Changes in tissue-plasminogen activator mRNA expression following corticalablation in the rat brain

Tissue plasminogen activator (tPA) has been used to treat acute thrombotic lesions. Roles other than the activation of fibrinolytic pathways have been suggested for tPA in the mature brain. We used the in situ hybridization t echnique to investigate the changes in tPA mRNA expression within the brain after cortical ablation. We found that expression of tPA mRNA started to i ncrease diffusely in the cortex ipsilateral to the injury 6 h after ablatio n. This increase had become prominent 24 h after ablation. On d 5, the expr ession of tPA mRNA had returned to that of the control animals except for t he area near the injury. We also found that administration of MK-801 before injury suppressed the increase of tPA mRNA in the ipsilateral cortex. Thes e results suggest that the increase in tPA mRNA is likely to be mediated vi a activation of NMDA receptors.