Two-bottle Tests Research Articles

TASTE RESPONSIVENESS TO FOOD-ASSOCIATED ACIDS IN THE SQUIRREL MONKEY (Saimiri sciureus)

The taste responsiveness of six adult squirrel monkeys to five food-associated acids was assessed in two-bottle preference tests of brief duration (5 min). In experiment 1 the monkeys were given the choice between tap water and defined concentrations of citric acid, ascorbic acid, malic acid, acetic acid, or tannic acid dissolved in tap water. In experiment 2 the animals were given the choice between a 50 mM sucrose solution and defined concentrations of the same acids dissolved in a 50 mM sucrose solution. With both procedures Saimiri sciureus significantly discriminated concentrations as low as 10 mM ascorbic acid and acetic acid, 5 mM citric acid and malic acid, and 0.2 mM tannic acid from the alternative stimulus. The results showed: (1) that squirrel monkeys respond to the same range of acid concentrations as other nonhuman primate species tested so far, (2) that Saimiri sciureus detects food-associated acids at concentrations well below those present in most fruits, and (3) that the responsiveness of this New World primate to acidic tastants was largely unaffected by the addition of a sweet-tasting substance. The results support the assumption that squirrel monkeys may use sourness and/or astringency of food-associated acids as a criterion for food selection.

Frugivory and taste responses to fructose and tannic acid in a prosimian primate and a didelphid marsupial

The taste responses to sweet and astringent compounds were investigated in two mammals of similar ecology, by using the classical method of the two-bottle test. The taste threshold for fructose was higher in Microcebus murinus, a prosimian primate, than in Caluromys philander, a didelphid marsupial. The profiles of suprathreshold responses resembled a dissymmetric bell-shaped curve, but the rate of consumption of sweet solutions up to maximal intake increased more rapidly in Microcebus than in Caluromys. Despite showing a photoperiod-synchronized physiology, Microcebus displayed no seasonal variation of the taste threshold and suprathreshold responses. The depressing effect of tanning acid on the ingestion of fructose solutions increased progressively with tannin concentration and was lower as fructose concentration increased. Inhibition thresholds for tannic acid were similar between the two species. The data suggest that adaptation to frugivorous diets is associated with globally similar shaping of the taste responses, even though subtle differences of palatability may account for differences of feeding selectivity.

Histaminergic Activation of Endogenous Angiotensin II Fails to Inhibit Alcohol Intake in Rats

Demonstrations that alcohol intake can be inhibited by pharmacological activation of the renal renin–angiotensin system (RRA) or injection of angiotensin II (ANG II) in rats led to this study of a role for endogenous ANG II in inhibition of alcohol intake in rats. Relatively small doses of histamine, above threshold for eliciting drinking of water and activation of the RRA, were injected SC in adult male Sprague–Dawley rats with access to 3.0% alcohol in 45-min one-bottle alcohol tests and in two-bottle tests in which alcohol and water were available at the midpoint of the 12-h dark phase. The 0.312 and 1.25 mg/kg doses of SC histamine elevated plasma renin activity to levels similar to those in rats that had just eaten food. Neither dose of histamine affected alcohol intake in one-bottle tests. A relatively large 10 mg/kg dose of histamine increased alcohol intake in a one-bottle test, but decreased alcohol intake and increased water intake in two-bottle tests. The inhibitory effect of the 10 mg/kg dose of histamine on alcohol intake was completely blocked by SC 10 mg/kg losartan, a selective AT 1 angiotensin receptor antagonist. This 10 mg/kg dose of losartan given alone, however, failed to increase alcohol intake in one- or two-bottle tests. These results generally do not support a role for endogenous ANG II as an inhibitory physiological signal in the control of alcohol ingestion in rats, because histaminergic activation of RRA, using small but physiologically meaningful doses of histamine, failed to inhibit alcohol intake.

