Sørensen J C, Dalmau I, Zimmer J, Finsen B
Department of Neurobiology, Institute of Anatomy, University of Aarhus, Denmark.
Exp Brain Res. 1996 Nov;112(2):203-12. doi: 10.1007/BF00227639.
Thalamic neuronal degeneration after neocortical lesions involve both anterograde and retrograde components. This study deals with the thalamic microglial response after neocortical aspiration lesions, using fluorogold fluorescent prelabeling, to identify retrogradely degenerating thalamocortical neurons, combined with histochemical or immunohistochemical staining of microglial cells. Adult male Wistar rats were injected with the retrograde fluorescent tracer fluorogold, in the right sensorimotor cortex (forepaw area) in order to retrogradely label thalamic neurons projecting to this area. After 1 week, the fluorogold injection site was removed by aspiration, axotomizing at the same time the thalamic projection neurons now retrogradely labeled with fluorogold. After 3, 7, 14, and 28 days the animals were killed and processed for nucleoside diphosphatase histochemistry or complement type 3 receptor immuno-histochemistry and class I and II major histocompatibility complex immunohistochemistry using OX42, OX18, and OX6 antibodies. The histological analysis showed a prominent and progressive nucleoside diphosphatase-, OX42-, and OX6-positive microglial cell response in the ventrolateral, posterior, and ventrobasal thalamic nuclei with ongoing retrograde and anterograde neuronal degeneration. Initially the reactive microglia had a bushy morphology and were succeeded by ameboid microglia and microglial cluster cells as the reaction progressed. However, in the reticular thalamic nucleus, which suffered exclusively anterograde neuronal degeneration, a different picture was seen with only bushy microglia. The neurons undergoing retrograde degeneration in the ventrolateral, posterior, and ventrobasal thalamic nuclei were retrogradely labeled by the fluorogold tracer. Individual nucleoside diphosphatase-, OX42-, or OX6-positive microglial cells extended long cytoplasmic processes surrounding fluorogold-labeled neurons and had in some cases apparently phagocytized these. Several microglial cells were thus double-labeled with nucleoside diphosphatase or OX42 and fluorogold. In addition, small nucleoside diphosphatase-positive, fluorogold-labeled perivascular cells were observed in the neocortex near the fluorogold-injected and ablated neocortical areas and in the ipsilateral thalamus. This study demonstrates: (1) that the microglial response to thalamic degeneration after neocortical lesion is graded with a limited reaction to the well-known massive anterograde axonal degeneration and a more extended reaction to the axotomy-induced retrograde cell death; and (2) that also perivascular cells and possibly macrophages may contribute to this reaction, as seen by uptake of fluorogold from axotomized neurons in the degenerating thalamic nuclei.
新皮层损伤后丘脑神经元变性涉及顺行和逆行成分。本研究利用荧光金荧光预标记来识别逆行性变性的丘脑皮质神经元，结合小胶质细胞的组织化学或免疫组织化学染色，探讨新皮层抽吸损伤后丘脑小胶质细胞的反应。成年雄性Wistar大鼠在右侧感觉运动皮层（前爪区域）注射逆行荧光示踪剂荧光金，以逆行标记投射到该区域的丘脑神经元。1周后，通过抽吸去除荧光金注射部位，同时切断现在被荧光金逆行标记的丘脑投射神经元的轴突。在3、7、14和28天后处死动物，并进行核苷二磷酸酶组织化学或补体3型受体免疫组织化学以及使用OX42、OX18和OX6抗体的I类和II类主要组织相容性复合体免疫组织化学处理。组织学分析显示，在腹外侧、后和腹基底丘脑核中，随着逆行和顺行神经元变性的持续，核苷二磷酸酶、OX42和OX6阳性小胶质细胞反应显著且呈进行性。最初，反应性小胶质细胞呈浓密形态，随着反应进展，依次被阿米巴样小胶质细胞和小胶质细胞簇细胞取代。然而，在仅发生顺行性神经元变性的丘脑网状核中，看到的是不同的情况，只有浓密的小胶质细胞。在腹外侧、后和腹基底丘脑核中发生逆行性变性的神经元被荧光金示踪剂逆行标记。单个核苷二磷酸酶、OX42或OX6阳性小胶质细胞伸出长的细胞质突起包围荧光金标记的神经元，在某些情况下显然吞噬了这些神经元。因此，一些小胶质细胞被核苷二磷酸酶或OX42与荧光金双重标记。此外，在荧光金注射和切除的新皮层区域附近的新皮层以及同侧丘脑中，观察到小的核苷二磷酸酶阳性、荧光金标记的血管周围细胞。本研究表明：（1）新皮层损伤后小胶质细胞对丘脑变性的反应是分级的，对众所周知大量的顺行性轴突变性反应有限，而对轴突切断诱导的逆行性细胞死亡反应更广泛；（2）如在变性丘脑核中从轴突切断的神经元摄取荧光金所见，血管周围细胞以及可能的巨噬细胞也可能参与了这一反应。
