Myers Kevin P, Ferris Jennifer, Sclafani Anthony
Department of Psychology, Bucknell University, Lewisburg, PA 17837, United States.
Physiol Behav. 2005 Mar 16;84(3):407-19. doi: 10.1016/j.physbeh.2005.01.001.
The purpose of these experiments was to determine if preweanling rats, like adults, are capable of learning to associate an arbitrary flavor with the postingestive effects of nutrients, and then demonstrate a preference for that flavor after weaning. In Experiment 1, preweanlings were trained daily from postnatal day (P) 16 through P19 with intraoral (IO) infusions of a grape or cherry flavor (CS+) mixed with 20% glucose (US), and the opposite flavor (CS-) mixed with 0.05% saccharin. After weaning, rats were given a 4-h two-bottle choice between the CS+ and CS- flavors both presented in 0.05% saccharin. Rats preferred the flavor previously paired with glucose. In Experiment 2 using similar methods, rats learned to prefer a flavor (CS+G) paired with a glucose US over a flavor (CS+S) paired with a sweeter but less nutritive sucrose US, indicating involvement of postingestive reinforcement. In Experiment 3 preweanling rats with IO and intragastric (IG) catheters were trained with a CS+ flavor paired with IG nutrient infusion, and a CS- flavor paired with no IG infusion. These rats showed no flavor preference 3 days after weaning, but did significantly prefer the CS+ flavor over the CS- flavor 10 days after weaning. Together these experiments demonstrate that neural mechanisms for flavor-nutrient associations are developed before weaning, allowing young rats to learn associations between arbitrary flavors and nutritive consequences. Thus nutrient conditioning may be one way that early experience (such as flavors from the maternal diet transmitted in milk) influences later dietary preferences.
这些实验的目的是确定断奶前的大鼠是否像成年大鼠一样，能够学会将一种任意的味道与营养物质摄入后的效应联系起来，并在断奶后表现出对该味道的偏好。在实验1中，从出生后第（P）16天到P19天，每天对断奶前的大鼠进行口腔内（IO）输注训练，将葡萄或樱桃味（条件刺激+，CS+）与20%葡萄糖（非条件刺激，US）混合，将相反的味道（条件刺激-，CS-）与0.05%糖精混合。断奶后，给大鼠提供4小时的两瓶选择，两瓶中分别装有0.05%糖精溶液中呈现的CS+和CS-味道。大鼠更喜欢先前与葡萄糖配对的味道。在实验2中，使用类似的方法，大鼠学会了更喜欢与葡萄糖非条件刺激配对的味道（CS+G），而不是与甜度更高但营养较少的蔗糖非条件刺激配对的味道（CS+S），这表明摄入后强化机制的参与。在实验3中，对带有IO和胃内（IG）导管的断奶前大鼠进行训练，将一种CS+味道与IG营养物质输注配对，将一种CS-味道与无IG输注配对。这些大鼠在断奶后3天没有表现出味道偏好，但在断奶后10天显著更喜欢CS+味道而不是CS-味道。这些实验共同表明，味道-营养关联的神经机制在断奶前就已发育，使幼鼠能够学习任意味道与营养后果之间的关联。因此，营养条件作用可能是早期经历（如母乳中传递的母体饮食味道）影响后期饮食偏好的一种方式。