Modification of Behavioral and Neural Taste Responses to NaCl in C57BL/6 Mice: Effects of NaCl Exposure and DOCA Treatment

To investigate the possible role of peripheral gustatory responsiveness to changes in NaCl acceptance, we studied NaCl consumption and the chorda tympani nerve responses to lingual application of NaCl in C57BL/6ByJ mice. The mice were treated with 300 mM NaCl (given to drink in 96-h two-bottle tests with water) or with injections of deoxycorticosterone acetate (DOCA; 33 mg/kg daily). Naı̈ve mice were neutral to 75 mM NaCl, but mice previously exposed to 300 mM NaCl avoided 75 mM NaCl. The NaCl-exposed (300 mM for 4 days and 75 mM for 2 days) mice had enhanced amiloride-sensitive components of the chorda tympani responses to 10–30 mM NaCl applied at room temperature (24°C). DOCA injections increased acceptance of 300 mM NaCl, but did not change the chorda tympani responses to 100–1000 mM NaCl. However, the DOCA-treated mice had enhanced amiloride-sensitive components of the chorda tympani responses to cold (12°C) 10–30 mM NaCl. These data suggest that peripheral gustatory responsiveness possibly contributes to the NaCl aversion induced by exposure to concentrated NaCl, but not to the DOCA-induced increase of NaCl acceptance.

Calcium-Deprived Rats Avoid Sweet Compounds

To characterize the link between calcium status and sweet solution intake, rats fed a diet containing 25 mmol Ca2+/kg (Ca-25, low calcium) or 150 mmol Ca2+/kg (Ca-150, control) were given 48-h two-bottle tests with a choice between water and various concentrations of a nutrient (sucrose, Polycose, ethanol and/or corn oil). Rats fed the Ca-25 diet had significantly lower sucrose intakes and preferences over the entire range tested (10–320 g/L) even though the same (Experiment 1), or identically treated (Experiment 2a) rats had normal Polycose and ethanol intakes and normal (Experiment 1, 2b) or significantly greater (Experiment 2a) corn oil intakes. In additional tests, rats fed the Ca-25 diet had significantly lower intakes relative to rats fed the Ca-150 diet of other sweeteners (30 mmol/L D-phenylalanine, 1 mmol/L saccharin and 0.3 mmol/L aspartame), significantly higher intakes of 0.5 mg/L capsaicin and 300 mmol/L monosodium glutamate, and normal intakes of 10 g/L or 80 g/L safflower oil and 10 g/L peanut oil. In a three-cup macronutrient selection experiment (Experiment 3), calcium-deprived rats ate significantly less of a high sucrose carbohydrate source and significantly more of a protein source than did controls. These results suggest that calcium deficiency reduces the rat’s liking for sweetness, irrespective of the type or form of sweetener, and that this is not due to a general reduction in energy intake.

Ketamine blocks a conditioned taste aversion (CTA) in neonatal rats 1

MICKLEY, G. A., M. A. SCHALDACH, K. J. SNYDER, S. A. BALOGH, T. LEN, K. NEIMANIS, P. M. GOULIS, J. HUG, K. SAUCHAK, D. R. REMMERS-ROEBER, C. WALKER AND B. K. YAMAMOTO. Ketamine Blocks a Conditioned Taste Aversion (CTA) in Neonatal Rats. PHYSIOL BEHAV 64(3) 381–390, 1998.—These experiments explored the effects of glutamate, N-methyl- d-aspartate (NMDA) receptor blockade on the formation, retention, and expression of conditioned taste aversion (CTA) in young rats. Previous data from our laboratory suggested that ketamine administration potentiates a CTA in E18 rat fetuses. The current studies investigated this phenomenon in neonates. High-pressure liquid chromatography (HPLC) methods were used to determine the amount of ketamine that must be injected intraperitoneally (i.p.) to achieve brain ketamine levels in neonates comparable to those found in the fetuses from our previous experiments. Then, on their day of birth, Sprague–Dawley rat pups received injections of either 0.1, 10, or 70 mg/kg of ketamine HCl, i.p. or a Sal control injection. One-half hour later, pups were injected orally with either Saccharin (Sac; 10 μL of 0.3%) or water followed by an injection of either lithium chloride (LiCl; 81 mg/kg) or Sal (i.p.). The CTA was evaluated in two different tests. Two weeks after conditioning, the dam was anesthetized and the frequency with which pups attached to Sac-painted nipples versus nipples painted with water was measured (i.e., the nipple taste test, NTT). Controls for state-dependent learning were run in which 10 mg/kg of ketamine or saline (Sal) was administered before both taste aversion conditioning and the NTT. After weaning, the CTA was also evaluated by measuring the amount of Sac (0.3%) or water consumed during a two-bottle test. Neonates that received Sal control injections before the Sac + LiCl pairing acquired CTAs and avoided Sac-painted nipples. However, the pups injected with ketamine on the conditioning day only (P0) did not avoid Sac-painted nipples (as compared to controls). Pups that had ketamine both at the time of CTA training and testing, or just before the NTT, also failed to avoid Sac-painted nipples. Ketamine’s acute effects apparently influenced the outcome of the NTT of state-dependent control subjects. Rat pups that received the highest doses of ketamine (10 or 70 mg/kg) and tasted Sac on P0 later failed to show a neophobia for Sac-painted nipples. Whereas, rat pups that received the high dose of ketamine and water on P0, later exhibited a neophobic response. These data suggest that ketamine did not impair the animal’s ability to taste Sac. These data reflecting a ketamine-induced blockade of neonatal CTAs may be contrasted with our previous findings in which ketamine potentiated fetal CTAs. However, they are in consonance with data from adult rats suggesting that ketamine can cause an amnesia for CTAs. NMDA receptor blockade may shape memory formation in a manner that is dependent on the stage of brain development.

