Analysis of the roles of NO-cGMP signaling cascade for long-term memory formation in an insect.

循环AMP通路在长时记忆（LTM）的形成中起重要作用。在一些物种中，一氧化氮(NO)-环GMP途径已被发现与cAMP途径平行并互补地作用于LTM的形成。本研究的目的是阐明NO-cGMP通路在LTM形成中的作用。我们通过系统地在蟋蟀体内共同注射各种“LTM诱导”和“LTM阻断”药物，研究了LTM形成的信号级联。多次嗅觉条件反射导致的长期记忆持续数天，而单次嗅觉条件反射诱导的记忆在数小时内消退。在多次试验前将形成NO、cGMP或cAMP的酶抑制剂注射到血淋巴中可阻断LTM，而在单次试验前注射NO供体、cGMP类似物或cAMP类似物可诱导LTM。通过注射NO供体或cGMP类似物结合单次调节诱导的LTM被cAMP途径抑制剂阻断，但cAMP类似物诱导的LTM不受NO-cGMP途径抑制剂的影响。环核苷酸门控通道（CNG通道）或钙调素抑制剂阻断cGMP类似物与单次调节配对诱导的LTM，但不影响cAMP类似物诱导的LTM。本研究首次提出cAMP途径是NO-cGMP途径形成LTM的下游靶点，CNG通道和钙钙调素在NO-cGMP途径和cAMP途径之间进行干预。

Cyclic AMP pathway plays an essential role in formation of long-term memory (LTM). In some species, the nitric oxide (NO)-cyclic GMP pathway has been found to act in parallel and complementary to the cAMP pathway for LTM formation. The aim of this study was to clarify the roles of the NO-cGMP pathway for the LTM formation. We have studied the signaling cascade underlying LTM formation by systematically co-injecting various 'LTM-inducing' and 'LTM-blocking' drugs in crickets. Multiple-trial olfactory conditioning led to LTM that lasted for several days, while memory induced by single-trial conditioning decayed away within several hours. Injection of inhibitors of the enzyme forming NO, cGMP or cAMP into the hemolymph prior to multiple-trial conditioning blocked LTM, whereas injection of an NO donor, cGMP analogue or cAMP analogue prior to single-trial conditioning induced LTM. Induction of LTM by injection of an NO donor or cGMP analogue paired with single-trial conditioning was blocked by inhibitors of the cAMP pathway, but induction of LTM by a cAMP analogue was unaffected by inhibitors of the NO-cGMP pathway. Inhibitors of cyclic nucleotide gated channel (CNG channel) or calmodulin blocked induction of LTM by cGMP analogue paired with single-trial conditioning, but they did not affect induction of LTM by cAMP analogue. This study suggests, for the first time, that the cAMP pathway is a downstream target of the NO-cGMP pathway for the formation of LTM and that the CNG channel and calcium-calmodulin intervene between the NO-cGMP pathway and the cAMP pathway.