Neuronal-glial differential expression of TGF-alpha and its receptor in the dorsal root ganglia in response to sciatic nerve lesion

The assessment of neuronal plasticity following sciatic nerve injuries in rats using electron microscopy and stereological methods

The transmission of signals to the cell body from injured axons induces significant alterations in primary sensory neurons located in the ganglion tissue, the site of the perikaryon of the affected nerve fibers. Disruption of the continuity between the proximal and distal ends leads to substantial adaptability in ganglion cells and induces macrophage-like activity in the satellite cells. Research findings have demonstrated the plasticity of satellite cells following injury. Satellite cells work together with sensory neurons to extend the interconnected surface area in order to permit effective communication. The dynamic cellular environment within the ganglion undergoes several alterations that ultimately lead to differentiation, transformation, or cell death. In addition to necrotic and apoptotic cell morphology, phenomena such as histomorphometric alterations, including the development of autophagic vacuoles, chromatolysis, cytosolic degeneration, and other changes, are frequently observed in cells following injury. The use of electron microscopic and stereological techniques for assessing ganglia and nerve fibers is considered a gold standard in terms of investigating neuropathic pain models, regenerative therapies, some treatment methods, and quantifying the outcomes of pharmacological and bioengineering interventions. Stereological techniques provide observer-independent and reliable results, which are particularly useful in the quantitative assessment of three-dimensional structures from two-dimensional images. Employing the fractionator and disector techniques within stereological methodologies yields unbiased data when assessing parameters such as number. The fundamental concept underlying these methodologies involves ensuring that each part of the structure under evaluation has an equal opportunity of being sampled. This review describes the stereological and histomorphometric evaluation of dorsal root ganglion neurons and satellite cells following nerve injury models.

Burn Injury-related Growth Factor Expressions and Their Potential Roles in Burn-related Neuropathies

In the context of burn injury, growth factors (GFs) play a significant role in mediating the complex local and systematic processes that occur. Among the many systemic complications that arise following a burn injury, peripheral neuropathy remains one of the most common. Despite the broad understanding of the effects GFs have on multiple tissues, their potential implications in both wound healing and neuropathy remain largely unexplored. Therefore, this review aims to investigate the expression patterns of GFs prominent during the burn wound healing process and explore the potential contributions these GFs have on the development of burn-related peripheral neuropathy.

Osteoclast-derived extracellular vesicles are implicated in sensory neurons sprouting through the activation of epidermal growth factor signaling

BACKGROUND

Different pathologies, affecting the skeletal system, were reported to display altered bone and/or cartilage innervation profiles leading to the deregulation of the tissue homeostasis. The patterning of peripheral innervation is achieved through the tissue-specific expression of attractive or repulsive axonal guidance cues in specific space and time frames. During the last decade, emerging findings attributed to the extracellular vesicles (EV) trading a central role in peripheral tissue innervation. However, to date, the contribution of EV in controlling bone innervation is totally unknown.

RESULTS

Here we show that sensory neurons outgrowth induced by the bone resorbing cells-osteoclasts-is promoted by osteoclast-derived EV. The EV induced axonal growth is achieved by targeting epidermal growth factor receptor (EGFR)/ErbB2 signaling/protein kinase C phosphorylation in sensory neurons. In addition, our data also indicate that osteoclasts promote sensory neurons electrophysiological activity reflecting a possible pathway in nerve sensitization in the bone microenvironment, however this effect is EV independent.

CONCLUSIONS

Overall, these results identify a new mechanism of sensory bone innervation regulation and shed the light on the role of osteoclast-derived EV in shaping/guiding bone sensory innervation. These findings provide opportunities for exploitation of osteoclast-derived EV based strategies to prevent and/or mitigate pathological uncontrolled bone innervation.

