Department of Neurobiology of Rhythms, UPR3212, Institute of Cellular and Integrative Neurosciences, University of Strasbourg, Strasbourg, France.
Eur J Neurosci. 2009 Oct;30(8):1527-36. doi: 10.1111/j.1460-9568.2009.06935.x. Epub 2009 Oct 12.
In several species, an acute injection of N-methyl-N-nitrosourea (MNU) induces a retinal degeneration characterized principally by a rapid loss of the outer nuclear layer, the other layers remaining structurally intact. It has, however, also been reported that down-regulation of melanopsin gene expression is associated with the degeneration and is detectable soon after injection. Melanopsin is expressed by a small subset of intrinsically photosensitive retinal ganglion cells and plays an important role in circadian behaviour photoentrainment. We injected MNU into Long Evans rats and investigated the ability of animals to entrain to three light/dark cycles of different light intensities (300, 15 and 1 lux). Control animals entrained their locomotor activity rhythms to the three cycles. In contrast, MNU-treated animals could only entrain properly to the 300 lux cycle. For the 15 lux cycle, their phase angle was much altered compared with control animals, and for the 1 lux cycle, MNU-injected animals were unable to photoentrain and exhibited an apparent free-run activity pattern with a period of 24.3 h. Subsequent to behavioural studies the animals were killed and rod, cone, melanopsin expression and melanopsin-expressing cells were quantified. Rod and cone loss was almost complete, melanopsin protein was reduced by 83% and melanopsin-expressing cells were reduced by 37%. Our study provides a comprehensive model of photoreceptor degeneration at the adult stage and a simple and versatile method to investigate the relation between retinal photoreceptors and the circadian system.
在几种物种中，急性注射 N-甲基-N-亚硝脲（MNU）会引起视网膜变性，主要表现为外核层迅速丧失，其他层结构完整。然而，也有报道称，黑视蛋白基因表达的下调与变性有关，并在注射后不久即可检测到。黑视蛋白由一小部分内在光敏性视网膜神经节细胞表达，在昼夜节律行为光适应中发挥重要作用。我们将 MNU 注射到长耳大鼠体内，并研究了动物适应三种不同光照强度（300、15 和 1 勒克斯）的光/暗循环的能力。对照动物适应了这三个周期的活动节律。相比之下，MNU 处理的动物只能正确适应 300 勒克斯的周期。对于 15 勒克斯的周期，它们的相位角与对照动物相比发生了很大的改变，而对于 1 勒克斯的周期，MNU 注射的动物无法进行光适应，表现出明显的自由运行活动模式，周期为 24.3 小时。行为研究后，处死动物并定量测量杆状细胞、锥状细胞、黑视蛋白表达和黑视蛋白表达细胞。杆状细胞和锥状细胞几乎完全丧失，黑视蛋白蛋白减少了 83%，黑视蛋白表达细胞减少了 37%。我们的研究提供了一个全面的成年阶段光感受器变性模型，以及一种简单而多功能的方法来研究视网膜光感受器与昼夜节律系统之间的关系。
