Subhadeep Duttagupta, Srikumar B N, Shankaranarayana Rao B S, Kutty Bindu M
Department of Neurophysiology, National Institute of Mental Health and Neuro Sciences (NIMHANS), Hosur Road, Bengaluru 560 029, India.
Department of Neurophysiology, National Institute of Mental Health and Neuro Sciences (NIMHANS), Hosur Road, Bengaluru 560 029, India.
Physiol Behav. 2017 Mar 1;170:124-132. doi: 10.1016/j.physbeh.2016.11.040. Epub 2016 Dec 23.
Neurodegeneration of hippocampal structures is implicated in Alzheimer's disease (AD). Patients with AD exhibit 'sundown syndrome' featuring mood swings and anxiety. Although there are studies demonstrating circadian rhythm disruption associated with sundown phenomenon, the mechanisms underlying the emotional disturbances remain elusive. In the present study, we examined the relationship between subiculum (a key hippocampal output structure) and anxiety. Our study demonstrates that bilateral ventral subicular lesion (VSL) leads to anxiogenic behavior. In the elevated plus maze test, VSL rats made less number of entries into the open arms and spent significantly more time in the closed arms. Similarly, in the light-dark exploration test, VSL rats spent significantly more time in the dark chamber and made fewer entries into the light chamber. VSL also produced significant neurodegeneration in the paraventricular, suprachiasmatic and dorsomedial nuclei of the hypothalamus. Exposing VSL rats to a short photoperiod regime (SPR; 06/18h light-dark cycle) for 21days ameliorated the anxiety-like behavior. VSL rats on SPR also exhibited increased food consumption and higher core body temperature. Our study supports the hypothesis that the ventral subiculum regulates anxiety-like behavior and that SPR helps in the alleviation of such behavior. Even though the mechanisms underlying anxiolytic effects of light-dark cycle manipulation are yet to be elucidated, such non-pharmacological strategies can help to mitigate anxiety-like behavior. A proper understanding of the effectiveness of photoperiod manipulation will help in developing strategies in the management of emotional disturbances associated with affective and neurodegenerative disorders including AD.
海马结构的神经退行性变与阿尔茨海默病（AD）有关。AD患者表现出以情绪波动和焦虑为特征的“日落综合征”。尽管有研究表明昼夜节律紊乱与日落现象有关，但情绪障碍的潜在机制仍不清楚。在本研究中，我们研究了海马下脚（海马的一个关键输出结构）与焦虑之间的关系。我们的研究表明，双侧腹侧海马下脚损伤（VSL）会导致焦虑行为。在高架十字迷宫试验中，VSL大鼠进入开放臂的次数较少，在封闭臂中花费的时间明显更多。同样，在明暗探索试验中，VSL大鼠在暗室中花费的时间明显更多，进入亮室的次数更少。VSL还在下丘脑室旁核、视交叉上核和背内侧核产生了明显的神经退行性变。将VSL大鼠暴露于短光照周期（SPR；06/18小时明暗循环）21天可改善焦虑样行为。处于SPR的VSL大鼠还表现出食物摄入量增加和核心体温升高。我们的研究支持以下假设：腹侧海马下脚调节焦虑样行为，SPR有助于减轻这种行为。尽管明暗循环调节的抗焦虑作用的潜在机制尚待阐明，但这种非药物策略有助于减轻焦虑样行为。正确理解光照周期调节的有效性将有助于制定管理与情感和神经退行性疾病（包括AD）相关的情绪障碍的策略。
