Assessment of aversive effects of methylone in male and female Sprague-Dawley rats: Conditioned taste avoidance, body temperature and activity/stereotypies

Male and female C57BL/6 mice display drug-induced aversion and reward in the combined conditioned taste avoidance/conditioned place preference procedure

BACKGROUND

Drugs of abuse have rewarding and aversive effects that, in balance, impact abuse potential. Although such effects are generally examined in independent assays (e.g., CPP and CTA, respectively), a number of studies have examined these effects concurrently in rats in a combined CTA/CPP design. The present study assessed if similar effects can be produced in mice which would allow for determining how each is affected by subject and experiential factors relevant to drug use and abuse and the relationship between these affective properties.

METHODS

Male and female C57BL/6 mice were exposed to a novel saccharin solution, injected (IP) with saline or 5.6, 10 or 18 mg/kg of the synthetic cathinone, methylone, and placed on one side of the place conditioning apparatus. The following day, they were injected with saline, given access to water and placed on the other side of the apparatus. After four conditioning cycles, saccharin avoidance and place preferences were assessed in a final two-bottle CTA test and a CPP Post-Test, respectively.

RESULTS

In the combined CTA/CPP design, mice acquired a significant dose-dependent CTA (p = 0.003) and a significant CPP (p = 0.002). These effects were independent of sex (all p's > 0.05). Further, there was no significant relationship between the degree of taste avoidance and place preference (p > 0.05).

CONCLUSIONS

Similar to rats, mice displayed significant CTA and CPP in the combined design. It will be important to extend this design in mice to other drugs and to examine the impact of different subject and experiential factors on these effects to facilitate predictions of abuse liability.

Effects of Methylone Pre-Exposure on Fluoxetine-Induced Conditioned Taste Avoidance in Male and Female Sprague-Dawley Rats

Background: Prior work has reported that a drug’s aversive effects (as indexed by taste avoidance conditioning) are attenuated when the pre-exposure and conditioning drugs are the same or different. The latter, otherwise known as cross-drug pre-exposure, is especially interesting as it has been used as a tool to assess mechanisms underlying the aversive effects of drugs. We previously reported that methylone pre-exposure differentially impacted the aversive effects of MDPV and MDMA (MDPV > MDMA), a difference consistent with the dopaminergic mediation of methylone’s aversive effects. To examine the possible role of serotonin (5-HT) in methylone’s aversive effects, the present study assessed the effects of methylone pre-exposure on taste avoidance induced by the 5-HT reuptake inhibitor fluoxetine. Methods: Male and female Sprague-Dawley rats were exposed to 10 mg/kg of methylone every 4th day (for a total of 5 injections) prior to taste avoidance training with 10 mg/kg of fluoxetine. Results: Fluoxetine induced significant taste avoidance (each p < 0.05) that was independent of sex. Methylone pre-exposure had no impact on avoidance produced by fluoxetine in either males or females (each p > 0.05). Conclusions: Methylone pre-exposure had no impact on fluoxetine-induced avoidance. These findings suggest that it is unlikely that 5-HT mediates the aversive effects of methylone. The implications of the present results for the mechanisms mediating methylone’s aversive effects were discussed. Understanding such mechanisms is important in predictions relevant to drug history and abuse liability as a variety of subject and experiential factors known to affect (reduce) a drug’s aversive effects may increase its use and potential for abuse.

Synthetic Cathinones and Neurotoxicity Risks: A Systematic Review

According to the EU Early Warning System (EWS), synthetic cathinones (SCs) are the second largest new psychoactive substances (NPS) class, with 162 synthetic cathinones monitored by the EU EWS. They have a similar structure to cathinone, principally found in Catha Edulis; they have a phenethylamine related structure but also exhibit amphetamine-like stimulant effects. Illegal laboratories regularly develop new substances and place them on the market. For this reason, during the last decade this class of substances has presented a great challenge for public health and forensic toxicologists. Acting on different systems and with various mechanisms of action, the spectrum of side effects caused by the intake of these drugs of abuse is very broad. To date, most studies have focused on the substances’ cardiac effects, and very few on their associated neurotoxicity. Specifically, synthetic cathinones appear to be involved in different neurological events, including increased alertness, mild agitation, severe psychosis, hyperthermia and death. A systematic literature search in PubMed and Scopus databases according to PRISMA guidelines was performed. A total of 515 studies published from 2005 to 2022 (350 articles from PubMed and 165 from Scopus) were initially screened for eligibility. The papers excluded, according to the criteria described in the Method Section (n = 401) and after full text analyses (n = 82), were 483 in total. The remaining 76 were included in the present review, as they met fully the inclusion criteria. The present work provides a comprehensive review on neurotoxic mechanisms of synthetic cathinones highlighting intoxication cases and fatalities in humans, as well as the toxic effects on animals (in particular rats, mice and zebrafish larvae). The reviewed studies showed brain-related adverse effects, including encephalopathy, coma and convulsions, and sympathomimetic and hallucinogenic toxidromes, together with the risk of developing excited/agitated delirium syndrome and serotonin syndrome.

