Widespread expression of olfactory cyclic nucleotide-gated channel genes in rat brain: Implications for neuronal signalling

The cyclic nucleotides cCAMP and cGMP are important intracellular messenger s involved in a wide variety of signal transduction events in the nervous s ystem. It has been proposed that cAMP/cGMP elicit some of their effects thr ough direct gating of a novel class of Ca2+-permeable ion channels that are termed cyclic nucleotide-gated (CNG) channels. Previous studies have ident ified the expression of a gene encoding one major CNG channel subtype, the olfactory receptor neuron alpha subunit, in the brain [El-Husseini et al. ( 1995) NeuroReport 6:1331-1335; Kingston et al. (1996a) Proc. Natl. Acad. Sc i. U.S.A. 93:10440-10445; Bradley et al. (1997) J. Neurosci. 17:1993-2085]. We, therefore, proposed that the actions of cAMP/cGMP on neurons in the br ain might occur through the activation of these CNG channels. To determine how widespread such a function might be, the regional and cellular distribu tion of the olfactory CNG channel a: subunit has been examined in detail. P rimers for multiple portions of the olfactory CNG channel were used in poly merase chain reaction (PCR) to amplify cDNA reverse-transcribed from severa l brain regions. The identities of PCR products were confirmed with Souther n blots and by sequencing. In situ hybridization experiments demonstrated l ocalization of CNG channel mRNA in discrete neuronal populations throughout the brain. In agreement with previous work, relatively strong hybridizatio n signals are present in neuronal cell bodies of the cerebellum, olfactory bulb, cerebral cortex, and brainstem. Additionally, somewhat lesser signals are found in thalamus, hypothalamus, midbrain, and spinal cord while no hy bridization signal was detectable in the caudate nucleus. This surprisingly wide distribution throughout the rat brain strengthens the hypothesis that CNG channels may influence numerous processes as downstream effecters of c yclic nucleotide cascades. Interestingly the distribution of CNG channels i s very similar to that of the nitric oxide/cGMP system, suggesting that one function of CNG channels in the brain could be to link diffusible messenge rs to elevated Ca2+ entry into neurons. Synapse 32:1-12, 1999. (C) 1999 Wil ey-Liss, Inc.