Consumption of electrolytes and quinine by mouse strains with different blood pressures 1

BACHMANOV, A.A., G. SCHLAGER, M.G. TORDOFF AND G.K. BEAUCHAMP. Consumption of electrolytes and quinine by mouse strains with different blood pressures. PHYSIOL BEHAV 64(3) 323–330, 1998.—Daily fluid intakes were measured using two-bottle tests in female mice of inbred strains with high (BPH/2), normal (BPN/3) or low (BPL/1) blood pressure. The mice were offered a choice between water and different concentrations of NaCl (37.5–600 mM), KCl (1–400 mM), CaCl 2 (1–100 mM) and quinine hydrochloride (0.003–1.0 mM). Compared with the normotensive strain, the hypertensive mice had higher water and total fluid intakes, and lower intakes of NaCl, KCl (only 200 mM) and quinine; the hypotensive mice had higher intakes of KCl (only 10–50 mM) and lower intakes of CaCl 2 and quinine. These data suggest that fluid and salt intake are not linearly related to blood pressure, but are independently determined in these strains. Certain concentrations of the salts were preferred relative to water, which depended on mouse genotype: the BPN/3 and BPL/1 mice strongly preferred 37.5–150 mM NaCl, the BPL/1 mice preferred 10–100 mM KCl, and the BPN/3 mice preferred 1–10 mM CaCl 2.

Increased flavor acceptance and preference conditioned by the postingestive actions of glucose

PEREZ, C., F. LUCAS AND A. SCLAFANI. Increased flavor acceptance and preference conditioned by the postingestive actions of glucose. PHYSIOL BEHAV 64(4) 483–492, 1998.—In Experiment 1, rats were given daily 2-h access to chow and water and 20-h access to flavored solutions (cherry or grape). On alternate days, one flavor (CS+) was paired with intragastric infusions of 16% glucose and another flavor (CS−) with IG water. In subsequent choice tests, the rats strongly preferred (95%) the CS+ to the CS−. CS+ intake also greatly exceeded CS− intake during one-bottle training sessions (71 vs. 18 g/20 h). This increased acceptance was due to both increased bout size and number. When CS+ was paired with IG water (extinction test), CS+ bout size declined to CS− levels, while CS+ bout number and total intake remained elevated. In Experiment 2, rats trained with sucrose octa acetate and citric acid solutions also showed increased CS+ acceptance and preference in one- and two-bottle tests, respectively. The rats also consumed more CS+ than CS− during short-term (30 min/day) one-bottle tests and intraoral intake tests under both deprived and ad lib. feeding conditions. These results demonstrate that the postingestive actions of glucose can condition substantial increases in flavor acceptance as well as flavor preference.

A common polygenic basis for quinine and PROP avoidance in mice.