2D <em>vs</em> 3D morphological analysis of dorsal root ganglia in health and painful neuropathy

Dorsal root ganglia (DRGs) are clusters of sensory neurons that transmit the sensory information from the periphery to the central nervous system, and satellite glial cells (SGCs), their supporting trophic cells. Sensory neurons are pseudounipolar neurons with a heterogeneous neurochemistry reflecting their functional features. DRGs, not protected by the blood brain barrier, are vulnerable to stress and damage of different origin (i.e., toxic, mechanical, metabolic, genetic) that can involve sensory neurons, SGCs or, considering their intimate intercommunication, both cell populations. DRG damage, primary or secondary to nerve damage, produces a sensory peripheral neuropathy, characterized by neurophysiological abnormalities, numbness, paraesthesia and dysesthesia, tingling and burning sensations and neuropathic pain. DRG stress can be morphologically detected by light and electron microscope analysis with alterations in cell size (swelling/atrophy) and in different subcellular compartments (i.e., mitochondria, endoplasmic reticulum, and nucleus) of neurons and/or SGCs. In addition, neurochemical changes can be used to portray abnormalities of neurons and SGC. Conventional immunostaining, i.e., immunohistochemical detection of specific molecules in tissue slices, can be employed to detect, localize and quantify particular markers of damage in neurons (i.e., nuclear expression of ATF3) or SGCs (i.e., increased expression of GFAP), markers of apoptosis (i.e., caspases), markers of mitochondrial suffering and oxidative stress (i.e., 8-OHdG), markers of tissue inflammation (i.e., CD68 for macrophage infiltration) etc. However classical (2D) methods of immunostaining disrupt the overall organization of the DRG, thus resulting in the loss of some crucial information. Whole-mount (3D) methods have been recently developed to investigate DRG morphology and neurochemistry without tissue slicing, giving the opportunity to study the intimate relationship between SGCs and sensory neurons in health and disease. Here, we aim to compare classical (2D) vs whole-mount (3D) approaches to highlight “pros” and “cons” of the two methodologies when analysing neuropathy-induced alterations in DRGs.

Obscure Involvement of MYC in Neurodegenerative Diseases and Neuronal Repair

MYC is well known as a potent oncogene involved in regulating cell cycle and metabolism. Augmented MYC expression leads to cell cycle dysregulation, intense cell proliferation, and carcinogenesis. Surprisingly, its increased expression in neurons does not induce their proliferation, but leads to neuronal cell death and consequent development of a neurodegenerative phenotype. Interestingly, while cancer and neurodegenerative diseases such as Alzheimer's disease are placed at the opposite sides of cell division spectrum, both start with cell cycle dysregulation and stimulation of proliferation. It seems that MYC action directed toward neuron cell proliferation and neural tissue repair collides with evolutional loss of regenerative capacity of CNS neurons in order to strengthen synaptic structure, to protect our cognitive abilities and therefore character. Accordingly, there are abundant mechanisms that block its expression and action specifically in the brain. Moreover, while MYC expression in brain neurons during neurodegenerative processes is related to their death, there are obvious evidences that MYC action after physical injury is beneficial in case of peripheral nerve recovery. MYC might be a useful tool to repair brain cells upon development of neurodegenerative disease or CNS trauma, including stroke and traumatic brain and spinal cord injury, as even imperfect axonal growth and regeneration strategies will likely be of profound benefit. Understanding complex control of MYC action in the brain might have important therapeutic significance, but also it may contribute to the comprehension of development of neurodegenerative diseases.

Role of EGFR in the Nervous System

Epidermal growth factor receptor (EGFR) is the first discovered member of the receptor tyrosine kinase superfamily and plays a fundamental role during embryogenesis and in adult tissues, being involved in growth, differentiation, maintenance and repair of various tissues and organs. The role of EGFR in the regulation of tissue development and homeostasis has been thoroughly investigated and it has also been demonstrated that EGFR is a driver of tumorigenesis. In the nervous system, other growth factors, and thus other receptors, are important for growth, differentiation and repair of the tissue, namely neurotrophins and neurotrophins receptors. For this reason, for a long time, the role of EGFR in the nervous system has been underestimated and poorly investigated. However, EGFR is expressed both in the central and peripheral nervous systems and it has been demonstrated to have specific important neurotrophic functions, in particular in the central nervous system. This review discusses the role of EGFR in regulating differentiation and functions of neurons and neuroglia. Furthermore, its involvement in regeneration after injury and in the onset of neurodegenerative diseases is examined.

