Monoamine levels and monoamine oxidase activity in different regions of rat brain as a function of age.

The levels of norepinephrine, dopamine, 5-hydroxytryptamine and the activity of monoamine oxidase were estimated in cerebral cortex, cerebellum, medulla oblongata, hypothalamus, striatum and midbrain of 21-day-old, 3-, 6-, 12- and 24-month-old male albino rats of Wistar strain. No significant change with age was found in the levels of all the three amines in cerebral cortex and cerebellum, while medulla oblongata showed a significant decrease of all the amines by 24 months of age. Hypothalamic norepinephrine, dopamine and striatal dopamine showed a highly significant decrease by 24 months of age, whereas 5-hydroxytryptamine in hypothalamus, norepinephrine and 5-hydroxytryptamine in striatum and dopamine in midbrain did not show any appreciable change with age. Monoamine oxidase activity in all the regions except cerebellum showed a significant increase by 24 months of age compared to 3- and 6-month-old rats.