Drug-induced Conditioned Place Preference Research Articles

Drug-Induced Conditioned Place Preference and Its Practical Use in Substance Use Disorder Research.

The conditioned place preference (CPP) paradigm is a well-established model utilized to study the role of context associations in reward-related behaviors, including both natural rewards and drugs of abuse. In this review article, we discuss the basic history, various uses, and considerations that are tied to this technique. There are many potential takeaway implications of this model, including negative affective states, conditioned drug effects, memory, and motivation, which are all considered here. We also discuss the neurobiology of CPP including relevant brain regions, molecular signaling cascades, and neuromodulatory systems. We further examine some of our prior findings and how they integrate CPP with self-administration paradigms. Overall, by describing the fundamentals of CPP, findings from the past few decades, and implications of using CPP as a research paradigm, we have endeavored to support the case that the CPP method is specifically advantageous for studying the role of a form of Pavlovian learning that associates drug use with the surrounding environment.

TAAR1 and Psychostimulant Addiction.

Trace amine-associated receptor 1 is one of the best-characterized receptors of trace amines. Growing evidence shows that TAAR1 negatively regulates the monoaminergic activity, including dopamine transmission in the mesocorticolimbic system. Neurochemical assays demonstrated that selective TAAR1 full and partial agonists were effective to prevent psychostimulants-induced dopamine transmission in vitro and in vivo. In the last decade, many preclinical models of psychostimulant addiction such as drug-induced behavioral sensitization, drug-induced conditioned place preference, drug self-administration, drug discrimination, and relapse models were used to assess the effects of TAAR1 agonists on psychostimulants' behavioral effects. In general, activation of TAAR1 attenuated while knockout of TAAR1 potentiated psychostimulant abuse-related behaviors. Here, we review the advances in TAAR1 and its agonists in modulating psychostimulant addiction. We discuss the similarities and differences between the neurochemical and behavioral effects of TAAR1 full and partial agonists. We also discuss several concerns including the abuse liability, sleep reduction, and species-dependent effects that might affect the successful translation of TAAR1 agonists from preclinical studies to clinical application. In conclusion, although further investigations are in need to address certain concerns and the underlying neural mechanisms, TAAR1 agonists appear to be a promising pharmacotherapy to treat psychostimulant addiction and prevent relapse.

The Hippocampus Is the Place to Be: Opioid Receptors and LTP

Nam etal. (2019) genetically modulate the expression of astrocytic μ-opioid receptors to reveal they are necessary for drug-induced conditioned place preference. These receptors trigger a mechanism involving metabotropic glutamate receptors to enhance hippocampal long-term potentiation, linking the conditioning to the location.

Sensitization-dependent nicotine place preference in the adult zebrafish

Sensitization of motor activity is a behavioural test to evaluate the effects of psychostimulants. Conditioned place preference (CPP) is an associative learning procedure to examine the rewarding properties of drugs. We aimed to assess whether motor sensitization to drugs of abuse can make zebrafish more vulnerable to establishing drug-induced CPP. We first evaluated sensitization of locomotor activity of zebrafish to repeated administrations of nicotine and cocaine during 5 days and after 5 days of withdrawal. After withdrawal, when zebrafish were re-exposed to the same dose of nicotine or cocaine locomotor activity was increased by 103% and 166%, respectively.Different groups of zebrafish were sensitized to nicotine or cocaine and trained on a nicotine-CPP task the day after withdrawal. The nicotine dose selected for sensitization was not effective for developing CPP in naïve zebrafish whereas it elicited CPP in zebrafish that were previously sensitized to nicotine or cocaine. Levels of nicotinic acetylcholine receptor β2, α6 and α7 subunit, Pitx3, and tyrosine hydroxylase 1 (TH1) mRNAs were increased in the brain of nicotine- and cocaine-sensitized zebrafish. Nicotine-CPP performed with drug-sensitized zebrafish provoked further enhancements in the expression of α6 and α7 subunit, Pitx3, and TH1 mRNAs suggesting that the expression of these molecules in the reward pathway is involved in both processes. Our findings indicate that repeated exposures to low doses of drugs of abuse can increase subject's sensitivity to the rewarding properties of the same or different drugs. This further suggests that casual drug intake increases the probability of becoming addict.

