Reversal by NGF of cytostatic drug-induced reduction of neurite outgrowth in rat dorsal root ganglia in vitro

Cytostatic drugs, like cisplatin, vincristine and taxol, when given to cancer patients may cause peripheral neuropathies. We were interested in the potential neuroprotective effects of neurotrophic factors against such neuropathies. To this aim we studied the effects of these cytostatic agents on sensory fibers located in the dorsal root ganglia (DRG) in vitro and studied whether nerve growth factor (NGF) could reverse the cytostatic induced morphological changes on intact DRG (1 DRG/well, n=10per dose). Neuritogenesis from DRG was measured with an image analysis system following exposure to different concentrations of cytostatic drugs in the presence of 3 ng NGF/ml and cytosine arabinoside (Ara-C, 10⁻⁶ M). Relative neurite outgrowth in intact DRG in culture was reduced dose-dependently, (a) by vincristine starting at a dose of 0.4 ng/ml for 2 days (−33% as compared to control; P < 0.001, Student's t-test); (b) by taxol 10 ng/ml (−60%; P< 0.001), and (c) by cisplatin 3 μg/ml (−47%, P < 0.001). Cisplatin also prevented the migration of satellite cells away from the intact DRG along the extending neurites into the well in contrast to control, vincristine, or taxol. To evaluate the neuroprotective potential of NGF in this in vitro cytostatic neuropathy model, we incubated intact DRG with cytostatic agents in combination with increasing amounts of NGF. Neurite outgrowth from DRG treated with vincristine (0.5 ng/ml) + NGF (3 ng/ml) for 2 days was significantly higher (+87%) than after treatment with vincristine + 1 ng NGF/ml (P < 0.001). Neutrite outgrowth from DRG treated with taxol (20 ng/ml) + NGF (3 ng/ml) for 2 days was significantly higher (+ 228%) than after taxol + 1 ng NGF/ml (P < 0.05). Neurotogenesis from DRG treated with cisplatin (2.5 μg/ml) + NGF (3 ng/ml) for 2 days was significantly increased (+105%) compared to treatment with cisplatin + 1 ng NGF/ml (P < 0.001). DRG thus appear to be a very suitable model for studying cytostatic drug-induced neuropathies in vitro and NGF has a clear neuroprotective effect on the vincristine-, taxol-, and cisplatin-induced neuropathies in this in vitro model.     

Differential effects of NGF, FGF, EGF, cAMP, and dexamethasone on neurite outgrowth and sodium channel expression in PC12 cells

PC12 cells are a pheochromocytoma cell line that can be made to differentiate into sympatheticlike neurons by nerve growth factor (NGF). An essential component of the NGF-induced differentiation is the development of action potentials and sodium channels. Using whole-cell clamp we have confirmed that NGF produces a 5- to 6-fold increase in sodium channel density. The sodium channels induced by NGF are not different from those in cells not treated with NGF and are similar to those in other cell types. Basic fibroblast growth factor (FGF), another growth factor that causes PC12 cells to differentiate into sympathetic-like neurons, also produces a 5- to 6-fold increase in sodium current density with channels indistinguishable from those in PC12 cells treated and not treated with NGF. Basic FGF produces the same or somewhat larger increase in sodium channel density but much less neurite outgrowth. In contrast, epidermal growth factor does not produce neurite outgrowth but induces a small, reproducible increase in sodium channel density. Cyclic AMP produces spike-like processes but not neurites and results in a decrease in sodium current and sodium current density. Dexamethasone, a synthetic glucocorticoid, inhibits the increase in sodium current and sodium current density but does not antagonize the neurite outgrowth induced by NGF. Thus, although the increase in sodium channel expression induced by NGF and basic FGF parallels the changes in morphology that lead to neurite outgrowth, it clearly does not depend on them. The results show that different aspects of neuronal differentiation might be independently regulated by the microenvironment.     

