Place Conditioning Procedure Research Articles

DBA/2J mice develop stronger lithium chloride-induced conditioned taste and place aversions than C57BL/6J mice

Genetic differences in lithium-induced conditioned aversion were examined using both place- and taste-conditioning procedures. In the place-conditioning procedure, adult male C57BL/6J (B6) and DBA/2J (D2) mice were exposed to a differential conditioning procedure in which each mouse received four 30-min pairings of a distinctive floor cue immediately after IP injections of either 0.75, 1.5, or 3.0 mEq/kg LiCl. A different floor cue was paired with saline injections. A separate group of control mice received saline injections paired with both floor types. Subsequent floor preference testing revealed greater conditioned aversion in D2 mice compared to B6 mice in groups receiving 3.0 mEq/kg LiCl. Lower LiCl doses did not produce conditioning in either strain. In a conditioned taste-aversion procedure, fluid-restricted mice received four trials in which access to 0.2 M NaCl solution was followed by IP injection of either 0.75, 1.5, 3.0, or 6.0 mEq/kg LiCl. D2 mice showed stronger conditioned taste aversion than B6 mice at all doses, suggesting that taste conditioning may be a more sensitive index of aversive drug sensitivity than place conditioning. These findings are not well explained by strain differences in general learning ability or by strain differences in stimulus salience or innate preference. Rather, these data appear more consistent with previous studies showing strain differences in lithium pharmacokinetics and in general sensitivity to aversive events.

Genetic differences in cocaine-induced conditioned place preference in mice depend on conditioning trial duration

In previous comparisons with C57BL/6J mice, DBA/2J mice have been characterized as "hyporesponsive" to cocaine's rewarding effect in the conditioned place-preference paradigm. This finding contrasts with other studies showing greater sensitivity of DBA/2J mice to the rewarding effects of ethanol and morphine in the place conditioning task. The purpose of the present study was to examine cocaine- induced place conditioning in both strains using apparatus and procedures similar to those used previously to assess ethanol and morphine preference conditioning. Mice from both strains were exposed to an unbiased place-conditioning procedure using 1, 10, or 30 mg/kg cocaine. Conditioning trial duration was 15, 30, or 60 min. In general, C57BL/6J mice displayed a significant conditioned place preference that was relatively unaffected by cocaine dose or trial duration. In contrast, DBA/2J mice showed no place conditioning at the shortest trial duration, but an increasing level of preference as trial duration increased. At the longest trial duration, both strains showed similar levels of place preference. Genetic differences in sensitivity to cocaine's rewarding effect depend critically on temporal parameters of the place-conditioning procedure. One possible interpretation of these findings is that short trial durations produce conditioned activity responses that interfere more with expression of conditioned place preference in DBA/2J mice than in C57BL/6J mice. More generally, these findings underscore the need for caution when drawing conclusions about genetic differences in place conditioning, especially when using this paradigm to evaluate the effects of gene knockouts or insertions on drug reward.

Conditioned increase in place preference by access to novel objects: antagonism by MK-801

In three separate place conditioning experiments with rats, repeated access to novel objects in one of two distinct environments conditioned an increase in preference for the novelty-paired environment. A conditioned increase in preference was found whether novel objects were paired with a randomly chosen environment or with the less preferred of two environments (conditioned against a preference). This enhanced preference did not depend on the control group employed. Control groups exposed only to the place conditioning apparatus or to both the apparatus and the novel objects showed no systematic shift in place preference. Intravenous infusions of cocaine also produced an increase in preference using the procedures employed with novel objects. Pretreatment with the N-methyl- d-aspartate (NMDA) receptor antagonist MK-801 (0.03 mg kg −1) blocked acquisition of the enhanced place preference conditioned by access to novel objects without decreasing time spent with objects or inducing a place aversion in controls. Combined, these results show that access to novel objects can serve as an appetitive stimulus like drugs of abuse and that this novelty-induced appetitive process involves NMDA receptors. These place-conditioning procedures may provide a good model for determining the behavioral and neural process underlying the appetitive effects of novelty.

