"The Effects of methamphetamine and cocaine on rats' Y-Maze performance using directional vs. visual cues"

Abstract

Two experiments in our laboratory have demonstrated that across a wide range of doses, amphetamine but not cocaine (COC) disrupts the discrimination performance of rats running toward the lighted arm of a Y-Maze. In these experiments we noticed that rats in the amphetamine group were repeatedly running in the same direction (e.g., always left) rather than toward the lighted arm. Since amphetamine increases stereotypic behavior we hypothesized that the disruption of performance in the amphetamine group was due to perseverative responding in one direction. To test this hypothesis rats were trained on a directional cue that would be compatible with perseverative responding. One group of rats (n=8) was trained to run to the right arm (R) for water reinforcement while a second group of rats (n=8) was trained to run to the left arm (L). After reaching a 90% correct stability criterion, the rats were tested with an ascending and descending series of either methamphetamine (0.56 to 2.0 mg/kg) or COC (3.0 to 20 mg/kg) counterbalanced across groups, with saline and no injection days interspersed. With the exception of the 20 mg/kg COC dose, neither METH nor COC produced a significant increase in errors for rats in the R Group. The L Group, showed a significant increase in errors for METH at 0.56, 1.0 and 2.0 mg/kg and COC at the 10 and 20 mg/kg doses. The results were surprising in that METH did not result in perseverative errors and that it selectively effected rats trained to run left. We are currently investigating the handedness of the rats to determine if that accounts for the selective effect on left trained rats.