Deafferentation leads to a down-regulation of nitric oxide synthase in the rat visual system

To test the hypothesis that monocular enucleation can cause a decrease in nitric oxide synthase (NOS) in subcortical visual centers, serial sections of superior colliculi and lateral geniculate nuclei from normal and enucleated rats were processed for NOS immunohistochemistry and NADPH-diaphorase histochemistry. Adjacent sections were also reacted for cytochrome oxidase, a metabolic marker, to demonstrate the change in energy demands. We found that both visual centers normally contained moderate levels of NOS, and eye removal caused a consistent down-regulation of NOS, NADPH-diaphorase and cytochrome oxidase on the deprived contralateral side. Optical densitometric values supported these findings (P < 0.01). Thus, the level and the activity of NOS are regulated by neuronal activity in the rat subcortical visual centers.