Manrique Tatiana, Morón Ignacio, Ballesteros María Angeles, Guerrero Rosa María, Fenton André A, Gallo Milagros
Institute of Neurosciences F. Oloriz, University of Granada, Spain.
Hippocampus. 2009 Jan;19(1):57-65. doi: 10.1002/hipo.20481.
Rats use time-of-day cues to modulate learned taste aversion memories. If adult rats are accustomed to drinking saline in the evening and they receive a lithium chloride injection after drinking saline in the morning, they form a stronger aversion to saline than rats that were conditioned after drinking saline at the familiar time. The difference indicated that the rats formed segregated representations of saline taste and the time of day the saline was consumed. This was inferred because the modulation of learning by time of day was observed when the aversions were tested at the familiar evening drinking time. If the rats had formed a compound representation of saline taste and the time of day it was consumed, the opposite pattern of differences would be expected. We used this modulation of learning by time of day to assay whether aged rats have an impaired ability to form segregated representations of experience. We find that aged rats had similar saline aversions if they were conditioned at either the familiar or the unfamiliar time of day. Furthermore, dorsal hippocampal lesions affecting also the overlying parietal cortex in the aged rats caused greater saline aversions if the rats were conditioned after drinking saline at the familiar time of day. This indicated that aged rats are aware of the time of day but after the lesion, they act as if they do not segregate saline taste from the time of day it was consumed. The results suggest that the ability to form segregated representations of a complex experience is impaired in aging and abolished by hippocampal lesions.
大鼠利用昼夜时间线索来调节习得的味觉厌恶记忆。如果成年大鼠习惯在傍晚饮用盐水，而在早晨饮用盐水后接受氯化锂注射，那么它们对盐水形成的厌恶感比在熟悉时间饮用盐水后接受条件反射的大鼠更强。这种差异表明，大鼠形成了对盐水味道以及饮用盐水时间的分离表征。得出这一推断是因为当在熟悉的傍晚饮水时间测试厌恶反应时，观察到了昼夜时间对学习的调节作用。如果大鼠形成了盐水味道与饮用时间的复合表征，那么预期会出现相反的差异模式。我们利用昼夜时间对学习的这种调节作用来测定老年大鼠形成经验分离表征的能力是否受损。我们发现，如果老年大鼠在熟悉或不熟悉的昼夜时间接受条件反射，它们对盐水的厌恶程度相似。此外，影响老年大鼠背侧海马以及上方顶叶皮质的损伤，会使大鼠在熟悉的昼夜时间饮用盐水后接受条件反射时产生更强的盐水厌恶。这表明老年大鼠能够感知昼夜时间，但在损伤后，它们的行为就好像没有将盐水味道与饮用时间区分开来。结果表明，形成复杂经验分离表征的能力在衰老过程中受损，并会因海马损伤而丧失。
