Embrylogical and histological study on monoamine and acetylcholine in rat heart

Monoamine and acetylcholine in rat heart were studied embrylogically. The following results were obtained. Monoamine was present in the heart in monoaminergic nerves which appeared in the atrium of the 14 day old fetus and in the ventriculum 3 days after birth. The distribution of monoamine in 7-14 day old rat hearts was similar, and that of 35 day old rats was identical to that of adult rats. Cholinergic nerves appeared in the atrium and ventriculum of the 20 day old fetus. Its distribution in 7-14 day old rats was similar, and that of 35 day rats was identical to taht of adult rats. Both nerves were already distributed at birth in the sinoatrial node and the atrioventricular node. The distribution in 35 day rats was identical to that of adult rats. Ordinary heart muscle cells also showed less positive cholinesterase activity than specific heart muscle cells at birth.