Ackroff Karen, Sclafani Anthony
Department of Psychology, Brooklyn College and The Graduate Center, City University of New York, Brooklyn, NY 11210, USA.
Physiol Behav. 2006 Sep 30;89(2):250-60. doi: 10.1016/j.physbeh.2006.06.003. Epub 2006 Jul 18.
In prior studies rats preferred a flavor (CS+HF) paired with intragastric (IG) infusions of a high-fat diet to a flavor (CS+HC) paired with a high-carbohydrate diet, yet just the opposite preference was observed with pure-nutrient infusions. The present study tested the hypothesis that variations in nutrient density as well as composition influence flavor learning. Animals were trained (22 h/day) with IG infusion of milk-based high-fat and high-carbohydrate liquid diets paired with intakes of flavored, noncaloric CS+ solutions. A third flavor, the CS-, was paired with water infusion. Standard chow was available ad libitum. The rats preferred both CS+ flavors to the CS-, whether the infused diets were dense (HF and HC, 2.1 kcal/ml) or dilute (hf and hc, 0.5 kcal/ml), indicating that all diet infusions were reinforcing. They consumed the CS+hc and CS+hf equally in training, and preferred the CS+hc, showing that at low-energy density carbohydrate was more reinforcing than fat. In contrast, CS+HF intake exceeded that of CS+HC in training, and the rats preferred the CS+HF to the CS+HC. In further tests the rats preferred the CS+HF to the CS+hc, the CS+HF to the CS+hf, and the CS+HC to the CS+hc; i.e., when the diets differed in energy density the flavors associated with the more concentrated infusions were preferred. In the absence of influence by flavor cues from the nutrients themselves, rats' preferences for flavors associated with diets high in fat or carbohydrate are dependent on energy density. The differential satiating effects of fat and carbohydrate may contribute to these density-dependent preferences.
在先前的研究中，与高脂饮食胃内输注配对的一种味道（条件刺激 + 高脂）的大鼠比与高碳水化合物饮食配对的味道（条件刺激 + 高碳水）的大鼠更偏好前者，但在纯营养输注时观察到的偏好却相反。本研究检验了营养密度以及成分的变化会影响味道学习的假设。动物接受训练（每天22小时），胃内输注以牛奶为基础的高脂和高碳水化合物液体饮食，并与有味道的无热量条件刺激 + 溶液的摄入配对。第三种味道，即条件刺激 - ，与水输注配对。标准食物可随意获取。无论输注的饮食是浓缩的（高脂和高碳水，2.1千卡/毫升）还是稀释的（低脂和低碳水，0.5千卡/毫升），大鼠对两种条件刺激 + 味道都比条件刺激 - 味道更偏好，这表明所有饮食输注都具有强化作用。它们在训练中对条件刺激 + 低碳水和条件刺激 + 低脂的摄入量相同，且更偏好条件刺激 + 低碳水，这表明在低能量密度下，碳水化合物比脂肪更具强化作用。相反，在训练中条件刺激 + 高脂的摄入量超过了条件刺激 + 高碳水的摄入量，并且大鼠对条件刺激 + 高脂的偏好高于条件刺激 + 高碳水。在进一步的测试中，大鼠对条件刺激 + 高脂的偏好高于条件刺激 + 低碳水，对条件刺激 + 高脂的偏好高于条件刺激 + 低脂，对条件刺激 + 高碳水的偏好高于条件刺激 + 低碳水；也就是说，当饮食在能量密度上不同时，与更浓缩输注相关的味道更受偏好。在没有来自营养物质本身味道线索影响的情况下，大鼠对与高脂肪或高碳水化合物饮食相关味道的偏好取决于能量密度。脂肪和碳水化合物不同的饱腹感效应可能导致了这些与密度相关的偏好。
