The clinical use of morphine to reduce pain is limited because of its drug tolerance, dependence and
addiction. In the present study, the tree shrews ( Tupaia belangeri chinensis
) developed morphine tolerance and chronic
morphine dependence by morphine injections with increasing doses (5, 10, 15, 20 mg/kg body weight for 7 days).
Meanwhile, the naloxone (1.25 mg/kg body weight)-induced conditioned place aversion (CPA) and the withdrawal
symptom were also found. The tree shrew model of chronic morphine dependence can be used to investigate the
withdrawal symptoms and to select potential withdrawal symptoms reducing drugs in the future.