mW. Each treatment lasted 3 min, resulting in a radiation exposure of 0.1 J/cm2.

RESULTS

A Mann-Whitney U test revealed a higher proliferation rate (p = 0.001) in all irradiated cultures in comparison with the controls.

CONCLUSION

According to these results, the effectiveness of green LED irradiation on fibroblasts in hyperglycemic circumstances is established. Future in vivo investigation would be worthwhile to investigate whether there are equivalent positive results in diabetic patients.

Effects of Chemical Modification of Lysine Residues on the Sweetness of Lysozyme

Lysozyme is a sweet-tasting protein with a sweetness threshold value of around 7 microM. To clarify the effect of basicity at the side chain of lysine residues on the threshold values of sweetness, charge-specific chemical modifications such as guanidination, acetylation and phosphopyridoxylation of lysine residues were performed. Sensory analysis showed that the sweetness threshold value of lysozyme was not changed by guanidination, whereas it was increased markedly by acetylation and phosphopyridoxylation. To confirm the importance of the basicity in the lysine residues in detail, purification of acetylated (Ac-) and phosphopyridoxylated (PLP-) lysozymes using SP-ion exchange column chromatography was performed. The threshold values were not changed by modification with fewer than two residues (approximately 7 microM), whereas the threshold values significantly increased to 15 and 34 microM when tetra-Ac and tri-PLP, respectively. Furthermore, sweetness was not detected at 30 microM (hexa-, penta-Ac and tetra-PLP). It should be noted that removal of the negative charges of the phosphate groups in the tri-PLP lysozyme by acid phosphatase resulted in the recovery of sweetness (6.4 microM), indicating that basicity at the position of the lysine residues is responsible for lysozyme sweetness and that strict charge complementarities might be required for interaction to its putative receptor.

The effect of growth regulators and sucrose on anthocyanin production in Camptotheca acuminata cell cultures

The effect of different concentrations of growth regulators and sucrose on anthocyanin production in cell suspension cultures of Camptotheca acuminata Decaisne (Nyssaceae) was described for the first time and qualitatively and quantitatively evaluated. Anthocyanin production was significantly greater in the presence of kinetin, compared to benzyladenine, with the greatest concentration observed in the presence of 2 microM kinetin. No significant differences in anthocyanin production were observed when comparing 2,4-dichlorophenoxyacetic acid to alpha-naphthaleneacetic acid, except when using 2 microM, 2,4-dichlorophenoxyacetic acid, which resulted in greater anthocyanin production. High sucrose concentration enhanced the production of anthocyanins. Based on the absence of anthocyanin production in the dark, we concluded that light was essential for stimulating anthocyanin production. The optimised medium consisted of: 2 microM kinetin, 2 microM 2,4-dichlorophenoxyacetic acid and 292 mM sucrose. HPLC/DAD and HPLC/MS analyses revealed that the main anthocyanin was Cy 3-O-galactoside and that the minor derivative was Cy 3-O-glucoside.

Screening of Bitterness-Suppressing Agents for Quinine: The Use of Molecularly Imprinted Polymers

The purpose of the present study was to examine the possibility of using molecularly imprinted polymers (MIPs) to screen for bitterness-suppressing agents. Quinine was selected as the bitter substance standard. L-arginine (L-Arg), L-ornithine (L-Orn), L-lysine (L-Lys), and L-citrulline (L-Ctr) were tested as bitterness suppressant candidates. In a high-performance liquid chromatography study using a uniformly sized MIP for cinchonidine, which has a very similar structure to quinine, the retention factor (k) of quinine was significantly shortened by the addition of L-Arg or L-Orn to the mobile phase, whereas slight or no decrease was observed when L-Ctr and L-Lys were added. The abilities of these amino acids to decrease the k of quinine were ranked in the following order: L-Arg = (L-Orn >(L-Ctr >>(L-Lys. A linear relationship between the reciprocal of k and the concentration of the amino acids indicated a single competitive model at a single site. The magnitude of the association constants obtained seemed to be directly related to the inhibitory effect of the test substances on the affinity of quinine for the receptor site. Nuclear magnetic resonance and molecular modeling studies suggested a one-to-two hydrogen-bonding-based complex formation of one quinine molecule with two methacrylic acid molecules (Q-2MAA) in chloroform. In the molecular modeling studies, the N--N distance of the quinine molecule in the assumed Q-2MAA complex was calculated to be 5.12 angstroms, similar to the N - N distances of the two amino acid complexes (L-Arg-2MAA, L-Orn-2MAA), which were 4.84 and 5.30 angstroms, respectively. This suggests that L-Arg and L-Orn may compete with the quinine molecule in the cinchonidine-imprinted space. Finally, the results of human gustatory sensation tests correlated well with the MIP data. The proposed method using MIPs seems to have a potential for screening bitterness-suppressing agents for quinine.

A structure-taste study of arylsulfonyl(cyclo)alkanecarboxylic acids

A number of sweeteners contain a sulfonyl group. In our current search for new glucophores several new compounds containing such group were obtained. A series of novel 1-phenylsulfonylcyklohexanecarboxylic acids and 2-arylsulfonylalkanecarboxylic acids was obtained and evaluated for their sweet taste quality. It has been found that methyl substituents are of the key importance for the activity of these compounds.

