The amygdala differentially regulates defensive behaviors evoked by CO₂

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Panic Disorder Research

Background:

• Carbon dioxide (CO2) inhalation is a known panicogen in humans, particularly in those with panic disorder.
• The amygdala's role in CO2-induced fear and panic is debated, with human studies suggesting it may oppose these responses, contrary to rodent models.

Purpose of the Study:

• To investigate the role of the amygdala in CO2-induced behavioral responses in mice.
• To clarify the amygdala's function in panic-related behaviors by creating lesions analogous to those in human studies.

Main Methods:

• Mice underwent amygdala lesions or sham procedures.
• Behavioral responses (freezing, jumping) to varying CO2 concentrations (10% and 20%) were assessed.
• Responses to predator odor and auditory stimuli were also evaluated.
• The effect of co-lesioning the dorsal periaqueductal gray was examined.

Main Results:

• Amygdala-lesioned mice showed reduced freezing but increased jumping behavior in response to 10% CO2 compared to controls.
• Jumping, observed in controls at 20% CO2, suggests it's a concentration-dependent response.
• Amygdala lesions specifically affected CO2 responses, not reactions to predator odor or auditory stimuli.
• Co-lesioning the dorsal periaqueductal gray abolished CO2-induced jumping in amygdala-lesioned mice.

Conclusions:

• The amygdala appears to have a dual role: promoting CO2-induced freezing and inhibiting CO2-induced jumping.
• These findings may help explain exaggerated CO2 responses in humans with amygdala damage or lesions.
• The dorsal periaqueductal gray is critical for mediating CO2-induced jumping, especially when the amygdala's inhibitory influence is removed.