Manuel Daza-Losada

Rewarding Effects and Reinstatement of MDMA-Induced CPP in Adolescent Mice

Although the rewarding effects of 3,4-methylenedioxy-metamphetamine (MDMA) have been demonstrated in self-administration and conditioned place preference (CPP) procedures, its addictive potential (ie, the vulnerability to relapse, measured by its ability to induce reinstatement of an extinguished response), remains poorly understood. In this study, the effects of MDMA (5, 10, and 20 mg/kg) on the acquisition, extinction and reinstatement of CPP were evaluated in mice, using two different protocols during acquisition of CPP. In the first experiment, animals were trained using a two-session/day schedule (MDMA and saline for 4 consecutive days), whereas in the second experiment, they were trained using an alternating day schedule (MDMA and saline each 48 h). After extinction, the ability of drug priming to reinstate CPP was evaluated. In Experiment 1, MDMA did not significantly increase the time spent in the drug-paired compartment during the post-conditioning (Post-C) test, although the preference was evident a week afterwards, lasting between 2 and 21 weeks. No reinstatement was observed after MDMA priming. In Experiment 2, all doses produced CPP in Post-C, which lasted between 1 and 4 weeks. MDMA induces reinstatement at doses up to 4 times lower than those used in conditioning. The analyses of brain monoamines revealed that the daily schedule of treatment induces a non-dose-dependent decrease in dopamine and serotonin (5-HT) in the striatum, whereas the alternating schedule produces a dose-dependent decrease of 5-HT in the cortex. These results demonstrate that MDMA produces long-lasting rewarding effects and reinstatement after extinction, suggesting the susceptibility of this drug to induce addiction.

Acute behavioural and neurotoxic effects of MDMA plus cocaine in adolescent mice.

The poly-drug pattern is the most common among those observed in MDMA users, with cocaine being a frequently associated drug. This study evaluates the acute effects of MDMA (5, 10 and 20 mg/kg), alone or in combination with cocaine (25 mg/kg), on motor activity, anxiety (elevated plus maze and social interaction test), memory and brain monoamines in adolescent mice. Both drugs, administered alone or concurrently, produced hyperactivity and a decrease in social contacts. However, an anxiolytic effect, studied by means of the elevated plus maze and expressed as an increase in the time spent on the open arms, was observed only in those animals treated with cocaine and MDMA. The passive avoidance task was affected only with the highest MDMA dose (20 mg/kg). Mice treated with MDMA did not present significant changes in brain monoamines, while those receiving MDMA and cocaine showed a decrease in DA in the striatum, which was accompanied by an increase in the serotonin concentration in the striatum and cortex 30 min after acute administration. In conclusion, the combined use of MDMA and cocaine produces a predominance of serotonin over DA, which is associated with an anxiolytic profile, defensive behaviours and fewer social contacts.

Acquisition and reinstatement of MDMA-induced conditioned place preference in mice pre-treated with MDMA or cocaine during adolescence.

Those who take ecstasy are more likely to consume other drugs than non‐users with cocaine abuse being reported by 75.5% of high school student MDMA (± 3,4‐methylenedioxymetamphetamine hydrochloride) users. The aim of this work was to evaluate the effects of exposure during adolescence to MDMA, cocaine or to both drugs on the MDMA‐induced conditioned place preference (CPP) in adult mice. Animals received two daily administrations of saline, 10 mg/kg of MDMA, 25 mg/kg of cocaine or 10 mg/kg of MDMA plus 25 mg/kg of cocaine over 3 days (from PD28 to 30). Three weeks after pre‐treatment, the MDMA‐induced CPP procedure was initiated (PD52). Acquisition of CPP was induced with a sub‐threshold dose of MDMA (1.25 mg/kg) only in animals treated during adolescence with MDMA alone. Preference was established in all the groups after conditioning with 10 mg/kg of MDMA, while the time required to achieve extinction was longer in those pre‐treated with cocaine or MDMA alone (46 and 28 sessions, respectively). Moreover, preference was reinstated with progressively lower priming doses of MDMA in mice pre‐treated with MDMA or cocaine alone. These results demonstrate that early exposure to MDMA or cocaine induces long‐lasting changes that last until adulthood and modify the response of animals to MDMA.

