Hypocretin and GABA Interact in the Pontine Reticular Formation to Increase Wakefulness

Study Objectives: Hypocretin-1/orexin A administered directly into the oral part of rat pontine reticular formation (PnO) causes an increase in wakefulness and extracellular gamma-aminobutyric acid (GABA) levels. The receptors in the PnO that mediate these effects have not been identified. Therefore, this study tested the hypothesis that the increase in wakefulness caused by administration of hypocretin-1 into the PnO occurs via activation of GABA(A) receptors and hypocretin receptors. Design: Within/between subjects. Setting: University of Michigan. Patients or Participants: Twenty-three adult male Crl:CD*(SD) (Sprague Dawley) rats. Interventions: Microinjection of hypocretin-1, bicuculline (GABA(A) receptor antagonist), SB-334867 (hypocretin receptor-1 antagonist), and Ringer solution (vehicle control) into the PnO. Measurements and Results: Hypocretin-1 caused a significant concentration-dependent increase in wakefulness and decrease in rapid eye movement (REM) sleep and non-REM (NREM) sleep. Coadministration of SB-334867 and hypocretin-1 blocked the hypocretin-1 induced increase in wakefulness and decrease in both the NREM and REM phases of sleep. Coadministration of bicuculline and hypocretin-1 blocked the hypocretin-1 induced increase in wakefulness and decrease in NREM sleep caused by hypocretin-1. Conclusion: The increase in wakefulness caused by administering hypocretin-1 to the PnO is mediated by hypocretin receptors and GABA(A) receptors in the PnO. These results show for the first time that hypocretinergic and GABAergic transmission in the PnO can interact to promote wakefulness.