Uridine attenuates morphine-induced conditioned place preference and regulates glutamate/GABA levels in mPFC of mice

Several lines of evidence suggest that uridine, as a neuromodulator, plays an important role in drug addiction. We previously found that uridine circumvents morphine-induced behavioral sensitization by decreasing the extracellular dopamine levels in the dorsal striatum. In the present study, the effects of uridine on morphine-induced conditioned place preference (CPP) and the possible roles of glutamate and GABA in the stress-induced reinstatement of CPP were investigated. First, the effects of uridine (1, 10 and 100mg/kg, i.p.) on the four defined phases - acquisition, expression, extinction and reinstatement (drug priming and restraint stress) - of morphine-induced CPP were studied. The results showed that pretreatment with uridine significantly blocked the acquisition and expression phases of CPP. Additionally, uridine also facilitated CPP extinction and inhibited stress-induced CPP reinstatement, although it failed to affect drug-induced CPP reinstatement. Since glutamatergic and GABAergic systems are both involved in CPP reinstatement, the extracellular levels of glutamate and GABA in the mPFC during the stress-induced CPP reinstatement were determined using in vivo microdialysis. The results showed that uridine attenuated the stress-induced glutamate increase in the mPFC without influencing the basal glutamate levels, and increased the levels of extracellular GABA in the mPFC both under normal physiological conditions and after the stress stimulus. Thus, our results indicate that uridine depresses the stress-induced reinstatement of CPP, simultaneously regulating glutamatergic and GABAergic neurotransmission in the mPFC. The present work provides further understanding of the role of uridine in morphine-induced neurobehavioral changes.

Calpain-GRIP Signaling in Nucleus Accumbens Core Mediates the Reconsolidation of Drug Reward Memory.

Exposure to drug-paired cues causes drug memories to be in a destabilized state and interfering with memory reconsolidation can inhibit relapse. Calpain, a calcium-dependent neutral cysteine protease, is involved in synaptic plasticity and the formation of long-term fear memory. However, the role of calpain in the reconsolidation of drug reward memory is still unknown. In the present study, using a conditioned place preference (CPP) model, we found that exposure to drug-paired contextual stimuli induced the activation of calpain and decreased the expression of glutamate receptor interacting protein 1 (GRIP1) in the nucleus accumbens (NAc) core, but not shell, of male rats. Infusions of calpain inhibitors in the NAc core immediately after retrieval disrupted the reconsolidation of cocaine/morphine cue memory and blocked retrieval-induced calpain activation and GRIP1 degradation. The suppressive effect of calpain inhibitors on the expression of drug-induced CPP lasted for at least 14 d. The inhibition of calpain without retrieval 6 h after retrieval or after exposure to an unpaired context had no effects on the expression of reward memory. Calpain inhibition after retrieval also decreased cocaine seeking in a self-administration model and this effect did not recover spontaneously after 28 d. Moreover, the knock-down of GRIP1 expression in the NAc core by lentivirus-mediated short-hairpin RNA blocked disruption of the reconsolidation of drug cue memories that was induced by calpain inhibitor treatment. These results suggest that calpain activity in the NAc core is crucial for the reconsolidation of drug reward memory via the regulation of GRIP1 expression.SIGNIFICANCE STATEMENT Calpain plays an important role in synaptic plasticity and long-term memory consolidation, however, its role in the reconsolidation of drug cue memory remains unknown. Using conditioned place preference and self-administration procedures, we found that exposure to drug-paired cues induced the activation of calpain and decreased glutamate receptor interacting protein 1 (GRIP1) expression in the nucleus accumbens (NAc) core. The inhibition of calpain activity in the NAc core immediately after retrieval disrupted the reconsolidation of cocaine/morphine cue memory that was blocked by prior GRIP1 knock-down. Our findings indicate that calpain-GRIP signaling is essential for the restabilization process that is associated with drug cue memory and the inhibition of calpain activity may be a novel strategy for the prevention of drug relapse.

