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 norm al 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 containe d moderate levels of NOS, and eye removal caused a consistent down-reg ulation of NOS, NADPH-diaphorase and cytochrome oxidase on the deprive d contralateral side. Optical densitometric values supported these fin dings (P < 0.01). Thus, the level and the activity of NOS are regulate d by neuronal activity in the rat subcortical visual centers.