Hyperthermic induction of the 27-kDa heat shock protein (Hsp27) in neuroglia and neurons of the rat central nervous system

The 27-kDa heat shock protein (Hsp27) is constitutively expressed in many n eurons of the brainstem and spinal cord, is strongly induced in glial cells in response to ischemia, seizures, or spreading depression, and is selecti vely induced in neurons after axotomy. Here, the expression of Hsp27 was ex amined in brains of adult rats from 1.5 hours to 6 days after brief hyperth ermic stress (core body temperature of 42 degreesC for 15 minutes). Twenty- four hours following hyperthermia, Western blot; analysis showed that Hsp27 was elevated in the cerebral cortex, hippocampus, cerebellum, and brainste m. Immunohistochemistry for Hsp27 revealed a time-dependent, but transient, increase in the level of Hsp27 immunoreactivity (Hsp27 IR) in neuroglia an d neurons. Hsp27 IR was detected in astrocytes throughout the brain and in Bergmann glia of the cerebellum from 3 hours to 6 days following heat shock . Peak levels were apparent at 24 hours, gradually declining thereafter. In addition, increases in Hsp27 TR were detected in the ependyma and choroid plexus. Hyperthermia induced Hsp27 IR in neurons of the subfornical organ a nd the area postrema within 3 hours and reached a maximum by 24 hours with a return to control levels 4-6 days after hyperthermia. Specific population s of hypothalamic neurons also showed Hsp27 IR after hyperthermia. These re sults demonstrate that hyperthermia induces transient expression of Hsp27 i n several types of neuroglia and specific populations of neurons. The patte rn of induced Hsp27 IR suggests that some of the activated cells are involv ed in physiological responses related to body fluid homeostasis and tempera ture regulation. (C) 2000 Wiley-Liss, Inc.