Retrograde tracing with Fluoro-Gold: different methods of tracer detectionat the ultrastructural level and neurodegenerative changes of back-filled neurons in long-term studies

Among the available retrograde fluorescent tracers Fluoro-Gold (FG) is part icularly advantageous because it (1) is not only detectable by fluorescence microscopy but also immunocytochemically, resulting in an almost complete staining of the dendritic arbor, (2) is visible in lysosome-like structures allowing for the identification of projection neurons at the ultrastructur al level, and (3) remains in the labeled neurons for extended periods of ti me. Photoconversion and immunostaining for FG, respectively, result in a st able, electron-dense reaction product. Thus, the retrogradely labeled cells can be analyzed quantitatively in the light- and electron microscope for t heir structural characteristics and input synapses. Long-term studies of ba ck-filled neurons provided evidence for neurotoxic effects of FG in these c ells. (C) 2000 Elsevier Science B.V. All rights reserved.