Downregulation of TrkA expression in primary sensory neurons after unilateral lumbar spinal nerve transection and some rescuing effects of nerve growth factor infusion

Peripheral nerve injury results in sprouting of sympathetic and sensory nerve terminals around large diameter neurons in the dorsal root ganglia (DRG), but the underlying mechanism is not clear. Current study sought to examine changes of the nerve growth factor (NGF) receptor TrkA in DRG and spinal cord after a spinal nerve transection by an immunohistochemical technique and to investigate effects of NGF on the expression of TrkA protein in the same animal model. In the control rat, TrkA immunoreactivity was localized to about 55 +/ -1% of total neurons in DRG and to laminae I and II of the spinal cord. The percentage of TrkA immunoreactive neurons in DRG and TrkA staining intensity of spinal cord were reduced 1 week after the nerve lesion. The changes became maximal 2 weeks, but recovered partially 4 weeks after the lesion. The size of TrkA immunoreactive neurons dramatically shifted to smaller sizes, becoming more remarkable 4 weeks after the lesion. In the contralateral DRG, the percentage of TrkA immunoreactive neurons also decreased significantly. Exogenous NGF delivered to DRG for 2 weeks partially reversed the reduction of TrkA expression as well as atrophy of TrkA immunoreactive neurons. No TrkA immunoreactive basket was found around neuronal somata. Our data show that unilateral peripheral nerve injury results in dynamic downregulation of TrkA in sensory neurons in bilateral DRG and spinal cord, and that TrkA expression in sensory neurons is partially regulated by target-derived NGF.     

Distinct sprouting responses of sympathetic and peptidergic sensory axons proximal to a sciatic nerve transection in guinea pigs and rats

Sprouting of sympathetic and peptidergic sensory neurones proximal to nerve lesions may reflect upregulation of growth factors around damaged dorsal root ganglion (DRG) cells. Axons containing noradrenaline or calcitonin gene-related peptide were visualized in DRGs and spinal roots of guinea pigs and rats. After sciatic transection in rats, varicose terminals of both types appeared around large DRG somata. These neurones were surrounded by proliferated satellite cells expressing glial fibrillary acidic protein (GFAP) and p75. This did not occur in guinea pigs. Instead, sympathetic axons grew through the DRG and centrally along the dorsal roots (which contained p75-positive glia), avoiding the DRG somata. Thus the glial reaction to peripheral injury differs between species such that, in guinea pigs, the environment in the spinal roots rather than in the DRGs favours sympathetic sprouting.     

Activation profile of dorsal root ganglia Iba-1 (+) macrophages varies with the type of lesion in rats

The interactions between neurons, immune and immune-like glial cells can initiate the abnormal processes that underlie neuropathic pain. In the peripheral nervous system the resident macrophages may play an important role. In this study we investigated in experimental adult Sprague-Dawley rats how Iba-1 (ionized calcium binding adaptor molecule 1) (+) resident macrophages in the dorsal root ganglion (DRG) are activated after a spinal nerve ligation (SNL) or streptozotocin (STZ)-induced diabetes. The activation profile was defined by comparing the responses of resident macrophages against microglia in the spinal cord as they share a common origin. After SNL, the Iba-1 (+) macrophages in L5 DRG reached their activation peak 5 days later, clustered as satellite cells around large A-neurons, expressed the MHC-II marker, but did not show p-p38 and p-ERK1/2 activation and did not secrete IL-18. After STZ-induced diabetes, the Iba-1 (+) macrophages reached their activation peak 1 week later in L4 and L5 DRG, remained scattered between neurons, expressed the MHC-II marker only in L5 DRG, did not show p-p38 and p-ERK1/2 activation and did not secrete any of the investigated cytokines/chemokines. These responses suggest that depending on the type of lesion DRG Iba-1 (+) resident macrophages have different activation mechanisms, which are dissimilar to those in microglia.     

