Kevin M. Creehan

Mephedrone (4-methylmethcathinone) supports intravenous self-administration in Sprague-Dawley and Wistar rats.

Recreational use of the drug 4‐methylmethcathinone (mephedrone; 4‐MMC) became increasingly popular in the United Kingdom in recent years, spurred in part by the fact that it was not criminalized until April 2010. Although several fatalities have been associated with consumption of 4‐MMC and cautions for recreational users about its addictive potential have appeared on Internet forums, very little information about abuse liability for this drug is available. This study was conducted to determine if 4‐MMC serves as a reinforcer in a traditional intravenous self‐administration model. Groups of male Wistar and Sprague‐Dawley rats were prepared with intravenous catheters and trained to self‐administer 4‐MMC in 1‐hour sessions. Per‐infusion doses of 0.5 and 1.0 mg/kg were consistently self‐administered, resulting in greater than 80% discrimination for the drug‐paired lever and mean intakes of about 2–3 mg/kg/hour. Dose‐substitution studies after acquisition demonstrated that the number of responses and/or the total amount of drug self‐administered varied as a function of dose. In addition, radiotelemetry devices were used to show that self‐administered 4‐MMC was capable of increasing locomotor activity (Wistar) and decreasing body temperature (Sprague‐Dawley). Pharmacokinetic studies found that the T1/2 of 4‐MMC was about 1 hour in vivo in rat plasma and 90 minutes using in vitro liver microsomal assays. This study provides evidence of stimulant‐typical abuse liability for 4‐MMC in the traditional pre‐clinical self‐administration model.

Effect of Ambient Temperature on the Thermoregulatory and Locomotor Stimulant Effects of 4-Methylmethcathinone in Wistar and Sprague-Dawley Rats

The drug 4-methylmethcathinone (4-MMC; aka, mephedrone, MMCAT, “plant food”, “bath salts”) is a recent addition to the list of popular recreational psychomotor-stimulant compounds. Relatively little information about this drug is available in the scientific literature, but popular media reports have driven recent drug control actions in the UK and several US States. Online user reports of subjective similarity to 3,4-methylenedioxymethamphetamine (MDMA, “Ecstasy”) prompted the current investigation of the thermoregulatory and locomotor effects of 4-MMC. Male Wistar and Sprague-Dawley rats were monitored after subcutaneous administration of 4-MMC (1–10 mg/kg ) using an implantable radiotelemetry system under conditions of low (23°C) and high (27°C) ambient temperature. A reliable reduction of body temperature was produced by 4-MMC in Wistar rats at 23°C or 27°C with only minimal effect in Sprague-Dawley rats. Increased locomotor activity was observed after 4-MMC administration in both strains with significantly more activity produced in the Sprague-Dawley strain. The 10 mg/kg s.c. dose evoked greater increase in extracellular serotonin, compared with dopamine, in the nucleus accumbens. Follow-up studies confirmed that the degree of locomotor stimulation produced by 10 mg/kg 4-MMC was nearly identical to that produced by 1 mg/kg d-methamphetamine in each strain. Furthermore, hypothermia produced by the serotonin 1A/7 receptor agonist 8-hydroxy-N,N-dipropyl-2-aminotetralin (8-OH-DPAT) was similar in each strain. These results show that the cathinone analog 4-MMC exhibits thermoregulatory and locomotor properties that are distinct from those established for methamphetamine or MDMA in prior work, despite recent evidence of neuropharmacological similarity with MDMA.

A Methamphetamine Vaccine Attenuates Methamphetamine-Induced Disruptions in Thermoregulation and Activity in Rats

