Dendritic Dopamine Release Research Articles

Dendritic dopamine: Studies on the release of endogenous dopamine from subcellular particles derived from dendrites of rat nigro-striatal neurons

During subcellular fractionation of rat substantia nigra, the dendrites of the nigro-striatal neurons give rise to particles as terminals do. Release of endogenous dopamine from these particles could be demonstrated with amphetamine but not with potassium. Under identical incubation conditions, subcellular particles derived from the terminal area showed a marked release of endogenous dopamine with both amphetamine and potassium. Also in contrast to the particles from terminals, dendritic particles lost their major content of dopamine during preincubation. The results favor the concept of dendritic dopamine release, but emphasized the difference between dendrites and terminals of the nigro-striatal neurons.

Nigral and striatal dopamine release under sensory stimuli.

SEVERAL groups have demonstrated the presence of a dopamine (DA)-sensitive adenylate cyclase in the substantia nigra. This adenylate cyclase is associated with postsynaptic dopaminergic receptors1–3, supporting the hypothesis of a dendritic release of DA originally suggested by Bjorklund and Lindvall4. Other reports provided further arguments in favour of this hypothesis. Exogenous 3H-DA, taken up in slices of the rat substantia nigra, was shown to be released by potassium through a calcium-dependent process5. Furthermore, spontaneous and evoked release of 3H-DA has been demonstrated in vivo in the cat substantia nigra6. The increase of 3H-DA release in the substantia nigra induced by amphetamine (10−6 M) or benztropine (10−6 M) is associated with a reduction of the transmitter release from nerve terminals in the ipsilateral caudate nucleus, suggesting a decreased activity of the nigrostriatal dopaminergic7 neurones. A similar phenomenon was seen in the caudate nucleus when DA (10−7 M) was directly introduced into the substantia nigra8. We present here a study of the effects of unilateral sensory stimulations on the release of DA from nerve terminals and dendrites of the two nigrostriatal dopaminergic pathways. Previous studies9 revealed an increase in the levels of homovanillic acid in the perfusates of the cat lateral ventricle during electrical stimulation of the paws.

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 vesicles1,2; histochemical studies have shown that the dendrites contain DA and are able to take it up3,4. There is also evidence that the components necessary for the synthesis and storage of DA are transported somatofugally in dendrites of substantia nigra3,5. 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 antagonists6,7. 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 nigra7. 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.