Autoradiographic studies on distribution of L-3,4-dihydroxyphenylalanine (L-DOPA)-14C and L-5-hydroxytryptophan (L-5-HTP)-14C in the cat brain.

The distribution and metabolism of L-DOPA-14C and L-5-HTP-14C in the cat brain were examined by means of autoradiography and chromatography. The results revealed that an appreciable amount of radioactivity in the gray matter, but not the white, and that the localization of radioactivity of L-DOPA and L-5-HTP significantly differed. After L-DOPA-14C administration, a high accumulation was found in the caudate nucleus, putamen and pallidum. With L-5-HTP-14C administration, high radioactivity was observed in the hypothalamus, raphe nucleus, substantia nigra, inferior olivalis and caudate nucleus. An analysis of the main metabolites of both amino acids in various regions of the brain was also made. When L-DOPA was given, a high concentration of dopamine was detected in the caudate nucleus, followed by the hypothalamus. In the case of L-5-HTP, a high concentration of serotonin was detected in the hypothalamus and the medulla oblongata. These results suggest that amines derived from exogenously administered L-DOPA and L-5-HTP accumulate in the brain regions known as the corresponding amine rich regions, under physiological conditions.