Behavioural neuroscience
Memory consolidation and reconsolidation of an inhibitory avoidance task in mice: Effects of a new different learning task

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Abstract

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.

Section snippets

Experimental animals

CF-1 male mice (FUCAL, Buenos Aires, Argentina) were used (age: 60–70 days; weight: 25–30g). They were individually identified and housed in stainless-steel cages, 15 per cage. The mice were kept in a climatized animal room (21–23°C) maintained on a 12-h light/dark cycle (lights on 06:00 h), with ad libitum access to dry food and tap water. Experiments were carried out in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals (NIH Publication No.

Results

Training step-through latencies differences among all the groups used in these experiments were not significant (TSTL=10 (8–2) s; H(19)=4.20; P>0.05).

Discussion

The results of the first series of experiments indicate that the immediate exposure to a potential new learning situation (nose-poke habituation) after the acquisition of a one-trial inhibitory avoidance, impaired retention performance of the original learning. The effect was observed across three consecutive retention test sessions, and was not seen if the exposure to the habituation learning task was carried out 3 h after the avoidance training. These results are, in general, similar to those

Acknowledgments

This work was supported by grant B028 from the University of Buenos Aires. M.G.B. is a fellow from (UBA). M.M.B., G.B.A. and C.M.B. are members of CONICET.

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    Both authors contributed equally to the work.

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