Lucas F, Sclafani A
Department of Psychology, Brooklyn College New York 11210, USA.
Am J Physiol. 1996 May;270(5 Pt 2):R1059-64. doi: 10.1152/ajpregu.1996.270.5.R1059.
During and after a meal, the presence of nutrients in the intestine can be rapidly detected and signaled to the brain via visceral afferents. Intestinal infusions of carbohydrate and fat suppress food intake, and this satiety action is inhibited by capsaicin, a neurotoxin that produces a partial visceral deafferentation. This study determined if the postingestive reinforcing action of nutrients is also suppressed by capsaicin treatment. Food-restricted control and capsaicin-treated rats were trained to drink a flavored solution paired with intraduodenal infusions of carbohydrate (Polycose solution) on some days and, on other days, a differently flavored solution paired with intraduodenal water infusions. In a choice test, both groups displayed a strong preference for the Polycose-paired flavor. In a subsequent satiety test, however, intraduodenal Polycose suppressed sucrose sham feeding in the controls but not in capsaicin-treated rats. The same rats were next trained to associate new flavors with intraduodenal fat (corn oil emulsion) and intraduodenal water infusions. During training, oil infusions reduced oral intakes in the controls much more than in the capsaicin-treated rats. Both groups reliably preferred the oil-paired flavor in the subsequent choice test. These results indicate that, unlike the satiating effect of intestinal carbohydrate and fat, the reinforcing actions of these nutrients are not mediated by capsaicin-sensitive visceral afferents. The data also imply that the postingestive reinforcement produced by nutrients is not dependent on the nutrients' satiating quality.
在进餐期间及之后，肠道中营养物质的存在能够迅速被检测到，并通过内脏传入神经向大脑发出信号。向肠道内输注碳水化合物和脂肪会抑制食物摄入，而这种饱腹感作用会被辣椒素抑制，辣椒素是一种能导致部分内脏去传入神经作用的神经毒素。本研究确定了辣椒素处理是否也会抑制营养物质的餐后强化作用。对食物受限的对照大鼠和经辣椒素处理的大鼠进行训练，让它们在某些日子饮用一种与十二指肠内输注碳水化合物（聚葡萄糖溶液）配对的调味溶液，而在其他日子饮用一种与十二指肠内输注水配对的不同调味溶液。在选择测试中，两组大鼠都对与聚葡萄糖配对的味道表现出强烈偏好。然而，在随后的饱腹感测试中，十二指肠内输注聚葡萄糖抑制了对照大鼠的蔗糖假饲，但对经辣椒素处理的大鼠却没有作用。接下来，对相同的大鼠进行训练，使其将新的味道与十二指肠内输注脂肪（玉米油乳剂）和十二指肠内输注水联系起来。在训练期间，输注油对对照大鼠口腔摄入量的减少幅度远大于经辣椒素处理的大鼠。在随后的选择测试中，两组大鼠都可靠地偏好与油配对的味道。这些结果表明，与肠道碳水化合物和脂肪的饱腹感作用不同，这些营养物质的强化作用不是由对辣椒素敏感的内脏传入神经介导的。数据还表明，营养物质产生的餐后强化作用并不依赖于营养物质的饱腹感特性。