Effects of propofol on conditioned place preference in male rats: Involvement of nitrergic system

ABSTRACTBackground: Drug-induced conditioned place preference (CPP) is linked to the addictive properties of the drug used. The number of studies that have investigated the effects of propofol on CPP is limited. Research findings suggest that nitric oxide (NO) might play an important role in substance use disorders. Objectives: The present study sought to investigate the role of the nitrergic system on the rewarding effects of propofol by using the CPP protocol in rats. Methods: The experiment followed habituation, pre-conditioning, conditioning, and post conditioning sessions. Male Wistar albino rats weighing 240–290 g were divided into eight groups: control (saline), propofol (10, 20, and 40 mg/kg), the NO synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) alone (30 and 60 mg/kg), and in combination with propofol (30 and 60 mg/kg L-NAME plus 40 mg/kg propofol) (n = 8 for each group). The CPP effects of propofol, L-NAME, saline, and their combinations were evaluated. All the drug and saline administrations were performed by intraperitoneal (ip) injections. Results: Propofol (10–40 mg/kg) produced CPP that was statistically significant relative to saline. Propofol-induced CPP was significantly reversed by pretreatment with L-NAME. When administered alone, L-NAME did not produce CPP and also did not produce any significant change on locomotor activity of naïve rats. Conclusion: Our results suggest that propofol produces CPP effects in rats and that NO-related mechanisms may be responsible for propofol-induced CPP. Thus, propofol might have the potential to be addictive, and this possibility should be considered during clinical applications of this drug.

Ibogaine and addiction in the animal model, a systematic review and meta-analysis.

Ibogaine is a naturally occurring substance which has been increasingly used in the lay-scene to reduce craving and relapse in patients with substance use disorders (SUDs). Although human clinical trials on the safety and efficacy of ibogaine are lacking, animal studies do support the efficacy of ibogaine. In this systematic review and meta-analysis (MA), we summarise these animal findings, addressing three questions: (1) does ibogaine reduce addictive behaviour in animal models of SUDs?; (2) what are the toxic effects of ibogaine on motor functioning, cerebellum and heart rhythm?; (3) what are neuropharmacological working mechanisms of ibogaine treatment in animal models of SUDs? MA of 27 studies showed that ibogaine reduced drug self-administration, particularly during the first 24 h after administration. Ibogaine had no effect on drug-induced conditioned place preference. Ibogaine administration resulted in motor impairment in the first 24 h after supplementation, and cerebral cell loss even weeks after administration. Data on ibogaines effect on cardiac rhythm, as well as on its neuropharmacological working mechanisms are limited. Our results warrant further studies into the clinical efficacy of ibogaine in SUD patients in reducing craving and substance use, but close monitoring of the patients is recommended because of the possible toxic effects. In addition, more work is needed to unravel the neuropharmacological working mechanisms of ibogaine and to investigate its effects on heart rhythm.

NMDA Receptors on Dopaminoceptive Neurons Are Essential for Drug-Induced Conditioned Place Preference.

Plasticity of the brain’s dopamine system plays a crucial role in adaptive behavior by regulating appetitive motivation and the control of reinforcement learning. In this study, we investigated drug- and natural-reward conditioned behaviors in a mouse model in which the NMDA receptor-dependent plasticity of dopaminoceptive neurons was disrupted. We generated a transgenic mouse line with inducible selective inactivation of the NR1 subunit in neurons expressing dopamine D1 receptors (the NR1D1CreERT2 mice). Whole-cell recordings of spontaneous EPSCs on neurons in the nucleus accumbens confirmed that a population of neurons lacked the NMDA receptor-dependent component of the current. This effect was accompanied by impaired long-term potentiation in the nucleus accumbens and in the CA1 area of the ventral, but not the dorsal, hippocampus. Mutant mice did not differ from control animals when tested for pavlovian or instrumental conditioning. However, NR1D1CreERT2 mice acquired no preference for a context associated with administration of drugs of abuse. In the conditioned place preference paradigm, mutant mice did not spend more time in the context paired with cocaine, morphine, or ethanol, although these mice acquired a preference for sucrose jelly and an aversion to naloxone injections, as normal. Thus, we observed that the selective inducible ablation of the NMDA receptors specifically blocks drug-associated context memory with no effect on positive reinforcement in general.

Rottlerin impairs the formation and maintenance of psychostimulant-supported memory.