Inbred strains of mice (Mus musculus) differ greatly in ability to taste various bitter compounds. For some compounds, the differences result from allelic variation at a single locus. However, segregation patterns incompatible with monogenic inheritance have been found for quinine avoidance. The Soa bitter sensitivity locus exerts some influence on this phenotype, but an unknown number of other loci also contribute. Relative avoidance patterns for quinine sulfate in panels of naive inbred strains resembled avoidance patterns for 6-n-propyl-2-thiouracil (PROP), suggesting a common genetic basis. In particular, C57BL/6J mice strongly avoided both 0.1 mM quinine sulfate and 1 mM PROP in two-bottle preference tests, whereas C3H/HeJ mice were indifferent to both. Therefore, 12 BXH/Ty recombinant inbred strains, derived from these strains, were tested with both solutions to begin identification of the unknown bitter loci. Naive mice were tested for four consecutive days with each compound (order counterbalanced). Some BXH/Ty strain means resembled those of the parent strains, but others were intermediate. This indicated recombination among loci affecting avoidance, and therefore polygenic inheritance. The strain means were highly correlated across compounds (r = 0.98), suggesting that the same polygenes controlled both phenotypes. The BXH/Ty means for both compounds were then compared with the strain genotypes at 212 chromosome position markers distributed throughout the genome. Eight markers on five chromosomes (3, 6, 7, 8 and 9) yielded significant correlations. Six of the markers were correlated with both phenotypes, again suggesting common polygenic inheritance. The marker with the highest correlation was Prp, tightly linked to Soa on chromosome 6. The correlated marker regions likely contain quantitative trait loci affecting bitter avoidance. The phenotypic similarity of PROP to quinine, rather than to phenylthiourea, apparently stemming from a common polygenic basis, indicates a difference between mice and humans in gustatory organization related to bitters.

Flavor preferences conditioned by intragastric sugar infusions in rats: maltose is more reinforcing than sucrose

AZZARA, A.V. AND A. SCLAFANI. Flavor preferences conditioned by intragastric sugar infusions in rats: maltose is more reinforcing than sucrose. PHYSIOL BEHAV 64(4) 535–541, 1998.—Prior research indicates that glucose conditions much stronger flavor preferences in rats than does fructose. This could occur because intestinal absorption of fructose is much slower than that of glucose and because fructose malabsorption may have aversive consequences. Fructose absorption is facilitated when glucose is also present in the gut. The present study therefore compared the flavor conditioning effects of maltose (a glucose + glucose disaccharide) to those of sucrose (a glucose + fructose disaccharide). In Experiment 1, rats had different flavors paired with intragastric infusions of 32% maltose (CS+M), 32% sucrose (CS+S), and water (CS–) 23 h/day. In subsequent two-bottle tests, both CS+ solutions were strongly preferred to the CS–, but the CS+M was also preferred (78%) to the CS+S. Experiment 2A revealed that the rats also learned to prefer a CS+M to a CS+S when 16% sugar infusions were used. In Experiment 2B, the same rats preferred a flavor paired with 16% maltose to a flavor paired with 8% maltose. They did not reliably prefer a flavor paired with 16% sucrose to a flavor paired with 8% maltose. These results demonstrate that the postingestive actions of maltose are more reinforcing than those of sucrose. This indicates that fructose is less reinforcing than glucose even when malabsorption is not a factor. In contrast to their preference for the CS+M over the CS+S, the rats preferred sucrose to maltose when drinking the sugars by mouth. Therefore, sugar preferences mediated by oral taste receptors differ from those conditioned by postoral nutrient detectors.

Measuring Gustatory Variation in Mice: A Short-term Fluid-Intake Test

KOTLUS, B. S. AND D. A. BLIZARD. Measuring gustatory variation in mice: A short-term fluid-intake test. Physiol Behav 64(1) 37–47, 1998. A short-term fluid-intake test is described which is directed at the study of individual variation in gustation in laboratory mice. To avoid position preferences associated with two-bottle tests, single graduated cylinders are used to present the solution. Intake of water and solutions is recorded for a 6-h period beginning 3 h prior to the dark phase of the light cycle. The timing of data collection ensures a stable baseline of fluid intake because it coincides with the period in which mice begin to drink. Food and water are available ad lib. at all other times so the test avoids the water restriction that is often used in gustatory studies. We report normative data on ten commonly used inbred strains for sucrose (100 m m), saccharin (10 m m), quinine (1.1 m m), HCl (1 and 3 m m), NaCl (320 m m), and monosodium glutamate (150 m m). Strain differences were pronounced for all tastants. Concurrent measures of food and fluid intake by C57BL/6J and DBA/2J mice demonstrated that the short-term reduction of fluid intake resulting from 6-h quinine administration, which was restricted to C57BL/6J mice, was associated with a minor reduction in food intake during the 6-h test and had no statistically significant effect on food or fluid intake during the 18-h post-test period or during a 6-h period the next day. The absence of large-scale or persistent nonspecific effects supports the use of the paradigm for screening of multiple solutions on the same animals. The reliability of the test is supported by positive correlations between repeated measurements of the same solution across substantial time intervals. Its ease of use, substantial reliability, and avoidance of water restriction make the test a very useful addition to screening tools in the field of gustation research.

