SELECTIVE NEUROTOXICITY OF RUTHENIUM RED IN PRIMARY CULTURES

The inorganic dye ruthenium red (RuR) has been shown to be neurotoxic in vivo when injected intracerebrally. In this work the toxicity of Ru R was compared in primary cultures of rat cortical neurons, cerebellar granule neurons and cerebellar astroglia. Microscopic examination of the cultures revealed that RuR penetrates the somata of both types of neurons used and produces vacuolization and loss and fragmentation of neurites. In contrast, no RuR was seen inside cultured astrocytes and no morphological signs of damage were observed in these cells. RuR tox icity was also assessed by immunocytochemistry of alpha-tubulin and by biochemical measurement of the reduction of (4,5-dimethylthiazol-2-yl )-2,5-diphenyltetrazolium bromide (MTT) by the cultured cells. The mor phological alterations in the neurons were closely correlated with los s of tubulin immunoreactivity and particularly with a notable decremen t in the ability to reduce MTT. Using the latter parameter, it was fou nd that neuronal damage was independent of the age of the cultures, au gmented progressively with time of incubation with RuR, from 8 to 24 h , and showed a clear dose-response curve from 20 to 100 mu M RuR. Astr ocytes showed only a slight decrease in MTT reduction after 24 h of in cubation with 100 mu M RuR. It is concluded that RuR seems to be toxic for neurons but not for astroglia, and that this selectivity is proba bly related to the ability of the neurons to internalize the dye. The possible mechanisms of RuR penetration and neuronal damage are discuss ed.