Ackroff K, Sclafani A
Department of Psychology, Brooklyn College, NY, USA.
Physiol Behav. 1996 Sep;60(3):927-32. doi: 10.1016/0031-9384(96)00155-2.
Rats can maintain energy intake in response to changes in the caloric density of food by compensatory shifts in the number and size of meals. This study challenged rats' regulation of intake in two ways: manipulating the caloric density covertly to remove orosensory cues and altering baseline meal patterns by increasing the cost of obtaining meals. Rats with gastric catheters were maintained on a complete liquid diet delivered by pumps to a drinking spout and to the stomach; within meals, a rat's licking at the spout controlled the timing and duration of the simultaneous isovolemic intragastric infusions. Prior to each meal, some of the rats were required to press a bar to activate the spout mechanism; when the meal cost was paid, a cue light signaled that licks would deliver food. The light remained on until the rat ceased licking for 10 consecutive min; to resume feeding, the rat had to pay the cost again. The standard diet pumped to the spout was prepared at 1 kcal/g; the intragastrically co-infused diet varied from 0 (water) to 2 kcal/g in 0.5-kcal/g increments. Each concentration was presented for at least 4 days. Separate groups of rats were studied at no cost, low cost (5 bar presses/meal), and high cost (80 bar presses/meal). As the infusate concentration increased, the rats ate fewer meals per day. Meal size by weight decreased as caloric density increased, with he largest meals taken when water was infused. Caloric meal size increased linearly with caloric density for all groups. Meal sizes in the low-cost group were similar to those of the no-cost group, but the latter took more meals per day and, therefore, consumed more total calories. High-cost meal patterns were parallel to those of the other groups, but with fewer, larger meals. All groups maintained a constant daily caloric intake across infusate concentrations. Meal patterns changed rapidly in response to these "covert" (untasted, isovolemic) changes in caloric density. Rats can, thus, integrate the cost of obtaining food and its postingestive benefits in the absence of mediating orosensory cues.
大鼠能够通过调整进食次数和食量来应对食物热量密度的变化，从而维持能量摄入。本研究从两个方面对大鼠的摄入量调节能力提出挑战：一是暗中改变热量密度以消除口腔感觉线索，二是通过增加获取食物的成本来改变基线进食模式。给植入胃导管的大鼠提供一种完全液体饮食，由泵输送到饮水口和胃中；在进食过程中，大鼠在饮水口的舔舐动作控制着同时进行的等容胃内输注的时间和持续时间。在每次进食前，部分大鼠需要按压杠杆来启动饮水口装置；支付进食成本后，提示灯会亮起，表明舔舐动作会提供食物。提示灯一直亮着，直到大鼠连续10分钟停止舔舐；要恢复进食，大鼠必须再次支付成本。泵送到饮水口的标准饮食制备为1千卡/克；胃内共同输注的饮食热量从0（水）到2千卡/克，以0.5千卡/克的增量变化。每个浓度至少持续呈现4天。分别对免费组、低成本组（每餐按压杠杆5次）和高成本组（每餐按压杠杆80次）的大鼠进行研究。随着输注液浓度的增加，大鼠每天进食的餐数减少。按重量计算的每餐食量随着热量密度的增加而减少，输注水时每餐食量最大。所有组的每餐热量食量均随热量密度呈线性增加。低成本组的每餐食量与免费组相似，但免费组每天进食次数更多，因此总热量摄入更多。高成本组的进食模式与其他组相似，但餐数更少、每餐食量更大。所有组在不同输注液浓度下均保持每日热量摄入恒定。进食模式会迅速响应热量密度的这些 “隐蔽”（未品尝、等容）变化。因此，在没有中介口腔感觉线索的情况下，大鼠能够综合考虑获取食物的成本及其摄入后的益处。