Involvement of central cannabinoid (CB1) receptors in the establishment of place conditioning in rats.

The involvement of cannabinoid processes in positive reinforcement was studied using an unbiased, one-compartment, conditioned place preference (CPP) procedure in rats. This was achieved by examining the ability of the selective antagonist of the CB1 cannabinoid receptor subtype, SR 141716, to counteract the CPP supported by classical reinforcers. The acquisition of CPP induced by cocaine (2 mg/kg), morphine (4 mg/kg) and food (standard chow and sucrose pellets) was dose-dependently blocked by pre-pairing administration of SR 141716 (0.03-3 mg/kg). However, SR 141716 (up to 10 mg/kg) did not significantly counteract the expression of cocaine-induced CPP. On the other hand, the synthetic CB receptor agonist, WIN 55212-2 (0.3-1 mg/kg), established a robust place aversion (CPA), as already described with other agonists, and CPP was never observed, even at 100-fold lower doses. The aversive effect of WIN 55212-2 was reversed by SR 141716 (0.3-1 mg/kg), suggesting that it was accounted for by the stimulation of CB1 receptors. These findings indicate that, on their own, CB receptor agonists are unable to generate the processes necessary to induce a pleasurable state in animals, as assessed in place conditioning procedures. Nevertheless, a cannabinoid link may be involved in the neurobiological events, allowing the perception of the rewarding value of various kinds of reinforcers. However, a permanent endogenous cannabinoid tone seems unlikely to be necessary to ensure the organism a basal hedonic level since, given alone, SR 141716 supported neither CPP nor CPA.

Long-term haloperidol administration enhances and short-term administration attenuates the behavioral effects of cocaine in a place conditioning procedure.

Many behavioral effects of cocaine are attenuated by dopamine (DA) receptor antagonists. Yet, long-term DA antagonist administration enhances neuronal responsiveness to DA in several pathways, including the mesolimbic system. This study compared the effects of short-term versus long-term administration of the DA antagonist, haloperidol, on cocaine place conditioning. In the short-term study, rats were maintained on haloperidol or vehicle for the 10 days of place conditioning. Place conditioning to moderate doses of cocaine (10-15 mg/kg) was attenuated significantly, consistent with the dopaminergic actions of haloperidol and cocaine. In the second study, rats were administered haloperidol after place conditioning which had no effect on the expression of this behavior. Finally, rats were maintained on haloperidol for 30 days prior to and throughout place conditioning and testing which resulted in significant place conditioning at low cocaine doses (2.5-7.5 mg/kg). Because these cocaine doses do not support place conditioning in vehicle-maintained rats, these data suggest that long-term haloperidol administration enhances the sensitivity to these behavioral effects in contrast to the attenuation seen with short-term haloperidol administration. These results have wide-ranging implications for cocaine abuse treatment, particularly among schizophrenic populations.

Reduced sensitivity to ethanol reward, but not ethanol aversion, in mice lacking 5-HT1B receptors.

Various serotonergic receptor systems are thought to influence the motivational effects of ethanol. This experiment characterized the acquisition of ethanol-induced conditioned taste aversion and ethanol-induced conditioned place reference in mutant knockout mice lacking 5-HT1b receptors. In the taste conditioning procedure, adult homozygous knockout mice (-/-) and homozygous wild-type mice (+/+) received access to 0.2 M NaCl solution, followed immediately by intraperitoneal injection of 0 to 4 g/kg of ethanol. Ethanol produced dose-dependent conditioned taste aversion that was the same in both genotypes. In the place conditioning procedure, knockout and wild-type mice received six pairings of a tactile stimulus with ethanol (2 g/kg, i.p.). A different tactile stimulus was paired with saline. Ethanol produced increases in locomotor activity, with wild-type mice showing higher levels of ethanol-stimulated activity than knockout mice during conditioning trials 5 and 6. Wild-type mice demonstrated conditioned place preference for the ethanol-paired stimulus. In contrast, knockout mice showed no evidence of place conditioning. These results are generally consistent with an important role for serotonergic systems in ethanol reward and specifically indicate that 5-HT1b receptors are important for ethanol's rewarding effects but not for ethanol's aversive effects.