Since brain proteins such as protein kinase C (PKC), brain-derived neurotrophic factor (BDNF), and mammalian target of rapamycin (mTOR) are involved in the establishment and maintenance of psychostimulant memory, we sought to determine if systemic treatment with rottlerin, a natural compound affecting all these proteins, may modulate stimulant-supported memory. Stimulant-induced conditioned place preference (CPP) was used in modeling stimulant-supported memory. Three cocaine (10 mg/kg; COC) or three methamphetamine (1 mg/kg; MA) conditioning trials reliably established the drug-induced CPP in male C57BL/6 mice. An intra-peritoneal rottlerin injection (5 mg/kg) at least 24 h prior to the first COC or first MA conditioning trial prevented the establishment of CPP. Following the establishment of the COC- or MA-induced CPP, saline conditioning trial was used to extinguish the CPP. Rottlerin (5 mg/kg, intra-peritoneal (i.p.)) administered 20 h prior to the first saline conditioning trial diminished subsequent drug- and stressor-primed reinstatement of the extinguished CPP. Rottlerin (5 mg/kg, i.p.) produced a fast-onset and long-lasting increase in hippocampal BDNF levels. However, treatment with a BDNF tropomyosin receptor kinase B (TrkB) receptor antagonist, K252a (5 μg/kg), did not affect rottlerin's suppressing effect on COC-induced CPP and treatment with 7,8-dihydroxyflavone (10 mg/kg x 6, 7,8-DHF), a selective TrkB agonist, prior to each conditioning trial did not affect COC-induced CPP. These results suggest that systemic rottlerin treatment may impair the formation of COC- and MA-supported memory. Importantly, such a treatment may advance our understanding of the underlying mechanism through which extinction training resulted in the "forgetting" of the COC- and MA-supported memory.

Treatment of heroin dependence with ibogaine

BackgroundThe use of the hallucinogen ibogaine as an anti-addiction agent has been described in several case reports, dating back to the eighties. The anti-addiction properties of ibogaine have been confirmed in a large body of animal work. Ibogaine has been shown to be effective in reducing withdrawal severity and substance use for a variety of substances, including cocaine and opiates. Animal studies also show some potentially dangerous adverse reactions, including cerebellar toxicity and potential cardiac effects. While pharmacological treatment options for opiate and cocaine dependence are still limited, ibogaine assisted treatment might be a promising new option. Therefore more systematic studies on its toxicity and efficacy are warranted. In our studies we address these two research questions: is ibogaine treatment for opiate dependence safe and effective for treating opiate withdrawal and relapse prevention? A secondary objective is to explore the pharmacokinetic properties of ibogaine.MethodsAnimal work: first we performed a systematic review and meta-analysis of animal studies on ibogaine. Thirty studies were included in the systematic review, of which 27 could be analyzed in meta-analysis. Human studies: fifteen opiate dependent patients will be treated with ibogaine (10 mg/kg), on top of treatment as usual. Ibogaine toxicity will be assessed through close monitoring with electrocardiography, with QTc prolongation as main outcome measure, repeated assessments of ataxia using the (SARA) and observation of psychotic symptoms by using the Delirium Observations Scale (DOS). Ibogaine efficacy will be measured, using repeated evaluations of opiate withdrawal severity (Subjective Opiate Withdrawal Scale: SOWS; Objective Opiate Withdrawal Scale: OOWS), craving intensity (using a Visual Analogue Scale) and substance use, with a six-month follow-up. Clinical observations in ibogaine treated individuals will be compared with a cohort of opiate dependent patients treated with a rapid detoxification procedure. Both acute and long-term effects will be linked with serum ibogaine and noribogaine levels.ResultsAnimal work: overall, ibogaine reduced drug self-administration, particularly during the first 24 hours after administration. Ibogaine had no effect on drug-induced conditioned place preference. Ibogaine administration resulted in motor impairment in the first 24 hours after supplementation, and cerebral cell loss even weeks after administration. Data on ibogaines effect on cardiac rhythm as well as on its neuropharmacological working mechanisms are limited. Human studies: human data are still being collected. Treatment of the first patients confirmed strong effects of ibogaine on heart rhythm (QTc prolongation) and ataxia, while the opiate withdrawal symptoms were relatively mild. The first observations on the clinical effect of ibogaine on craving and substance use will also be shared.ConclusionsBased on our meta-analysis of animal data, there is strong evidence that ibogaine is effective in reducing drug self-administration in animals. This warrants further studies into the clinical efficacy of ibogaine in substance dependent patients in reducing craving and substance use. Our first clinical experiences in a limited number of patients confirm that ibogaine treatment may be effective in reducing opiate withdrawal, but can potentially have transient cardiac and cerebellar toxicity.Disclosure of interestThe authors have not supplied his declaration of competing interest.

