Sweet Taste Of Sucrose Research Articles

An attempt to condition flavour preference induced by oral and/or postoral administration of 16% sucrose in pigs

The present study investigated the acquisition of conditioned flavour preferences in pigs using the caloric value and/or sweet taste of sucrose. Nine water-deprived juvenile pigs were given four three-day conditioning sessions during which they received flavoured solutions as conditioned stimuli (CS). The CS solutions were paired with three treatments that generated a gustatory and/or a caloric reinforcement (US). The CS++ solution was added with 16% sucrose and paired with an intraduodenal (ID) infusion of water, the CS+ solution was paired with an ID infusion of 16% sucrose and the CS− solution was paired with an ID infusion of water. One and two weeks after conditioning, the water-deprived pigs were subjected to two-choice preference tests with the unreinforced CS solutions. Solutions intake, behavioural activity and some drinking parameters were measured. Despite no difference in CS intake during conditioning, the animals spent less time inactive and more time standing during CS++ than CS+ conditioning. When receiving CS++, the pigs explored the drinking trough more than when receiving CS−. Compared to the CS− condition, the numbers of drinking episodes and intra-drinking episode (IDE) pauses were also 36% and 49% lesser in the CS++ condition, but these differences were not significant. During the two-choice tests, the pigs did not show significant preferences. Nevertheless, during the first session, the pigs seemed to show a slight preference for the CS++ (57% of total intake) compared to CS+. The duration of CS++ drinking episodes represented 64% of the total duration compared to CS+ and CS− . The total time spent drinking the CS++ also represented 57% of the total time in the CS++ vs. CS– test. To conclude, although no clear-cut preferences were found during two-choice tests, the oral perception of 16% sucrose during conditioning induced changes in behavioural activities, motivational responses and microstructure of CS intake, suggesting the importance of oral food perception for food selection processes in pigs. Further studies are needed to investigate the impact of water deprivation on the expression of flavour preferences in pigs.

Selective dopaminergic lesions of the ventral tegmental area impair preference for sucrose but not for male sexual pheromones in female mice

The role of the meso-accumbens dopaminergic pathway in reward-related behaviours is the subject of intense investigation. In this regard, here we analyse the effects of specific lesions of dopaminergic cells of the ventral tegmental area (VTA) of female mice on two goal-directed behaviours, namely sucrose preference (intake of sucrose solution vs. water) and preference for male sexual pheromones (exploration of male-soiled vs. clean bedding). The results indicate that partial lesions of the VTA that impair neither locomotion nor general exploratory behaviour reduce the preference for sucrose (over a 48-h period) but do not alter the innate attraction that females display for male sexual pheromones (in 5-min tests). This differential effect of the lesions can be interpreted as demonstrating the existence of separate neural mechanisms and circuits for signalling the reward of different natural reinforcers (e.g. sweet taste of sucrose and sexual pheromones). Alternatively, VTA lesions may result in an impaired attribution of incentive salience (which depends on the dopaminergic tegmento-striatal system) of sucrose-predicting cues, thus leading to a long-term decrease in sucrose consumption. By contrast, the same lesions do not affect the unconditioned attraction to male-derived pheromones, which may depend on amygdalo-striatal pathways.

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.

Pharmacology of Flavor Preference Conditioning in Sham-Feeding Rats: Effects of Dopamine Receptor Antagonists

YU, W.-Z., R. M. SILVA, A. SCLAFANI, A. R. DELAMATER AND R. J. BODNAR. Pharmacology of flavor preference conditioning in sham-feeding rats: Effects of dopamine receptor antagonists. PHARMACOL BIOCHEM BEHAV 65(4) 635–647, 2000.—Opioid and dopamine systems are both implicated in the response to sweet solutions. Our laboratory previously reported that the opioid antagonist, naltrexone, reduced the intake of sweet solutions, yet had little or no effect on sucrose-conditioned flavor preferences in sham-feeding rats. The present study examined the role of dopamine D 1 and D 2 receptors in the expression of flavor preferences conditioned by the sweet taste of sucrose. All sessions were conducted under sham-feeding conditions to minimize postingestive influences. Training was accomplished by adding a novel flavor (CS+) to a 16% sucrose solution, a different flavor (CS−) to a less-preferred 0.2% saccharin solution in alternating, one-bottle sessions. Preferences were assessed in two-bottle tests with the CS+ and CS− flavors presented in mixed sucrose (8%)–saccharin (0.1%) solutions following systemic doses of 0, 50, 200, 400, or 800 nmol/kg of the D 2 antagonist, raclopride (Experiment 1) or the D 1 antagonist, SCH23390 (Experiment 2) under either food-restricted or unrestricted conditions. Rats significantly preferred the CS+ solutions in vehicle tests, and displayed equipotent and dose-dependent reductions in total intake and CS+ preference following either D 1 or D 2 receptor antagonism. Similar results were obtained with SCH23390 and raclopride in Experiment 3 conducted with water-restricted rats. These data indicate that dopaminergic D 1 and D 2 receptors play pivotal and functionally equivalent roles in the expression of flavor preferences conditioned by the sweet taste of sucrose.

Pharmacology of Flavor Preference Conditioning in Sham-Feeding Rats: Effects of Naltrexone

YU, W.-Z., A. SCLAFANI, A. R. DELAMATER AND R. J. BODNAR. Pharmacology of flavor preference conditioning in sham-feeding rats: Effects of naltrexone. PHARMACOL BIOCHEM BEHAV 63(4) 573–584, 1999.—Relatively little is known about the neurochemical and pharmacological mechanisms involved in flavor preference learning. The present study examined the ability of the opioid antagonist, naltrexone to alter the acquisition and expression of flavor preferences conditioned by the sweet taste of sucrose. This was accomplished by adding a novel flavor (the CS+) to a sucrose solution, and a different flavor (the CS−) to a less-preferred saccharin solution. Rats were trained to drink these solutions with an open gastric fistula (sham-feeding), which minimized postingestive actions. Food-restricted (Experiments 1 and 2A) and ad lib-fed (Experiment 2B) rats were given either limited (Experiment 1) or unlimited (Experiment 2) access to the CS+ and CS− solutions during one-bottle training. Preferences were assessed in two-bottle tests (with the CS+ and CS− flavors presented in mixed sucrose–saccharin solutions) following vehicle or naltrexone (0.1–10 mg/kg, SC) treatment. The rats displayed significant CS+ preferences following vehicle, particularly after unlimited access training. In four of five experiments, naltrexone significantly reduced total intakes during the two-bottle, sham-feeding tests. Except for one instance, however, the drug failed to block the preference for the CS+ flavor over the CS− flavor. The effects of naltrexone (0.1 mg/kg) on the acquisition of flavor preferences were studied in sham-feeding rats under limited (Experiment 3A) and unlimited (Experiment 3B) training access conditions. Rats treated with naltrexone during training displayed similar CS+ preferences as did saline-treated rats, even though they consumed less CS+ during training. The naltrexone-trained rats also displayed smaller reductions in total or CS+ intakes than did saline-trained rats when all rats were treated with a 2.5 mg/kg dose of naltrexone during testing. As in previous studies, these results show that naltrexone significantly reduces the intake of sweet solutions, yet it has little or no effect on the acquisition or expression of flavor preferences conditioned by sucrose in sham-feeding rats.