Mephedrone (4-methylmethcathinone), a principal constituent of psychoactive bath salts, produces behavioral sensitization in rats

Abstract

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. © 2013 Elsevier Ireland Ltd.