Effect of the CB1 cannabinoid agonist WIN 55212-2 on the acquisition and reinstatement of MDMA-induced conditioned place preference in mice

BackgroundNumerous reports indicate that MDMA users consume other psychoactive drugs, among which cannabis is one of the most common. The aim of the present study was to evaluate, using the conditioned place preference, the effect of the cannabinoid agonist WIN 55,212-2 on the rewarding effects of MDMA in mice.MethodsIn the first experiment adolescent mice were initially conditioned with 1.25, 2.5 or 5 mg/kg of MDMA or 0.1 or 0.5 mg/kg of WIN and subsequently with both drugs. Reinstatement of the extinguished preference by priming doses was performed in the groups that showed CPP. In the second experiment, animals were conditioned with 2.5 or 5 mg/kg of MDMA and, after extinction, reinstatement of the preference was induced by 0.5 or 0.1 mg/kg of WIN.ResultsA low dose of WIN 55212-2 (0.1 mg/kg) increased the rewarding effects of low doses of MDMA (1.25 mg/kg), although a decrease in the preference induced by MDMA (5 and 2.5 mg/kg) was observed when the dose of WIN 55212-2 was raised (0.5 mg/kg). The CB1 antagonist SR 141716 also increased the rewarding effects of the lowest MDMA dose and did not block the effects of WIN. Animals treated with the highest WIN dose plus a non-neurotoxic dose of MDMA exhibited decreases of striatal DA and serotonin in the cortex. On the other hand, WIN 55212-2-induced CPP was reinstated by priming injections of MDMA, although WIN did not reinstate the MDMA-induced CPP.ConclusionsThese results confirm that the cannabinoid system plays a role in the rewarding effects of MDMA and highlights the risks that sporadic drug use can pose in terms of relapse to dependence. Finally, the potential neuroprotective action of cannabinoids is not supported by our data; on the contrary, they are evidence of the potential neurotoxic effect of said drugs when administered with MDMA.

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.

The Novelty-Seeking Phenotype Modulates the Long-Lasting Effects of Intermittent Ethanol Administration during Adolescence

The aim of the present study was to investigate if a novelty-seeking phenotype mediates the long-lasting consequences of intermittent EtOH intoxication during adolescence. The hole board test was employed to classify adolescent mice as High- or Low-Novelty Seekers. Subsequently, animals were administered ethanol (1.25 or 2.5 g/kg) on two consecutive days at 48-h intervals over a 14-day period. Anxiety levels - measured using the elevated plus maze- spontaneous motor activity and social interaction test were studied 3 weeks later. A different set of mice underwent the same procedure, but received only the 2.5 g/kg dose of ethanol. Three weeks later, in order to induce CPP, the same animals were administered 1 or 6 mg/kg of cocaine or 1 or 2.5 mg/kg MDMA. The results revealed a decrease in aggressive behaviors and an anxiolytic profile in HNS mice and longer latency to explore the novel object by LNS mice. Ethanol exposure enhanced the reinforcing effects of cocaine and MDMA in both groups when CPP was induced with a sub-threshold dose of the drugs. The extinguished cocaine-induced CPP (1 and 6 mg/kg) was reinstated after a priming dose in HNS animals only. Our results confirm that intermittent EtOH administration during adolescence induces long-lasting effects that are manifested in adult life, and that there is an association between these effects and the novelty-seeking phenotype.

Adolescent pre‐exposure to ethanol and 3,4‐methylenedioxymethylamphetamine (MDMA) increases conditioned rewarding effects of MDMA and drug‐induced reinstatement

Many adolescents often take ethanol (EtOH) in combination with 3,4‐methylenedioxymethylamphetamine (MDMA). In the present work, we used a mouse model to study the effect of repeated pre‐exposure during adolescence to EtOH (2 g/kg), MDMA (10 or 20 mg/kg) or EtOH + MDMA on the rewarding and reinstating effects of MDMA in the conditioned place preference (CPP) paradigm. Pre‐exposure to EtOH, MDMA or both increased the rewarding effects of a low dose of MDMA (1.25 mg/kg). These pre‐treatments did not affect the acquisition of the CPP induced by 5 mg/kg of MDMA. However, the CPP was more persistent in mice pre‐exposed to both doses of MDMA or to EtOH + MDMA20. After extinction of the CPP induced by 5 mg/kg of MDMA, reinstatement was observed in all groups with a priming dose of 2.5 mg/kg of MDMA, in the groups pre‐exposed to EtOH or MDMA alone with a priming dose of 1.25 mg/kg, and in the groups pre‐treated with MDMA alone with a priming dose of 0.625 mg/kg. Pre‐treatment during adolescence with MDMA or EtOH induced long‐term changes in the level of biogenic amines [dihydroxyphenyl acetic acid, homovanillic acid, dopamine turnover, serotonin (5‐hydroxytryptamine, 5‐HT) and 5‐hydroxyindole acetic acid (5‐HIAA) in the striatum, and 5‐HT and 5‐HIAA in the cortex] after the first reinstatement test, although these effects depended on the dose used during conditioning. These results suggest that exposure to EtOH and MDMA during adolescence reinforces the addictive properties of MDMA.

