Pharmacological characterization of apoptotic cell death in a model of photothrombotic brain injury in rats.

We have shown recently in rats that photothrombotic local brain injury that is induced by the intravenous injection of the photosensitive dye rose bengal and skull irradiation with a beam of focused light can trigger the expression of the protein p53 and initiate DNA damage in the area surrounding the thrombotic/necrotic core. We hypothesize that these changes are the signs of injury-induced apoptosis. We used pharmacological tools to characterize the injury-triggered DNA damage that we assayed by TUNEL-labeling, followed by a computer-assisted quantitative analysis. In addition, the morphology of apoptotic cells was visualized by fluorescent staining with propidium iodide. The pharmacological approach included: (a) the inhibition of endonucleases by intracerebroventricular injection of aurintricarboxylic acid (ATA, 20 micrograms/5 microliters); (b) the inhibition of protein synthesis by injecting cycloheximide subcutaneously (2.5 mg/kg); and (c) the blockade of glutamate receptors by injecting 2.5 mg/kg dizolcipine (MK-801) intravenously. These treatments significantly reduced the number of apoptotic cells that we counted in the area surrounding the necrotic core. The results show that injury-induced DNA damage involved de novo synthesis of proteins and an activation of endonucleases, suggesting the occurrence of apoptosis. In this model, apoptosis was associated with an activation of glutamate receptors. Treatments targeted at halting the apoptotic process might provide protection after stroke or after trauma to the brain.