The effect of mephedrone on human neuroblastoma and astrocytoma cells

Mephedrone is an illegal drug that is used recreationally. Few studies have been conducted to investigate the mechanisms by which mephedrone is harming cells. In this research, we investigated the effect of mephedrone using toxicology coupled with LC-MS/MS based metabolomics in the two CNS derived cell lines. Methods of assessment such as neutral red (NR) assay, dimethylthiazolyl diphenyltetrazolium bromide (MTT), lactose dehydrogenase (LDH) measurement, and morphology were performed to identify the effect on cell viability and to identify the best concentration to be used in a metabolomics study. A concentration of 100 μM of mephedrone was used in the metabolomic experiment because at this concentration mephedrone had induced several intracellular changes. Although there no clear indicators of cellular damage caused by mephedrone. In astrocytes there was a clear indication that cell membrane function might be impaired by depletion of ether lipids.

How hydrogen bonding and π-π interactions synergistically facilitate mephedrone adsorption by bio-sorbent: An in-depth microscopic scale interpretation

Mephedrone (4-methylmethcathinone, MEPH) exhibited severe ecologic hazards and health detriments. A novel deep eutectic solvent functionalized magnetic ZIF-8/hierarchical porous carbon (DMZH) with excellent selectivity, interference resistance and recyclability, was developed for the rapid adsorption of MEPH. Initially, potential adsorption sites of MEPH were predicted. Then, π-π and hydrogen bonding interactions were proposed and verified from characterizations, comparative experiments and theoretical calculations. The synergistic effects of the hydrogen bonding and π-π interactions increased the adsorption energies from -15.26 kcal⋅mol-1 to -21.83 kcal⋅mol-1, enhanced the degree of π-dissociation, enlarged the π-π isosurface area, extended the van der Waals surface mutual penetration distance, achieving stronger affinity and remarkable adsorption. Furthermore, offset (parallel-displaced) π-π stacking form existed between DMZH and MEPH. DMZH acted as the hydrogen bond donor and MEPH served as the hydrogen bond acceptor to form O-H⋯O and N-H⋯O hydrogen bonding interaction. Profiting from the synergistic effects, DMZH showed satisfactory adsorption for MEPH within 20 min with a maximum adsorption capacity of 3270.11 μg∙g-1, displayed excellent performance in wide pH range of 5∼11 and in the coexistence of multi-chemicals.

The pharmacology and neurotoxicology of synthetic cathinones

The synthetic cathinones are man-made compounds derived from the naturally occurring drug cathinone, which is found in the khat plant. The drugs in this pharmacological class that will be the focus of this chapter include mephedrone, MDPV, methcathinone and methylone. These drugs are colloquially known as "bath salts". This misnomer suggests that these drugs are used for health improvement or that they have legitimate medical uses. The synthetic cathinones are dangerous drugs with powerful pharmacological effects that include high abuse potential, hyperthermia and hyperlocomotion. These drugs also share many of the pharmacological effects of the amphetamine class of drugs including methamphetamine, amphetamine and MDMA and therefore have high potential to cause damage to the central nervous system. The synthetic cathinones are frequently taken in combination with other psychoactive drugs such as alcohol, marijuana and the amphetamine-like stimulants, creating a situation where heightened pharmacological and neurotoxicological effects are likely to occur. Despite the structural features shared by the synthetic cathinones and amphetamine-like stimulants, including their actions at monoamine transporters and receptors, the effects of the synthetic cathinones do not always match those of the amphetamines. In particular, the synthetic cathinones are far less neurotoxic than their amphetamine counterparts, they produce a weaker hyperthermia, and they cause less glial activation. This chapter will briefly review the pharmacology and neurotoxicology of selected synthetic cathinones with the aim of delineating key areas of agreement and disagreement in the literature particularly as it relates to neurotoxicological outcomes.

The role of the L-arginine-NO-cGMP-dependent pathway in the development of sensitization to mephedrone effects on the locomotor activity in mice

Mephedrone, a popular psychostimulating substance widely used illegally in recreational purposes, exerts in rodents that regularly and intermittently were exposed to it a sensitized response to the drug. Behavioral sensitization is one of experimental models of drug dependency/abuse liability. In the present study we evaluated a potential involvement of the L-arginine-NO-cGMP pathway in the development of sensitization to the mephedrone-induced hyperlocomotion. Locomotor activity was measured automatically and experiments were performed on male Albino Swiss mice. We demonstrated that a 5-day administration of 7-nitroindazole (10 or 20 mg/kg/day) and L-NAME (50 mg/kg/day) suppressed the development of sensitization to the mephedrone-induced hyperlocomotion. As for L-arginine (125 or 250 mg/kg/day) and methylene blue (5 or 10 mg/kg/day) the obtained outcomes are inconclusive. Furthermore, the lower dose of L-NAME (25 mg/kg/day) surprisingly potentiated the development of sensitization to the mephedrone-induced effects on the spontaneous locomotor activity in mice. In conclusion, our data demonstrated that modulators of the L-arginine-NO-cGMP pathway may differently affect the development of sensitization to the locomotor stimulant effects of mephedrone. Inhibition of neuronal nitric oxide synthase (NOS) seems to prevent this process quite profoundly, non-selective inhibition of NOS may have a dual effect, whereas inhibition of soluble guanylate cyclase may only partially suppress the development of sensitization to the mephedrone-induced effects.

Portable near infrared spectroscopy for the isomeric differentiation of new psychoactive substances

Rapid and efficient identification of the precise isomeric form of new psychoactive substances (NPS) by forensic casework laboratories is a relevant challenge in the forensic field. Differences in legal status occur for ring-isomeric species of the same class, thus leading to different penalties and judicial control. Portable systems such as near-infrared (NIR) spectroscopy recently emerged as suitable techniques for the on-scene identification of common drugs of abuse such as cocaine, MDMA and amphetamine. This way, the overall forensic process becomes more efficient as relevant information on substance identity becomes available directly at the scene of crime. Currently, no NIR-based applications exist for the rapid, on-scene detection of NPS isomers. Herein, we present the differentiation of cathinone and phenethylamine-type NPS analogues based on their NIR spectrum recorded in 2 seconds on a portable 1350 - 2600 nm spectrometer. A prior developed data analysis model was found suitable for the identification of the methylmethcathinone (MMC) isomers 2-MMC, 3-MMC and 4-MMC. In 51 mixtures and 22 seized casework samples, the correct isomeric form was detected in all cases except for a few mixtures with an active ingredient content of 10 wt%. These results show the feasibility of on-site NPS detection as presumptive test performed directly at the scene of crime with a small size NIR-spectrometer. Additionally, in the illicit drug analysis laboratory the combination of NIR and GC-MS analysis might be suitable for robust identification of NPS isomers and analogues.

Binge-like mephedrone treatment induces memory impairment concomitant with brain kynurenic acid reduction in mice

While mephedrone (4-methylmethcathinone), a synthetic cathinone derivative, is widely abused by adolescents and young adults, the knowledge about its long-term effects on memory processes is limited. Kynurenic acid (KYNA) is a neuroactive metabolite of the kynurenine pathway of tryptophan degradation. KYNA is considered an important endogenous modulator influencing physiological and pathological processes, including learning and memory processes. The aim of this study was to determine whether (A) binge-like mephedrone administration (10.0 and 30.0 mg/kg, intraperitoneally, in 4 doses separated by 2 h) induces memory impairments, assessed 2, 8 and 15 days after mephedrone cessation in the passive avoidance test in mice, and whether (B) KYNA is involved in these memory processes. To clarify the role of KYNA in the mephedrone effects, its level in the murine brain in vivo, and in cortical slices in vitro, as well as the activities of kynurenine aminotransferases (KATs) I and II were assessed. Furthermore, cell line experiments were conducted to investigate the effects of mephedrone on normal human brain cells. Our results showed memory impairments 8 and 15 days after binge-like mephedrone administration. At the same time, reduction in the KYNA level in the murine brain was noted. In vitro studies showed no effect of mephedrone on the production of KYNA in cortical slices or on the activity of the KAT I and II enzymes. Finally, exposure of normal cells to mephedrone in vitro resulted in a modest reduction of cell viability and proliferation.

Behavioral patterns of people who use synthetic psychostimulants: Results of a qualitative study in St. Petersburg, Russia

BACKGROUND

Russia, like many other places, is currently experiencing a proliferation of new psychoactive substances, many of which are psychostimulants. In St. Petersburg, these appear to be mostly congeners of cathinone. We sought to obtain qualitative data to better understand the impact on the health and behaviors of people who use drugs (PWUD) by recruiting individuals who reported recent use of psychostimulants.

METHODS

In-depth qualitative data on current drug use and its effects were collected through thirty interviews (n=30) and two focus groups (n=10: five male, five female). The interviews and focus groups also provided data on the social contexts of drug use including sexual behaviors and associated medical issues. Secondary data about online drug purchases were obtained from a source that accesses and analyzes darknet purchases. Qualitative data were initially coded using a priori codes developed on the basis of the interview guide, and then data were coded again inductively based on emergent findings from the data. Thematic analysis was carried out using OpenCode 4.0 qualitative data analysis software.

RESULTS

Thematic analysis of the interviews and focus groups identified distinct differences in behavior patterns between older, more experienced PWUD and a "new generation" of PWUD. Routes of initiation of drug use and sexual behaviors associated with drug use differed, but both groups reported high levels of unsafe injection and sexual behaviors. In interpreting the texts and purchasing data, we have attempted to anticipate how the drug use patterns can influence HIV transmission.

CONCLUSIONS

The emergence of a new class of psychostimulant drugs presents new threats to the health of drug users and new opportunities to intervene to reduce those risks. The information obtained may assist HIV/AIDS prevention specialists and drug user support groups in their efforts to decrease unsafe drug use and sexual behaviors.

