Immunohistochemical evidence and ultrastructural compartmentalization of anew antioxidant enzyme in the rat substantia nigra

We previously described in the rat the presence of dehydroascorbate reducta se, an enzyme regenerating ascorbic acid, which is constantly lost during o xidative processes occurring at a fast rate within the central nervous syst em. In the present study, we specifically evaluate the occurrence of this e nzyme in the rat substantia nigra by using immunohistochemistry, and by ana lyzing the neuronal compartmentalization of dehydroascorbate reductase with in nigral neurons by immunoblotting and transmission electron microscopy co upled with immunocytochemistry. The enzyme occurs in various portions of th e substantia nigra, but it is more abundant in the ventromedial part extend ing through the ventral tegmental area, and the dorsal portion, involving t he pars compacta. Within nigral neurons, the cytosolic enzyme is present in a perinuclear position, close to mitochondria, and in the nuclear membrane ; we also found the enzyme in nigral axons close to the myelin sheath. In a ddition, dehydroascorbate reductase was present in the nucleus of nigral ne urons. The nuclear occurrence of the enzyme was confirmed by immunocytochem ical labelling and immunoblotting of isolated nuclei. The nuclear enzyme wa s constantly evident as clusters of immunogold particles on chromatin. This localization suggests new roles for dehydroascorbate reductase (eg. preven tion of DNA oxidative damage and regulation of gene transcription).