Structure-Activity Relationship of N-Ethyl-Hexedrone Analogues: Role of the α-Carbon Side-Chain Length in the Mechanism of Action, Cytotoxicity, and Behavioral Effects in Mice

Synthetic cathinones are β-keto amphetamine derivatives whose appearance has increased dramatically in the past decades. N-Ethyl substituted cathinones have been proven to potently inhibit dopamine (DA) uptake and induce psychostimulant and rewarding effects in mice. However, little is known about the influence of the alpha-carbon side-chain length of N-ethyl cathinones on their pharmacological and toxicological effects. Thus, the aim of this study was to synthesize and investigate the in vitro and in vivo effects of five N-ethyl substituted cathinones: N-ethyl-cathinone (NEC), N-ethyl-buphedrone (NEB), N-ethyl-pentedrone, N-ethyl-hexedrone (NEH), and N-ethyl-heptedrone. HEK293 cells expressing the human DA or serotonin transporter (hDAT and hSERT) were used for uptake inhibition and binding assays. PC12 cells were used for the cytotoxicity assays. Swiss CD-1 mice were used to study the in vivo psychostimulant, anxiogenic, and rewarding properties. Our results show that all tested cathinones are able to inhibit DA uptake and are DAT-selective. The potency of DA uptake inhibitors increases with the elongation of the aliphatic side chain from methyl to propyl and decreases when increasing from butyl to pentyl, which correlates with an inverted U-shape psychostimulant response in mice at the medium dose tested. On the other hand, an increase in the α-carbon side-chain length correlates with an increase in the cytotoxic properties in PC12 cells, probably due to better membrane penetration. Moreover, all the cathinones tested have shown higher cytotoxicity than methamphetamine. Finally, our study not only demonstrated the rewarding properties of NEC and NEB but also the anxiety-like behavior induced at high doses by all the cathinones tested.

Repeated administration of N-ethyl-pentedrone induces increased aggression and impairs social exploration after withdrawal in mice

N-ethyl-pentedrone (NEPD, 2-(ethylamino)-1-phenyl-1-pentanone) is one of the latest synthetic cathinone derivatives that emerged into the illicit drug market. This drug has psychostimulant properties and has been related with several intoxications and even fatalities. However, information about the consequences of its acute and repeated consumption is lacking. Thus, the aim of our study was to investigate the behavioral effects after both acute and repeated NEPD exposure as well as the neurochemical changes. Male OF1 mice were treated with an acute dose (1, 3 or 10 mg/kg, i.p.) or received repeated injections of these doses (twice/day, 5 days) of NEPD. Shortly after drug-exposure or during drug-withdrawal, anxiety-like behavior, aggressiveness, social interaction, depressive-like symptoms, body weight and temperature were assessed. Also, monoamine synthesis enzymes, levels of neurotransmitters and their precursors and main metabolites, as well as ΔFosB, were determined in striatum and prefrontal cortex from post-mortem tissue. Acute administration of NEPD induced anxiolytic effects and reduced social exploration whereas during withdrawal after repeated administration the anxiolytic effect had vanished, and the reduced social exploration was still present and accompanied with increased aggressive behavior. Moreover, NEPD (10 mg/kg) induced slight hyperthermia and reduced weight gain during the repeated administration, whereas increased locomotor activity and lack of depressive symptoms were found during withdrawal. This was accompanied by increased plasma corticosterone and decrease in striatal dopamine. Finally, the long-lasting and robust increase in ΔFosB levels found in striatum after NEPD chronic exposure suggests a high risk of dependence. The increased aggressivity and locomotor activity, together with this potential of inducing dependence justify a warning about the risks of consumption of NEPD if translated to humans.

Neuropsychopharmacology of Emerging Drugs of Abuse: meta- and para-Halogen-Ring-Substituted α-PVP (“flakka”) Derivatives

