Effects Of CCK-8on Acquisition Conditioned Place Aversion Induced By Morphine Withdrawal In Rats

Objective: Morphine is one of the most widely used addictive drugs.Opioid dependence is a chronic relapsing disorder in the brain characterizedby compulsive drug taking, inability to limit the intake of drugs, and theemergence of withdrawal syndrome after cessation of drug taking. Negativeaffection induced by drugs-withdraw is one of powerful reinforcers. Addictsoften compulsively use drug to escape the negative affection derived from thedrug withdrawal, which contributes so much to the relapse or sustained drugabuse. To date, we have known little biological mechanism underlying it.Cholecystokinin(CCK)as a neuropeptide widely distribute the central nervoussystem, with a variety of physiological functions. CCK-8is the most potentendogenous antiopioid peptides and regulating opioid dependence andtolerance process.Our previous observation shows that exogenous CCK-8and CCKreceptor antagonists could alleviate morphine withdrawal symptoms andblocked the acquisition and restrike of conditioned place preference (CPP). Wewant to establish a CPA model and to observe effects of endogenous orexogenous CCK-8on acquisition conditioned place aversion and withdrawalsymptoms induced by morphine withdrawal. That would provide the evidencefor CCK-8application in drug treatment in the future.Methods: To build the CPA modle Wistar rats (weighing200±10g) werereceived an injection of morphine from Day1to Day7(total injection6and ahalf days), twice a day (8AM;8PM and10mg/kg/time, subcutaneousinjection) for Chronic morphine dependent. In the Day6, the animals receivedan injection of naloxone (0.03mg/kg, i.p.) to produce withdrawal syndromes,then in the drug-paired compartment for40min. To investigate the effect ofendogenous CCK on acquisition conditioned place aversion,the animals werereceived an injection of CCK antagonists(10μg/rat, i.c.v.)15min before naloxone-induced withdraw. To investigate the effect of exogenous CCK-8onacquisition conditioned place aversion,the animals were received an injectionof different dose CCK-8(0.01,0.1,1μg/rat, i.c.v.)15min beforenaloxone-induced withdraw. There were more groups to investigate theantagonists' effects on exogenous CCK-8(0.1μg/rat) group, rats were injectedwith antagonists15min before receiving0.1ug CCK-8, to verify whether theantagonists were able to reverse the effect of0.1ug CCK-8on naloxone-induced CPA.The CPA scores were presented as Mean±value-standard deviation (S.D.),analyzed with ANOVA and Bonferroni's test using SPSS13.0statisticalprogram. Non-parametric statistics were performed for all behavioral patterns.A level of P<0.05was considered as statistical significance.Results: The animals can acquire significant conditioned place aversionby our model.①CCK2receptor antagonis(tLY-288,513; i.c.v.),but not CCK1receptor antagonist(L-364,718) was given15min before naloxone cansignificant decrease the CPA scores.②T he differentdose of CCK-8(0.01,0.1,1μg; i.c.v.) administered alone, induced neither CPA nor placepreference.③0.1μg and1μg of CCK-8administered15min before naloxoneblocked the acquisition of CPA.The0.01μg of CCK-8did not have the effect.④T he CCK1receptor antagonist(L-364,718),but not the CCK2receptorantagonist was able to reverse the effect of0.1μg CCK on naloxone-inducedCPA.⑤C CK-8(0.1,1μg)and CCK2receptor antagonist (L-364,718)ameliorated withdrawal symptoms, but the0.01μg and CCK1receptorantagonist had no effect.Conclusions:The work presented here identifies the endogenous CCK isnecessary for rats to acquire the CPA induced by morphine withdraw andhigh-dose exogenous CCK-8inhibit the acquisition of CPA. The difference effects of endogenous and exogenous CCK were participated by CCK2receptor and CCK1receptor, respectively.