Developmental expression of intracellular targets of cGMP in rat visual cortex and alteration with dark rearing

We describe the temporal pattern of mRNA expression of some of the molecular components of the NO/cGMP second messenger system in the developing rat visual cortex and the effect of dark rearing on their expression levels using semiquantitative RT-PCR. mRNA expression for these molecules was altered by dark rearing in one of three ways: (1) no change - rod, olfactory, and cone/testis CNG channels, nonselective cation channels gated by cyclic nucleotides and highly permeable to Ca²⁺; (2) decrease - cyclic nucleotide phosphodiesterases which regulate cyclic nucleotide levels, and soluble guanylyl cyclase, the key synthetic enzyme producing cGMP and potently activated by nitric oxide; and (3) increase - cGMP kinase I, a key enzyme activated by cGMP to phosphorylate a variety of intracellular proteins including cytoskeletal elements. These data suggest important and distinct roles for the cGMP system in both early and late developmental events in the rat visual cortex.