Effect of hypoxia on the retina and superior colliculus of neonatal pigs

PurposeTo evaluate the effect of hypoxia on the neonatal pig retina and brain, we analysed the retinal ganglion cells (RGCs) and neurons in the superior colliculus, as well as the response of astrocytes in both these central nervous system (CNS) structures.MethodsNewborn pigs were exposed to 120 minutes of hypoxia, induced by decreasing the inspiratory oxygen fraction (FiO2: 10–15%), followed by a reoxygenation period of 240 minutes (FiO2: 21–35%). RGCs were quantified using Brn3a, a specific nuclear marker for these cells, and apoptosis was assessed through the appearance of active caspase-3. A morphometric analysis of the cytoskeleton of astrocytes (identified with GFAP) was performed in both the retina and superior colliculus.ResultsHypoxia produced no significant change in the RGCs, although, it did induce a 37.63% increase in the number of active caspase-3 positive cells in the superior colliculus. This increase was particularly evident in the superficial layers of the superior colliculus, where 56.93% of the cells were positive for active caspase-3. In addition, hypoxia induced changes in the morphology of the astrocytes in the superior colliculus but not in the retina.ConclusionsHypoxia in the neonatal pig does not affect the retina but it does affect more central structures in the brain, increasing the number of apoptotic cells in the superior colliculus and inducing changes in astrocyte morphology. This distinct sensibility to hypoxia may pave the way to design specific approaches to combat the effects of hypoxia in specific areas of the CNS.

研究目的 为评估缺氧对新生猪视网膜与大脑的影响，本研究分析了视网膜神经节细胞（Retinal Ganglion Cells, RGCs）、上丘神经元，以及这两种中枢神经系统（Central Nervous System, CNS）结构内的星形胶质细胞响应情况。
研究方法 将新生仔猪暴露于吸入氧分数（inspiratory oxygen fraction, FiO2）为10%~15%的环境中120分钟以诱导缺氧，随后进行240分钟复氧，复氧阶段吸入氧分数调整为21%~35%。采用特异性核标记物Brn3a对视网膜神经节细胞进行定量分析，并通过活化半胱氨酸天冬氨酸蛋白酶-3（active caspase-3）的表达水平评估细胞凋亡情况。同时对视网膜与上丘中经胶质纤维酸性蛋白（Glial Fibrillary Acidic Protein, GFAP）标记的星形胶质细胞骨架开展形态计量学分析。
研究结果 缺氧未对视网膜神经节细胞造成显著改变，但可使上丘内活化半胱氨酸天冬氨酸蛋白酶-3阳性细胞数量增加37.63%。该增加现象在上丘浅层尤为显著，该区域内56.93%的细胞呈活化半胱氨酸天冬氨酸蛋白酶-3阳性。此外，缺氧可诱导上丘星形胶质细胞形态发生变化，但未对视网膜星形胶质细胞产生影响。
研究结论 新生猪缺氧暴露不会损伤视网膜，但会累及大脑内更靠中枢的结构，表现为上丘凋亡细胞数量增加以及星形胶质细胞形态改变。这种对缺氧的差异化敏感性，可为设计针对性干预策略以对抗中枢神经系统特定区域的缺氧损伤提供理论依据。