DIFFERENTIAL INDUCTION OF HEAT-SHOCK MESSENGER-RNA IN OLIGODENDROCYTES, MICROGLIA, AND ASTROCYTES FOLLOWING HYPERTHERMIA

A time course analysis of hsp70 mRNA induction in response to a physio logically relevant increase in body temperature of 2.6 degrees C was p erformed in the rabbit forebrain. A protocol that combined in situ hyb ridization and cytochemistry on the same tissue section was employed t o identify reactive glial cell types. Cytochemical markers for astrocy tes, microglia, and oligodendrocytes were utilized in combination with a DIG-labelled hsp70 riboprobe, which permitted mRNA localization at high resolution. Four glial cell body-enriched regions of the rabbit f orebrain were examined, namely, cortical layer 1, hippocampal fissure, corpus callosum, and fimbria. Maximal hsp70 mRNA induction was observ ed in 2 and 3 h hyperthermic animals. The colocalization analysis demo nstrated that hsp70 mRNA was induced in oligodendrocytes and microglia , but not in forebrain GFAP positive astrocytes. In addition, cell cou nts were performed which showed that almost all oligodendrocytes induc ed hsp70 mRNA while a subpopulation of microglial cells responded. The se data are consistent with the notion that oligodendrocytes, microgli a, and astrocytes exhibit distinct thresholds for activation of the he at shock response following a physiologically relevant increase in bod y temperature.