Raw data which were used for creating graphs.

The nematode Caenorhabditis elegans memorizes various external chemicals, such as ions and odorants, during feeding. Here we find that C. elegans is attracted to the monosaccharides glucose and fructose after exposure to these monosaccharides in the presence of food; however, it avoids them without conditioning. The attraction to glucose requires a gustatory neuron called ASEL. ASEL activity increases when glucose concentration decreases. Optogenetic ASEL stimulation promotes forward movements; however, after glucose conditioning, it promotes turning, suggesting that after glucose conditioning, the behavioral output of ASEL activation switches toward glucose. We previously reported that chemotaxis toward sodium ion (Na+), which is sensed by ASEL, increases after Na+ conditioning in the presence of food. Interestingly, glucose conditioning decreases Na+ chemotaxis, and conversely, Na+ conditioning decreases glucose chemotaxis, suggesting the reciprocal inhibition of learned chemotaxis to distinct chemicals. The activation of PKC-1, an nPKC ε/η ortholog, in ASEL promotes glucose chemotaxis and decreases Na+ chemotaxis after glucose conditioning. Furthermore, genetic screening identified ENSA-1, an ortholog of the protein phosphatase inhibitor ARPP-16/19, which functions in parallel with PKC-1 in glucose-induced chemotactic learning toward distinct chemicals. These findings suggest that kinase–phosphatase signaling regulates the balance between learned behaviors based on glucose conditioning in ASEL, which might contribute to migration toward chemical compositions where the animals were previously fed.

秀丽隐杆线虫（Caenorhabditis elegans）在取食过程中能够记忆多种外界化学物质，包括离子与气味剂。本研究发现，在食物存在的条件下经单糖葡萄糖与果糖暴露后，秀丽隐杆线虫会表现出对这两种单糖的趋向性；但未经条件化训练时，线虫则会避开它们。对葡萄糖的趋向性依赖于名为ASEL的味觉神经元。当葡萄糖浓度降低时，ASEL神经元的活动会显著增强。光遗传激活ASEL可促进线虫的向前运动；但经葡萄糖条件化训练后，光遗传激活ASEL则会诱导线虫发生转向，这表明葡萄糖条件化后，ASEL激活的行为输出会转向与葡萄糖相关的调控模式。我们此前曾报道，由ASEL感知的钠离子（Na+）趋化性，在食物存在的条件下经钠离子条件化训练后会增强。有趣的是，葡萄糖条件化训练会降低线虫对钠离子的趋化性，反之亦然：钠离子条件化训练会降低线虫对葡萄糖的趋化性，这提示不同化学物质的习得性趋化性之间存在相互抑制作用。在葡萄糖条件化训练后，ASEL神经元中蛋白激酶C-1（PKC-1，一种新型蛋白激酶C ε/η同源物）的激活可增强线虫对葡萄糖的趋化性，并降低其对钠离子的趋化性。此外，通过遗传筛选，我们发现了环腺苷酸磷酸化调节蛋白ARPP-16/19（一种蛋白磷酸酶抑制剂）的同源物ENSA-1，其在葡萄糖诱导的不同化学物质趋化性学习过程中，与PKC-1发挥平行调控功能。上述研究结果表明，激酶-磷酸酶信号通路可调控基于ASEL神经元中葡萄糖条件化的习得行为平衡，这或许有助于线虫迁移至其此前曾取食过的化学物质富集区域。