Further examination of ontogenetic limitations on conditioned taste aversion

This study was to resolve a discrepancy in the literature as to the capability of infant rats in acquiring conditioned taste aversion. Previous studies had indicated that during the 1st postnatal week, an aversion to saccharin could be conditioned when paired with lithium chloride (LiCl). Analogous conditioning with sucrose did not seem to occur until the end of the 2nd postnatal week, however, even though sucrose is discriminated from water and preferred before then. We observed that 5- and 9-day old pups express conditioned taste aversion to both saccharin and sucrose flavors that previously were paired with illness induced by LiCl. This learning occurred only when several hours separated cannulation and conditioning. A number of other factors that seemed likely to determine this early learning were found to have no effect. Thus it appears that rats can learn taste aversions very early in life, but only under certain circumstances. The results are discussed with reference to Vogt and Rudy's (1984) conclusions on the ontogeny of taste guided behaviors in the rat.     

Strain differences in sucrose- and fructose-conditioned flavor preferences in mice

Genetic factors strongly influence the intake and preference for sugar and saccharin solutions in inbred mouse strains. The present study determined if genetic variance also influences the learned preferences for flavors added to sugar solutions. Conditioned flavor preferences (CFPs) are produced in rodents by adding a flavor (CS+) to a sugar solution and a different flavor (CS-) to a saccharin solution (CS-) in one-bottle training trials; the CS+ is subsequently preferred to the CS- when both are presented in saccharin solutions in two-bottle tests. With some sugars (e.g., sucrose), flavor preferences are reinforced by both sweet taste and post-oral nutrient effects, whereas with other sugars (e.g., fructose), sweet taste is the primary reinforcer. Sucrose and fructose were used in three experiments to condition flavor preferences in one outbred (CD-1) and eight inbred strains which have "sensitive" (SWR/J, SJL/J, C57BL/10J, C57BL/6J) or "sub-sensitive" (DBA/2J, BALB/cJ, C3H/HeJ, 129P3/J) sweet taste receptors (T1R2/T1R3). Food-restricted mice of each strain were trained (1 h/day) to drink flavored 16% sucrose (CS+ 16S, Experiment 1), 16% fructose (CS+ 16F, Experiment 2) or 8% fructose+0.2% saccharin (CS+ 8F, Experiment 3) solutions on five alternate days and a differently flavored saccharin solution (0.05% or 0.2%, CS-) on the other five alternating days. The CS+ and CS- flavors were presented in 0.2% saccharin for two-bottle testing over six days. All strains preferred the CS+ 16S to CS- although there were significant strain differences in the magnitude and persistence of the sucrose preference. The strains also differed in the magnitude and persistence of preferences for the CS+ 16F and CS+ 8F flavors over the CS- with two strains failing to prefer the fructose-paired flavors. Sucrose conditioned stronger preferences than did fructose which is attributed to differences in the taste and post-oral actions of the sugars. These differential training intakes may not have influenced the sucrose-CFP because of the post-oral reinforcing actions of sucrose. Overall, sweet sensitive and sub-sensitive mice did not differ in sucrose-CFP, but unexpectedly, the sub-sensitive mice displayed stronger fructose-CFP. This may be related to differential training intakes of CS+ and CS- solutions: sweet sensitive mice consumed more CS- than CS+ during training while sub-sensitive mice consumed more CS+.     

Flavor preferences conditioned by sucrose depend upon training and testing methods: two-bottle tests revisited

