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 receptors^1–3, supporting the hypothesis of a dendritic release of DA originally suggested by Björklund 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.