Mild Transient Hypercapnia as a Novel Fear Conditioning Stimulus Allowing Re-Exposure during Sleep

Area of Science:

• Neuroscience
• Sleep Science
• Behavioral Science

Background:

• Sleep is implicated in traumatic memory consolidation.
• Sleep disorder treatment may alleviate PTSD symptoms.
• Rodent fear conditioning models investigate fear and sleep relationships.

Purpose of the Study:

• To develop and validate a novel conditioning stimulus (CS) for fear studies during sleep.
• To investigate the physiological responses to a new CS.
• To establish a model for exploring sleep-dependent fear mechanisms.

Main Methods:

• Mild transient hypercapnia (mtHC) and tone were used as CSs paired with footshock in male FVB/J mice.
• Physiological responses (heart rate, plasma epinephrine) were measured.
• Animals were re-exposed to the CS during sleep in a proof-of-principle experiment.

Main Results:

• Both tone and mtHC predicted footshock, eliciting fear responses.
• mtHC induced mild hypertension, conditioned bradycardia, and a smaller epinephrine increase compared to tone.
• Fear conditioning did not affect the overall 24-hour sleep-wake profile.

Conclusions:

• Mild transient hypercapnia (mtHC) is an effective, safe, and sleep-compatible conditioning stimulus.
• This novel model facilitates research into sleep's role in maladaptive fear and PTSD.
• Future studies can explore sleep-dependent mechanisms of fear responses.