Sex differences in inflammatory cytokine levels following synthetic cathinone self-administration in rats

Synthetic cathinones are used as stimulants of abuse. Many abused drugs, including stimulants, activate nuclear factor-κB (NF-κB) transcription leading to increases in NF-κB-regulated pro-inflammatory cytokines, and the level of inflammation appears to correlate with length of abuse. The purpose of this study was to measure the profile of IL-1α, IL-1β, IL-6, CCL2 and TNF-α in brain and plasma to examine if drug exposure alters inflammatory markers. Male and female Sprague-Dawley rats were trained to self-administer α-pyrrolidinopentiophenone (α-PVP) (0.1 mg/kg/infusion), 4-methylmethcathinone (4MMC) (0.5 mg/kg/infusion), or saline through autoshaping, and then self-administered for 21 days during 1 h (short access; ShA) or 6 h (long access; LgA) sessions. Separate rats were assigned to a naïve control group. Cytokine levels were examined in amygdala, hippocampus, hypothalamus, prefrontal cortex, striatum, thalamus, and plasma. Rats acquired synthetic cathinone self-administration, and there were no sex differences in drug intake. Synthetic cathinone self-administration produced sex differences in IL-1α, IL-1β, IL-6, CCL2 and TNF-α levels. There were widespread increases in inflammatory cytokines in the brains of male rats compared to females, particularly for 4MMC, whereas females were more likely to show increased inflammatory cytokines in plasma compared to saline groups than males. Furthermore, these sex differences in cytokine levels were more common after LgA access to synthetic cathinones than ShA. These results suggest that synthetic cathinone use likely produces sex-selective patterns of neuroinflammation during the transition from use to abuse. Consequently, treatment need may differ depending on the progression of synthetic cathinone abuse and based on sex.

Insight into Glutamatergic Involvement in Rewarding Effects of Mephedrone in Rats: In Vivo and Ex Vivo Study

Mephedrone is a widely used drug of abuse, exerting its effects by interacting with monoamine transporters. Although this mechanism has been widely studied heretofore, little is known about the involvement of glutamatergic transmission in mephedrone effects. In this study, we comprehensively evaluated glutamatergic involvement in rewarding effects of mephedrone using an interdisciplinary approach including (1) behavioural study on effects of memantine (non-selective NMDA antagonist) on expression of mephedrone-induced conditioned place preference (CPP) in rats; (2) evaluation of glutamate concentrations in the hippocampus of rats following 6 days of mephedrone administration, using in vivo magnetic resonance spectroscopy (MRS); and (3) determination of glutamate levels in the hippocampus of rats treated with mephedrone and subjected to MRS, using ion-exchange chromatography. In the presented research, we confirmed priorly reported mephedrone-induced rewarding effects in the CPP paradigm and showed that memantine (5 mg/kg) was able to reverse the expression of this effect. MRS study showed that subchronic mephedrone administration increased glutamate level in the hippocampus when measured in vivo 24 h (5 mg/kg, 10 mg/kg and 20 mg/kg) and 2 weeks (5 mg/kg and 20 mg/kg) after last injection. Ex vivo chromatographic analysis did not show significant changes in hippocampal glutamate concentrations; however, it showed similar results as obtained in the MRS study proving its validity. Taken together, the presented study provides new insight into glutamatergic involvement in rewarding properties of mephedrone.

Post-mortem distribution of mephedrone and its metabolites in body fluids and organ tissues of an intoxication case

New psychoactive substances (NPS) are substances that continue to appear on the drug market to bypass controlled substance legislation. Mephedrone or 4-methylmethcathinone is becoming the most popular new psychoactive substance among youth as a recreational drug. The present study describes the optimization and validation of a sensitive method that combined clean up procedure and LC-MS/MS technique designed to simultaneously determine the presence of Mephedrone and its two metabolites (normephedrone as active metabolite and dyhidromephedrone) in post-mortem specimens (body fluids and organ tissues). To date, this is the first determination of Mephedrone metabolites in post-mortem specimens. The validated method was applied to a fatal Mephedrone intoxication case. The distribution of the three analytes in different post-mortem matrices was presented. The toxicological results of the studied case are discussed, along with autopsy, histopathological evidence and crime-scene information. The toxicological results presented in the study provide new data relative to mephedrone and the distribution of its metabolites in post-mortem specimens. In our opinion, the metabolite concentration database must be developed because the metabolites may be linked to toxicity. The pattern of parent drug and its metabolites can be helpful in the interpretation of fatal cases involving mephedrone, which will contribute to the currently limited knowledge about mephedrone and metabolites concentrations.

Alpha-pyrrolidinopentiophenone and mephedrone self-administration produce differential neurochemical changes following short- or long-access conditions in rats

Stimulant-induced neurochemical changes may occur at different times for different brain regions or neurotransmitter systems. This study sought to examine the behavioral and neurochemical effects of extended access to α-pyrrolidinopentiophenone (α-PVP) and 4-methylmethcathinone (4MMC). Male and female Sprague-Dawley rats were trained to self-administer α-PVP (0.1 mg/kg/infusion) or 4MMC (0.5 mg/kg/infusion) through autoshaping, and then self-administered for 21 days during 1 h (short access; ShA) or 6 h (long access; LgA) sessions. Separate rats were assigned to a naïve control group. Amygdala, hippocampus, hypothalamus, prefrontal cortex (PFC), striatum, and thalamus were extracted, and tissue was analyzed with electrochemical detection and liquid chromatography mass spectrometry. Rats acquired self-administration of α-PVP and 4MMC, and LgA rats showed more escalation of self-administration than ShA rats. Synthetic cathinone administration produced several effects on neurotransmitters. LgA self-administration of α-PVP increased 5-HIAA levels in all brain regions, compared to control. In contrast, both LgA and ShA 4MMC self-administration decreased 5-HT and 5-HIAA levels in most brain regions. LgA exposure to both synthetic cathinones increased DOPAC levels in hypothalamus and striatum, and increased HVA levels in striatum compared to control. LgA self-administration of either synthetic cathinone produced region-specific increases in NE levels, whereas ShA self-administration lowered NE levels in select locations compared to control. These alterations in neurotransmitter levels indicate that synthetic cathinone use may produce differential neurochemical changes during the transition from use to abuse, and that 21 days of self-administration only models the beginning stages of dysregulated drug intake.

The psychoactive drug of abuse mephedrone differentially disrupts blood-brain barrier properties

Background

Synthetic cathinones are a category of psychostimulants belonging to the growing number of designer drugs also known as “Novel Psychoactive Substances” (NPS). In recent years, NPS have gained popularity in the recreational drug market due to their amphetamine-like stimulant effects, low cost, ease of availability, and lack of detection by conventional toxicology screening. All these factors have led to an increase in NPS substance abuse among the young adults, followed by spike of overdose-related fatalities and adverse effects, severe neurotoxicity, and cerebral vascular complications. Much remains unknown about how synthetic cathinones negatively affect the CNS and the status of the blood-brain barrier (BBB).

Methods

We used in vitro models of the BBB and primary human brain microvascular endothelial cells (hBMVEC) to investigate the effects of the synthetic cathinone, 4-methyl methcathinone (mephedrone), on BBB properties.

Results

We showed that mephedrone exposure resulted in the loss of barrier properties and endothelial dysfunction of primary hBMVEC. Increased permeability and decreased transendothelial electrical resistance of the endothelial barrier were attributed to changes in key proteins involved in the tight junction formation. Elevated expression of matrix metalloproteinases, angiogenic growth factors, and inflammatory cytokines can be explained by TLR-4-dependent activation of NF-κB signaling.

Conclusions

In this first characterization of the effects of a synthetic cathinone on human brain endothelial cells, it appears clear that mephedrone-induced damage of the BBB is not limited by the disruption of the barrier properties but also include endothelial activation and inflammation. This may especially be important in comorbid situations of mephedrone abuse and HIV-1 infections. In this context, mephedrone could negatively affect HIV-1 neuroinvasion and NeuroAIDS progression.

Vulnerability factors for mephedrone-induced conditioned place preference in rats-the impact of sex differences, social-conditioning and stress

RATIONALE

Mephedrone is a frequently overused drug of abuse that belongs to the group of novel psychoactive substances. Although its mechanism of action, as well as toxic and psychoactive effects, has been widely studied, the role of different factors that could contribute to the increased vulnerability to mephedrone abuse is still poorly understood.

OBJECTIVES

The aim of the presented study was to assess the impact of several factors (sex differences, social-conditioning, and chronic mild unpredictable stress - CMUS) on the liability to mephedrone-induced reward in Wistar rats.

METHODS

The rewarding effects of mephedrone in male and female rats were assessed using the conditioned place preference (CPP) procedure. Furthermore, the impact of social factor and stress was evaluated in male rats using social-CPP and CMUS-dependent CPP, respectively.

RESULTS

Mephedrone induced classic-CPP in female (10 mg/kg), as well as in male (10 and 20 mg/kg) rats. However, the impact of mephedrone treatment during social-CPP was highly dose-dependent as the rewarding effects of low dose of mephedrone (5 mg/kg; non-active in classic-CPP) were potentiated when administered during social-conditioning. Interestingly, social-conditioning with a higher dose of 20 mg/kg (that induced classic-CPP) was able to reverse these effects. Finally, CMUS potentiated rewarding effects of a low dose of mephedrone (5 mg/kg) and increased the level of corticosterone in rats' prefrontal cortex and hippocampus.

CONCLUSIONS

Altogether, the presented results give new insight into possible factors underlying the vulnerability to mephedrone abuse and can serve as a basis for further studies assessing mechanisms underlying observed effects.

