The inducible 70,000 molecular/weight heat shock protein is expressed in the degenerating dentate hilus and piriform cortex after systemic administration of kainic acid in the rat

Using both immunohistochemistry and in situ hybridization, we examined the rat brain for the expression of the inducible 70,000 mol. wt heat shock protein, Hsp70, at 3, 6, 12, and 24 h after systemic administration of kainic acid. In contrast to previous reports, the present study demonstrates that neurons in the regions most susceptible to seizure-induced cell death accumulate both Hsp70 messenger RNA and protein. Neurons in the dentate hilus and piriform cortex contained Hsp70 messenger RNA at 6 h and protein at 12 h. These neurons contained little or no Hsp70 messenger RNA or protein at 24 h when the majority of cells in these areas were pyknotic. Injured neurons in areas such as the parietal cortex, which are less susceptible to seizure-induced cell death, expressed and maintained high levels of Hsp70 messenger RNA and protein at 12 and 24 h. This work suggests that Hsp70 messenger RNA and protein are rapidly and transiently expressed in dying neurons, and contradicts the notion that Hsp70 only accumulates in injured neurons that survive.