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Identification of Orexin and Endocannabinoid Receptors in Adult Zebrafish Using Immunoperoxidase and Immunofluorescence Methods
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Orexin directly excites orexin neurons through orexin 2 receptor

Akihiro Yamanaka1, Sawako Tabuchi, Tomomi Tsunematsu

  • 1Section of Cell Signaling, Okazaki Institute for Integrative Bioscience, National Institute of Natural Sciences, Okazaki 444-8787, Japan. yamank@nips.ac.jp

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience
|September 24, 2010
PubMed

Insights

Orexin neurons directly activate themselves via the orexin 2 receptor (OX2R), forming a positive-feedback circuit. This mechanism is crucial for maintaining arousal and wakefulness.

Area of Science:

  • Neuroscience
  • Sleep Research
  • Neuroendocrinology

Background:

  • Orexin neurons (hypocretin neurons) are vital for regulating sleep-wake cycles and maintaining arousal.
  • The precise mechanisms of orexin neuron activation and their role in arousal are not fully understood.

Purpose of the Study:

  • To investigate the direct and indirect activation pathways of orexin neurons.
  • To determine the specific orexin receptor involved in orexin neuron activation.
  • To elucidate the role of orexin neuron network activity in arousal maintenance.

Main Methods:

  • Electrophysiological recordings (depolarization, inward currents) in orexin neurons.
  • Pharmacological manipulations using TTX, AP-5, and CNQX.
  • Analysis of orexin receptor 1 (OX1R) and orexin receptor 2 (OX2R) knockout mice.
  • Immunoelectron microscopy to identify synaptic contacts between orexin neurons.

Main Results:

  • Orexin B directly activates orexin neurons, evidenced by inward currents even in the presence of synaptic blockers.
  • Orexin B-induced depolarization is primarily mediated by the orexin 2 receptor (OX2R), as it is abolished in OX2R knockout mice.
  • Immunoelectron microscopy revealed direct synaptic connections between orexin neurons, resembling glutamatergic synapses.

Conclusions:

  • Orexin neurons form a positive-feedback circuit, involving both direct and indirect pathways, to maintain high activity levels.
  • Activation of orexin neurons via OX2R plays a critical role in the maintenance of arousal.
  • This positive-feedback loop contributes to sustained wakefulness.

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