Dopaminergic activation of reticulata neurones in the substantia nigra

Abstract

Dendritic release of dopamine (DA) in substantia nigra (SN) is well established in various experimental situations1–3 Morphological substrates for DA storage exist in dendrites4,5, as do dendro-dendritic6 and dendro-axonic7 contacts. DA receptors in SN are located on both cells8 and striato-nigral terminals9,10. DA is thought to regulate the activity of neighbouring dopaminergic neurones through its dendritic release by a local feedback mechanism11,12. However, dendrites of DA neurones also ramify close to the neuropil of non-dopaminergic reticulata neurones in SN. The question has arisen whether dendritically released DA might also influence these neurones which, to a large extent, project to ventromedial thalamus (VM) and superior colliculus13. A necessary condition would be that they are sensitive to DA. In the experiments reported here this was found to be the case—a considerable proportion of nigrothalamic neurones were activated by iontophoretically applied DA. This contrasts with its known depressant effect on pars compacta DA neurones 12 which we confirmed.