An evaluation of the acidogenic potential of maltodextrins in vivo

Maltodextrins are a group of oligosaccharides, which are being increasingly used as a source of carbohydrate in many commercially available foods and drinks. This study investigated the effect of three different maltodextrins on the pH of dental plaque, in vivo, in 10 adult volunteers using the plaque harvesting method. The three maltodextrins tested in this study were DE=5.5, 14.0 and 18.5 (DE=dextrose equivalents), made up as 10% solutions. Also, three commercially available maltodextrin containing children's drinks were evaluated for their acidogenicity. 10% sucrose and 10% sorbitol solutions were used as positive and negative controls, respectively. The minimum pH achieved for DE=5.5, 14.0 and 18.5 was 5.83+/-0.30, 5.67+/-0.24 and 5.71+/-0.29, respectively, and were significantly higher as compared with that for 10% sucrose (5.33+/-0.17). The area under the curve was the least for DE=5.5 (12.03+/-4.64), followed by DE=18.5 (13.13+/-8.87) and DE=14.0 (17.35+/-6.43), but were all significantly smaller as compared with 10% sucrose (24.50+/-8.64). The minimum pH achieved for the infant drinks was 6.01+/-0.24, 5.99+/-0.28 and 5.8+/-0.19 for the Lemon Barley and Camomile Herbal baby drink, Mixed Citrus and Hibiscus baby drink, and Infant Milk, respectively. It was concluded that though maltodextrins appeared to be significantly less acidogenic than 10% sucrose, they can lead to a substantial drop in plaque pH and may, therefore, have a potential to cause demineralisation of enamel.

An artificial sweetener stimulates the sweet taste in insect: dual effects of glycyrrhizin in Phormia regina

Glycyrrhizin, found in the root of licorice (Glycyrrhizia glabra), has been used extensively as a non-sugar sweetener for humans and also as a medicine. As far as we know, the present work is the first report describing that a non-sugar sweetener for humans induces a sweet taste in insects. In behavioural experiments, we found that glycyrrhizin induced the feeding response, including full proboscis extension in the blowfly, Phormia regina. Glycyrrhizin also induced impulses of the sugar receptor cell in the labellar chemosensillum, which is highly specialized for the tastes of sugars and nucleotides. The optimum concentration of glycyrrhizin was 3.0 mM, which is much lower than that of sucrose. It has been established that multiple receptor sites, the pyranose receptor site (P site) and the furanose receptor site (F site), are present in the sugar receptor cell of the blowfly and the fleshfly. The inhibitors specific to the P site, starch and PCMB (p-chloromercuribenzoate), partially inhibited glycyrrhizin-induced responses but not levan (an inhibitor to the F site), indicating that the P site on the sugar receptor cell is involved in the glycyrrhizin action but not the F site. When 30 s stimulation with 3.0 mM glycyrrhizin was repeated with an interval of 3--10 min, the impulse frequency to the second stimulus was higher than that to the first one and doubled within 6 min. The first stimulus lasting longer than 10 s potentiated the impulse generation and reduced the adaptation rate during the second stimulus. These results suggest that, in addition to the action via the P site, an additional mechanism, possibly in the signal transduction cascade of the sugar receptor cell, may be involved in the action of glycyrrhizin.

Sugar replacers and the FDA noncariogenicity claim

In 1996, the U.S. Food and Drug Administration (FDA) approved the use of a "health claim" based on the association between sugar replacers and the nonpromotion of dental caries. Small packages of products containing such sweeteners may state "Does not promote tooth decay" or "May reduce the risk of tooth decay." Larger packages must include additional information, such as "Frequent eating of foods high in sugars and starches as between-meal snacks can promote tooth decay." FDA criteria state that these products must not only be "sugar-free," but they must also contain a noncariogenic sugar replacer and not lower plaque pH below 5.7 either during consumption or up to 30 minutes after consumption when tested by in vivo pH telemetry. Many people might reduce their caries risk by using sugar-free products, and the FDA claim can help consumers identity such products. Dental hygienists are ideal sources of consumer information about sugar replacers, and can help clients distinguish between the new FDA claim and advertising claims that are not regulated by FDA. The purpose of this article is to provide dental hygienists with information on sugar replacers that will help clients make appropriate nutrition choices.

