Retrograde neuronal labeling of motoneurons in the rat by fluorescent tracers, and quantitative analysis of oxidative enzyme activity in labeled neurons.

Extensor digitorum longus motoneurons in the rat spinal cord were identified by retrograde labeling with two fluorescent tracers, Fast blue (FB) and Nuclear yellow (NY). Labeled motoneurons had a blue fluorescent cytoplasm at 360 nm excitation wavelength with FB, and a golden-yellow fluorescent nucleus with NY on the cryostat section. Labeled motoneurons were further examined for succinate dehydrogenase activity on the same section used for identification of the motoneurons. This study demonstrates that fluorescent dyes are useful for neuroanatomical studies by the retrograde axonal transport method, and that quantitative analysis of metabolic activity in labeled motoneurons is also possible.