Sucrose Responsiveness Research Articles

Reversing Drought‐Induced Losses in Grain Yield: Sucrose Maintains Embryo Growth in Maize

Large losses in yield can occur in maize (Zea mays L.) growing in water‐limited conditions (low Ψw), particularly during flowering and early embryo growth where grain number is decreased. However, embryo growth is maintained where otherwise none would occur if the stems are infused with photosynthate (sucrose) and other nutrients (amino acids, salts, vitamins, and hormones) during exposure to low Ψw. In the present investigation, we deleted or supplied various components of the complete infusion mediumto identify the active solute. Infusions involved making a cavity in a stem internode, filling the cavity with water, sealing the cavity, and connecting the interior of the cavity to an external reservoir of the medium. A field experiment at high Ψw showed that wounds and enhanced nutrient supplies from the infusions did not alter embryo growth or yield. In controlled environment chambers, low Ψw was imposed by withholding water for 6 d beginning 5 d prior to pollinations. A new infusion was made each day for 5 d as the low Ψw developed around pollination. The low Ψw virtually eliminated grain development. Sucrose infusion reversed this loss and no other component of the medium showed activity under our conditions. In plants receiving no sucrose at low Ψw, ovary sucrose content was moderately lower and starch much lower than in controls. In plants receiving sucrose at low Ψw, ovary sucrose content was higher than in controls and starch recovered moderately. The difference in sucrose and starch responses indicates that carbohydrate metabolism was altered in the ovaries at low Ψw. Embryo survival correlated more closely with the content of starch than sucrose. We conclude that there were two effects of low Ψw that contributed to arrested embryo growth: a decreased sucrose flux and an altered carbohydrate metabolism in the ovaries.

Gurmarin inhibition of sweet taste responses in mice.

The inhibitory effects of gurmarin (a peptide isolated from the leaves of Gymnema sylvestre) on sweet taste responses were studied by examining the chorda tympani nerve responses to various taste substances before and after lingual treatment with gurmarin in C57BL and BALB mice. Treatment with gurmarin at 3 micrograms/ml or more selectively suppressed responses to sucrose without affecting responses to NaCl, HCl, and quinine in C57BL mice, whereas gurmarin at 100 micrograms/ml did not significantly suppress sucrose responses in BALB mice. Responses to various sweet substances in C57BL mice decreased to approximately 45-75% of control after gurmarin, and the suppressive effect of gurmarin was reversible. The profile of the residual responses of C57BL mice to various sweeteners after gurmarin was almost identical to that of BALB mice, which was hardly affected by gurmarin. These results strongly suggest that there are at least two types of sweet taste receptors in mice, gurmarin-sensitive and -insensitive. Probably, C57BL and BALB mice share an identical gurmarin-insensitive receptor, and C57BL mice also have a gurmarin-sensitive receptor.

Modulators of the adenylate cyclase system can alter electrophysiological taste responses in gerbil

The adenylate cyclase system has been implicated in taste transduction. The purpose of this study was to determine whether application of modulators of the adenylate cyclase system to the tongue alter taste responses. Integrated chroda tympani (CT) recordings were made in gerbils to bitter, sweet, salty, sour, and glutamate tastants before and after a 4-min application of four types of modulators of the adenylate cyclase system. The four types of modulators tested were: a) NaF, a compound that promotes dissociation of GTP binding protein; b) forskolin, a powerful stimulant of adenylate cyclase; c) 8-bromoadenosine 3′ : 5′-cyclic monophosphate sodium salt (8BrcAMP) and N 6, 2′-O-dibutyryl-adenosine 3′ : 5′-cyclic monophosphate sodium salt (DBcAMP), two membrane permeable forms of cAMP; and d) 1-(5-isoquinolinylnsulfonyl)-2- methylpiperazine dihydrochloride (H-7) and N-(2-[methylamino]ethyl)-5-isoquinolinesulfonamide dihydrochloride) (H-8), which are protein kinase inhibitors. The taste compounds tested were: NaCl (30 mM), monosodium glutamate-MSG (50 mM), sucrose (30 mM), HCl (5 mM and 10 mM), KCl (300 mM), quinine HCl (30 mM), MgCl 2 (30 mM), erythromycin (0.7mM and 1 mM), HCl (5 mM and 10 mM), and urea (2 M). The main findings were as follows. NaF (20 mM) significantly inhibited responses to bitter compounds up to 35% and enhanced the response to sucrose by 30%. NaCl (20 mM), used as a control for NaF, inhibited most responses up to 78% with no enhancement of sucrose as seen with NaF. 8BrcAMP (1.16 mM) reduced the responses to bitter-tasting quinine HCl, MgCl 2, and erythromycin but not to urea. It also blocked the responses to KCl and HCl which have bitter components. There was a slight enhancement of the sucrose response. It had no significant effect on NaCl or MSG. A similar trend was found for 5 mM DBcAMP. H-7 (300 μM) slightly altered responses to several stimuli. These data indicate that modulation of the adenylate cyclase system can affect the amplitude of neural responses of some bitter and sweet taste responses.