Failure to Change Exploration or Saccharin Preference In Rats Exposed to Chronic Mild Stress

HARRIS, R. B. S., J. ZHOU, B. D. YOUNGBLOOD, G. N. SMAGIN AND D. H. RYAN. Failure to change exploration or saccharin preference in rats exposed to chronic mild stress. PHYSIOL BEHAV 63(1) 91–100, 1998.—Chronic mild stress (CMS) exposes animals to unpredictable stressors. Reduced consumption of sucrose or saccharin solutions by CMS rats has been used as a putative measure of anhedonia, typical of depression. Our objective was to determine whether saccharin consumption and preference and suppression of exploratory and rearing behaviors in the open field were reliable indicators of CMS-induced behavioral depression. In Experiment 1, male Wistar rats subjected to 6 weeks of CMS consumed significantly less food and gained less weight than controls. CMS did not effect saccharin intake, or preference, measured in a two-bottle test with water. CMS rats exposed to a novel open field showed increased exploration and rearing. In a second test, performed immediately after a novel stress of restraint, there were no differences in exploratory or rearing behavior of CMS and control rats. In Experiment 2, CMS was reduced to 3 weeks and rats were single or group housed in their home cages. Open field activity of CMS rats was similar to that in Experiment 1. Saccharin preference of CMS rats was significantly suppressed when tested after 24 hours of water deprivation, but was not different from controls after 5 hours of water deprivation. In the final experiment Sprague Dawley rats behaved the same as Wistar rats in the CMS paradigm. Therefore, the CMS protocol used in these experiments did not induce behaviors indicative of depression but did cause a mild anorexia and weight loss. Saccharin intake of CMS rats was dependent upon their dehydration state and could not be attributed to stress-induced anhedonia.

Learned Suppression of Intake Based on Anticipated Calories: Cross-Nutrient Comparisons

Warwick, Z. S., K. J. Bowen and S. J. Synowski. Learned suppression of intake based on anticipated calories: Cross-nutrient comparisons. Physiol Behav 62(6) 1319–1324, 1997.—Following training with distinctively flavored solutions which differ in calories and thus in their postingestive effects, rats demonstrate flavor–postingestive consequence learning by preferentially consuming one of the flavors in two-bottle tests (both flavors presented in nutrient-identical solutions). The direction of the preference—for the flavor previously paired with more calories (F-hi) or for the flavor previously paired with fewer calories (F-lo)—depends critically upon the magnitude of postingestive effects experienced during training. The most frequent and more thoroughly investigated observation has been preferential consumption of F-hi (conditioned flavor preference). However, when relatively concentrated solutions (e.g., 5% and 30% sucrose) are used as the training nutrients, F-lo is preferentially consumed in two-bottle tests. This lesser intake of F-hi presumably reflects its previous association with the more potent satiating effect of the highly concentrated nutrient: conditioned satiety. The present series of experiments explored conditioned satiety across nutrient types. In each experiment, rats consumed 30 mL of distinctively flavored nutritive solution per day, alternating between a distinctively flavored high-calorie (1.6 kcal/mL) solution and a lower calorie (0.2 kcal/mL) solution containing a different flavor. Two-bottle testing evaluated whether conditioned satiety was evident. Experiment 1 found that rats trained with sucrose, fructose, glucose, maltodextrin, or saccharin-sweetened medium-chain triglyceride oil emulsion preferentially consumed F-lo in two-bottle tests. In contrast, rats trained with corn oil emulsions tended to preferentially consume F-hi. In Experiment 2, increasing the number of corn oil calories associated with F-hi produced a tendency toward preferential intake of F-lo in two-bottle tests. In Experiment 3, rats consumed a high-fat maintenance diet; sucrose-trained rats again consumed more F-lo than F-hi, whereas rats trained with corn oil emulsions showed a tendency (nonsignificant) to consume more F-lo in two-bottle tests. In Experiment 4, however, adding saccharin to corn oil emulsions did produce conditioned satiety. These findings demonstrate conditioned satiety as a robust phenomenon across various nutrient types; however, corn oil calories entrain conditioned satiety only under certain conditions.

