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.