Rapid forgetting of social transmission of food preferences in aged rats: relationship to hippocampal CREB activation.

A major characteristic of age-related changes in memory in rodents is an increase in the rate of forgetting of new information, even when tests given soon after training reveal intact memory. Interference with CREB functions similarly results in rapid decay of memory. Using quantitative immunocytochemistry, the present experiment examined the number of CREB- and pCREB-immunoreactive neurons in three regions of the dorsal and ventral hippocampus (dentate gyrus, CA3, and CA1) as a function of age and training. Rats were trained in a social transmission of food preference task. Using different food pairings, memory was tested in each rat immediately and 1, 2, 3, and 7 d later. Both young and old rats had intact and comparable memory scores at the immediate and 24-h tests, but old rats exhibited more rapid forgetting thereafter relative to that of young rats. The main findings were that training resulted in large increases in the number of pCREB-immunoreactive cells throughout the hippocampus in both young and aged rats. However, particularly in the ventral hippocampus, the training-elicited increase in pCREB-positive neurons was significantly lower in old than in young rats. Based on Western blot analyses in a separate set of rats, CREB levels were not responsive to training but were lower in the ventral hippocampus of old rats than of young rats. The present findings suggest that lower activation of CREB after training may contribute to the rapid forgetting seen in aged rats.