睡眠在衰老过程中对学习记忆的影响及机制研究

Aging is accompanied by a progressive decline in memory and cognitive function. Aging people also experience a deterioration of sleep quality and efficiency. Although it is widely acknowledged that sleep has a critical role in learning and memory, the link between age-related sleep disruption and memory deficits remains unclear. We have previously shown that learning-induced formation of new synaptic connections in the cortex represents structural changes correlated with long-term memory storage. Our preliminary data suggests that sleep promotes synapse formation and performance improvement after learning in young adult animals. Moreover, learning-induced synapse formation is reduced in the motor cortex of aged mice. SST neurons target and regulate the activities of pyramidal neurons during sleep, and maybe affect the time and structure of sleep. Based on these findings, we hypothesize that age-related sleep impairment contributes to the reduction in learning-dependent synaptic plasticity and behavioral improvement. The reduction of SST neurons activities is important to sleep disruption during aging, and increasing the activities of SST neurons maybe improve the sleep quality and synaptic plasticity induced by motor-learning. In this application, we will test this hypothesis by combining in vivo imaging of synapse structure and function, electroencephalography recording and behavioral testing in the same animals. The proposal has six specific aims. In the first aim, we will examine the role of sleep in learning-dependent synapse remodeling and behavioral performance in young, middle-aged and old mice. This will test the hypothesis that the benefit of sleep in promoting synapse formation and memory encoding is diminished in older mice. In the second aim, we will use in vivo calcium imaging to determine whether sleep-dependent reactivation of task-related neurons is reduced in aging and whether such deficiency in sleep reactivation mediates learning-related synaptic deficits. In the third aim, we will investigate the role of REM sleep in potentiation of learning-induce spines in young, middle-age and old mice. In the fourth aim, we will test the calcium activities of interneurons (including PV, VIP and SST neurons) during sleep in young, middle-age and old mice. In the fifth aim, we will test the relationship between SST neurons and pyramidal neurons, and determine whether and how SST neurons regulate pyramidal neurons and sleep structure. In the sixth aim, we will investigate whether increasing the activities of SST neurons improve sleep structure and learning-induced synaptic plasticity in old mice. The proposed project explores, for the first time, the role and mechanism of sleep in age-related decline in learning and memory at the level of individual neurons and synapses in the living brain. Successful completion of the project will lay the foundation for future studies exploring the mechanisms by which sleep abnormalities contribute to cognitive dysfunction in neurological diseases such as Alzheimer’s disease.

衰老过程伴随认知功能的下降。老年人也会经历睡眠质量的下降。年龄相关的睡眠中断在记忆缺陷中的作用和机制尚不清楚。我们的研究表明，运动训练后睡眠能促进新突触的形成；老年动物中，学习诱导的新突触的形成下降；SST神经元可以调控兴奋性神经元的活性，并可能调节睡眠。基于此，我们有如下假说：年龄相关的睡眠缺陷导致突触可塑性和运动能力的下降；SST神经元活性降低是睡眠缺陷的重要因素，提高SST神经元活性改善睡眠及突触可塑性。我们将使用活体双光子成像、电生理记录和行为学从以下几个方面来研究：睡眠在青年、中年和老年小鼠突触可塑性中的作用；兴奋性神经元在睡眠期间的重新激活；REM睡眠在新突触强化过程中的作用；抑制性神经元在睡眠期间的活性；SST神经元对锥体神经元的调控；激活老年小鼠的SST神经元能否改善睡眠和突触可塑性。我们将首次在活体大脑的神经元和突触水平证明睡眠在年龄相关的学习记忆下降中的作用及机制。

衰老过程伴随认知功能的下降。老年人也会经历睡眠质量的下降。年龄相关的睡眠中断在记忆缺陷中的作用，及导致睡眠中断的潜在机制尚不清楚。为了解决这些问题，我们使用活体双光子显微成像技术、电生理记录手段和行为学测试方法研究：1）青年（2月龄）、中年（12月龄）和老年（18月龄）小鼠的睡眠模式、运动学习能力和学习相关的突触可塑性；2）青年、中年和老年小鼠中兴奋性锥体细胞和抑制性神经元在睡眠期的活性；3）青年、中年和老年小鼠中锥体细胞在睡眠期的重激活程度；4）抑制性SST神经元对锥体细胞活性及睡眠模式的调节作用；5）通过化学遗传学手段DREADD/CNO激活SST神经元后，老年小鼠睡眠模式、运动学习能力及学习相关突触可塑性的改善。我们发现：随着年龄的增长，小鼠的非快速动眼睡眠（NREM）和快速动眼睡眠（REM）时长减少、运动学习能力下降、学习诱导的新突触的形成降低且新突触的强化程度减弱；2）第V层锥体细胞的活性在REM期明显弱于跑步时，有助于睡眠的维持；而随着年龄的增长，锥体细胞的活性显著提升，可能是导致睡眠减少的重要因素；3) 衰老过程中，锥体细胞在NREM期的重激活程度明显降低，引起学习相关的新突触形成的减少；4）抑制性SST神经元在REM期的活性非常高，其作用于树突枝干，抑制锥体细胞的活性，进而维持REM睡眠状态；5）随着年龄的增长，SST神经元在REM期的活性下降，可能导致兴奋性锥体细胞活性的增高，REM睡眠缩短；6）老年小鼠中通过化学遗传学手段DREADD/CNO，可以有效提高SST神经元的活性，抑制REM期锥体细胞活性，改善小鼠的运动学习能力，及学习相关的新突触的强化程度。根据我们的数据和结果，在临床应用上，可探索和开发作用于SST神经元的药物或治疗手段，通过调节其活性改变锥体细胞活性，并改善睡眠和学习记忆。