Figure 2.

Effects of morphine on the induction of conditioned place preference. (A) Diagram outlining the behavioral procedures. (B) Tree shrews that received alternating injections of morphine and saline showed a significant preference for the morphine-paired chamber. (C) The vertical jump number of the morphine-conditioned tree shrews in the morphine-paired chamber significantly increased on the test day. (D) The amount of shuttles between the cage and nest box of morphine-conditioned tree shrews in the morphine-paired chamber had an increasing trend on the test day. (E) The amount of shuttles between the two chambers of morphine- and saline- conditioned tree shrews had no change. Blank and solid columns represent data from pre- and post-conditioning tests, respectively. * p < 0.05, pretest vs. test. The data are expressed as means ± SEM, and analyzed using two-way ANOVA followed by Bonferroni post hoc test, n = 5–6.