Neurite outgrowth in normal and injured primary sensory neurons reveals different regulation by nerve growth factor (NGF) and artemin

Neurotrophic factors have been intensively studied as potential therapeutic agents for promoting neural regeneration and functional recovery after nerve injury. Artemin is a member of the glial cell line-derived neurotrophic factor (GDNF) family of ligands (GFLs) that forms a signalling complex with GFRα3 and the tyrosine kinase Ret. Systemic administration of artemin in rodents is reported to facilitate regeneration of primary sensory neurons following axotomy, improve recovery of sensory function, and reduce sensory hypersensitivity that is a cause of pain. However, the biological mechanisms that underlie these effects are mostly unknown. This study has investigated the biological significance of the colocalisation of GFRα3 with TrkA (neurotrophin receptor for nerve growth factor [NGF]) in the peptidergic type of unmyelinated (C-fibre) sensory neurons in rat dorsal root ganglia (DRG). In vitro neurite outgrowth assays were used to study the effects of artemin and NGF by comparing DRG neurons that were previously uninjured, or were axotomised in vivo by transecting a visceral or somatic peripheral nerve. We found that artemin could facilitate neurite initiation but in comparison to NGF had low efficacy for facilitating neurite elongation and branching. This low efficacy was not increased when a preconditioning in vivo nerve injury was used to induce a pro-regenerative state. Neurite initiation was unaffected by artemin when PI3 kinase and Src family kinase signalling were blocked, but NGF had a reduced effect.     

NGF对烧伤大鼠血清引起纹状体神经元细胞毒性的影响

观察NGF对烧伤大鼠血清引起神经毒性的影响。初步探讨NGF对烧伤后神经元损伤的保护作用及其机制,测定烧伤大鼠纹状体组织NO和LDH含量;给予原代培养纹状体神经元不同浓度NCF24h后,加入不同浓度烧伤大鼠血清,测定细胞存活率及培养液中NO含量,大鼠烧伤后,纹状体组织NO和LDH含量明显升,烧伤大鼠血清可引起卢培养的纹状体神经元存活率下降,培养液中NO含量升高,NGF能降低纹状体组织中NO和LDH的含量,提高培养的纹状体神经元的存活率,减少培养液中NO含量,其作用呈剂量依赖性,NGF对神经元存活率的影响与NO含量呈显著负相关,NGF对烧伤大鼠血甭引起的纹状体神经元损伤有保护作用。其作用机制可能是通过抑制NO的神经毒性。     

Nerve growth factor and a fibroblast growth factor-like neurotrophic activity in cerebrospinal fluid of brain injured human patients

We report here the presence of nerve growth factor (NGF) in the cerebrospinal fluid (CSF) of some brain-injured human patients soon after injury. The NGF was quantified against a recombinant human NGF standard in a two-site enzyme-linked immunoabsorbant assay using antibodies against murine B NGF. None of the samples collected more than 2 days after injury contained detectable levels of NGF. When the CSF was assayed for the ability to promote neurite outgrowth from PC12 cells, neurite outgrowth was reduced, but not completely blocked, by antibodies to B NGF, suggesting that there were other biologically active factors present. Fibroblast growth factor (FGF) also promotes neurite outgrowth in PC12 cells. In an initial screening for the presence of FGF, we employed PC12 cells and NR119 cells, PC12 variants in which recombinant human B NGF, but not recombinant human basic FGF, promotes neurite outgrowth. CSF from brain injury patients promoted greater neurite outgrowth from PC12 cells than from NR119 cells, suggesting that some of the biological activity associated with the injury CSF may be due a FGF. This possibility is further supported by the observation that the biological activity of the injury CSF significantly reduced by batch absorption with heparin Sepharose, suggesting the presence of a heparin binding neurotrophic factor. Neurotrophic factors appear in CSF as a consequence of diverse types of brain injury, including head trauma, intracerebral hemorrhage and subarachnoid hemorrhage. The appearance of these factors may reflect important common elements in the complex series of cellular changes occuring in response to acute brain injury.     

1,1,3 tricyano-2-amino-1-propene (Triap): a small molecule which mimics or potentiates nerve growth factor

1,1,3 Tricyano-2-amino-1-propene (Triap) is a small molecular weight compound which increases the rate of nerve and tissue regeneration in several experimental systems. Early experiments with this compound showed that, like nerve growth factor (NGF), Triap induced neurite formation in chick spinal ganglia. To assess the similarity between NGF and Triap, we compared the effects of Triap and NGF on a rat pheochromocytoma cell line (PC12) and on cell survival in a primary chick neuronal culture. In the latter, Triap at less than 0.01 nM preserved neurons and caused them to extend neurites as did 1 nM NGF. Triap induced neurite outgrowth in the PC12 cell line giving a maximal response (40-50% of the maximal response of NGF) at a concentration of 20 micrograms/ml (151 microM). Triap's morphological effects were not inhibited by antibodies directed against NGF or the NGF receptor. Low concentrations of Triap also potentiated the morphological effects of NGF. Triap induced an increase in cell-substratum adhesion and cellular hypertrophy in PC12 cells and also potentiated the adhesive actions of NGF. Triap had no effect on ornithine decarboxylase activity even though it potentiated NGF's effects on this enzyme. These data indicate that Triap induces neurotrophic effects and does not seem to act through the same mechanisms as NGF but can potentiate many of NGF's morphological and biochemical actions.     

