| Objective: Drug dependence is a chronic, relapsing disease, characterized by compulsive drug craving and use and by neurochemical and molecular changes in the brain. In our country the drug of abuse is opioid.Two concepts contribute to opioid dependence: physical dependence,manifested by a withdrawal (abstinence) syndrome produced by abrupt cessation of opioid, and psychologic dependence, accompanied by feelings of satisfaction and a desire to repeat the drug experience or to avoid the discontent of not having it. Endogenous opioid, opioid receptor and adaptive changes of signal transudations are involved in opioid dependence. CCK is discovered initially in the gut as a gastrointestinal hormone with the function of contracting gallbladder and mediating pancreatic secretion, and subsequently localized in the central and peripheral nervous system as aneurotransmitter or neuromodulator. CCK-8 is the strongest endogenous anti-opioid substance. Previous studies indicated that CCK-8 participated in the chronic dependence of morphine,but the mechanisms are remain unknown. To explore the possible function of CCK-8, this study observed the changes of CCK-8 expression of prefrontal cortex,striatum and hippocampus in morphine dependent and withdrawal rats.Methods: 36 healthy Wistar rats, male, weighting from 180g to 200g, were randomly divided into three groups: NS control group (NS group), morphine dependent group (MOR group) and naloxone precipitated withdrawal group (NAL group).Five incremental dose (10mg·kg-1, 20mg·kg-1, 30mg·kg- 1,40mg·kg - 1, 50mg·kg - 1) of morphine was injected subcutaneously to establish the physical dependent model in rats. Withdrawal syndromes was induced by intraperitoneal injection of naloxone (5mg·kg-1). The animal model was evaluated by observing the naloxone-precipitated withdrawal syndromes. Rats were killed to isolate prefrontal cortex, striatum and hippocampus 1h after naloxone precipitation. CCK-8 mRNA expression was determined by reverse transcription polymerase chain reaction(RT-PCR). CCK-8 protein expression was determined by immunohistochemica(lIHC)method. The results were analyzed with SPSS 11.5 statistics software, and a level of P<0.05 was considered statistically significant.Results:1. The establishment of morphine dependent model in rats. The body weight loss of NS group and MOR group was 1.85±0.62g and 2.63±0.8g , respectively. The body weight loss in NAL group (13.67±2.5g) were remarkably increased compared with MOR group (P<0.01). There was no jumping in the NS group and MOR group, while the number of jumping of naloxone precipitated withdrawal rats (33.7±3.99) was obviously increased compared with MOR group (P<0.01). After naloxone precipitation, the morphine dependent rats immediately had wet dog shaking, escape attempt, teeth chatting, drooling, diarrhea and body wrenching. The score in NAL group was 32.7±3.62 (compared with MOR group P<0.01), the scores of NS group and MOR group were zero.2. CCK-8 mRNA expression of prefrontal cortex, striatum and hippocampus in morphine dependent and withdrawal rats. CCK-8 mRNA expression of striatum in MOR group (0.609±0.030) was higher than in NS group (0.458±0.062) (P<0.01), while it decreased noticeably in NAL group (0.437±0.059), compared with MOR group(P<0.01), no difference between NAL group and NS group (P>0.05). There was no change of CCK-8 mRNA expression in prefrontal cortex and hippocampus in different groups(P>0.05).3. CCK-8 protein expression of prefrontal cortex, striatum and hippocampus in morphine dependent and withdrawal rats. CCK-8 protein expression of striatum in MOR group (1.300±0.067) was higher than in NS group (0.956±0.058) (P<0.01), while it decreased noticeably in NAL group (0.956±0.084), compared with MOR group (P<0.01),. no difference between NAL group and NS group (P>0.05). There was no change of CCK-8 protein expression in prefrontal cortex and hippocampus in different groups (P>0.05). Conclusion:1. CCK-8 mRNA and protein expression increased in striatum in chronic morphine dependent rats, naloxone could reverse this effect.2. There was no change of CCK-8 mRNA and protein expression in prefrontal cortex and hippocampus in morphine dependent and withdrawal rats. |
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