Simpson Gregory R, Riley Anthony L
Department of Psychology, University of Miami, 5665 Ponce de Leon Blvd Coral Gables, FL, 33146-0751, USA.
Pharmacol Biochem Behav. 2005 Mar;80(3):471-9. doi: 10.1016/j.pbb.2005.01.003.
Repeated morphine preexposure has been reported to enhance measures of morphine reward (conditioned place preference; CPP) and attenuate measures of morphine aversion (conditioned taste aversion; CTA). These effects are generally independently assessed, limiting the ability to determine if the enhancing and attenuating effects of morphine exposure are mediated by a common factor. To assess any potential relationship between these two effects, the present study examined the impact of morphine preexposure on these motivational properties of morphine using a combined CTA/CPP procedure in which the same animals receive concurrent taste and place conditioning. Specifically, male Sprague-Dawley rats were preexposed to morphine [5 mg/kg; subcutaneously (sc)] or equivolume drug vehicle. Following preexposure, animals were given saccharin to drink and injected with morphine sulfate (1 or 5 mg/kg sc) or drug vehicle (CTA). Immediately thereafter, they were placed on one side of a two-compartment chamber (CPP). On the next day, they were given water followed by injections of the drug's vehicle and then placed in the other compartment. There were four such conditioning cycles after each of which a CTA and CPP test were given. While preexposure to morphine attenuated morphine-induced CTAs, morphine-induced CPPs were enhanced within the same animals. These effects of morphine preexposure were dose- and time-dependent and parallel. These data indicate that the attenuating and sensitizing effects of morphine preexposure on taste aversions and place preferences, respectively, could be mediated by a common mechanism, although other possibilities for these effects of morphine preexposure remain.
据报道，重复给予吗啡预处理可增强吗啡奖赏效应（条件性位置偏爱；CPP）的测量指标，并减弱吗啡厌恶效应（条件性味觉厌恶；CTA）的测量指标。这些效应通常是独立评估的，这限制了确定吗啡暴露的增强和减弱效应是否由共同因素介导的能力。为了评估这两种效应之间的任何潜在关系，本研究使用联合CTA/CPP程序，在同一动物同时接受味觉和位置条件反射的情况下，研究了吗啡预处理对吗啡这些动机特性的影响。具体而言，将雄性Sprague-Dawley大鼠预先暴露于吗啡[5mg/kg；皮下注射（sc）]或等体积的药物载体。预处理后，给动物饮用糖精，并注射硫酸吗啡（1或5mg/kg sc）或药物载体（CTA）。此后立即将它们置于两室箱的一侧（CPP）。第二天，给它们水，然后注射药物载体，然后将它们置于另一室。共有四个这样的条件反射周期，每个周期后进行一次CTA和CPP测试。虽然预先暴露于吗啡可减弱吗啡诱导的CTA，但在同一动物中吗啡诱导的CPP增强。吗啡预处理的这些效应是剂量和时间依赖性的且呈平行关系。这些数据表明，吗啡预处理对味觉厌恶和位置偏爱的减弱和敏感化效应可能由共同机制介导，尽管吗啡预处理的这些效应还有其他可能性。
