How do chemicals in brain like dopamine affect the behaviour, lack of which cause behavioural problems, is there a test to check the levels and cure?

Great Question. There are three major Dopamine pathways in the brain that help regulate emotions, blood pressure, movements, etc. When overactive can cause psychotic disorders, ; ocd etc. When underactive can cause symptoms of parkinsons. Most disorders of Dopamine are treated based on symptomatology. Either replace or suppress domanine activity. I am not aware of a generalized test commonly given to ck dopamine.