Pre- and postsynaptic markers of cholinergic neurons in the cerebral cortex of rats of different ages.

In order to investigate the effect of aging on postsynaptic muscarinic binding, we measured 3H-PZ binding in the cerebral cortex of male Fisher 344 rats of different ages. ChAT activity was measured as a presynaptic marker of the cholinergic system. Total and salt-soluble AChE activities were also measured. Maximal binding of 3H-PZ and ChAT activity did not change during aging. The ratio of detergent-soluble AChE to salt-soluble AChE was lower in 30-month-old rats than in 4-month-old rats. The results of the present study do not indicate that the amount of M1 muscarinic receptors proposed to be located postsynaptically decreases during aging. In senescent rats, however, the proportions of salt-soluble and detergent-soluble AChE may differ from those in young rats.