Induction of HSP70 mRNA and HSP70 protein in the hippocampus of the developing gerbil following transient forebrain ischemia

The effects of a 20-min transient episode of forebrain ischemia on the induction of HSP70 mRNA and protein, and the histopathological outcome in the hippocampus of the developing gerbil, were examined at postnatal days (P) 7, 15, 21 and 30 and in adulthood. 4 days after the ischemic episode, P7 gerbils did not show apparent histological abnormalities; however, from P15 onwards, ischemia resulted in necrosis in selected areas of the hippocampus. At P15 and P21, necrosis was observed in the base of the granular cell layer of the dentate gyrus and in the CA3 pyramidal cell layer, whereas at P30 and adult necrosis was apparent in the CA1 pyramidal cell layer. HSP70 mRNA induction was not found in ischemic P7 and P15 gerbils while, from P21 onwards, induction was observed in the dentate gyrus and CA1 pyramidal cell layer. In addition, at P30 and adult, HSP70 mRNA expression was also seen in CA3 pyramidal cell layer. Induction of HSP70 immunoreactivity was not seen at P7 but, from P15 onwards, ischemia induced HSP70 immunoreactivity in different areas: in dentate gyrus granular and molecular layers, from P15 onwards; in CA1 pyramidal cell layer, from P21 onwards; and in CA3 pyramidal cell layer, from P30 onwards. Results show selective age-dependent patterns of vulnerability to ischemia in the gerbil hippocampus which, overall, were not well-correlated to the corresponding HSP70 mRNA and protein induction patterns.