Retrieval enhancement in mice by pretest amphetamine injection after a long retention interval

Abstract

Mice were trained to avoid one compartment of a shuttlebox using the procedures of Pavlovian fear conditioning, and retention was measured 1 day later and 1 month later using an active avoidance test. Good retention was evident at 1 day, but substantial forgetting occurred after 1 month, performance levels in this group being equivalent to those exhibited by sham-conditioned animals. Treatment with d-amphetamine (2.0 mg/kg) before testing restored retention to levels shown by mice tested 1 day after conditioning. When retention was tested with a passive avoidance test, amphetamine increased rather than decreased latencies of animals tested 1 month after conditioning. Amphetamine did not decrease latencies of sham-conditioned mice tested in active avoidance and did not enhance the performance of those with strong memory tested 1 day following training in either active or passive tests. Amphetamine also enhanced retrieval in mice in which conditioning was weakened by a reduction in shock level rather than by imposition of a long retention interval. These findings add to the growing evidence that retention of weak memories can be facilitated by monoaminergic stimulation of retrieval mechanisms.

Long-term retention of fear-potentiated startle following a short training session

“…These results are consistent with previous studies using a CER task, in which four CS-US pairings were sufficient to produce reliableCER 24 h and 90 days after training (Gleitman & Holmes, 1967) and in which a single CS-US pairing produced reliable CER 29 days after training (Shurtleff & Ayres, 1981). However, the present results contrast with some literature using avoidance measures as an index of fear conditioning, in which animals show poor performance after only a few days (D. E. McAllister & W. R. McAllister, 1968;Quartermain& Judge, 1983;Quartermain& Jung, 1988;Spear et al, 1980). The relative permanence of potentiated startle in the present study may indicate rela-tively strong conditioned fear generated with relatively few training trials.…”

“…Four CS-US pairings have been shown to produce comparable CER 24 hand 90 days after training (Gleitman & Holmes, 1967). On the other hand, avoidance measures revealed significant performance decrements 14 days after three es-us pairings in mice (Quartermain & Judge, 1983;Quartermain & Jung, 1989). Even after as many as 35 CS-US pairings, rats tested on avoidance measures show significantly lower retention performance a few days after original training (D. E. McAllister & W. R. McAIlister , 1968;Spear, Hamberg, & Bryan, 1980).…”

“…That is, conditioned stimuli (CSs) come to elicit defense reactions only when appropriately paired with noxious unconditioned stimuli (USs). One of the distinguishing characteristics of conditioned fear is that it can be demonstrated in avoidance tasks (Quartermain & Judge, 1983;Quartermain & Jung, 1989), conditioned emotional response (CER) procedures (Brophy & Tremblay, 1971;Gleitman & Holmes, 1967;Leaf & Muller, 1965;Mahoney & Ayres, 1976), conditioned freezing measures (Blanchard & Blanchard, 1969;Fanselow & Bolles, 1979), and the potentiated startle paradigm (Brown, Kalish, & Farber, 1951;Davis, Schlesinger, & Sorenson, 1989) after very few, and often single, CS-US pairings.…”

ACTH-induced recovery of extinguished avoidance responding

“…Furthermore, Judge and Quartermain (as described in Quartermain & Judge, 1983) found that forgetting produced by a long retention interval could be alleviated by pretest injections of amphetamine and that pretest injections of amphetamine were effective in reducing longterm retention deficits even when given 24 h prior to test. Quartermain and Judge (1983) suggested that the amphetamine injection reactivated the earlier established memory and caused further processing of that memory (cf. Ebner, Tisdale, & Riccio, 1978;Spear, Hamberg, & Bryan, 1980).…”

“…A likely explanation of these results is that exogenous administration of ACTH shortly prior to test maximizes the similarity of internal states present at training and testing. As the resemblance of training and testing sessions increases, the probability of retrieving information acquired during the training session also increases (d. Mactutus, McCutcheon, & Riccio, 1980;Quartermain & Judge, 1983;Richardson, Guanowsky, Ahlers, & Riccio, 1984;Spear, 1973Spear, , 1978. If this is, indeed, the mechanism by which the findings of the first two experiments can bebest explained, then delaying the test for some period after administration of ACTH should reduce or eliminate the recovery of the extinguished memory.…”