Nigral and striatal dopamine release under sensory stimuli.

Abstract

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.