[Interactions of cerebral serotonin and catecholamines].

It has been demonstrated that the administration of large doses of dopa or 5-hydroxytryptophan (5-HTP) affected not only dopamine (DA) or serotonin (5-HT) neurons but also other neurons. This report concerns the effects of tryptophan, 5-HTP or dopa on concentrations of 5-HT, DA, norepinephrine, and their metabolites in p-chlorophenylalanine-, 5,7-dihydroxytryptamine (5,7-DHT)- or non-treated rat brain. The results were as follows: 1) When the brain DA levels increased more than six-fold after the i.p. administration of l-dopa, the brain 5-HT levels significantly decreased, and 5-hydroxyindoleacetic acid (5-HIAA) levels significantly increased. 2) In the nerve ending fraction of rat brain, the administration of l-dopa induced the largest increase of DA levels in the striatum, while administration of dl-5-HTP produced the largest increase of 5-HT levels in the hypothalamus. These results suggest that the distribution of newly synthesized 5-HT or DA after the administration of 5-HTP or dopa, respectively, depends not only on that of aromatic l-amino acid decarboxylase, but also on that of nerve cells which selectively take up 5-HTP or dopa or that of synaptic vesicles which selectively take up 5-HT or DA. 3) The large doses of 5-HTP administration to 5,7-DHT pretreated rats induced the largest increase of 5-HT levels in the striatum. Thus, results in the present study indicate that the distribution of DA or 5-HT after the administration of dopa or 5-HTP, respectively, depends on the doses of dopa or 5-HTP given as well as the presence or absence of the lesioned 5-HT or DA neurons.