Changes in the molecular structure of synthetic cathinones has led to an increase in the number of novel emerging drugs in the illicit drug market at an unprecedented rate. Unfortunately, little is known about the neuropsychopharmacology of recently emerged halogen-substituted α-PVP derivatives. Thus, the aim of this study was to investigate the role of para- and meta-halogen (F-, Cl-, and Br-) substitutions on the in vitro, in silico, and in vivo effects of α-pyrrolidinopentiophenone (α-PVP) derivatives. HEK293 cells expressing the human dopamine or serotonin transporter (hDAT and hSERT) were used for the uptake inhibition and transporter affinity assays. Molecular docking was used to model the interaction mechanism against DAT. Swiss CD-1 mice were used for the horizontal locomotor activity, open field test, and conditioned place preference paradigm. All compounds demonstrated potent DA uptake inhibition and higher DAT selectivity than cocaine. Meta-substituted cathinones showed higher DAT/SERT ratios than their para- analogs, which correlates with an increased psychostimulant effect in vivo and with different meta- and para-in silico interactions at DAT. Moreover, all compounds induced rewarding and acute anxiogenic effects in mice. In conclusion, the present study demonstrates the role of meta- and para-halogen substitutions in the mechanism of action and provides the first evidence of the rewarding and anxiety-like properties of halogenated α-PVP derivatives.

3,4-Methylenedioxy methamphetamine, synthetic cathinones and psychedelics: From recreational to novel psychotherapeutic drugs

The utility of classical drugs used to treat psychiatric disorders (e.g., antidepressants, anxiolytics) is often limited by issues of lack of efficacy, delayed onset of action or side effects. Psychoactive substances have a long history of being used as tools to alter consciousness and as a gateway to approach the unknown and the divinities. These substances were initially obtained from plants and animals and more recently by chemical synthesis, and its consumption evolved toward a more recreational use, leading to drug abuse-related disorders, trafficking, and subsequent banning by the authorities. However, these substances, by modulation of certain neurochemical pathways, have been proven to have a beneficial effect on some psychiatric disorders. This evidence obtained under medically controlled conditions and often associated with psychotherapy, makes these substances an alternative to conventional medicines, to which in many cases the patient does not respond properly. Such disorders include post-traumatic stress disease and treatment-resistant depression, for which classical drugs such as MDMA, ketamine, psilocybin and LSD, among others, have already been clinically tested, reporting successful outcomes. The irruption of new psychoactive substances (NPS), especially during the last decade and despite their recreational and illicit uses, has enlarged the library of substances with potential utility on these disorders. In fact, many of them were synthetized with therapeutic purposes and were withdrawn for concrete reasons (e.g., adverse effects, improper pharmacological profile). In this review we focus on the basis, existing evidence and possible use of synthetic cathinones and psychedelics (specially tryptamines) for the treatment of mental illnesses and the properties that should be found in NPS to obtain new therapeutic compounds.

Impact of adolescent methamphetamine use on social cognition: A human-mice reverse translation study

BACKGROUND

Methamphetamine dependence is associated with social cognition deficits that may underpin negative social outcomes. However, there are considerable inter-individual differences in social cognition within people with methamphetamine dependence, with age of onset of methamphetamine use being a potential contributing factor.

MATERIALS AND METHODS

We conducted two sequential studies examining the link between age of onset of methamphetamine use (adolescence versus young adulthood) and performance in social cognition tests: (1) a human cross-sectional study in 95 participants with methamphetamine dependence varying in age of onset (38 with adolescent onset and 57 with adult onset) and 49 drug-naïve controls; (2) a mice study in which we tested the effects of methamphetamine exposure during adolescence versus young adulthood on social interaction and aggression, and their potential neurochemical substrates in the striatal dopaminergic system.

RESULTS

We initially showed that people with methamphetamine dependence who started use in adolescence had higher antisocial beliefs (p = 0.046, Cohen's d=0.42) and worse emotion recognition (p = 0.031, Cohen's d=0.44) than those who started use during adulthood. We reasoned that this could be due to either social cognition deficits leading to earlier onset of methamphetamine use, or methamphetamine-induced neuroadaptive effects specific to adolescence. Mice experiments showed that methamphetamine exposure during adolescence specifically decreased social investigation during social interaction and upregulated striatal tyrosine hydroxylase (p < 0.05, Bonferroni corrected). There was no evidence of adolescent-specific methamphetamine effects on aggression or other measures of dopaminergic function.

CONCLUSION

Together, translational findings demonstrate heightened sensitivity to methamphetamine effects on social cognition during adolescence.