Chronic morphine consumption decreases wheel running and wheel running-reinforced behavior in rats

The purpose of this experiment was to evaluate the effects of morphine self-administration on wheel running and wheel running-reinforced lever pressing in rats. The home cage was equipped with a bottle that contained either water, a saccharin-flavored 0.5-mg/ml morphine solution, or saccharin (0.25%). The bottle was available for either 1 or 3 h. The bottle was then removed, and 20-22 h after removal, the rats were moved to an operant chamber in which lever presses earned 15 s access to a running wheel (according to a variable interval (VI) 40-s schedule). The morphine condition was in effect for 69 days, and consumption gradually increased to a level of 67 mg/kg/day. During the morphine condition, wheel running and lever pressing decreased. Following the removal of morphine, (so that the home-cage bottles provided a 0.25% saccharin solution), the two instrumental behaviors increased to the pre-morphine (water) levels. However, the increases were not immediate, and in the first post-morphine session, lever pressing and wheel turning remained at the depressed morphine level. The post-morphine increase in lever pressing was substantially larger than the increase in wheel running. The results support the hypothesis that chronic opiate consumption reduces the frequency of some nondrug-related behaviors, and that this, in turn, increases preference for the opiate.

The suppressive effects of intraperitoneal cocaine are augmented when evaluated in nondeprived rats

Rats suppress intake of a saccharin conditioned stimulus (CS) when paired with all drugs of abuse tested including morphine, cocaine, heroin, amphetamine, and ethanol. Although most of these drugs suppress intake when administered via a range of routes, the efficacy of cocaine is an exception. Specifically, cocaine-induced suppression of saccharin intake is much greater when administered subcutaneously than when administered intraperitoneally. The subcutaneous route of administration of cocaine, however, is somewhat problematic because, unless diluted, can cause stark necrosis. The present study, then, reexamined the effectiveness of intraperitoneal cocaine using less restrictive deprivation regimens that are known to facilitate the expression of the phenomenon. The results showed that, while only a 10- and 20-mg/kg dose of cocaine suppressed intake of the saccharin CS when evaluated in moderately water-deprived rats, all doses tested (i.e., 5, 10, and 20 mg/kg) significantly reduced CS intake when saccharin-cocaine pairings were evaluated in rats maintained on food and water ad libitum. Taken together, these data show that rats will readily avoid intake of a saccharin cue when paired with the intraperitoneal administration of cocaine and that the magnitude of the effect is augmented when examined in a need-free state.

D1 but not D2 dopamine receptor antagonism blocks the acquisition of a flavor preference conditioned by intragastric carbohydrate infusions

The effects of dopamine D1 (SCH23390) and D2 (raclopride) receptor antagonists on the acquisition and expressions of flavor preferences conditioned by the postingestive actions of sucrose were investigated. Food-restricted rats were trained in one-bottle sessions to associate one flavored saccharin solution (CS+) with intragastric (i.g.) infusions of 16% sucrose, and another flavored saccharin solution (CS-) with water infusions. Flavor preferences were then measured in two-bottle tests. In Experiment 1A, rats that received the D2 antagonist (raclopride, 200 nmol/kg; RAC group) throughout training consumed less CS+ and CS- than did saline-treated Control rats; a saline-treated Yoked group had its intake limited to that of the RAC group. All three groups displayed CS+ preferences during two-bottle tests when treated with saline or raclopride, except at doses that greatly suppressed intake. Experiment 1B obtained similar results with rats treated with 400 nmol/kg raclopride throughout training. In Experiment 2, rats that received the D1 antagonist (SCH23390, 200 nmol/kg; SCH group) throughout training consumed less CS+ and CS- than did saline-treated Control rats; a saline-treated Yoked group had its intake limited to that of the SCH group. Unlike the Control and Yoked groups, the SCH group failed to prefer the CS+ to the CS- in two bottle tests. SCH23390 treatment during two-bottle testing did not block CS+ preference in the Control or Yoked groups, except at doses that greatly suppressed intake. We conclude that D1, but not D2, dopamine receptors are critically involved in the acquisition of a sucrose-conditioned flavor preference, and both receptor subtypes have a more limited role in the expression of this preference.

