Since the initial demonstration of induction of the major mammalian stress (heat shock) protein, hsp70, after transient ischemia, efforts have been directed toward a) quantitating increased transcription of hsp70 and other stress-inducible mRNAs after ischemia, and b) immunocytochemical localization of hsp70 induction in gerbil brain. Induction of both hsp70 and ubiquitin mRNA sequences have now been demonstrated after ischemia using cDNA probes. Ubiquitin mRNA is only modestly induced (70% increase) and peaks at 6 hr recirculation. Hsp70 mRNA is more strongly induced (more than 2-fold) and peaks at 12 hr, coincident with the time of maximal hsp70 translation previously determined. A striking temporal and anatomical pattern of hsp70 induction was demonstrated in post-ischemic brain using monoclonal antibodies considered specific for inducible forms of the hsp70 family. Control animals showed immunoreactivity which was restricted to ependymal cells lining the ventricles, and this remained unchanged after ischemia. During 24 hr recirculation after 10 min ischemia, hsp70 immunoreactivity appeared in dentate granule cells, in neurons of habenula and striatum, and in a number of basal forebrain and cortical regions. At 48 hr intense reactivity was evident in CA3 neurons of hippocampus. By 96 hr immunoreactivity was restricted to some residual staining of CA3 with strong labeling of entorhinal and other cortical regions. It is of interest that positive cells are found in hippocampus and other limbic structures, circuitry which may be the anatomical substrate for proposed excitotoxic mechanisms of neuronal loss after ischemia. Accumulation of hsp70 was apparent in CA3 and dentate granule cells which survive transient ischemia, but was greatly attenuated in CA1 neurons which do not. This heterogeneity in hsp70 induction may reflect variations in post-ischemic metabolic stress as well as in the response to stress of various cell populations.
