Fig. 6.

Actions of 1,25D/VDR on serotonin dynamics in the CNS at the serotonin synapse. This model depicts the fine-tuning of serotonin levels by 1,25D via transcriptional regulation of TPH2, SERT, and MAO-A; the result of which is the potentiation of serotonergic nerve transmission. Initially, (left) 1,25D induces TPH2 to enhance serotonin output and, because circled pathway 3 (reuptake and degradation) is attenuated by 1,25D via repression of SERT and MAO-A, serotonin action is spurred at both presynaptic (circled pathway 2) and postsynaptic (circled pathway 1) sites through type 1A and 2A serotonin receptors, respectively