Evelyn F. McKnight Brain Institute, University of Arizona, Tucson, AZ 85724, USA.
Hippocampus. 2012 Oct;22(10):2080-93. doi: 10.1002/hipo.22066.
Object recognition memory requires the perirhinal cortex (PRC) and this cognitive function declines during normal aging. Recent electrophysiological recordings from young rats have shown that neurons in Layer V of the PRC are activated by three-dimensional objects. Thus, it is possible that age-related object recognition deficits result from alterations in PRC neuron activity in older animals. To examine this, the present study used cellular compartment analysis of temporal activity by fluorescence in situ hybridization (catFISH) with confocal microscopy to monitor cellular distributions of activity-induced Arc RNA in layer V of the PRC. Activity was monitored during two distinct epochs of object exploration. In one group of rats (6 young/6 aged) animals were placed in a familiar testing arena and allowed to explore five different three-dimensional objects for two 5-min sessions separated by a 20-min rest (AA). The second group of animals (6 young/6 aged) also explored the same objects for two 5-min sessions, but the environment was changed between the first and the second epoch (AB). Behavioral data showed that both age groups spent less time exploring objects during the second epoch, even when the environment changed, indicating successful recognition. Although the proportion of active neurons between epochs did not change in the AA group, in the AB group more neurons were active during epoch 2 of object exploration. This recruitment of neurons into the active neural ensemble could serve to signal that familiar stimuli are being encountered in a new context. When numbers of Arc positive neurons were compared between age groups, the old rats had significantly lower proportions of Arc-positive PRC neurons in both the AA and AB behavioral conditions. These data support the hypothesis that age-associated functional alterations in the PRC contribute to declines in stimulus recognition over the lifespan.
物体识别记忆需要双侧杏仁旁皮层（PRC），而这种认知功能会随着正常衰老而下降。最近对年轻大鼠的电生理记录表明，PRC 第五层的神经元会被三维物体激活。因此，年龄相关的物体识别缺陷可能是由于老年动物 PRC 神经元活性的改变所致。为了研究这一点，本研究使用荧光原位杂交（catFISH）结合共聚焦显微镜对时间活动的细胞区室分析，监测 PRC 第五层中活性诱导的 Arc RNA 的细胞分布。在两个不同的物体探索时期监测活性。在一组大鼠（6 只年轻/6 只年老）中，将动物放置在熟悉的测试场中，并允许它们在两个 5 分钟的时间段内探索五个不同的三维物体，两个时间段之间有 20 分钟的休息时间（AA）。第二组动物（6 只年轻/6 只年老）也在两个 5 分钟的时间段内探索相同的物体，但在第一和第二时间段之间环境发生了变化（AB）。行为数据表明，两个年龄组在第二个时间段内探索物体的时间都减少了，即使环境发生了变化，这表明它们已经成功识别了物体。尽管在 AA 组中两个时间段之间活跃神经元的比例没有变化，但在 AB 组中，在物体探索的第二个时间段内有更多的神经元活跃。这种将神经元募集到活跃的神经集合中可以作为在新环境中遇到熟悉刺激的信号。当比较年龄组之间的 Arc 阳性神经元数量时，在 AA 和 AB 行为条件下，年老大鼠的 PRC 中 Arc 阳性神经元的比例明显较低。这些数据支持这样的假设，即 PRC 中与年龄相关的功能改变导致了一生中对刺激识别的下降。