Oral testosterone self-administration in male hamsters

The addiction potential of anabolic steroids remains largely unexplored. Here, we demonstrate voluntary oral testosterone intake in hamsters. Using a 2-bottle choice test, males preferred an aqueous solution of 200 microg/ml testosterone over vehicle. However, the taste of testosterone is not highly preferred. Addition of testosterone at 400 microg/ml increased fluid consumption from the nonpreferred bottle in a 2-bottle choice test, but cholesterol at the same concentration reduced drinking, suggesting that testosterone reward is not common to all sterols. With food-induced drinking, testosterone maintained fluid intake when food was withdrawn. These data demonstrate that oral self-administration of testosterone is reinforcing in hamsters, suggesting the potential for dependence in human users.

Sweet pregnane glycosides from Telosma procumbens

An intensely sweet polyoxypregnane glycoside, telosmoside A15 (15), was isolated from an Asian Asclepiadaceae plant, Telosma procumbens, collected in Vietnam. This is the first time a sweet pregnane glycoside has been found, and its sweetness intensity is 1000 times greater than that of sucrose. From the same plant, 17 other new glycosides were isolated, having the same aglycone; they are named telosmosides A1-A14 (1-14) and A16-A18 (16-18). Some of these glycosides are also sweet, but others are tasteless or bitter. Chemical structures of the 18 glycosides were determined, and the structure-taste relationship was discussed.

Effect of saccharin on antibacterial activity of chlorhexidine gel

Although chlorhexidine is the most effective agent against dental plaque it is extremely bitter. To prepare formulations, it is necessary to use flavoring and sweetening, which can inhibit the antibacterial effect of chlorhexidine. Saccharin has been considered a compatible substance to use in chlorhexidine rinse or gel preparations; however, the effect of a range of concentrations has not been studied. To evaluate the effect of different concentrations of saccharin on the antibacterial activity of chlorhexidine gel, hydroxy-ethyl-cellulose gels containing 1.0% chlorhexidine digluconate and 0.0 to 1.0% sodium saccharin were prepared. Activity against Streptococcus mutans was evaluated using the agar diffusion method and determination of MIC values. The inhibitory zones of growth were 7.83 +/- 0.54 mm when no saccharin was added to the chlorhexidine gel and 7.75 +/- 0.50, 7.63 +/- 0.48, 6.21 +/- 0.40, 4.13 +/- 0.38, when the concentrations of saccharin in the gels were 0.02, 0.10, 0.5, and 1.0%, respectively. The range of MIC values was 1-2 micrograms/ml, with saccharin concentrations of 0%, 0.02, and 0.1%. In contrast, the MIC values were 4-8 and 8-16 micrograms/ml with saccharin concentrations of 0.5% and 1.0%, respectively. The paired "t" test showed that 0.5 and 1.0% sodium saccharin inhibit the antibacterial activity of 1% digluconate chlorhexidine gel. These in vitro results suggest that saccharin may inhibit the efficacy of chlorhexidine against mutans streptococci, depending on the concentration.

Delta(9)-THC stimulates food intake in Lewis rats: effects on chow, high-fat and sweet high-fat diets

Free-feeding adult male Lewis rats were administered intraperitoneal (i.p.) Delta(9)-tetrahydrocannabinol (THC) in doses of 0.5, 1.0 and 2.5 mg/kg, and effects on food intake were measured at 1, 2, 4, 6 and 24 h postinjection. Rats were fed rat chow, a high-fat diet (HF) or a high-fat sweetened (HFS) diet. Small increases in HF and HFS intake following doses of 0.5 or 1.0 mg/kg were seen at 1, 2 and 4 h, but not 6 or 24 h compared to vehicle intake. Increases following 0.5 and 1.0 mg/kg did not differ from each other at any time point and 2.5 mg/kg produced smaller differences at all time points. There was no difference between HF or HFS intake at any time point although larger increases were seen in the HF group compared to both chow and HFS following 0.5 and 1.0 mg/kg. This work confirms previous data in both humans and rats indicating a stimulatory role for cannabinoids in ingestive behavior.

