Aonuma Hitoshi, Kaneda Mugiho, Hatakeyama Dai, Watanabe Takayuki, Lukowiak Ken, Ito Etsuro
Research Center of Mathematics for Social Creativity, Research Institute for Electronic Science, Hokkaido University, Sapporo 060-0811, Japan; CREST, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan.
Laboratory of Functional Biology, Kagawa School of Pharmaceutical Sciences, Tokushima Bunri University, Sanuki 769-2193, Japan.
Neurobiol Learn Mem. 2017 May;141:189-198. doi: 10.1016/j.nlm.2017.04.010. Epub 2017 Apr 24.
The pond snail Lymnaea stagnalis is capable of learning taste aversion by pairing presentations of a sucrose solution and an electric shock and consolidating it into long-term memory (LTM), which is referred to as conditioned taste aversion (CTA). We asked here if the neurotransmitter octopamine is involved in CTA. We first determined the levels of octopamine and its catabolites in the central nervous system (CNS) of snails with varying degrees of food deprivation, because CTA grades are correlated with degrees of food deprivation. We next manipulated the octopamine signaling using both an agonist and an antagonist of octopamine receptors and correlated their respective effects with CTA grades. We found that snails with the least amount of food-deprivation obtained the best CTA grade and had low levels of octopamine; whereas the most severely food-deprived snails did not form CTA and had the highest CNS octopamine levels. In modestly food-deprived snails, octopamine application increased the basal level of feeding response to a sucrose solution, and it did not obstruct CTA formation. Application of phentolamine, an octopamine receptor antagonist, to the most severely food-deprived snails decreased the basal level of feeding elicited by sucrose, but it did not enhance CTA formation. We conclude that octopamine involvement in CTA formation in Lymnaea is at best weak, and that the changes in CNS octopamine content are an epiphenomenon.
椎实螺（Lymnaea stagnalis）能够通过将蔗糖溶液的呈现与电击配对来学习味觉厌恶，并将其巩固为长期记忆（LTM），这被称为条件性味觉厌恶（CTA）。我们在此询问神经递质章鱼胺是否参与CTA。我们首先测定了不同程度食物剥夺的蜗牛中枢神经系统（CNS）中章鱼胺及其代谢产物的水平，因为CTA等级与食物剥夺程度相关。接下来，我们使用章鱼胺受体的激动剂和拮抗剂来操纵章鱼胺信号，并将它们各自的作用与CTA等级相关联。我们发现，食物剥夺最少的蜗牛获得了最佳的CTA等级，且章鱼胺水平较低；而食物剥夺最严重的蜗牛没有形成CTA，且中枢神经系统中的章鱼胺水平最高。在适度食物剥夺的蜗牛中，施用章鱼胺会增加对蔗糖溶液的基础摄食反应水平，并且不会阻碍CTA的形成。向食物剥夺最严重的蜗牛施用章鱼胺受体拮抗剂酚妥拉明，会降低蔗糖引起的基础摄食水平，但不会增强CTA的形成。我们得出结论，章鱼胺对椎实螺CTA形成的参与作用至多很微弱，且中枢神经系统中章鱼胺含量的变化是一种附带现象。
