Circadian changes of acetylcholine, choline acetyltransferase, acetylcholinesterase and muscarinic receptors in mouse brain

By means of radioisotope, the daily changes of cholinergic nervous markers, acetylcholine (ACh), choline acetyltransferase (ChAT), acetylcholinesterase (AChE) and muscarinic receptors in the mouse brain were measured in September and October. The mice were housed 5 animals to a cage under natural light-dark cycle (12 : 12) for 7 d in the laboratory room at 18-22 degrees C. The determinations of ACh were taken, every 2 h, to assess the brain ACh of 5 mice for 24 consecutive hours. M-cholinergic receptors, ChAT and AChE activity were examined at 10:00, 16:00 and 22:00. The results demonstrated that the ACh contents, ChAT activity and muscarinic receptor Bmax value were high at 10:00, low at 16:00 and 22:00. However, AChE maximum activity was found at 16:00, minimum activity at 22:00. But the affinity of muscarinic receptors to [3H]QNB did not show any significant daily changes. These data strongly suggested that in mouse brain the cholinergic nervous markers showed a clear daily rhythm.