COMT and depressive disorder: Patients with depression are known to have low BH441 and folate.42 Moreover, elevated serotonin has been reported to bind to COMT and overlap with SAM‐binding sites, thereby inhibiting COMT by preventing SAM binding.43 Therefore, high serotonin in vehicle‐treated FSL rats could have caused reduced dopamine degradation via SAM‐dependent COMT.