FOXO3a as a sensor of unilateral nerve injury in sensory neurons ipsilateral, contralateral and remote to injury

Emerging evidence supports that the stress response to peripheral nerve injury extends beyond the injured neuron, with alterations in associated transcription factors detected both locally and remote to the lesion. Stress-induced nuclear translocation of the transcription factor forkhead class box O3a (FOXO3a) was initially linked to activation of apoptotic genes in many neuronal subtypes. However, a more complex role of FOXO3a has been suggested in the injury response of sensory neurons, with the injured neuron expressing less FOXO3a. To elucidate this response and test whether non-injured sensory neurons also alter FOXO3a expression, the temporal impact of chronic unilateral L4–6 spinal nerve transection on FOXO3a expression and nuclear localization in adult rat dorsal root ganglion neurons ipsilateral, contralateral or remote to injury relative to naïve controls was examined. In naïve neurons, high cytoplasmic and nuclear levels of FOXO3a colocalized with calcitonin gene related peptide, a marker of the nociceptive subpopulation. One hour post-injury, an acute increase in nuclear FOXO3a in small size injured neurons occurred followed by a significant decrease after 1, 2 and 4 days, with levels increasing toward pre-injury levels by 1 week post-injury. A more robust biphasic response to the injury was observed in uninjured neurons contralateral to and those remote to injury. Nuclear levels of FOXO3a peaked at 1 day, decreased by 4 days, then increased by 1 week post-injury, a response mirrored in C4 dorsal root ganglion neurons remote to injury. This altered expression contralateral and remote to injury supports that spinal nerve damage has broader systemic impacts, a response we recently reported for another stress transcription factor, Luman/CREB3. The early decreased expression and nuclear localization of FOXO3a in the injured neuron implicate these changes in the cell body response to injury that may be protective. Finally, the broader systemic changes support the existence of stress/injury-induced humeral factor(s) influencing transcriptional and potentially behavioral changes in uninjured dorsal root ganglion neurons. Approval to conduct this study was obtained from the University of Saskatchewan Animal Research Ethics Board (protocol #19920164).

Axonal outgrowth, neuropeptides expression and receptors tyrosine kinase phosphorylation in 3D organotypic cultures of adult dorsal root ganglia

Limited knowledge from mechanistic studies on adult sensory neuronal activity was generated, to some extent, in recapitulated adult in vivo 3D microenvironment. To fill this gap there is a real need to better characterize the adult dorsal root ganglia (aDRG) organotypic cultures to make these in vitro systems exploitable for different approaches, ranging from basic neurobiology to regenerative therapies, to address the sensory nervous system in adult stage. We conducted a direct head-to-head comparison of aDRG and embryonic DRG (eDRG) organotypic culture focusing on axonal growth, neuropeptides expression and receptors tyrosine kinase (RTK) activation associated with neuronal survival, proliferation and differentiation. To identify alterations related to culture conditions, these parameters were also addressed in retrieved aDRG and eDRG and compared with organotypic cultures. Under similar neurotrophic stimulation, aDRG organotypic cultures displayed lower axonal outgrowth rate supported by reduced expression of growth associated protein-43 and high levels of RhoA and glycogen synthase kinase 3 beta mRNA transcripts. In addition, differential alteration in sensory neuropeptides expression, namely calcitonin gene-related peptide and substance P, was detected and was mainly pronounced at gene expression levels. Among 39 different RTK, five receptors from three RTK families were emphasized: tropomyosin receptor kinase A (TrkA), epidermal growth factor receptors (EGFR, ErbB2 and ErbB3) and platelet-derived growth factor receptor (PDGFR). Of note, except for EGFR, the phosphorylation of these receptors was dependent on DRG developmental stage and/or culture condition. In addition, EGFR and PDGFR displayed alterations in their cellular expression pattern in cultured DRG. Overall we provided valuable information particularly important when addressing in vitro the molecular mechanisms associated with development, maturation and regeneration of the sensory nervous system.

