Multiple forms of monoamine oxidase in developing chick brain.

The developmental change in the multiplicity of monoamine oxidase (MAO) forms of chick brain was studied with regard to substrate specificity and inhibitor sensitivity. The developmental pattern of MAO activity towards beta-phenylethylamine was generally similar to that of MAO activity towards 5-hydroxytryptamine. The inhibition study showed that the ratio of type A MAO to type B MAO in chick brain increased during development. This is quite different from results obtained in mice, rats, guinea pigs, and humans, and is not consistent with the idea that in immature brain type A MAO predominates.