Expression of neuronal nitric oxide synthase variant, nNOS-mu, in rat brain

Neuronal nitric oxide synthase (nNOS) is alternatively spliced. An nNOS splice variant form, nNOS-mu, was first found to be selectively expressed in rat skeletal muscle and heart. To date, the expression of nNOS-mu in the brain has not been well characterized. The aim of this study was to determine whether nNOS-mu is expressed in rat brain, and whether nNOS-mu exhibits a specific expression pattern. To analyze the expression of nNOS-mu, we generated a monoclonal antibody that is specific for nNOS-mu. An immunoblot analysis using this antibody showed that nNOS-mu is expressed in the rat brain at a measurable level, which was 10.3% of total nNOSs. In rat brain, the nNOS-mu expression was high in the mesencephalon and the cerebellum. nNOS-mu was immunohistochemically localized in neurites and perikarya of large neurons. In the cerebellum, granule cells showed marked staining, while weak staining was detected in basket and stellate cells. This expression pattern is different from that described for nNOS and suggests that nNOS-mu plays unique roles in different neurons.