This study investigated the signaling cascades involved in the long-term storage of the balance between defensive and appetitive behaviors observed when the mollusk Aplysia is exposed to aversive experience. In Aplysia, repeated trials of aversive stimuli induce concurrent sensitization of defensive withdrawal reflexes and suppression of feeding for at least 24 h. This long-term storage of the balance between withdrawal reflexes and feeding is sustained, at least in part, by increased excitability of the tail sensory neurons (SNs) controlling the withdrawal reflexes, and by decreased excitability of feeding decision-making neuron B51. Nitric oxide (NO) is required for the induction of both long-term sensitization and feeding suppression. At the cellular level, NO is also required for long-term decreased B51 excitability but not for long-term increased SN excitability. Here, we characterized the signaling cascade downstream of NO contributing to the long-term storage of the balance between withdrawal reflexes and feeding. We found protein kinase G (PKG) necessary for both long-term sensitization and feeding suppression, indicating that a NO-PKG cascade governs the long-term storage of the balance between defensive and appetitive responses in Aplysia. The role of PKG on feeding suppression was paralleled at the cellular level where a cGMP-PKG pathway was required for long-term decreased B51 excitability. In the defensive circuit, the cGMP-PKG pathway was not necessary for long-term increased SN excitability, suggesting that other cellular correlates of long-term sensitization might depend on the GMP-PKG cascade to sustain the behavioral change.

中文翻译：

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蛋白激酶G在海ly中由厌恶性刺激诱导的防御和食性之间的长期平衡中起关键作用。

这项研究调查了当软体动物海ly暴露于厌恶经历时，在防御行为和食欲行为之间长期保持平衡的信号级联反应。在Aplysia中，对厌恶性刺激的反复试验诱导了防御性撤退反射的同时敏化和至少24 h的进食抑制。撤退反射和进食之间平衡的这种长期储存至少部分地通过控制撤退反射的尾巴感觉神经元（SN）的兴奋性以及进食决策神经元B51的兴奋性降低而得以维持。一氧化氮（NO）是诱导长期致敏和抑制进食所必需的。在蜂窝一级，长期降低B51的兴奋性也不需要NO，但对于长期增加的SN兴奋性也不需要。在这里，我们表征了NO下游的信号级联反应，有助于长期储存撤退反射和进食之间的平衡。我们发现蛋白激酶G（PKG）对于长期致敏和进食抑制都是必需的，表明NO-PKG级联控制海藻中防御和食性反应之间的平衡的长期存储。PKG在抑制摄食上的作用在细胞水平上是平行的，在细胞水平上，cGMP-PKG通路是长期降低B51兴奋性所必需的。在防御电路中，cGMP-PKG途径对于长期提高SN兴奋性不是必需的，