Dopaminergic activation of reticulata neurones in the substantia nigra.

Dendritic release of dopamine (DA) in substantia nigra (SN) is well established in various experimental situations. Morphological substrates for DA storage exist in dendrites, as do dendro-dendritic and dendro-axonic contacts. DA receptors in SN are located on both cells and striato-nigral terminals. DA is thought to regulate the activity of neighbouring dopaminergic neurones through its dendritic release by a local feedback mechanism. However, dendrites of DA neurones also ramify close to the neuropil of non-dopaminergic reticulata neurones in SN. The question has arisen whether dendritically release DA might also influence these neurones which, to a large extent, project to ventromedial thalamus (VM) and superior colliculus. 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 which we confirmed.