Extracellular Matrix and Astrocytic Response during Regeneration following Cryogenic Injury in Adult Rat Cerebral Cortex

Choi, Soo Im; Yang, Woo Ick; Kim, Tae Seung

Abstract

Astrocytes are the most numerous cellular elements in the cerebrum, and they normally have a very slow turnover rate. But during regeneration after injury, they proliferate markedly resulting in astrogliosis. The extracellular matrix in the central nervous system is present in the vessel walls and in the external glia limitans as a basal lamina. The presence of an intact extracellular matrix framework is important in regeneration after injury. Understanding the properties of astrocytic proliferation will be helpful to find out new treatment for functional recovery in the central nervous system. In this study, after cryogenic injury was performed on the cerebral cortex in rats, changes in astrocytes and the extracellular matrix were observed using light microscopy, immunohistochemical stain for glial fibrillary acidic protein(GFAP), proliferating cell nuclear antigen(PCNA), fibronectin, laminin, and type IV collagen, autoradiography and electron microscopy. The results were as follows; 1) The coagulative necrosis, which followed cryogenic injury on the cerebral cortex was healed, forming a new pia mater above the lesion. 2) Some of the PCNA positive cells were astrocytes and some of the GFAP positive cells showed a positive reaction to PCNA. 3) Proliferating astrocytes labelled by autoradiography or immunohistochemical stain for PCNA reached maximal numbers 3days after the injury and they were no longer found 2 weeks after injury. 4) In autoradiography with immunohistochemical stain for GFAP, about 1% of GFAP positive astrocytes were labelled by autoradiography and in double immunohistochemical stain for PCNA and GFAP, about 8-16% of GFAP positive astrocytes were also stained by PCNA. 5) In immunohistochemical stain for fibronectin, laminin and type IV collagen, laminin and type IV collagen were present in the newly formed blood vessel walls and fibronectin showed a diffuse positive reaction within the lesion. The new pia mater was formed within 2 weeks after the injury. 6) On electron microscopic examination, basal lamina material was found in the vessel wall 1 week after the injury and at 2 weeks, a nearly complete and continuous basal lamina was formed although the thickness was uneven. According to these findings, astrocytes in the cerebral cortex of adult rats proliferate very early in the regenerative period after cryogenic injury. At 2 weeks after the injury, this regeneration ceases and the damaged basal lamina of pia mater and vessel wall were reconstituted.