CCI does not reduce the access frequency, but shows transient reduction of total time accessed per observation session. A and B show the summary number of access and cumulative duration of access per 30 m observation session for a cohort of 5 rats, starting with conditioning for 5 days (dashed line) and after the CCI surgery (solid line). C. Weight distribution data (Left–Right) for CCI (solid square, n = 5) and sham surgery (open square, n = 4) assessed on post-CCI days 1–5. A two-way ANOVA demonstrated significant effects of both group (sham vs. CCI) and time treatments. Post-hoc comparison of the means with Sidk–Bonferroni correction for multiple t-tests showed statistically significant difference between the sham and CCI groups for all time points (**P < 0.01, ***P < 0.001, ****P < 0.0001) with exception of post-operation day 3. D. The weight distribution bias reported as Left–Right over a period of 21 days for CCI animals (n = 6 for each group). The measurements were obtained at the indicated time points after CCI (open circles). The morphine cohort (solid squares) received 2 mg/kg i.p. 30 min prior to the weight distribution assessment. A two-way ANOVA demonstrated significant effects of both group (morphine vs. vehicle) and time treatments, and post-hoc comparison of the means with Sidk–Bonferroni correction for multiple t-tests showed statistically significant difference between the morphine and vehicle groups for all time points (***P < 0.001, ****P < 0.0001).