Hypocretin/orexin prevents recovery from sickness

Area of Science:

• Neuroscience
• Sleep Research
• Immunology

Background:

• Sickness behavior encompasses lethargy, depression, and reduced concentration, often triggered by inflammation.
• Lipopolysaccharide (LPS) injection induces lethargy by inhibiting hypocretin signaling, crucial for maintaining vigilance.
• The hypocretin system's role in sleep-arousal balance during sickness requires further investigation.

Purpose of the Study:

• To investigate the impact of hypocretin neuron ablation on sleep-wake activity during LPS-induced sickness behavior.
• To compare the recovery of physical activity in mice with and without hypocretin neurons following LPS administration.

Main Methods:

• Utilized hypocretin-ataxin-3 transgenic mice with ablated hypocretin neurons and age/gender-matched wild-type littermates.
• Administered LPS at Zeitgeber time 8.0 and monitored sleep-wake activity and physical activity recovery.

Main Results:

• LPS injection increased non-rapid eye movement (REM) sleep in wild-type mice.
• Hypocretin-deficient mice exhibited a further increase in non-REM sleep and a marked reduction in awakening.
• While wild-type mice showed incomplete physical activity recovery, ataxin-3 transgenic mice recovered fully.

Conclusions:

• Absence of hypocretin neurons may promote deeper resting and faster recovery from sickness behavior.
• The hypocretin system plays a significant role in modulating sleep and arousal responses to inflammatory stimuli.