Fig. 3
The topographical organization of the SCN. More than ten distinct neuronal populations have been identified in the suprachiasmatic nucleus (SCN), but the primary neuronal populations responsible for regulating circadian rhythms are AVP (arginine vasopressin) and VIP (vasoactive intestinal peptide) neurons. AVP neurons (green shade) and VIP neurons (red shade) are topographically arranged in the shell and core regions of the SCN, respectively. The black arrows indicate the intercellular projection of circadian rhythms, with a stronger signal transmission from the core to the shell. Furthermore, astrocytes and microglia are present throughout the SCN, and emerging evidence highlights their significant roles in regulating circadian function. Abbreviations: AVP: Arginine vasopressin, AII: Angiotensin II, BNST: Bed nucleus of the stria terminalis, CALR: Calretinin, DR, MnR: Dorsal and median raphe nucleus, DMH: Dorsomedial hypothalamic nucleus, ENK: Enkephalin, GABA: γ-aminobutyric acid, GHT: Geniculohypothalamic tract, GRP: Gastrin-releasing peptide, IGL: Thalamic intergeniculate leaflet, LHN: Lateral habenula nucleus in the thalamus, mPOA: Medial preoptic area, NMS: Neuromedin S, NPT: Neuropeptide Y, NT: Neurotensin, PVN: Paraventricular nucleus of the hypothalamus, PVT: Paraventricular thalamic nucleus, RHT: Retinohypothalamic tract, SCN: Suprachiasmatic nucleus, VIP: Vasoactive intestinal peptide