Using the context preexposure facilitation effect to study long-term context memory in preweanling, juvenile, adolescent, and adult rats.

The present study used the context preexposure facilitation effect (CPFE) to examine long-term retention of incidental context learning in periweanling, adolescent and adult rats. The CPFE is a variant of contextual fear conditioning in which encoding the context representation, associating this representation with shock, and expressing the context-shock association each occur on separate occasions. Experiment 1 manipulated the retention interval-1d, 8d, 15d, or 22d-between context preexposure and training with immediate shock to determine how long the encoded context could be remembered (testing always occurred 24h following training). The other factors were age-postnatal day (PND) 24 vs 31-and training group-Preexposed to the training context (Pre) vs. an alternate context (Alt-Pre). At both ages, significantly more freezing was evident in the Pre vs. Alt Pre Groups at the 24h, 8d and 15d retention intervals but not at the 22d interval, indicating that juvenile-adolescent rats remember the context for up to 15d. In contrast, context memory persists for 22days in adult rats (Experiment 2); and is not evident after 24h, 8d, or 15d retention intervals in PND 17 rats (Experiment 3). The present study illustrates the value of the CPFE paradigm for investigations of long-term context memory in developing rats. Implications for the neurobiology of infantile amnesia are discussed.