Evgeny Fesenko, Stanislav Kolesnikov, and Arkady Lyubarsky discovered in 1985 that cyclic guanosine monophosphate (cGMP) can initiate the photoresponse in rods. Soon after, the role of cNMP in gated ion channels of chemosensitive cilia of olfactory sensory neurons was reported by Tadashi Nakamura and Geoffrey Gold. In 1992 Lawrence Haynes and King-Wai Yau uncovered cNMP’s role in the light-dependent cyclic-nucleotide-gated channel of cone photoreceptors.[1] By the end of the decade, the presence of two types of intramembrane receptors was understood: Rs (which stimulates cyclase) and Ri (which inhibits cyclase).