Wastewater-based epidemiology combined with local prescription analysis as a tool for temporalmonitoring of drugs trends - A UK perspective

This paper reports the application of wastewater-based epidemiology (WBE) for the monitoring of one city in the UK in years 2014-2018 as a means of 1) exploring relative temporal changes of illicit drug usage trends across 5 sampling weeks in 5 years, (2) assessing policy impact in reducing drug consumption, focussing particularly on mephedrone, which was classified as a class B drug in the UK in 2010, and the effects of subsequent regulation such as the novel psychoactive substances (NPS) bill of 2016, (3) investigating temporal changes in consumption of prescription pharmaceuticals vs illicit drug usage, and (4) comparing consumption of prescription drugs with WBE to enable more accurate verification of prescription drugs with abuse potential. Mephedrone was quantified only for the first two years of the study, 2014-2015, and remained undetected for the next three years of the study. This shows that given enough time changes in drug policy can have an effect on drug consumption. However, after the introduction of the 2016 NPS bill, between the third and fourth study years, there was an observable increase in the consumption of "classic" drugs of abuse such as cocaine, MDMA and ketamine suggesting a shift away from novel psychoactives. The unique prescription dataset allowed for a more accurate calculation of heroin consumption using morphine by examining other sources morphine. Additionally, for compounds with controlled prescription like methadone, trends in consumption estimated by wastewater and trends in prescription correlated. Wastewater-based epidemiology is a powerful tool for examining whole populations and determining the efficacy and direction of government actions on health, as it can, alongside prescription and wider monitoring data, provide a clear insight into what is being consumed by a population and what action is needed to meet required goals.

Mephedrone and MDMA: A comparative review

Mephedrone and MDMA are both constituents of party drugs, with mephedrone being relatively new compared to MDMA. This review compares current knowledge regarding the patterns of usage and neuropsychobiological effects of both mephedrone and MDMA. Both drugs share common psychoactive effects, the duration of which is significantly shorter with mephedrone use, attributing towards a pattern of binge use among users. Both drugs have also been associated with adverse health, psychiatric, and neurocognitive problems. Whilst there is extensive research into the psychobiological problems induced by MDMA, the evidence for mephedrone is comparatively limited. The adverse effect profile of mephedrone appears to be less severe than that of MDMA. Users often believe it to be safer, although both drugs have been associated with overdoses. The neurotoxic potential of mephedrone appears to be low, whereas MDMA can cause long-term damage to the serotonergic system, although this needs further investigation. The abuse liability of mephedrone is significantly greater than that of MDMA, raising concerns regarding the impact of lifetime usage on users. Given that mephedrone is relatively new, the effects of long-term exposure are yet to be documented. Future research focused on lifetime users may highlight more severe neuropsychobiological effects from the drug.

Synthetic psychoactive cathinones: hypothermia and reduced lethality compared to methamphetamine and methylenedioxymethamphetamine

RATIONALE

Synthetic psychoactive cathinones (SPCs) are drugs with psychostimulant and entactogenic properties like methamphetamine (MA) and 3,4-methylenedioxymethamphetamine (MDMA). Despite clinical reports of human overdose, it remains to be determined if SPCs have greater propensity for adverse effects than MA or MDMA.

OBJECTIVES

To determine whether the SPCs cathinone (CAT), methcathinone (MCAT), mephedrone (MMC), and methylenedioxypyrovalerone (MDPV) have lower LD50 values than MA or MDMA.

METHODS

Male and female C57Bl/6J mice received single injections of one of 6 doses of a test drug (0-160 mg/kg IP). Temperature and behavioral observations were taken every 20 min for 2 h followed by euthanasia of surviving mice. Organs were weighed and evaluated for histopathological changes.

RESULTS

LD50 values for MA and MDMA, 84.5 and 100.9 mg/kg respectively, were similar to previous observations. The LD50 for MMC was 118.8 mg/kg, but limited lethality was observed for other SPCs (CAT, MCAT, MDPV), so LD50 values could not be calculated. For all drugs, death was associated with seizure, when it was observed. Rather than hyperthermia, dose-dependent hypothermia was observed for MMC, MDPV, CAT, and MCAT. Contrary to initial expectations, none of the SPCs studied here had LD50 values lower than MA or MDMA.

CONCLUSIONS

These data indicate that, under the conditions studied here: (1) SPCs exhibit less lethality than MA and MDMA; (2) SPCs impair thermoregulation; (3) effects of SPCs on temperature appear to be independent of effects on lethality.

The Psychiatric Characteristics of People on a Mephedrone ("bath salts") Binge

Background: Despite solutions presented by the European Union and national regulations introduced by many countries, the problem of mephedrone (4-MMC) is growing. Objectives: The aim of this study was to investigate the effect of regular mephedrone intake with other psychoactive substances on the clinical picture of patients, including self-harms and suicide attempts. Methods: The study involved a group of 601 patients addicted to mephedrone who were admitted to a psychiatric hospital between 2010 and 2018 due to regular mephedrone intake. Results: There was a statistically significant relationship between sleep disorders and mephedrone combined with alcohol (p < .05) or cannabinols (p < .05). However, the highest number of statistically significant correlations was reported when mephedrone was combined with opioids. There was a growing year-on-year percentage of people who attempted suicide because of regular mephedrone intake (p < .001). The more psychoactive substances were combined with mephedrone, the greater the risk of attempted suicide (p < .01). 20% of the examined group were hospitalized several times. Among those hospitalized several times, significantly more people took more than one additional psychoactive substance (p < .01). Conclusions: The more psychoactive substances combined with mephedrone, the more clinical symptoms are associated with it.

Synthetic cathinone self-administration in female rats modulates neurotransmitter levels in addiction-related brain regions

Synthetic cathinones are used for their stimulant-like properties. Stimulant-induced neurochemical changes are thought to occur at different times in different brain regions and neurotransmitter systems. This study sought to examine the behavioral and neurochemical effects of α-pyrrolidinopentiophenone (α-PVP) and mephedrone (4MMC) in female rats. Methods probed the chronology of effects of synthetic cathinone exposure. Female rats were trained to self-administer α-PVP, 4MMC, or saline. Drug exposure ceased after 7 days of autoshaping for half of each drug group; the other half self-administered for another 21 days. Amygdala, hippocampus, hypothalamus, PFC, striatum, and thalamus were extracted, and tissue was analyzed with electrochemical detection and liquid chromatography mass spectrometry. Responding was minimal during autoshaping; thus, most infusions were delivered noncontingently in the autoshaping phase. Rats acquired self-administration of α-PVP and 4MMC. Synthetic cathinone administration, and duration of exposure produced several effects on neurotransmitters. α-PVP primarily increased serotonin, 5-hydroxy-3-acetic acid (5-HIAA), norepinephrine, and glutamate in hypothalamus. In contrast, 4MMC decreased serotonin and 5-HIAA in several brain regions. Longer durations of exposure to both synthetic cathinones increased 5-HIAA, norepinephrine, and glutamate in multiple brain regions compared to the short exposure during autoshaping. Notably, both α-PVP and 4MMC produced minimal changes in dopamine levels, suggesting that the dopaminergic effects of these synthetic cathinones are transient. These alterations in neurotransmitter levels indicate that synthetic cathinone use may produce differential neurochemical changes during the transition from use to abuse.

Mephedrone Impact on Matrix Metalloproteinases Activity - Do they Influence the Memory Processes?

BACKGROUND

The use of drugs of addiction, as mephedrone, is associated with functional neuronal disorders due to remodeling of the nervous tissue. Key enzymes in remodeling are extracellular matrix (ECM) proteases like matrix metalloproteases (MMPs). Recently, MMPs have been of great interest as some studies point to a fact that the alterations in structural remodeling of synaptic connections modify learning-dependent changes, which remain active even after a prolonged period of abstinence. This entails a continuous development of dependence.

OBJECTIVES

The aim of the study was to determine the influence of subchronic exposure to three different doses of mephedrone on the activity of MMP-2 and 9 in hippocampus and prefrontal cortex and how this was correlated with memory processes in mice.

METHODS

The homogenates of hippocampus and cortex were assayed for MMP-2 and MMP-9 activity by gelatin zymography. Memory consolidation processes were evaluated in the passive avoidance (PA) test.

RESULTS

The study confirmed the dose-dependent increase in activity of MMP-2 and -9 exerted by subchronic administration of mephedrone. Moreover, the highest dose of mephedrone attenuated consolidation of memory and learning processes.

CONCLUSIONS

We could hypothesize that inhibition of MMPs can be considered as a therapeutic option for the treatment of addictive behaviors associated with cognitive processes. Moreover, further studies are required to find out if elevated activities of MMPs contribute to brain damage or recovery from brain damage caused directly by mephedrone.

Mephedrone Concentrations in Cases of Clinical Intoxication

BACKGROUND

Mephedrone (4-methylmethcathinone, 4-MMC), a ring-substituted synthetic cathinone derivative has become established as a permanent illicit drug in the dynamic new psychoactive substances (NPS) scene.

OBJECTIVE

This review summarizes current knowledge on mephedrone concentrations in biological samples from cases of acute intoxications (fatal and non-fatal), pharmacokinetics studies, wastewater and anonymous pooled urine analysis in order to provide an overview of the reliable scientific knowledge on toxicokinetics of mephedrone in humans.

METHOD

The PubMed® database complemented with Google Scholar® was systematically searched to find published cases of mephedrone intoxications. The searches were done using the keyword "mephedrone OR 4- methylmethcathinone" in association to each of the following strategies: i) "intoxication OR poisoning"; ii) "(blood OR serum OR plasma") OR "urine" OR ("saliva OR oral fluid") OR "hair"; iii) "forensic toxicology samples"; iv) "wastewater OR sewage OR pooled urine" and v) "toxicity OR death OR fatal".

RESULTS

Since 2010, a total of 97 fatal cases and 57 non-fatal intoxication cases were identified that presented mephedrone concentrations in human biological matrices attributed directly or indirectly to mephedrone. Typical subjects involved were young male with concomitant use of other drugs (psychostimulants, cannabis, alcohol and other depressants). Mephedrone mean blood concentration from fatal cases was 2,663 ng/mL (range 51-22,000 ng/mL), from non-fatal cases was 166 ng/mL (range, 13-412 ng/mL), that resulted in a similar range from data found in controlled studies with no acute toxicity associated (135 ng/mL, range 52-218 ng/mL). Forensic epidemiology studies based on wastewater and anonymous pooled urine analysis point towards similar variations in use (nightclub scene) to those self-reported in surveys and questioners.

