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Cyclic Nucleotide-Gated Channels, Nitric Oxide, and Neural Function

Cyclic nucleotide-gated (CNG) channels are nonselective cation channels that are activated by direct interaction of the second messengers cAMP and cGMP. Once activated, they provide for membrane depolarization and Ca2+ influx into cells. The functions of CNG channels are tightly coupled to the mechanisms by which cAMP and cGMP are regulated in neurons, namely through activation of G-protein–coupled membrane receptors and through the nitric oxide/guanylyl cyclase signaling system. These functions are best understood in sensory neurons of the vertebrate visual and olfactory system, where CNG channels are critical components of the signal transduction apparatus. The family of known CNG channels is expanding, and there is now increasing evidence that these channels are also present in many other areas of the nervous system. Based on their role in sensory neurons, a functional framework for the role of CNG channels in the CNS is provided.