Concepción Roger-Sánchez

Effect of adolescent exposure to WIN 55212-2 on the acquisition and reinstatement of MDMA-induced conditioned place preference

The present study employs a conditioned place preference procedure (CPP) to examine the effects of exposure to the cannabinoid agonist WIN 55212-2 (WIN) (0.1 and 0.5mg/kg) during adolescence on the reinforcing properties of +/-3,4-methylenedioxymetamphetamine hydrochloride (MDMA) (1.25 and 2.5mg/kg) in mice. On postnatal day (PD) 27, animals received a daily injection of the assigned treatment on 5 consecutive days, and three days later the place conditioning procedure was initiated (PD 35). The results suggest that pre-exposure to cannabinoids strengthens the properties of MDMA and favors reinstatement of the craving for the drug, which endorses the gateway hypothesis.

Role of the Dopaminergic System in the Acquisition, Expression and Reinstatement of MDMA-Induced Conditioned Place Preference in Adolescent Mice

Background The rewarding effects of 3,4-methylenedioxy-metamphetamine (MDMA) have been demonstrated in conditioned place preference (CPP) procedures, but the involvement of the dopaminergic system in MDMA-induced CPP and reinstatement is poorly understood. Methodology/Principal Findings In this study, the effects of the DA D1 antagonist SCH 23390 (0.125 and 0.250 mg/kg), the DA D2 antagonist Haloperidol (0.1 and 0.2 mg/kg), the D2 antagonist Raclopride (0.3 and 0.6 mg/kg) and the dopamine release inhibitor CGS 10746B (3 and 10 mg/kg) on the acquisition, expression and reinstatement of a CPP induced by 10 mg/kg of MDMA were evaluated in adolescent mice. As expected, MDMA significantly increased the time spent in the drug-paired compartment during the post-conditioning (Post-C) test, and a priming dose of 5 mg/kg reinstated the extinguished preference. The higher doses of Haloperidol, Raclopride and CGS 10746B and both doses of SCH 23390 blocked acquisition of the MDMA-induced CPP. However, only Haloperidol blocked expression of the CPP. Reinstatement of the extinguished preference was not affected by any of the drugs studied. Analysis of brain monoamines revealed that the blockade of CPP acquisition was accompanied by an increase in DA concentration in the striatum, with a concomitant decrease in DOPAC and HVA levels. Administration of haloperidol during the Post-C test produced increases in striatal serotonin, DOPAC and HVA concentrations. In mice treated with the higher doses of haloperidol and CGS an increase in SERT concentration in the striatum was detected during acquisition of the CPP, but no changes in DAT were observed. Conclusions/Significance These results demonstrate that, in adolescent mice, the dopaminergic system is involved in the acquisition and expression of MDMA-induced CPP, but not in its reinstatement.

Age- and sex-related differences in the acquisition and reinstatement of ethanol CPP in mice.

Many people begin to experiment with alcohol during adolescence, an important developmental period during which sex differences in the effects of ethanol appear. In the present study we evaluated the effect of ethanol (0, 0.625, 1.25 or 2.5 g/kg) on the acquisition of a conditioned place preference (CPP) in early and late adolescent male and female mice. In addition, we assessed the capacity of ethanol to induce reinstatement of the CPP after its extinction. CPP was induced in early and late adolescent females with 2.5 g/kg, and in early adolescent males with 1.25 or 2.5 g/kg of ethanol. No CPP was observed in late adolescent males. Priming with ethanol reinstated the CPP induced by the highest dose in early adolescent male and early and late adolescent female mice. Our data suggest that early adolescents of both sex and late adolescent females are particularly vulnerable to the effects of ethanol.

Role of the nNOS gene in ethanol-induced conditioned place preference in mice.

Nitric oxide (NO) produced by neuronal nitric oxide synthase (nNOS) has a role in synaptic plasticity, and evidence suggests its role in a range of effects produced by alcohol in the central nervous system. The aim of the current study was to investigate the role of the nNOS gene in the development of ethanol-induced conditioned place preference (CPP) in mice. The CPP paradigm is designed to investigate the reinforcing properties of drugs of abuse and the development of maladaptive behaviors, such as conditioned response to drug-associated stimuli, after repeated drug exposure. Adult male and female wild type (WT) and nNOS knockout (KO) mice on a mixed B6;129S genetic background were trained by a morning saline session and afternoon ethanol (1, 2, and 3 g/kg; intraperitoneally) session for 4 days. Place preference in a drug-free state was recorded on the following day. Results show that WT males and females developed robust CPP, whereas nNOS KO mice did not (with the exception of female nNOS KO mice conditioned by 2 g/kg ethanol). The differential response of WT and nNOS KO mice was not due to genotypic differences in motor behavior. To investigate if the absence of the nNOS gene causes specific impairment in processing the motivational effect of ethanol or an overall impairment in associative learning, WT and nNOS KO mice were trained by LiCl (150 mg/kg) which causes conditioned place aversion (CPA). Results show that both WT and nNOS KO mice developed significant CPA. The findings that the absence of the nNOS gene impaired ethanol-induced CPP but not LiCl-induced CPA suggest that NO signaling has a specific role in processing the motivational effect of ethanol. Hence, inhibition of nNOS may attenuate the development of maladaptive behaviors associated with alcohol exposure.

