Catecholamine and indoleamine levels in chick cultured neurons and embryonic brain

Catecholamine and indoleamine levels were determined in cultured neurons from chick embryos and in the homologous embryonic cerebral hemispheres in order to study their neurotransmission systems. The seeding of a large number of cells resulted in a pure neuronal culture made of clusters interconnected by processes. Norepinephrine, which was absent from the starting material of the culture, appeared on the 2nd day and then decreased. A small amount of epinephrine was present on the 2nd day and decreased thereafter. Dopamine was not detected. In the cerebral hemispheres of chick embryos, dopamine appreared on the 10th day in ovo and increased steadily up to the 18th day. Epinephrine was also present in the cerebral hemispheres. Its level increased up to the 14th day and then decreased. Indoleamines were measured in the same material. The level of serotonin was markedly higher than that of catecholamines and it increased during cultivation. Tryptophan was already present in the starting material and its amount increased during cultivation. The level of 5-hydroxyindoleacetic acid changed like that of serotonin. In the embryonic cerebral hemispheres, the concentration of serotonin was highest on the 12th day after incubation and then decreased. Tryptophan level decreased steadily all during the embryogenesis. These results were discussed on the ground of differences in the synthesized neurotransmitters.