Effect of salivation on neural taste responses in freely moving rats: analyses of salivary secretion and taste responses of the chorda tympani nerve

The outer surface of the mammalian taste receptor cell is usually covered with saliva, which may affect the initial process of gustation. To ascertain the interaction between salivation and gustation, salivary secretion from the submandibular and parotid glands and taste responses of the chorda tympani nerve were analyzed in the rat, during grooming, eating, and licking of the four standard taste stimuli (sucrose, NaCl, HCl, and quinine hydrochloride). Regions of the tongue surface bathed by saliva secreted from the each gland were examined, and it was found that: (1) Rats frequently groomed, and the anterior part of the tongue, innervated by the chorda tympani nerve, was usually covered with a mixture of submandibular saliva and substances on the body surface. (2) Licking of acceptable sucrose and NaCl solutions elicited initial phasic and long-lasting tonic taste responses, and did not evoked saliva enough to wash away the stimuli from the oral cavity. Licking of rejectable quinine evoked only a small phasic taste response and was followed by taste rejection behavior, accompanied by maximum salivation which could wash out the stimuli. (3) When taste responses were compared under awake and anesthetized (the tongue adapted to water) condition, sucrose response was larger, while responses to other taste stimuli were smaller under the awake condition. Rise time of the phasic NaCl response was longer under the awake condition. These taste response alterations may reflect the effects of prolonged adaptation of the tongue to the mixture of submandibular saliva and body surface substances, and flow rate of licked taste stimuli on the tongue surface.

Simultaneous determination of glucose and sucrose by a dual‐working electrode multienzyme sensor flow‐injection system

AbstractA dual‐working electrode (K1 and K2) multienzyme sensor, made of carbon paste, glucose oxidase (GOD) membrane (on K1) and invertase (INV)/mutarotase (MUT)/GOD membrane (on K2), is proposed for simultaneous determination of glucose and sucrose. Interference to the K2 caused by H2O2 produced in the enzyme reaction on K1 can be eliminated by depositing a catalase (CAT) layer between K1 and K2. Acceleration of glucose mutarotation by MUT was found to be three times faster than by phosphate buffer. Glucose was determined directly from the response of K1, while sucrose was computed based on a formula derived from a two‐point calibration method. The maximum concentration of sucrose that could be determined depended strongly on the concentration of coexisting glucose. The activities of immobilized GOD, INV, MUT, and CAT were examined individually and found stable at room temperature for at least 1 month. The final loss of sucrose response activity was found to be due to denaturation of INV.

Responses of single hamster parabrachial neurons to binary taste mixtures of citric acid with sucrose or NaCl.

