[Brain dopamine and brain disorders - and what we have learned from these studies (author's transl)]

1. Two examples are given to illustrate the role of dopamine in brain disorders: a) In Parkinson's disease there is a marked deficiency of dopamine in several subcortical brain regions, particularly the striatum (caudate nucleus and putamen) and substantia nigra. This extensive dopaminergic denervation of the basal ganglia results in compensatory pre- and postsynaptic changes, i.e. increase in neuronal activity in the remaining dopamine neurons, and increase in the number of the postsynaptic dopamine receptor sites. These changes are of great functional significance, inter alia for the therapeutic efficacy of L-dopa as an antiparkinson medication. - b) Recently, increased number of dopamine receptors has been measured in the striatum and nucleus accumbens of patents dying with schizophrenic symptomatology. This observation, taken together with the fact that all antipsychotically effective neuroleptics are potent blockers of brain dopamine receptors, has lead to the hypothesis that dopaminergic brain mechanisms are involved in the pathophysiology of the schizophrenic disorder(s). 2. The possible involvement of brain dopamine receptors in brain disorders raises the more basic question as to the physiological role of the diverse dopamine (and other monoamine) receptors in brain function. Since in the brain the majority of the monoamine-containing nerve terminals are devoid of synaptic contacts, a nonsynaptic role for dopamine (and other brain amines) is envisaged, e.g. modulation of neuronal impulse activity characterized by long lasting changes in reactivity of the neuronal elements and circuits.