Effect of adolescent exposure to MDMA and cocaine on acquisition and reinstatement of morphine-induce CPP.

It is well known that an elevated percentage of ecstasy users also consume cocaine. Recently, it has been reported that a high frequency of heroin smokers first consumed heroin under the effects of ecstasy with the hope of reducing the stimulant effects of the latter drug. The aim of the present study was to evaluate the effect of exposure to MDMA and cocaine during adolescence on morphine-induced conditioned place preference (CPP) and reinstatement in adulthood. In the first experiment, adolescent mice were exposed to six injections of MDMA and three weeks later their response to the reinforcing properties of 40 mg/kg of morphine was evaluated using the CPP paradigm. All the treatment groups developed the same magnitude of morphine-induced preference and, after CPP was extinguished, it was restored in all the groups with a priming dose of 10 mg/kg of morphine. Only mice that had been treated with 10 or 20 mg/kg of MDMA had their morphine-induced preference reinstated after receiving only 5 mg/kg of morphine. In the second experiment, adolescent mice were similarly treated with six administrations of cocaine (25 mg/kg) or cocaine plus MDMA (5, 10 or 20 mg/kg), and their response to morphine-induce CPP was evaluated three weeks later. Similarly to the first experiment, all the groups developed a preference for the morphine-paired compartment, but this preference was not reinstated with a priming dose of 10 mg/kg of morphine following extinction, as was the case among the control animals. These results lead us to hypothesize that periadolescent MDMA exposure alters responsiveness to the rewarding properties of morphine, highlighting MDMA as a gateway drug whose use may increase the likelihood of dependence on other drugs.

Effects of extended cocaine conditioning in the reinstatement of place preference

Rats allowed extended access to cocaine self-administration develop a number of symptoms of addiction, such as greater susceptibility to drug-induced relapse. Using the conditioned place preference (CPP), the number of conditioning training sessions was increased in order to augment exposure to contextual cues associated with the effects of a drug. Mice were conditioned with a steady dose of 6 or 25 mg/kg of cocaine for 4, 8, 12, 16, 20 or 40 days. Weekly sessions of extinction followed the establishment of preference, after which a priming dose of cocaine was administered to reinstate the extinguished preference. The magnitude of the place preference effect was equal in all groups, independently of the number of conditioning sessions. The persistence of the place preference was not related with the number of sessions. Higher responsiveness to reinstatement of the extinguished preference occurred only with an intermediate number of conditioning sessions. In this way, the relation between the number of training sessions and vulnerability to relapse appeared to follow an inverted U-shaped function. Our results suggest that increasing the number of conditioning sessions from 12 to up to 16, without increasing the amount of drug administered, can be of great use in the study of vulnerability to relapse.

Behavioural and neurotoxic long-lasting effects of MDMA plus cocaine in adolescent mice

The poly-drug pattern is the most common among MDMA users, with cocaine being a frequently associated drug. The aim of the present work was to evaluate the behavioural and neurotoxic long-term effects of exposure during adolescence to MDMA alone or plus cocaine. Mice of 28 to 30 days of age received a treatment of two daily injections of an identical dose of MDMA (5, 10 or 20 mg/kg), alone or plus cocaine (25 mg/kg), for 3 days (6 administrations). Three weeks after receiving MDMA, an increase in the time dedicated by the animals to social contacts with their conspecifics was observed, whilst their behaviour in the elevated plus maze showed no differences from that of non-treated mice. After being exposed to MDMA plus cocaine, mice spent more time in social contacts during the interaction test, as well as exhibiting an anxiolytic profile in the elevated plus maze, with an increase in the time and number of entries in the open arms. The activity of mice treated with cocaine alone or plus MDMA remained constant; the decrease observed among the rest of the animals after the second hour was absent in their case. The level of dopamine in the striatum was diminished in mice treated with 20 mg/kg of MDMA, but this neurotransmitter was not affected in animals exposed to the same dose plus cocaine. The present results highlight pronounced alterations in the behaviour of adult mice after exposure to MDMA and cocaine during adolescence, and demonstrate that these long-term effects can occur without the dopaminergic system becoming affected.