TRANSIENT EXPRESSION OF CALCIUM-INDEPENDENT NITRIC-OXIDE SYNTHASE IN BLOOD-VESSELS DURING BRAIN-DEVELOPMENT

The calcium-independent nitric oxide synthase, known as NOS-II or indu cible NOS, is only present in adult brain during pathologies that invo lve inflammatory events. We sought to establish whether NOS-II tvas al so expressed in the course of normal brain development, NOS-II mRNA, m easured by quantitative polymerase chain reaction, appeared during the perinatal period in different brain areas. It was detected on embryon ic day 14, the earliest time analyzed, and then levels decayed until t he first postnatal week when a second, more robust phase of expression arose to peak around postnatal day 7. Expression then declined to neg ligible levels in adulthood, Immunohistology revealed translation of t he NOS-II protein in both embryonic and postnatal animals, localized t o parenchymal blood vessels, whereas no vessel staining was detected i n adults. Furthermore, NOS-II mRNA and enzymatic activities were prese nt in isolated brain microvessels from developing animals but not from adults, and P7 vessels contained a 125 kDa protein band detected with a monoclonal antibody raised against rat NOS-II protein, These result s indicate that the calcium-independent NOS mRNA and functional protei n are transiently expressed in vessels throughout the brain in the cou rse of normal development.