Hatos Center for Neuropharmacology, Department of Psychiatry and Biobehavioral Sciences, Semel Institute for Neuroscience and Human Behavior, University of California, 675 Charles E Young Dr. South, MRL #2762, Los Angeles, CA 90095, USA; Department of Psychology, University of California, Los Angeles, CA, USA.
Hatos Center for Neuropharmacology, Department of Psychiatry and Biobehavioral Sciences, Semel Institute for Neuroscience and Human Behavior, University of California, 675 Charles E Young Dr. South, MRL #2762, Los Angeles, CA 90095, USA.
Appetite. 2018 Apr 1;123:135-145. doi: 10.1016/j.appet.2017.12.009. Epub 2017 Dec 14.
Like drug addiction, cues associated with palatable foods can trigger food-seeking, even when sated. However, whether susceptibility to the motivating influence of food-related cues is a predisposing factor in overeating or a consequence of poor diet is difficult to determine in humans. Using a rodent model, we explored whether a highly palatable 'junk food' diet impacts responses to reward-paired cues in a Pavlovian-to-instrumental transfer test, using sweetened condensed milk (SCM) as the reward. The hedonic impact of SCM consumption was also assessed by analyzing licking microstructure.
To probe the effects of pattern and duration of junk food exposure, we provided rats with either regular chow ad libitum (controls) or chow plus access to junk food for either 2 or 24 h per day for 1, 3, or 6 weeks. We also examined how individual susceptibility to weight gain related to these measures.
Rats provided 24 h access to the junk food diet were insensitive to the motivational effects of a SCM-paired cue when tested sated even though their hedonic experience upon reward consumption was similar to controls. In contrast, rats provided restricted, 2 h access to junk food exhibited a cue generalization phenotype under sated conditions, lever-pressing with increased vigor in response to both a SCM-paired cue, and a cue not previously paired with reward. Hedonic response was also significantly higher in these animals relative to controls.
These data demonstrate that the pattern of junk food exposure differentially alters the hedonic impact of palatable foods and susceptibility to the motivating influence of cues in the environment to promote food-seeking actions when sated, which may be consequential for understanding overeating and obesity.
与美味食物相关的线索可以引发觅食行为，即使在已经饱食的情况下也是如此。然而，对于与食物相关的线索的易感性是导致过量进食的一个潜在因素，还是不良饮食的结果，这在人类中很难确定。本研究使用一种啮齿动物模型，探讨了高可口性“垃圾食品”饮食是否会影响到在条件性食物线索到工具性条件反射转移测试中对奖赏相关线索的反应，其中甜味炼乳（SCM）被用作奖赏。通过分析舔舐的微观结构，我们还评估了 SCM 消耗的享乐影响。
为了探究垃圾食品暴露模式和持续时间的影响，我们给予大鼠自由摄取普通食物（对照组）或普通食物加每日 2 或 24 小时的垃圾食品摄入，持续 1、3 或 6 周。我们还检查了个体对体重增加的易感性与这些措施的关系。
即使在吃饱的情况下，给予大鼠 24 小时的垃圾食品摄入，它们对 SCM 配对线索的动机效应不敏感，尽管它们在奖赏消费时的享乐体验与对照组相似。相比之下，给予大鼠限制的 2 小时垃圾食品摄入，在吃饱的条件下表现出线索泛化表型，在响应 SCM 配对线索和之前未与奖赏配对的线索时，杠杆按压的力度增加。这些动物的享乐反应也明显高于对照组。
这些数据表明，垃圾食品暴露的模式会改变可口食物的享乐影响，并改变对环境线索的动机影响的易感性，从而促进在吃饱的情况下觅食行为的发生，这可能对理解过量进食和肥胖具有重要意义。