In confirmation of prior work, rats given one-bottle training with flavored 5% and 30% sucrose solutions (CS5 and CS30) strongly preferred the CS5 when both flavors were presented in intermediate 17.5% sucrose solutions. The CS5 preference has been attributed to a conditioned satiety response to the CS30 flavor, but equal intakes of CS5 and CS30 in one-bottle tests did not support this view. To determine if sweetness differences between training and test solutions contributed to the CS5 preference, new rats were trained and tested with flavored 10% sucrose solutions. One flavor (CS5) was paired with matched intragastric (ig) water infusions (=net 5% solution) and another flavor (CS30) was paired with matched infusions of 50% sucrose (=net 30% solution) during one-bottle training. In two-bottle tests with both flavors paired with an intermediate infusion (25%=net 17.5%), the rats initially showed no overall preference for the CS5 or CS30. Following additional training, the rats significantly preferred the CS30 to the CS5. The intragastric data suggested that a change in sweet taste context between training and testing might have accounted for the strong CS5 preference obtained in the first experiment. This was confirmed in a third experiment in which rats were trained with flavored 5% and 30% sucrose solutions and then given two-bottle tests with both flavors presented either in 5% sucrose or 30% sucrose. Rats tested with 30% sucrose strongly preferred the CS5 flavor, whereas rats tested with 5% sucrose significantly preferred the CS30 flavor. Thus, the outcome of two-bottle flavor preference tests and presumably other tests of conditioned flavor reward may be greatly influenced by the solutions used in the tests. The impact of this variable may be greatest when the training solutions do not substantially differ in their net postingestive reinforcing actions. This appears to be the case with 5% and 30% sucrose solutions because the satiating effect of the concentrated solution tends to counteract its nutrient reinforcing action.     

Sucrose taste but not Polycose taste conditions flavor preferences in rats

Rats have an inborn preference for sweet taste and learn to prefer flavors associated with sweetness. They are also strongly attracted to the taste of glucose polymers (e.g., Polycose). This "poly" taste differs in quality from the sweet taste of sugar. To determine if poly taste, like sweet taste, conditions flavor preferences rats were trained with a distinctive flavor (CS+) added to 2% Polycose solution and a different flavor (CS-) added to plain water. In a subsequent two-bottle test the rats did not prefer the CS+ to CS- when both flavors were presented in water. In contrast, other rats significantly preferred a CS+ flavor that had been paired with 2% sucrose. Adding saccharin to a flavored Polycose solution did not improve CS+ flavor learning; rather, Polycose appeared to overshadow saccharin-induced conditioning. Flavor conditioning by a 16% Polycose solution was assessed using a sham-feeding procedure to prevent post-oral reinforcement. Although the rats sham-fed substantial amounts of the CS+ flavored Polycose solution, they failed to prefer the CS+ to the CS- flavor. This contrasts with the preference other rats displayed for a CS+ paired with sham-fed sucrose. Why attractive sweet and poly tastes differ in their ability to condition flavor preferences is not certain, although some findings suggest that they differentially activate dopamine and/or serotonin circuits involved in flavor learning.     

Interactions of temperature and taste in conditioned aversions

The influence of temperature on taste cues and the ability to discriminate and learn about different temperatures of foods are important factors regulating ingestion. The goal of this research was to demonstrate that thermal orosensory input can serve as a salient stimulus to guide ingestive behavior in the rat, and also that it interacts with gustatory input during choice and conditioned aversion experiments. A novel apparatus with Peltier refrigerators was used to control the temperature of solutions in 10-min, 2-bottle tests. It was determined that naive rats preferred cold water (10 °C) to warm water (40°). When cold water was paired with a toxic LiCl injection, rats avoided cold water and drank warm water, thus demonstrating that cold water could serve as the conditioned stimulus in a conditioned temperature aversion. Rats conditioned against cold water could discriminate 10 °C water from 16 °C water, but not from 13 °C water, thus showing an ability to discriminate orosensory thermal cues to within 3-6 °C. Rats also generalized conditioned aversions from cold water to cold saccharin and cold sucrose solutions. However, if rats were conditioned against a compound taste and thermal stimulus (10 °C, 0.125% saccharin), the rats could distinguish and avoid each component individually, i.e., by avoiding cold water or warm saccharin. Finally, daily 2-bottle extinction tests were used to assess the strength of aversions conditioned against a taste cue (0.25 M sucrose), a thermal cue (10 °C water), or the combination. Aversions to taste or temperature alone persisted for 7-14 days of extinction testing, but the combined taste-temperature aversion was stronger and did not extinguish after 20 days of extinction testing. These results demonstrate that temperature can serve as a salient cue in conditioned aversions that affect ingestion independent of taste cues or by potentiating taste cues.     

