Biopsychology Area, Dept. of Psychology, Stony Brook University, Stony Brook, NY, USA.
Neuropeptides. 2010 Oct;44(5):445-51. doi: 10.1016/j.npep.2010.04.003. Epub 2010 May 23.
Prior research has shown that the neuropeptide galanin strongly stimulates food intake in sated rats when food is made freely available. However, when access to food is made contingent upon lever pressing on a reinforcement schedule, no such stimulation occurs. This dissociation is consistent with the theorized "behavioral energizing" function of the ascending mesolimbic dopamine system, which purports that this ascending dopamine system is involved in only the goal directed effort maintaining (appetitive) and not the hedonic (consummatory) aspects of reward. Further, these results suggest that galanin may play an inhibitory role therein, or itself may be inhibited by mesolimbic dopamine activity underlying instrumental behavior. Prior research into this phenomenon has only utilized caloric foods or water, so the current work assessed the generality of this finding by determining if a similar dissociation also applies to commodities with other properties. For the present experiments, two commodities which varied in the dimensions of palatability and caloric load but which are both known to serve as reinforcers in other settings were chosen. In the first experiment, under the current single commodity free consumption test conditions shown to be sensitive to galanin effects of food and water consumption, galanin did not significantly alter the consumption of caloric laden but poorly palatable 7% alcohol solution. However, in the second experiment, galanin significantly increased free consumption of a highly palatable but non-caloric 0.2% saccharin solution but not when operant responding was required for access to saccharin, extending the basic appetitive-consummatory dissociation observed for food. Taken together, these results suggest that the gustatory properties may be a specific factor involved in galanin stimulation of free consumption, and that there may be a continuum of influence of galanin based on the relative "elasticity" of the commodities as reinforcers.
先前的研究表明，神经肽甘丙肽在给已饱食的大鼠提供自由获取的食物时，会强烈刺激其摄食。然而，当获取食物取决于压杆以强化程序进行时，这种刺激就不会发生。这种分离与假定的中脑边缘多巴胺系统的“行为激发”功能一致，该系统声称，这个上升的多巴胺系统仅参与目标导向的努力维持（食欲），而不参与奖励的享乐（满足）方面。此外，这些结果表明，甘丙肽可能在其中发挥抑制作用，或者本身可能受到中脑边缘多巴胺活动的抑制，这种多巴胺活动是工具行为的基础。先前对这一现象的研究仅使用了热量食物或水，因此当前的工作通过确定类似的分离是否也适用于具有其他特性的商品，来评估这一发现的普遍性。在目前的实验中，选择了两种商品，它们在美味和热量负荷方面有所不同，但在其他环境中都被认为是强化物。在第一个实验中，在当前的单一商品自由消费测试条件下，甘丙肽对食物和水的消费没有显著影响，这些条件被证明对甘丙肽的作用敏感。然而，在第二个实验中，甘丙肽显著增加了对高度美味但无热量的 0.2%糖精溶液的自由消费，但当需要操作反应才能获得糖精时，甘丙肽不会增加糖精的自由消费，从而扩展了对食物观察到的基本食欲-满足的分离。总之，这些结果表明，味觉特性可能是甘丙肽刺激自由消费的一个特定因素，而且可能存在一个基于商品作为强化物的相对“弹性”的甘丙肽影响连续体。
