Changes in CREB and deltaFosB are associated with the behavioural sensitization induced by methylenedioxypyrovalerone.

Methylenedioxypyrovalerone (MDPV) is a synthetic cathinone which has recently emerged as a designer drug of abuse. The objective of this study was to investigate the locomotor sensitization induced by MDPV in adolescent mice, and associated neuroplastic changes in the nucleus accumbens and striatum through deltaFosB and CREB expression. Behavioural testing consisted of three phases: Phase I: conditioning regimen with MDPV (0.3 mg/kg/day for five days) or saline; Phase II: resting (11 days); Phase III: challenged with MDPV (0.3 mg/kg), cocaine (10 mg/kg) or saline on day 16 for both groups. Mice repeatedly exposed to MDPV increased locomotor activity by 165-200% following acute MDPV or cocaine administration after an 11-day resting period, showing a MDPV-induced sensitization to itself and to cocaine. An explanation for this phenomenon could be the common mechanism of action between these two psychostimulants. Furthermore, the MDPV challenge resulted in higher levels of phospho-CREB in MDPV-conditioned mice compared with MDPV-naive mice, probably due to an up-regulation of the cAMP pathway. Likewise, MDPV exposure induced a persistent increase in the striatal expression of deltaFosB; the priming dose of MDPV also produced a significant increase in the accumbal expression of this transcription factor. This study constitutes the first evidence that an exposure to a low dose of MDPV during adolescence induces behavioural sensitization and provides a neurobiological basis for a relationship between MDPV and cocaine. We hypothesize that, similar to cocaine, both CREB and deltaFosB play a role in the induction of this behavioural sensitization.

Local Control of Extracellular Dopamine Levels in the Medial Nucleus Accumbens by a Glutamatergic Projection from the Infralimbic Cortex.

It is generally assumed that infralimbic cortex (ILC) and prelimbic cortex, two adjacent areas of the medial prefrontal cortex (mPFC) in rodents, provide selective excitatory glutamatergic inputs to the nucleus accumbens (NAc) shell and core, respectively. It is also generally believed that mPFC influences the extracellular levels of dopamine in the NAc primarily by an excitatory collateral to the ventral tegmental area (VTA). In the present study, we first established the existence of a selective functional connection between ILC and the posteromedial portions of the VTA (pmVTA) and the mNAc shell (pmNAc shell), by measuring striatal neuronal activation (immunohistochemical analysis of ERK1/2 phosphorylation) and glutamate release (in vivo microdialysis) upon ILC electrical stimulation. A novel optogenetic-microdialysis approach allowed the measurement of extracellular concentrations of glutamate and dopamine in the pmNAc shell upon local light-induced stimulation of glutamatergic terminals from ILC. Cortical electrical and local optogenetic stimulation produced significant increases in the extracellular concentrations of glutamate and dopamine in the pmNAc shell. Local blockade of glutamate release by perfusion of an adenosine A2A receptor antagonist in the pmNAc shell blocked the dopamine release induced by local optogenetic stimulation but only partially antagonized dopamine release induced by cortical electrical stimulation. The results demonstrate that ILC excitatory afferents directly modulate the extracellular concentration of dopamine in the pmNAc shell, but also support the involvement of an indirect mechanism of dopamine control, through a concomitant ILC-mediated activation of the pmVTA. Significance statement: We established the existence of a functional connection between the infralimbic cortex (ILC) and the posteromedial portions of the ventral tegmental area (pmVTA) and the medial nucleus acumbens shell (pmNAc shell). A novel optogenetic-microdialysis approach allowed us to demonstrate that local glutamate release from glutamatergic terminals from the ILC exert a significant modulation of extracellular concentration of dopamine in the pmNAc shell. This mechanism provides the frame for a selective cortical-mediated tonic dopaminergic modulation of specific striatal compartments.

The combination of ethanol with mephedrone increases the signs of neurotoxicity and impairs neurogenesis and learning in adolescent CD-1 mice.

A new family of psychostimulants, under the name of cathinones, has broken into the market in the last decade. In light of the fact that around 95% of cathinone consumers have been reported to combine them with alcoholic drinks, we sought to study the consequences of the concomitant administration of ethanol on mephedrone -induced neurotoxicity. Adolescent male Swiss-CD1 mice were administered four times in one day, every 2h, with saline, mephedrone (25mg/kg), ethanol (2; 1.5; 1.5; 1g/kg) and their combination at a room temperature of 26±2°C. The combination with ethanol impaired mephedrone-induced decreases in dopamine transporter and tyrosine hydroxylase in the frontal cortex; and in serotonin transporter and tryptophan hydroxylase in the hippocampus by approximately 2-fold, 7days post-treatment. Furthermore, these decreases correlated with a 2-fold increase in lipid peroxidation, measured as concentration of malondialdehyde (MDA), 24h post-treatment, and were accompanied by changes in oxidative stress-related enzymes. Ethanol also notably potentiated mephedrone-induced negative effects on learning and memory, as well as hippocampal neurogenesis, measured through the Morris water maze (MWM) and 5-bromo-2'-deoxyuridine staining, respectively. These results are of special significance, since alcohol is widely co-abused with amphetamine derivatives such as mephedrone, especially during adolescence, a crucial stage in brain maturation. Given that the hippocampus is greatly involved in learning and memory processes, normal brain development in young adults could be affected with permanent behavioral consequences after this type of drug co-abuse.

