Thus, a number of earlier works provided evidence of reduced expression of dopamine receptors, DAT and tyrosine hydroxylase (TH; the rate-limiting enzyme necessary for dopamine synthesis) in post-mortem brains of people with AD, particularly in mesocorticolimbic areas such as the PFC, NAc and hippocampus (88–94). This evidence concerns the gene SLC6A3 and Alzheimer disease.