Structure-sweetness relationship in thaumatin: importance of lysine residues

To clarify the structural basis for the sweetness of thaumatin I, lysine-modified derivatives and carboxyl-group-modified derivatives were prepared by chemical modification followed by chromatographic purification. The sweetness of derivatives was evaluated by sensory analysis. Phosphopyridoxylation of lysine residues Lys78, Lys97, Lys106, Lys137 and Lys187 markedly reduced sweetness. The intensity of sweetness was returned to that of native thaumatin by dephosphorylation of these phosphopyridoxylated lysine residues except Lys106. Pyridoxamine modification of the carboxyl group of Asp21, Glu42, Asp60, Asp129 or Ala207 (C-terminal) did not markedly change sweetness. Analysis by far-UV circular dichroism spectroscopy indicated that the secondary structure of all derivatives remained unchanged, suggesting that the loss of sweetness was not a result of major disruption in protein structure. The five lysine residues, modification of which affected sweetness, are separate and spread over a broad surface region on one side of the thaumatin I molecule. These lysine residues exist in thaumatin, but not in non-sweet thaumatin-like proteins, suggesting that these lysine residues are required for sweetness. These lysine residues may play an important role in sweetness through a multipoint interaction with a putative thaumatin receptor.

Flavor preferences conditioned by intragastric infusion of ethanol in rats

Sprague-Dawley rats were trained 22 h/day to associate a flavored solution [conditioned stimulus (CS+)] with intragastric infusions of 6% ethanol and another flavored solution (CS-) with water infusions. The infusions were matched to the CS intakes so that the animals determined their timing and size. In Phase 1, chow and water were available ad libitum, and both CS flavors were initially sweetened with saccharin that was then faded out. The rats displayed a preference for the CS+ over the CS- under both reinforced and extinction conditions. When food-restricted in Phase 2, the rats displayed an increased preference for the CS+. In Phase 3, the rats were fed ad libitum chow and given preference tests with the CS+ paired with ethanol infusions of increasing concentration (6%, 12%, 18%, and 24%). Their preference for the CS+ over the CS- persisted, and self-administered ethanol dose increased with concentration to 5 g/kg/day. The ethanol-based conditioned flavor preference resembled those conditioned by carbohydrate and fat infusions, suggesting that at least some of reinforcing ability of ethanol may be related to its postingestive nutritive effects.

Cellular responses of NG108-15 and SK-N-MC lines to sweet and bitter tastants as measured by extracellular acidification rates

The Cytosensor microphysiometer device (Molecular Devices, Sunnyvale, CA) is capable of detecting small changes in cellular metabolism in response to specific bioactive ligands by measuring the extracellular acidification rate (ECAR). By measuring the ECAR we were able to detect responses of tissue culture cell lines to a variety of sweet- and bitter-tasting compounds. We examined in detail the responses of the NG108-15 (mouse neuroblastoma x rat glioma hybrid) and SK-N-MC (human neuroepithelioma) cell lines. We determined that NG108-15 cells were consistently very responsive to several potent sweeteners and bitter compounds, such as sodium saccharin, guanidino- sweeteners, denatonium benzoate, quinine, and ranitidine. These compounds could evoke changes in cellular metabolism (measured as ECAR) that were rapid in onset, saturable with respect to ligand concentration, and sensitive to several inhibitors of G-protein-coupled receptor signaling pathways. In sharp contrast, the neuroepithelioma SK-N-MC did not respond to any of the sweet or bitter compounds. Rapid changes in ECAR were easily detectable in both cell lines with the calcium ionophore A23187. Bradykinin elicited changes in the ECAR only in the NG108-15 cell line, which is known to express the B2 receptor. The changes in ECAR of the NG108-15 cell line in response to sweet and bitter taste compounds suggest these cells may expresses a receptor(s) specific for small sapid molecules.

Saccharin activates cation conductance via inositol 1,4,5-trisphosphate production in a subset of isolated rod taste cells in the frog