Place conditioning with alcohol in alcohol-preferring and -nonpreferring rats

A place-conditioning procedure was used to examine the effect of selective breeding for ethanol preference on sensitivity to the rewarding and/or aversive effects of ethanol. On 4 alternate days, groups of seven to eight alcohol-preferring (P) and alcohol-nonpreferring (NP) rats received IP injections of 0.0 (saline controls), 0.5, 1.0, or 1.5 g ethanol/kg body wt. immediately before 15-min confinement in a novel environment. On the 4 intervening days the same rats received saline injections before 15 min confinement in a different environment. On day 9, a 15-min choice test was given with no injections, in which the rats could move freely between the ethanol and the saline-paired environments. Dose-dependent avoidance of the ethanol-paired environment was observed in both lines of rats (1.0 and 1.5 g/kg), but the magnitude of the avoidance was less in the P relative to the NP rats, indicating that ethanol was less aversive for the P rats. No evidence for a place preference was observed in either line with any of the ethanol doses. An innate reduced sensitivity to the aversive effects of ethanol in rats of the P line and/or an enhanced sensitivity to the aversive effects of ethanol in rats of the NP line may contribute to the different levels of oral ethanol self-administration observed in these selectively bred rat lines.

Effects of dopaminergic D3-receptor-preferring ligands on the acquisition of place conditioning in rats.

The involvement of a D3 receptor-mediated control of dopamine (DA) function in motivational processes was investigated in rats by examining the ability of two D3 receptor-preferring ligands (7-OH-DPAT and l-nafadotride) to establish incentive learning and/or to modulate the reinforcing properties of food. This was done using a place conditioning procedure which consisted of repeated pairings of a drug (or food + drug) with a single environmental cue, the floor texture of an open field. (+/-)7-OH-DPAT, a partially selective D3 receptor agonist, produced a biphasic effect: the time spent on the drug-paired texture was reduced by 4 and 8µg/kg and lengthened by 4.0mg/kg, suggesting intrinsic aversive and appetitive potentials, depending on the dose. The D3 receptor preferring antagonist, l-nafadotride, did not establish place conditioning and seemed therefore devoid of intrinsic reinforcing properties. However, when food was provided during the conditioning sessions preceded by drug administration, a low dose of l-nafadotride (0.12mg/kg) but not higher doses, lengthened the time spent on the food-paired texture. Although the preferential affinity ratio of the two ligands in favour of the D3 vs. D2 subtype is low, these results suggest that DA function in the structures involved in incentive learning could be controlled through inhibitory D3 (or 'D2-like') receptor-mediated processes. Conditioned place aversion would indicate an impaired DA transmission due to a selective stimulation of these receptors, whereas their selective blockade would induce the inverse effect, providing that DA release was sufficient (as during eating) in the pathways involved in reward-related processes. The reversal of the effects of the two compounds at larger doses would likely result from an interaction with other subtypes of 'D2-like' receptors.

Stereospecific reversal of stress-induced anhedonia by mianserin and its (+)-enantiomer.

Chronic sequential exposure to a variety of mild unpredictable stressors has previously been found to depress the consumption of a dilute (1%) sucrose solution and to inhibit food-induced place preference conditioning. In the present study, using a simplified version of the mild stress procedure, the decreased sucrose intake was reversed by chronic (4 weeks) treatment with the atypical antidepressant mianserin. The racemic compound (+/-)-mianserin (5 mg/kg per day) and one of its enantiomers, (+)-mianserin (2.5 mg/kg) were effective in this model; a lower dose of (+/-)-mianserin (2.5 mg/kg), and the other enantiomer. (-)-mianserin (2.5 mg/kg), were ineffective. Vehicle-treated stressed animals were also subsensitive to food reward in the place conditioning procedure: normal place preference conditioning was reinstated by chronic treatment with (+/-)-mianserin (5 mg/kg) or (+)-mianserin, but not by the lower dose of (+/-)-mianserin (2.5 mg/kg) or by (-)-mianserin. Raclopride (100 micrograms/kg) reinstated the decrease in sucrose intake in stressed animals successfully treated with (+/-)- or (+)-mianserin. The results suggest that (+)-mianserin is the active enantiomer in reversing chronic mild stress-induced anhedonia, and further support the hypothesis of a dopaminergic mechanism of antidepressant action in this paradigm.

