Effects of glucocorticoids on memory retrieval and reconsolidation of recent and remote memories in mice

  Introduction: Previous studies demonstrated that the systemic injection of corticosterone impairs both retrieval and reconsolidation of fear memory in experimental animals. Here, we investigated whether these disrupting effects of corticosterone depend on the age (recent or remote) of the memory in mice.   Materials and Methods: Mice were trained and tested in an inhibitory avoidance task (50 Hz, 1mA for 3 S). Corticosterone (1, 3 and 10mg/kg) injected 30 min before of retrieval test of either a two-day recent or 36-day remote memory. Memory retrieval tested during 10 min. For memory reconsolidation experiments immediately after memory reactivation of two-day recent or 36-day remote memories, mice received corticosterone (1, 3 and 10mg/kg) or vehicle. Two, five, seven and nine days after memory reactivation, mice were returned to the context for 10 min, and step-through latency was recorded.   Results: For memory retrieval, corticosterone impaired subsequent expression of both recent and remote memories. Similar effect was found on the reconsolidation of both memories. Additionally, a higher dose of corticosterone was needed to impair retrieval and reconsolidation of remote memory. No significant differences were found on the amount of memory deficit induced by corticosterone among memories with different age.  Conclusion: Our data indicate that the efficacy of corticosterone in impairing retrieval and reconsolidation of fear memory is not limited to the age of memory