Locomotor activity and discriminative stimulus effects of five novel synthetic cathinone analogs in mice and rats

Background: The development of novel synthetic psychoactive substances continues to accelerate. There are little or no data on the pharmacological mechanisms, behavioral effects, or abuse liability of many of the newer compounds, despite increasing reports of severe adverse effects in recreational users. Methods: The current study investigated the discriminative stimulus and locomotor stimulant effects of a group of synthetic cathinone analogs: N-ethylpentylone, dimethylone, dibutylone, clephedrone, 3',4'-tetramethylene-alpha-pyrrolidinovalerophenone (TH-PVP). Locomotor activity was assessed in an open-field assay using Swiss-Webster mice. Discriminative stimulus effects were assessed in Sprague-Dawley rats trained to discriminate either cocaine, methamphetamine or MDMA from vehicle. Results: N-Ethylpentylone, dimethylone, dibutylone and clephedrone increased locomotor activity. Maximal effects were similar among the test compounds. Relative potencies were: methamphetamine > N-ethylpentylone > clephedrone > dimethylone > MDMA > cocaine > dibutylone. TH-PVP dose-dependently depressed locomotor activity. N-Ethylpentylone, dimethylone, dibutylone and clephedrone substituted fully for the discriminative stimulus effects of methamphetamine. N-Ethylpentylone, dibutylone and clephedrone fully substituted for cocaine, whereas dimethylone produced a maximum of 67% drug-appropriate responding. Dimethylone, dibutylone and clephedrone fully substituted for MDMA, whereas N-ethylpentylone produced only 50% drug-appropriate responding. TH-PVP produced a maximum of 38% methamphetamine-appropriate responding, 50% cocaine-appropriate responding, and less than 1% MDMA-appropriate responding. Conclusions: These data provide initial evidence that the novel psychoactive substances N-ethylpentylone, dimethylone, dibutylone, and clephedrone demonstrate potential for abuse as psychostimulants and/or club drugs, given their ability to stimulate locomotor activity and their substitution for the discriminative stimulus effects of methamphetamine, cocaine and/or MDMA. TH-PVP has minimal activity in the assays tested and may have little or no abuse liability.