Dopamine metabolism in characterised neurones ofPlanorbis 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 ofPlanorbis 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 pretreatment 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.