Osborne N N, Larsen A, Barnett N L
Nuffield Laboratory of Ophthalmology, University of Oxford, United Kingdom.
Invest Ophthalmol Vis Sci. 1995 Jul;36(8):1692-700.
To compare the effects of glutamate agonists and different types of ischemic insult on choline acetyltransferase (ChAT) immunoreactivity in the rat retina.
Rat retinas were exposed to different glutamate agonists in vivo or in vitro for specific periods of time, and the retinas were then fixed and processed for the localization of ChAT immunoreactivity. In other experiments, rats were administered an ischemic insult either by ligaturing the carotids (two-vessel occlusion [2-VO] procedure), cannulating the anterior chamber, and raising the intraocular pressure (high intraocular pressure [HIOP] procedure) or placing a ligature around the optic nerve sufficiently tightly to prevent blood flow through the central retinal artery (vascular ligation [VL] procedure). The electroretinogram was recorded, and, after a specific period of time, reperfusion was allowed to occur. Thirty to 36 hours after reperfusion, the retinas were dissected and processed for the localization of ChAT, as well as for parvalbumin, Thy-1, and alpha PKC immunoreactivities.
Of the glutamate agonists tested, only kainate reduced ChAT immunoreactivity significantly in vivo and in vitro. This effect of kainate could be counteracted by the antagonist CNQX (6-cyano-2,3-dihydroxy-7-nitroquinoxaline-2,3-dione). The ChAT immunoreactivity was unaffected in retinas in which ischemia was induced by the 2-VO procedure. In contrast, ChAT immunoreactivity was obliterated in retinas in which the HIOP was used and drastically reduced when the VL procedure was used. Interestingly, neither alpha PKC nor Thy-1 immunoreactivities were affected in retinas subjected to HIOP or VL methods. However, parvalbumin immunoreactivity was reduced in the HIOP model but only slightly altered in the VL model.
The current results suggest that kainate receptors are associated with the cholinergic retinal neurones in the rat retina. Activation of these receptors by kainate causes a reduction in the neurones' ChAT content. This effect can be mimicked by subjecting the retina to a sufficiently harsh ischemic insult, as occurs in the VL and HIOP procedures. When the ischemic insult is mild, as in the 2-VO procedure, no obvious change in ChAT immunoreactivity is apparent. The HIOP procedure for inducing an ischemic insult was found to be the most severe of the three procedures used, because ChAT immunoreactivity was obliterated and clear changes in the parvalbumin immunoreactivity also were recorded. Interestingly, neither the HIOP nor the VL procedures caused a change in the Thy-1 and alpha PKC immunoreactivities.
比较谷氨酸激动剂和不同类型的缺血性损伤对大鼠视网膜中胆碱乙酰转移酶（ChAT）免疫反应性的影响。
将大鼠视网膜在体内或体外暴露于不同的谷氨酸激动剂特定时间段，然后固定视网膜并进行处理以定位ChAT免疫反应性。在其他实验中，通过结扎颈动脉（双血管闭塞[2-VO]手术）、前房插管并升高眼压（高眼压[HIOP]手术）或在视神经周围足够紧密地放置结扎线以阻止视网膜中央动脉的血流（血管结扎[VL]手术）对大鼠进行缺血性损伤。记录视网膜电图，在特定时间段后，允许再灌注发生。再灌注30至36小时后，解剖视网膜并进行处理以定位ChAT，以及小清蛋白、Thy-1和α-PKC免疫反应性。
在所测试的谷氨酸激动剂中，只有海人酸在体内和体外均显著降低ChAT免疫反应性。海人酸的这种作用可被拮抗剂CNQX（6-氰基-2,3-二羟基-7-硝基喹喔啉-2,3-二酮）抵消。在通过2-VO手术诱导缺血的视网膜中，ChAT免疫反应性未受影响。相反，在使用HIOP手术的视网膜中ChAT免疫反应性消失，而在使用VL手术时ChAT免疫反应性大幅降低。有趣的是，在接受HIOP或VL方法的视网膜中，α-PKC和Thy-1免疫反应性均未受影响。然而，在HIOP模型中小清蛋白免疫反应性降低，而在VL模型中仅略有改变。
当前结果表明海人酸受体与大鼠视网膜中的胆碱能视网膜神经元相关。海人酸激活这些受体会导致神经元的ChAT含量降低。这种效应可通过使视网膜遭受足够严重的缺血性损伤来模拟，如在VL和HIOP手术中所发生的那样。当缺血性损伤较轻时，如在2-VO手术中，ChAT免疫反应性无明显变化。发现用于诱导缺血性损伤的HIOP手术是所使用的三种手术中最严重的，因为ChAT免疫反应性消失，并且小清蛋白免疫反应性也有明显变化。有趣的是，HIOP和VL手术均未导致Thy-1和α-PKC免疫反应性发生变化。
