PubMed · 37600
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W Zenker. 1979-06-30. [The endogenous morphines].. https://pubmed.ncbi.nlm.nih.gov/37600/
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Although schizophrenia may result from dysfunction of the cerebral cortex the possible indirect involvement of the basal ganglia may be important as this neural system provides a major neural system through which the cortex affects behavior. Processing of cortical input occurs within the striatum, which is the main component of the basal ganglia, where excitatory cortical input is transformed to oppositely modulate the output nuclei of the basal ganglia. The details of this transformation, as well as the role of dopamine in this process, are beginning to unfold. Striatal projections to the globus pallidus, through connections with the subthalamic nucleus, modulate excitatory input to the output neurons of the basal ganglia, GABAergic neurons in the internal segment of the globus pallidus and in the substantia nigra, whereas striatal projections directly to these neurons, provide inhibitory inputs. Thus, cortically driven activity in these two striatal output pathways oppositely modulate the output neurons of the basal ganglia. Dopamine appears to play a crucial role in this transformation. D1 and D2 dopamine receptors are specifically expressed by striatonigral and striatopallidal neurons, respectively. The direct action of dopamine through these receptors appears to oppositely modulate the responsiveness of striatal output pathways to cortical input. Insights into the role of dopaminergic function within the basal ganglia may have direct relevance to the development of treatments for schizophrenia.
The growth of our knowledge of Parkinson's disease over the past 175 years represents an enormous and at times stormy intellectual voyage. It required the contributions of many scientists and clinicians in many disciplines, and its progress inevitably reflected the general progress of biomedical science over the past 2 centuries. The advances in the past half century clearly depended on the great advances achieved in that time in histochemistry, neurochemistry, and neuropharmacology as well as in clinical neurology and neuropathology. Advances in the future will similarly depend on progress in modern neuroscience.
The success of L-dopa therapy in patients with Parkinson's disease and the concepts discussed in this article are summarized in Figure 6. Even in advanced stages of disease, 80% of parkinsonian disability remains responsive to L-dopa therapy. The 50% of the response contaminated by response fluctuations should be viewed, at least in part, as a hopeful sign that the system is still responding to L-dopa therapy. Unfortunately suboptimal control of response fluctuations is still a source of consternation for patient and treating physicians alike. Response fluctuations notwithstanding, it should be emphasized that patients actually do better at every stage of disease for having been on L-dopa, as recently confirmed in a retrospective study of the relationship between response fluctuations and the timing of initiation of therapy. To the extent that the increasing frequency, amplitude, and complexity of response fluctuations add to the overall parkinsonian disability, the phenomenon demands a better understanding that will hopefully lead to better corrective or preventive measures.