 Some are used for medical or recreational purposes, but neurochemists have also developed a variety of research drugs, some of which bind with high affinity to specific types of dopamine receptors and either agonize or antagonize their effects, and many that affect other aspects of dopamine physiology, including dopamine transporter inhibitors, VMAT inhibitors, and enzyme inhibitors.A number of studies have reported an age-related decline in dopamine synthesis and dopamine receptor density (i.e., the number of receptors) in the brain.This decline has been shown to occur in the striatum and extrastriatal regions.