1. Although taste experience generally arises from a mixture of gustatory stimuli, most neurophysiological studies of the mammalian central gustatory system have focused on responses to single chemical stimuli. Recently, in a study of single third-order neurons in the hamster parabrachial nucleus (PbN), we reported that mixture suppression occurs in the responses to binary mixtures of sucrose and QHCl presented to the anterior tongue. Mixture suppression was reflected both in reduced response frequencies and in an altered pattern of responses across neurons. In the current report we extend our investigation of CNS neuron responses to binary mixtures of heterogeneous stimuli to include sucrose+citric acid mixtures and NaCl+citric acid mixtures. The response to each mixture was compared with the response to the more effective component (MEC) presented alone, and those that differed by more than a selected criterion (based on response variability) were identified. 2. For all mixture responses recorded, 29% (79/256) involved mixture suppression (mixture response < MEC response), only 6% (18/276) were greater than the response to MEC, and 65% (179/276) did not differ from the response to the MEC. 3. In Experiments 1 and 2, neurons were tested with four concentrations of sucrose or citric acid each presented alone and in binary mixtures with a single strong concentration of the other stimulus. Sucrose suppression (mixture response < sucrose response) occurred in 24% of mixture responses and was exhibited almost exclusively by sucrose-best neurons, primarily to the mixtures that contained the stronger sucrose and citric acid concentrations. Sucrose suppression involved a 40% reduction of mixture response frequencies compared with responses to the sucrose component alone. 4. In Experiments 3 and 4, neurons were tested with four concentrations of NaCl or citric acid each presented alone and in binary mixtures with a single strong concentration of the other stimulus. NaCl suppression (mixture response < NaCl response) occurred in 21% of mixture responses and was displayed by both sucrose-best and NaCl-best neurons. NaCl suppression involved a 28% reduction in mixture response frequencies compared with responses to the NaCl component alone. In all experiments citric acid suppression (mixture response < citric acid response) was observed in only 6% of mixture responses and was relatively small in magnitude. 5. The across-neuron patterns (ANPs) of taste responses, which are correlated with behavioral measures of taste similarity, were compared for mixtures and components.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses of single hamster parabrachial neurons to binary taste mixtures: mutual suppression between sucrose and QHCl.

1. Although taste experience typically arises from a mixture of gustatory stimuli, nearly all previous neurophysiological studies of the mammalian central gustatory system have focused on responses to single chemical stimuli. To begin to systematically examine CNS responses to taste mixtures, we recorded the extracellular activity of single third-order neurons in the hamster PbN to anterior tongue stimulation with binary mixtures of sucrose and QHCl. In experiment 1, neurons were tested with four concentrations of sucrose (0.001, 0.01, and 1.0 M) presented alone and mixed with 0.1 M QHCl. In experiment 2, neurons were tested with four concentrations of QHCl (0.00032, 0.0032, 0.032, and 0.1 M) presented alone and mixed with 1.0 M sucrose. 2. The response to each binary mixture was compared with the response to the more effective component (MEC) presented alone, and those that differed by more than a selected criterion (based on response variability) were identified. Of all mixture responses, 37% (59/158) involved mixture suppression (mixture response < MEC response), only 4% (6/158) were greater than the MEC, and 59% (94/158) were classified as not different than the response to the MEC. Most neurons that displayed mixture suppression did so at several mixture concentrations. 3. Sucrose suppression (mixture response < sucrose response) was prevalent among neurons most responsive to sucrose and for the mixtures that contained the stronger sucrose concentrations. Among neurons that displayed sucrose suppression, the magnitude of suppression was significantly correlated with sucrose response magnitude but not with QHCl response magnitude. These and other factors suggest that a neuron's capacity to display sucrose suppression to sucrose+QHCl mixtures is related to its sucrose sensitivity. 4. QHCl suppression (mixture response < QHCl response) was less prevalent than sucrose suppression, and the neurons that displayed QHCl suppression were almost exclusively a subset of those that displayed sucrose suppression to the same or different mixtures. This finding and the observation that one-third of all mixture responses involved mutual suppression (response to the mixture less than that to either component alone), suggest an association between the factors underlying sucrose suppression and QHCl suppression. 5. The across-neuron patterns (ANPs) of taste responses, which are thought to represent taste quality, were compared for mixtures and components. In general, the ANP for each mixture was similar to (significantly correlated with) the ANP of the more stimulatory component. However, for the mixture that evoked the greatest sucrose suppression, the mixture ANP was more similar to the ANP of the less stimulatory component.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of inorganic constituents of saliva on taste responses of the rat chorda tympani nerve