Behavioural and neurochemical effects after repeated administration of N-ethylpentylone (ephylone) in mice

N-ethyl-pentylone (NEP), also known as 'ephylone' and N-ethylnorpentylone, has been identified as one of the most recent novel psychostimulants to emerge into the illicit drug market and it has been associated with some intoxications and even fatalities. However, little is known about the consequences of its repeated consumption as well as the role of the monoaminergic system in such consequences. Thus, the aim of our study was to investigate the neurochemical profile and the behavioural effects after both acute and repeated NEP exposure. Male OF1 mice were acutely (1, 3, 10 mg/kg, i.p.) or repeatedly (1, 3, 10 mg/kg, i.p., 5 days, twice/day) exposed to NEP, and anxiety-like behaviour, aggressiveness, social interaction, depressive-like symptoms, body temperature, changes in monoaminergic enzymes and neurotransmitters levels as well as ΔFosB in striatum and prefrontal cortex (PFC) from post-mortem tissue were analysed short after drug-exposure or during drug-withdrawal. Acute administration of NEP induced anxiolytic effects but also an aggressive behaviour and social exploration deficits in mice, which persist during NEP-withdrawal. Moreover, NEP induced hyperthermia as well as depressive-like symptoms after repeated administrations that may be related to the decrease in serotonin and noradrenaline levels observed in striatum and PFC. Finally, the long-term increase in ΔFosB levels in striatum after NEP chronic exposure points to a high risk of dependence. Altogether indicates that NEP consumption induces different neurological and neuropsychiatric disorders accompanied by changes in the monoaminergic system, posing a threat to public health.

Structure-Activity Relationship of Novel Second-Generation Synthetic Cathinones: Mechanism of Action, Locomotion, Reward, and Immediate-Early Genes

Several new synthetic cathinones, which mimic the effect of classical psychostimulants such as cocaine or MDMA, have appeared in the global illicit drug market in the last decades. In fact, the illicit drug market is continually evolving by constantly adding small modifications to the common chemical structure of synthetic cathinones. Thus, the aim of this study was to investigate the in vitro and in vivo structure–activity relationship (SAR) of six novel synthetic cathinones currently popular as recreational drugs, pentedrone, pentylone, N-ethyl-pentedrone (NEPD), N-ethyl-pentylone (NEP), 4-methyl-pentedrone (4-MPD), and 4-methyl-ethylaminopentedrone (4-MeAP), which structurally differ in the absence or presence of different aromatic substituents and in their amino terminal group. Human embryonic kidney (HEK293) cells expressing the human isoforms of SERT and DAT were used for the uptake inhibition and release assays. Moreover, Swiss CD-1 mice were used to investigate the psychostimulant effect, rewarding properties (3, 10, and 30 mg/kg, i.p.), and the induction of immediate-early genes (IEGs), such as Arc and c-fos in the dorsal striatum (DS) and ventral striatum (VS) as well as bdnf in the medial prefrontal cortex (mPFC), of the test compounds. Our results demonstrated that all tested synthetic cathinones are potent dopamine (DA) uptake inhibitors, especially the N-ethyl analogs, while the ring-substituted cathinones tested showed higher potency as SERT inhibitors than their no ring-substituted analogs. Moreover, unlike NEP, the remaining test compounds showed clear “hybrid” properties, acting as DAT blockers but SERT substrates. Regarding the locomotion, NEP and NEPD were more efficacious (10 mg/kg) than their N-methyl analogs, which correlates with their higher potency inhibiting the DAT and an overexpression of Arc levels in the DS and VS. Furthermore, all compounds tested induced an increase in c-fos expression in the DS, except for 4-MPD, the least effective compound in inducing hyperlocomotion. Moreover, NEP induced an up-regulation of bdnf in the mPFC that correlates with its 5-HTergic properties. Finally, the present study demonstrated for the first time that NEP, 4-MPD, and 4-MeAP induce reward in mice. Altogether, this study provides valuable information about the mechanism of action and psychostimulant and rewarding properties as well as changes in the expression of IEGs related to addiction induced by novel second-generation synthetic cathinones.

Cannabidiol Modulates the Motivational and Anxiety-Like Effects of 3,4-Methylenedioxypyrovalerone (MDPV) in Mice

3,4-Methylenedioxypyrovalerone (MDPV) is a new psychoactive substance (NPS) and the most widespread and life-threatening synthetic cathinone of the "bath salts". Preclinical research has proven the cocaine-like psychostimulant effects of MDPV and its potential for abuse. Cannabidiol (CBD) is a non-psychotropic phytocannabinoid that has emerged as a new potential treatment for drug addiction. Here, we tested the effects of CBD (20 mg/kg) on MDPV (2 mg/kg)-induced conditioned place preference and MDPV (0.05 and 0.075 mg/kg/infusion) self-administration paradigms. In addition, we assessed the effects of the co-administration of CBD and MDPV (3 and 4 mg/kg) on anxiety-like behaviour using the elevated plus maze (EPM). CBD mitigated the MDPV-induced conditioned place preference. On the contrary, CBD administration throughout the MDPV (0.075 mg/kg/infusion) self-administration increased drug-seeking and taking behaviours, but only in the high-responders group of mice. Furthermore, CBD exerted anxiolytic-like effects, exclusively in MDPV-treated mice. Taken together, our results indicate that CBD modulation of MDPV-induced motivational responses in mice varies depending on the requirements of the learning task, resulting in a complex response. Therefore, further research attempting to decipher the behavioural and molecular interactions between CBD and MDPV is needed.