Cannabidiol disrupts the reconsolidation of contextual drug-associated memories in Wistar rats.

In addicts, craving and relapse are frequently induced by the recall of memories related to a drug experience. Several studies have demonstrated that drug-related memories are reactivated after exposure to environmental cues and may undergo reconsolidation, a process that can strengthen memories. Thus, reactivation of mnemonic traces provides an opportunity for disrupting memories that contribute to the pathological cycle of addiction. Here we used drug-induced conditioned place preference (CPP) to investigate whether cannabidiol (CBD), a phytocannabinoid, given just after reactivation sessions, would affect reconsolidation of drug-reward memory, reinstatement of morphine-CPP, or conditioned place aversion precipitated by naltrexone in Wistar rats. We found that CBD impaired the reconsolidation of preference for the environment previously paired with both morphine and cocaine. This disruption seems to be persistent, as the preference did not return after further reinstatement induced by priming drug and stress reinstatement. Moreover, in an established morphine-CPP, an injection of CBD after the exposure to a conditioning session led to a significant reduction of both morphine-CPP and subsequent conditioned place aversion precipitated by naltrexone in the same context. Thus, established memories induced by a drug of abuse can be blocked after reactivation of the drug experience. Taken together, these results provide evidence for the disruptive effect of CBD on reconsolidation of contextual drug-related memories and highlight its therapeutic potential to attenuate contextual memories associated with drugs of abuse and consequently to reduce the risk of relapse.

Cues predicting drug or food reward restore morphine-induced place conditioning in mice lacking delta opioid receptors

The exact role of delta opioid receptors in drug-induced conditioned place preference (CPP) remains debated. Under classical experimental conditions, morphine-induced CPP is decreased in mice lacking delta opioid receptors (Oprd1 (-/-)). Morphine self-administration, however, is maintained, suggesting that drug-context association rather than drug reward is deficient in these animals. This study further examined the role of delta opioid receptors in mediating drug-cue associations, which are necessary for the expression of morphine-induced CPP. We first identified experimental conditions under which Oprd1 (-/-) mice are able to express CPP to morphine (5, 10 or 20 mg/kg) in a drug-free state and observed that, in this paradigm, CPP was dependent on circadian time conditions. We then took advantage of this particularity to assess the ability of various cues (internal or discrete), predicting either drug or food reward, to restore CPP induced by morphine (10 mg/kg) in Oprd1 (-/-) mice in conditions under which they normally fail to express CPP. We found that presentation of circadian, drug or auditory cues, predicting morphine or food reward, restored morphine CPP in Oprd1 (-/-) mice, which then performed as well as control mice. This study reveals that, in contrast to spatial cues, internal or discrete morphine-predicting stimuli permit full expression of morphine CPP in Oprd1 (-/-) mice. Delta receptors, therefore, appear to play a crucial role in modulating spatial contextual cue-related responses. This activity may be critical when context gains control over behavior, as is the case for context-induced relapse in drug abuse.

Disruption of Conditioned Drug Memories

We first made a brief review on historical development of drug craving theories. A special emphasis was given on the proposal that conditioned drug memories can be a critical psychopathological basis to elicit compulsive drug taking, craving and subsequent relapse. We then discussed the different processes associated with drug learning and memory as well as recent findings pertaining to these processes, specifically using the conditioned place preference (CPP) paradigm as a model for assessing these conditioned drug memories. Over this decade, many factors have been identified to affect the acquisition, consolidation, expression and reconsolidation of such a drug-induced CPP memory in rodents. Since reactivation of the established drug-induced CPP memory and modification of the reactivated memory are two core components for developing potential treatments, a few theoretical and practical considerations in the CPP paradigm are provided and discussed accordingly.

