Lonstein Joseph S, Linning-Duffy Katrina, Tang Yuping, Moody Anna, Yan Lily
Department of Psychology, Michigan State University, East Lansing, MI, USA.
Neuroscience Program, Michigan State University, East Lansing, MI, USA.
Eur J Neurosci. 2021 Apr 26. doi: 10.1111/ejn.15248.
The neuropeptide orexin/hypocretin is implicated in sleep and arousal, energy expenditure, reward, affective state and cognition. Our previous work using diurnal Nile grass rats (Arvicanthis niloticus) found that orexin mediates the effects of environmental light, particularly daytime light intensity, on affective and cognitive behaviours. The present study further investigated how daytime light intensity affects the central orexin system in male and female grass rats. Subjects were housed for 4 weeks in 12:12 hr dim light:dark (50 lux, dimLD) or in 12:12 hr bright light:dark cycle (1000 lux, brightLD). Day/night fluctuations in some orexin measures were also assessed. Despite similar hypothalamic prepro-orexin mRNA expression across all conditions, there were significantly more orexin-immunoreactive neurons, larger somata, greater optical density or higher orexin A content at night (ZT14) than during the day (ZT2), and/or in animals housed in brightLD compared to dimLD. Grass rats in brightLD also had higher cisternal CSF levels of orexin A. Furthermore, orexin receptor OX1R and OX2R proteins in the medial prefrontal cortex were higher in brightLD than dimLD males, but lower in brightLD than dimLD females. In the CA1 and dorsal raphe nucleus, females had higher OX1R than males without any significant effects of light condition, and OX2R levels were unaffected by sex or light. These results reveal that daytime light intensity alters the central orexin system of both male and female diurnal grass rats, sometimes sex-specifically, and provides insight into the mechanisms underlying how daytime light intensity impacts orexin-regulated functions.
神经肽食欲素/下丘脑泌素与睡眠和觉醒、能量消耗、奖赏、情感状态及认知有关。我们之前利用昼行性尼罗草鼠（非洲沼鼠）开展的研究发现，食欲素介导环境光照，尤其是白天光照强度对情感和认知行为的影响。本研究进一步探究了白天光照强度如何影响雄性和雌性草鼠的中枢食欲素系统。将实验对象置于12小时暗光：12小时黑暗（50勒克斯，暗光周期）或12小时亮光：12小时黑暗周期（1000勒克斯，亮光周期）环境中饲养4周。还评估了一些食欲素指标的昼夜波动情况。尽管在所有条件下下丘脑前食欲素原mRNA表达相似，但夜间（ZT14）而非白天（ZT2），和/或与暗光周期组相比，亮光周期组动物体内有更多食欲素免疫反应性神经元、更大的胞体、更高的光密度或更高的食欲素A含量。亮光周期组草鼠的脑池脑脊液中食欲素A水平也更高。此外，内侧前额叶皮质中的食欲素受体OX1R和OX2R蛋白在亮光周期组雄性草鼠中高于暗光周期组，但在亮光周期组雌性草鼠中低于暗光周期组。在CA1区和中缝背核，雌性草鼠的OX1R高于雄性草鼠，且不受光照条件的显著影响，而OX2R水平不受性别或光照的影响。这些结果表明，白天光照强度会改变雄性和雌性昼行性草鼠的中枢食欲素系统，有时具有性别特异性，并为白天光照强度影响食欲素调节功能的潜在机制提供了见解。