Role of amino terminal substitutions in the pharmacological, rewarding and psychostimulant profiles of novel synthetic cathinones

The emergence of new synthetic cathinones continues to be a matter of public health concern. In fact, they are quickly replaced by new structurally related alternatives. The main goal of the present study was to characterize the pharmacological profile, the psychostimulant and rewarding properties of novel cathinones (pentedrone, N-ethyl-pentedrone, α-PVP, N,N-diethyl-pentedrone and α-PpVP) which only differs in their amino terminal substitution. Rat synaptosomes were used for [³H]dopamine uptake experiments. HEK293 transfected cells (hDAT, hSERT, hOCT; human dopamine, serotonin and organic cation transporter) were also used for [³H]monoamine uptake and transporter binding assays. Molecular docking was used to investigate the effect of the amino substitutions on the biological activity. Hyperlocomotion and conditioned place preference paradigm were used in order to study the psychostimulant and rewarding effects in mice. All compounds tested are potent inhibitors of DAT with very low affinity for SERT, hOCT-2 and -3, and their potency for inhibiting DAT increased when the amino-substituent expanded from a methyl to either an ethyl-, a pyrrolidine- or a piperidine-ring. Regarding the in vivo results, all the compounds induced an increase in locomotor activity and possess rewarding properties. Results also showed a significant correlation between predicted binding affinities by molecular docking and affinity constants (Ki) for hDAT as well as the cLogP of their amino-substituent with their hDAT/hSERT ratios. Our study demonstrates the role of the amino-substituent in the pharmacological profile of novel synthetic cathinones as well as their potency inhibiting DA uptake and ability to induce psychostimulant and rewarding effects in mice.

Effects of High-Fat Diet and Maternal Binge-Like Alcohol Consumption and Their Influence on Cocaine Response in Female Mice Offspring

BACKGROUND

Prenatal alcohol exposure is a leading cause of neurobehavioral and neurocognitive deficits collectively known as fetal alcohol spectrum disorders, including eating disorders and increased risk for substance abuse as very common issues. In this context, the present study aimed to assess the interaction between prenatal and lactation alcohol exposure (PLAE) and a high-fat diet (HFD) during childhood and adolescence.

METHODS

Pregnant C57BL/6 mice underwent a procedure for alcohol binge drinking during gestation and lactation periods. Subsequently, PLAE female offspring were fed with an HFD for 8 weeks, and thereafter, nutrition-related parameters as well as their response to cocaine were assessed.

RESULTS

In our model, feeding young females with an HFD increased their triglyceride blood levels but did not induce overweight compared with those fed with a standard diet. Moreover, PLAE affected how females responded to the fatty diet as they consumed less food than water-exposed offspring, consistent with a lower gain of body weight. HFD increased the psychostimulant effects of cocaine. Surprisingly, PLAE reduced the locomotor responses to cocaine without modifying cocaine-induced reward. Moreover, PLAE prevented the striatal overexpression of cannabinoid 1 receptors induced by an HFD and induced an alteration of myelin damage biomarker in the prefrontal cortex, an effect that was mitigated by an HFD-based feeding.

CONCLUSION

Therefore, in female offspring, some effects triggered by one of these factors, PLAE or an HFD, were blunted by the other, suggesting a close interaction between the involved mechanisms.

Effects of MDMA on neuroplasticity, amyloid burden and phospho-tau expression in APPswe/PS1dE9 mice

BACKGROUND

3,4-Methylenedioxymethamphetamine (MDMA) is still one of the most consumed drugs by adolescents. Its abuse is related with cognitive impairment, which seems due to maladaptive plasticity and neural stress. In turn, new hypotheses suggest that Alzheimer's disease (AD) may be promoted by neural stressors.

AIMS AND METHODS

To test if there is an increase in vulnerability to AD after chronic MDMA consumption, we investigated the effects of this drug on recognition memory and its neurotoxic and neuroplastic effects in a transgenic mouse model of presymptomatic familiar AD (APP/PS1 dE9, Tg).

