Time-dependent changes of astrocytes following microinjection of kainic acid and irradiation by gamma-knife in adult rat brain

objective: Two groups of rats were microinjected with kainic acid (KA) and irradiated with gam ma knife respectively on unilateral nucleus caudate-putamen to compare the response of astrocytes. Methods: The astrocytes were identified with anti-GFAP immunohistochemical ABC method and the progress of their reaction to the 2 insults was examined from 3 h to 30 d after the lesion. Results: Both lesions could induce hyperplasia and hypertrophy of astrocytes and 2 types of GFAP-ir cells were found, one with small cell body and thin process, and the other with hypertrophic cell body and thick and long process. The timecourse of GFAP expression in the 2 groups was different. In KA microinjection group, large necrotic area was ob served in the target within 24 h. Three days later, a few astrocytes appeared around the necrosis. With in crease of the survival time, hyperplasia and hypertrophy of astrocytes began to increase. Whereas in gamma knife group, hyperplasia and hypertrophy were evident from 3 h to 7 d and necrotic dots could be seen in the target on day 14. On day 30, necrosis was tnore obvious with gradual variations in GFAP expression around the necrotic area. Conclusion: The above results indicated that GFAP could be used as a marker for CNS in jury; the difference in their timing and distribution pattern suggested different mechanisms in KA microinjec tion group and gamma-knife irradiation group.