TIME-COURSE CHANGES IN THE DOPAMINERGIC NIGROSTRIATAL SYSTEM FOLLOWING TRANSECTION OF THE MEDIAL FOREBRAIN-BUNDLE - DETECTION OF OXIDATIVELY MODIFIED PROTEINS IN SUBSTANTIA-NIGRA

We studied the time course of oxidatively modified proteins in the nig rostriatal dopaminergic system following transection of the medial for ebrain bundle by quantifying the number of carbonyl groups coupled to striatal and nigral protein homogenates, an index of metal-catalyzed o xidations. We found a striking effect of axotomy on the number of oxid atively modified proteins in the substantia nigra but not in the stria tum within the first 5 days postlesion. This effect was correlated wit h the neurochemical activity of the dopaminergic and seretoninergic sy stems in the substantia nigra, which suggests a role of dopamine- and serotonin-derived radical oxygen species in the oxidative stress detec ted in this brain area. We then searched for the type of cell death in the substantia nigra following axotomy. The fragmentation pattern obt ained by agarose gel electrophoresis of DNA isolated from nigral tissu e was indicative of cell death being entirely necrotic. In fact, no ev idence of apoptosis was detected at any postlesion time as revealed by TdT-mediated dUTP-biotin nick end-labeling (TUNEL) staining. The cour se of necrotic cell death in the substantia nigra coincided with the m aximal levels of oxidatively modified proteins in the substantia nigra , suggesting a link between oxidative stress and nerve cell death and also coinciding with the neurochemical activity of both dopaminergic a nd serotoninergic systems.