Polyethylene glycol-induced calcium appetite.

Polyethylene glycol (PEG) has been used to investigate the physiological basis of sodium intake because it sequesters sodium from the extracellular fluid (ECF) and causes rats to drink concentrated NaCl solutions. To test the hypothesis that PEG also depletes ECF calcium and thus activates calcium intake, male Sprague-Dawley rats received two-bottle tests with a choice between a taste solution and water. Relative to intakes after control injections, rats injected with PEG (5 ml of 30% wt/wt sc) drank significantly greater volumes of several calcium solutions (0.1, 1, 10, or 32 mM CaCl2 or 10 or 100 mM calcium lactate). They also drank more 10 mM SrCl2, 300 mM NaCl, and 100 mM KHCO3, drank less 10 mM sodium saccharin, and did not alter intakes of 10 or 100 mM KCl, 32 mM NH4Cl, 10 mM AlCl3, 10 mM FeCl2, 100 mM CaCl2, or 1,000 mM NaCl. Thus PEG treatment produced an appetite that was specific to low and moderate concentrations of calcium, sodium, and perhaps bicarbonate. The physiological basis for this appetite was explored. At 24 h after PEG injection, plasma total calcium concentrations were either unaltered or increased, but plasma ionized calcium concentrations were reduced. Concentrations of parathyroid hormone and calcitonin but not 1 alpha, 25-dihydroxyvitamin D3 were elevated. Perhaps one or more of these changes in calcium homeostasis is responsible for the increased calcium intake. Whatever the mechanism, it is clear that PEG treatment induces an appetite for calcium in addition to the well-known appetite for sodium.

Unexpressed morphine conditioned salt aversion: procedural variants and hypertonicity of salt

Previous work has demonstrated that rats that received a sodium chloride (salt) solution paired with a high dose of morphine do not directly express a conditioned salt aversion (decreased intake) in a one-bottle test. Importantly, lithium conditioned salt aversions and morphine conditioned saccharin aversions are readily expressed. The present study examined two possible accounts of the failure for morphine conditioned salt aversion to be directly expressed. Experiment 1 eliminated an account based on procedural variations that were uncontrolled in the original salt and saccharin conditioning protocols ( Bevins et al., 1996). Experiment 2 eliminated a hypertonic account that argues that the high concentrations of salt in the previous work (1% and greater) interfered with direct expression of salt aversion by inducing continual drinking. Rats given a non-hypertonic salt solution (0.3%) paired with morphine still did not express a salt aversion in a one-bottle test. A two-bottle testing procedure, however, revealed a robust salt aversion with the non-hypertonic solution.

Taste reactivity in high-alcohol-sensitive and low-alcohol-sensitive rats

High, low, and control alcohol-sensitive (HAS, LAS, CAS, respectively) rats were tested for their perception of the taste of alcohol using the taste reactivity test. Reactivity tests with a single concentration of sucrose and quinine were also done. After initial taste reactivity, all rats were tested for alcohol consumption in a standard two-bottle test (water in the second bottle). Postconsumption taste reactivity tests completed the experiment. Results indicated that HAS, LAS, and CAS rats did not differ significantly in their taste reactivity response to a range of alcohol concentrations (5–40%), nor did they differ significantly in response to sucrose or quinine. Reactivity responses were similar for each group before and after the consumption tests. Despite the lack of line differences in taste reactivity, HAS and LAS rats consumed significantly less alcohol than the CAS rats during the two-bottle access tests. The present results are in contrast to research done with rats selectively bred for alcohol consumption (Alcohol Preferring and Nonpreferring rats, High Alcohol Drinking and Low Alcohol Drinking rats), which exhibit clear line differences in patterns of reactivity changes following alcohol access. The selection phenotype of alcohol sensitivity appears to be independent of rats' behavioral response to the taste of alcohol.