RESULTS

MDMA-treated animals showed recognition memory deficits, regardless of genotype, which were accompanied by changes in plasticity markers. Tg mice showed an impaired expression of Arc compared with wild-type animals, but exposure to MDMA induced an increase in the expression of this factor of the same percentage in both genotypes. However, the expression of c-fos, BDNF and p-CREB was not significantly altered by MDMA treatment in Tg mice. Although Tg mice had higher free choline levels than wild-type mice (about 123%), MDMA did not modify these levels in any case, ruling out any specific effect of this drug on the acetylcholine pathway. MDMA treatment significantly increased the presence of cortical amyloid plaques, as well as Aβ40, Aβ42 and secreted APPβ levels in Tg mice. These plaques were accompanied by increased tau phosphorylation (S199), which does not seem to occur via the canonic pathway involving AKT, CDK5 or GSK3β.

CONCLUSIONS

The present results support previous evidences that MDMA can contribute to the amyloid cascade.

Neuroadaptive changes and behavioral effects after a sensitization regime of MDPV

3,4-methylenedioxypyrovalerone (MDPV) is a synthetic cathinone with cocaine-like properties. In a previous work, we exposed adolescent mice to MDPV, finding sensitization to cocaine effects, and a higher vulnerability to cocaine abuse in adulthood. Here we sought to determine if such MDPV schedule induces additional behavioral-neuronal changes that could explain such results. After MDPV treatment (1.5 mg kg^-1, twice daily, 7 days), mice were behaviorally tested. Also, we investigated protein changes in various brain regions. MDPV induced aggressiveness and anxiety, but also contributed to a faster habituation to the open field. This feature co-occurred with an induction of ΔFosB in the orbitofrontal cortex that was higher than its expression in the ventral striatum. Early after treatment, D2R:D1R ratio pointed to a preponderance of D1R but, upon withdrawal, the ratio recovered. Increased expression of Arc, CDK5 and TH, and decrease in DAT protein levels persisted longer after withdrawal, pointing to a neuroplastic lasting effect similar to that involved in cocaine addiction. The implication of the hyperdopaminergic condition in the MDPV-induced aggressiveness cannot be ruled out. We also found an initial oxidative effect of MDPV, without glial activation. Moreover, although initially the dopaminergic signal induced by MDPV resulted in increased ΔFosB, we did not observe any change in NFκB or GluA2 expression. Finally, the changes observed after MDPV treatment could not be explained according to the autoregulatory loop between ΔFosB and the epigenetic repressor G9a described for cocaine. This provides new knowledge about the neuroadaptive changes involved in the vulnerability to psychostimulant addiction.

Maternal separation increases alcohol-drinking behaviour and reduces endocannabinoid levels in the mouse striatum and prefrontal cortex

Childhood adversity is associated with an increased risk of mood, anxiety and substance use disorders. Maternal separation is a reliable rodent model of early life adversity that leads to depression-like symptoms, which may increase the vulnerability to alcohol consumption during adolescence. However, the specific alterations in the pattern of alcohol consumption induced by maternal separation and the underlying molecular mechanisms are still unclear. The purpose of this study is to evaluate the long-term effects of maternal separation with early weaning (MSEW) on emotional and social behaviour, alcohol rewarding properties, and alcohol consumption, abstinence and relapse in adolescent male C57BL/6 mice. In addition, endocannabinoid and monoamine levels were analysed in discrete brain areas. Results showed that MSEW mice presented emotional alterations related to depressive-like behaviour and modified endocannabinoid levels in the striatum and the prefrontal cortex. MSEW mice also showed impairments in alcohol-induced conditioned place preference and higher alcohol intake in a model of binge drinking. Moreover, MSEW animals displayed a higher propensity to relapse in the two-bottle choice paradigm following a period of alcohol abstinence associated with reduced monoamine levels in the striatum. Such results indicate that exposure to early life stress increased the vulnerability to alcohol binge-drinking during adolescence, which may be partially explained by decreased sensitivity to alcohol rewarding properties and the ability to potentiate alcohol intake following a period of abstinence.