The expression patterns of beta1,4 galactosyltransferase I and V mRNAs, and Galbeta1-4GlcNAc group in rat gastrocnemius muscles post sciatic nerve injury

Glycosylation is one of the most important post-translational modifications. It is clear that the single step of beta1,4-galactosylation is performed by a family of beta1,4-galactosyltransferases (beta1,4-GalTs), and that each member of this family may play a distinct role in different tissues and cells. beta1,4-GalT I and V are involved in the biosynthesis of N-linked oligosaccharides and play roles in sciatic nerve regeneration after sciatic nerve injury. In the present study, the expression of beta1,4-galactosyltransferase (beta1,4-GalT) I, V mRNAs and Galbeta1-4GlcNAc group were examined in rat gastrocnemius muscles after sciatic nerve crush and transection. Real time PCR revealed that beta1,4-GalT I and V mRNAs expressed at a high level in normal gastrocnemius muscles and decreased gradually from 6 h, reached the lowest level at 2 weeks, then restored gradually to relatively normal level at 4 weeks after sciatic nerve crush. In contrast, in sciatic nerve transection model, beta1,4-GalT I and V mRNAs decreased gradually from 6 h, and remained on a low level at 4 weeks in gastrocnemius muscles after sciatic nerve transection. In situ hybridization indicated that beta1,4-GalT I and V mRNAs localized in numerous myocytes and muscle satellite cells under normal conditions and at 4 weeks after sciatic nerve crush, and in a few muscle satellite cells at 4 weeks after sciatic nerve transection. Furthermore, lectin blotting showed that the expression level of the Galbeta1-4GlcNAc group decreased from 6 h, reached the lowest level at 2 weeks, and restored to relatively normal level at 4 weeks after sciatic nerve crush. RCA-I lectin histochemistry demonstrated that Galbeta1-4GlcNAc group localized in numerous membranes of myocytes and muscle satellite cells in normal and at 4 weeks after sciatic nerve crush, and in a few muscle satellite cells at 2 and 4 weeks after sciatic nerve transection. These results indicated that the expressions of beta1,4-GalT I, V mRNAs and Galbeta1-4GlcNAc group were involved in the process of denervation and reinnervation, which suggests that beta1,4-GalT I, V mRNAs and Galbeta1-4GlcNAc group may play an important role in the muscle regeneration.

Expression change of beta-1,4 galactosyltransferase I, V mRNAs and Galbeta1,4GlcNAc group in rat sciatic nerve after crush

Glycosylation is one of the most important post-translational modifications. It is clear that the single step of beta-1,4-galactosylation is performed by a family of beta-1,4-galactosyltransferases (beta-1,4-GalTs), and that each member of this family may play a distinct role in different tissues and cells. beta-1,4-GalT I and V are involved in the biosynthesis of N-linked oligosaccharides. In the present study, Real-time PCR revealed that the beta-1,4-GalT I and V mRNAs reached peaks at 2 w after sciatic nerve crush. In situ hybridization showed that at 1 d after sciatic nerve crush, the expression levels of beta-1,4-GalT I and V mRNAs were strong at the crush site, and decreased gradually from crush site to the distal segments. In addition, combined in situ hybridization for beta1,4-GalT I and V mRNAs and immunohistochemistry for S100 showed that beta1,4-GalT I and V mRNAs were mainly located in Schwann cells. Lectin blot showed that the expression of Galbeta1,4GlcNAc group increased at 6 h immediately, reached a peak at 12 h and remained elevated up to 4 w after sciatic nerve crush. In conclusion, beta1,4-GalT I and V might play important roles in the regeneration of the injured sciatic nerve, and upregulation of Galbeta1,4GlcNAc group might be correlated with the process of the sciatic nerve injury.