Conditioned place aversion produced by microinjections of substance P into the periaqueductal gray of rats.

The dorsal periaqueductal gray (DPAG) is one of the main structures involved in the integration of defensive behavior in the brain. In order to investigate the participation of neuropeptides in the generation of aversive states, semicarbazide, a glutamic acid decarboxylase inhibitor, and substance P, an active neuropeptide, were injected into the DPAG and their effects evaluated in the open field and the place conditioning tests. While semicarbazide and substance P both increased locomotor activity only substance P increased grooming in the open field. In the place conditioning procedure similar aversion conditioning was produced by both drugs. These results confirm previous data showing that semicarbazide in the DPAG causes place aversion through reduction of tonic inhibitory mechanisms on neural substrates of aversion. Such mechanisms may include substance P neurons as substance P microinjection into the DPAG also functioned as an unconditioned stimulus in the place aversion test.

Clonidine attenuates conditioned aversion produced by naloxone-precipitated opiate withdrawal

Clonidine, an α 2-adrenoreceptor agonist, is used to alleviate withdrawal severity during detoxification from chronic opiate use. The effectiveness of clonidine has been challenged because it attenuates some, but not all, withdrawal signs in humans and nimals. Because somatic assessments may not reflect opiate withdrawal aversion, this study used a one-trial place conditioning procedure. Naloxone was paired with the most preferred side and the amount of time spent on this side and on the vehicle-paired side was measured after training. This procedure led to a dose-related decrease in the time spent on the naloxone-paired side in morphine-exposed rats, but not in non-morphine-exposed rats. This conditioned place aversion shown by morphine-exposed rats was significantly attenuated by clonidine. These results suggest that in addition to clonidine's ability to lessen some somatic signs of opiate withdrawal, it also attenuates the aversive aspects of this state.

Conditioned place aversion induced by 5-HT1c receptor antagonists

A place-conditioning procedure was used to investigate the affective properties in rats of non-selective serotonin receptor antagonists (mianserin, eltoprazine and ketanserin) differing from each other by their affinity for 5-HT1C and 5-HT2 receptors among others. At the highest dose tested (10 mg/kg, i.p.), the mixed 5-HTlC /5-HT2 receptor antagonist mianserin produced a significant place aversion to the drug-paired compartment. The 5-HT1B receptor agonist/5-HT1C receptor antagonist eltoprazine induced a place aversion at doses of 1 and 10 mg/kg. In contrast, the 5-HT2 receptor antagonist ketanserin produced neither place aversion nor place preference at the doses tested (1 or 10 mg/kg, i.p.). The preferential 5-HT1C receptor agonist mCPP was given prior to mianserin or eltoprazine administration. mCPP (1 mg/kg, i.p.) significantly prevented the conditioned place aversion produced by mianserin or eltoprazine, without exhibiting any aversive or rewarding effect by itself. These results suggest that acute 5-HT1C receptor blockade is involved in the production of aversive effects of mianserin and eltoprazine.

