REACTIVE ASTROCYTIC RESPONSE AND INCREASED PROLIFERATING CELL NUCLEAR ANTIGEN EXPRESSION IN CEREBRAL CORTEX OF ENVENOMED RATS

The regional distribution and the appearance of astrocytes expressing glial fibrillary acidic protein (GFAP), S100 protein, and proliferating cell nuclear antigen (PCNA) were determined in the cerebral cortex of normal and cobra venom intoxicated rats. Male rats were divided to three groups intramuscularly treated with a single injection of either physiological saline solution or ½ LD50 or LD50 of cobra venom respectively. Formalin-fixed paraffin-embedded brain sections of animals of the three groups were immunohistochemically studied according to avidin-biotin-peroxidase complex method using antibodies against GFAP, S100 protein and PCNA. As biomarkers of cerebral neurotoxicity, dose and time dependent increases in the expression of GFAP and S100 protein were observed. Marked increases in the expression of GFAP and S100 protein were common in high dose (LD50) envenomed rats 72 h after venom injection, whereas in low dose (½ LD50) envenomed rats only moderate increases of these two proteins were detected 72 h post-treatment. Similar pattern of expression was also observed for PCNA in the cerebral cortex layer III but not in layer II or layer I. PCNA, the indicator of cell proliferation, was highly expressed in cerebral cortex of envenomed rats if compared with control animals. These results demonstrate that intramuscular injection of cobra venom produces enhanced cell proliferation as measured by PCNA staining, and reactive astrocytosis as ascertained by increased GFAP and S100 immunoreactivities. This may represent a protective response of the cerebral cortex by which the brain is able to remove injured cells and protect the remaining neurons by PCNA expression. Furthermore, these observations affirm the usefulness of GFAP, S100 and PCNA immunohistochemistry as a sensitive biomarker of neurotoxicity.