Tetracaine at a small concentration delayed nerve growth without destroying neurites and growth cones

Local anesthetics have direct neurotoxicity and induce growth cone collapse when applied to neurons at large concentrations. However, the effects of prolonged exposure to local anesthetics at a small concentration have never been studied. We examined whether neurite growth was slowed by tetracaine at small concentrations in chick embryo dorsal root ganglions. The effects of tetracaine were examined microscopically and by a neurite growth rate assay, quantitative morphologic assay, growth cone collapse assay, and Western blot assay. Neurite growth 24 and 48 h after application was delayed significantly when tetracaine was applied at a concentration larger than 5 microM. Filopodia of growth cones retracted, and their number was significantly decreased 24 and 48 h after the application of 10 and 20 microM of tetracaine. The quantity of actin in cell bodies increased, contrary to the effect on neurites and growth cones, where actin decreased 48 h after the application of 5, 10, and 20 microM of tetracaine. In conclusion, continuous exposure to tetracaine at small concentrations delayed neurite growth, reduced the number of filopodia, and decreased actin content.