Interesting stuff. The positive effects of exercise are likely due, at least in part, to the effect of exercise on modulating levels of neuronal growth factors, such as glial cell-derived neurotrophic factor (GDNF) which promotes the survival and differentiation of dopaminergic neurons, the neurons lost during the progression of Parkinson's disease. Direct GDNF brain infusions have shown potential but this is obviously a pretty invasive approach.
As well as exercise, it seems like iboga(ine) may be also promising in treating Parkinson's disease, as it has been found to cause a long-term increase in GDNF expression via a positive feedback loop. I made this link a while back, and interestingly recently met and spoke to someone from the Beckley Foundation who is planning to conduct research on this.
https://www.dmt-nexus.me...aspx?g=posts&t=13217