Activation of microglia in kainic acid induced rat retinal apoptosis

We applied a variety of methods to follow the course of kainic acid (KA) in duced retinal apoptosis, especially with regard to the spatial and temporal aspects. At 24 h after KA injection, a massive cell increase, which showed terminal transferase-mediated dUTP nick-end-labeling technique positive si gnals, was observed in all of the retinal layers, with the exception of the outer nuclear and photoreceptor layers. Electron microscopy further confir med that these cells might be apoptotic body ingesting phagocytes, whose fu nction seemed to correlate with bcl-2 mRNA up-regulation. When histochemica l studies were performed to determine the cellular identity of the phagocyt es, the microglia were thought to be the one and only type of phagocytes in volved in the KA-induced retinal apoptosis, In conclusion, we demonstrated that after KA injection, microglia were the only phagocytes to participate in clearing apoptotic debris from the inner retinal layers, and that their function might correlate with the change in expression of the bcl-2 gene fa mily. (C) 2000 Published by Elsevier Science Ireland Ltd.