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. Author manuscript; available in PMC: 2020 Mar 4.
Published in final edited form as: Anesth Analg. 2019 Jan;128(1):161–167. doi: 10.1213/ANE.0000000000003345

Figure 3.

Figure 3.

Morphine pretreatment exacerbates postoperative pain. Rats were pretreated with morphine according to 2 different schedules: morphine administration from days −14 to −8 (5 mg/kg twice a day), followed by vehicle twice daily from days −7 to −1 (“morphine −14”); vehicle administration twice daily from days −14 to −8 followed by morphine from days −7 to −1 (5 mg/kg twice a day; “morphine −7”). All rats then received laparotomy. Von Frey thresholds were determined before morphine/vehicle (day −14), and across a timecourse after surgery. Data are presented as mean ± standard error of the mean; n = 6/group; **P < .01, ***P < .001.