THE RESPONSE OF NEURONS AND MICROGLIA TO BLAST INJURY IN THE RAT-BRAIN

Rats subjected to a single non-penetrative blast were examined for pos sible neuronal damage and glial reaction by immunohistochemistry and e lectron microscopy. The most dramatic feature in rats killed between 1 and 14 days after the blast was the widespread response of microglial cells in various parts of the brain in which the cells were hypertrop hied and their surface antigens, like complement type three receptors (CR3), were upregulated. The blast wave also induced the vigorous expr ession of major histocompatibility complex (MHC) class I and II (Ia) a ntigens. In rats killed 21 days after the blast, the elevated immunore activity of microglia had subsided and at 28 days both the microglial external morphology and immunoreactivity were comparable to those of n ormal animals. In rats killed 4-7 days after the blast, the neurons in the cerebral and cerebellar cortex appeared normal except for the occ urrence of some 'darkened' dendrites. The incidence of 'darkened' dend rites was most common in rats killed at day 14 but they were absent at 21 and 28 days. Microglial cells were closely associated with some of the 'darkened' dendrites. Results in this study show that a non-penet rative blast in rats provokes a widespread microglial activation sugge sting increased endocytosis and immunological responses. However, it r emains uncertain whether such a drastic response was a direct activati on of the cells by the blast wave or elicited indirectly by some chemi cal factors released from the damaged brain tissues.