The effects of saliva on the taste responses of the chorda tympani nerve to the 4 standard chemical stimuli (sucrose, NaCl, HCl, and quinine hydrochloride) and water were investigated in anesthetized rats. When the tongue was adapted to pilocarpine-stimulated whole saliva (pH 8.7), the magnitude of neural response to sucrose was about 2 times that obtained when the tongue was adapted to distilled water. Under saliva-adapted conditions, the magnitude of responses to other taste stimuli was reduced by 10-30%, and the water response appeared. These changes were dependent on the concentration of electrolytes (Na+, K+, Cl-, and HCO3-) and on the pH of the saliva. When the tongue was adapted to 10-30 mM NaHCO3 (pH 8.4-8.6), taste and water responses were similar to those under saliva-adapted conditions. Single fiber analyses revealed that the enhancement of the sucrose response after adaptation to NaHCO3 was produced by an increased overall activity of sucrose-responsive fibers. The correlation coefficients of the magnitude of the taste responses between the 4 taste stimuli remained unchanged, but the water response showed a high correlation to HCl and quinine hydrochloride responses after adaptation. Possible mechanisms for the effects of saliva on taste and water responses were discussed.

Forage Yield and Sucrose Response of Rhodes and Ruzi Grass to Cutting Height and Cutting Frequency Under Irrigation

The development of irrigated pastures in the Sudan is still at its infancy. The present study determined the influence of 2 cutting heights (2.5 and 5.0 cm) and 4 cutting frequencies (4-, 6-, 8-, and 10-week) on forage yield as dry matter and forage sucrose of Rhodes grass (Chloris gayana Kunth. cv. Massaba) and Ruzi grass (Brachiaria ruziziensis Germain et Everard cv. Congo Signal) under irrigated conditions. Forage yield interactions involving species X cutting height X cutting frequency were significant. These yield interactions were attributed to differences in growth period and growth rhythm of the two species. On average, Rhodes exhibited a short growth period (13 months) compared to Ruzi grass (20 months). Forage yield and forage sucrose were, on average, superior in Ruzi compared to Rhodes grass. Forage yield and forage sucrose averaged 5.2 t ha−1 and 7.2 % fw sucrose in Ruzi compared to 2.8 t ha−1 and 6.9 % fw sucrose in Rhodes grass. Forage yield and forage sucrose of both species were negatively correlated with cutting frequency. The highest forage yield may be obtained at an 8-week cutting frequency in Rhodes (45.6 t ha−1 yr−1) compared to a 10-week cutting frequency in Ruzi grass (88 t ha−1 yr−1). Results suggest that very high forage yields as dry matter and forage sucrose of Rhodes and Ruzi grass may be possible under irrigated conditions in the Sudan at a cutting frequency of between 8 to 10 weeks.

Inhibition of Sucrose Enhancer Effect of the Potato Proteinase Inhibitor II Promoter by Salicylic Acid

Effect of salicylic acid (SA) on the expression of the potato proteinase inhibitor (PI) II promoter was studied with transgenic tobacco plants (Nicotiana tabacum) carrying a gene fusion between the PI-II promoter and the chloramphenicol acetyltransferase (cat) reporter. As previously observed, the PI-II promoter was inducible by wounding and the promoter activity was further enhanced by sucrose. Addition of SA did not influence the wound induction of the PI-II promoter but significantly inhibited the sucrose response. The 5'-deletion mutant -573 was unable to respond to wounding but did respond to sucrose and SA. The 3'-deletion analysis indicated the presence of a sucrose-responsive element between -574 and -520. A study of the insertion mutants revealed the function of another sucrose-responsive element between -522 and -500. Enhancer effects of these sucrose-responsive elements were inhibited by SA. These studies suggest that SA inhibits PI-II promoter activity by decreasing the sucrose response. Analysis of SA-related chemicals revealed that only acetyl-SA showed a similar inhibitory effect, and other hydroxybenzoic acids had little or no effect on the sucrose enhancer activity. Therefore, it seems that the interaction between SA and the receptor molecule is specific.

