HTR1A and Anxiety: On the other hand, global knockout of all 5-HT1A receptors would allow for hyper-activation of raphe neurons (due to absence of 5-HT1A autoreceptor) and activation of pyramidal 5-HT2A receptors that is not antagonized by pyramidal 5-HT1A receptors due to their homologous and heterologous (5-HT2A-mediated) desensitization, leading to increased anxiety.