EFFECT OF AGING ON THE BASAL EXPRESSION OF C-FOS, C-JUN, AND EGR-1 PROTEINS IN THE HIPPOCAMPUS

In the present study the effect of aging on the basal expression of th ree different immediate early genes (IEGs) was investigated. The prote in products of c-fos, c-jun, and egr-1 genes were visualized immunohis tochemically in the rat hippocampus of young adult (4-month-old) and o ld rats (20-month-old). Astrocytes were quantified by GFAp immunostain ing to determine whether changes in the expression of IEGs were correl ated with modifications in this marker of degenerative changes. In the young adult rat brain, basal levels of c-Jun and Egr-1 but not c-Fos were detected within the hippocampal formation. Whereas Very high basa l levels of c-Jun were found in the dentate granule cells and in the p yramidal cells of the ventral hippocampus, Egr-1 was highly expressed in the CA1 pyramidal cells of the dorsal hippocampus. Aging was accomp anied by a decrease in Epr-l expression, by a decrease in total cell d ensity, as well as by a loss of astrocytes in CA1 subfields. In contra st, basal expression of c-Fos and c-Jun as well as astrocyte density w ithin the dentate gyrus were not affected by aging. No difference in t hese markers was observed in aged rats with or without impairment in s patial learning in a water maze. It was concluded that although these changes may reflect senescence-induced decline of brain function, they do not constitute the defect underlying the age-associated reduction in mnesic capability. Copyright (C) 1996 Elsevier Science Inc.