The abuse of psychoactive 'bath salts' containing cathinones such as 3,4-methylenedioxypyrovalerone (MDPV) is a growing public health concern, yet little is known about their pharmacology. Here, we evaluated the effects of MDPV and related drugs using molecular, cellular, and whole-animal methods. In vitro transporter assays were performed in rat brain synaptosomes and in cells expressing human transporters, while clearance of endogenous dopamine was measured by fast-scan cyclic voltammetry in mouse striatal slices. Assessments of in vivo neurochemistry, locomotor activity, and cardiovascular parameters were carried out in rats. We found that MDPV blocks uptake of [ 3 H]dopamine (IC 50 ¼ 4.1 nM) and [ 3 H]norepinephrine (IC 50 ¼ 26 nM) with high potency but has weak effects on uptake of [ 3 H]serotonin (IC 50 ¼ 3349 nM). In contrast to other psychoactive cathinones (eg, mephedrone), MDPV is not a transporter substrate. The clearance of endogenous dopamine is inhibited by MDPV and cocaine in a similar manner, but MDPV displays greater potency and efficacy. Consistent with in vitro findings, MDPV (0.1-0.3 mg/kg, intravenous) increases extracellular concentrations of dopamine in the nucleus accumbens. Additionally, MDPV (0.1-3.0 mg/kg, subcutaneous) is at least 10 times more potent than cocaine at producing locomotor activation, tachycardia, and hypertension in rats. Our data show that MDPV is a monoamine transporter blocker with increased potency and selectivity for catecholamines when compared with cocaine. The robust stimulation of dopamine transmission by MDPV predicts serious potential for abuse and may provide a mechanism to explain the adverse effects observed in humans taking high doses of 'bath salts' preparations.

Nicotine has been shown to maintain intravenous self-administration behaviour in humans and laboratory animals. However, factors critical in the initiation of nicotine self administration are not well defined. In particular genetic differences and effects of pre-exposure to nicotine have not been examined. Male Sprague-Dawley or Long-Evans rats were surgically prepared with indwelling jugular catheters and 3 days later received chronic injections of nicotine (0.4 mg/kg SC) or vehicle (saline, 1 ml/kg) for 7 days in their home cage. The next day, 2-h daily test sessions were initiated, during which rats were given the opportunity to nose-poke for nicotine infusions (0.015, 0.03 or 0.06 mg/kg per infusion) under a one-response fixed-ratio (FR-1) schedule of reinforcement with a 20-s time out after each infusion. One hole was defined as active while pokes in the other hole were recorded but had no scheduled consequence. The response requirement was increased progressively to five (FR-5) over successive sessions. Both saline- and nicotine-pretreated Sprague-Dawley rats showed a preference for the active hole, while only the saline-pretreated Long-Evans rats acquired the self-administration as defined by significant differences between responding in the active versus the inactive holes. The Fisher (F344) and Lewis inbred strains also failed to acquire self-administration of nicotine under these conditions. With Sprague-Dawley and Long-Evans rats that acquired the self-administration, and showed stable levels of maintained responding for nicotine, substituting saline for the nicotine or pretreating with mecamylamine (2.0 mg/kg SC) extinguished the behaviour. When dose per infusion was varied, an inverted U-shaped dose-response curve was obtained. These results support previous reports that nicotine can serve as a reinforcer in rodents and demonstrate that environmental factors such as prior nicotine exposure or genetic factors such as rat strain can affect acquisition of nicotine self-administration.

Rationale 3,4-Methylenedioxypyrovalerone (MDPV) and 3,4-methylenedioxy-N-methylcathinone (methylone) are synthetic drugs found in so-called “bath salts” products. Both drugs exert their effects by interacting with monoamine transporter proteins. MDPV is a potent uptake blocker at transporters for dopamine and norepinephrine while methylone is a non-selective releaser at transporters for dopamine, norepinephrine and serotonin (5-HT). Objectives We hypothesized that prominent 5-HT-releasing actions of methylone would render this drug less reinforcing than MDPV. Methods To test this hypothesis, we compared behavioral effects of MDPV and methylone using intravenous (i.v.) self-administration on a fixed-ratio 1 schedule in male rats. Additionally, neurochemical effects of the drugs were examined using in vivo microdialysis in nucleus accumbens, in a separate cohort of rats. Results MDPV self-administration (0.03 mg/kg/inj) was acquired rapidly, and reached 40 infusions per session, similar to the effects of cocaine (0.5 mg/kg/inj), by the end of training. By contrast, methylone self-administration (0.3 & 0.5 mg/kg/inj) was acquired slowly, and response rates only reached 20 infusions per session by the end of training. In dose substitution studies, MDPV and cocaine displayed typical inverted U-shaped dose-effect functions, but methylone did not. In vivo microdialysis revealed that i.v. MDPV (0.1 and 0.3 mg/kg) increased extracellular dopamine while i.v. methylone (1 and 3 mg/kg) increased extracellular dopamine and 5-HT. Conclusions Our findings support the hypothesis that elevations in extracellular 5-HT in the brain can dampen positive reinforcing effects of cathinone-type drugs. Nevertheless, MDPV and methylone are both self-administered by rats suggesting these drugs possess significant abuse liability in humans.