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. Author manuscript; available in PMC: 2021 May 18.
Published in final edited form as: Addict Biol. 2020 Oct 19;26(3):e12973. doi: 10.1111/adb.12973

FIGURE 6.

FIGURE 6

Effects of previous morphine experience and withdrawal on motivation to SA oxycodone in the progressive ratio (PR) test. Data are the average (+SEM) of 2d of 2 h/days PR testing. A, Total number of infusions, B, active lever presses, and C, break point, which is the last ratio completed to earn a reinforcer. N = 7–12 rats/group. *p < 0.05 compared to Veh of the same sex. D, Pearson r correlation was conducted on the sum of infusions on maintenance days 8–10 compared to the PR break point. A significant positive correlation was found (r = 0.758) such that the more oxycodone self-administered at the end of the maintenance phase of SA, the higher the PR break point. Data from females previously exposed to morphine and withdrawal are represented with grey circles, whereas all other groups are represented with dark squares. Linear regression analysis was also conducted: R2 = 0.574, p < 0.001