A critical role of the central amygdala nucleus in relapse to methamphetamine seeking after voluntary abstinence

Rationale and Objective: We recently developed a rat model of relapse to methamphetamine seeking after voluntary abstinence. The mechanisms underlying this form of relapse are unknown. Here, we studied the role of central amygdala (CeA) and its forebrain projections in relapse after voluntary abstinence. Methods: We trained rats to self-administer palatable food (6 d, 2-h/d) and intravenous methamphetamine (15 d, 2-h/d). We then assessed methamphetamine seeking in extinction tests after 14 voluntary abstinence days (achieved via a discrete choice procedure between methamphetamine and palatable food). Results: Relapse to methamphetamine seeking after voluntary abstinence was associated with increased expression of the activity marker Fos in CeA but not basolateral amygdala (BLA). Systemic injections of SCH39166 (D1-family receptor antagonist [20 µg/kg]) decreased relapse to methamphtemaine seeking and Fos expression in CeA. Using RNAscope in-situ hybridization we found that the majority of Fos positive neurons co-labelled with dopamine Drd1, but not Drd2 in CeA. CeA injections of SCH39166 (0.5-1.0 µg/side) decreased relapse to methamphetamine seeking after voluntary abstinence; CeA injection of raclopride (D2-family receptor antagonist [1.0 µg/side]) or BLA injections of SCH39166 (1.0 µg/side) had no effect. Double-labeling analysis of Fos with the retrograde tracer cholera toxin subunit-B (CTb, injected into CeA) showed that relapse after voluntary abstinence was associated with selective activation of ventral anterior insula (AIV) neurons projecting to CeA.Conclusions: Results demonstrate a critical role of CeA Drd1 in relapse to methamphetamine seeking after voluntary abstinence and further suggest a role of AIV→CeA projection in this form of relapse