Differential expression of heat shock protein 70 gene between the cortex and caudate after transient focal cerebral ischaemia in rats

In relation to changes of total protein synthesis, induction of 70-kDa heat shock protein (HSP70) mRNA was examined by Northern blot and in situ hybridization after 30 min of transient middle cerebral artery (MCA) occlusion of rats. HSP70 mRNA was not present in the control condition of brain. With reperfusion, the mRNA was greatly induced along with the recovery of total protein synthesis in the cerebral cortex and lateral caudate of the ipsilateral hemisphere. However, the level of the mRNA reached a maximum earlier in the lateral caudate (at 3 h) than in the cortex (at 8 h), and the maximum amount of the mRNA was much smaller in the caudate than in the cortex. Total protein synthesis in the lateral caudate did not completely recover until 7 days. Histological examination showed a severe damage in cells of lateral caudate, while cells in the cortex were almost normal at 7 days. No difference in the brain temperature was observed between the two regions. These results show that the induction of HSP70 mRNA correlates with the recovery of protein synthesis in brain cells after a transient ischaemia, and that the HSP70 gene expression is different at the transcriptional level between the cortical and caudate cells after the transient ischaemia.