CONCLUSION

Mephedrone blood concentrations in cases of fatal intoxications were higher than in non-fatal cases. In both cases, great variability in mephedrone concentration potentially attributable to interindividual differences in pharmacokinetics-pharmacodynamics and poly-drug use complicates the interpretation of the forensic toxicological analysis.

Dopaminergic Effects of Major Bath Salt Constituents 3,4-Methylenedioxypyrovalerone (MDPV), Mephedrone, and Methylone Are Enhanced Following Co-exposure

Designer drug mixtures popularized as "bath salts" often contain the synthetic cathinones 3,4 methylenedioxypyrovalerone (MDPV), mephedrone, and methylone in various combinations. However, most preclinical investigations have only assessed the effects of individual bath salt constituents, and little is known about whether co-exposure to MDPV, mephedrone, and methylone produces significant neuropharmacological interactions. This study evaluated and compared how MDPV, mephedrone, and methylone influence discrete brain tissue dopamine (DA) levels and motor stimulant responses in mice when administered alone and as a ternary mixture. Male adolescent Swiss-Webster mice received intraperitoneal injections of saline or 1 or 10 mg/kg doses of MDPV, mephedrone, or methylone, or a cocktail of all three cathinones at doses of 1, 3.3, or 10 mg/kg each. The effect of each treatment on DA and DA metabolite levels in mesolimbic and nigrostriatal brain tissue was quantified 15 min after a single exposure using HPLC-ECD. Additionally, locomotor activity was recorded in mice after acute (day 1) and chronic intermittent (day 7) dosing. MDPV, mephedrone, and methylone produced dose-related increases in mesolimbic and nigrostriatal DA levels that were significantly enhanced following their co-administration. In addition, mice treated with the cathinone cocktail displayed decreased locomotor activity on day 1 that was exacerbated by day 7 and not observed with any of the drugs alone. Our findings demonstrate a significant enhanced effect of MDPV, mephedrone, and methylone on both DA, and these effects on DA result in significant alterations in locomotor activity.

Analysis of neurotransmitter levels in addiction-related brain regions during synthetic cathinone self-administration in male Sprague-Dawley rats

RATIONALE

Synthetic cathinones are used as stimulants of abuse. Different stimulants may induce distinct rates of disease progression, yielding neurochemical changes that may vary across brain regions or neurotransmitter systems.

OBJECTIVES

This research sought to behaviorally and chemically differentiate stages of synthetic cathinone abuse through rodent self-administration and measurement of the neurotransmitter profile in multiple brain regions.

METHODS

Male rats were trained to self-administer α-PVP, mephedrone (4MMC), or saline. Half of each drug group stopped self-administering after autoshaping; the other half self-administered for another 21 days. Brain tissue from amygdala, hippocampus, hypothalamus, PFC, striatum, and thalamus was profiled with electrochemical detection to assess neurotransmitter levels.

RESULTS

During autoshaping, the majority of infusions were delivered noncontingently. In the self-administration phase, rats responded more for α-PVP and 4MMC than for saline, demonstrating that both synthetic cathinones were reinforcing. Longer durations of exposure elevated 5-HIAA in hypothalamus, PFC, and hippocampus, indicating that learning may produce changes in addiction-related brain regions. Both synthetic cathinones decreased norepinephrine in hippocampus, while α-PVP decreased glutamate in hippocampus and PFC, and 4MMC decreased glutamate in thalamus. Furthermore, α-PVP increased dopaminergic metabolites in striatum, whereas 4MMC decreased serotonin in the amygdala, hippocampus, and PFC. Interestingly, neither synthetic cathinone affected dopamine levels despite their functional effects on the dopaminergic system.

CONCLUSIONS

In summary, the neurotransmitter changes observed here suggest that synthetic cathinone use likely produces sequential neurochemical changes during the transition from use to abuse. Consequently, treatment need may differ depending on the progression of synthetic cathinone abuse.

Effects of repeated treatment with methcathinone, mephedrone, and fenfluramine on intracranial self-stimulation in rats

RATIONALE

Synthetic cathinones constitute a class of abused drugs that can act at dopamine, norepinephrine, and serotonin transporters (DAT, NET, and SERT, respectively). Intracranial self-stimulation (ICSS) is a preclinical procedure that can be used to evaluate abuse potential of drugs, and prior studies have indicated that abuse-related ICSS effects of monoamine-transporter substrates, including some synthetic cathinones, are positively correlated with drug selectivity for DAT vs. SERT. Abuse potential of drugs can also be influenced by regimens of repeated drug exposure, but the role of repeated exposure on abuse-related ICSS effects of synthetic cathinones has not been examined.

OBJECTIVES

This study used ICSS to evaluate effects of repeated treatment with the DAT>SERT substrate methcathinone, the DAT<SERT substrate fenfluramine, and the DAT≈SERT substrate mephedrone.

METHODS

Male Sprague-Dawley rats were trained in a frequency-rate ICSS procedure, and different groups were used to evaluate effects of methcathinone, mephedrone, and fenfluramine before, during, and after regimens of repeated treatment with the designated drug.

RESULTS

Before repeated treatment, methcathinone produced dose-dependent and abuse-related ICSS facilitation, fenfluramine produced dose-dependent ICSS depression, and mephedrone produced mixed effects that included both facilitation and depression. Chronic treatment produced no change in effects of methcathinone, but complete tolerance to effects of fenfluramine. For mephedrone, chronic treatment produced partial tolerance to ICSS depression and enhanced expression of ICSS facilitation.

CONCLUSIONS

Repeated exposure to mixed-action DAT≈SERT substrates such as mephedrone can result in increased abuse potential due to sustained expression of DAT-mediated abuse-related effects and tolerance to SERT-mediated abuse-limiting effects.

Dissociation between hypothermia and neurotoxicity caused by mephedrone and methcathinone in TPH2 knockout mice

RATIONALE

Mephedrone is a commonly abused constituent of "bath salts" and has many pharmacological effects in common with methamphetamine. Despite their structural similarity, mephedrone differs significantly from methamphetamine in its effects on core body temperature and dopamine nerve endings. The reasons for these differences remain unclear.

OBJECTIVES

Mephedrone elicits a transient hypothermia which may provide intrinsic neuroprotection against methamphetamine-like toxicity to dopamine nerve endings. Furthermore, evidence in the literature suggests that this hypothermia is mediated by serotonin. By utilizing transgenic mice devoid of brain serotonin, we determined the contribution of this neurotransmitter to changes in core body temperature as well as its possible role in protecting against neurotoxicity. The effects of methcathinone and 4-methyl-methamphetamine, two structural analogs of mephedrone and methamphetamine, were also evaluated in these mice.

RESULTS

The hypothermia induced by mephedrone and methcathinone in wild-type mice was not observed in mice lacking brain serotonin. Despite preventing drug-induced hypothermia, the lack of serotonin did not alter the neurotoxic profiles of the test drugs.

CONCLUSIONS

Serotonin is a key mediator of pharmacological hypothermia induced by mephedrone and methcathinone, but these body temperature effects do not contribute to dopamine nerve ending damage observed in mice following treatment with mephedrone, methcathinone or 4-methyl-methamphetamine. Thus, the key component of methamphetamine neurotoxicity lacking in mephedrone remains to be elucidated.

Effects of cocaine on the discriminative stimulus and reinforcing effects of mephedrone in male rats

RATIONALE

Abuse of cathinones has been a worldwide health concern for some time. Their chemical structures and wide variation in pharmacodynamic effects have led to clinical and preclinical effects that can be both similar to and different from other psychoactive substances such as methylenedioxymethamphetamine (MDMA), methamphetamine, and cocaine.

OBJECTIVE

The present study examined the discriminative stimulus and reinforcing effects of mephedrone to further characterize the behavioral and pharmacological profile of this first-generation substituted methcathinone.

METHODS

Rats were trained to discriminate mephedrone (3.2 mg/kg) from saline under a fixed-ratio 20 (FR-20) schedule of food presentation. After establishing dose-effect curves for increasing cumulative doses of mephedrone, substitution tests were conducted with bupropion (5.6-32 mg/kg), cocaine (1.8-18 mg/kg), morphine (0.56-10 mg/kg), and amitriptyline (3.2-32 mg/kg). In addition, cocaine (3.2-18 mg/kg) and the serotonin type-2 (5-HT2) receptor antagonist ritanserin (1, 3.2, and 10 mg/kg) were administered prior to the cumulative doses of mephedrone. Lastly, varying infusion doses of cocaine were substituted for mephedrone in subjects trained to self-administer mephedrone, and varying infusion doses of mephedrone were substituted for cocaine in subjects trained to self-administer cocaine to assess the importance of drug history on the reinforcing effects of mephedrone.

RESULTS

Of the drugs tested, cocaine had the highest level of mephedrone-lever responding when administered alone (73.5%). In combination with mephedrone, cocaine shifted the mephedrone dose-effect curve upwards in an infra-additive manner. Ritanserin had a small, but non-significant, effect on mephedrone's discriminative stimulus effects. An extensive history (baseline) of cocaine self-administration increased mephedrone self-administration compared to that obtained in mephedrone-trained subjects, whereas a baseline of mephedrone self-administration decreased cocaine self-administration compared to that obtained in cocaine-trained subjects.

CONCLUSION

The similarity between the discriminative stimulus effects of cocaine and mephedrone in male rats suggests an important overlap and the relative importance of the dopamine (DAT) and serotonin (SERT) transporters. The self-administration data suggest that mephedrone is less reinforcing than cocaine, but that a history of responding for cocaine can increase the reinforcing effects of mephedrone.

Effects of dopaminergic and serotonergic compounds in rats trained to discriminate a high and a low training dose of the synthetic cathinone mephedrone

RATIONALE

The underlying pharmacological mechanisms of mephedrone, especially as related to interactions with different neurotransmitter systems, are a critical area of study as mephedrone continues to be abused.

