[Influence of dopamine on pars reticulata neurones of substantia nigra (author's transl)].

1 Dendrites of the dopamine neurones of pars compacta extend into pars reticulata of substantia nigra. The aim of the present study was to investigate whether dendritically released dopamine would be able to influence pars reticulata neurones. 2 In order to test this hypothesis, we have studied the effects of iontophoretically applied dopamine on pars reticulata neurones of substantia nigra in rats under chloralhydrate and under urethane anaesthesia. 3 The dopamine neurones of pars compacta and the neurones of pars reticulata were distinguished by their histological localization (Fig. 1 A) and their electrophysiological characteristics (Fig. 2). Sixty percent of reticulata neurones were antidromically excited from ipsilateral ventromedial thalamus (Fig. 4). 4 Both nigrothalamic and non-nigrothalamic neurones of pars reticulata were activated by iontophoretically applied dopamine, but never depressed (Fig. 5). This effect was blocked by iontophoretically applied fluphenazine. 5 The percentage of reticulata neurones excited by dopamine depended upon the anaesthetic agent: 39% when chloralhydrate, 8% when urethane was used (Table I). 6 As described before by others, dopamine neurones were depressed by dopamine (82%), but never excited (Fig. 6). This effect was also sensitive to fluphenazine. 7 The present results would support the concept that dendritically released dopamine not only affects other nigral dopamine neurones, but also influences non-dopaminergic nigral neurones, some of which project outside the basal ganglia.