Growth factors differentially regulate neuronal Cav channels via ERK-dependent signalling

Voltage-gated calcium channels (Ca(v)) are tonically up-regulated via Ras/extracellular signal-regulated kinase (ERK) signalling in sensory neurones. However, the mechanisms underlying the specificity of cellular response to this pathway remain unclear. Neurotrophic factors are attractive candidates to be involved in this process as they are key regulators of ERK signalling and have important roles in neuronal survival, development and plasticity. Here, we report that in rat dorsal root ganglion neurones, endogenous nerve growth factor (NGF), glial derived neurotrophic factor (GDNF) and epidermal growth factor (EGF) are all involved in tonic ERK-dependent up-regulation of Ca(v) channels. Chronic (overnight) deprivation of growth factors inhibits total Ca(v) current according to developmental changes in expression of the cell surface receptors for NGF, GDNF and EGF. Whilst EGF specifically regulates transcriptional expression of Ca(v)s, NGF and GDNF also acutely modulate Ca(v) channels within a rapid ( approximately 10min) time-frame. These acute effects likely involve changes in the biophysical properties of Ca(v)s, including altered channel gating rather than changes in surface expression. Furthermore, NGF, GDNF and EGF differentially regulate specific populations of Ca(v)s. Thus, ERK-dependent regulation of Ca(v) activity provides an elegant and extremely flexible system with which to tailor calcium influx to discrete functional demands.

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.

Expression of beta-1,4-galactosyltransferase-I in rat during inflammation

beta-1,4-Galactosyltransferase-I (beta-1,4-GalT-I) which is one of the best-studied glycosyltransferases, plays a key role in the synthesis of selectin ligands such as sialy Lewis (sLe( x )) and sulfated sLe( x ). Previous studies showed that inflammatory responses of beta-1,4-GalT-I-deficient mice were impaired because of the defect in selectin-ligand biosynthesis. However, the expression of beta-1,4-GalT-I during inflammation and its biological function remains to be elucidated. Real-time PCR showed that intraperitoneal administration of LPS strongly induced beta-1,4-GalT-I mRNA expression in the lung, heart, liver, spleen, kidney, lymph node, hippocampus, and testis, as well as in the cerebral cortex. In the rat lung, liver and testis, LPS stimulation of beta-1,4-GalT-I mRNA expression is time-dependent and biphasic. Lectin-fluorescent staining with RCA-I showed that LPS induced expression of galactose-containing glycans in rat lung and liver to the higher lever. Morphology analysis observed that galactose-containing glycans and beta-1,4-GalT-I mRNA was mostly expressed in neutrophils, macrophages and endothelial cells. These findings indicated that beta-1,4-GalT-I may play an important role in the inflammation reaction.

The ADAMs family: coordinators of nervous system development, plasticity and repair

A disintegrin and metalloprotease (ADAM) transmembrane proteins have metalloprotease, integrin-binding, intracellular signaling and cell adhesion activities. In contrast to other metalloproteases, ADAMs are particularly important for cleavage-dependent activation of proteins such as Notch, amyloid precursor protein (APP) and transforming growth factor alpha (TGFalpha), and can bind integrins. Not surprisingly, ADAMs have been shown or suggested to play important roles in the development of the nervous system, where they regulate proliferation, migration, differentiation and survival of various cells, as well as axonal growth and myelination. On the eleventh anniversary of the naming of this family of proteins, the relatively unknown ADAMs are emerging as potential therapeutic targets for neural repair. For example, over-expression of ADAM10, one of the alpha-secretases for APP, can prevent amyloid formation and hippocampal defects in an Alzheimer mouse model. Another example of this potential neural repair role is the finding that ADAM21 is uniquely associated with neurogenesis and growing axons of the adult brain. This comprehensive review will discuss the growing literature about the roles of ADAMs in the developing and adult nervous system, and their potential roles in neurological disorders. Most excitingly, the expanding understanding of their normal roles suggests that they can be manipulated to promote neural repair in the degenerating and injured adult nervous system.

