Intracellular calcium increases in growth cones exposed to tetracaine.

UNLABELLED: Neurotoxicity of local anesthetics has been reported for both matured and growing neurons. In the present study, we examined if tetracaine increases Ca(2+) concentration during growth cone collapse. Intracellular Ca(2+) concentration was measured by fura 2/AM after exposure to tetracaine. Tetracaine (1-2 mM) induced increases in intra-growth cone Ca(2+) concentration (P < 0.01). The Ca(2+) hot spot was expanded into the neurite from the periphery towards the cell body. When tetracaine was applied to growth cones in Ca(2+) free media, the increase was minor. However, tetracaine induced growth cone collapse even in the culture media, which did not contain Ca(2+). Ni(2+) (100 microM; a general Ca(2+) channel inhibitor) and BAPTA-AM (5 microM; intracellular Ca(2+) chelator) could not inhibit growth cone collapse induced by 1-2 mM tetracaine. Tetracaine (>1 mM) induces collapse and Ca(2+) increase at growth cones simultaneously; however, these two phenomena might be provoked independently. IMPLICATIONS: Tetracaine induced intracellular Ca(2+) increases and growth cone collapse in dorsal root ganglion neurons. The Ca(2+) hot spot in the growth cone expanded into the neurite from periphery towards the cell body.

Neurotrophic factors can partially reverse morphological changes induced by mepivacaine and bupivacaine in developing sensory neurons.

UNLABELLED: Both bupivacaine and mepivacaine induce morphological changes in growing neurons. We designed this study to investigate the role of some neurotrophic factors (NTFs) in supporting developing neurons exposed to the deleterious effects of these drugs. Dorsal root ganglia were isolated from chick embryos and exposed to either bupivacaine or mepivacaine. After 60 min of exposure, the culture media were replaced with fresh culture media free from local anesthetics. NTFs-brain-derived NTF, glial-derived NTF, or neurotrophin-3-were added to the replacement media, and the cells were examined up to 48 h after the washout. The growth cone collapse assay was applied by a quantitative method of assessment. When the replacement media were not supported by any NTF, the growth cone collapse values were significantly larger than the control values at 20 h after the washout of mepivacaine and 48 h after the washout of either bupivacaine or mepivacaine (P < 0.05). However, when any of the NTFs were used, the collapsing activity was significantly attenuated, and growth cone collapse values showed no statistically significant differences in comparison with the control values at these time points (P > 0.05). We conclude that several NTFs support the recovery of neurons after exposure to local anesthetics. The supporting effects of NTFs on the reversibility of mepivacaine-induced collapse tended to be more obvious than those seen after the bupivacaine washout. IMPLICATIONS: Three neurotrophic factors (NTFs) can partially support the reversibility of mepivacaine- and bupivacaine-induced growth cone collapse in growing primary cultured sensory neurons. The effect of NTFs is more apparent after mepivacaine than after bupivacaine washout.

Growth cone collapsing effect of lidocaine on DRG neurons is partially reversed by several neurotrophic factors.

BACKGROUND: Local anesthetics were suggested to have a potential for neurotoxicity in both clinical reports and laboratory experiments. Growing neurons have been shown to be susceptible to the toxic effects of local anesthetics in culture. These findings have generated the interest in factors that would rescue the neurons affected by the neurotoxicity of local anesthetics. METHODS: Primary cultured dorsal root ganglia were isolated from age-matched chick embryos and exposed to lidocaine. After 60 min of exposure, the culture media were replaced to wash out the lidocaine. Neurotrophic factors (NTFs)-brain-derived neurotrophic factor, glial-derived neurotrophic factor, or neurotrophin 3-were added to the replacement media to examine the capacity of these NTFs to support the reversibility of the lidocaine-induced growth cone collapse. The growth cone collapse assay was applied a quantitative method of assessment. RESULTS: When any of the three NTFs was added to the replacement media at a minimum concentration of 10 ng/ml, significantly high reversibility of the lidocaine-induced growth cone collapse was observed, especially at 48 h after washout (P < 0.05). At that time point, there was no significant difference between the values of growth cone collapse percentage in the cells that were exposed to lidocaine and supported by the NTFs after the washout, and the control cells (not exposed to lidocaine) (P > 0.05). CONCLUSION: The NTFs-brain-derived neurotrophic factor, glial-derived neurotrophic factor, and neurotrophin 3-were demonstrated to support the reversibility of lidocaine-induced growth cone collapse in primary cultured sensory neurons, an effect that was concentration- and time-dependent. Because similar effects were observed after tetracaine washout, the supporting effects of NTFs may not be specific to lidocaine.

The neurotoxicity of local anesthetics on growing neurons: a comparative study of lidocaine, bupivacaine, mepivacaine, and ropivacaine.

UNLABELLED: Local anesthetics can be neurotoxic. To test the hypothesis that exposure to local anesthetics produces morphological changes in growing neurons and to compare this neurotoxic potential between different local anesthetics, we performed in vitro cell biological experiments with isolated dorsal root ganglion neurons from chick embryos. The effects of lidocaine, bupivacaine, mepivacaine, and ropivacaine were examined microscopically and quantitatively assessed using the growth cone collapse assay. We observed that all local anesthetics produced growth cone collapse and neurite degeneration. However, they showed significant differences in the dose response. The IC(50) values were approximately, 10(-2.8) M for lidocaine, 10(-2.6) M for bupivacaine, 10(-1.6) M for mepivacaine, and 10(-2.5) M for ropivacaine at 15 min exposure. Some reversibility was observed after replacement of the media. At 20 h after washout, bupivacaine and ropivacaine showed insignificant percentage growth cone collapse in comparison to their control values whereas those for lidocaine and mepivacaine were significantly higher than the control values. Larger concentrations of the nerve growth factor (NGF) did not improve this reversibility. In conclusion, local anesthetics produced morphological changes in growing neurons with significantly different IC(50). The reversibility of these changes differed among the four drugs and was not influenced by the NGF concentration. IMPLICATIONS: Local anesthetics induce growth cone collapse and neurite degeneration in the growing neurons. Mepivacaine was safer than lidocaine, bupivacaine, and ropivacaine for the primary cultured chick neurons.