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Keywords:

  • EEG;
  • hypocretin;
  • orexin;
  • overexpression;
  • sleep–wake pattern;
  • transgenic

Abstract

Aim:  Orexin/hypocretin peptides are expressed in the lateral hypothalamus and involved in the regulation of autonomic functions, energy homeostasis and arousal states. The sleep disorder narcolepsy, which is characterized by excessive daytime sleepiness and occurrence of sudden rapid eye movement (REM) sleep, is associated with a loss of orexin neurones. Our study investigated the effects of orexins on sleep–wake patterns in a novel transgenic mouse line overexpressing the human prepro-orexin (hPPO) gene under the control of its endogenous promoter.

Methods:  Orexin overexpression was investigated by PCR, Southern and Western blotting as well as immunohistochemistry. Polysomnographic recordings were performed for analyses of sleep–wake patterns and for electroencephalographic activity during 24 h baseline and during and after 6 h of sleep deprivation (SD).

Results:  Transgenic hPPO mice had increased expression of human prepro-orexin (hPPO) and orexin-A in the hypothalamus. Transgene expression decreased endogenous orexin-2 receptors but not orexin-1 receptors in the hypothalamus without affecting orexin receptor levels in the basal forebrain, cortex or hippocampus. Transgenic mice compared with their wild type littermates showed small but significant differences in the amount of waking and slow wave sleep, particularly during the light–dark transition periods, in addition to a slight reduction in REM sleep during baseline and during recovery sleep after SD.

Conclusion:  The hPPO-overexpressing mice show a small reduction in REM sleep, in addition to differences in vigilance state amounts in the light/dark transition periods, but overall the sleep–wake patterns of hPPO-overexpressing mice do not significantly differ from their wild type littermates.