Hayward M D, Low M J
The Vollum Institute, Oregon Health & Science University, Portland, OR 97201, USA.
Brain Res Bull. 2001 Dec;56(6):537-43. doi: 10.1016/s0361-9230(01)00626-8.
Mice are powerful models to investigate the genetic basis of food reward because many spontaneous obesity mutants exist and the murine genome is accessible to selectively targeted manipulations. Experiments in rats have shown that opioid receptor blockade reduces operant responding to food reinforcers. The present study investigated whether DBA/2J mice would display similar behavior in response to an opioid antagonist. Twelve male DBA/2J mice were trained to lever press for food reinforcers and subsequently randomized in a within subjects design for no injection, saline injection, or 10 mg/kg naloxone injection intraperitoneal (i.p.) 20 min before each daily trial under ad lib or food-deprived conditions. A significant main effect of injection occurred to reduce lever pressing by the mice. However, a greater pharmacological effect of naloxone occurred compared with saline on the operant responding only under the food-deprived conditions. Interestingly, the percentage of dispensed food pellets actually consumed was significantly reduced after naloxone injection compared with saline injection for either chow-based or sucrose pellets under ad lib or deprived feeding conditions. These data suggest that opioids specifically influence consumatory behavior in mice, but our findings on instrumental behavior were confounded by an independent inhibitory effect of an i.p. saline injection.
小鼠是研究食物奖赏遗传基础的有力模型，因为存在许多自发性肥胖突变体，并且鼠类基因组易于进行选择性靶向操作。在大鼠身上进行的实验表明，阿片受体阻断会降低对食物强化物的操作性反应。本研究调查了DBA/2J小鼠在阿片拮抗剂作用下是否会表现出类似行为。12只雄性DBA/2J小鼠被训练按压杠杆以获取食物强化物，随后在自由进食或食物剥夺条件下，每天试验前20分钟，按照受试者内设计随机分为不注射、注射生理盐水或腹腔注射10mg/kg纳洛酮三组。注射产生了显著的主效应，使小鼠的杠杆按压次数减少。然而，只有在食物剥夺条件下，纳洛酮对操作性反应的药理作用才比生理盐水更大。有趣的是，在自由进食或剥夺进食条件下，无论是基于食物的颗粒还是蔗糖颗粒，注射纳洛酮后实际消耗的分发食物颗粒百分比与注射生理盐水相比均显著降低。这些数据表明，阿片类物质特异性地影响小鼠的消费行为，但我们关于工具性行为的研究结果因腹腔注射生理盐水的独立抑制作用而混淆。
