10.3969/j.issn.1008-9691.2013.03.005

OBJECTIVESome animal models apply morphine in the drinking water to generate addiction, but related reports are not free of conflicting results. Accordingly, this study aimed to figure out if chronic consumption of morphine in the drinking water can induce morphine addiction in Wistar rats.

METHODSFor 3 weeks, the animals received a daily morphine dose of 35 mg/kg by offering a calculated volume of sugar water (5% sucrose) with morphine (0.1 mg/ml) to each rat; animals receiving just sugar water served as controls. Immediately after the treatment phase, the tail immersion test was used to check for morphine tolerance, and all animals were then kept on tap water for one week (withdrawal phase). Afterwards, all rats were allowed to choose their drinking source by offering two bottles, containing sugar water without and with morphine, simultaneously for two days (preference phase).

RESULTSWhile the chronic consumption of morphine led to a reduction in body weight and to morphine tolerance, the morphine-treated Wistar rats did not show any preference for the opiate-containing sugar water.

CONCLUSIONBody weight loss and tolerance do not reveal a condition of drug craving, and current animal models should be re-evaluated regarding their potential to establish morphine addicted animals.

Animals ; Body Weight ; drug effects ; Choice Behavior ; drug effects ; Disease Models, Animal ; Drug Tolerance ; Male ; Morphine ; administration & dosage ; Morphine Dependence ; Pain Measurement ; drug effects ; Rats ; Rats, Wistar ; Time Factors

Objective To investigate the genetic polymorphism of mec Ⅰ in the clinical isolates of methicillin-resistant Staphylococcus anreus(MRSA).Methods 40 isolates(MRSA)carrying mecA gene were selected randomly from the clinical isolates of Staphylococcus anreus from Jan,2005 to Aug,2006 in our hospital.The mec Ⅰ gene was detected by PCR followed with sequencing.Staphylococcal cassette chromosome mec(SCCmec)in MRSA were detected by multiplex-PCR.Agar dilution method was used for determining the MICs of oxacillin against MRSA.Results 35 of 40(87.5%)MRSA carried mec Ⅰ gene.All isolates carrying mec Ⅰ gene have mecI 202C→T substitution,which resulted in Gln at 68 aminophenol position replaced by stop condon.32 isolates carried single point mutation.3 isolates carried double-point mutation,including additonal A at 3 positon,A→C at 41 position and C→T at 142 position beside C→T at 202 position,respectively.Among 35 isolates carrying mec Ⅰ gene,there were 27 isolates of SCCmec Ⅲ, 7 isolates of SCCmec Ⅲ A and 1 isolate of SCCmec Ⅱ.Among 5 isolates with deletion of mec Ⅰ gene,there were 3 isolates of SCCmecⅣ,1 isolate of SCCmec Ⅰ and 1 isolate of non-known SCCmec tpye.The MICs of oxacillin were 256-512 ?g/ml,≥512 ?g/ml and 8-256 ?g/ml in 31 isolates with single point mutation at 202 position in mec Ⅰ gene,3 isolates with double-point mutation in mecI gene and 5 isolates with deletion of mec Ⅰ gene,respectively.1 isolate with single point mutation in mec Ⅰ gene had contrary result(MIC