OBJECTIVE

Direct-acting 5-HT_2A/2C receptor agonists and antagonists and D_1-3 receptor antagonists were examined in two groups of rats trained to discriminate mephedrone. A high dose of mephedrone was trained to extend previous results with traditional monoamine transporter inhibitors and substrate releasers. A very low dose of mephedrone was trained to preferentially capture serotonergic activity and to minimize the influence of rate-decreasing effects on substitution patterns. Selective 5-HT_2A/2C and D_1-3 receptor antagonists were examined in both groups.

METHODS

Male Sprague-Dawley rats were trained to discriminate either a low dose of 0.5 mg/kg mephedrone (N = 24) or a high dose of 3.2 mg/kg mephedrone (N = 11) from saline.

RESULTS

In the low training-dose group, mephedrone, MDMA, methamphetamine, d-amphetamine, cocaine, and enantiomers of mephedrone substituted for mephedrone; mCPP partially substituted overall for mephedrone; and DOI, WAY163909, and morphine failed to substitute for mephedrone. In the high training-dose group, only mephedrone and MDMA substituted for mephedrone. Sulpiride produced a small antagonism of the low training dose of mephedrone while SCH23390, SB242084, and ketanserin altered response rates.

CONCLUSIONS

A lower training dose of mephedrone produces a discriminative stimulus fully mimicked by MDMA, methamphetamine, cocaine, and d-amphetamine, whereas a higher training dose of mephedrone requires a discriminative stimulus that was only mimicked by MDMA. Dopaminergic or serotoninergic antagonists failed to produce significant blockade of mephedrone at either training dose.

A comparison of mitochondrial toxicity of mephedrone on three separate parts of brain including hippocampus, cortex and cerebellum

Mephedrone (4-methylmethcathinone) is a new and popular drug of abuse and also widely available on the internet and still legal in some parts of the world. The central nervous system is the target of mephedrone and recent evidence suggested that mephedrone could affect mitochondria in brain tissue. However, the underlying mechanisms of mephedrone toxicity in brain mitochondria have not yet been well understood. In this study, mitochondria from three separate parts of rat brain hippocampus, cortex, and cerebellum were obtained using differential centrifugation and were incubated with different concentrations of mephedrone (3, 6 and 12 μM). Then, the mitochondrial parameters toxicity were determined. The results showed that mephedrone (3, 6 and 12 μM) induced impairment in the activity of the mitochondrial complex II and IV. Also, mephedrone (3, 6 and 12 μM) increased mitochondrial reactive oxygen species (ROS) level, collapsed mitochondria membrane potential (MMP), induced swelling in the mitochondria and damaged the mitochondrial outer membrane (MOM) in the mitochondria obtained from hippocampus, cortex, and cerebellum, which in all cases is associated with the cytochrome c release. Furthermore, increased disturbance in oxidative phosphorylation was also shown by the decrease in ATP level in mephedrone-treated mitochondria indicating mitochondrial dysfunction in separate parts of the brain. This study suggests that mephedrone via increasing oxidative stress and impairment of the mitochondrial respiratory chain in the hippocampus, cortex, and cerebellum may play a key role in the neurotoxicity.

An observational study on the sub-acute effects of mephedrone on mood, cognition, sleep and physical problems in regular mephedrone users

RATIONALE

Mephedrone (4-methylmethcathinone; 4-MMC) is a novel recreational drug similar to methylenedioxymethamphetamine (MDMA) and amphetamine. Several adverse effects have been reported, but little is known about its sub-acute effects.

OBJECTIVES

To study sub-acute effects of mephedrone over a period of 9 days.

METHODS

Recreational mephedrone users were recruited and followed over a time period of 9 days. It was recorded whether participants consumed mephedrone or not within the period of testing; those who did were compared to those who did not. Forty-six regular mephedrone users (22 males, 24 females) participated, 21 participants voluntarily opted to consume mephedrone 1-3 days after baseline and 25 opted to abstain. Participants were assessed at baseline on a multitude of measures and provided daily reports on cognition, sleep, mood, physical problems, mephedrone cravings and substance use on each subsequent day of the study. The study controlled for psychopathology, sleep, past and current substance use, impulsivity and demographics.

RESULTS

Those who consumed mephedrone reported persistent negative mood, physical problems and fatigue, compared to those who did not-after controlling for baseline group differences in sleep and subsequent alcohol and cannabis use.

CONCLUSIONS

The results provide the first prospective evidence of the duration and extent of specific undesirable sub-acute effects of mephedrone in regular recreational users and indicate sub-acute effects of mephedrone on mood, fatigue and physical symptoms.

Effects of N-Alkyl-4-Methylamphetamine Optical Isomers on Plasma Membrane Monoamine Transporters and Abuse-Related Behavior

4-Methylamphetamine (4-MA) is an emerging drug of abuse that acts as a substrate at plasma membrane transporters for dopamine (DAT), norepinephrine (NET), and serotonin (SERT), thereby causing nonexocytotic release of monoamine transmitters via reverse transport. Prior studies by us showed that increasing the N-alkyl chain length of N-substituted 4-MA analogues converts 4-MA from a transportable substrate (i.e., releaser) at DAT and NET to a nontransported blocker at these sites. Here, we studied the effects of the individual optical isomers of N-methyl-, N-ethyl-, and N- n-propyl 4-MA on monoamine transporters and abuse-related behavior in rats because action/function might be related to stereochemistry. Uptake inhibition and release assays were conducted in rat brain synaptosomes whereas electrophysiological assessments of drug-transporter interactions were examined using cell-based biosensors. Intracranial-self-stimulation in rats was employed to assess abuse potential in vivo. The experimental evidence demonstrates that S(+) N-methyl 4-MA is a potent and efficacious releaser at DAT, NET, and SERT with the highest abuse potential among the test drugs, whereas R(-) N-methyl 4-MA is a less potent releaser with reduced abuse potential. The S(+)ethyl analogue has decreased efficacy as a releaser at DAT but retains full release activity at NET and SERT with a reduction in abuse-related effects; the R(-)ethyl analogue has a similar profile but is less potent. S(+) N-Propyl 4-MA is a nontransported blocker at DAT and NET but an efficacious releaser at SERT, whereas the R enantiomer is almost inactive. In conclusion, the S enantiomers of the N-alkyl 4-MA analogues are most potent. Lengthening the N-alkyl chain converts compounds from potent nonselective releasers showing abuse-related effects to more selective SERT releasers with no apparent abuse potential.

Potential pro-oxidative effects of single dose of mephedrone in vital organs of mice

BACKGROUND

Mephedrone is a recreationally used synthetic cathinone, relatively new abusive substances with molecular structure similar to amphetamine. As there is still lack of scientific data regarding mechanisms of action as well as metabolism of mephedrone, especially in aspects other than neurotoxicity, addiction or behavioral changes, therefore we aimed, for the first time, to investigate potential pro-oxidative actions of a single dose of mephedrone in organs other than brain and its structures, i.e. in liver, kidneys, heart and spleen of Swiss mice.

METHODS

The following biomarkers of oxidative stress were measured: concentration of ascorbic acid (AA) and malondialdehyde (MDA) as well as total antioxidant capacity (TAC) of the tissues homogenates.

RESULTS

Our study revealed that mephedrone intoxication induces oxidative stress by reducing concentration of AA and TAC and increasing concentration of MDA in these organs.

CONCLUSIONS

Such occurred state of antioxidant-oxidant imbalance may be etiopathological factor of a number of severe diseases within cardiovascular, digestive as well as immunological systems.

The Effects of Exposure to Mephedrone During Adolescence on Brain Neurotransmission and Neurotoxicity in Adult Rats

According to the European Drug Report (2016), the use of synthetic cathinones, such as mephedrone, among young people has rapidly increased in the last years. Studies in humans indicate that psychostimulant drug use in adolescence increases risk of drug abuse in adulthood. Mephedrone by its interaction with transporters for dopamine (DAT) and serotonin (SERT) stimulates their release to the synaptic cleft. In animal studies, high repeated doses of mephedrone given to adolescent but not adult mice or rats induced toxic changes in 5-hydroxytryptamine (5-HT) neurons. The aim of our study was to investigate the effects of mephedrone given in adolescence on brain neurotransmission and possible neuronal injury in adult rats. Adolescent male rats were given mephedrone (5 mg/kg) for 8 days. In vivo microdialysis in adult rats showed an increase in dopamine (DA), 5-HT, and glutamate release in the nucleus accumbens and frontal cortex but not in the striatum in response to challenge dose in animals pretreated with mephedrone in adolescence. The 5-HT and 5-hydroxyindoleacetic acid contents decreased in the striatum and nucleus accumbens while DA turnover rates were decreased in the striatum and nucleus accumbens. The oxidative damage of DNA assessed with the alkaline comet assay was found in the cortex of adult rats. Therefore, the administration of repeated low doses of mephedrone during adolescence does not seem to induce injury to 5-HT and DA neurons. The oxidative stress seems to be responsible for possible damage of cortical cell bodies which causes maladaptive changes in serotonergic and dopaminergic neurons.