Sucrose mimics the light induction of Arabidopsis nitrate reductase gene transcription.

Nitrate reductase, the first enzyme in nitrate assimilation, is located at the crossroad of two energy-consuming pathways: nitrate assimilation and carbon fixation. Light, which regulates the expression of many higher-plant carbon fixation genes, also regulates nitrate reductase gene expression. Located in the cytosol, nitrate reductase obtains its reductant not from photosynthesis but from carbohydrate catabolism. This relationship prompted us to investigate the indirect role that light might play, via photosynthesis, in the regulation of nitrate reductase gene expression. We show that sucrose can replace light in eliciting an increase of nitrate reductase mRNA accumulation in dark-adapted green Arabidopsis plants. We show further that sucrose alone is sufficient for the full expression of nitrate reductase genes in etiolated Arabidopsis plants. Finally, using a reporter gene, we show that a 2.7-kilobase region of 5' flanking sequence of the nitrate reductase gene is sufficient to confer the light or the sucrose response.

Sensory responses, dietary-induced obesity and biochemical values in Sprague-Dawley rats

Food intake and body weight gain variability in Sprague-Dawley (SD) rats exposed to a palatable high-fat diet were examined in relation to sensory responses and biochemical parameters in two experiments. In the first experiment, varying sucrose concentrations (4–32% wt./vol.) were randomly presented for 20 minutes to ad lib chow-fed rats. Each rat's sensory response was expressed as Beta (B), or the slope of the regression between solute intake and concentration, and used to assign rats to diet groups. In the second experiment, responsiveness to fat emulsions (1–37%) were similarly measured and categorized. In both experiments sensory responses to sucrose were significantly related to weight gain/ fatness on the high-fat diet (lab chow-corn oil). Sensory responsiveness to the fat emulsions was unrelated to sucrose responsiveness or to high-fat feeding. Biochemical parameters (insulin, cholesterol, triglycérides, lipoproteins) reflected increased caloric (fat) intake, as well as sucrose responsiveness. Predictors (sensory responses, biochemical values) of response to chronic (4 months) or short-term (<2 months) high-fat diets are discussed.

Specificity of amiloride inhibition of hamster taste responses

Amiloride, a blocker of epithelial sodium channels, was found to have significant effects on electrophysiological and behavioral taste responses in the golden hamster ( Mesocricetus auratus). Recordings from the whole chorda tympani nerve showed that amiloride rapidly, reversibly, and competitively inhibited responses to NaCl applied to the anterior tongue. The apparent dissociation constant for amiloride binding, extrapolated to zero NaCl concentration, was 10 nM, a value comparable to estimates for various transporting tight epithelia. Recordings from single chorda tympani nerve fibers showed that 10 μM amiloride completely inhibited responses of Na-selective N fibers but had minimal effect on responses of electrolyte-sensitive H fibers, even though both types of fibers responded well to 0.1 M NaCl. Sucrose responses were not affected by amiloride. Addition of 100 μM amiloride to 0.1 M NaCl consistently increased consumption of NaCl in two-bottle drinking tests. These data suggest that one mechanism by which the taste of NaCl is sensed, which does not require adsorption or a second messenger, involves entry of Na + into taste bud cells through an amiloride-blockade sodium channel. Taste bud cells utilizing this mechanism exclusively activate N fibers, which are involved in the control of NaCl intake. A different mechanism for the detection of NaCl and other electrolytes is utilized by taste bud cells that activate H fibers.

