Posttraining presentation of a flashing light alters retrieval of a two-way active avoidance task in rats.

Rats were trained and tested in a two-way active avoidance task (30 trials, 0.4-mA footshock, 24-h training-test interval). Exposure to an open field with flashing light (60-W lamp, 30 Hz, for 7 min, OFL) 2 h after training caused a retrieval impairment for the avoidance task, a phenomenon called retroactive interference. Animals familiarized with the OFL 24 h before training showed no retrieval impairment when exposed to the OFL 2 h after training. Both adrenal medullectomy (performed 7 to 14 days before training) and dexamethasone treatment (2 mg/kg, injected IP 24 h and 12 h before training) prevented the OFL interfering effect. Time-course experiments revealed that OFL presented either 1 or 4 h after training caused no retrieval deficit, and that animals exposed to the OFL 2 h after training and receiving another OFL presentation 1 or 2 h, but not 4 h, prior to testing had normal retrieval performance. These results suggest: 1) that the retroactive interference caused by presentation of OFL 2 h after training is due to failure of retrieval of the avoidance task since it is counteracted by the pretest presentation to the OFL, 2) that the OFL-induced retrieval interfering effect partly depends on the novelty of the OFL situation, and on the functional integrity of pituitary ACTH and adrenomedullar-dependent mechanisms and 3) that there are different mechanisms involved in posttraining and pretest OFL effects since they present distinct time-courses.

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.