Comparative study of retrograde amnesia in rats on active and passive avoidance tasks and spontaneous recovery of memory.

Naive and pretrained rats were trained in two active avoidance paradigms using a pole-climbing box and in a single-trial passive avoidance task using a T-maze. They were then subjected to amnestic treatments with electroshock, leptazol, pentobarbitone, or ether anesthesia. Single retention tests were given at 20-24, 44-48, or 68-96 h posttreatment. Electroshock and leptazol seizures produced retrograde amnesia in all three paradigms, provided that seizures were maximal and retention was tested before 48 h. Prior treatment with anticonvulsant drugs prevented amnesia. Ether and pentobarbitone anesthesia failed to produce amnesia in all three tasks. A trend of recovery from amnesia was observed in the electroshock and leptazol groups when tested for retention 48-96 h posttreatment. On the other hand, the non-amnesic control, pentobarbitone, and ether groups showed signs of forgetting at these longer intervals. Consolidation failure and/or retrieval block was surmised to be the cause of amnesia; recovery was the possible result of removing the block.