The D3 dopamine receptors are coded by the DRD3 gene, which is found on chromosome 3q13.3 [66], and are densely located in the limbic subcortical regions of the brain, specifically the NAc, thalamus, hypothalamus, and the cerebellum [58]. They are also distributed throughout the ventral striatal complex, which plays a role in the reward and gratification processes of addictive behavior [58]. Experimental evidence shows that repeated administration of opioids, psychostimulants, and L-dopa, a dopaminergic agonist precursor, induces the expression of D3 receptors in the dorsal striatum in animal models, thereby providing support for the involvement of these receptors in the behavioural sensitization of drug dependence [58, 67]. Post-mortem studies reported an elevated level of D3 receptors in the ventral striatum of cocaine fatalities, leading to the consideration of the DRD3 gene as a candidate for susceptibility to drug dependence [67].