Conditioned acceptance and preference but not altered taste reactivity responses to bitter and sour flavors paired with intragastric glucose infusion

Nutrient-conditioned flavors preferences are thought to involve an increase in flavor palatability (hedonic evaluation). Consistent with this view is the recent finding that a sweet flavor paired with intragastric glucose infusions elicited more hedonic taste reactivity (TR) responses than did an alternative sweet flavor paired with intragastric water. The generality of this finding was examined by conditioning preferences for inherently avoided nonsweet flavors. Rats were trained in 20 h/day and then 30 min/day sessions with a CS+ flavor (sour citric acid or bitter sucrose octaacetate) paired with intragastric 16% glucose infusion, and the opposite flavor (CS-) paired with intragastric water. Glucose conditioning increased the CS+ acceptance in one-bottle tests and produced a 95% CS+ preference in two-bottle sessions. Yet, TR responses to brief intraoral infusions of the two CS flavors did not differ, even after extensive testing. Subsequent choice tests revealed that a 1% fructose solution was preferred to the CS-, whereas the CS+ was preferred to 1% and 2% fructose and equally preferred to 4%, 8%, and 16% fructose. These results indicate that strong nutrient-conditioned flavor preferences are not always associated with increased flavor palatability as measured by TR tests. Therefore, nonhedonic processes, perhaps increased incentive salience, appear to mediate the enhanced preference and acceptance conditioned by postingestive nutrient actions.     

Duodenal pain and spinal morphine induce conditioned taste aversion in rats

Conditioned taste aversion (CTA) is a behavioural response essential to the survival of an individual. The combination of taste and odour of most foods provides a strong conditioned stimulus (CS) for an animal to respond in an appropriate way to any harmful unconditioned stimuli (US) that follow. The most widely used conditioned stimuli are drinkable sweet solutions, such as saccharin and sucrose. CTA-like responses are also found for environmental unconditioned stimuli, but these usually take longer training. In the present study, the aversive nature of a duodenal distention with an implanted balloon catheter was studied in freely moving rats using either CTA against a sucrose solution, or a light-dark passive avoidance (PA) paradigm. In addition, the effect of spinal morphine on CTA and the cardiovascular response to duodenal distention were studied. CTA could be induced by a single, but long-lasting 20-minute duodenal distention, which did not induce PA behaviour in a light-dark box. Spinal infusion of morphine alone induced CTA, suggesting that the model is unsuitable to investigate spinal pharmacological modulation of visceral pain. Spinal morphine did reduce the cardiovascular response to duodenal distention, strengthening its validity as a visceral pain model. Since CTA is a complicating factor in the field of chemotherapy in cancer patients and spinal morphine causes nausea and vomiting in humans, CTA may also complicate spinal drug treatment or anaesthesia.     

Electrophysiology of appetitive taste and appetitive taste conditioning in humans

The present study examines two novel aspects of appetitive processing and conditioning: the electrophysiological response to (a) the appetitive taste of a sweet fluid and (b) appetitively/taste conditioned visual stimuli. Event-related potentials (ERPs) were recorded from 32 subjects while they performed a taste conditioning task, in which two symbols were paired with a sweet or a neutral fluid. The results show a clear P1/N1/P2 complex, and a late positive potential (P3) with maxima at right fronto-central electrode sites, in response to the taste stimuli. Of these components particularly the P3 showed robust differences between the sweet and neutral taste. In addition, the electrophysiological response to the taste conditioned stimuli (CS), also showed the expected differences for both P2 and P3 at frontocentral electrodes. The present data demonstrate that the employed paradigm is a useful methodology to study the electrophysiological responses to unconditioned appetitive stimuli. Since appetitive conditioning is assumed to be disturbed in many psychopathological conditions, such as substance dependence, depression and eating disorders, this paradigm could be employed to get more insight in these conditions in humans.     