Discrimination between cocaine-associated context and cue in a modified conditioned place preference paradigm: Role of the nNOS gene in cue conditioning

The conditioned place preference (CPP) paradigm entails appetitive learning and is utilized to investigate the motivational effects of drug and natural reward in rodents. However, a typical CPP design does not allow dissociation between cue- and context-dependent appetitive learning. In humans, context and cues that had been associated with drug reward can elicit conditioned response and drug craving. Therefore, we investigated (a) methods by which to discriminate between cue- and context-dependent appetitive learning, and (b) the role of the neuronal nitric oxide synthase (nNOS) gene in appetitive learning. Wild-type (WT) and nNOS knockout (KO) mice were trained by cocaine (20 mg/kg) in a discrete context paired with a light cue (a compound context-cue stimulus). In test 1, approach behaviour to either the training context or to the cue in a novel context was determined. WT mice showed robust preference for both cocaine-associated context and cue. nNOS KO mice acquired approach behaviour for the cocaine-associated context but not cue. This finding suggests that the nNOS gene is required for cue-dependent appetitive learning. On the following day (test 2), mice were tested for approach behaviour to the compound context-cue stimulus. Context but not cue exposure in test 1 reduced approach behaviour to the compound context-cue stimulus in test 2, suggesting that repeated context but not cue exposures diminished the conditioned response. Hence, this modified CPP paradigm is useful for the investigation of approach behaviour for both drug-associated context and cue, and allows further investigation of mechanisms underlying cue- and context-dependent appetitive learning.

Pharmacological modulation of protein kinases as a new approach to treat addiction to cocaine and opiates.

Drug addiction shares brain mechanisms and molecular substrates with learning and memory processes, such as the stimulation of glutamate receptors and their downstream signalling pathways. In the present work we provide an up-to-date review of studies that have demonstrated the implication of the main memory-related calcium-dependent protein kinases in opiate and cocaine addiction. The effects of these drugs of abuse in different animal models of drug reward, dependence and addiction are altered by manipulation of the mitogen-activated protein kinase (MAPK) family, particularly extracellular signal regulated kinase (ERK), calcium/calmodulin-dependent kinase II (CaMKII), the protein kinase C (PKC) family (including PKMζ), cAMP-dependent protein kinase A (PKA), cGMP-dependent protein kinase G (PKG), the phosphatidylinositol 3-kinase (PI3K) pathway and its downstream target mammalian target of Rapamycin (mTOR), cyclin-dependent kinase 5 (Cdk5), heat-shock proteins (Hsp) and other enzymes and proteins. Research suggests that drugs of abuse induce dependence and addiction by modifying the signalling pathways that involve these memory-related protein kinases, and supports the idea that drug addiction is an excessive aberrant learning disorder in which the maladaptive memory of drug-associated cues maintains compulsive drug use and contributes to relapse. Moreover, the studies we review offer new pharmacological strategies to treat opiate and cocaine dependence based on the manipulation of these protein kinases. In particular, disruption of reconsolidation of drug-related memories may have a high therapeutic value in the treatment of drug addiction.

`Up-regulation of histone acetylation induced by social defeat mediates the conditioned rewarding effects of cocaine

Social defeat (SD) induces a long-lasting increase in the rewarding effects of psychostimulants measured using the self-administration and conditioned place procedures (CPP). However, little is known about the epigenetic changes induced by social stress and about their role in the increased response to the rewarding effects of psychostimulants. Considering that histone acetylation regulates transcriptional activity and contributes to drug-induced behavioral changes, we addressed the hypothesis that SD induces transcriptional changes by histone modifications associated with the acquisition of place conditioning. After a fourth defeat, H3(K9) acetylation was decreased in the hippocampus, while there was an increase of HAT and a decrease of HDAC levels in the cortex. Three weeks after the last defeat, mice displayed an increase in histone H4(K12) acetylation and an upregulation of histone acetyl transferase (HAT) activity in the hippocampus. In addition, H3(K4)me3, which is closely associated with transcriptional initiation, was also augmented in the hippocampus three weeks after the last defeat. Inhibition of HAT by curcumin (100mg/kg) before each SD blocked the increase in the conditioned reinforcing effects of 1mg/kg of cocaine, while inhibition of HDAC by valproic acid (500mg/kg) before social stress potentiated cocaine-induced CPP. Preference was reinstated when animals received a priming dose of 0.5mg/kg of cocaine, an effect that was absent in untreated defeated mice. These results suggest that the experience of SD induces chromatin remodeling, alters histone acetylation and methylation, and modifies the effects of cocaine on place conditioning. They also point to epigenetic mechanisms as potential avenues leading to new treatments for the long-term effects of social stress on drug addiction.