The combination of MDPV and ethanol results in decreased cathinone and increased alcohol levels. Study of such pharmacological interaction

Methylenedioxypyrovalerone (MDPV) is a new psychostimulant cathinone acting as a selective dopamine transporter blocker. Due to the concomitant consumption of ethanol (EtOH) and new psychoactive substances, it is of interest to explore a possible pharmacological interaction between MDPV and EtOH. In locomotor activity assays, EtOH (1g/kg i.p.) elicited a reduction in the stimulant effect induced by low doses of MDPV (0.1-0.3mg/kg, s.c.) in rats, jointly with a decrease in blood and brain MDPV concentrations. Experiments in rat liver microsomes showed different effects depending on the [MDPV]/[EtOH] relationship, evidencing, at certain concentrations, the enhancing effect of EtOH on MDPV metabolism. These suggest that EtOH interacts with MDPV at microsomal level, increasing its metabolic rate. The interaction between both substances was also supported by results in plasma EtOH concentration, which were significantly increased by MDPV, in such a manner that EtOH elimination rate was significantly reduced. The possible toxicological impact of this phenomenon deserves further investigation. In contrast, the rewarding properties of MDPV were unaltered by EtOH. Microdialysis experiments verified that, in the NAcc, both substances could also act synergistically, in such a manner that extracellular dopamine concentrations are maintained. Finally, if the psychostimulant effect induced by MDPV decreased with EtOH, it could favor the boosting and re-dosing in search of the desired effects. However, as the rewarding effect of each dose of the substance would not decrease, the addictive liability could increase considerably. Moreover, we must warn about the increase in EtOH concentrations when consumed concomitantly with MDPV.

Exposure of adolescent mice to 3,4-methylenedioxypyrovalerone increases the psychostimulant, rewarding and reinforcing effects of cocaine in adulthood

BACKGROUND AND PURPOSE

3,4-Methylenedioxypyrovalerone (MDPV) is a synthetic cathinone with powerful psychostimulant effects. It selectively inhibits the dopamine transporter (DAT) and is 10-50-fold more potent as a DAT blocker than cocaine, suggesting a high abuse liability. The main objective of the present study was to assess the consequences of an early (adolescence) MDPV exposure on the psychostimulant, rewarding and reinforcing effects induced by cocaine in adult mice.

EXPERIMENTAL APPROACH

Twenty-one days after MDPV pretreatment (1.5 mg·kg^-1 , s.c., twice daily for 7 days), adult mice were tested with cocaine, using locomotor activity, conditioned place preference and self-administration (SA) paradigms. In parallel, dopamine D₂ receptor density and the expression of c-Fos and ΔFosB in the striatum were determined.

KEY RESULTS

MDPV treatment enhanced the psychostimulant and conditioning effects of cocaine. Acquisition of cocaine SA was unchanged in mice pretreated with MDPV, whereas the breaking point achieved under a progressive ratio programme and reinstatement after extinction were higher in this group of mice. MDPV decreased D₂ receptor density but increased ΔFosB expression three-fold. As expected, acute cocaine increased c-Fos expression, but MDPV pretreatment negatively influenced its expression. ΔFosB accumulation declined during MDPV withdrawal, although it remained elevated in adult mice when tested for cocaine effects.

CONCLUSION AND IMPLICATIONS

MDPV exposure during adolescence induced long-lasting adaptive changes related to enhanced responsiveness to cocaine in the adult mice that seems to lead to a higher vulnerability to cocaine abuse. This particular behaviour correlated with increased expression of ΔFosB.

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.

Concentrations of MDPV in rat striatum correlate with the psychostimulant effect

3,4-methylenedioxypyrovalerone or MDPV is a synthetic cathinone with psychostimulant properties more potent than cocaine. We quantified this drug in the striatum after subcutaneous administration to rats. MDPV reached the brain around 5 min after its administration and peaked at 20-25 min later. The elimination half-life in the striatum (61 min) correlates with the decrease in the psychostimulant effect after 60 min. Around 11% of the administered dose reached the striatum and, considering a homogeneous brain distribution, we determined that around 86% of the plasma MDPV is distributed to the brain. MDPV induced a dose-dependent increase in locomotor activity, rearing behaviour and stereotypies, all prevented by haloperidol. A plot of locomotor activity or stereotypies versus MDPV striatal concentrations over time showed a direct relationship between factors. No free MDPV metabolites were detected in plasma, at any time, but hydrolysis with glucuronidase allowed us to identify mainly three metabolites, one of them for the first time in rat plasma. The present results contribute to evidence that MDPV induces hyperlocomotion mainly through a dopamine-dependent mechanism. Good correlation between behavioural effects and striatal levels of MDPV leads us to conclude that its psychostimulant effect is mainly due to a striatal distribution of the substance. The present research provides useful information on the pharmacokinetics of MDPV, and can help design new experiments with kinetics data as well as provide a better understanding of the effects of MDPV in humans and its potential interactions.

