NEURONAL NITRIC-OXIDE SYNTHASE ALTERNATIVELY SPLICED FORMS - PROMINENT FUNCTIONAL LOCALIZATIONS IN THE BRAIN

Neuronal nitric-oxide synthase (nNOS) is subject to alternative splici ng, In mice with targeted deletions of exon 2 (nNOS(Delta/Delta)), two alternatively spliced forms, nNOS beta and gamma, which lack exon 2, have been described, We have compared localizations of native nNOS alp ha and nNOS beta and gamma by in situ hybridization and immunohistoche mistry in wild-type and nNOS(Delta/Delta) mice, To assess nNOS catalyt ic activity in intact animals we localized citrulline, which is formed stoichiometrically with NO, by immunohistochemistry. nNOS beta is pro minent In several brain regions of wild-type animals and shows 2-to 3- fold up-regulation in the cortex and striatum of nNOS(Delta/Delta) ani mals, The persistence of much nNOS mRNA and protein, and distinct citr ulline immunoreactivity (cit-IR) in the ventral cochlear nuclei and so me cit-IR in the striatum and lateral tegmental nuclei, indicate that nNOS beta is a major functional form of the enzyme in these regions, T hus, nNOS beta, and possibly other uncharacterized splice forms, appea r to be important physiological sources of NO in discrete brain region s and may account for the relatively modest level of impairment in nNO S(Delta/Delta) animals.