title: Insomnia Caused by Serotonin Depletion is Due to Hypothermia.
abstract: OBJECTIVE
  Serotonin (5-hydroxytryptamine, 5-HT) neurons are now thought to promote wakefulness. Early experiments using the tryptophan hydroxylase inhibitor para-chlorophenylalanine (PCPA) had led to the opposite conclusion, that 5-HT causes sleep, but those studies were subsequently contradicted by electrophysiological and behavioral data. Here we tested the hypothesis that the difference in conclusions was due to failure of early PCPA experiments to control for the recently recognized role of 5-HT in thermoregulation.
  
  
  METHODS
  Adult male C57BL/6N mice were treated with PCPA (800 mg/kg intraperitoneally for 5 d; n = 15) or saline (n = 15), and housed at 20 °C (normal room temperature) or at 33 °C (thermoneutral for mice) for 24 h. In a separate set of experiments, mice were exposed to 4 °C for 4 h to characterize their ability to thermoregulate.
  
  
  RESULTS
  PCPA treatment reduced brain 5-HT to less than 12% of that of controls. PCPA-treated mice housed at 20 °C spent significantly more time awake than controls. However, core body temperature decreased from 36.5 °C to 35.1 °C. When housed at 33 °C, body temperature remained normal, and total sleep duration, sleep architecture, and time in each vigilance state were the same as controls. When challenged with 4 °C, PCPA-treated mice experienced a precipitous drop in body temperature, whereas control mice maintained a normal body temperature.
  
  
  CONCLUSIONS
  These results indicate that early experiments using para-chlorophenylalanine that led to the conclusion that 5-hydroxytryptamine (5-HT) causes sleep were likely confounded by hypothermia. Temperature controls should be considered in experiments using 5-HT depletion.
authors.affiliation: Department of Neurology, University of Iowa Carver College of Medicine, Iowa City, IA.
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Murray
authors.affiliation: Department of Neurology, University of Iowa Carver College of Medicine, Iowa City, IA.|Department of Neurology, Yale School of Medicine, New Haven, CT.|Veterans Affairs Medical Center, West Haven, CT.
authors.forename: Gordon F
authors.initials: GF
authors.lastname: Buchanan
authors.affiliation: Department of Neurology, University of Iowa Carver College of Medicine, Iowa City, IA.|Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA.|Veterans Affairs Medical Center, Iowa City, IA.
authors.forename: George B
authors.initials: GB
authors.lastname: Richerson
mesh_terms: D000818:Animals; D001831:Body Temperature / Q000187:drug effects / Q000502:physiology; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D015986:Confounding Factors, Epidemiologic; D010134:Fenclonine / Q000008:administration & dosage / Q000494:pharmacology; D007035:Hypothermia / Q000139:chemically induced / Q000150:complications* / Q000503:physiopathology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D012701:Serotonin / Q000172:deficiency*; D012890:Sleep / Q000187:drug effects / Q000502:physiology; D007319:Sleep Initiation and Maintenance Disorders / Q000139:chemically induced / Q000150:complications* / Q000503:physiopathology*; D013696:Temperature; D014365:Tryptophan Hydroxylase / Q000037:antagonists & inhibitors; D014851:Wakefulness / Q000187:drug effects / Q000502:physiology
chemical_list: D012701:Serotonin; D014365:Tryptophan Hydroxylase; D010134:Fenclonine
keywords: ascending reticular activating system (ARAS); para-chlorophenylalanine (PCPA); serotonin; sleep; thermoregulation