Neurotoxicity Induced by Mephedrone: An up-to-date Review

Mephedrone is a β-ketoamphetamine belonging to the family of synthetic cathinones, an emerging class of designer drugs known for their hallucinogenic and psychostimulant properties as well as for their abuse potential. The aim of this review was to examine the emerging scientific literature on the possible mephedrone-induced neurotoxicity, yet not well defined due to the limited number of experimental studies, mainly carried on animal models. Relevant scientific articles were identified from international literature databases (Medline, Scopus, etc.) using the keywords: “Mephedrone”, “4-MMC,” “neurotoxicity,” “neuropharmacology”, “patents”, “monoamine transporters” and “neurochemical effects”. Of the 498 sources initially found, only 36 papers were suitable for the review. Neurotoxic effect of mephedrone on 5-HT and DA systems remains controversial. Although some studies in animal models reported no damage to DA nerve endings in the striatum and no significant changes in brain monoamine levels, some others suggested a rapid reduction in 5-HT and DA transporter function. Persistent serotonergic deficits were observed after binge like treatment in a warm environment and in both serotonergic and dopaminergic nerve endings at high ambient temperature. Oxidative stress cytotoxicity and an increase in frontal cortex lipid peroxidation were also reported. In vitro cytotoxic properties were also observed, suggesting that mephedrone may act as a reductant agent and can also determine changes in mitochondrial respiration. However, due to the differences in the design of the experiments, including temperature and animal model used, the results are difficult to compare. Further studies on toxicology and pharmacology of mephedrone are therefore necessary to establish an appropriate treatment for substance abuse and eventual consequences for public health.

Effect of the combination of mephedrone plus ethanol on serotonin and dopamine release in the nucleus accumbens and medial prefrontal cortex of awake rats

Cathinones, such as mephedrone (Meph), are often co-abused with alcoholic drinks. In the present study, we investigated the combined effects of Meph plus ethanol (EtOH) on neurotransmitter release in the nucleus accumbens (NAc) and the medial prefrontal cortex (mPFC). A guide canula was stereotaxically implanted into either the NAc or the mPFC of male Sprague-Dawley rats. Seven days after surgery, a microdialysis probe was inserted and rats were administered saline, EtOH (1 g/kg, i.p.), Meph (25 mg/kg, s.c.), or their combination, and dialysates were collected. Serotonin (5-HT), dopamine (DA), and their metabolites (5-HIAA, DOPAC and HVA) were determined through high-pressure liquid chromatography coupled to mass spectrometry. 5-HT and DA peaked 40 min after Meph administration (with or without EtOH co-treatment) in both areas. EtOH combined with Meph increased the 5-HT release compared with the rats receiving Meph alone (85% in NAc, 65% in mPFC), although the overall change in the area under the curve only reached statistical significance in the NAc. In mPFC, the increased release of 5-HT lasted longer in the combination than that in the Meph group. Moreover, EtOH potentiated the psychostimulant effect of Meph measured as a locomotor activity. Given that both 5-HT and DA are also related with reward and impulsivity, the observed effects point to an increased risk of abuse liability when combining Meph with EtOH compared with consuming these drugs alone.

Evaluation of training dose in male Sprague-Dawley rats trained to discriminate 4-methylmethcathinone

RATIONALE

Although the synthetic cathinone 4-methylmethcathinone (4-MMC, mephedrone) has been a subject of intensive research investigation, the pharmacological mechanisms involved in its interoceptive stimulus effects have yet to be fully characterized.

OBJECTIVE

The present study employed drug discrimination methods in rats to compare the interoceptive stimulus properties of two different training doses of 4-MMC to other substances with similar pharmacological actions.

METHODS

Sixteen male Sprague-Dawley rats were trained to discriminate either 1.0 mg/kg (N = 8) or 3.0 mg/kg (N = 8) 4-MMC from saline. Substitution tests were conducted with drugs that increase extracellular monoamine levels (d-amphetamine, (+)-methamphetamine, 4-MMC, MDMA, MDPV, and (-)-cocaine), a serotonin releaser (+)-fenfluramine, and a serotonergic (5-HT_2A) hallucinogen (+)-LSD.

RESULTS

Stimulus control was established in fewer sessions in the subjects trained with 3.0 mg/kg compared to those trained with 1.0 mg/kg 4-MMC. Cocaine, MDMA, and d-amphetamine produced full substitution in the 1.0 mg/kg 4-MMC-trained rats at doses that did not decrease response rate. However, doses of test drugs that engendered > 80% 4-MMC-lever selection concurrently produced rate-decreasing effects in rats trained to discriminate 3.0 mg/kg 4-MMC.

CONCLUSIONS

These findings further characterize the interoceptive stimulus effects of 4-MMC and indicate that these effects vary little with training dose; however, qualitative differences in substitutability of test drugs were observed between training groups. This study expands existing knowledge regarding the psychopharmacology of 4-MMC and the potential neurochemical substrates contributing to its subjective effects.

PLDT (planarian light/dark test): an invertebrate assay to quantify defensive responding and study anxiety-like effects

BACKGROUND

Planarians, like rodents, instinctively spend more time in dark versus light environments when given a choice. This behavioral phenomenon is called negative phototaxis, which may reflect defensive responding related to an anxiety-like phenotype.

NEW METHOD

We propose a planarian light/dark test, designated PLDT, to predict anxiogenic- or anxiolytic-like effects. Experimentally, we placed a planarian at the midline of a Petri dish, containing test compound or water, that was split evenly into light and dark compartments and determined time spent in the light over 10min.

RESULTS

A clinically-approved benzodiazepine agonist (clorazepate; 10μM) increased time spent in the light whereas an inverse benzodiazepine agonist (FG-7142; 1, 10μM) produced the opposite response. Fluoxetine (1μM) or ethanol (1%), as well as the 'bath salt' cathinone S-mephedrone (300μM), enhanced time spent in the light. Planarians exposed to predator (frog) odor spent more time in the dark.

COMPARISON WITH EXISTING METHODS

The light/dark box (LDB) test in rodents is used to screen putative medications for possible anxiolytic and anxiogenic effects. Our results showing that time spent in the light by planarians is enhanced by common anxiety-relieving drugs (e.g. benzodiazepine agonist, ethanol, fluoxetine) and decreased by anxiogenic substances (e.g. predator odor, benzodiazepine inverse agonist) reveal directionally similar effects in the established (LDB) and new (PLDT) assays.

CONCLUSION

Our data identify the PLDT as a cost-effective, invertebrate assay for quantifying the effects of practically any water-soluble substance on defensive responding and for studying and teaching anxiety-like responses in a living organism.

Synthetic cathinones and stereochemistry: S enantiomer of mephedrone reduces anxiety- and depressant-like effects in cocaine- or MDPV-abstinent rats

BACKGROUND AND PURPOSE

The neuropharmacological profile of the synthetic cathinone mephedrone (MEPH) is influenced by stereochemistry. Both MEPH enantiomers are monoamine transporter substrates, but R-MEPH is primarily responsible for rewarding effects of MEPH as it produces greater locomotor activation and intracranial self-stimulation than S-MEPH. S-MEPH is a 50-fold more potent 5-HT releaser than R-MEPH and does not place preference in rats. MEPH is also structurally similar to the cathinone derivative bupropion, an antidepressant and smoking cessation medication, suggesting MEPH has therapeutic and addictive properties.

METHODS

We tested the hypothesis that S-MEPH reduces anxiety- and depression-like behaviors in rats withdrawn from chronic cocaine or methylenedioxypyrovalerone (MDPV) using the elevated plus maze (EPM) and forced swim test (FST), respectively. Rats were tested 48-h after a binge-like paradigm (3×/day for 10days in 1-h intervals) of cocaine (10mg/kg), MDPV (1mg/kg) or saline. In vitro studies assessed the receptor binding and activity of S-MEPH.

KEY RESULTS

Rats withdrawn from chronic cocaine or MDPV displayed an increase in anxiety- and depression-like behaviors that was antagonized by treatment with S-MEPH (10, 30mg/kg). S-MEPH displayed affinity, but not agonist activity, for 5-HT₂ receptors (2A-2C) and showed negligible affinity for dopaminergic, adrenergic and nicotinic receptors.

CONCLUSION AND IMPLICATION

S-MEPH attenuated withdrawal behaviors following chronic cocaine or MDPV, perhaps through 5-HT release and/or 5-HT₂ receptor interactions. The present data suggest S-MEPH may be a possible structural and pharmacological template to develop maintenance therapy for acute anxiety and depression during early withdrawal from psychostimulant abuse.

Assessing the role of dopamine in the differential neurotoxicity patterns of methamphetamine, mephedrone, methcathinone and 4-methylmethamphetamine

Methamphetamine and mephedrone are designer drugs with high abuse liability and they share extensive similarities in their chemical structures and neuropharmacological effects. However, these drugs differ in one significant regard: methamphetamine elicits dopamine neurotoxicity and mephedrone does not. From a structural perspective, mephedrone has a β-keto group and a 4-methyl ring addition, both of which are lacking in methamphetamine. Our previous studies found that methcathinone, which contains only the β-keto substituent, is neurotoxic, while 4-methylmethamphetamine, which contains only the 4-methyl ring substituent, elicits minimal neurotoxicity. In the present study, it was hypothesized that the varying neurotoxic potential associated with these compounds is mediated by the drug-releasable pool of dopamine, which may be accessed by methamphetamine more readily than mephedrone, methcathinone, and 4-methylmethamphetamine. To test this hypothesis, l-DOPA and pargyline, compounds known to increase both the releasable pool of dopamine and methamphetamine neurotoxicity, were combined with mephedrone, 4-methylmethamphetamine and methcathinone. Methamphetamine was also tested because of its ability to increase releasable dopamine. All three regimens significantly enhanced striatal neurotoxicity and glial reactivity for 4-methylmethamphetamine. Methcathinone neurotoxicity and glial reactivity were enhanced only by l-DOPA. Mephedrone remained non-neurotoxic when combined with either l-DOPA or pargyline. Body temperature effects of each designer drug were not altered by the combined treatments. These results support the conclusion that the neurotoxicity of 4-methylmethamphetamine, methcathinone and methamphetamine may be differentially regulated by the drug-releasable pool of dopamine due to β-keto and 4-methyl substituents, but that mephedrone remains non-neurotoxic despite large increases in this pool of dopamine. This article is part of the Special Issue entitled 'Designer Drugs and Legal Highs.'

Pharmacological profile of mephedrone analogs and related new psychoactive substances

BACKGROUND

Mephedrone is a synthetic cathinone and one of the most popular recreationally used new psychoactive substances. The aim of the present study was to characterize the in vitro pharmacology of novel analogs of mephedrone and related newly emerged designer stimulants.

