Fluoro-Gold's toxicity makes it inferior to True Blue for long-term studies of dorsal root ganglion neurons and motoneurons.

We studied the long-term effects of two retrogradely transported fluorescent dyes on survival of dorsal root ganglion neurons (DRGNs) and motoneurons (MNs). In adult female rats, we labeled DRGNs and MNs by soaking the cut sciatic nerve in Fluoro-Gold or True Blue. With True Blue, we found no difference in the number of labeled MNs or DRGNs in rats surviving 4 days or 20 weeks after nerve soak. With Fluoro-Gold, labeled DRGNs and MNs were decreased at 20 weeks compared with 4 days. Since there was no offsetting increase in unlabeled DRGNs at 20 weeks, Fluoro-Gold caused cell death.