Role of chronotype in depression

Table 3 Neurotransmitter systems and their interactions with circadian rhythms, chronotype, and depression

Neurotransmitter	Key mechanisms in circadian regulation	Circadian rhythm associations	Chronotype-specific differences	Link to depression
5-HT[51-61]	Regulates nonphotic phase shifts in the SCN; activity of 5-HT and SERT mRNA expression follow robust circadian rhythms	5-HT turnover peaks in hippocampus during ZT18-ZT22; disrupted 5-HT circadian alignment in evening chronotypes	Evening chronotypes exhibit heightened 5-HT misalignment; morning light enhances 5-HT signaling in evening types	5-HT dysregulation correlates with depression severity and prevalence; stress-induced 5-HT dysfunction increases depression susceptibility
DA[62-72]	Modulates reward processing and circadian timing via retinal and SCN signaling; DA transporter sensitivity shows diurnal variation	Evening chronotypes have blunted daytime DA peaks; chronic misalignment exacerbates DA-driven anhedonia	Evening chronotypes exhibit altered DA transporter sensitivity; DA fluctuations align with chronotype-dependent motivation deficits	DA dysregulation underlies anhedonia in depression; bidirectional feedback loop with circadian arousal patterns
NE[22,73-75]	Regulated by the LC in a diurnal pattern tied to sleep-wake cycles; influences circadian plasticity (e.g., PER3 expression)	NE turnover peaks during ZT22-ZT2; evening chronotypes show blunted NE peaks and elevated nighttime levels	LC dysfunction in evening types disrupts NE circadian release; NE dysregulation interacts with pubertal sleep shifts in adolescents	NE imbalance exacerbates stress responses and depressive symptoms; bright light therapy modulates NE release in the SCN

5-HT: 5-hydroxytryptamine; DA: Dopamine; mRNA: Message RNA; NE: Norepinephrine; SCN: Suprachiasmatic nucleus; SERT: Serotonin transporter; LC: Locus coeruleus.