associated with a connection to mood disorders, npas2 has been found to be involved with dopamine degradation. this was first suggested by the observation that the clock components bmal1 and npas2 transcriptionally activated a luciferase reporter driven by the murine monoamine oxidase a ("maoa") promoter in a circadian fashion. this suggested that these two clock components (bmal1 and npas2) directly regulated "maoa" transcription. subsequent findings discovered positive transcriptional regulation of bmal1/npas2 by per2. in mice lacking per2, both "maoa" mrna and maoa protein levels were decreased. therefore, dopamine degradation was reduced, and dopamine levels in the nucleus accumbens were increased. these findings indicate that degradation of monoamines is regulated by the circadian clock. it is very likely that the described clock-mediated regulation of monoamines is relevant for humans, because single-nucleotide polymorphisms in "per2, bmal1", and "npas2" are associated in an additive fashion with seasonal affective disorder or winter depression.