Activation of microglia and p38 mitogen-activated protein kinase in the dorsal column nucleus contributes to tactile allodynia following peripheral nerve injury

The activation of glial cells in the CNS has been suggested to be involved in abnormal pain sensation after peripheral nerve injury. Previous studies demonstrated phosphorylation of p38 mitogen-activated protein kinase (MAPK) in spinal cord glial cells after peripheral nerve injury, and such phosphorylation has been suggested to be involved in the development of neuropathic pain. The aim of this study was to examine the dorsal column nuclei for phosphorylation of p38 MAPK following peripheral nerve injury and to explore a possibility of its contribution to neuropathic pain. Immunohistochemical labeling for phosphorylated p38 (p-p38) MAPK was performed in histological sections of the rat spinal cord and medulla oblongata after the fifth lumbar (L5) spinal nerve ligation (SNL). The number of p-p38 MAPK-immunoreactive (IR) cells was significantly increased in the L5 dorsal horn and the gracile nucleus ipsilateral to the injury at days 3-21 after SNL. Double immunofluorescence labeling with cell-specific markers revealed that p-p38 MAPK-IR cells co-expressed OX-42, suggesting their microglial identity. Increased immunofluorescence labeling for OX-42 indicated that microglial cells were activated by SNL in the L5 dorsal horn and the gracile nucleus ipsilateral to the injury. Continuous infusion of a p38 MAPK inhibitor into the cisterna magna for 14 days beginning on the day of SNL suppressed the development of tactile allodynia, but not thermal hyperalgesia induced by nerve injury. These results demonstrate that SNL activates p38 MAPK pathway in microglia in the gracile nucleus as well as in the spinal cord dorsal horn. Activation of p38 MAPK in medullary microglia may contribute to the pathogenesis of neuropathic pain.     

Anatomical localization and expression pattern for the NMDA-2D receptor subunit in a rat model of neuropathic pain

The N-methyl-d-aspartate receptor (NMDAR) has been implicated in the etiology of chronic pain. In this regard, this study sought to characterize the localization and expression pattern for the NMDAR-2D subunit in a rat model of neuropathic pain. To this end, one group of rats, 3 weeks post-dorsal root rhizotomy (DRR) and a second group, 3 weeks post-spinal nerve ligation (SNL) and sham surgery, were generated. Dorsal root ganglia (DRG) and/or lumbar spinal cord were excised from DRR, naïve, SNL and sham rats. Both immunohistochemical and real-time PCR analysis confirmed discrete NMDAR-2D subunit expression within the DRG and dorsal horn. However, no overt differences in staining intensity or expression were noted between DRG and spinal cord sections obtained from the different surgical groups. Results also demonstrated that the NMDAR-2D subunit was present within Neu N+ cells in the spinal cord and DRG, but excluded from cells labeled with the astrocytic marker, GFAP, and the microglial maker, OX-42. Lastly, the NMDAR-2D subunit was not co-expressed within neurokinin-1 (NK-1)+ or neurofilament-52 (N-52)+ neurons, but the antibody did co-label a number of isolectin B4+ (IB4) DRG cells. Together, these findings seem to suggest that the NMDAR-2D receptor subunit is present within the cell body region of a population of small diameter sensory afferents and post-synaptically within second order dorsal horn neurons. Although these data suggest that the NMDAR-2D subunit is well poised anatomically to modulate pain neurotransmission, the expression pattern for this subunit is not altered in rats demonstrating the presence of neuropathic-like pain behavior.     

Progress in dorsal root ganglion neurosteroidogenic activity: Basic evidence and pathophysiological correlation

Dorsal root ganglia (DRG) which contain glial cells and somas of primary sensory neurons are pivotal for neural transmission between the peripheral and central nervous systems. It is well established that neuropeptides such as substance P and calcitonin gene-related peptide located in DRG neurons control sensory and pain mechanisms. However, contrary to the brain and spinal cord which are extensively investigated, DRG received little attention. Therefore, the current knowledge on DRG may be far to represent their complete neurochemical potential. For instance, until 1997, nothing was known on DRG neurosteroidogenic ability but recently, several investigations have shown that DRG contain various key enzymes synthesizing neuroactive neurosteroids. To provide new advances into DRG neurochemistry, we reviewed and highlighted herein basic and functional evidence showing that neurosteroids are produced in DRG through a neuron-glia crosstalk mechanism. Indeed, key enzymes producing neurosteroids including pregnenolone, progesterone, dihydroprogesterone and estradiol are differentially expressed in DRG cell types. Cytochrome P450side-chain-cleavage is located in DRG neurons and satellite glial cells, 3β-hydroxysteroid dehydrogenase is expressed in Schwann cells and neurons, 5α-reductase is localized in satellite glial and Schwann cells (not in neurons) while aromatase is present in neurons but not in glia. Recent studies also revealed that DRG neurosteroidogenesis is a physiologically relevant process selectively regulated under pathological conditions. Acting through paracrine and autocrine mechanisms, endogenous neurosteroids modulate DRG sensory functions and protect DRG neurons against death. The paper suggests that DRG neurosteroidogenic components may be targeted for the development of therapies against peripheral nerve injury-induced afferent noxious stimulations.     

