Puhl Matthew D, Blum Joshua S, Acosta-Torres Stefany, Grigson Patricia S
Department of Neural and Behavioral Sciences, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
Behav Pharmacol. 2012 Feb;23(1):43-53. doi: 10.1097/FBP.0b013e32834eb060.
One of the most menacing consequences of drug addiction is the devaluation of natural rewards (e.g. food, sex, work, money, caring for one's offspring). However, evidence also suggests that natural rewards, such as an enriched environment, can devalue drugs of abuse. Thus, this study used a rodent model to test whether exposure to an enriched environment could protect adult rats from acquiring cocaine self-administration and from the resultant drug-induced devaluation of a natural saccharin reward cue. Adult male Sprague-Dawley rats were implanted with intravenous jugular catheters. Rats were then separated into two housing conditions: an enriched condition, including social companions(four/cage) and novel objects (e.g. balls, polyethylene tubes, paper, etc.), and a nonenriched condition where the rats were singly housed with no novel objects. During testing, the rats were given 5-min access to 0.15% saccharin, followed by 1 h to self-administer saline or cocaine (0.167 mg/infusion) on fixed ratio and progressive ratio schedules of reinforcement. The results showed that rats that were singly housed in the nonenriched environment fell into two groups: low drug-takers (n=34) and high drug-takers (n=12). In comparison, only one out of the 22 rats housed in the enriched environment was a high drug-taker. Thus, all rats in the enriched environment, except one, behaved like low drug-takers under the nonenriched condition. As such, these rats self-administered almost no drug on either the fixed ratio or the progressive ratio schedule of reinforcement and were extremely slow to self-administer their first cocaine infusion. Interestingly, despite their very low levels of drug self-administration, low-drug-taking rats housed in the enriched environment continued to avoid intake of the drug-associated saccharin cue. Taken together, these data suggest that the enriched environment itself served as a salient natural reward that reduced cocaine seeking and cocaine taking, but had little impact on avoidance of the cocaine-paired taste cue. The protective effects of the enriched environment were robust and, as such, have important implications for the methods used in the study of drug addiction in animal models and for the prevention, and possibly the treatment, of the disease in adult humans.
药物成瘾最具威胁性的后果之一是自然奖赏（如食物、性、工作、金钱、照顾后代）的贬值。然而，有证据表明，诸如丰富环境等自然奖赏也会使滥用药物贬值。因此，本研究使用啮齿动物模型来测试暴露于丰富环境是否能保护成年大鼠不染上可卡因自我给药行为，以及免受药物导致的自然糖精奖赏线索贬值的影响。成年雄性斯普拉格 - 道利大鼠植入颈静脉导管。然后将大鼠分为两种饲养条件：丰富环境组，包括社交同伴（每笼4只）和新奇物品（如球、聚乙烯管、纸等）；非丰富环境组，大鼠单独饲养且没有新奇物品。在测试期间，给予大鼠5分钟时间接触0.15%的糖精，随后1小时让它们在固定比率和累进比率强化程序下自我注射生理盐水或可卡因（每次注射0.167毫克）。结果显示，单独饲养在非丰富环境中的大鼠分为两组：低药物摄取者（n = 34）和高药物摄取者（n = 12）。相比之下，饲养在丰富环境中的22只大鼠中只有1只是高药物摄取者。因此，丰富环境中的所有大鼠（除1只外）在非丰富条件下的行为都像低药物摄取者。也就是说，这些大鼠在固定比率或累进比率强化程序下几乎不自我给药，并且首次自我注射可卡因的速度极慢。有趣的是，尽管饲养在丰富环境中的低药物摄取大鼠药物自我给药水平极低，但它们仍继续避免摄取与药物相关的糖精线索。综上所述，这些数据表明丰富环境本身作为一种显著的自然奖赏，减少了对可卡因的寻求和摄取，但对避免与可卡因配对的味觉线索影响不大。丰富环境的保护作用很强，因此对动物模型中药物成瘾研究方法以及成人该疾病的预防乃至治疗都具有重要意义。