Conditioned place preference induced by social play behavior: Parametrics, extinction, reinstatement and disruption by methylphenidate

In this study, we investigated behavioral factors underlying conditioned place preference (CPP) induced by social interaction in adolescent rats. We found that the magnitude of socially-induced CPP depended on the social motivation of the animals and on the amount of training. After extinction, socially-induced CPP could be reinstated by a single reconditioning session. Treatment with methylphenidate, which disrupts social play behavior in adolescent rats, but not social exploratory behavior, prevented the development of socially-induced CPP. Interestingly, methylphenidate by itself induced CPP. These data demonstrate that: 1. social interaction is rewarding in adolescent rats; 2. appetitive and mnemonic factors influence the development of socially-induced CPP; 3. comparable to drug-induced CPP, socially-induced CPP can be extinguished and reinstated; 4. social play is likely to be the most rewarding aspect of social interaction in adolescent rats; 5. social context influences the subjective effects of methylphenidate.

The NMDA antagonist MK-801 disrupts reconsolidation of a cocaine-associated memory for conditioned place preference but not for self-administration in rats

Recent research suggests that drug-related memories are reactivated after exposure to environmental cues and may undergo reconsolidation, a process that can strengthen memories. Conversely, reconsolidation may be disrupted by certain pharmacological agents such that the drug-associated memory is weakened. Several studies have demonstrated disruption of memory reconsolidation using a drug-induced conditioned place preference (CPP) task, but no studies have explored whether cocaine-associated memories can be similarly disrupted in cocaine self-administering animals after a cocaine priming injection, which powerfully reinstates drug-seeking behavior. Here we used cocaine-induced CPP and cocaine self-administration to investigate whether the N-methyl-D-aspartate receptor antagonist (+)-5methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) given just prior to reactivation sessions would suppress subsequent cocaine-primed reinstatement (disruption of reconsolidation). Systemic injection of MK-801 (0.05 or 0.20 mg/kg administered intraperitoneally) in rats just prior to reactivation of the cocaine-associated memory in the CPP context attenuated subsequent cocaine-primed reinstatement, while no disruption occurred in rats that did not receive reactivation in the CPP context. However, in rats trained to self-administer cocaine, systemic administration of MK-801 just prior to either of two different types of reactivation sessions had no effect on subsequent cocaine-primed reinstatement of lever-pressing behavior. Thus, systemic administration of MK-801 disrupted the reconsolidation of a cocaine-associated memory for CPP but not for self-administration. These findings suggest that cocaine-CPP and self-administration do not use similar neurochemical processes to disrupt reconsolidation or that cocaine-associated memories in self-administering rats do not undergo reconsolidation, as assessed by lever-pressing behavior under cocaine reinstatement conditions.

Methamphetamine-disrupted sensory processing mediates conditioned place preference performance

Drug memory plays an important role in priming subsequent drug use. We used drug-induced conditioned place preference (CPP) as a paradigm to study such drug memory. In this paradigm, repeated association of specific environmental cues with abused drug-induced subjective euphoria has been suggested to motivate later biased approaching behavior toward the euphoria-linked environment at a drug-free status. Our previous report indicated that formation of methamphetamine-induced CPP was independent of de novo protein synthesis. We suspected that methamphetamine-produced effects independent of its hedonic value may be responsible for the drug-induced place preference. One such possibility was that methamphetamine treatment directly disrupted the sensory encoding process and rodents’ novelty-seeking propensity consequently determined the biased place performance. We observed that mice undergoing three times of methamphetamine and compartment pairings exhibited similar compartment preference as those with only one or two methamphetamine-compartment pairings even though they all experienced three vehicle-compartment pairings. Moreover, 30 min before the CPP test, single methamphetamine injection at a dose of 1 mg/kg abolished methamphetamine (1 mg/kg)-induced CPP, while one dose of cocaine (5 mg/kg) did not affect cocaine (5 mg/kg)-induced CPP under a similar protocol. Finally, pretreatment with 1 mg/kg of methamphetamine impaired the spontaneous alteration and recognition performance in Y maze task and impeded the object recognition performance. Taken together, we conclude that methamphetamine-induced CPP performance may be, in part, caused by methamphetamine-impaired sensory processing.