BACKGROUND There are no approved pharmacotherapies for d-methamphetamine (METH) addiction and existing therapies have limited efficacy. Advances in using immunotherapeutic approaches for cocaine and nicotine addiction have stimulated interest in creating a similar approach for METH addiction. This study investigated whether active vaccination against METH could potentially attenuate responses to METH in vivo. METHODS Male Sprague Dawley rats (n = 32) received a four-boost series with one of three candidate anti-METH vaccines (MH2[R], MH6, and MH7) or a control keyhole limpet hemocyanin conjugate vaccine. Effects of METH on rectal temperature and wheel activity at 27°C ambient temperature were determined. The most efficacious vaccine, MH6, was then contrasted with keyhole limpet hemocyanin conjugate vaccine in a subsequent experiment (n = 16), wherein radiotelemetry determined home cage locomotor activity and body temperature at 23°C ambient temperature. RESULTS The MH6 vaccine produced high antibody titers with nanomolar affinity for METH and sequestered METH in the periphery of rats. In experiment 1, the thermoregulatory and psychomotor responses produced by METH at 27°C were blocked in the MH6 group. In experiment 2, METH-induced decreases in body temperature and locomotor activity at 23°C were also attenuated in the MH6 group. A pharmacokinetic study in experiment 2 showed that MH6-vaccinated rats had higher METH serum concentrations, yet lower brain METH concentrations, than control rats, and METH concentrations correlated with individual antibody titer. CONCLUSIONS These data demonstrate that active immunopharmacotherapy provides functional protection against physiological and behavioral disruptions induced by METH.

Reciprocal inhibitory effects of intravenous d-methamphetamine self-administration and wheel activity in rats

BACKGROUND Some epidemiological and cessation studies suggest physical exercise attenuates or prevents recreational drug use in humans. Preclinical studies indicate that wheel activity reduces cocaine self-administration in rats; this may, however, require the establishment of compulsive wheel activity. METHODS Effects of concurrent wheel activity on intravenous d-methamphetamine (METH) self-administration were examined in male Wistar and Sprague Dawley rats with negligible prior wheel experience. Wistar rats self-administered METH (0.05 mg/kg/inf) under a fixed-ratio 1 (FR1) schedule with concurrent access to an activity wheel during sessions 1-14, 8-21 or 15-21. Control rats which did not self-administer METH had access to an activity wheel during sessions 1-14, 8-21 or 15-28. Sprague Dawley rats self-administered METH (0.1 mg/kg/inf) under FR1 for 14 sessions with either concurrent access to a locked or an unlocked activity wheel. RESULTS METH self-administration was lower when the wheel was available concurrently from the start of self-administration training in both strains, even though Sprague Dawley rats self-administered twice as many METH infusions and ran one-sixth as much on the wheel compared to Wistar rats. Wheel access initiated after 7 or 14 days had no effect on METH self-administration in Wistar rats. Wheel activity was significantly reduced in these groups compared with the group with concurrent wheel and METH access for the first 14 sessions. CONCLUSIONS These data show that METH self-administration is reduced by exercise if initiated from the start of self-administration and that prior METH self-administration experience interferes with the value of exercise as a reinforcer.

Changes in ambient temperature differentially alter the thermoregulatory, cardiac and locomotor stimulant effects of 4-methylmethcathinone (mephedrone)

BACKGROUND The substituted cathinone compound known as mephedrone (4-methylmethcathinone; 4-MMC) has become popular with recreational users of psychomotor-stimulant compounds. Only recently have the first preclinical studies provided information about this drug in the scientific literature; nevertheless, media reports have led to drug control actions in the UK and across several US states. Rodent studies indicate that 4-MMC exhibits neuropharmacological similarity to 3,4-methylenedioxymethamphetamine (MDMA) and prompt investigation of the thermoregulatory, cardiac and locomotor effects of 4-MMC. This study focuses on the role of ambient temperature, which has been shown to shift the effects of MDMA from hyperthermic to hypothermic. METHODS Male Sprague-Dawley rats were monitored after subcutaneous administration of 4-MMC (1.0-5.6 mg/kg) using an implantable radiotelemetry system under conditions of low (20 °C) and high (30 °C) ambient temperature. RESULTS A pharmacokinetic study found a T(max) of 0.25 h and a C(max) of 1206 ng/ml after 5.6 mg/kg 4-MMC. A dose-dependent reduction of body temperature was produced by 4-MMC at 20 °C but there was no temperature change at 30 °C. Increased locomotor activity was observed after 4-MMC administration under both ambient temperatures, however, significantly more activity was observed at 30 °C. Heart rate was slowed by 1.0 and 5.6 mg/kg 4-MMC at 20°C, and was slower in the 30 °C vs. 20 °C condition across all treatments. CONCLUSION These results show that the cathinone analog 4-MMC exhibits in vivo thermoregulatory properties that are distinct from those produced by MDMA.