METHODS

We determined norepinephrine, dopamine, and serotonin transporter inhibition potencies and monoamine release in transporter-transfected human embryonic kidney 293 cells. We also assessed monoamine receptor and transporter binding affinities.

RESULTS

Mephedrone analogs potently inhibited the norepinephrine transporter and, with the exception of 3-methylmethcathinone (3-MMC), inhibited the serotonin transporter more potently than the dopamine transporter. Similar to classic amphetamines, mephedrone analogs were substrate-type monoamine releasers. 5-(2-Aminopropyl)indole (5-IT) was a highly potent monoamine transporter inhibitor and a releaser of dopamine and serotonin. 4-Methylamphetamine (4-MA) mediated efflux of all three monoamines and inhibited the serotonin transporter more potently than the dopamine transporter, unlike amphetamine. N-methyl-2-aminoindane (N-methyl-2-AI) was a selective norepinephrine transporter inhibitor and norepinephrine releaser, whereas 5-methoxy-6-methyl-2-aminoindane (MMAI) was a selective serotonin transporter inhibitor and serotonin releaser. All of the drugs interacted with monoamine receptors.

CONCLUSION

The predominant actions on serotonin vs. dopamine transporters suggest that dimethylmethcathinones, 4-MA, and MMAI cause entactogenic effects similar to 3,4-methylenedioxymethamphetamine, whereas 3-MMC, 5-IT, and N-methyl-2-AI have more stimulant-type properties like amphetamine. Because of pharmacological and structural similarity to mephedrone, similar health risks can be expected for these analogs. This article is part of the Special Issue entitled 'Designer Drugs and Legal Highs.'

Neurotoxicology of Synthetic Cathinone Analogs

The present review briefly explores the neurotoxic properties of methcathinone, mephedrone, methylone, and methylenedioxypyrovalerone (MDPV), four synthetic cathinones most commonly found in "bath salts." Cathinones are β-keto analogs of the commonly abused amphetamines and display pharmacological effects resembling cocaine and amphetamines, but despite their commonalities in chemical structures, synthetic cathinones possess distinct neuropharmacological profiles and produce unique effects. Among the similarities of synthetic cathinones with their non-keto analogs are their targeting of monoamine systems, the release of neurotransmitters, and their stimulant properties. Most of the literature on synthetic cathinones has focused on describing their properties as psychostimulants, their behavioral effects on locomotion, memory, and potential for abuse, whereas descriptions of their neurotoxic properties are not abundant. The biochemical gauges of neurotoxicity induced by non-keto analogs are well studied in humans and experimental animals and include their ability to induce neuroinflammation, oxidative stress, excitotoxicity, temperature alterations as well as dysregulation of neurotransmitter systems and induce changes in monoamine transporters and receptors. These neurotoxicity gauges will serve as parameters to discuss the effects of the four previously mentioned synthetic cathinones alone or in combination with either another cathinone or with some of their non-keto analogs. Bath salts are not a defined combination of drugs and may consist of one synthetic cathinone compound or combinations of more cathinones. Furthermore, this review also presents some of the mechanisms that are thought to underlie this toxicity. A better understanding of the cellular and molecular mechanisms involved in the synthetic cathinones-induced neurotoxicity should contribute to generate modern therapeutic approaches to prevent or attenuate the adverse consequences of use of these drugs in humans.

Monoaminergic toxicity induced by cathinone phthalimide: An in vitro study

Bath salts, or synthetic cathinones, have cocaine-like or amphetamine-like properties and induce psychoactive effects via their capacity to modulate serotonin (5-HT) and dopamine (DA). Structurally distinct synthetic cathinones are continuously being generated to skirt existing drug laws. One example of these modified compounds is cathinone phthalimide (CP), which has already appeared on the global market. The lack of toxicological studies on the effects of CP on monoaminergic systems led to the development of the present study in order to generate an acute toxicity profile for CP, and to clarify whether it primarily affects both dopamine and serotonin, like the synthetic cathinones mephedrone and methylone, or primarily affects dopamine, like 3, 4-methylenedioxypyrovalerone (MDPV). For the first time, the toxicity profile of CP (10μM-1000μM) is reported. In pheochromocytoma cells, exposure to CP induced cell death, and altered mitochondrial function, as well as intracellular DA and 5-HT levels; at the same time, reduced glutathione (GSH) levels remained unaffected. This seems to indicate that CP functions like mephedrone or methylone. The role of CP metabolites, the effect of CP induced hyperthermia on neurotoxicity, and its ability to traverse the blood-brain barrier warrant further consideration.

Atypical binding at dopamine and serotonin transporters contribute to the discriminative stimulus effects of mephedrone

Mephedrone (4-methylmethcathinone), a constituent of the recreational substances known as "bath salts", is a synthetic cathinone that can produce auditory and visual hallucinations, as well as problematic cardiovascular effects. This study compared the discriminative stimulus effects of mephedrone (0.32-10 mg/kg) with other prototypical drugs of abuse: cocaine (0.56-32 mg/kg), d-amphetamine (0.18-3.2 mg/kg), ketamine (1.8-18 mg/kg), phencyclidine (PCP, 1-5.6 mg/kg), heroin (1-10 mg/kg), 2,5-dimethoxy-4-iodoamphetamine (R-DOI, 0.1-1 mg/kg), Δ⁹-tetrahydrocannabinol (Δ^9-THC 0.56-5.6 mg/kg), 3,4-methylenedioxyamphetamine (MDA, 0.32-5.6 mg/kg), methylphenidate (1-10 mg/kg), and 3,4-methylenedioxypyrovalerone (MDPV, 0.56-5.6 mg/kg). The discriminative stimulus effects of mephedrone were also assessed after administration of the sigma receptor antagonist rimcazole (0.32-10 mg/kg), the relatively selective norepinephrine transporter (NET) inhibitor desipramine (1.8-18 mg/kg), and the selective serotonin transporter (SERT) inhibitor fluoxetine (1-18 mg/kg). Initially, rats were trained to discriminate an intraperitoneal injection of mephedrone (3.2 mg/kg) from saline under a fixed-ratio 20 schedule of food presentation. Following training, cumulative doses of mephedrone and the other drugs were administered to test for substitution (80% drug-lever responding). Of the drugs tested, including those that were tested in combination with mephedrone (i.e., rimcazole, desipramine, and fluoxetine), only cocaine fully substituted for mephedrone without substantially decreasing response rate. In addition, the three drugs administered in combination with mephedrone shifted the cumulative dose-effect curves leftward (percent drug-lever responding) and down (response rate), although fluoxetine did so in a dose-dependent manner ranging from antagonism to potentiation. In summary, the discriminative stimulus effects of mephedrone were most similar to those for the central nervous system (CNS) stimulant, cocaine, and SERT and DAT activity were necessary for these effects.

Is the recent emergence of mephedrone injecting in the United Kingdom associated with elevated risk behaviours and blood borne virus infection?

The recent, and rapid, emergence of injection of the short-acting stimulant mephedrone (4-methylmethcathione) has resulted in concerns about increased infection risks among people who inject drugs (PWID). Data from the bio-behavioural surveillance of PWID in the United Kingdom were analysed to examine the impact of mephedrone injection on infections among PWID. During the year preceding the survey, 8.0% of PWID (163/2,047) had injected mephedrone. In multivariable analyses, those injecting mephedrone were younger, less likely to have injected opiates, and more likely to have injected cocaine or amphetamines, used needle/syringe programmes or sexual health clinics, been recruited in Wales and Northern Ireland or shared needles/syringes. There were no differences in sexual risks. Those injecting mephedrone more often had hepatitis C antibodies (adjusted odds ratio (AOR) = 1.51; 95% confidence interval (CI): 1.08-2.12), human immunodeficiency virus (AOR = 5.43; 95% CI: 1.90-15.5) and overdosed (AOR = 1.70; 95% CI: 1.12-2.57). There were no differences in the frequency of injecting site infections or prevalence of hepatitis B. The elevated levels of risk and infections are a concern considering its recent emergence. Mephedrone injection may currently be focused among higher-risk or more vulnerable groups. Targeted responses are needed to prevent an increase in harm.

Decoding the Structure of Abuse Potential for New Psychoactive Substances: Structure-Activity Relationships for Abuse-Related Effects of 4-Substituted Methcathinone Analogs

Many cathinone analogs act as substrates or inhibitors at dopamine, norepinephrine, and serotonin transporters (DAT, NET, SERT, respectively). Drug selectivity at DAT vs. SERT is a key determinant of abuse potential for monoamine transporter substrates and inhibitors, such that potency at DAT > SERT is associated with high abuse potential, whereas potency at DAT < SERT is associated with low abuse potential. Quantitative structure-activity relationship (QSAR) studies with a series of 4-substituted methcathinone analogs identified volume of the 4-position substituent on the methcathinone phenyl ring as one structural determinant of both DAT vs. SERT selectivity and abuse-related behavioral effects in an intracranial self-stimulation procedure in rats. Subsequent modeling studies implicated specific amino acids in DAT and SERT that might interact with 4-substituent volume to determine effects produced by this series of cathinone analogs. These studies illustrate use of QSAR analysis to investigate pharmacology of cathinones and function of monoamine transporters.