[Integrated evaluation of chewing gums and candies influence in oral cavity]

In a blind study on 210 medical students during 3 months the influence of 5 types of chewing gums with sugar substitutes (Orbit, Dirol, Stimorol) and 1 type of candy with sucrose upon saliva properties, saliva flow and oral microflora activity were examined. Flow rate of saliva, its pH (mixed saliva), influence upon test sugar and carbamide pH curves, concentrations of carbamide, Ca and phosphate in saliva were determined. It is shown than frequent and prolong use of chewing gums reduced stimulated and unstimulated saliva flow. Frequent use of chewing gums with carbamide provoked increased activity of ureapositive oral microflora. Degree of alkaline changes of mixed saliva pH in case of 3-month use of chewing gums Orbit and Stimorol pro Z was reduced. Chewing gums had weak hygienic efficacy.

Depressive symptoms and taste reactivity in humans

Animal studies suggest that induction of depression-like states may alter preference for sweet tastants. A major goal of the present study was to search for correlations between depressive symptoms measured by the Beck Depression Inventory (BDI) and taste responses to sweet and bitter substances. Thirty-three nonclinical volunteers rated intensity and pleasantness of chocolate and vanilla milk as well as of sucrose- and quinine-soaked filter paper disks. Reactivity to citric acid (sour) and sodium chloride (salty) was also tested with the paper disk methodology. Taste detection thresholds were assessed by means of electrogustometry. A weak inverse relationship was found between the BDI scores (range: 3-33) and rated intensity of paper disks soaked in 60% sucrose. No correlations were found between depressive symptoms and intensity, pleasantness or identification of the other samples. Similarly, there was no relationship between the BDI scores and responses to chocolate and vanilla milk. BDI scores were not associated with electrogustometric thresholds. These data suggest that depressive symptoms may not influence taste reactivity in nonclinical population.

The NMDA receptor channel blocker memantine and opioid receptor antagonist naltrexone inhibit the saccharin deprivation effect in rats

Several drugs, such as N-methyl-D-aspartate (NMDA) receptor channel blockers (memantine), naltrexone (but not naloxone) and acamprosate, have previously been reported to attenuate the expression of the alcohol deprivation effect, a phenomenon seen as an increase in post-deprivation alcohol consumption. The present study aimed to evaluate the effects of these drugs on the development and expression of the saccharin deprivation effect in adult male Wistar rats. Memantine (13 mg/kg per day) and naltrexone (5 mg/kg, twice daily), but not naloxone (24 mg/kg per day) or acamprosate (200 mg/kg, twice daily), prevented the increase in the consumption of saccharin after a 1-week deprivation from free-choice, unlimited access to saccharin (0.1%, w/v). Taken together with the results of previous studies, these results suggest that naltrexone and memantine attenuate the expression of both the alcohol and saccharin deprivation effects.

Role of gustatory thalamus in anticipation and comparison of rewards over time in rats

Rats reduce intake of a palatable saccharin solution when it is followed by access to a preferred sucrose solution. This phenomenon, referred to as an anticipatory contrast effect (ACE), is thought to occur because the value of the saccharin conditioned stimulus pales in comparison to the highly rewarding sucrose unconditioned stimulus expected in the near future. Although relatively little is known about the underlying neural substrates, lesions of the gustatory thalamus fully disrupt the phenomenon (Reilly S, Bornovalova M, and Trifunovic R. Behav Neurosci 118: 365-376, 2004; Reilly S and Pritchard TC. Behav Neurosci 110: 746-759, 1996). The present set of experiments revisited this issue to determine the nature of this deficit. Rats with bilateral ibotenic acid lesions of the gustatory thalamus were given 3-min access to 0.15% saccharin and, after a 0-s or 5-min interval, were given 3-min access to either the same saccharin solution or a highly preferred 1.0 M sucrose solution. In experiment 1, ACE testing began with the 5-min interstimulus interval (ISI) and then switched to the 0-s ISI. For experiment 2, the order of ISI testing was reversed. The results show that axon-sparing, neurotoxic lesions of the gustatory thalamus prevent ACEs with a 0-s ISI and lead to a reversal (i.e., a reinforcement effect) with a 5-min ISI. Together, the results suggest that the lesion leads to a specific reward comparison deficit, whereby the rats fail to compare the value of an available reward with the memory of a preferred reward that is anticipated in the near future.

The High-Ethanol Preferring rat as a model to study the shift between alcohol abuse and dependence

The High-Ethanol Preferring line of rats (HEP), recently selected by R.D. Myers, is characterised by a high voluntary consumption of alcohol (3-4 g/kg/day for males and 6-8 g/kg/day for females, when a 10% ethanol solution is available as a choice vs. water) and a high sensitivity to taste reinforcement (saccharin, quinine). Our previous data obtained with HEP rats showed no evidence of development of dependence after long-term sustained alcohol intake. In this study, we subjected these rats to several long-term administration protocols suggested to favour the development of alcohol dependence, including multiple alcohol concentrations or sweetened alcohol solutions (ethanol 10% or 20%+saccharin), and deprivation periods. The results showed no increase in alcohol consumption, no shift of preference for alcohol solutions when offered as a free choice vs. a preferred saccharin solution, and a very limited alcohol-deprivation effect when alcohol is made available after a period of deprivation, the three criteria used to demonstrate the development of dependence. Regardless of the method used, HEP rats failed to show dependence after long-term, heavy ethanol consumption. Resistance to ethanol dependence may in fact be genetically influenced and the HEP rat appears as a valuable model to search for factors involved in the transition from alcohol abuse to dependence.

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.