Memory consolidation and reconsolidation of an inhibitory avoidance task in mice: effects of a new different learning task.

CF-1 male mice were trained in an inhibitory avoidance task using a high footshock (1.2mA, 50Hz, 1 s) in order to reduce the influence of extinction on retention performance. A single session of 5 min exposure to a hole-board (nose-poke behavior), either immediately after training or the first retention test (memory reactivation) impaired retention performance over two consecutive days. The effects were time-dependent since they were not observed when the exposure to the hole-board was delayed 3 h. When mice were habituated to the hole-board (5 min/day, 5 days), and then trained in an inhibitory avoidance task, the immediately post-training or memory reactivation exposure to the hole-board did not modify retention performance over two consecutive days. The effects of the post-reactivation acute exposure to the hole-board were long-lasting (21 days). Reinstatement was not observed in our experimental conditions. The non-spontaneous recovery of retention performance over 21-days and the lack of reinstatement, suggest that the impairment of retention performance observed was not probably due to a deficit in memory retrieval. These findings suggest that the exposure to a potential new learning situation impairs not only memory consolidation but also memory reconsolidation of the original learning task.