Characterization of the turning response of dorsal root neurites toward nerve growth factor.

This study reports that chick dorsal root ganglion neurites undergo a rapid (20 min) reorientation of their direction of growth in response to nerve growth factor (NGF) concentration gradients in vitro. Dorsal root ganglia from chick embryos were explanted onto a collagen-poly-L-lysine substrate. After 24-48 h in culture, NGF gradients were applied to individual growth cones via a micropipette containing 50 biological units NGF/ml. The growth cones turned and grew toward these NGF sources. This turning response was not caused by the trophic effects of NGF on neurite initiation, survival, or growth rate. Dorsal root neurites also grew toward sources of mono- and dibutyryl cyclic adenosine monophosphate (dB cAMP), cyclic guanosine monophosphate (cGMP), and elevated calcium in the presence of the calcium ionophore A23187. These results are consistent with the hypothesis that intracellular levels of cAMP and /or cGMP and calcium may play a role in the turning response of dorsal root neurites toward NGF, but do not establish a causal relationship between the mechanisms of action of NGF, cyclic nucleotides and calcium. Total growth cone adherence to the substrate was measured using a timed microjet of perfusion medium. NGF increased the adherence of growth cones to the substrate, but caffeine and dB cAMP which also elicit the positive turning response, decreased growth cone adherence. Calcium, which did not elicit the positive turning response, produced a greater growth cone adherence to the substrate than that observed with NGF. Although these results do not rule out a role of adhesion changes in axonal turning to NGF, they show that a general increase in adherence does not correlate well with the rapid turning response observed in this study.

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1P536 Single molecule imaging of nerve growth factor receptor trkA expressed in the growth cones of dorsal root ganglion explants(26. Single molecule biophysics,Poster Session,Abstract,Meeting Program of EABS & BSJ 2006)

Seibutsu Butsuri ◽

10.2142/biophys.46.s280_4 ◽

2006 ◽

Vol 46 (supplement2) ◽

pp. S280

Author(s):

Tomomi Tani ◽

Kenta Saito ◽

Takeharu Nagai

Keyword(s):

Nerve Growth Factor ◽

Growth Factor ◽

Dorsal Root Ganglion ◽

Single Molecule ◽

Dorsal Root ◽

Poster Session ◽

Growth Factor Receptor ◽

Growth Cones ◽

Nerve Growth ◽

Meeting Program

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Direct Neurotoxicity of Tetracaine on Growth Cones and Neurites of Growing Neurons In Vitro

Anesthesiology ◽

10.1097/00000542-200109000-00027 ◽

2001 ◽

Vol 95 (3) ◽

pp. 726-733 ◽

Cited By ~ 25

Author(s):

Shigeru Saito ◽

Inas Radwan ◽

Hideaki Obata ◽

Kenichiro Takahashi ◽

Fumio Goto

Keyword(s):

Nerve Growth Factor ◽

Growth Factor ◽

Dorsal Root Ganglion ◽

Growth Cone ◽

Local Anesthetics ◽

Dorsal Root ◽

Sympathetic Ganglion ◽

Growth Cones ◽

Growth Cone Collapse ◽

Neuronal Tissues

Background Local anesthetics have direct neurotoxicity on neurons. However, precise morphologic changes induced by the direct application of local anesthetics to neurons have not yet been fully understood. Also, despite the fact that local anesthetics are sometimes applied to the sites where peripheral nerves may be regenerating after injury, the effects of local anesthetics on growing or regenerating neurons have never been studied. Methods Three different neuronal tissues (dorsal root ganglion, retinal ganglion cell layer, and sympathetic ganglion chain) were isolated from an age-matched chick embryo and cultured for 20 h. Effects of tetracaine were examined microscopically and by a quantitative morphologic assay, growth cone collapse assay. Results Tetracaine induced growth cone collapse and neurite destruction. Three neuronal tissues showed significantly different dose-response, both at 60 min and at 24 h after the application of tetracaine (P < 0.01). The ED50 values (mean +/- SD) at 60 min were 1.53+/-1.05 mM in dorsal root ganglion, 0.15+/-0.05 mM in retinal, and 0.06+/-0.02 mM in sympathetic ganglion chain cultures. The ED50 values at 24 h were 0.43+/-0.15 mM in dorsal root ganglion, 0.07+/-0.03 mM in retinal, and 0.02+/-0.01 mM in sympathetic ganglion chain cultures. Concentration of nerve growth factor in the culture media did not influence the ED50 values. The growth cone collapsing effect was partially reversible in dorsal root ganglion and retinal neurons. However, in the sympathetic ganglion culture, no reversibility was observed after exposure to 1 mM tetracaine for 10 or for 60 min. Bupivacaine had similar neurotoxicity to the three types of growing neurons. (The ED50 values at 60 min were 2.32+/-0.50 mM in dorsal root ganglion, 0.96+/-0.16 mM in retinal, and 0.18+/-0.05 mM in sympathetic ganglion chain cultures. The ED50 values at 24 h were 0.34+/-0.09 mM in dorsal root ganglion, 0.21+/-0.06 mM in retinal, and 0.45+/-0.10 mM in sympathetic ganglion chain cultures.) Conclusions Short-term exposure to tetracaine produced irreversible changes in growing neurons. Growth cones were quickly affected, and neurites degenerated subsequently. Sensitivity varied with neuronal type and was not influenced by the concentration of nerve growth factor. Because a similar phenomenon was observed after exposure to bupivacaine, the toxicity to growing neurons may not be unique to tetracaine.

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