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. 2023 Feb 14;17:1094241. doi: 10.3389/fnins.2023.1094241

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Copyright © 2023 Crawford, Taylor, Park, Rios, Bunch, Greenwood, Lopez Sanchez and Gonzales.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Mean (±SEM) active nose pokes, active nose pokes during the stimulus presentation, and inactive nose pokes in late adolescent male and female rats (n = 6–8/sex) during the seven fentanyl-only acquisition test days. Rats were pre-treated with fentanyl (10 or 100 μg/kg) or saline from PD 4 to PD 9 and started sucrose training on PD 40. After reaching the criterion for sucrose-rewarded nose pokes, rats underwent a four-phase sucrose fade out/fentanyl fade in procedure and then were assessed for 7 days for fentanyl-only reinforcement.