Can the Dopamine (DA) receptor count take a significant drop over the course of life or does it stay constant? I read that low D2 (Dopamine receptor type 2) receptor count does not cause Parkinson's Disease (PD) and has some interesting effects instead, but what abut low D1 (Dopamine receptor type 1) receptor count? What are its effects? All I found is this. Is D1 receptor only related to motor activities?
I found some research papers on how to measure the DA receptor count, but are those tests publicly available and affordable? Is there any indirect way to determine D1 & D2 receptor count?
Disclaimer: This is not a self-help question, and PD is not my focus. I am trying to form a theory that requires easy way to measure DA level plus D1 and D2 receptor count, but sadly I am not part of any university with biology department to go seek advice from.