Age differences in water maze performance and swimming behavior in the rat

This study was designed to determine the earliest age at which a water maze task could be used to measure learning in rats. In Experiment 1, 24 litters of Sprague-Dawley rats were used. Eight litters per group were tested beginning at 18, 28, or 38 days of age for their ability to learn a positional discrimination in a Y-shaped water maze. Results indicated that the 28 day olds were better able to learn the task than were the 18 or 38 day groups. Performance by the 38 day olds was impaired by an immobilization response. This response is known to be influenced by catecholaminergically-active drugs [18, 19, 20], and may result from ongoing maturation in these systems. The difference in learning abilities between the 18 day and 28 day groups was further investigated in Experiment 2. In this study, 24 litters of Sprague-Dawley rats were tested for acquisition of the discrimination at 18, 20, or 22 days of age. At each age, 8 litters were tested. Results showed that significant improvements in the ability to learn the Y-maze task occurred between 20 and 22 days of age. Results of both experiments suggest that this measure of learning may be employed in rats as young as 22 days of age, but should be avoided in 38 day old rats.