NGF induces neurite outgrowth via a decrease in phosphorylation of myosin light chain in PC12 cells.

The relationship between phosphorylation of myosin light chain (MLC) and neurite outgrowth induced by nerve growth factor (NGF) was studied in PC12 cells. Inhibitors of Rho kinase, HA-1077 or Y-27632 also induced neurite outgrowth. As already reported botulinum exoenzyme C3 which inactivates Rho protein also induced neurite outgrowth. Calyeulin A, an inhibitor of phosphatase counteracted both NGF- and C3- induced neurite outgrowth. Treatments of both NGF and C3 resulted in significant and transient decrease in phosphorylated MLC. These results suggest that NGF induces neurite outgrowth of PC12 by a transient decrease in phosphorylated MLC which is brought about by activation of MLC phosphatase via inhibition of Rho-Rho kinase pathway.     

Delayed administration of NGF reverses nerve injury induced central alterations of primary afferents.

We have examined whether delayed exogenous NGF administered to an axotomised peripheral nerve reverses the increased transganglionic choleragenoid (CTB) labelling in lamina II. Two, four, eight or 18 weeks after bilateral sciatic nerve section, NGF was applied unilaterally for an additional 2-week period to the transected nerve stump. The transganglionic choleragenoid labelling and substance P (SP) expression were determined and compared to the contralateral axotomised side in the spinal cord dorsal horn. Delayed NGF administration reversed the transganglionic choleragenoid labelling in lamina II when administered 2 or 18 weeks after the sciatic nerve lesion, but not at 4 or 8 weeks. There was also a clear recovery of SP on the axotomised, NGF-treated side 2 or 18 weeks after the sciatic nerve lesion, but not at the intermediate survival times. At the longer survival time, however, there was a recovery of SP regardless of NGF treatment. These results suggest that there is a critical window as to when NGF administration can be effective in reversing axotomy-induced changes in the spinal cord.     

Retroviral transfer of the beta-nerve growth factor gene into murine neuroectodermal tumor cells modulates cell proliferation rate, neurite formation, and NGF binding site expression

The response of wild-type and genetically engineered neuroectodermal tumor (NET) cells to exogenous and endogenously synthesized nerve growth factor (NGF) was investigated. Differences in cell proliferation rate, neurite formation, and expression of NGF binding sites were quantitatively determined. Ecotropic retroviral vectors were used to transfer the genes for beta-galactosidase (beta-GAL) and NGF into wild-type C-1300 and Neuro-2A murine neuroblastoma (MNB) and rat pheochromocytoma (PC-12) cells. Conditioned media obtained from NET cells infected with the NGF gene contained biologically active NGF, whereas media from beta-GAL infected cells did not. Infection with the NGF vector induced a short-term decrease in cell proliferation rate and increased neurite formation in wild-type, substrate-adherent PC-12 and Neuro-2A MNB cells (P > 0.05). Incubation of wild-type C-1300, Neuro-2A MNB, and PC-12 cells with NGF (0-200 ng/ml) for 5 days significantly reduced proliferation rates in a concentration-dependent manner and increased neurite extrusion. All NGF-NET cells had a significantly diminished response to the antiproliferative action of exogenous NGF. Ligand binding assays with 125I-NGF demonstrated a marked reduction in the number of NGF binding sites on NGF-NET cells compared to wild type. The attenuated response of NGF-NET cells to exogenous NGF correlated positively with the down-regulation of NGF binding sites. In conclusion, beta-NGF gene transfer into wild-type NET cells induces the synthesis and secretion of NGF, temporarily decreases cell proliferation rate, increases neurite extrusion, down-regulates NGF binding sites, and reduces NET cell responsiveness to NGF. A putative role for NGF may be the modulation of NET cell proliferation and differentiation.     

