Regional distribution of Hsp70 in the CNS of young and old food-restrictedrats following hyperthermia

We examined the effect of aging on the capacity of the brain to produce hea t shock protein (Hsp70) in response to heat stress, using high-powered micr owaves (HPM, 2.06 GHz, 2.2 W/cm(2)) to induce hyperthermia for periods so b rief that thermoregulatory factors were functionally eliminated as confound ing variables. Unanesthetized young (6 months) and old (25 months) male, fo od-restricted Sprague-Dawley rats were exposed to HPM to induce a mean peak tympanic temperature (T-ty) of 42.2 degreesC within 30 s. T-ty returned to < 40.0 degreesC within 6 min post-exposure in both age groups. Rats were e uthanized 6 or 24 h later for immunohistochemical determination of Hsp70 ac cumulation in 10 brain regions. HPM exposure induced significant increases in 7 of the 10 regions. There were no significant differences observed in t he pattern or density of Hsp70 accumulation between the young and old rats at 6 h post-HPM exposure, with the exception of the medial vestibular nucle us, which demonstrated significantly greater Hsp70 accumulation in the old rats. There were significant differences between the age groups at 24 h pos t-exposure, however, there was no general pattern; i.e., depending on the b rain region, aged rats displayed significantly greater, lesser, or similar increases in Hsp70 expression compared with young. Taken together, these re sults demonstrate that the brain of aged, food-restricted rats does not dis play a loss of capacity to accumulate Hsp70 in response to heat stress. (C) 2001 Elsevier Science Inc.