Calcium imaging of central amygdala activity after escalation of fentanyl self-administration

The central amygdala (CeA) is involved in opioid relapse-associated behaviors. This study determined if escalation of fentanyl intake as modeled by long-access (LgA) self-administration (SA) alters ex vivo neuronal activity in CeA in response to fentanyl during acute withdrawal and protracted abstinence. Adult male and female Sprague-Dawley rats were trained to self-administer fentanyl or saline across 7 daily 1-h short access (ShA) sessions, followed by 21 6-h long access (LgA) sessions. Following acute (17 h) or protracted (30 days) withdrawal, withdrawal signs were assessed and rats were euthanized for CeA calcium imaging in brain slices. Fentanyl rats demonstrated reduced basal frequency of activity after 30 days withdrawal, but not after 17 h withdrawal. Regardless of SA group, acute fentanyl application in slices reduced activity (frequency, duration, active cell number) of CeA neurons. In acute withdrawal, the magnitude to which acute fentanyl suppressed CeA neuronal activity was smaller in fentanyl SA rats, relative to saline SA controls. However, the magnitude of acute fentanyl effect on suppression of CeA activity was greater in fentanyl SA rats (vs. saline SA controls) after protracted abstinence.