Regardless of causes, the process that kills neurons in the SN of the PWP is the hyperactive activated microglia. That is pretty well established.

If a rat is exposed to endotoxins from very common gram negative bacteria while it is still in the womb, three PD-critical things happen:


1) There are fewer neurons in the SN;
2) The response to stress is changed and results in cortisol related problems.
3) Once past puberty, the rat will have an exagerated response to future exposure of the brain to the endotoxin. In particular, the microglia will react and then fail to shut down.

The SN has one of the greatest densities of microglia in the brain.

Green tea ingredient ECEG (that's close ) stops microglial hyperaction. There may be others.