Mephedrone ('meow'): recent studies using animal models

Introduction and aims: Mephedrone (4-methylmethcathinone, 'Meow') is a drug that has rapidly increased in popularity in recent years. Users report mephedrone as having the stimulant-like qualities of methamphetamine and cocaine, combined with the prosocial, entactogenic effects of MDMA. The toxicity of mephedrone is uncertain and requires study. Design and methods: Experiments were undertaken in rats to assess the effects of mephedrone. These include biotelemetry studies (to assess effects on body temperature and cardiovascular parameters), self-administration studies (to examine rewarding properties), Fos immunohistochemistry studies (to examine brain activation), and behavioural studies of acute and long-term effects. Results: Mephedrone was intravenously self-administered by rats across a wide dose range. Rats given mephedrone showed increased locomotor activity with extreme hyperactivity and tachycardia observed with high doses. At normal ambient temperatures mephedrone caused few body temperature changes but at ambient temperatures of 30°C a potentially lethal hyperthermia was observed (body temperatures >40°C). Patterns of brain activation obtained with mephedrone resembled a mixture of MDMA and methamphetamine, and were consistent with an effect of the drug on dopamine, serotonin and oxytocin systems. Weeks after repeated exposure to mephedrone rats showed impaired object recognition memory but few signs of long-term neurotransmitter depletion. Discussion and conclusions: These results confirm user reports of MDMA/cocaine like properties of mephedrone and suggest compulsive patterns of use may emerge. They also flag the possible danger of using the drug in hot environments. Finally the possibility that long-term memory impairment may occur with mephedrone is of concern, and warrants study in user populations.