HSP70 heat shock protein induction following global ischemia in the rat

Stress proteins, including the 70 kD heat shock protein (HSP70), are induced in injured cells. The present study was designed to characterize the cells injured by global ischemia in rat brain. Adult rats were subjected to forebrain ischemia using bilateral carotid occlusion and systemic hypotension. HSP70 protein immunostaining of brain sections was performed using the C92 monoclonal antibody one day later. HSP70 immunoreactive cells were found in many brain regions including cortex. HSP70 positive neurons in cortex were found in certain laminae, especially layers 2 and 3. Acid fuchsin positive neurons, cells presumed to be dead, were located only in the layers of cortex where HSP70 immunoreactive neurons were found and were infrequent compared to the large number of HSP70 positive neurons. HSP70 immunoreactive glial cells were detected at the margins of ischemic areas, and were mostly OX42 immunoreactive microglia plus some GFAP immunoreactive astrocytes. In some animals HSP70 stained bipolar cells were detected in the striatum and in white matter which may be type 2 astrocytes. These findings confirm that global ischemia injures microglia and astrocytes, and that cells in a given ischemic region sustain varying degrees of injury--from the HSP70 stained neurons that likely survive the ischemia to acid fuchsin stained cells that die.