In the current paper, four types of 5-HT heteroreceptor complexes (5-HT1AR-FGFR1, 5-HT1A-5-HT2AR, OXTR-5-HT2A/C) have been selected to give insights into this novel field with a focus on their relevance for depression. The gene discussed is HTR1A; the disease is depressive symptom measurement.