Age-related differences in appetitive trace conditioning and novel object recognition procedures

Appetitive trace conditioning (TC) was examined over 6 months in younger-adult (2-8 months) and middle-aged (12-18 months) male Wistar RccHan rats to test for early age-related impairment in working memory. Novel object recognition (NOR) was included as a comparison task to provide a positive control in the event that the expected impairment in TC was not demonstrated. The results showed that TC improved at both ages at the 2s but not at the 10s trace interval. There was, however, evidence for reduced improvement from one day to the next in the middle-aged cohort tested with the 2s trace conditioned stimulus. Moreover, within the 10s trace, responding progressively distributed later in the trace interval, in the younger-adult but not the middle-aged cohort. Middle-aged rats showed NOR discriminative impairment at a 24h but not at a 10 min retention interval. Object exploration was overall reduced in middle-aged rats and further reduced longitudinally. At the end of the study, assessing neurochemistry by HPLC-ED showed reduced 5-HIAA/5-HT in the dorsal striatum of the middle-aged rats and some correlations between striatal 5-HIAA/5-HT and activity parameters. Overall the results suggest that, taken in isolation, age-related impairments may be overcome by experience. This recovery in performance was seen despite the drop in activity levels in older animals, which might be expected to contribute to cognitive decline.

为探究工作记忆中与年龄相关的早期损伤，研究人员对年轻成年（2-8月龄）和中年（12-18月龄）雄性Wistar RccHan大鼠开展了为期6个月的食欲痕迹条件反射（TC）检测。新物体识别（NOR）被纳入作为对照任务，以在预期的TC损伤未被证实的情况下提供阳性对照。结果显示，2秒痕迹间隔下两个年龄段的TC表现均有所改善，但10秒痕迹间隔下无改善；然而，接受2秒痕迹条件刺激测试的中年组，次日改善程度出现降低。此外，10秒痕迹间隔内年轻成年组的反应逐渐向间隔后期分布，中年组则无此现象。中年大鼠在24小时记忆保持间隔下表现出NOR辨别损伤，但10分钟间隔下无此损伤。中年大鼠的物体探索行为总体减少，且随时间推移进一步降低。研究结束时，通过高效液相色谱-电化学检测（HPLC-ED）评估神经化学特征发现，中年大鼠背侧纹状体中5-HIAA/5-HT比值降低，且纹状体5-HIAA/5-HT与活动参数存在一定相关性。总体而言，结果表明若单独考量，与年龄相关的损伤或可通过经验克服；尽管老年动物活动水平下降（通常被认为会加剧认知衰退），但其表现仍出现恢复。