Intrathecal Lamotrigine Attenuates Mechanical Allodynia and Suppresses Microglial and Astrocytic Activation in a Rat Model of Spinal Nerve Ligation

Purpose

Lamotrigine, a novel anticonvulsant, is a sodium channel blocker that is efficacious in certain forms of neuropathic pain. Recently, microglial and astrocytic activation has been implicated in the development of nerve injury-induced neuropathic pain. We have assessed the effects of continuous intrathecal administration of lamotrigine on the development of neuropathic pain and glial activation induced by L5/6 spinal-nerve ligation in rats.

Materials and Methods

Following left L5/6 spinal nerve ligation (SNL), Sprague-Dawley male rats were intrathecally administered lamotrigine (24, 72, or 240 µg/day) or saline continuously for 7 days. Mechanical allodynia of the left hind paw to von Frey filament stimuli was determined before surgery (baseline) and once daily for 7 days postoperatively. On day 7, spinal activation of microglia and astrocytes was evaluated immunohistochemically, using antibodies to the microglial marker OX-42 and the astrocyte marker glial fibrillary acidic protein (GFAP).

Results

Spinal-nerve ligation induced mechanical allodynia in saline-treated rats, with OX-42 and GFAP immunoreactivity being significantly increased on the ipsilateral side of the spinal cord. Continuously administered intrathecal lamotrigine (240 µg/day) prevented the development of mechanical allodynia, and lower dose of lamotrigine (72 µg/day) ameliorated allodynia. Intrathecal lamotrigine (72 and 240 µg/day) inhibited nerve ligation-induced microglial and astrocytic activation, as evidenced by reduced numbers of cells positive for OX-42 and GFAP.

Conclusion

Continuously administered intrathecal lamotrigine blocked the development of mechanical allodynia induced by SNL with suppression of microglial and astrocytic activation. Continuous intrathecal administration of lamotrigine may be a promising therapeutic intervention to prevent neuropathy.     

ATP-sensitive potassium currents in rat primary afferent neurons: biophysical,pharmacological properties,and alterations by painful nerve injury

ATP-sensitive potassium (K_ATP) channels may be linked to mechanisms of pain after nerve injury, but remain under-investigated in primary afferents so far. We therefore characterized these channels in dorsal root ganglion (DRG) neurons, and tested whether they contribute to hyperalgesia after spinal nerve ligation (SNL). We compared K_ATP channel properties between DRG somata classified by diameter into small or large, and by injury status into neurons from rats that either did or did not become hyperalgesic after SNL, or neurons from control animals. In cell-attached patches, we recorded basal K_ATP channel opening in all neuronal subpopulations. However, higher open probabilities and longer open times were observed in large compared to small neurons. Following SNL, this channel activity was suppressed only in large neurons from hyperalgesic rats, but not from animals that did not develop hyperalgesia. In contrast, no alterations of channel activity developed in small neurons after axotomy. On the other hand, cell-free recordings showed similar ATP sensitivity, inward rectification and unitary conductance (70–80 pS) between neurons classified by size or injury status. Likewise, pharmacological sensitivity to the K_ATP channel opener diazoxide, and to the selective blockers glibenclamide and tolbutamide, did not differ between groups. In large neurons, selective inhibition of whole-cell ATP-sensitive potassium channel current (I_K(ATP)) by glibenclamide depolarized resting membrane potential (RMP). The contribution of this current to RMP was also attenuated after painful axotomy. Using specific antibodies, we identified SUR1, SUR2, and Kir6.2 but not Kir6.1 subunits in DRGs. These findings indicate that functional K_ATP channels are present in normal DRG neurons, wherein they regulate RMP. Alterations of these channels may be involved in the pathogenesis of neuropathic pain following peripheral nerve injury. Their biophysical and pharmacological properties are preserved even after axotomy, suggesting that K_ATP channels in primary afferents remain available for therapeutic targeting against established neuropathic pain.     