Role of test activity in ethanol-induced disruption of place preference expression in mice

Reduced expression of a drug-induced conditioned place preference (CPP) may reflect a decrease in the drug's conditioned rewarding effects. However, CPP is also open to disruption by processes unrelated to the underlying motivation. In unpublished studies, we previously observed that ethanol pretreatment before testing disrupted expression of ethanol-induced CPP in DBA/2J mice. We hypothesized that this interference effect was due to large ethanol-induced increases in activity. The present studies were designed to examine the relationship between test activity and expression of ethanol-induced CPP both in the presence and absence of ethanol. To assess the generality of this relationship, we examined these effects both in DBA/2J (which are highly activated by ethanol) and in NZB/B1NJ mice (which show similar CPP, but less ethanol-induced activation). In separate experiments, inbred mice from each strain underwent ethanol (2 g/kg) place conditioning. Saline or ethanol was then administered immediately before the test. Ethanol, given immediately before the test, blocked the expression of ethanol CPP in DBA/2J, but not in NZB/B1NJ mice. Moreover, ethanol significantly increased test activity levels in DBA/2J and to a much lesser degree in NZB/B1NJ mice. Correlation analyses showed an inverse phenotypic relationship between preference and test activity, reflecting stronger preferences in less active mice. Disruption of ethanol-CPP observed in DBA/2J mice may be a consequence of high ethanol-induced activity levels. More generally, these studies suggest that competing behaviors can affect expression of a drug-induced CPP independent of affecting the conditioned rewarding effects of the drug.

Drug-induced conditioned place preference and aversion in mice

This protocol describes the equipment and methods used to establish conditioned place preference (CPP) or aversion (CPA). Place conditioning is a form of Pavlovian conditioning routinely used to measure the rewarding or aversive motivational effects of objects or experiences (e.g., abused drugs). Here, we present a place conditioning procedure that has been used extensively to study the motivational effects of ethanol and other abused drugs in mice. This protocol involves three phases: (i) habituation (or a pretest), (ii) conditioning of an association between the drug and a tactile or visual stimulus and (iii) a test that offers a choice between the drug-associated cue and a neutral cue. If the drug has motivational significance, mice will spend significantly more time (CPP) or less time (CPA) in proximity to the drug-associated cue. Potential problems in the design and interpretation of place conditioning studies are discussed. A typical experiment lasts 2 weeks.

Cocaine-but not methamphetamine-associated memory requires de novo protein synthesis

Context-induced drug craving and continuous drug use manifest the critical roles of specific memory episodes associated with the drug use experiences. Drug-induced conditioned place preference (CPP) in C57BL/6J mouse model, in this regard, is an appropriate behavioral paradigm to study such drug use-associated memories. Requirement of protein synthesis in various forms of long-term memory formation and storage has been phylogenetically demonstrated. This study was undertaken to study the requirement of protein synthesis in the learning and memory aspect of the conditioned place preference induced by cocaine and methamphetamine, two abused drugs of choice in local area. Since pCREB has been documented as a candidate substrate for mediating the drug-induced neuroadaptation, the pCREB level in hippocampus, nucleus accumbens, and prefrontal cortex was examined for its potential participation in the formation of CPP caused by these psychostimulants. We found that cocaine (2.5 and 5.0 mg/kg/dose)-induced CPP was abolished by the pretreatment of anisomycin (50 mg/kg/dose), a protein synthesis inhibitor, whereas methamphetamine (0.5 or 1.0 mg/kg/dose)-induced CPP was not affected by the anisomycin pretreatment. Likewise, cocaine-induced CPP was mitigated by another protein synthesis inhibitor, cycloheximide (15 mg/kg/injection) pretreatment, whereas methamphetamine-induced CPP remained intact by such pretreatment. Moreover, anisomycin treatment 2 h after each drug-place pairing disrupted the cocaine-induced CPP, whereas the same treatment did not affect methamphetamine-induced CPP. An increase of accumbal pCREB level was found to associate with the learning phase of cocaine, but not with the learning phase of methamphetamine. We further found that intraaccumbal CREB antisense oligodeoxynucleotide infusion diminished cocaine-induced CPP, whereas did not affect the methamphetamine-induced CPP. Taken together, these data suggest that protein synthesis and accumbal CREB phosphorylation are essential for the learning and consolidation of the cocaine-induced CPP, whereas methamphetamine-induced CPP may be unrelated to the synthesis of new proteins.