EFFECTS OF AGE ON PILOCARPINE-INDUCED C-FOS EXPRESSION IN RAT HIPPOCAMPUS AND CORTEX

The effect of age on pilocarpine-induced expression of the immediate-e arly gene c-fos was examined in the hippocampus and cortex of Long-Eva ns rats. Rats were treated with either pilocarpine (25 mg/kg) or salin e, and sacrificed 90 min, following injection. The level of c-Sos mRNA and Fos-like protein expression was determined using in situ hybridiz ation histochemistry, and immunocytochemistry, respectively. In saline -treated animals, comparable levels of c-fos mRNA and Fos-like protein were observed in the hippocampus and cortical regions of young (6 mon th) and aged (24-26 months) rats. The expression of Fos-like protein f ollowing pilocarpine treatment was increased, however, in frontal, ret rosplenial, and cingulate cortex of aged compared to young rats. In fr ontal and retrosplenial cortex, the changes in Fos-like protein were a ccompanied by changes in c-fos mRNA expression. In contrast, no age di fference was detected in the hippocampus or parietal cortex of pilocar pine-treated rats. These regionally-specific age differences in respon se to pilocarpine administration suggest that mechanisms localized to those areas play an important role in determining the response to chol inergic stimulation mediated through post-synaptic muscarinic receptor s. (C) 1998 Elsevier Science Inc.