Cannabidiol fails to reverse hypothermia or locomotor suppression induced by Δ9‐tetrahydrocannabinol in Sprague‐Dawley rats

Growing evidence shows cannabidiol (CBD) modulates some of the effects of Δ9‐tetrahydrocannabinol (THC). CBD is a constituent of some strains of recreational cannabis but its content is highly variable. High CBD strains may have less memory‐impairing effects than low‐CBD strains and CBD can reverse behavioural effects of THC in monkeys. CBD/THC interactions in rodents are more complicated as CBD can attenuate or exacerbate the effects of THC. This study was undertaken to determine if CBD could reverse hypothermia or hypolocomotor effects caused by THC in rats.

Effects of active anti-methamphetamine vaccination on intravenous self-administration in rats

BACKGROUND d-Methamphetamine (METH) addiction is a serious public health concern for which successful treatment remains elusive. Immunopharmacotherapy has been shown to attenuate locomotor and thermoregulatory effects of METH. The current study investigated whether active vaccination against METH could alter intravenous METH self-administration in rats. METHODS Male Sprague-Dawley rats (Experiment 1: N=24; Experiment 2: N=18) were vaccinated with either a control keyhole-limpet hemocyanin conjugate vaccine (KLH) or a candidate anti-METH vaccine (MH6-KLH) or. Effects of vaccination on the acquisition of METH self-administration under two dose conditions (0.05, 0.1mg/kg/inf) and post-acquisition dose-substitution (0, 0.01, 0.05, 0.20mg/kg/inf, Experiment 1; 0.01, 0.05, 0.10, 0.15mg/kg/inf, Experiment 2) during steady-state responding were investigated. Plasma METH concentrations were determined 30min after an acute challenge dose of 3.2mg/kg METH. RESULTS Active vaccination inhibited the acquisition of METH self-administration under the 0.1mg/kg/inf dose condition, with 66% of the MH6-KLH-vaccinated rats compared to 100% of the controls reaching criteria, and produced transient and dose-dependent effects on self-administration during the maintenance phase. Under the 0.05mg/kg/inf dose condition, MH6-KLH-vaccinated rats initially self-administered more METH than controls, but then self-administration decreased across the acquisition phase relative to controls; a subsequent dose-response assessment confirmed that MH6-KLH-vaccinated rats failed to acquire METH self-administration. Finally, plasma METH concentrations were higher in MH6-KLH-vaccinated rats compared to controls after an acute METH challenge, and these were positively correlated with antibody titers. CONCLUSIONS These data demonstrate that active immunopharmacotherapy for METH attenuates the acquisition of METH self-administration.

One day access to a running wheel reduces self-administration of d-methamphetamine, MDMA and Methylone

BACKGROUND Exercise influences drug craving and consumption in humans and drug self-administration in laboratory animals, but the effects can be variable. Improved understanding of how exercise affects drug intake or craving would enhance applications of exercise programs to human drug users attempting cessation. METHODS Rats were trained in the intravenous self-administration (IVSA) of D-methamphetamine (METH; 0.05 mg/kg/inf), 3,4-methylenedioxymethamphetamine (MDMA; 0.5 mg/kg/inf) or methylone (0.5 mg/kg/inf). Once IVSA was established, the effect of ∼ 22 h of wheel access in the home cage on subsequent drug taking was assessed in a two cohort crossover design. RESULTS Provision of home cage wheel access during the day prior to IVSA sessions significantly decreased the self-administration of METH, MDMA and methylone. At the individual level, there was no correlation between the amount a rat used the wheel and the size of the individuals decrease in drug intake. CONCLUSIONS Wheel access can reduce self-administration of a variety of psychomotor stimulants. It does so immediately, i.e., without a need for weeks of exercise prior to drug access. This study therefore indicates that future mechanistic investigations should focus on acute effects of exercise. In sum, the results predict that exercise programs can be used to decrease stimulant drug use in individuals even with no exercise history and an established drug taking pattern.

