Age-differences in choline acetyltransferase activities and muscarinic receptor binding in brain regions of C57BL/6J mice.

Muscarinic receptor binding and choline acetyltransferase, (ChAT, EC.2.3.1.6.) activity were assayed in four brain regions of C57BL/6J mice of four ages (4, 12, 18, and 24 months). In the cerebellum, there were no age differences in either of the cholinergic markers. However, significant age differences were noted in the Vmax for ChAT and in the Bmax for [3H]quinuclidinyl benzilate ( [3H]QNB) in the cortex, striatum and hippocampus. Increases were noted in Vmax of the synthetic enzyme in all three regions and for Bmax in the hippocampus. Bmax for [3H]QNB decreased in the cortex and striatum. The high- and lower-affinity muscarinic binding constants, the percentage of muscarinic binding to high affinity sites determined by carbamylcholine displacement of [3H]QNB, as well as the affinities of ChAT for acetyl coenzyme A and choline chloride showed no age differences in any brain region.