Fig. (1).
Many biological variables are associated with sleep patterns. The interveining hormonal and humoral substances acting to affect sleep are known in many cases; such substances act over different time lines to alter expressions of sleep phenotypes. Abbreviations: CRH, corticotropin releasing hormone; GHRH, growth hormone releasing hormone; PGD2, prostaglandin D2; VIP, vasoactive intestinal polypeptide; TNF, tumor necrosis factor alpha; CCK, cholecystokinin; NPY, neuro-peptide Y; GABA, gamma amino butyric acid; NO, nitric oxide.