Figure 1.

A schematic of the experimental timeline that shows the type and order of interventions in the 27-day protocol used for mice that had received an n-3 PUFA-enriched or control diet for 8 weeks prior to the start of the protocol. Following the implant of the jugular catheter (IVSA surgery), mice underwent daily sessions where, after acquisition of remifentanil self-administration, oxycodone or saline infusion was self-administered for 10 days (the maintenance phase), followed by 5 days of extinction (extinction 1, 1E), in which no further drug was delivered but the same environment and reward-associated cues were presented. This was followed by a 2-day period of reinstatement (reinstatement) in which oxycodone was administered at the same dose and cues as used during maintenance. Thereafter the mice underwent a second extinction (extinction 2, 2E) over the following 5 days under the same conditions as during 1E. Fecal boli were collected before the surgery and at each change in this protocol as indicated. The light–dark (LD) test was conducted before the surgery and on the second day of 2E. Brain tissue was collected at the end of the protocol for microglial analysis using immunohistochemistry (IHC).