Neuronal changes and oxidative stress in adolescent rats after repeated exposure to mephedrone

Mephedrone is a new designer drug of abuse. We have investigated the neurochemical/enzymatic changes after mephedrone administration to adolescent rats (3×25 mg/kg, s.c. in a day, with a 2 h interval between doses, for two days) at high ambient temperature (26±2 °C), a schedule that intends to model human recreational abuse. In addition, we have studied the effect of mephedrone in spatial learning and memory. The drug caused a transient decrease in weight gain. After the first dose, animals showed hypothermia but, after the subsequent doses, temperature raised over the values of saline-treated group. We observed the development of tolerance to these thermoregulatory effects of mephedrone. Mephedrone induced a reduction of the densities of dopamine (30% in the frontal cortex) and serotonin (40% in the frontal cortex and the hippocampus and 48% in the striatum) transporters without microgliosis. These deficits were also accompanied by a parallel decrease in the expression of tyrosine hydroxylase and tryptophan hydroxylase 2. These changes matched with a down-regulation of D2 dopamine receptors in the striatum. Mephedrone also induced an oxidative stress evidenced by an increase of lipid peroxidation in the frontal cortex, and accompanied by a rise in glutathione peroxidase levels in all studied brain areas. Drug-treated animals displayed an impairment of the reference memory in the Morris water maze one week beyond the cessation of drug exposure, while the spatial learning process seems to be preserved. These findings raise concerns about the neuronal long-term effects of mephedrone.

Serotonin is involved in the psychostimulant and hypothermic effect of 4-methylamphetamine in rats

4-Methylamphetamine (4-MA) has recently emerged as a designer drug of abuse in Europe and it is consumed always with amphetamine. There have been reported some deaths and non-fatal intoxications related to 4-MA. We investigated the changes in locomotor activity and body temperature after 4-MA administration to male Sprague-Dawley rats. Our experiments were carried out at a normal or high ambient temperature. 4-MA (2.5-10mg/Kg, given subcutaneously) increased, in a dose-dependent manner, the horizontal locomotor activity that was significantly reduced by ketanserin, p-cholorophenylalanine (pCPA) or haloperidol, but not by pindolol. In addition, we have studied the effect of 4-MA on core body temperature by means of an implanted electronic thermograph, enabling continuous measurement of body temperature. We observed a dose-dependent hypothermic response to 4-MA that reached a maximum 45 min after a single injection. We also evidenced slight tachyphylaxis to the hypothermic effect when 4-MA was administered four times in a 2h interval. The pre-treatment of animals with pCPA or pindolol, but not with ketanserin, fully abolished the hypothermic effect of 4-MA. With all that, we conclude that hypothermia induced by 4-MA is due to the release of 5-HT which activates postsynaptic 5-HT1A receptors.

Serotonergic impairment and memory deficits in adolescent rats after binge exposure of methylone

Methylone is a cathinone derivative that has recently emerged as a designer drug of abuse in Europe and the USA. Studies on the acute and long-term neurotoxicity of cathinones are starting to be conducted. We investigated the neurochemical/enzymatic changes indicative of neurotoxicity after methylone administration (4 × 20 mg/kg, subcutaneously, per day with 3 h intervals) to adolescent rats, to model human recreational use. In addition, we studied the effect of methylone on spatial learning ad memory using the Morris water maze paradigm. Our experiments were carried out at a high ambient temperature to simulate the hot conditions found in dance clubs where the drug is consumed. We observed a hyperthermic response to methylone that reached a peak 30 min after each dose. We determined a serotonergic impairment in methylone-treated rats, especially in the frontal cortex, where it was accompanied by astrogliosis. Some serotonergic alterations were also present in the hippocampus and striatum. No significant neurotoxic effect on the dopaminergic system was identified. Methylone-treated animals only displayed impairments in the probe trial of the Morris water maze, which concerns reference memory, while the spatial learning process seemed to be preserved.

