Reversal of retrieval impairment caused by retroactive interference on a two-way active avoidance task in rats

Rats were exposed to an open field with flashing light (OFL; 60-W lamp, 30 Hz, for 7 min) 2 h after training and/or 2 h before testing in a two-way active avoidance task (30 trials, 0.5-mA footshock). Post-training OFL presentation caused retroactive interference, i.e., a retrieval impairment/amnesia for the avoidance task. Pretest OFL exposure reversed the post-training OFL-induced retrieval deficit. Diazepam (2.0 mg/kg), atropine (2.0 mg/kg), and methylatropine (0.1 mg/kg) administered before post-training OFL presentation blocked the OFL amnesic effect. However, these drugs did not counteract the pretest OFL-induced recovery of retrieval. Atropine and methylatropine administered 2 h before testing to rats receiving only post-training OFL presentation canceled the OFL-interfering effect. These results suggest: (1) that the amnesic effect of post-training OFL is due to failure of retrieval of the avoidance task, (2) that the reversal of this retrieval impairment by pretest OFL exposure may involve either priming or state-dependent mechanisms, and (3) that there are different modulatory mechanisms involved in post-training and pretest OFL effects.