HTR4 and major depressive disorder: We found no statistically significant association between cerebral 5-HT4R BPND and testosterone (γ1MDD = 0.0001, CI: −0.006; 0.007, p = 0.97) nor estradiol (γ2MDD = 0.64, CI: −0.75; 2.03, p = 0.36) in men with MDD.