Species difference in sensitivity to ethanol's hedonic effects

Recent research suggests that rats and mice differ in their sensitivity to ethanol's rewarding effect in the place conditioning paradigm. However, these species have not previously been examined in a comparable manner. The present study compared genetically heterogeneous rats and mice using an identical place conditioning procedure. Each animal received four pairings of a distinctive tactile floor stimulus with injection of ethanol (1.5 g/kg); a different tactile stimulus was paired with saline injection. Ethanol suppressed activity in rats but elevated activity in mice. As in most previous studies with drug-naive animals, rats showed aversion whereas mice showed preference for the ethanol-paired stimulus. This difference cannot be attributed to differences in housing conditions, apparatus, stimuli, or temporal parameters. Rather, it appears to represent a species difference in initial sensitivity to ethanol's hedonic effects. If one assumes that ethanol is both rewarding and aversive, this outcome might be explained by a species difference in tolerance/sensitization, the timecourse of the biphasic hedonic response to a single ethanol exposure, or selective association. Together with other recent studies from this laboratory, the present findings suggest the mouse may well be the species of choice for studying preferences conditioned by ethanol.

Reversal of stress-induced anhedonia by the atypical antidepressants, fluoxetine and maprotiline.

Chronic exposure to mild unpredictable stress has previously been found to depress the consumption of palatable sweet solutions. In the present study this effect was reversed by chronic (9 weeks) treatment with the atypical antidepressants, fluoxetine and maprotiline (5 mg/kg/day); the non-antidepressant chlordiazepoxide was ineffective. Stressed animals were also subsensitive to food reward in the place conditioning procedure; however, fluoxetine and maprotiline treated animals showed normal place preference conditioning. Acute pretreatment with raclopride (100 micrograms/kg) selectively reversed the recovery of sucrose drinking in antidepressant-treated stressed animals. These results extend previous reports of the efficacy of tricyclic antidepressants in this paradigm, and support the hypothesis of a dopaminergic mechanism of antidepressant action.

Operant place conditioning measures examined using morphine reinforcement

A new place conditioning procedure for assessing drug reinforcement, based on drug administration following chamber entry, was examined in rats and compared to conditioned place preference (which is based on chamber exposure of drugged animals). Besides relative time subsequently spent in the morphine chamber, choices between the drug and nondrug chambers were recorded during the time test and during a discrete-trials choice test. In some experiments, either choices or latencies of chamber entry were recorded during training. Most choice and latency measures showed larger reinforcement effects than did time spent. Placement training was somewhat less effective than operant place conditioning overall, but produced significant time differences and discrete-trial choices in four of five groups. With intravenous morphine, the lengthy chamber exposures generally used in conditioned place preference were unnecessary.

An animal model of anhedonia: attenuation of sucrose consumption and place preference conditioning by chronic unpredictable mild stress

Chronic exposure to very mild unpredictable stress has previously been found to depress the consumption of, and preference for, highly palatable sweet solutions. The present study used the place conditioning procedure to investigate whether these effects result from a decreased sensitivity to reward. Rats were subjected to chronic mild unpredictable stress for a total of 4 weeks. During weeks 3 and 4, they received four training trials, in which rewards were presented in a distinctive environment, and four further non-rewarded trials in a different environment. The rewards used in different experiments were food pellets, dilute (0.7%) and concentrated (34%) sucrose solutions, and dl-amphetamine sulphate (0.5 and 1.0 mg/kg). In all experiments, non-stressed animals showed an increase in preference for the environment associated with reward; in stressed animals, these effects were abolished or greatly attenuated. Chronic unpredictable mild stress, which may be comparable in intensity to the difficulties people encounter in their daily lives, appears to cause a generalized decrease in sensitivity to rewards.

Place conditioning with d-amphetamine: The effect of the CS-UCS interval and evidence of a place avoidance