Responses from parabrachial gustatory neurons in behaving rats

1. The responses of a total of 70 single neurons were recorded from the parabrachial nuclei (PBN) in awake rats. In 59 neurons, sapid stimuli (0.5 ml) elicited significant taste responses. Of these 59 neurons, 10 also had significant responses to water. The mean spontaneous rate of the taste neurons was 13.4 +/- 6.9 (SD) spikes/s. Of the remaining 11 neurons, 9 responded significantly only to water; 2 had no significant responses to the standard fluid stimuli. 2. Based on the magnitude of their response to our four standard stimuli, the taste neurons were classified as follows: 42 NaCl-best, 14 sucrose-best, 2 citric acid-best, and 1 QHCl-best. Of these, 25 responded only to one of four sapid stimuli; 20 of these specific cells responded only to NaCl. All the remaining 34 neurons responded to two or more of the four sapid stimuli, with NaCl and sucrose responsiveness dominant. For the 59 taste neurons, the mean entropy for the absolute value of the responses was 0.68; for the excitatory activity alone, it was 0.58. 3. The mean responses to NaCl and sucrose concentration series increased monotonically. Except at the lowest concentration, responses to citric acid also increased monotonically, but with a lower slope. Mean responses to QHCl, however, remained stable or even decreased with increasing concentration. Thus the power functions for the NaCl and sucrose intensity-response series were higher than those of citric acid and QHCl. 4. A hierarchical cluster analysis of 59 parabrachial neurons suggested four different categories: NaCl-best, sucrose-best, citric acid-best, and QHCl-best. These categories were less evident in the two-dimensional space produced by multidimensional analysis, because the positions of NaCl- and sucrose-best neurons formed a continuum in which neural response profiles change successively from sucrose-specific to NaCl-specific. 5. The results were consistent with previous anatomic and neurophysiological data suggesting convergence in the medulla of sensory input from receptors in the nasoincisor ducts (NID) and on the anterior tongue (AT). Taste buds in the NID respond preferentially to sucrose, whereas those on the AT respond more to NaCl.(ABSTRACT TRUNCATED AT 400 WORDS)

Interaction Between Fructose and Glucose on the Regulation of the Nuclear Precursor for mRNA-S14

We have examined the mechanism of the carbohydrate induction of rat hepatic mRNA-S14 to the intragastric administration of sucrose and its constituent hexoses, fructose and glucose. A maximal sucrose response (26-fold) was obtained with 2 ml of 60% sucrose/100 g of body weight, yet equimolar concentrations of fructose and glucose were not able to reproduce the response. Fructose yielded less than one-third the response observed with sucrose, whereas glucose administration was ineffective. On the other hand, the simultaneous administration of both hexoses restored the full response observed with sucrose. The synergism between fructose and glucose was not due to the administration of extra calories or enhanced insulin release but was correlated with altered carbohydrate metabolism as reflected by the hepatic pyruvate content (0.058 +/- 0.003 mumol/g fasting, 0.067 +/- 0.009 glucose treated, 0.218 +/- 0.030 fructose treated, 0.292 +/- 0.015 sucrose treated). The time course of induction of mRNA-S14 nuclear precursor in response to fructose, glucose, or sucrose correlated with the mature mRNA-S14 values. In addition, enhanced transcriptional activity of the S14 gene was observed after sucrose feeding (from 25 +/- 8 ppm baseline to 108 +/- 40 ppm at 4 h) and fructose feeding (40 +/- 21 ppm at 4 h). These studies demonstrate that the carbohydrate regulation of mRNA-S14 is due to a synergistic interaction between fructose and glucose reflected in the hepatic pyruvate content and leading to the induction of the nuclear precursor with an associated increase in transcriptional activity of the S14 gene.

Effects of isoproterenol treatment on gustatory neural responses in three inbred strains of mice

1. 1. Treatment of a β-agonist, isoproterenol, for 5 days reduced chorda tympani responses to sucrose by about 40% of the control without affecting responses to other taste stimuli, such as NaCl, HC1 and quinine HC1, in BALB/cCrSlc mice whereas such reduction of sucrose responses was not observed in C57BL/6-CrSlc and C3H/HeSlc mice, although in the latter two strains long-lasting off-responses to quinine HC1 appeared after the treatment. 2. 2. In BALB mice, the magnitude of reduction of sucrose responses by isoproterenol increased with prolonging the treatment from 1 to 5 days, although it reached almost its maximum level by the 3 days treatment. 3. 3. BALB mice with the removal of the submandibular glands showed slightly greater control responses of the chorda tympani nerve to sucrose than BALB mice with the sham-operation or the removal of the sublingual glands, and showed no significant reduction of sucrose responses by isoproterenol treatment. 4. 4. These results suggest that isoproterenol probably did not act directly on sweetener receptors of taste cell membranes but affect them through the submandibular salivary system.