Ingestion patterns of food, water, saccharin and sucrose in streptozotocin-induced diabetic rats

Changes in preference for sweet tasting solutions have previously been reported in diabetic rats. The present study was designed to use detailed analyses of drinking patterns to investigate changes in sweet taste perception in rats made diabetic with a streptozotocin (SZ) injection and tested with saccharin and a broad range of sucrose concentrations. Although meal patterns in diabetic rats have been studied extensively, drinking patterns and their relation to meal patterns have not been described. A second goal of this research was to use the detailed patterns of eating and drinking of the diabetic rat in an effort to understand the resulting hyperphagia. Rats were given IP injection of SZ or saline. Following the SZ injection, the rats showed marked increase in blood glucose levels, an increase in food and fluid intake and they failed to gain weight. The SZ-injected rats showed a loss of preference for saccharin and for high concentrations of sucrose. Patterns of sucrose ingestion that are correlated with taste perception were distorted in the diabetic rats. The detailed pattern analysis of eating showed that the diabetic-induced hyperphagia resulted from a marked increase in length of eating bouts. The increase in fluid intake in the diabetic rats resulted from both an increase in frequency and length of drinking bouts. Circadian patterns of both food and fluid ingestion were maintained in the diabetic rats.     

A comparison between taste avoidance and conditioned disgust reactions induced by ethanol and lithium chloride in preweanling rats

Adult rats display taste avoidance and disgust reactions when stimulated with gustatory stimuli previously paired with aversive agents such as lithium chloride (LiCl). By the second postnatal week of life, preweanling rats also display specific behaviors in response to a tastant conditioned stimulus (CS) that predicts LiCl‐induced malaise. The present study compared conditioned disgust reactions induced by LiCl or ethanol (EtOH) in preweanling rats. In Experiment 1 we determined doses of ethanol and LiCl that exert similar levels of conditioned taste avoidance. After having equated drug dosage in terms of conditioned taste avoidance, 13‐day‐old rats were given a single pairing of a novel taste (saccharin) and either LiCl or ethanol (2.5 g/kg; Experiment 2). Saccharin intake and emission of disgust reactions were assessed 24 and 48 hr after training. Pups given paired presentations of saccharin and the aversive agents (ethanol or LiCl) consumed less saccharin during the first testing day than controls. These pups also showed more aversive behavioral reactions to the gustatory CS than controls. Specifically, increased amounts of grooming, general activity, head shaking, and wall climbing as well as reduced mouthing were observed in response to the CS. Conditioned aversive reactions but not taste avoidance were still evident on the second testing day. In conclusion, a taste CS paired with postabsorptive effects of EtOH and LiCl elicited a similar pattern of conditioned rejection reactions in preweanling rats. These results suggest that similar mechanisms may be underlying CTAs induced by LiCl and a relatively high EtOH dose. © 2010 Wiley Periodicals, Inc. Dev Psychobiol 52: 545–557, 2010.     

Conditioned taste avoidance induced by lactose ingestion in adult rats

Because adult rats have very low levels of the intestinal enzyme lactase, the ingestion of appreciable quantities of the disaccharide lactose may cause gastrointestinal distress. The present experiment was designed to demonstrate that adult rats will learn to avoid previously neutral stimuli which have been paired with lactose ingestion. Adult rats ingested both a novel solution [either tap water (WA) or 0.1% saccharin (SA)] and a novel food substance (49% powdered lab chow + 50% added disaccharide + 1% saccharin) during a single conditioning session. The added disaccharide was either sucrose (group SU-SA), lactose (groups HL-SA and HL-WA), or equal amounts of these two disaccharides (group LL-SA); a fifth group (LC-SA) consumed a sucrose-containing diet to which lithium chloride was added (5 mg per 1 g of diet). Separate feeding tests and drinking tests, carried out over several weeks, were used to assess the extent of conditioned taste avoidance. In the four feeding tests, rats were allowed to ingest powdered lab chow with added saccharin (but without added disaccharide), while in the four drinking tests, rats chose between tap water and a 0.1% saccharin solution. Group HL-SA demonstrated a substantial conditioned avoidance in both feeding and drinking tests, but group HL-WA showed avoidance only in feeding tests. Conditioned avoidance was weak in group LL-SA; the strongest avoidance was observed in lithium chloride-treated rats (group LC-SA). Results are related to previous research and to the hypothesis that a learned avoidance of milk may facilitate the weaning process in mammals.     

