General Anesthesia-activated Neurons in the Central Amygdala Mediate Antinociception: Distinct Roles in Acute versus Chronic Phases of Nerve Injury.

Summary

Using TRAP2 labeling, electrophysiology, and chemogenetics in mice, the study shows that general anesthesia-activated GABAergic neurons in the central amygdala increase nociceptive thresholds in physiological and subacute nerve injury phases but have reduced antinociception in chronic phases. Chronic spared nerve injury is associated with increased excitability of Fos-negative CeA neurons and downregulation of KCC2, implicating chloride homeostasis in pain chronification.

Key Findings

• Isoflurane robustly induced Fos in GABAergic CeA neurons; TRAP2-labeled CeAGA neurons showed higher excitability and distinct action potential patterns.
• Chemogenetic activation of CeAGA neurons increased nociceptive thresholds in naive and 2-week post-SNI mice, but antinociception was modest at 8 weeks.
• In chronic SNI, Fos-negative CeA neurons (not CeAGA) became hyperexcitable, associated with downregulation of KCC2 in the CeA.

Clinical Implications

Identifies CeA circuitry and KCC2-mediated chloride regulation as potential targets for perioperative analgesia and prevention of pain chronification after nerve injury.

Limitations

• Preclinical mouse model limits direct translatability to humans
• Causality of KCC2 dysregulation was inferred but not directly manipulated in vivo

Future Directions

Test KCC2-restoring interventions and CeA circuit modulation in chronic pain models and evaluate translational biomarkers for human studies.