A recreational dose of methylphenidate, but not methamphetamine, decreases anxiety-like behavior in female rats

Methylphenidate (MPH) and methamphetamine (METH) are two commonly abused psychomotor stimulants that impact anxiety, but in a manner that is currently unclear. This study adds to the literature by testing the effects of MPH and METH on anxiety in adult female rats, which has not previously been studied. In Experiment1, changes in anxiety-like behavior were determined using the Elevated Plus Maze (EPM) following either an acute injection of saline, METH (1 mg/kg), or MPH (10 mg/kg). Changes in general locomotion were measured using the open field test. MPH, but not METH, significantly decreased anxiety; MPH and METH were associated with increased activity in the open field. In Experiment2, we compared the effects of three once daily injections of saline to MPH (10 mg/kg) or METH (1 mg/kg). As with the acute dosing, repeated exposure to MPH, but not METH, decreased anxiety, and both drugs increased locomotion. Neither acute nor chronic dosing produced a change in locomotion during the EPM, indicating that the anxiolytic effects of MPH are independent of changes in locomotor behavior. These findings add further clarification to the literature investigating the psychoactive properties of MPH, with a special and needed emphasis on female behavior.