Monoamine oxidase (MAO) activity in the brain and peripheral tissues of newborn ground squirrel, as well as its evolution during postnatal development were studied. 2. Monoamine oxidase activity in the brain stem and liver, at the day of birth is significantly higher (P less than 0.01; P less than 0.005) than in adults. 3. After that, enzyme activity decreases, but at the 25th day, e.g. at the day of the opening of the eyes, still remains significantly above the adult's value (P less than 0.01). 4. The results indicate some species specificity concerning the level and the evolution of cerebral and hepatic MAO activity as compared to the rats.