Intra- and Extraneuronal Changes of Immunofluorescence Staining for TNF- and TNFR1 in the Dorsal Root Ganglia of Rat Peripheral Neuropathic Pain Models

1. Several lines of evidence suggest that cytokines and their receptors are initiators of changes in the activity of dorsal root ganglia (DRG) neurons, but their cellular distribution is still very limited or controversial. Therefore, the goal of present study was to investigate immunohistochemical distribution of TNF-alpha and TNF receptor-1 (TNFR1) proteins in the rat DRG following three types of nerve injury. 2. The unilateral sciatic and spinal nerve ligation as well as the sciatic nerve transection were used to induce changes in the distribution of TNF-alpha and TNFR1 proteins. The TNF-alpha and TNFR1 immunofluorescence was assessed in the L4-L5 DRG affected by nerve injury for 1 and 2 weeks, and compared with the contralateral ones and those removed from naive or sham-operated rats. A part of the sections was incubated for simultaneous immunostaining for TNF-alpha and ED-1. The immunofluorescence brightness was measured by image analysis system (LUCIA-G v4.21) to quantify immunostaining for TNF-alpha and TNFR1 in the naive, ipsi- and contralateral DRG following nerve injury. 3. The ipsilateral L4-L5 DRG and their contralateral counterparts of the rats operated for nerve injury displayed an increased immunofluorescence (IF) for TNF-alpha and TNFR1 when compared with DRG harvested from naive or sham-operated rats. The TNFalpha IF was increased bilaterally in the satellite glial cells (SGC) and contralaterally in the neuronal nuclei following sciatic and spinal nerve ligature. The neuronal bodies and their SGC exhibited bilaterally enhanced IF for TNF-alpha after sciatic nerve transection for 1 and 2 weeks. In addition, the affected DRG were invaded by ED-1 positive macrophages which displayed simultaneously TNFalpha IF. The ED-1 positive macrophages were frequently located near the neuronal bodies to occupy a position of the satellites. 4. The sciatic and spinal nerve ligature resulted in an increased TNFR1 IF in the neuronal bodies of both ipsi- and contralateral DRG. The sciatic nerve ligature for 1 week induced a rise in TNFR1 IF in the contralateral DRG neurons and their SGC to a higher level than in the ipsilateral ones. In contrast, the sciatic nerve ligature for 2 weeks caused a similar increase of TNFR1 IF in the neurons and their SGC of both ipsi- and contralateral DRG. The spinal nerve ligature or sciatic nerve transection resulted in an increased TNFR1 IF located at the surface of the ipsilateral DRG neurons, but dispersed IF in the contralateral ones. In addition, the SGC of the contralateral in contrast to ipsilateral DRG displayed a higher TNFR1 IF. 5. Our results suggest more sources of TNF-alpha protein in the ipsilateral and contralateral DRG following unilateral nerve injury including macrophages, SGC and primary sensory neurons. In addition, the SGC and macrophages, which became to be satellites, are well positioned to regulate activity of the DRG neurons by production of TNF-alpha molecules. Moreover, the different cellular distribution of TNFR1 in the ipsi- and contralateral DRG may reflect different pathways by which TNF-alpha effect on the primary sensory neurons can be mediated following nerve injury.