Variation in Intake of Sweet and Bitter Solutions by Inbred Strains of Golden Hamsters

Variation in intake of sweet and bitter solutions by inbred strains of laboratory mice has helped identify genes related to taste behaviors; but similar information is not available for golden hamsters (Mesocricetus auratus ), a species used much in taste research. Thus, 6-hour, 1-bottle intake by water-replete hamsters of 7 inbred strains was measured for water and 2 concentrations of sucrose, maltose, D-phenylalanine (D-Phe), and sodium saccharin, which are sweet; and quinine.HCl, L-phenylalanine (L-Phe), caffeine, and sucrose octaacetate (SOA), which are bitter to humans. Difference scores (DIF), calculated as solution intake minus mean baseline water intake (mL) for each animal, were evaluated by analysis of variance. Compared to ACN, CN, APA, APG, and CBN, five strains with similar DIF for all compounds, GN, an ancestral strain of ACNT, and ACNT preferred sucrose, caffeine, and SOA more strongly; ACNT also preferred saccharin and maltose more strongly and rejected quinine more strongly. Narrow sense heritabilities for the 6 compounds for which strain differences were revealed ranged from 0.31 to 0.57. Genetic correlations indicated the strain variations in intake of sucrose, saccharin, SOA, and caffeine were coupled; a statistical association with several possible interpretations. Intakes of the two amino acids, preferred D-Phe and aversive L-Phe, did not reveal strain differences, and heritability ranged from 0.13 to 0.23 for the two optical isomers. Thus, although, compared to mice, genetic variation in laboratory hamsters may be small, genetic differences that influence taste behaviors in existing strains may help identify relevant genes.     

Taste preferences in a free-choice situation following electrical stimulation and lesion of septal area in rats

In the present study, electrical stimulation of medical or laternal septal areas and total or restricted lesions of these were conducted to observe the effect on ingestion of primary taste solutions in a free-choice situation. Stimulation induced a specific decrease in the intake of NaCl solution and had no effect on saccharin, acetic acid and quinine solutions and water. Total septal lesion or restricted lesions of medial or lateral septal areas induced hyperdipsia in rats. The lesioned rats, in a free-choice situation preferred NaCl, saccharin, as well as acetic acid solutions. This increase in acetic acid intake after lesion suggests that sour taste is also affected. Furthermore, there was no consumption of quinine solution before and after the lesion. This might be due to the presence of sweet tasting saccharin solution in this free-choice situation. These results indicate that the septal area causes aversion to NaCl intake, probably by inhibiting lateral hypothalamic neurons responsible for NaCl ingestion. The consumption of large quantities of saccharin, NaCl and acetic acid after the septal lesion suggests that the rats become overresponsive to taste factors in a free-choice situation.     

Bilateral lesions of the thalamic trigeminal orosensory area dissociate natural from drug reward in contrast paradigms

