Dopamine selectively increases ³H-GABA release from slices of rat substantia nigra in vitro

Abstract

THE firing rate of the dopaminergic neurones in the substantia nigra (s. nigra) of mammalian brain is controlled largely by descending striatonigral neurones. But new evidence suggests that the activity of nigral neurones may also be modulated by local circuits within the s. nigra, involving a local dendritic release of dopamine². The demonstration that dopamine is present in³, and released^4–6 from, the dendrites of nigral neurones both in vitro and in vivo supports this concept. The precise site of action of dopamine in the s. nigra is not known, but a dopamine-sensitive adenylate cyclase has been described in this brain region⁷, apparently located presynaptically on the terminals of striatonigral afferents^8–10 containing either γ-aminobutyric acid (GABA) or substance p^11,12. To determine whether presynaptic dopamine receptors in s. nigra are associated with substance P or GABA-containing axon terminals, we have investigated the effects of dopamine on the release of substance P and GABA from superfused slices of rat s. nigra in vitro. Our results show that dopamine stimulates selectively the release of GABA from nerve terminals in s. nigra.