Disclaimer: I am not a doctor or expert in anatomy. Some ideas and thoughts that might be useful to researchers.
Dopamine producing cells lost.
Dopamine does not cross BBB Blood Brain Barrier thus L-DOPA is administered.
Can brain cells be generated in the lab?
Could brain cells that are made of a patients own tissue be reproduced in the lab and then reinserted?
Likely very difficult to get skin grafts right, probably much more difficult to get a brain graft correct.
The idea sounds impossible, experimentation on animals could likely lead to gains or losses. People could wrongly be upsold to animals.
Do people ever get a stroke in the Midbrain, Cerebral Aqueduct? Building cells that wouldn’t be rejected based on a patients own cells seems like it might be possible, one would have to confirm on animals though animal cells might react differently.
Is it even possible to access the Midbrain without deeply damaging the brain? Could similar neurons be added to another part of the brain with low impact? Could a machine that listens to chemical signals in the brain lead to L-DOPA or Dopamine released past the BBB?
A small machine that delivers dopamine based upon listening to Neuronal Tracts related to midbrain seems like it might be possible. Again the idea sounds risky and could easily be done wrong.
Potential insight from companies like Neuralink might be able to lead to gains. Proof of concept without side effects in animals seems critical. Without side effects in animals might not amp in the same way with People that are required to rely upon Reason and Logic that could be damaged.
I might not adequately understand other potential factors outside of Dopamine loss. Potential for solve one problem but not effectively solve another.
Likely some ideas considered before. That said there has been great advancements in technologies like MRI and Supercomputing that could lead to a much greater level of precision and accuracy once thought impossible. Technology like Medicine is not a cure all, can be useful, will be more useful knowing what it can achieve and what it cannot and that is changing and improving constantly.
If impossible today, it might be possible 20 years from now. Million Times speed ups of processing over the past is now available, and many times faster speed ups are likely in the future.