Temporally graded, age-related impairments in spatial memory in the rat.

We report here on the analysis of data from 6-, 12-, and 24-month-old Long-Evans rats tested in the Morris water maze. The animals were given 18 trials over a 5-day period with the platform submerged (spatial condition); 3 trials on the first day, 4 trials on each of the subsequent 3 days, followed by 3 trials on the fifth day. On the sixth day, the animals were given five trials in which the platform was elevated above the water level (cued condition). Over the 18 trials in the spatial condition, the 24-month-old animals took significantly longer to find the platform than did the 6-month-old animals; the performance of the 12-month-day animals lay between the older and younger groups. We then analyzed the latency data depending on the position of the trial in that day of testing: The first trial of each day followed the preceding trial by 20-22 hours, whereas the last trial of each day followed the preceding trial by only 20 minutes. The performance of the 12-month-old animals on the first trial of the second, third, and fourth days of testing was indistinguishable from that of the 24-month-old animals. Whereas, the performance of the 12-month-old animals on the last trial of the second, third, and fourth days of testing was indistinguishable from that of the 6-month-old animals. An analysis of the distance data (distance covered before locating the platform) revealed the same pattern of results.(ABSTRACT TRUNCATED AT 250 WORDS)