Dopamine metabolism in characterised neurones of Planorbis corneus

A sensitive chromatographic procedure was used to study the metabolism of [14C]tyrosine, [3H]DOPA and [3H]dopamine in 3 defined cell-types situated in the nervous system of Planorbis corneus. One of the cell-types contains dopamine (GDC), the other serotonin (GSC) and the other neither amine (GC). The GDCs metabolise [14C]tyrosine to form DOPA and dopamine while the other two cells lack this ability. In contrast, the GDCs and the GSC, but not the GCs, metabolise [3H]DOPA to form dopamine. In addition the GDCs incorporate radioactivity from [3H]DOPA into DOPAC, homovanillic acid and methoxytyramine. After incubation of cells in [3H]dopamine, only the GDCs metabolise it to form DOPAC, homovanillic acid and methoxytyramine. In no instance did the GDCs form significant amounts of noradrenaline from the incorporated radioactive substances. These results, together with data on the amine histochemistry of the individual cell-types following pretretment of animals with drugs known to affect specific enzymes in the synthesis of amine transmitter substances, clearly demonstrate that the GDCs alone have the enzymes requisite for the biosynthesis and catabolism of dopamine, but not noradrenaline.