Effects of electrical stimulation and norepinephrine on cyclic-AMP levels in the cerebral cortex of the aging rat.

One to 24 month old rats were anesthetized with alpha-chloralose, their cerebral cortices exposed surgically and subjected in vivo to stimulation by norepinephrine (1.0mM for 5 minutes) or electrical pulses (100 pulses/s for 10 s). After microwave fixation, cortical samples were analyzed for cyclic-AMP by the Gilman method. In similarly prepared but unstimulated control animals, cyclic-AMP levels were found to be three to four-fold lower in older than in younger rats, a pattern previously reported for unanesthetized rats. Both norepinephrine and electrical pulses led to cyclic AMP increases. With increasing age the cyclic-AMP levels attained under both stimulus conditions declined, with the levels achieved in the two cases becoming increasingly divergent.