Anterior Insular-nucleus Accumbens Pathway Controls Refeeding-induced Analgesia under Chronic Inflammatory Pain Condition

Abstract

Feeding behaviors are closely associated with chronic pain in adult rodents. Our recent study revealed that 2 h refeeding after 24 h fasting (i.e., refeeding) attenuates pain behavior under chronic inflammatory pain conditions. However, while brain circuits mediating fasting-induced analgesia have been identified, the underlying mechanism of refeeding-induced analgesia is still elusive. Herein, we demonstrate that the neural activities in the nucleus accumbens shell (NAcS) and anterior insular cortex (aIC) were increased in a modified Complete Freund's Adjuvant (CFA)-induced chronic inflammatory pain condition, which was reversed by refeeding. We also found that refeeding reduced the enhanced excitability of aIC^CaMKII-NAcS^D2R projecting neurons in this CFA model. Besides, chemogenetic inhibition of aIC^CaMKII-NAcS^D2R neural circuit suppressed chronic pain behavior while activation of this circuit reversed refeeding-induced analgesia. Thus, the present study suggests that aIC^CaMKII-NAcS^D2R neural circuit mediates refeeding-induced analgesia, thereby serving as a potential therapeutic target to manage chronic pain.

Keywords: chronic inflammatory pain; dopamine; insular cortex; nucleus accumbens; refeeding.