Department of Psychology, Programs in Animal Behavior and Neuroscience, Bucknell University, Lewisburg, PA 17837, USA.
Physiol Behav. 2013 Feb 17;110-111:179-89. doi: 10.1016/j.physbeh.2013.01.004. Epub 2013 Jan 10.
Rats learn to prefer flavors associated with postingestive effects of nutrients. The physiological signals underlying this postingestive reward are unknown. We have previously shown that rats readily learn to prefer a flavor that was consumed early in a multi-flavored meal when glucose is infused intragastrically (IG), suggesting rapid postingestive reward onset. The present experiments investigate the timing of postingestive fat reward, by providing distinctive flavors in the first and second halves of meals accompanied by IG fat infusion. Learning stronger preference for the earlier or later flavor would indicate when the rewarding postingestive effects are sensed. Rats consumed sweetened, calorically-dilute flavored solutions accompanied by IG high-fat infusion (+ sessions) or water (- sessions). Each session included an "Early" flavor for 8min followed by a "Late" flavor for 8min. Learned preferences were then assessed in two-bottle tests (no IG infusion) between Early(+) vs. Early(-), Late(+) vs. Late(-), Early(+) vs. Late(+), and Early(-) vs. Late(-). Rats only preferred Late(+), not Early(+), relative to their respective (-) flavors. In a second experiment rats trained with a higher fat concentration learned to prefer Early(+) but more strongly preferred Late(+). Learned preferences were evident when rats were tested deprived or recently satiated. Unlike with glucose, ingested fat appears to produce a slower-onset rewarding signal, detected later in a meal or after its termination, becoming more strongly associated with flavors towards the end of the meal. This potentially contributes to enhanced liking for dessert foods, which persists even when satiated.
老鼠学会偏爱与营养摄入后效应相关的味道。这种摄入后奖励的生理信号尚不清楚。我们之前曾表明，当葡萄糖被胃内输注时，老鼠很容易学会偏爱在多味餐的早期消耗的味道，这表明快速的摄入后奖励开始。本实验通过在餐的前半部分和后半部分提供独特的味道，并伴随胃内脂肪输注，研究了摄入后脂肪奖励的时间。对早期或晚期味道的更强偏好表明何时感知到奖励性摄入后效应。老鼠消耗含糖、热量稀释的味道溶液，同时进行胃内高脂肪输注（+ 期）或水（- 期）。每个期包括 8 分钟的“早期”味道，然后是 8 分钟的“晚期”味道。然后在两瓶测试（无胃内输注）中评估习得的偏好，即早期（+）与早期（-）、晚期（+）与晚期（-）、早期（+）与晚期（+）以及早期（-）与晚期（-）之间。与各自的（-）味道相比，老鼠只偏爱晚期（+），而不偏爱早期（+）。在第二个实验中，用更高脂肪浓度训练的老鼠学会偏爱早期（+），但更强烈地偏爱晚期（+）。当老鼠在禁食或最近饱食时进行测试时，就会出现习得的偏好。与葡萄糖不同，摄入的脂肪似乎产生了一个较慢的起始奖励信号，在进食后期或结束后被检测到，与进食结束时的味道联系更紧密。这可能有助于增强对甜点的喜爱，即使在饱食时也能持续。
