Hebda-Bauer E K, Morano M I, Therrien B
School of Nursing, University of Michigan, Ann Arbor, MI 48109, USA.
Brain Res. 1999 May 8;827(1-2):93-103. doi: 10.1016/s0006-8993(99)01310-4.
The hippocampus is one of the first brain structures to show age-related changes. Moreover, hippocampal neurons are endangered by prolonged exposure to high circulating levels of corticosterone with stress or aging. We examined the effects of aging and high corticosterone levels on spatial learning, a key hippocampal function. Young (4-6 months), old (23-25 months), and very old (31 months) male Fischer-344xBrown Norway (F-344xBN) rats received six pre-testing days in the Morris water task to determine baseline spatial learning performance. Next, half the animals in each group were given daily corticosterone injections for 15 days. During the last six injection days, all animals underwent post-testing in the Morris water task with the environment and goal location changed. Baseline, peak, and clearance plasma corticosterone levels were determined. During pre-testing, old animals swam as directly to the goal as the young, but very old animals were significantly impaired. During post-testing, both old and very old non-injected animals had significantly greater directional heading errors and flatter learning curves than the young. Among injected animals, the very old performed as well as the young, but the old did not. Old animals who did not show improvement during the first three pre-testing days were responsible for the old impairment during post-testing. Thus, only very old F-344xBN rats are impaired when initially exposed to a spatial learning task, but half the old and all very old animals are impaired when the environment is changed. Very old F-344xBN rats, however, demonstrate enhanced spatial learning when exposed to corticosterone injections.
海马体是最早出现与年龄相关变化的脑结构之一。此外，海马体神经元会因长期处于应激或衰老导致的高循环皮质酮水平而受到损害。我们研究了衰老和高皮质酮水平对空间学习（一种关键的海马体功能）的影响。年轻（4 - 6个月）、老年（23 - 25个月）和极老年（31个月）的雄性Fischer - 344xBrown Norway（F - 344xBN）大鼠在莫里斯水迷宫任务中接受了6天的预测试，以确定基线空间学习表现。接下来，每组中的一半动物每天接受皮质酮注射，持续15天。在最后6天的注射期间，所有动物在莫里斯水迷宫任务中进行测试，环境和目标位置发生了变化。测定了基线、峰值和清除期血浆皮质酮水平。在预测试期间，老年动物游向目标的路线与年轻动物一样直接，但极老年动物明显受损。在测试后，未注射的老年和极老年动物的方向误差显著更大，学习曲线比年轻动物更平缓。在注射的动物中，极老年动物的表现与年轻动物一样好，但老年动物则不然。在预测试的前三天没有表现出改善的老年动物导致了测试后的老年动物受损。因此，只有极老年的F - 344xBN大鼠在最初接触空间学习任务时受损，但当环境改变时，一半的老年动物和所有极老年动物都会受损。然而，极老年的F - 344xBN大鼠在接受皮质酮注射时表现出空间学习能力增强。
