Leslie and Susan Gonda (Goldschmied) Multidisciplinary Brain Research Center, Mina and Everard Goodman Faculty of Life Sciences, Bar Ilan University, Ramat Gan, Israel.
PLoS One. 2012;7(9):e45241. doi: 10.1371/journal.pone.0045241. Epub 2012 Sep 28.
Aplysia feeding is a model system for examining the neural mechanisms by which changes in motivational state control behavior. When food is intermittently present, Aplysia eat large meals controlled by a balance between food stimuli exciting feeding and gut stimuli inhibiting feeding. However, when food is continuously present animals are in a state in which feeding is relatively inhibited and animals eat little. We examined which stimuli provided by food and feeding initiate steady-state inhibition of feeding, and which stimuli maintain the inhibition.
Multiple stimuli were found to control entry into the steady-state inhibition, and its maintenance. The major variable governing entry into the steady-state is fill of the gut with bulk provided by food, but this stimulus cannot alone cause entry into the steady-state. Food odor and nutritional stimuli such as increased hemolymph glucose and L-arginine concentrations also contribute to inhibition of feeding leading to entry into the steady-state. Although food odor can alone cause some inhibition of feeding, it does not amplify the effect of gut fill. By contrast, neither increased hemolymph glucose nor L-arginine alone inhibits feeding in hungry animals, but both amplify the inhibitory effects of food odor, and increased glucose also amplifies the effect of gut fill. The major variable maintaining the steady-state is the continued presence of food odor, which can alone maintain the steady-state for 48-72 hrs. Neither increased glucose nor L-arginine can alone preserve the steady-state, although they partially preserve it. Glucose and arginine partially extend the effect of food odor after 72 hrs.
These findings show that control of Aplysia feeding is more complex than was previously thought, in that multiple inhibitory factors interact in its control.
食蟹海兔的进食是一个研究动机状态如何改变控制行为的神经机制的模型系统。当食物间歇性出现时，食蟹海兔会进食大量食物，这是由食物刺激进食和肠道刺激抑制进食之间的平衡控制的。然而，当食物持续存在时，动物处于进食相对抑制的状态，进食量很少。我们研究了哪些食物和进食提供的刺激会引发进食的稳态抑制，以及哪些刺激会维持这种抑制。
发现多种刺激因素控制着进入稳态抑制及其维持。控制进入稳态抑制的主要变量是肠道被食物提供的大量物质填充，但这种刺激本身不能引起进入稳态抑制。食物气味和营养刺激物，如增加血淋巴葡萄糖和 L-精氨酸浓度，也有助于抑制进食，从而进入稳态抑制。虽然食物气味本身可以引起一些进食抑制，但它不能放大肠道填充的效果。相比之下，增加的血淋巴葡萄糖或 L-精氨酸单独都不能抑制饥饿动物的进食，但两者都能放大食物气味的抑制作用，增加葡萄糖也能放大肠道填充的作用。维持稳态的主要变量是食物气味的持续存在，它本身可以维持稳态 48-72 小时。增加的葡萄糖或 L-精氨酸都不能单独维持稳态，尽管它们部分维持了稳态。葡萄糖和精氨酸在 72 小时后部分延长了食物气味的作用。
这些发现表明，食蟹海兔进食的控制比以前认为的要复杂得多，因为多个抑制因素相互作用控制着进食。
