A histochemical study on the central effect of monoamine precursors

A histochemical investigation has been made on the central monoamine neurons after the administration of monoamine precursors and peripheral decarboxylase inhibitor in experimental animals and the results are summarized as below: (1) Catecholamine fluorescence in the brain reduces and yellowish indoleamine fluorescence manifests after the treatment with 5HTP alone and Ro4-4602 plus 5HTP. These findings support the view that catecholamine is likely to be replaced by indoleamine. (2) Ro4-4602 does not cause directly any change in central catecholamine neurons except in median eminence where the inhibitor causes a decrease in dopamine fluorescence. The findings indicate that the inhibitor may act in the hypothalamus as same manner as in the peripheries, because the hypothalamus is presumably lacking of blood brain barrier. (3) L-Dopa alone and L-Dopa plus Ro4-4602 enhance dopamine fluorescence in the substantia nigra and the median eminence, especially an increase in the extra-neuronal fluorescence can be seen in the latter. This indicates the releasing of amines from cell body into extraneuronal spaces.