HTR1A and major depressive disorder: Furthermore, depression involves reduced activity of the serotonergic system, particularly through alterations in the activity or expression of the 5-Hydroxytryptamine (serotonin) receptor 1A (5-HT1A) in brain areas such as the prefrontal cortex, which is responsible for regulation of mood, emotional processing, and memory (Limón-Morales et al., 2023).