From:  Functional interactions between neurotransmitters and neuropeptides in regulating suprachiasmatic nucleus function and circadian rhythms

Neurotransmitters and their probable location

NeurotransmittersAfferent inputSCNEfferent output
Arginine vasopressin (AVP)++
Vasoactive intestinal peptide (VIP)+++
gamma-aminobutyric acid (GABA)+++
Gastrin releasing peptide (GRP)+
Pituitary adenylate cyclase-activating peptide (PACAP)+
Dopamine+
Glycine++
Glutamate++
Serotonin (5HT)+
Neuropeptide Y+
Acetylcholine+
Cholecystokinin+
Melatonin+
Melanopsin++
Prokineticin 2++
Orexin+
Pigment dispersing factor (PDF)+
Nitric oxide (NO)+
Histamine+
Neurotensin (NT)+
Met-enkephalin (m ENK)+
Substance P++
Neuromedin S (NMS)+
Somatostatin (SSA)++
Calbindin (CalB)++
Calretinin (CALR)++
Angiotensin II (ANGII)++
Galanin (Gal)++
Oxytocin (OX)+
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SCN: suprachiasmatic nucleus; +: presence of the neurotransmitter