Release of dopamine from dendrites in rat substantia nigra

THERE is increasing evidence that neurotransmitter synthesis, storage and release are not confined to axon terminals. Much of this evidence has come from studies of the dopaminergic neurones of the substantia nigra (see Fig. 1). The terminal dendritic processes of dopamine (DA) neurones in substantia nigra are varicose and contain clusters of small vesicles^1,2; histochemical studies have shown that the dendrites contain DA and are able to take it up ^3,4. There is also evidence that the components necessary for the synthesis and storage of DA are transported somatofugally in dendrites of substantia nigra^3,5. Finally, the local application of DA agonists to the substantia nigra produces an inhibition of firing of neurones in the pars compacta that is blocked by DA antagonists^6,7. On the basis of these observations, it has been proposed that a local dendritic release of DA may modify the excitability of dopaminergic neurones in substantia nigra ⁷. There has, however, been no direct demonstration of transmitter release from these or other dendrites. In this study we present evidence for the release of DA from dendrites of dopaminergic neurones in rat substantia nigra.