Construction And Application Of A Video-Computer Assisted Conditioned Place Preference ExperimentalSystem In Mice

1 ObjectiveAddiction continues to exact enormous human and financial costs on society. Psychological dependence and relapse are the most difficult and important topics in this research area. There are mainly three behavioral pharmacological experiments, including self-administration, drug discrimination and conditioned place preference (CPP), frequently used in studies on psychological dependence. The CPP procedure offers some advantages when compared with the other two experiments, such as the simple apparatus, the short experiment period, the results devoid of direct drug and operant style effects, capability of measuring both rewarding and aversive effects of drugs and so on.Polysubstance abuse is being the major abuse pattern, in which opioids in combination with ethanol is popular. Polysubstance abuse is more difficult to diagnose and treat and is more dangerous than sole drug abuse. An improved understanding of the interaction between ethanol and opioids will lead to more effective treatments for the polysubstance addicts There are few reports available on the effects of ethanol on opioids-mduced psychological dependence.The objective of the present study was to construct a video-computer assisted conditioned place preference experimental system in mice and set up morphine-induced conditioned place preference in mice. On this basis, we investigated the effects of ethanol on morphine-induced CPP.2 Materials and Methods2.1 System constructionThe video-computer assisted conditioned place preference experimental system in mice is composed of several shuttle boxes (lxw*h= 30*15x15cm) which were divided into a gray and a black compartments of equal size, a sound-proof container (lx\vxh= 60 *60* 120cm), video apparatus and a computer.The video was analyzed using MiceTrack software designed by our research group.2.2 AnimalsMale adult 1CR mice.2.3 MethodsThe place-preference conditioning schedule consisted of two phases1) Conditioning phase, during which mice were treated for 8 consecutive days with alternate injection of morphine-HCl (lOmg per kg body weight in a volume of 10ml per kg body weight, i.p.) or saline. Conditioning sessions were carried out over a 50min period immediately after injection. Mice were confined to the gray compartment after drug injection and to the black compartment after saline injection Saline conditioning was conducted before confinement to either compartment2) Testing Phase, during which video was captured and tests of conditioning were performed as follows: the partition separating the two compartments was changed to be 7cm above the floor allowing free access for mice to each compartment for 15min, 24h after the final conditioning session.To investigate the chronic effects of ethanol on morphine-induced CPP, ethanol was administered in drinking water at increasing concentrations of 0-10%V/V for 7 days, before conditioning phase. Tests of mice movement were conducted 24h after the final conditioning session and 10 days after last tests to observe CPP formation and extinction respectively.2.4 Data analysisThe sojourn time in the gray compartment (TG), the total distance the mice moved (TD), and the Crossing Times between the two compartments were obtained Statistical analysis methods included one-way ANOVA, multi-way ANOVA, Wilcoxon signed rank test, Kruskal-Wallis test and Kendall's T-b bwanatecorrelations test. 3 Results3.1 The characteristics of the SystemMice moved freely in the shuttle box in a quiet, dim environment. Data were objective obtained by analyzing the video using MiceTrack software which is flexible and can analyze several parameters simultaneously.32 The chronic effects of Ethanol on Morphine-induced CPP and locomotor activity of mice 3.2.1 The formation and extinction of CPPThe mean TG 24h after the final conditioning session(TGl) of Mice free of ethanol but treated with morphine( 1 Omg/kg, i.p.) was significantly longer than controKtheir deviation is...