CEP-1347 promotes survival of NGF responsive neurones in primary DRG explants

CEP-1347 inhibits the signalling pathway of c-jun-N-terminal kinase, and is neuroprotective in vivo and in vitro. Embryonic chick dorsal root ganglion neurones are dependent on NGF for survival and neurite outgrowth; NGF withdrawal results in apoptotic cell death. We examined the neuroprotective and neurite outgrowth promoting activity of CEP-1347 in dissociated DRG neurones and in primary DRG explants. CEP-1347 was as effective as NGF in promoting survival of dissociated DRG neurones, but caused only limited neurite outgrowth from DRG explants. When NGF was subsequently added to CEP-1347 treated explants, the outgrowth increased to a similar level to explants which had received NGF throughout. CEP-1347 may be a useful tool to maintain viable DRG explants to allow evaluation of neurite outgrowth promoting compounds and dissection of survival and neurite outgrowth signalling pathways.     

Neurite outgrowth and GAP-43 mRNA expression in cultured adult rat dorsal root ganglion neurons: Effects of NGF or prior peripheral axotomy

Adult dorsal root ganglion (DRG) cells are capable of neurite outgrowth in vivo and in vitro after axotomy. We have investigated, in cultured adult rat DRG cells, the relative influence of nerve growth factor (NGF) or a prior peripheral nerve lesion on the capacity of these neurons to produce neurites. Since there is evidence suggesting that the growth-associated protein GAP-43 may play a crucial role in axon elongation during development and regeneration, we have also compared the effect of these treatments on GAP-43 mRNA expression. NGF increased the early neurite outgrowth in a subpopulation of DRG cells. This effect was substantially less, however, than that resulting from preaxotomy, which initiated an early and profuse neurite outgrowth in almost all cells. No difference in the expression of GAP-43 mRNA was found between neurons grown in the presence or absence of NGF over 1 week of culture, in spite of the increased growth produced by NGF. In contrast, cultures of neurons that had been preaxotomized showed substantial increase in GAP-43 mRNA and NGF had, as expected, a significant effect on substance P mRNA levels. Two forms of growth may be present in adult DRG neurons: an NGF-independent, peripheral nerve injury-provoked growth associated with substantial GAP-43 upregulation, and an NGF-dependent growth that may underlie branching or sprouting of NGF-sensitive neurons, but which is not associated with increased levels of GAP-43 mRNA. © 1994 Wiley-Liss, Inc.     

Angiotensin II and NGF differentially influence microtubule proteins in PC12W cells: role of the AT2 receptor

Angiotensin AT₂ receptors have been shown to play a role in cell differentiation characterized by neurite outgrowth in neuronal cells of different origin. To further investigate AT₂ receptor-mediated events leading to neurite formation, we examined the effect of AT₂ receptor stimulation on the microtubule components, β-tubulin, MAP1B and MAP2, by Western blot analysis and immunofluorescence in quiescent and nerve growth factor (NGF)-differentiated PC12W cells. These proteins are involved in neurite extension and neuronal maturation. Whereas NGF (0.5, 10, and 50 ng/ml) up-regulated these proteins after 3 days of stimulation, angiotensin II (ANG II; 10⁻⁷ M) induced a different pattern. In quiescent PC12W cells, AT₂ receptor stimulation up-regulated polymerized β-tubulin and MAP2 but down-regulated MAP1B protein levels. In PC12W cells, differentiated by NGF (0.5 ng/ml), ANG II elevated polymerized β-tubulin and reduced MAP1B. All ANG II effects were abolished by the AT₂ receptor antagonist PD123177 (10⁻⁵ M) but not affected by the AT₁ receptor antagonist losartan (10⁻⁵ M). These results implicate a specific role of AT₂ receptors in cell differentiation and nerve regeneration via regulation of the cytoskeleton.     

Electrical stimulation induces calcium‐dependent release of NGF from cultured Schwann cells

