DRD2 and major depressive disorder: Dysfunction of these dimers has been associated with multiple diseases, e.g., pre-eclampsia (angiotensin II type 1 and bradykinin receptor B2 heterodimer complexes) [18], schizophrenia (dopamine D2 receptor (D2R) heterocomplexes) [19], depression (serotonin 1A receptor 5-HT1A and serotonin 7 receptor 5-HT7 heterocomplexes, galanin receptor type 1 (GalR1), type 2 (GalR2), and 5-HT1A heterocomplexes) [20,21,22,23,24,25,26].