HTR1A and supranuclear palsy, progressive, 1: Our findings indicated the changes of MSN in PSP correlated specifically with a decrease in the D2 receptor, NET receptor, MOR receptor, and two serotonin receptors (5‐HT1A and 5‐HT4), as did increases in the levels of the α4β2 and 5‐HT1B receptors (Figure 5).