The transduction mechanism of the conductance activated by saccharin was analysed in isolated bullfrog taste cells under whole-cell voltage-clamp. Bath application of 30 mM saccharin induced an inward current of -34 +/- 12 pA (mean +/- SEM, n = 10) at a membrane potential of -50 mV in 10 (23%) of 44 rod cells. The concentration-response relationship for the saccharin-gated current was consistent with that of the gustatory neural response. The saccharin-induced current was accompanied with a conductance increase under internal low Cl- condition (E(Cl) = -56 mV), suggesting that saccharin activated a cation conductance. The reversal potential of the saccharin-induced current was -17 +/- 2 mV (n = 10). Intracellular dialysis of 0.5 mM guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S) completely blocked the saccharin-induced response, suggesting the involvement of a G protein in the transduction. The dialysis of heparin (1 mg/mL) also inhibited the response almost completely, but the dialysis of 1 mM 8-Br-cAMP did not affect the response significantly. Intracellular 50 microM inositol 1,4,5-trisphosphate (1,4,5 InsP(3)) also induced the inward current in five (38%) of 13 rod cells, but intracellular Pasteurella multocida toxin (5 microg/mL, G alpha q-coupled PLC activator) did not elicit any response in the cells. The results suggest that saccharin mainly activates a cation conductance in frog taste cells through the mediation of IP3 production.

Small-bowel absorption of D-tagatose and related effects on carbohydrate digestibility: an ileostomy study

BACKGROUND

The ketohexose D-tagatose is a new sweetener with a low energy content. This low energy content may be due to either low absorption of the D-tagatose or decreased absorption of other nutrients.

OBJECTIVE

The aims of this study were to measure the excretion of D-tagatose from the human small bowel, to calculate the apparent absorption of D-tagatose, and to study the effects of D-tagatose on the small-bowel excretion of other carbohydrates.

DESIGN

A controlled diet was served for 2 periods of 2 d during 3 consecutive weeks to 6 ileostomy subjects. In one of the periods, 15 g D-tagatose was added to the diet daily. Duplicate portions of the diet and ileostomy effluents were freeze-dried and analyzed to calculate the apparent net absorption of D-tagatose and carbohydrates.

RESULTS

Median D-tagatose excretion was 19% (range: 12-31%), which corresponded to a calculated apparent absorption of 81% (69-88%). Of the total amount of D-tagatose excreted [2.8 g (1.7-4.4 g)], 60% (8-88%) was excreted within 3 h. Between 3 and 5 h, 32% (11-82%) was excreted. Excretion of wet matter increased by 41% (24-52%) with D-tagatose ingestion. Sucrose and D-glucose excretion increased to a small extent, whereas no significant changes were found in the excretion of dry matter, energy, starch, or D-fructose.

CONCLUSIONS

The apparent absorption of 15 g D-tagatose/d was 81%. D-Tagatose had only a minor influence on the apparent absorption of other nutrients.

Effect of xylitol on growth of Streptococcus pneumoniae in the presence of fructose and sorbitol

Xylitol is effective in preventing acute otitis media by inhibiting the growth of Streptococcus pneumoniae. To clarify this inhibition we used fructose, which is known to block similar growth inhibition observed in Streptococcus mutans. In addition, we evaluated the efficacy of sorbitol in inhibiting the growth of pneumococci, as sorbitol is widely used for indications similar to those for which xylitol is used. The addition of 5% xylitol to the growth medium resulted in marked growth inhibition, an effect which was totally eliminated in the presence of 1, 2.5, or 5% fructose but not in the presence of 1 or 5% glucose, 1% galactose, or 1% sucrose. This finding implies that xylitol-induced inhibition of pneumococcal growth is mediated via the fructose phosphotransferase system in a way similar to that in which mutans group streptococcal growth is inhibited. The addition of sorbitol at concentrations of 1, 2.5, or 5% to the growth medium did not affect the growth of pneumococci and neither inhibited nor enhanced the xylitol-induced growth impairment. Thus, it seems that xylitol is the only commercially used sugar substitute proven to have an antimicrobial effect on pneumococci.

Xylitol-induced elevated expression of the gbpC gene in a population of Streptococcus mutans cells

Xylitol possesses a unique property distinct from the other caries-preventive sweeteners. This sugar alcohol cannot be metabolized to acids but is taken up by Streptococcus mutans and accumulated as a toxic sugar-phosphate in the cells, resulting in growth inhibition. Due to the accumulation, xylitol induces biological responses including the emergence of xylitol-insensitive populations. Therefore, we expected another response induced by xylitol and found a new phenomenon, that cells repeatedly cultured in the presence of xylitol evolved into those exhibiting an elevated dextran-dependent aggregation phenotype. This phenotype was found to result from expression of the gbpC gene, which was previously reported to be expressed only under certain stress conditions. Construction of a Strep. mutans isogenic mutant carrying the gbpC::lacZ fusion gene indicated that gbpC expression of cells repeatedly cultured in the presence of xylitol was elevated 20-fold. DNA transfer experiments indicated that this phenotypic change did not appear to be due to a mutation. These cells also exhibited decreased adhesion to glass surfaces when grown in the presence of sucrose. This may be one of the ways by which some populations of Strep. mutans are removed from dental plaques.