Alteration of dorsal root ganglion P2X3 receptor expression and function following spinal nerve ligation in the rat

One subtype of ATP-gated ion channel, the P2X₃ receptor, is expressed primarily on peripheral sensory neurons. While it is known that P2X₃ receptors can participate in certain forms of nociceptive signaling, their involvement in neuropathic pain transmission is not known. We have examined the expression and function of P2X₃ receptors in a rat spinal nerve ligation model of neuropathic pain. Fourteen days following L5/L6 spinal nerve ligation, the corresponding dorsal root ganglia (DRG) were removed from animals exhibiting mechanical allodynia, and these were studied using immunohistochemical and electrophysiological techniques. Using a polyclonal antibody to label the P2X₃ receptor, a significant reduction in neuronal P2X₃ immunoreactivity was observed in the ipsilateral (injured) L5 and L6 DRG following nerve ligation. In vitro electrophysiological analysis of acutely isolated DRG neurons revealed a similar decrease in functional P2X₃-containing receptors. In small diameter (22–25 μm) neurons, a significant reduction in the number of cells exhibiting a response to α,β-meATP was observed. However, a subset of small diameter neurons retained P2X₃ responses of equal amplitude to those recorded from naive and sham control DRG neurons. Interestingly, P2X₃ immunoreactivity and P2X₃-like responses were also detected in a subset of larger diameter (50 μm) neurons and the number and amplitude of these responses were unchanged after spinal nerve ligation. These results suggest that, while there appears to be a decrease in fast desensitizing P2X₃ receptors following L5/L6 nerve ligation injury, certain subsets of small and large DRG neurons maintain normal P2X₃ receptor expression and function. These remaining receptors may provide a P2X₃ receptor-mediated component to neuropathic pain. Electronic Publication     

外源性NGF对大鼠坐骨神经切断缝合术后脊髓和背根节CGRP表达的影响

观察外源性神经生长因子(NGF)对坐骨神经切断立即缝合后大鼠脊髓和背根节(DRG)内不同时间点降钙素基因相关肽(CGRP)表达的影响。成年SD雄性大鼠随机分为NGF组、生理盐水(NS)组、假手术组与正常对照组。实验组动物右侧坐骨神经切断后立即缝合,每天给予NGF(400单位/kg腹腔注射),动物分别存活1、3、5、7、14、21、28d,免疫组织化学方法结合图像分析检测相应节段脊髓和背根节内CGRP的表达。结果表明,NGF处理组术侧背根节与脊髓后角内的CGRP表达明显高于同时间点的NS对照组,平均光密度值相比P<0.05。但各组中脊髓前角运动神经元内的CGRP表达没有明显变化(P>0.05)。结果提示外源性的NGF能明显增加损伤后背根节感觉神经元与损伤侧脊髓后角的CGRP表达,对CGRP在脊髓前角运动神经元内的表达没有明显影响。     

Expression of brain-derived neurotrophic factor in rat dorsal root ganglia, spinal cord and gracile nuclei in experimental models of neuropathic pain.

Chronic constriction injury of the sciatic nerve and lumbar L5 and L6 spinal nerve ligation provide animal models for pain syndromes accompanying peripheral nerve injury and disease. In the present study, we evaluated changes in brain-derived neurotrophic factor (BDNF) immunoreactivity in the rat L4 and L5 dorsal root ganglia (DRG) and areas where afferents from the DRG terminates (the L4/5 spinal cord and gracile nuclei) in these experimental models of neuropathic pain. Chronic constriction injury induced significant increase in the percentage of small, medium and large BDNF-immunoreactive neurons in the ipsilateral L4 and L5 DRG. Following spinal nerve ligation, the percentage of large BDNF-immunoreactive neurons increased significantly, and that of small BDNF-immunoreactive neurons decreased markedly in the ipsilateral L5 DRG, while that of BDNF-immunoreactive L4 DRG neurons of all sizes showed marked increase. Both chronic constriction injury and spinal nerve ligation induced significant increase in the number of BDNF-immunoreactive axonal fibers in the superficial and deeper laminae of the L4/5 dorsal horn and the gracile nuclei on the ipsilateral side.Considering that BDNF may modulate nociceptive sensory inputs and that injection of antiserum to BDNF significantly reduces the sympathetic sprouting in the DRG and allodynic response following sciatic nerve injury, our results also may suggest that endogenous BDNF plays an important role in the induction of neuropathic pain after chronic constriction injury and spinal nerve ligation. In addition, the increase of BDNF in L4 DRG may contribute to evoked pain which is known to be mediated by input from intact afferent from L4 DRG following L5 and L6 spinal nerve ligation.     