In Experiment 1, a dose-response study of place conditioning with amphetamine was conducted. Male Sprague-Dawley rats receiving 0.0, 0.05, 0.1, 0.5, 2.0, 5.0, 7.5, or 10.0 mg/kg of d-amphetamine underwent 104-day cycles of place conditioning. On alternate days, each rat was injected with its designated dose of amphetamine while confined to its originally nonpreferred end of a three-compartment, straight alley box. On intervening days, each rat was injected with saline while confined to its originally preferred compartment. Following each 4-day cycle, a choice test was administered in which each rat was allowed 20 min of access to the entire alley box. Doses of amphetamine (≥0.5 mg/kg) induced a significant avoidance of the compartment in which amphetamine had been administered. In Experiment 2, animals received 0.0, 0.5, 2.0, or 5.0 mg/kg of amphetamine and underwent place conditioning procedures identical to those for the animals in Experiment 1. Unlike in Experiment 1, the animals were given a single choice test following 104-day place conditioning cycles. All groups that received amphetamine exbibited-a-eonditioned place avoidance. In Experiment 3, the effect of various CS-UCS intervals on place conditioning with 2.0 mg/kg of amphetamine was examined. Animals that received amphetamine immediately following their removal from the chamber exhibited a conditioned place avoidance.

Nicotine conditions place preferences after intracerebral administration in rats

A single-trial place conditioning procedure, one treatment and one non-treatment during two daily conditioning sessions followed by a single test session on the 3rd day, was used to examine the place conditioning effects of intracerebrally administered nicotine. In the first series of experiments, Sprague-Dawley male rats were implanted unilaterally with guide cannulas aimed at the lateral ventricle. After 1 week, rats received either "treatment" (nicotine in 2 microliters phosphate buffer or 2 microliters of buffer alone) or "no treatment" (no injections) before being placed in the black or white compartment of a three-compartment place-conditioning apparatus for 20 min. The next day the rats received the opposite treatment before being conditioned in the opposite compartment. On day 3, animals had free access to the entire apparatus for 15 min and the time spent in each compartment was recorded automatically. Even though the rats exhibited a baseline bias for the black compartment, intracerebroventricular nicotine induced positive place preferences relative to buffer control, i.e. if treatments were paired with the black compartment, nicotine enhanced the preference for the black compartment, and if the treatments were paired with the white compartment, nicotine induced a preference for the white compartment. In addition, the nicotine-induced preference response was antagonized by the co-intraventricular administration of mecamylamine. In a second series of experiments, animals were implanted unilaterally with guide cannulas aimed at the pendunculopontine tegmental nucleus of the mesopontine tegmentum. Nicotine microinjection, 1.2-18.5 nmol in 0.5 microliter buffer, induced a dose-dependent positive place preference response.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphine-induced place conditioning is not confounded by drug-induced alterations in locomotor activity.

The influence of locomotor activity and environmental familiarity upon the reinforcing effects of morphine was examined in an unbiased place preference conditioning procedure. Groups of rats were trained to associate one distinctive environment with morphine and another with saline. One group was made tolerant to the locomotor activity effects of morphine by the SC administration of morphine (5.0 mg/kg/12 hr) for four days prior to conditioning. The other group received injections of saline. Administration of morphine, at doses which decreased locomotor activity, resulted in marked preferences for the drug-associated place in saline-treated rats. In contrast, chronic morphine treatment resulted in tolerance to the sedative effects of morphine and an abolition of the morphine-induced place preference. These results indicate that in the place conditioning procedure, measures of reinforcement are not confounded by drug-induced increases in activity.

Aversive property of opioid receptor blockade in drug-naive mice.

The motivational effect of naloxone administration in the non-dependent laboratory mouse was examined with taste and place conditioning procedures. Thus, male CD1 mice without any history of drug exposure avoided a cue paired with three SC injections of as little as 0.1 mg/kg naloxone HCl. The aversive effect of naloxone was also seen in DBA/2 and C57BL/6 mice. In addition, it only occurred with the minus isomer and not the plus isomer, and it was potentiated by implantation, 3 days prior to training, of a morphine-containing (37.5 mg) but not a placebo pellet. Naloxone injection, therefore, acts as an aversive stimulus in naive mice and this is probably produced by decreases in activity of endogenous opioid peptide systems. Together with other data, the present results support the conclusion that the aversive effect of opioid receptor blockade in the opiate non-dependent organism may be general to a wide range of species including primates. The importance of training and testing variables for observing the naloxone aversive effect is discussed. Advantages of studying preference conditioning with mice are also given.