Alcohol enhances the psychostimulant and conditioning effects of mephedrone in adolescent mice; postulation of unique roles of D3 receptors and BDNF in place preference acquisition.

BACKGROUND AND PURPOSE: The psychostimulant mephedrone is often consumed in combination with alcohol (EtOH). This kind of drug consumption during adolescence is a matter of concern. EXPERIMENTAL APPROACH: We studied, in adolescent CD-1 mice, whether EtOH could enhance the psychostimulant (locomotor acivity) and rewarding [conditioned place preference (CPP)] effects of mephedrone. We also determined the transcriptional changes associated with a conditioning treatment with these drugs. KEY RESULTS: Mephedrone (10 mg·kg(-1)) increased locomotor activity, which was further enhanced by 40% when combined with EtOH (1 g·kg(-1)). This enhancement was blocked by haloperidol. Furthermore, mephedrone (25 mg·kg(-1)) induced CPP, which increased by 70% when administered with a dose of EtOH that was not conditioning by itself (0.75 g·kg(-1)). There was enhanced expression of the D3 dopamine receptor mRNA (Drd3) and Arpc5 in all drug-treated groups. The D3 receptor antagonist SB-277011A and the BDNF receptor antagonist ANA-12 completely prevented CPP as well as the increases in Drd3 in all groups. Accordingly, increased expression of BDNF mRNA in medial prefrontal cortex was detected at 2 and 4 h after mephedrone administration. CONCLUSIONS AND IMPLICATIONS: If translated to humans, the enhancement of mephedrone effects by ethanol could result in increased abuse liability. D3 receptors and BDNF play a key role in the establishment of CPP by mephedrone, although an accompanying increase in other synaptic plasticity-related genes may also be necessary.

Protracted treatment with MDMA induces heteromeric nicotinic receptor up-regulation in the rat brain: an autoradiography study.

Previous studies indicate that 3,4-methylenedioxy-methamphetamine (MDMA, ecstasy) can induce a heteromeric nicotinic acetylcholine receptor (nAChR, mainly of α4ß2 subtype) up-regulation. In this study we treated male Sprague-Dawley rats twice-daily for 10 days with either saline or MDMA (7 mg/kg) and sacrificed them the day after to perform [(125)I]Epibatidine binding autoradiograms on serial coronal slices. MDMA induced significant increases in nAChR density in the substantia nigra, ventral tegmental area, nucleus accumbens, olfactory tubercle, anterior caudate-putamen, somatosensory, motor, auditory and retrosplenial cortex, laterodorsal thalamus nuclei, amygdala, postsubiculum and pontine nuclei. These increases ranged from 3% (retrosplenial cortex) to 30 and 34% (amygdala and substantia nigra). No increased α4 subunit immunoreactivity was found in up-regulated areas compared with saline-treated rats, suggesting a post-translational mechanism as occurs with nicotine. The heteromeric nAChR up-regulation in certain areas could account, at least in part, for the reinforcing, sensitizing and psychiatric disorders observed after long-term consumption of MDMA.

Heteromeric nicotinic receptors are involved in the sensitization and addictive properties of MDMA in mice.

We have investigated the effect of nicotinic receptor ligands in the behavioral sensitization (hyperlocomotion) and rewarding properties (conditioned place preference paradigm, CPP) of 3,4-methylenedioxy-methamphetamine (MDMA) in mice. Each animal received intraperitoneal pretreatment with either saline, dihydro-ß-erythroidine (DHßE, 1 mg/kg) or varenicline (VAR, 0.3 mg/kg), 15 min prior to subcutaneous saline or MDMA (5 mg/kg), for 10 consecutive days. On day 1, both DHßE and VAR inhibited the MDMA-induced hyperlocomotion. After 10 days of treatment, MDMA induced a hyperlocomotion that was not reduced (rather enhanced) in antagonist-pretreated animals. This early hyperlocomotion was accompanied by a significant increase in heteromeric nicotinic receptors in cortex that was not blocked by DHßE or VAR. Behavioral sensitization to MDMA was highest 2 weeks after the discontinuation of MDMA treatment. This additional increase in sensitivity was prevented in animals pretreated with DHßE or VAR. At this time, MDMA-treated mice showed a significant increase in heteromeric receptors in cortex that was prevented by DHßE and VAR. An involvement of α7 nicotinic receptors in this effect is ruled out. MDMA (10 mg/kg) induced positive CPP that was abolished by DHßE (2 mg/kg) and VAR (2 mg/kg). Moreover, chronic nicotine pretreatment (2 mg/kg, ip, b.i.d., for 14 days) caused MDMA, administered at a low dose (3 mg/kg), to induce CPP, which would otherwise not occur. Finally, present results point out that heteromeric nicotinic receptors are involved in locomotor sensitization and addictive potential induced by MDMA. Thus, varenicline might be a useful drug to treat both tobacco and MDMA abuse at once.