Activation of fibroblast growth factor receptor by axotomy, through downstream p38 in dorsal root ganglion, contributes to neuropathic pain

The possible involvement of fibroblast growth factor receptor (FGFR) activation in the dorsal root ganglion (DRG) was examined following peripheral nerve injury in the rat. Ligation of the sciatic nerve down-regulated FGFR2, -3 and -4 mRNA; however, the expression of FGFR1 mRNA showed no change. Activation of FGFR was examined by immunohistochemistry using an antibody of the phosphorylated form of FGFR1-4. Ligation of the sciatic nerve produced phosphorylation of FGFR in the L4 and 5 DRG ipsilateral to the injury, starting at 3 days after the lesion and persisting for more than 30 days. Substantial activation of FGFR was observed, mainly in unmyelinated small DRG neurons that co-expressed phosphorylated p38 mitogen-activated protein kinase (MAPK). Continuous intrathecal infusion of the FGFR1 inhibitor, 3-[3-(2-carboxyethyl)-4-methylpyrrol-2-methylidenyl]-2-indolinone, reduced p38 MAPK phosphorylation in the DRG and pain-related behaviors in the partial sciatic nerve model rat without affecting on the activation of spinal glia cells (microglia and astrocyte). In the injured small DRG neurons, activation of FGFR1 may contribute to the generation of neuropathic pain by activating p38 MAPK.     

Reg-2 expression in dorsal root ganglion neurons after adjuvant-induced monoarthritis

Reg-2 is a secreted protein that is expressed de novo in motoneurons, sympathetic neurons, and dorsal root ganglion (DRG) neurons after nerve injury and which can act as a Schwann cell mitogen. We now show that Reg-2 is also upregulated by DRG neurons in inflammation with a very unusual expression pattern. In a rat model of monoarthritis, Reg-2 immunoreactivity was detected in DRG neurons at 1 day, peaked at 3 days (in 11.6% of DRG neurons), and was still present at 10 days (in 5%). Expression was almost exclusively in the population of DRG neurons that expresses the purinoceptor P2X(3) and binding sites for the lectin Griffonia simplicifolia IB4, and which is known to respond to glial cell line-derived neurotrophic factor (GDNF). Immunoreactivity was present in DRG cell bodies and central terminals in the dorsal horn of the spinal cord. In contrast, very little expression was seen in the nerve growth factor (NGF) responsive and substance P expressing population. However intrathecal delivery of GDNF did not induce Reg-2 expression, but leukemia inhibitory factor (LIF) had a dramatic effect, inducing Reg-2 immunoreactivity in 39% of DRG neurons and 62% of P2X(3) cells. Changes in inflammation have previously been observed predominantly in the neuropeptide expressing, NGF responsive, DRG neurons. Our results show that changes also take place in the IB4 population, possibly driven by members of the LIF family of neuropoietic cytokines. In addition, the presence of Reg-2 in central axon terminals implicates Reg-2 as a possible modulator of second order dorsal horn cells.     

Minocycline prevents impaired glial glutamate uptake in the spinal sensory synapses of neuropathic rats

Activation of glutamate receptors and glial cells in the spinal dorsal horn are two fundamental processes involved in the pathogenesis of various pain conditions, including neuropathic pain induced by injury to the peripheral or central nervous systems. Numerous studies have demonstrated that minocycline treatment attenuates allodynic and hyperalgesic behaviors induced by tissue inflammation or nerve injury. However, the synaptic mechanisms by which minocycline prevents hyperalgesia are not fully understood. We recently reported that deficient glutamate uptake by glial glutamate transporters (GTs) is key for the enhanced activation of N-methyl-d-aspartate (NMDA) receptors in the spinal sensory synapses of rats receiving partial sciatic nerve ligation (pSNL). In this study, we investigated how minocycline affects activation of NMDA receptors in the spinal sensory synapses in rats with pSNL by whole cell recordings of NMDA currents in spinal laminea I and II neurons from spinal slices. The effects of minocycline treatments on the dorsal horn expression of glial GTs and astrocyte marker glial fibrillary acidic protein (GFAP) were analyzed by immunohistochemistry. We demonstrated that normalized activation of NMDA receptors in synapses activated by both weak and strong peripheral input in the spinal dorsal horn is temporally associated with attenuated mechanical allodynia in rats with pSNL receiving intraperitoneal injection of minocycline. Minocycline ameliorated both the downregulation of glial GT expression and the activation of astrocytes induced by pSNL in the spinal dorsal horn. We further revealed that preventing deficient glial glutamate uptake at the synapse is crucial for preserving the normalized activation of NMDA receptors in the spinal sensory synapses in pSNL rats treated with minocycline. Our studies suggest that glial GTs may be a potential target for the development of analgesics.     

