Effect of phase shift on monoamine oxidase activity in different regions of the rat brain as a function of age

The effect of reversed light-dark cycle on the monoamine oxidase activity of different regions of the rat brain in various age groups was studied. Twenty-one-day-old rats showed an irregular pattern of shift in the appearance of the peak activity. In the case of 3-, 6-, and 12-month-old rats, all the regions of the brain became synchronized to the altered environmental condition, and the peak MAO activity was shifted by 180 degrees. In the cerebral cortex of 24-month-old rats the peak was shifted by only 60 degrees, whereas a 120 degrees shift was observed for all the other regions. The present study suggests that the synchronizing effect of the light-dark cycle is age dependent.