Predicting the Abuse Liability of Entactogen-Class, New and Emerging Psychoactive Substances via Preclinical Models of Drug Self-administration

Animal models of drug self-administration are currently the gold standard for making predictions regarding the relative likelihood that a recreational drug substance will lead to continued use and addiction. Such models have been found to have high predictive accuracy and discriminative validity for a number of drug classes including ethanol, nicotine, opioids, and psychostimulants such as cocaine and methamphetamine. Members of the entactogen class of psychostimulants (drugs that produce an "open mind state" including feelings of interpersonal closeness, intimacy and empathy) have been less frequently studied in self-administration models. The prototypical entactogen 3,4-methylenedioxymethamphetamine (MDMA; "Ecstasy") supports self-administration but not with the same consistency nor with the same efficacy as structurally related drugs amphetamine or methamphetamine. Consistent with these observations, MDMA use is more episodic in the majority of those who use it frequently. Nevertheless, substantial numbers of MDMA users will meet the criteria for substance dependence at some point in their use history. This review examines the currently available evidence from rodent self-administration studies of MDMA and two of the new and emerging psychoactive substances (NPS) that produce entactogen type neuropharmacological responses - mephedrone (4-methylmethcathinone; 4MMC; "meow meow") and methylone (3,4-methylenedioxymethcathinone). Overall, the current evidence predicts that these NPS entactogens have enhanced abuse liability compared with MDMA.

I like the old stuff better than the new stuff? Subjective experiences of new psychoactive substances

BACKGROUND

Over the past decade, monitoring systems have identified the rapid emergence of new psychoactive substances (NPS). While the use of many NPS is minimal and transitory, little is known about which products have potential for capturing the attention of significant proportions of the drug consuming market. The aim of this study was to explore self-reported experiences of three commonly used NPS classes within the Australian context (synthetic cathinones, hallucinogenic phenethylamines and hallucinogenic tryptamines) relative to traditional illicit drug counterparts.

METHODS

Frequent psychostimulant consumers interviewed for the Australian Ecstasy and related Drugs Reporting System (EDRS) (n=1208) provided subjective ratings of the pleasurable and negative (acute and longer-term) effects of substances used in the last six months on the last occasion of use, and the likelihood of future use.

RESULTS

Stimulant-type NPS (e.g., mephedrone, methylone) were rated less favourably than ecstasy and cocaine in terms of pleasurable effects and likelihood of future use. DMT (a hallucinogenic tryptamine) showed a similar profile to LSD in terms of pleasurable effects and the likelihood of future use, but negative effects (acute and comedown) were rated lower. Hallucinogenic phenethylamines (e.g., 2C-B) showed a similar negative profile to LSD, but were rated as less pleasurable and less likely to be used again.

CONCLUSION

The potential for expanded use of stimulant-type NPS may be lower compared to commonly used stimulants such as ecstasy and cocaine. In contrast, the potential of DMT may be higher relative to LSD given the comparative absence of negative effects.

Mephedrone and 3,4-methylenedioxy-methamphetamine: Comparative psychobiological effects as reported by recreational polydrug users

AIMS

The purpose of this study was to compare the effects of mephedrone and 3,4-methylenedioxy-methamphetamine (MDMA), as reported by young recreational polydrug users.

METHODS

152 MDMA users and 81 mephedrone users were recruited through snowballing on social network sites. They completed a standard online questionnaire for either mephedrone or MDMA. The questions covered the average amount taken per session, the longest duration of usage in the last 12-months, subjective effects while on-drug, and recovery effects in the days afterwards.

RESULTS

Mephedrone users reported a significantly longer maximum session of use than MDMA users. Mephedrone users also reported a significantly greater average amount used per session. The majority of on-drug subjective ratings did not differ between drugs, with similar increases in entactogenic effects. Although mephedrone users did report significantly more frequent issues with sleeping, anger and anxiety. In relation to recovery, mephedrone users reported more frequent craving, nasal irritation, paranoia, and relationship difficulties. Mephedrone users also rated general recovery effects as more severe over the seven-day period following use, taking more days to feel normal.

CONCLUSIONS

The acute effects of MDMA and mephedrone were broadly similar. However, the recovery period for mephedrone was more enduring, possibly due to the longer duration of acute session usage.

Novel psychoactive substances: An investigation of temporal trends in social media and electronic health records

BACKGROUND

Public health monitoring is commonly undertaken in social media but has never been combined with data analysis from electronic health records. This study aimed to investigate the relationship between the emergence of novel psychoactive substances (NPS) in social media and their appearance in a large mental health database.

METHODS

Insufficient numbers of mentions of other NPS in case records meant that the study focused on mephedrone. Data were extracted on the number of mephedrone (i) references in the clinical record at the South London and Maudsley NHS Trust, London, UK, (ii) mentions in Twitter, (iii) related searches in Google and (iv) visits in Wikipedia. The characteristics of current mephedrone users in the clinical record were also established.

RESULTS

Increased activity related to mephedrone searches in Google and visits in Wikipedia preceded a peak in mephedrone-related references in the clinical record followed by a spike in the other 3 data sources in early 2010, when mephedrone was assigned a 'class B' status. Features of current mephedrone users widely matched those from community studies.

CONCLUSIONS

Combined analysis of information from social media and data from mental health records may assist public health and clinical surveillance for certain substance-related events of interest. There exists potential for early warning systems for health-care practitioners.

Caffeine alters the behavioural and body temperature responses to mephedrone without causing long-term neurotoxicity in rats

Administration of caffeine with 3,4-methylenedioxymethamphetamine (MDMA) alters the pharmacological properties of MDMA in rats. The current study examined whether caffeine alters the behavioural and neurochemical effects of mephedrone, which has similar psychoactive effects to MDMA. Rats received either saline, mephedrone (10 mg/kg), caffeine (10 mg/kg) or combined caffeine and mephedrone intraperitoneally twice weekly on consecutive days for three weeks. Locomotor activity (days 1 and 16), novel object discrimination (NOD, day 2), elevated plus maze (EPM) exploration (day 8), rectal temperature changes (day 9) and pre-pulse inhibition (PPI) of acoustic startle response (day 15) were assessed. Seven days after the final injection, brain regions were collected for the measurement of 5-hydroxytryptamine (5-HT), dopamine and their metabolites. Combined caffeine and mephedrone further enhanced the locomotor response observed following either drug administered alone, and converted mephedrone-induced hypothermia to hyperthermia. Co-administration also abolished mephedrone-induced anxiogenic response on the EPM, but had no effect on NOD or PPI. Importantly, no long-term neurotoxicity was detected following repeated mephedrone alone or when co-administered with caffeine. In conclusion, the study suggests a potentially dangerous effect of concomitant caffeine and mephedrone, and highlights the importance of taking polydrug use into consideration when investigating the acute adverse effect profile of popular recreational drugs.

Sensitization to the locomotor stimulant effects of "bath salt" constituents, 4-methylmethcathinone (4-MMC) and 3,4-methylenedioxypyrovalerone (MDPV), in male Sprague-Dawley rats

BACKGROUND

Synthetic cathinones, 4-methylmethcathinone (4-MMC) and 3,4-methylenedioxypyrovalerone (MDPV), serve as a substrate or blocker at monoaminergic transporters, respectively, and produce locomotor stimulant effects in rodents. The present study investigated in rats the effects of repeated exposure to 4-MMC, MDPV, or mixtures of the two on the induction of locomotor sensitization and expression of cross-sensitization to cocaine.

METHODS

Seventy-two male Sprague-Dawley rats received daily intraperitoneal injections of saline, MDPV (0.5mg/kg), 4-MMC (0.5, 1.0, or 2.0mg/kg) or mixtures of 0.5mg/kg MDPV+4-MMC (0.5, 1.0, or 2.0mg/kg) for seven consecutive days. Locomotor activity was recorded on days 1 and 7 and again after an acute injection of 5mg/kg cocaine following a 10day drug washout period.

RESULTS

Rats injected with 0.5mg/kg MDPV, 0.5, 1.0, or 2.0mg/kg 4-MMC, or 2.0mg/kg 4-MMC+0.5mg/kg MDPV displayed time-dependent increases in horizontal activity that were augmented on day 7 compared to day 1. In addition, rats pretreated with 0.5mg/kg MDPV, 2.0mg/kg 4-MMC, or mixtures of 4-MMC+MDPV displayed an enhanced response to cocaine.

CONCLUSIONS

Locomotor responses sensitize to MDPV and to certain mixtures of MDPV and 4-MMC following repeated dosing. Furthermore, previous exposure to these substances may produce cross-sensitization to the locomotor stimulant effects of cocaine. Considered together with recent findings that 4-MMC and MDPV have different sites of action, but both influence monoaminergic functioning, further investigations utilizing a variety of behavioral assays may prove informative regarding the abuse liability of synthetic cathinone mixtures.

Effect of Some Psychoactive Drugs Used as 'Legal Highs' on Brain Neurotransmitters

New psychoactive "designer drugs" are synthetic compounds developed to provide similar effects to illicit drugs of abuse, but not subjected to legal control. The rapidly changing legal status of novel psychoactive drugs triggers the development of new compounds, analogs of well-known amphetamine or mescaline. New designer drugs used as substitutes in ecstasy pills are the least investigated and can cause life-threatening effects on users. The aim of our research was to examine the effects of acute administration of 4-methoxyamphetamine (PMA, 5 and 10 mg/kg), 4-methoxy-N-methylamphetamine (PMMA, 5 and 10 mg/kg), and mephedrone (MEPH, 5, 10 and 20 mg/kg) on extracellular and tissue level of dopamine (DA), 5-hydroxytryptamine (5-HT) and their metabolites in rat brain, by microdialysis method in freely moving animals and HPLC. Similarly to 3,4-methylenedioxymethamphetamine (MDMA, 5 and 10 mg/kg) PMA, PMMA and MEPH enhanced the release of DA and 5-HT in rat striatum, nucleus accumbens, and frontal cortex. DA tissue content was increased by MEPH and PMMA in striatum, by MEPH, PMA, and PMMA in nucleus accumbens, and by PMA in frontal cortex. Instead, cortical DA level was decreased by MEPH and PMMA. MEPH did not influence 5-HT tissue level in striatum and nucleus accumbens, but decreased its level in frontal cortex. PMMA increased 5-HT content in striatum, while PMA enhanced it in nucleus accumbens and frontal cortex. Observed changes in brain monoamines and their metabolites by new psychoactive drugs suggest that these drugs may be capable of development of dependence. Further experiments are needed to fully investigate the neurotoxic and abuse potential of those drugs.