Autoradiographic studies on the uptake of 3H-dopamine by neurons and astrocytes in explant and primary cultures of rat CNS: effects of uptake inhibitors

Abstract The cellular localization of the uptake of 3 H-dopamine was studied in explant and primary cultures from various regions of rat central nervous system by means of autoradiography. In explant cultures of substantia nigra, 3 H-dopamine was taken up by cell bodies and processes of many neurons. In cultures from striatum, cerebellum and spinal cord, neuronal cell bodies were not labelled, whereas outgrowing nerve fibres revealed intense uptake of the monoamine. Uptake of 3 H-dopamine by neurons was Na+- and temperature-dependent, suggesting an active uptake mechanism. In explant cultures, astrocytes did not accumulate 3 H-dopamine, whereas in primary cultures, which were prepared from the same regions of rat central nervous system as the explant cultures, astrocytes also revealed uptake of this monoamine. The intensity of labelling was dependent on the incubation time. Little uptake of 3 H-dopamine was observed after an incubation time of 5 min and only after 10–15 min did the astrocytes show moderate labelling. Uptake of 3 H-dopamine by astrocytes was not Na+- and temperature-dependent, indicating that glial cells do not possess an active uptake mechanism for this monoamine. This is consistent with biochemical investigations by other laboratories, demonstrating that astrocytes accumulate 3 H-dopamine by a facilitated diffusion system. Addition of the uptake inhibitors nomifensine or GBR 12909 to explant cultures markedly reduced or inhibited uptake of 3 H-dopamine by neurons at a concentration of 10−6 M. In contrast, accumulation of 3 H-dopamine by astrocytes in primary cultures was only slightly affected by nomifensine at 10−6 M. At the highest concentration used (10−5 M), nomifensine also blocked the uptake of 3 H-dopamine by astrocytes. Our finding that GBR 12909 almost completely inhibited the uptake of 3 H-dopamine by astrocytes already at 10−6 M suggests that this compound is a more potent inhibitor of the glial uptake of dopamine than nomifensine.