Epidermal growth factor-dependent enhancement of axonal regeneration in the pond snail Lymnaea stagnalis: role of phagocyte survival

Peripheral nerve injury triggers complex responses from neuronal as well as from multiple nonneuronal cell types. These responses are coordinated by a wide spectrum of secreted and nonsecreted factors, including growth factors, cytokines, and cell adhesion molecules. These molecules originate from different sources and act both locally at the site of injury as well as centrally at the location of the neuronal cell bodies. One of the signal systems frequently implicated in this process is the epidermal growth factor (EGF) family and its receptors. Expression of members of this family as well as that of EGF-receptors is upregulated in different cell types after peripheral nerve injury. However, the functional significance of this response is unclear. Using a simple invertebrate model system (Lymnaea stagnalis), the present study implicates the EGF/EGF-receptor system in the survival of ionized calcium-binding adaptor molecule 1 (Iba1)-positive phagocytes that reside in the nervous system. We show that inhibiting the EGF-signaling pathway enhances cell death in this type of cell, an effect paralleled by a substantial reduction in axonal regeneration. Therefore, complementing our previous observation that Lymnaea EGF provides trophic support to axotomized neurons, the present results emphasize the significance of nonneuronal actions of EGF receptor ligands in axonal regeneration. Thus, we add a novel perspective to the ongoing discussion on the functional significance of the EGF signaling system in the injury responses of the nervous system.

Long-term activation of c-Fos and c-Jun in optic nerve head astrocytes in experimental ocular hypertension in monkeys and after exposure to elevated pressure in vitro

This study investigates whether the immediate early gene (IEG) products c-Fos and c-Jun are activated in vivo in monkeys with experimental glaucoma, and in vitro in cultured human ONH astrocytes exposed to hydrostatic pressure (HP). Three Rhesus monkeys with mild glaucomatous damage (mean intraocular pressure (IOP) 27 +/- 1.3 mm Hg approximately 42 weeks) and three with moderate glaucomatous damage (mean IOP 44 +/- 6.7% mm Hg approximately 11 weeks) were used for this study; the contralateral eye served as normal control (mean IOP 18.6 +/- 1.7 mm Hg). ONH tissues were stained with GFAP, DAPI, and c-Jun or c-Fos, and transcription factor positive and negative nuclei were counted to determine nuclear localization. Cultured human normal and glaucomatous ONH astrocytes exposed to elevated HP served as the in vitro model of elevated pressure. Activation and nuclear localization of c-Fos and c-Jun increased significantly in the monkeys with elevated IOP. These data correlated with axonal loss, reactive astrocytes, and remodeling of the optic disc. Cultured human ONH astrocytes showed increased nuclear localization of c-Fos and c-Jun under exposure to HP. Immunohistochemistry demonstrated that the upstream regulators of c-Fos and c-Jun, ERK-MAPK and MAPKp38 localized to the nuclei of ONH astrocytes in monkeys with experimental glaucoma. Taken together, these results demonstrate c-Fos and c-Jun activation in ONH astrocytes in vivo and in vitro, and that activation of both transcription factors is associated with ERK and MAPKp38 activation in experimental glaucoma, suggesting that activation of transcription factors may participate in the induction and maintenance of the reactive astrocyte phenotype in glaucomatous optic neuropathy.

Satellite glial cells in sensory ganglia: from form to function

Current information indicates that glial cells participate in all the normal and pathological processes of the central nervous system. Although much less is known about satellite glial cells (SGCs) in sensory ganglia, it appears that these cells share many characteristics with their central counterparts. This review presents information that has been accumulated recently on the physiology and pharmacology of SGCs. It appears that SGCs carry receptors for numerous neuroactive agents (e.g., ATP, bradykinin) and can therefore receive signals from other cells and respond to changes in their environment. Activation of SGCs might in turn influence neighboring neurons. Thus SGCs are likely to participate in signal processing and transmission in sensory ganglia. Damage to the axons of sensory ganglia is known to contribute to neuropathic pain. Such damage also affects SGCs, and it can be proposed that these cells have a role in pathological changes in the ganglia.

Effects of complete Freund's adjuvant on immunohistochemical distribution of IL-1beta and IL-1R I in neurons and glia cells of dorsal root ganglion

AIM

To investigate the effects of complete Freund adjuvant (CFA) on inflammatory hyperalgesia and morphological change of the coexistence of interleukin-1 beta (IL-1beta) and type I IL-1 receptor (IL-1RI) in neurons and glia cells of rat dorsal root ganglion (DRG).