Production of nerve growth factor (NGF) from Schwann cells (SCs) progressively declines in the distal stump, if axonal regeneration is staggered across the suture site after peripheral nerve injuries. This may be an important factor limiting the outcome of nerve injury repair. Thus far, extensive efforts are devoted to modulating NGF production in cultured SCs, but little has been achieved. In the present in vitro study, electrical stimulation (ES) was attempted to stimulate cultured SCs to release NGF. Our data showed that ES was capable of enhancing NGF release from cultured SCs. An electrical field (1 Hz, 5 V/cm) caused a 4.1‐fold increase in NGF release from cultured SCs. The ES‐induced NGF release is calcium dependent. Depletion of extracellular or/and intracellular calcium partially/ completely abolished the ES‐induced NGF release. Further pharmacological interventions showed that ES induces calcium influx through T‐type voltage‐gated calcium channels and mobilizes calcium from 1, 4, 5‐trisphosphate‐sensitive stores and caffeine/ryanodine‐sensitive stores, both of which contributed to the enhanced NGF release induced by ES. In addition, a calcium‐triggered exocytosis mechanism was involved in the ES‐induced NGF release from cultured SCs. These findings show the feasibility of using ES in stimulating SCs to release NGF, which holds great potential in promoting nerve regeneration by enhancing survival and outgrowth of damaged nerves, and is of great significance in nerve injury repair and neuronal tissue engineering. © 2009 Wiley‐Liss, Inc.     

Enhancement of NGF- and cholera toxin-induced neurite outgrowth by butyrate in PC12 cells

It has been shown that sodium butyrate (NaBu) does not elicit neurite outgrowth of PC12, one of the most widely used cell lines as a model of neuronal differentiation. In this study, the effects of NaBu on nerve growth factor (NGF)- and cholera toxin-induced neurite outgrowth in PC12 cells were examined. NaBu dose-dependently enhanced neurite formation induced by both agents. The maximum responses obtained at 0.5 mM NaBu were nearly twice those of the inducers alone. Propionate and valerate were also effective, but acetate and caproate were ineffective. Among the butyrate analogs with a moiety of three to five carbon atoms tested, isobutyrate, isovalerate, vinylacetate and 3-chloropropionate enhanced neurite outgrowth promoted by both inducers. However, neither alpha-, beta-, and gamma-aminobutyrates nor alpha-, beta-, and gamma-hydroxybutyrates were effective. All of the effective short-chain fatty acids and their analogs increased the level of histone acetylation, while ineffective ones did not. Furthermore, Helminthosporium carbonum toxin (HC toxin), a structurally dissimilar inhibitor of histone deacetylase, mimicked the effect of butyrate. These results suggest that NaBu enhances neurite outgrowth induced by NGF and cholera toxin in PC12 cells through a mechanism involving an increase in the level of histone acetylation.     

Dose and duration of nerve growth factor (NGF) administration determine the extent of behavioral recovery following peripheral nerve injury in the rat

Nerve growth factor (NGF) has been previously shown to support neuron survival and direct neurite outgrowth in vitro, and to enhance axonal regeneration in vivo. However, a systematic analysis of NGF dose and dose duration on behavioral recovery following peripheral nerve injury in rodents has not been previously investigated. Here, we show that NGF promotes a bell shaped dose–response, with an optimal threshold effect occurring at 800 pg/μl. High dose NGF inhibited regeneration. However, this effect could be reversed through functional blockade of p75 receptors, thus implicating these receptors as mediators of the inhibitory response. Longer term evaluation showed that animals administered NGF at 80 ng/day for 3 weeks had greater sensorimotor recovery compared to all other treatment groups. These animals made significantly fewer errors during skilled locomotion, and displayed both increased vertical and fore-aft ground reaction forces during flat surface locomotion. Furthermore, terminal electrophysiological and myological assessments (EMG, wet gastrocnemius muscle weights) corroborated the behavioral data. Overall, these data support the hypothesis that both appropriate dose and duration of NGF are important determinants of behavioral recovery following nerve injury in the rat.     

p75 and TrkA receptors are both required for uptake of NGF in adult sympathetic neurons: use of a novel fluorescent NGF conjugate

We have developed and tested the biological activity and specificity of a novel fluorescent dextran-Texas Red–nerve growth factor (DTR–NGF) conjugate. DTR–NGF was found to promote survival and neurite outgrowth in cultured dissociated sympathetic neurons similarly to native NGF. The conjugate was taken up and transported retrogradely by terminal sympathetic nerves innervating the iris to neurons in the ipsilateral superior cervical ganglion (SCG) of young adult rats. Uptake and transport was assessed by counting numbers of labelled neurons and by measuring intensity of neuronal labelling using confocal microscopy and image analysis. DTR–NGF labelling in SCG neurons was shown to be dose-dependent with an EC₅₀ of 75 ng. Similar concentrations of unconjugated DTR resulted in no neuronal labelling. DTR–NGF uptake was competed off using a 50-fold excess of native NGF, resulting in a 73% reduction in numbers of labelled neurons. Pretreatment of nerve terminals with function-blocking antibodies against the low (p75) and high (TrkA) affinity NGF receptors resulted in a large (85–93%) reduction in numbers of DTR–NGF labelled neurons. Anti-p75 and anti-TrkA antibodies had comparable effects which were concentration-dependent. These findings indicate that both receptors are required for uptake of NGF in adult rat sympathetic neurons. In particular, the results provide strong evidence that the p75 receptor plays a more active role in transducing the NGF signal than has been proposed.     

