BACKGROUND AND PURPOSESynthetic cathinones, commonly referred to as 'bath salts', are a group of amphetamine-like drugs gaining popularity worldwide. 4-Methylmethcathinone (mephedrone, MEPH) is the most commonly abused synthetic cathinone in the UK, and exerts its effects by acting as a substrate-type releaser at monoamine transporters. Similar to other cathinone-related compounds, MEPH has a chiral centre and exists stably as two enantiomers: R-mephedrone (R-MEPH) and S-mephedrone (S-MEPH). EXPERIMENTAL APPROACHHere, we provide the first investigation into the neurochemical and behavioural effects of R-MEPH and S-MEPH. We analysed both enantiomers in rat brain synaptosome neurotransmitter release assays and also investigated their effects on locomotor activity (e.g. ambulatory activity and repetitive movements), behavioural sensitization and reward. KEY RESULTSBoth enantiomers displayed similar potency as substrates (i.e. releasers) at dopamine transporters, but R-MEPH was much less potent than S-MEPH as a substrate at 5-HT transporters. Locomotor activity was evaluated in acute and repeated administration paradigms, with R-MEPH producing greater repetitive movements than S-MEPH across multiple doses. After repeated drug exposure, only R-MEPH produced sensitization of repetitive movements. R-MEPH produced a conditioned place preference whereas S-MEPH did not. Lastly, R-MEPH and S-MEPH produced biphasic profiles in an assay of intracranial self-stimulation (ICSS), but R-MEPH produced greater ICSS facilitation than S-MEPH. CONCLUSIONS AND IMPLICATIONSOur data are the first to demonstrate stereospecific effects of MEPH enantiomers and suggest that the predominant dopaminergic actions of R-MEPH (i.e. the lack of serotonergic actions) render this stereoisomer more stimulant-like when compared with S-MEPH. This hypothesis warrants further study. Abbreviations

Background Nicotine is one of the world’s most addictive substances and the primary reason that humans inhale tobacco smoke. The pharmacological effects of nicotine can be investigated in planarians, aquatic flatworms that possess an integrated neural network including cephalic ganglia that some consider the earliest “brain” and spinal cord. Here, we tested the hypothesis that nicotine exposure elicits mammalian-like behaviors in planarians. Methods Planarian motility and stereotypy (C-shape hyperkinesias) were quantified following acute nicotine exposure. During repeated nicotine exposure, we investigated the presence of withdrawal, tolerance, behavioral sensitization, and environmental place conditioning. Results Acute nicotine exposure increased stereotypical activity and elicited biphasic effects on motility. A low concentration (0.01 mM) increased motility whereas higher concentrations (0.3 – 10 mM) elicited the opposite effect. Planarians exposed to nicotine (0.03 mM) for 60 min and then tested in water displayed reduced motility that was not observed during exposure to water, acute nicotine, or continuous nicotine. Nicotine-treated planarians withdrawn from the drug for 3 days before being challenged with nicotine displayed behavioral sensitization at low concentrations (0.1, 0.3 mM) but tolerance at higher concentrations (1, 3 mM). Planarians conditioned with nicotine in the ambient light (non-preferred environment) displayed a reduction in their natural preference for a dark environment. Conclusions The present results suggest nicotine elicits mammalian-like effects in planarians, including decreased motility and increased stereotypy following acute administration and abstinence-induced withdrawal, behavioral sensitization, tolerance, and place conditioning during repeated exposure.

Clinical psychiatric disorders of depression, anxiety, and substance abuse are most prevalent after traumatic brain injury (TBI). Pre-clinical research has focused on depression and anxiety post-injury; however, virtually no data exist examining whether the preference for illicit drugs is affected by traumatic injury in the developing adolescent brain. Using the controlled cortical impact (CCI) model of TBI and the conditioned place preference (CPP) assay, we tested the underlying hypothesis that brain injury during adolescence exacerbates the rewarding properties of cocaine in adulthood possibly through an active inflammatory status in the mesolimbic pathway. Six-week old, C57BL/6 mice sustained a single CCI-TBI to the right somatosensory cortex. CPP experiments with cocaine began 2 weeks post-TBI. Animals receiving cocaine displayed significant place preference shifts compared to saline controls. Further, within the cocaine-experienced cohort, moderate CCI-TBI during adolescence significantly increased the preference shift in adulthood when compared to naïve controls. Additionally, persistent neuroinflammatory responses were observed in the cortex, nucleus accumbens (NAc), and ventral tegmental area post-CCI-TBI. Significant increases in both astrocytic, glial fibrillary acidic protein, and microglial, ionization basic acid 1, markers were observed in the NAc at the end of CPP testing. Moreover, analysis using focused array gene expression panels identified the upregulation of numerous inflammatory genes in moderate CCI-TBI animals, compared to naïve controls, both in the cortex and NAc at 2 weeks post-TBI, before onset of cocaine administration. These results suggest that sustaining moderate TBI during adolescence may augment the rewarding effects of psychostimulants in adulthood, possibly by induction of chronic mesolimbic neuroinflammation.

Levamisole is estimated by the Drug Enforcement Agency (DEA) to be present in about 80% of cocaine seized in the United States and linked to debilitating, and sometimes fatal, immunologic effects in cocaine abusers. One explanation for the addition of levamisole to cocaine is that it increases the amount of product and enhances profits. An alternative possibility, and one investigated here, is that levamisole alters cocaine's action in vivo. We specifically investigated effects of levamisole on cocaine's stereotypical and place-conditioning effects in an established invertebrate (planarian) assay. Acute exposure to levamisole or cocaine produced concentration-dependent increases in stereotyped movements. For combined administration of the two agents, isobolographic analysis revealed that the observed stereotypical response was enhanced relative to the predicted effect, indicating synergism for the interaction. In conditioned place preference (CPP) experiments, cocaine produced a significant preference shift; in contrast, levamisole was ineffective at all concentrations tested. For combination experiments, a submaximal concentration of cocaine produced CPP that was enhanced by inactive concentrations of levamisole, indicating synergism. The present results provide the first experimental evidence that levamisole enhances cocaine's action in vivo. Most important is the identification of synergism for the levamisole/cocaine interaction, which now requires further study in mammals.

Background The present study tested the hypothesis that mephedrone (MEPH) produces behavioral sensitization (i.e., a progressive increase in motor response during repeated psychostimulant exposure) in rats. Methods MEPH was administered in two paradigms: 1) a 7-day variable-dosing paradigm (15 mg/kg on the first day, 30 mg/kg for 5 days, 15 mg/kg on the last day) and 2) a 5-day constant-dosing paradigm (15 mg/kg for 5 days). Following 10 days of drug absence, rats were challenged with MEPH (15 mg/kg). Results MEPH challenge produced enhancement of repetitive movement compared to acute MEPH exposure in both paradigms. Sensitization of repetitive movements to MEPH was also detected following a shorter (2-day) absence interval, before initiation of an absence interval (i.e., following repeated daily exposure), and across context-independent and –dependent dosing schedules. A lower dose of MEPH (5 mg/kg) did not produce sensitization of repetitive movement. Sensitization of ambulatory activity was not detected in any experimental paradigm. Conclusion These results suggest that repeated MEPH exposure produces preferential sensitization to repetitive movement produced by acute MEPH challenge. Our findings suggest that MEPH is a unique stimulant displaying weak sensitizing properties with overlapping, but distinctive, features relative to established psychostimulant drugs.