title: Melatonin as a hypnotic: con.
abstract: The physiological roles of melatonin are still unclear despite almost 50 years of research. Elevated melatonin levels from either endogenous nocturnal production or exogenous daytime administration are associated in humans with effects including increased sleepiness, reduced core temperature, increased heat loss and other generally anabolic physiological changes. This supports the idea that endogenous melatonin increases nocturnal sleep propensity, either directly or indirectly via physiological processes associated with sleep. The article "Melatonin as a hypnotic--Pro", also in this issue, presents evidence to support this viewpoint. We do not entirely disagree, but nevertheless feel this is an overly simplistic interpretation of the available data. Our interpretation is that melatonin is primarily a neuroendocrine transducer promoting an increased propensity for 'dark appropriate' behavior. Thus, it is our view that exogenous melatonin is only hypnotic in those species or individuals for which endogenous melatonin increases sleep propensity and is consequently a dark appropriate outcome. Evidence supporting this position is drawn primarily from studies of exogenous administration of melatonin and its varied effects on sleep/wake behavior based on dose, time of administration, age and other factors. From this perspective, it will be shown that melatonin can exert hypnotic-like effects but only under limited circumstances.
authors.affiliation: Centre for Sleep Research, University of South Australia, Basil Hetzel Institute, The Queen Elizabeth Hospital, Woodville, SA 5011, Australia. cameron.vdh@unisa.edu.ac
authors.forename: Cameron J
authors.initials: CJ
authors.lastname: van den Heuvel
authors.forename: Sally A
authors.initials: SA
authors.lastname: Ferguson
authors.forename: M Mila
authors.initials: MM
authors.lastname: Macchi
authors.forename: Drew
authors.initials: D
authors.lastname: Dawson
mesh_terms: D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects; D002940:Circadian Rhythm / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D006801:Humans; D006993:Hypnotics and Sedatives / Q000008:administration & dosage*; D008550:Melatonin / Q000008:administration & dosage* / Q000097:blood; D017440:Photoperiod; D012890:Sleep / Q000187:drug effects*; D007319:Sleep Initiation and Maintenance Disorders / Q000097:blood / Q000188:drug therapy*; D014851:Wakefulness / Q000187:drug effects
chemical_list: D006993:Hypnotics and Sedatives; D008550:Melatonin