Substance abuse and addiction are associated with an apparent devaluation of, and inattention to, natural rewards. This consequence of addiction can be modeled using a reward comparison paradigm where rats avoid intake of a palatable taste cue that comes to predict access to a drug of abuse. Evidence suggests rats avoid intake following such pairings, at least in part, because the taste cue pales in comparison to the highly rewarding drug expected in the near future. In accordance, lesions of the gustatory thalamus or cortex eliminate avoidance of a taste cue when paired with either a drug of abuse or a rewarding sucrose solution, but not when paired with the aversive agent, LiCl. The present study used bilateral ibotenic acid lesions to evaluate the role of a neighboring thalamic structure, the trigeminal orosensory area (TOA), in avoidance of a gustatory cue when paired with sucrose (experiment 1), morphine (experiment 2), cocaine (experiment 3), or LiCl (experiment 4). The results show that the TOA lesion disrupts, but does not eliminate avoidance of a taste cue that predicts access to a preferred sucrose solution and leaves intact the development of a LiCl-induced conditioned taste aversion. The lesion does, however, eliminate the suppression of intake of a taste cue when paired with experimenter-administered morphine or cocaine using our standard parameters. As such, this is the first manipulation found to dissociate avoidance of a taste cue when mediated by a sweet or by a drug of abuse.     

Ethanol-conditioned flavor preferences compared with sugar- and fat-conditioned preferences in rats

Rats can learn to prefer flavors paired with ethanol and various nutrients. The present study examined the relative strengths of flavor preferences conditioned by 5% ethanol and isocaloric solutions of 7.18% sucrose, 7.18% fructose, or 3.26% corn oil. In three experiments, nondeprived rats were trained with different flavored solutions (conditioned stimuli, CS) paired with intragastric (IG) infusions: a CS+E flavor paired with ethanol infusion, a second CS+ paired with a nutrient infusion, and a CS- paired with water infusion. In two-bottle tests, rats strongly preferred a sucrose-paired CS+S over the CS- and over the CS+E. The preference for the CS+E over CS- was weaker. These effects occurred when the rats drank substantially more CS+S than CS+E in training and when training intakes were matched. Similar results were obtained when the nutrient infusion was fructose or corn oil, except that preferences for the CS+F or CS+O over the CS+E were less pronounced than with CS+S. Consistent with the IG results, rats trained to drink flavored sucrose and ethanol solutions preferred the CS+S to CS+E in a flavored water test. These results confirm prior reports of ethanol-conditioned preferences but show that ethanol is less effective than other nutrients at isocaloric concentrations. The marked individual differences in ethanol-conditioned preferences may be related to the impact of the sugar or fat infusions on the reward evaluation of the ethanol-paired flavor.     

Conditioned changes in appetitive and consummatory responses to flavors paired with oral or nutrient reinforcement among adult rats

Recent studies of the behavioral organization of conditioned flavor preferences have suggested the involvement of at least two separate learning systems-an appetitive response system sensitive to the oral hedonic properties of the reinforcer, and a consummatory response system sensitive to its nutrient properties. However, these prior studies were conducted with weanling rats, that differ from adults in terms of their prior experience with food, their learning competencies, and the peculiar ontogenetic constraints on their behavior. It is, therefore, unknown whether flavor preference behaviors are similarly organized in adult rats. In this experiment, adult rats were trained to associate a specific CS flavor with either the sweet taste or the postingestive nutrient effects of sucrose. Conditioned appetitive orienting and consummatory oral responding to the CS flavors were then measured. Unlike weanling rats, adult rats exhibited both conditioned appetitive behavior and conditioned consummatory behavior in response a CS that was previously paired with either oral hedonic or nutrient reinforcement. These results suggest a set of important developmental changes in the neurobehavioral mechanisms of flavor preference learning in the postweaning period.     

Effects of taste stimulation on beta-endorphin levels in rat cerebrospinal fluid and plasma

Opioids are suggested to be involved in generation of palatability and facilitation of consumption of food and fluid. We measured the level of an endogenous opioid, beta-endorphin, in the cerebrospinal fluid (CSF) and plasma after free drinking of water and taste solutions in Wistar rats. When the water-deprived animals were allowed to drink 10 mL of water, the level of beta-endorphin increased significantly 60 and 90 min after the start of drinking in both samples. beta-Endorphin in the CSF increased most after ingestion of 0.5 M sucrose and 0.005 M saccharin followed by 0.1 M NaCl, 0.1 mM quinine and water. An intragastric infusion of 7 mL of water did not change the beta-endorphin level. Essentially the same results were obtained for plasma samples except that NaCl and quinine solutions did not increase beta-endorphin levels. Sucrose became ineffective in releasing beta-endorphin in both samples after the establishment of conditioned taste aversions to this taste stimulus. These results suggest that the release of beta-endorphin is positively correlated with the palatability of taste stimuli, and that CSF beta-endorphin also reflects the reinforcement of fluid intake in thirsty animals.     

