Abstract
AChE activity in mouse brain stem reticular formation was studied at 4hr intervals for 48 hr at 4 different times of the year under normal (LD 12/12) and constant light (LL) regimens. Under both illumination regimens, a significant ultradian rhythm of AChE activity was observed. In the investigated seasons of the year, changes in AChE behaviour were limited to mean activity of the enzyme (median) as well as to the amplitude and acrophase of the rhythm.