TWIK-Related Spinal Cord K+ Channel Expression Is Increased in the Spinal Dorsal Horn after Spinal Nerve Ligation

Purpose

The TWIK-related spinal cord K⁺ channel (TRESK) has recently been discovered and plays an important role in nociceptor excitability in the pain pathway. Because there have been no reports on the TRESK expression or its function in the dorsal horn of the spinal cord in neuropathic pain, we analyzed TRESK expression in the spinal dorsal horn in a spinal nerve ligation (SNL) model.

Materials and Methods

We established a SNL mouse model by using the L5-6 spinal nerves ligation. We used real-time polymerase chain reaction and immunohistochemistry to investigate TRESK expression in the dorsal horn and L5 dorsal rot ganglion (DRG).

Results

The SNL group showed significantly higher expression of TRESK in the ipsilateral dorsal horn under pain, but low expression in L5 DRG. Double immunofluorescence staining revealed that immunoreactivity of TRESK was mostly restricted in neuronal cells, and that synapse markers GAD67 and VGlut2 appeared to be associated with TRESK expression. We were unable to find a significant association between TRESK and calcineurin by double immunofluorescence.

Conclusion

TRESK in spinal cord neurons may contribute to the development of neuropathic pain following injury.     

GABAA receptor modulation in dorsal root ganglia in vivo affects chronic pain after nerve injury

Neuropathic pain (NPP) due to sensory nerve injury is, in part, the result of peripheral sensitization leading to a long-lasting increase in synaptic plasticity in the spinal dorsal horn. Thus, activation of GABA-mediated inhibitory inputs from sensory neurons could be beneficial in the alleviation of NPP symptoms. Dorsal root ganglia (DRG) conduct painful stimulation from the periphery to the spinal cord. Long-lasting down-regulation in GABA tone or sensitivity in DRG neurons has been reported in animals with neuropathy. To determine the function of GABA in DRG in the development of NPP, we examined how the acute pharmacological GABA(A)-receptor modulation of L5 DRG in vivo affects the development of NPP in rats with crush injury to the sciatic nerve. Direct application of muscimol and gaboxadol, GABA(A) agonists, to L5 DRG immediately after injury induced dose-dependent alleviation, whereas bicuculline and picrotoxin, GABA(A) antagonists, worsened NPP postaxonal injury. The pain-alleviating effects of muscimol and gaboxadol were blocked by bicuculline. Muscimol, applied at the time of injury, caused complete and long-lasting abolishment of NPP development. However, when muscimol was applied after NPP had already developed, its pain-alleviating effect, although significant, was short-lived. Using a fluorescent tracer, sodium fluorescein, we confirmed that local DRG application results in minimal spread into the corresponding dorsal horn of the ipsilateral spinal cord. GABA(A) receptors in DRG are important in the development of NPP after peripheral nerve injury, making timely exogenous GABAergic manipulation at the DRG level a potentially useful therapeutic modality.     

Isolation and characterization of neural crest progenitors from adult dorsal root ganglia

After peripheral nerve injury, the number of sensory neurons in the adult dorsal root ganglia (DRG) is initially reduced but recovers to a normal level several months later. The mechanisms underlying the neuronal recovery after injury are not clear. Here, we showed that in the DRG explant culture, a subpopulation of cells that emigrated out from adult rat DRG expressed nestin and p75 neurotrophin receptor and formed clusters and spheres. They differentiated into neurons, glia, and smooth muscle cells in the presence or absence of serum and formed secondary and tertiary neurospheres in cloning assays. Molecular expression analysis demonstrated the characteristics of neural crest progenitors and their potential for neuronal differentiation by expressing a set of well-defined genes related to adult stem cells niches and neuronal fate decision. Under the influence of neurotrophic factors, some of these progenitors gave rise to neuropeptide-expressing cells and protein zero-expressing Schwann cells. In a 5-bromo-2'-deoxyuridine chasing study, we showed that these progenitors likely originate from satellite glial cells. Our study suggests that a subpopulation of glia in adult DRG is likely to be progenitors for neurons and glia and may play a role in neurogenesis after nerve injury. Disclosure of potential conflicts of interest is found at the end of this article.