Dose and time-dependent selective neurotoxicity induced by mephedrone in mice

Mephedrone is a drug of abuse marketed as 'bath salts". There are discrepancies concerning its long-term effects. We have investigated the neurotoxicity of mephedrone in mice following different exposition schedules. Schedule 1: four doses of 50 mg/kg. Schedule 2: four doses of 25 mg/kg. Schedule 3: three daily doses of 25 mg/kg, for two consecutive days. All schedules induced, in some animals, an aggressive behavior and hyperthermia as well as a decrease in weight gain. Mephedrone (schedule 1) induced dopaminergic and serotoninergic neurotoxicity that persisted 7 days after exposition. At a lower dose (schedule 2) only a transient dopaminergic injury was found. In the weekend consumption pattern (schedule 3), mephedrone induced dopamine and serotonin transporter loss that was accompanied by a decrease in tyrosine hydroxylase and tryptophan hydroxylase 2 expression one week after exposition. Also, mephedrone induced a depressive-like behavior, as well as a reduction in striatal D2 density, suggesting higher susceptibility to addictive drugs. In cultured cortical neurons, mephedrone induced a concentration-dependent cytotoxic effect. Using repeated doses for 2 days in an elevated ambient temperature we evidenced a loss of frontal cortex dopaminergic and hippocampal serotoninergic neuronal markers that suggest injuries at nerve endings.

Mephedrone pharmacokinetics after intravenous and oral administration in rats: relation to pharmacodynamics

RATIONALE

Mephedrone (4-methylmethcathinone) is a still poorly known drug of abuse, alternative to ecstasy or cocaine.

OBJECTIVE

The major aims were to investigate the pharmacokinetics and locomotor activity of mephedrone in rats and provide a pharmacokinetic/pharmacodynamic model.

METHODS

Mephedrone was administered to male Sprague-Dawley rats intravenously (10 mg/kg) and orally (30 and 60 mg/kg). Plasma concentrations and metabolites were characterized using LC/MS and LC-MS/MS fragmentation patterns. Locomotor activity was monitored for 180-240 min.

RESULTS

Mephedrone plasma concentrations after i.v. administration fit a two-compartment model (α = 10.23 h(-1), β = 1.86 h(-1)). After oral administration, peak mephedrone concentrations were achieved between 0.5 and 1 h and declined to undetectable levels at 9 h. The absolute bioavailability of mephedrone was about 10% and the percentage of mephedrone protein binding was 21.59 ± 3.67%. We have identified five phase I metabolites in rat blood after oral administration. The relationship between brain levels and free plasma concentration was 1.85 ± 0.08. Mephedrone induced a dose-dependent increase in locomotor activity, which lasted up to 2 h. The pharmacokinetic-pharmacodynamic model successfully describes the relationship between mephedrone plasma concentrations and its psychostimulant effect.

CONCLUSIONS

We suggest a very important first-pass effect for mephedrone after oral administration and an easy access to the central nervous system. The model described might be useful in the estimation and prediction of the onset, magnitude, and time course of mephedrone pharmacodynamics as well as to design new animal models of mephedrone addiction and toxicity.

An integrated pharmacokinetic and pharmacodynamic study of a new drug of abuse, methylone, a synthetic cathinone sold as "bath salts"

INTRODUCTION

Methylone (3,4-methylenedioxymethcathinone) is a new psychoactive substance and an active ingredient of "legal highs" or "bath salts". We studied the pharmacokinetics and locomotor activity of methylone in rats at doses equivalent to those used in humans.

MATERIAL AND METHODS

Methylone was administered to male Sprague-Dawley rats intravenously (10mg/kg) and orally (15 and 30 mg/kg). Plasma concentrations and metabolites were characterized by LC/MS and LC-MS/MS fragmentation patterns. Locomotor activity was monitored for 180-240 min.

RESULTS

Oral administration of methylone induced a dose-dependent increase in locomotor activity in rats. The plasma concentrations after i.v. administration were described by a two-compartment model with distribution and terminal elimination phases of α=1.95 h(-1) and β=0.72 h(-1). For oral administration, peak methylone concentrations were achieved between 0.5 and 1h and fitted to a flip-flop model. Absolute bioavailability was about 80% and the percentage of methylone protein binding was of 30%. A relationship between methylone brain levels and free plasma concentration yielded a ratio of 1.42 ± 0.06, indicating access to the central nervous system. We have identified four Phase I metabolites after oral administration. The major metabolic routes are N-demethylation, aliphatic hydroxylation and O-methylation of a demethylenate intermediate.

DISCUSSION

Pharmacokinetic and pharmacodynamic analysis of methylone showed a correlation between plasma concentrations and enhancement of the locomotor activity. A contribution of metabolites in the activity of methylone after oral administration is suggested. Present results will be helpful to understand the time course of the effects of this drug of abuse in humans.