Mutual induction of TGFbeta1 and NGF after treatment with NGF or TGFbeta1 in grafted chromaffin cells of the adrenal medulla

Chromaffin cells have been recognized for their ability to transform into sympathetic ganglion-like cells in response to nerve growth factor (NGF) or to stimulation of other neurotrophic factors. Transforming growth factor beta (TGFbeta) family members have been shown to potentiate the effect of different trophic factors. The aim of this study was to investigate if TGFbeta may influence NGF-induced neuronal transformation and regulation of NGF, TGFbeta1, and their receptors in the adult rat chromaffin tissue after grafting. Intraocular transplantation of adult chromaffin tissue was employed and grafts were treated with TGFbeta1 and/or NGF. Graft survival time was 18 days after which the grafts were processed for TGFbeta luciferase detection assay, NGF enzyme immunoassay, or in situ hybridization. In grafts stimulated with NGF, increased levels of TGFbeta1 and TGFbeta1 mRNA were detected. When grafts instead were treated with TGFbeta1, enhanced levels of NGF protein were found. Furthermore, a positive mRNA signal corresponding to the transforming growth factor II receptor (TbetaRII) was found in the chromaffin cells of the normal adrenal medulla as well as after grafting. No increase of TbetaRII mRNA levels was detected after transplantation or after TGFbeta1 treatment. Instead a reduction of TbetaRII mRNA expression was noted after NGF treatment. NGF stimulation of grafts increased the message for NGF receptors p75 and trkA in the chromaffin transplants. Grafts processed for evaluations of neurite outgrowth were allowed to survive for 28 days and were injected weekly with NGF and/or TGFbeta1. NGF treatment resulted in a robust innervation of the host irides. TGFbeta1 had no additive effect on nerve fiber formation when combined with NGF. Combined treatment of NGF and anti-TGFbeta1 resulted in a significantly larger area of reinnervation. In conclusion, it was found that NGF and TGFbeta1 may regulate the expression of each other's protein in adult chromaffin grafts. Furthermore, TbetaRII mRNA was present in the adult rat chromaffin cells and became downregulated as a result of NGF stimulation. Although no synergistic effects of TGFbeta1 were found on NGF-induced neurite outgrowth, it was found that TGFbeta1 and NGF signaling are closely linked in the chromaffin cells of the adrenal medulla.     

NGF Depletion Reduces Ipsilateral and Contralateral Trigeminal Satellite Cell Reactions after Inferior Alveolar Nerve Injury in Adult Rats

Following peripheral nerve injury, neuronal cell functions in sensory ganglia shift from normal maintenance and neurotransmission toward survival and regeneration. A rapid modulation of glial cell activity, which is related to changes in neuronal-support cell interaction, also occurs after nerve injury. Nerve growth factor (NGF) is required for the survival and maintenance of specific populations of sensory and sympathetic neurons, and changes in neuronal gene expression after axonal injury are due in part to a loss of NGF retrograde transport from the periphery to the cell body. A similar role for NGF in modulating support cell responses to peripheral nerve injury, however, has not been demonstrated. Using an autoimmune model, we assessed the effects of NGF depletion in adult rats on the injury-induced expression of glial fibrillary acid protein immunoreactivity (GFAP-IR) in the ipsilateral and contralateral trigeminal ganglia (TG). Unilateral inferior alveolar nerve crush resulted in abilateral,NGF-dependent trigeminal satellite cell response. In control rats there was a widespread induction of GFAP-IR in the ipsilateral as well as the contralateral TG. In contrast, GFAP-IR was reduced to the mandibular division of the ipsilateral TG in NGF-depleted rats, and the contralateral up-regulation of GFAP-IR was entirely abolished. Bilateral sympathectomy failed to mimic the effects of autoimmunization. Our results provide evidence that NGF depletion inhibits injury-induced satellite cell responses, independent of its effects on sympathetic nerve function.