It's not useful to think of individual photons as having "id numbers", because they don't. Photons are accounting devices to keep track of the strength and direction of electromagnetic waves. It's like the dollars in your bank account: they don't have individual identity either.

And we're not concerned that, with L-dopa treatment, some dopamine-releasing neurons that aren't affected by Parkinson's will now release too much dopamine? I would be afraid of schizophrenia for example.

Thank you for that. Do the dopamine-releasing neurons take up L-dopa, turn it into dopamine, and then release it at the synapse?

Thank you for that. Do the dopamine-releasing neurons take up L-dopa, turn it into dopamine, and then release it at the synapse?

But given that, how come we treat Parkinson's by flooding the brain with dopamine? We wouldn't shovel valves into an apartment to repair a broken toilet valve.

>increase the activity of remaining dopaminergic neurons of the SNpc

When you say "dopaminergic neurons", do you mean neurons that release dopamine or neurons that are affected by dopamine?