Methylone pre-exposure differentially impacts the aversive effects of MDPV and MDMA in male and female Sprague-Dawley rats: Implications for abuse vulnerability

BACKGROUND

Polydrug use is well documented in synthetic cathinone users, although the consequences of such use are not well characterized. In pre-clinical research, a pre-exposure to a drug has been reported to attenuate the aversive effects of other drugs which has implications for their abuse potential. The goal of the present study was to investigate the impact of pre-exposure to the synthetic cathinone methylone on the aversive effects of MDPV and MDMA.

METHOD

Male and female Sprague-Dawley rats were exposed to 10 mg/kg of methylone every 4th day (for a total of five injections) prior to taste avoidance training with 1.8 mg/kg of MDPV or 1 mg/kg of MDMA.

RESULTS

MDPV and MDMA induced taste avoidance in males and females (all p's < 0.05). In males, methylone pre-exposure attenuated the avoidance induced by MDPV and MDMA (all p's < 0.05) with the attenuation greater with MDPV. In females, methylone pre-exposure attenuated avoidance induced by MDPV (all p's < 0.05), but it had no effect on those induced by MDMA (all p's > 0.05).

CONCLUSIONS

The effects of exposure to methylone on taste avoidance induced by MDPV and MDMA were drug- (MDPV > MDMA) and sex- (MDMA only in males) dependent. The attenuating effects of methylone pre-exposure on MDPV and MDMA were discussed in terms of their shared neurochemical action. These findings suggest that a history of methylone use may reduce the aversive effects of MDPV and MDMA which may have implications for polydrug use involving the synthetic cathinones.

Effects of the Phenethylamine 2-Cl-4,5-MDMA and the Synthetic Cathinone 3,4-MDPHP in Adolescent Rats: Focus on Sex Differences

The illicit drug market of novel psychoactive substances (NPSs) is expanding, becoming an alarming threat due to increasing intoxication cases and insufficient (if any) knowledge of their effects. Phenethylamine 2-chloro-4,5-methylenedioxymethamphetamine (2-Cl-4,5-MDMA) and synthetic cathinone 3,4-methylenedioxy-α-pyrrolidinohexanophenone (3,4-MDPHP) are new, emerging NPSs suggested to be particularly dangerous. This study verified whether these two new drugs (i) possess abuse liability, (ii) alter plasma corticosterone levels, and (iii) interfere with dopaminergic transmission; male and female adolescent rats were included to evaluate potential sex differences in the drug-induced effects. Findings show that the two NPSs are not able to sustain reliable self-administration behavior in rats, with cumulatively earned injections of drugs being not significantly different from cumulatively earned injections of saline in control groups. Yet, at the end of the self-administration training, females (but not males) exhibited higher plasma corticosterone levels after chronic exposure to low levels of 3,4-MDPHP (but not of 2-Cl-4,5-MDMA). Finally, electrophysiological patch-clamp recordings in the rostral ventral tegmental area (rVTA) showed that both drugs are able to increase the firing rate of rVTA dopaminergic neurons in males but not in females, confirming the sex dimorphic effects of these two NPSs. Altogether, this study demonstrates that 3,4-MDPHP and 2-Cl-4,5-MDMA are unlikely to induce dependence in occasional users but can induce other effects at both central and peripheral levels that may significantly differ between males and females.

Impact of the Aversive Effects of Drugs on Their Use and Abuse

Drug use and abuse are complex issues in that the basis of each may involve different determinants and consequences, and the transition from one to the other may be equally multifaceted. A recent model of the addiction cycle (as proposed by Koob and his colleagues) illustrates how drug-taking patterns transition from impulsive (acute use) to compulsive (chronic use) as a function of various neuroadaptations leading to the downregulation of DA systems, upregulation of stress systems, and the dysregulation of the prefrontal/orbitofrontal cortex. Although the nature of reinforcement in the initiation and mediation of these effects may differ (positive vs. negative), the role of reinforcement in drug intake (acute and chronic) is well characterized. However, drugs of abuse have other stimulus properties that may be important in their use and abuse. One such property is their aversive effects that limit drug intake instead of initiating and maintaining it. Evidence of such effects comes from both clinical and preclinical populations. In support of this position, the present review describes the aversive effects of drugs (assessed primarily in conditioned taste aversion learning), the fact that they occur concurrently with reward as assessed in combined taste aversion/place preference designs, the role of aversive effects in drug-taking (in balance with their rewarding effects), the dissociation of these affective properties in that they can be affected in different ways by the same manipulations, and the impact of various parametric, experiential, and subject factors on the aversive effects of drugs and the consequent impact of these factors on their use and abuse potential.