Escalation of intravenous self‐administration of methylone and mephedrone under extended access conditions

The recreational use of substituted cathinones continues to grow as a public health concern in the United States. Studies have shown that extended access to intravenous (i.v.) self‐administration of stimulants, such as cocaine and methamphetamine, results in escalation of drug intake relative to shorter access; however, little is known about the impact of extended access on self‐administration of entactogen class stimulants such as methylone and 4‐methylmethcathinone (mephedrone). Male Wistar rats were randomly assigned to short‐access (ShA, 2‐ h) and long‐access (LgA, 6‐ h) groups and trained to self‐administer methylone or mephedrone (0.5 mg/kg/infusion) using a fixed‐ratio 1 response contingency. The methylone‐trained groups were evaluated on a progressive‐ratio (PR) procedure incorporating dose‐substitution of methylone (0.125–2.5 mg/kg/infusion), mephedrone (0.125–2.5 mg/kg/infusion) or methamphetamine (MA; 0.01–0.5 mg/kg/infusion). Mephedrone‐trained rats were similarly evaluated on a PR with mephedrone and MA. Rats trained with LgA to methylone and mephedrone earned more infusions during acquisition compared with ShA groups. Mephedrone‐trained LgA rats reached significantly higher breakpoints than all other groups in mephedrone and MA PR tests. Methylone‐trained LgA rats exhibited a rightward shift of the peak effective dose but no overall efficacy change compared with methylone‐trained ShA rats. These findings show that the self‐administration of mephedrone escalates under LgA conditions in a manner similar to traditional stimulants whereas escalation of 6 h intakes of methylone is not accompanied by differences in PR performance. Thus mephedrone represents the greater risk for dysregulated drug consumption.

Active vaccination attenuates the psychostimulant effects of α-PVP and MDPV in rats

&NA; Recreational use of substituted cathinones continues to be an emerging public health problem in the United States; cathinone derivatives &agr;‐pyrrolidinopentiophenone (&agr;‐PVP) and 3,4‐methylenedioxypyrovalerone (MDPV), which have been linked to human fatalities and show high potential for abuse liability in animal models, are of particular concern. The objective of this study was to develop an immunotherapeutic strategy for attenuating the effects of &agr;‐PVP and MDPV in rats, using drug‐conjugate vaccines created to generate antibodies with neutralizing capacity. Immunoconjugates (&agr;‐PVP‐KLH and MDPV‐KLH) or the control carrier protein, keyhole limpet hemocyanin (KLH), were administered to groups (N = 12) of male Sprague‐Dawley rats on Weeks 0, 2 and 4. Groups were administered &agr;‐PVP or MDPV (0.0, 0.25, 0.5, 1.0, 5.0 mg/kg, i.p.) in acute drug challenges and tested for changes in wheel activity. Increased wheel activity produced by &agr;‐PVP or MDPV in the controls was attenuated in the &agr;‐PVP‐KLH and MDPV‐KLH vaccinated groups, respectively. Rectal temperature decreases produced by MDPV in the controls were reduced in duration in the MDPV‐KLH vaccine group. A separate group (N = 19) was trained to intravenously self‐administer &agr;‐PVP (0.05, 0.1 mg/kg/inf) and vaccinated with KLH or &agr;‐PVP‐KLH, post‐acquisition. Self‐administration in &agr;‐PVP‐KLH rats was initially higher than in the KLH rats but then significantly decreased following a final vaccine booster, unlike the stable intake of KLH rats. The data demonstrate that active vaccination provides functional protection against the effects of &agr;‐PVP and MDPV, in vivo, and recommend additional development of vaccines as potential therapeutics for mitigating the effects of designer cathinone derivatives. HighlightsThe novel drugs alpha‐pyrrolidinopentiophenone (&agr;‐PVP) and 3,4‐methylenedioxypyrovalerone (MDPV) have high abuse potential.There are no currently available therapies to treat stimulant abuse, including MDPV and &agr;‐PVP.Drug‐conjugate vaccines were created to generate antibodies to neutralize MDPV and &agr;‐PVP.Increased wheel activity was produced by &agr;‐PVP or MDPV in the controls but not the vaccinated groups.Self‐administration of &agr;‐PVP was disrupted in the vaccinated group.