Effects of age on water escape behavior and on repeated acquisition in rats.

The standard water escape task in a circular pool measures predominantly spatial reference memory (RM). We first tested 3- and 24-month-old Wistar rats (WISW:Bor) in the standard task. The RM performance of the 24-month-old animals was impaired in comparison to that of the 3-month-old rats. In a second experiment, we compared the performance of 24-month-old rats with that of 3-month-old animals, using the repeated acquisition paradigm originally described by Whishaw (Physiology and Behavior, 35, 139-143, 1985; Behavioral Brain Research, 24, 59-72, 1987). In this paradigm, the decrease in escape latency from the first to the second trial within trial pairs measures predominantly spatial working memory (WM). The young rats acquired the task within the first sessions. In contrast, the 24-month-old animals did not acquire the task, even after 12 daily training sessions. It is not clear, however, whether the poor performance of the old rats on the repeated acquisition task reflects impaired WM or whether they did not acquire the procedural aspects of the task.