Involvement of 5-hydroxytryptamine 5-HT3 serotonergic receptors in the acquisition and reinstatement of the conditioned place preference induced by MDMA

Some MDMA (3,4-methylenedioxymethamphetamine) users develop dependence as a result of chronic consumption. The present study evaluated the role of 5-hydroxytryptamine 5-HT₃ receptors in the acquisition, expression and reinstatement of the conditioned place preference (CPP) induced by MDMA. Adolescent male mice were conditioned with 10 mg/kg of MDMA and then treated with 1 or 3mg/kg of the 5-hydroxytryptamine 5-HT₃ antagonist MDL72222 during acquisition of conditioning (experiment 1), before expression of CPP in a post-conditioning test (experiment 2) or before a reinstatement test (experiment 3). MDL72222 was devoid of motivational effects but blocked acquisition of the MDMA-induced CPP. Moreover, following extinction, the low dose of MDL72222 blocked reinstatement of the CPP induced by priming with MDMA. Acute MDMA reduced levels of dihydroxypheylacetic acid (DOPAC) in the striatum and levels of acid 5-hydroxyindoleacetic (5-HIAA) in the cortex. Acute MDMA+MDL72222 also reduced striatal DOPAC. The repeated co-administration of MDMA plus MDL72222 (on PND 32-34-36-38) increased dopamine and decreased DOPAC in the striatum, and increased cortical serotonin and enhanced transporters of dopamine and serotonin. The acute administration (on PND ±55) of MDMA or MDL72222 increased levels of dopamine and reduced those of DOPAC in the striatum and co-administration of MDMA plus MDL72222 increased striatal serotonin. Our results confirm that 5-hydroxytryptamine 5-HT₃ receptors are involved in the acquisition of conditioned rewarding effects of MDMA and demonstrate that these receptors are also involved in reinstatement after extinction.

Role of dopamine neurotransmission in the long-term effects of repeated social defeat on the conditioned rewarding effects of cocaine.

Numerous studies report that social defeat stress alters dopamine (DA) neurotransmission in several areas of the brain. Alterations of the mesolimbic dopaminergic pathway are believed to be responsible for the increased vulnerability to drug use observed as a result of social stress. In the present study, we evaluated the influence of DA receptors on the long-term effect of repeated social defeat (RSD) on the conditioned rewarding and reinstating effects of cocaine. For this purpose, the D1R antagonist SCH 23390 and the D1R antagonist raclopride were administered 30min before each social defeat and a cocaine-induced CPP procedure was initiated three weeks later. The expression of the D1R and D2R was also measured in the cortex and hippocampus throughout the entire procedure. Mice exposed to RSD showed an increase in the conditioned rewarding effects of cocaine that was blocked by both DA receptors antagonists when a subthreshold dose of cocaine was employed. However, while the vulnerability to reinstatement of the preference induced by 25mg/kg cocaine-induced CPP was abolished by the D1R antagonist, it was practically unaffected by raclopride. Increases in D2R receptor levels were observed in the cortex of defeated animals after the first and fourth social defeats and in the hippocampus 3weeks later. Nevertheless, D1R receptor levels in the hippocampus decreased only after the last social defeat. Our results confirm that RSD enhances the conditioned rewarding effects of cocaine and that both DA receptors are involved in this enduring effect of social stress.

Neurochemical substrates of MDMA reward: effects of the inhibition of serotonin reuptake on the acquisition and reinstatement of MDMA-induced CPP.

Different neurotransmitter brain systems have been implicated in the rewarding effects of 3,4-methylenedioxymetamphetamine (MDMA), including dopamine or serotonin. Serotonin selective reuptake inhibitors (SSRI) are a commonly prescribed therapy for psychiatric disorders, and the SSRI fluoxetine is recommended for MDMA users due to its neuroprotective effect against MDMAinduced neurotoxicity. In the present work, we employed the conditioned place preference (CPP) paradigm to study how the inhibition of serotonin reuptake with fluoxetine affected the rewarding and reinstating effects of MDMA in adolescent male mice. Firstly, we evaluated the motivational effects of fluoxetine (1 and 10 mg/kg), administered alone or with a sub-threshold dose of MDMA (1.25 mg/kg). In a second experiment we evaluated the effects of a pretreatment with fluoxetine (1 and 10 mg/kg) on the subsequent acquisition of a CPP induced by MDMA (1.25 mg/kg). The effects of a priming dose of fluoxetine (1 and 10 mg/kg), MDMA (5 or 1.25 mg/kg) or both drugs together on the reinstatement of a previously extinguished CPP induced by MDMA (10 mg/kg) were studied in a third experiment. Fluoxetine did not induce motivational effects but did increase the rewarding effects of a sub-threshold dose of MDMA, and pretreatment with the high dose of fluoxetine had the same effect. Fluoxetine did not induce cross-reinstatement of the MDMA CPP, but the combination of an ineffective priming dose of MDMA and the highest dose of fluoxetine did induce reinstatement of CPP. Neurochemical experiments demonstrated alterations in monoamine levels of MDMA treated mice produced by fluoxetine. As a whole, these results show that the inhibition of serotonin reuptake potentiates the acquisition and reinstatement of MDMA-induced CPP and supports a role for serotonin in MDMA-induced reward.