Self-organizing neural networks for screening and development of novel artificial sweetener candidates

The use of Kohonen feature maps for the visualization of various aspects of molecular similarity is briefly reviewed and illustrated. It is shown that a specific feature of self-organizing maps (SOM) makes them of special interest for the screening of compounds. In particular, these methods were used to design candidates for new sweeteners, which were then synthesized.

Cortical cholinergic activity is related to the novelty of the stimulus

A number of studies have related cholinergic activity to the mediation of learning and memory. However, the acetylcholine (ACh) participation has been recently implicated in the early stages of memory formation but not during retrieval. The aim of the present study is to evaluate ACh release in the insular cortex (IC) during presentation of different taste stimuli and during their re-exposition by means of the free-moving microdialysis technique. We evaluated the changes in ACh release when a novel taste, saccharin or quinine was presented to the rat and after several presentations of saccharin. Unilateral microdialysis was performed in the IC 1 h before and 1 h after the presentation of: (1) a familiar stimulus (water), (2) a novel taste (quinine), (3) another novel taste (saccharin), (4) a second presentation, (5) a third presentation, and (6) a fourth presentation of saccharin. The volume consumed by the animals was registered as a behavioral parameter. The ACh levels from the microdialysis fractions were analyzed by an HPLC-ED system. Biochemical results showed a significant increment in the cortical ACh release induced by a novel stimulus compared with the release observed during the presentation of a familiar stimulus. The ACh release observed after several presentations of the stimuli decreased to the same levels as those produced by the familiar taste, indicating an inverse relationship between familiarity and cortical ACh release. These results suggest that the cholinergic system plays an important role in the identification and characterization of different kinds of stimuli.

Role of D(1) and D(2) dopamine receptors in the acquisition and expression of flavor-preference conditioning in sham-feeding rats

The present study examined the effects of D(1) and D(2) antagonists on flavor-preference conditioning by the sweet taste of sucrose. All sessions were conducted under sham-feeding conditions to minimize post-ingestive influences. The rats were trained in alternating, one-bottle sessions to sham-feed a 16% sucrose solution containing one novel flavor (CS+) and a less-preferred 0.2% saccharin solution containing a different flavor (CS-). Three groups of food-restricted rats were treated with either vehicle (control group), the D(1) antagonist, SCH23390 (200 nmol/kg), or the D(2) antagonist, raclopride (200 nmol/kg) during one-bottle training. A fourth group (yoked group) was vehicle-treated and its training intakes were matched to that of the D(1) and D(2) drug groups. Preferences were assessed in two-bottle tests with the CS+ and CS- flavors presented in mixed 8% sucrose+0.1% saccharin solutions following systemic doses of 0, 200, or 800 nmol/kg of either the D(1) or D(2) antagonists. All groups significantly preferred the CS+ flavor in vehicle tests, although the preferences were weaker in the D(1), D(2), and yoked groups compared to the control group. All groups selectively reduced their CS+ intakes when treated with either D(1) or D(2) antagonists during two-bottle testing, and the CS+ preference was blocked at the higher doses. These data show that D(1) and D(2) receptor antagonists block the expression of a sucrose-conditioned preference, but produces substantially lesser effects upon the acquisition of this form of flavor conditioning.