The role of sucrose-sensitive neurons in ingestion of sweet stimuli by hamsters

The relationship between sweet preference and activity in sucrose-sensitive chorda tympani nerve fibers was investigated in hamsters (Mesocricetus auratus). Without exception, hamsters increased consumption of aqueous solutions of nonsweet 0.1 M NaCl, 0.001 M quinine-HCl, 0.01 M citric acid, 0.001 M dithiothreitol, 0.01 M pyridine, 0.01 M 2-phenylethanol, 0.005 M i-amyl acetate, 0.01 M vanillin, half-saturated 1-menthol and 0.033 mM capsaicin if they were made sweet by adding 0.5 M sucrose. Since sucrose activates chorda tympani S fibers, activity in these nerve fibers may be sufficient for increased preference. To determine if S-fiber activity is necessary for preference, equally preferred sweet stimuli were presented to the tongue while recording responses of single chorda tympani fibers. S fibers were clearly activated by 0.03 M sucrose, 0.001 M Na saccharin, 0.01 M D-phenylalanine, 0.1 M glycine, 0.005 M dulcin and 0.03 M Na 2-mercaptoethanesulfonate but not by 0.01 M Ca cyclamate and 0.003 M Na 3-nitrobenzenesulfonate. Ca cyclamate weakly activated H fibers and Na 3-nitrobenzenesulfonate weakly activated N fibers. Thus, S-fiber chorda tympani activity may be sufficient but not necessary for sweet preference, which may be influenced by activity in fibers of other taste nerves.     

Reduced palatability in drug-induced taste aversion: II. Aversive and rewarding unconditioned stimuli

Drugs of abuse are known to reduce intake of a taste conditioned stimulus (conditional stimulus, CS), a behavioral response sometimes seen as paradoxical because the same drugs also serve as rewards in other behavioral procedures. In the present study we compared patterns of intake and palatability (assessed using microstructural analysis of licking) for a standard saccharin CS paired with the following: lithium chloride, morphine, amphetamine, or sucrose. We found that morphine and amphetamine, like lithium-induced illness, each suppressed CS intake and caused a reduction in saccharin palatability. Sucrose, a rewarding stimulus, did not reduce the palatability of the saccharin CS. We interpret these finds as evidence that drugs of abuse induce conditioned taste aversions.     

Intraseptal microinjections of carbachol and angiotensin II in rats: effects on taste preferences

The present study examined the effects of carbachol and angiotensin II injected into the medial and lateral septal areas (MSA and LSA) on the ingestion of primary taste solutions in a free-choice situation. The injection of carbachol or angiotensin II into MSA and LSA of water sated rats evoked a preference for the sweet tasting saccharin solution and water. The lateral septal rats also preferred acetic acid solution. Only the total fluid intake differed significantly among the four groups. In the water deprived rats injection of chemical to the respective groups induced the ingestion of NaCl solution. The MSA rats on injection of carbachol also preferred saccharin apart from NaCl. There was a significant difference in the NaCl intake among the four groups. The quinine solution was not consumed by all the groups. These results indicate that both the carbachol and angiotensin II induce the ingestion of saccharin, NaCl and water. The MSA might be more sensitive in inducing NaCl intake as compared with LSA during deprivation schedule and cholinergic stimulation. The LSA also evokes a preference for the sour tasting acetic acid. Furthermore, the data also suggest that the neurons sensitive to angiotensin are more potent than cholinergic neurons of LSA in producing salt preference.