Uncontrollable water deliveries and subsequent finickiness

The present experiment investigated the alteration of ingestive behaviors as an outcome of exposure to uncontrollable water deliveries in order to examine the mechanisms underlying finickiness. The experiment employed a single treatment session during which rats were exposed to response-contingent, response-independent, or no-water deliveries in a triadic design. Subsequent two-bottle tests (quinine vs. water) conducted in the treatment apparatus revealed finickiness about the novel, bitter quinine solution in rats previously exposed to uncontrollable water deliveries. Thus, finickiness does not depend on the fear of aversive events, such as shock, but may be explained in terms of stress induction. The persistence of the finickiness effect for the 4 days of testing supports the interpretation that finickiness reflects a long-lasting associative component of helplessness.

Pain Sensitivity following Taste Aversion Conditioning: Analgesia Depends on the Method Used to Assess Taste Aversion Learning

Previous reports indicate that a conditioned analgesic response may be elicited by reexposure to a gustatory CS that has been previously paired with an analgesia-producing agent such as morphine. The current experiments examine the extent to which this observed analgesic response can be attributed to the particulars of the procedures used to assess conditioned taste aversion, rather than to a conditioning of an analgesic CR per se. Experiment 1 indicated that animals given pairings of a taste with lithium chloride (LiCl) will upon reexposure to the taste CS alone (one-bottle test) not only express a conditioned taste aversion, but will also express a decrease in pain sensitivity. This analgesic response was evident immediately following CS reexposure and 15 min following the assessment of taste aversion learning. The results further indicated that the analgesic response was unaffected by pretest administration of naloxone, indicating that the response was not mediated by opioid pain inhibition systems. Experiment 2 indicated that the analgesic response observed in the first experiment was not evident when taste aversion conditioning was assessed using a choice procedure (two-bottle test). Implications of these data for explanations of conditioned analgesia are discussed.

Liquid baits for rodent control: A comparison of wild Norway versus wild ricefield rat response to glucose plus saccharin solutions

A series of two-bottle tests were conducted with wild Norway ( Rattus norvegicus) and wild ricefield ( Rattus rattus mindanensis) rats to assess liquid bait consumption levels. Glucose, a natural sugar, and saccharin, an artificial sweetening agent, were tested against a combination of the sweeteners in water solution with each rat species. Water baseline data indicated that ricefield rats drank relatively more water per day. No species differences, however, were found for consumption levels of 3.0% glucose or for 0.125% saccharin when fluid intake levels were adjusted for mean body weight differences between species using metabolic size data transformations to yield relative consumption levels. A species difference was shown for relative consumption of the mixture of 3.0% glucose plus 0.125% saccharin in water solution with either sweetener as the alternate choice. Ricefield rats showed a two-fold increase in relative consumption of the mixture compared with solutions of either sweetener alone. Norway rats, in contrast, showed a synergistic six-fold increase in relative consumption of the mixture compared with solutions of either component alone. A second series of two-bottle choice tests with new groups of rats showed that both saccharin and glucose solution consumption levels were similar in the two species. The lack of glucose plus saccharin synergism in the ricefield rat response was found to be related to less preference by ricefield rats for glucose when paired with saccharin solution compared to the Norway rat preference pattern. Implications on the potential application of these results to the control of the two species using liquid bait stations are discussed and summarized.

Morphine enhances selection of both sucrose and ethanol in a two-bottle test

The influence of a low dose of morphine on the self-selection of alcohol and sucrose solutions is investigated. When given a choice between sucrose sweetened ethanol and plain water, rats show a significant preference for the sweetened ethanol. However, when given a choice between sweetened ethanol and sweetened water, rats increase consumption of sweetened water. These results suggest that the low-dose morphine enhancement of sweetened alcohol solutions is mediated by the reinforcing properties of sucrose not ethanol. However, when rats received small doses of morphine and a choice between unsweetened ethanol and water, the rats increase consumption of ethanol. Therefore, a low dose of morphine enhances the self-selection of both sucrose and ethanol solutions. This provides additional confirmation that opioids may enhance the rewarding properties of a variety of appetite reinforcers.