下列何種環核苷酸(Cyclic Nucleotide)是嗅覺神經元(Olfactory Receptor Neuron)內的訊息傳遞者(Second Messenger),它的濃度可因嗅覺分子結合到嗅覺受體後而增加?
cGMP
cAMP
cTMP
cCMP