Quantitative evaluation of the bitterness of commercial medicines using a taste sensor

The bitterness of 11 commercial medicines was evaluated both by a multichannel taste sensor and in human gustatory sensation tests with 15 volunteers. For basic drugs with amino groups in the molecule, such as quinine, there was a comparatively strong relative response electric potential (mV) of channels 1 or 2, those containing negatively charged membranes and the bitterness determined by human gustatory sensation tests. The suppression of the bitterness of quinine by sucrose and aspartame could be quantified using the artificial taste sensor and the results concurred with those from gustatory sensation tests. The usefulness of the sensor was thus confirmed for this type of compound. Anionic drugs, such as diclofenac sodium or salicylic acid gave rise in a negative response electric potential in channels 5 or 6, those containing positively charged membrane, seemed to be useful information even though their tastes are being sour rather than bitter. For drugs with both an amino (cationic) group and carboxylic acid (anionic) group in the molecule, such as theophylline, caffeine, and metronidazole, the relative response electric potential (mV) of channels containing negatively charged membranes was not increased, even though bitterness was observed in human gustatory sensation tests. Therefore, a different design of membrane component is required for more general evaluation of the bitterness of various medicines.

Ketamine blocks a taste recognition memory in fetal rats

Decisions about novelty/familiarity are critical in determining whether or not information should be attended to, and possibly encoded, for long-term storage. We have reported that fetal and neonatal rats exhibit an increase in orofacial movements (e.g., perseverative mouthing and mouth movements, and licks) upon tasting saccharin (SAC), if it was experienced previously. E19 rat fetuses can acquire this taste recognition memory and retain it for at least 5 days (P3). In the current study, we sought to evaluate the role of N-methyl-D-aspartate (NMDA) receptors in establishing a taste recognition memory. Pregnant Sprague-Dawley rats received ketamine (NMDA receptor antagonist) (doses: 0, 50, or 100 mg/kg, i.p.). One-half hour later, we performed a reversible spinal block on each pregnant dam, and E19 fetuses received an oral injection of 10 microl, 0.3% SAC or water (control) while in utero. The uterus was replaced and the pups were later born via a normal vaginal delivery. On P3, all pups experienced oral lavage of 10 microl, 0.3% SAC, and motor responses were recorded. As expected, non-drugged control neonates tasting familiar SAC exhibited significantly more perseverative mouth movements, as well as total mouth movements and licks, than did pups tasting novel SAC. However, this taste recognition memory response was not observed in rats exposed to ketamine in utero. The data suggest that early non-associative taste memories may be disrupted by NMDA receptor blockade.

Multiple remote-US preexposures and the blocking effect produced by a proximal-US

Weanling, young-adult, and old-age Wistar albino rats were used to determine whether number of unconditioned stimulus (US) presentations, given 24 h or more (remote preexposure) prior to conditioning, alters the blocking effect of a single-US preexposure given 2 h before (proximal) taste aversion conditioning. As the number of remote-US preexposures increased from 0 to 6, the ability of the proximal-US preexposure to block conditioning initially increased then decreased for all age groups. Of the models put forth to explain US preexposure effects on conditioned taste aversion (CTA), only Wagner's information processing model adequately explained the reduction of the blocking effect of the proximal-US preexposure produced as a result of increasing remote-US preexposures.

Effect of stevioside on PAH transport by isolated perfused rabbit renal proximal tubule

Stevioside, a non-caloric sweetening agent, is used as a sugar substitute. An influence of stevioside on renal function has been suggested, but little is known about its effect on tubular function. Therefore, the present study was designed to explore the direct effect of stevioside on transepithelial transport of p-aminohippurate (PAH) in isolated S2 segments of rabbit proximal renal tubules using in vitro microperfusion. Addition of stevioside at a concentration of 0.45 mM to either the tubular lumen, bathing medium, or both at the same time had no effect on transepithelial transport of PAH. Similarly, a concentration of 0.70 mM (maximum solubility in the buffer) when present in the lumen, had no effect on PAH transport. However, this concentration in the bathing medium inhibited PAH transport significantly by about 25-35%. The inhibitory effect of stevioside was gradually abolished after it was removed from the bath. Addition of 0.70 mM stevioside to both lumen and bathing medium at the same time produced no added inhibitory effect. Stevioside at this concentration has no effect on Na+/K+-ATPase activity as well as cell ATP content. These findings suggest that stevioside, at a pharmacological concentration of 0.70 mM, inhibits transepithelial transport of PAH by interfering with the basolateral entry step, the rate-limiting step for transepithelial transport. The lack of effect of stevioside on transepithelial transport of PAH on the luminal side and its reversible inhibitory effect on the basolateral side indicate that stevioside does not permanently change PAH transport and should not harm renal tubular function at normal human intake levels.