Inhibitory effects of some heavy metal ions on taste nerve responses in mice.

Effects of treating the tongue with 7 heavy metal salts on chorda tympani nerve responses to sweet, salty, sour, and bitter stimuli were studied in ddy mice. CuCl2 and ZnCl2 at 10(-5) M inhibited responses to sucrose and Na saccharin without affecting responses to the other taste stimuli. Inhibition of responses to sweet stimuli was reversible, but recovery was very slow. No such selective inhibition of sweet responses was observed with FeSO4, MnCl2, CoCl2, NiCl2 or CdCl2. FeSO4 (1 mM) had a very small effect on all responses. CdCl2 (1 mM) depressed responses to all the stimuli to some extent. MnCl2, CoCl2, and NiCl2 (1 mM) slightly inhibited responses to NaCl and quinine hydrochloride, but not HCl. Responses to sweet stimuli were slightly inhibited by 1 mM MnCl2 or CoCl2. Kinetic analyses of the inhibition of sucrose responses by CuCl2 indicate that it is a competitive inhibition. Based on the results it is hypothesized that Cu2+ and possibly Zn2+ also compete with sweet-tasting molecules for receptor proteins while other heavy metal ions do not possess a strong ability to bind to the proteins.

Ethanol reinforced responding in the rat: Relation of ethanol introduction to later ethanol responding

Rats, maintained on ad lib food and water, were trained to lever press on a concurrent schedule using water and sucrose (10% w/v) as the fluids presented contingent on responding. Each fluid was associated with a lever and available on a fixed ratio eight (FR8) response requirement. The lever with which each fluid was paired was alternated daily. When stable responding occurred, ethanol was substituted for water, first at low concentrations, and then slowly increased to 5% (v/v). When stable sucrose-ethanol responding was reached, the response requirement for sucrose was altered to fixed ratio requirements of either FR32 or FR64. Moderate, but unstable increments in the number of ethanol responses occurred during the increased sucrose response requirements. Following the sucrose response requirement manipulation, water was substituted for the sucrose. Ethanol responding was found to fall to or below prior baseline levels. Weight reduction by food restriction failed to increase ethanol responding. The levels of ethanol responding resulting from this introduction procedure were always much lower independent of body weight than previously reported levels found in rats trained to respond for ethanol using a different procedure of initial ethanol introduction.

Development of chorda tympani taste responses in rat.

To learn whether neurophysiological taste responses change during structural development of the gustatory system, we recorded from the chorda tympani nerve in rats aged 7 to 92 days after birth. Chemical stimuli applied to the anterior tongue included four monochloride salts, two acids, sucrose, and urea. Responses to all chemicals were obtained as early as 7 days postnatally. Developmental changes in salt, acid, and sucrose responses were observed. Relative to NaCl and LiCl, NH4Cl and KCl gradually decrease in effectiveness as taste stimuli; or, relative to NH4Cl and KCl, NaCl and LiCl become more effective stimuli. These changes are similar to those observed prenatally and postnatally in sheep. Also, relative to NaCl, citric acid, hydrochloric acid, and sucrose become less effective stimuli; or, NaC1 becomes more effective as a stimulus, relative to these acids and sucrose. The period of most rapid functional change overlaps a period of rapid structural change. It seems most reasonable to hypothesize that the altering taste responses reflect developmental changes in receptor membrane composition. Since the taste system is not programmed to respond in a mature manner from the moment function begins, there is ample opportunity for changing taste experience to influence the developing taste system.

Advantages of fructose over sucrose and glucose Endocrine responses to sugar ingestion in man

Advantages of fructose over sucrose and glucose Endocrine responses to sugar ingestion in man