Effects of repeated treatment with methcathinone, mephedrone, and fenfluramine on intracranial self-stimulation in rats.

Abstract

Synthetic cathinones constitute a class of abused drugs that can act at dopamine, norepinephrine, and serotonin transporters (DAT, NET, and SERT, respectively). Intracranial self-stimulation (ICSS) is a preclinical procedure that can be used to evaluate abuse potential of drugs, and prior studies have indicated that abuse-related ICSS effects of monoamine-transporter substrates, including some synthetic cathinones, are positively correlated with drug selectivity for DAT vs. SERT. Abuse potential of drugs can also be influenced by regimens of repeated drug exposure, but the role of repeated exposure on abuse-related ICSS effects of synthetic cathinones has not been examined. This study used ICSS to evaluate effects of repeated treatment with the DAT>SERT substrate methcathinone, the DAT<SERT substrate fenfluramine, and the DAT≈SERT substrate mephedrone. Male Sprague-Dawley rats were trained in a frequency-rate ICSS procedure, and different groups were used to evaluate effects of methcathinone, mephedrone, and fenfluramine before, during, and after regimens of repeated treatment with the designated drug. Before repeated treatment, methcathinone produced dose-dependent and abuse-related ICSS facilitation, fenfluramine produced dose-dependent ICSS depression, and mephedrone produced mixed effects that included both facilitation and depression. Chronic treatment produced no change in effects of methcathinone, but complete tolerance to effects of fenfluramine. For mephedrone, chronic treatment produced partial tolerance to ICSS depression and enhanced expression of ICSS facilitation. Repeated exposure to mixed-action DAT≈SERT substrates such as mephedrone can result in increased abuse potential due to sustained expression of DAT-mediated abuse-related effects and tolerance to SERT-mediated abuse-limiting effects.