METHODS

The pain-related parameters and the expression of IL-1RI and IL-1beta positive neurons and glia cells of DRG in normal saline (NS) and adjuvant-induced arthritic (AA) group were examined with pain behavior assessment methods and immunohistochemical assay, respectively.

RESULTS

Five hours, 1 d, and 2 d after intra-articular injection of 50 microL CFA, tactile hyperalgesia induced by CFA was observed in the foot flexion and extension scores of the ipsilateral hindpaw of AA group. Three days after injection, the distribution of IL-1RI/IL-1beta double-stained coexisted neurons and glia cells were observed in ipsilateral DRG of both groups. The number of IL-1beta positive neurons, IL-1RI positive neurons, IL-1beta/IL-1RI double-stained neurons, and IL-1RI positive glia cells in ipsilateral DRG of the AA group were higher than that of NS group (P<0.05 or P<0.01).

CONCLUSION

The coexistence of IL-1beta and IL-1RI in neurons and nonneuronal cells suggests an as yet unknown autocrine and/or paracrine function of IL-1beta in the DRG. The function was enhanced in articular arthritis induced by CFA and could play an important role in hyperalgesia under inflammatory conditions.

Amphiregulin acts as an autocrine survival factor for adult sensory neurons

We studied the effect of amphiregulin on axonal outgrowth and survival in sensory neurons in organ cultured and dissociated mouse dorsal root ganglia (DRG). Amphiregulin at 20 ng/ml stimulated axonal outgrowth in both preparations. The EGF receptor inhibitor AG1478 inhibited outgrowth at 10 microM but not at 1 microM, where it abolished the stimulatory effects of amphiregulin. Fluoro-Jade staining and neuronal counting showed that more neurons survived in culture in the presence of amphiregulin while AG1478 at 10 microM but not 1 microM increased cell death. Small and medium sized neurons were immunopositive for both amphiregulin and the EGF receptor. Taken together these results suggest that amphiregulin can act as an autocrine survival factor for sensory neurons and stimulate axonal outgrowth through the EGF receptor.

The effects of axotomy on neurons and satellite glial cells in mouse trigeminal ganglion

Damage to peripheral nerves induces ectopic firing in sensory neurons, which can contribute to neuropathic pain. As most of the information on this topic is on dorsal root ganglia we decided to examine the influence of infra-orbital nerve section on cells of murine trigeminal ganglia. We characterized the electrophysiological properties of neurons with intracellular electrodes. Changes in the coupling of satellite glial cells (SGCs) were monitored by intracelluar injection of the fluorescent dye Lucifer yellow. Electrophysiology of SGCs was studied with the patch-clamp technique. Six to eight days after axotomy, the percentage of neurons that fire spontaneously increased from 1.6 to 12.8%, the membrane depolarized from -51.1 to -45.5 mV, the percentage of cells with spontaneous potential oscillations increased from 19 to 37%, the membrane input resistance decreased from 44.4 to 39.5 MOmega, and the threshold for firing an action potential decreased from 0.61 to 0.42 nA. These changes are consistent with increased neuronal excitability. SGCs were mutually coupled around a given neuron in 21% of the cases, and to SGCs around neighboring neurons in only 4.8% of the cases. After axotomy these values increased to 37.1 and 25.8%, respectively. After axotomy the membrane resistance of SGCs decreased from 101 MOmega in controls to 40 MOmega, possibly due to increased coupling among these cells. We conclude that axotomy affects both neurons and SGCs in the trigeminal ganglion. The increased neuronal excitability and ectopic firing may play a major role in neuropathic pain.

Increased gene expression of beta-1,4-galactosyltransferase I in rat injured sciatic nerve

During neurite outgrowth on basal lamina, cell-surface beta-1,4-galactosyltransferase I (beta-1,4-GalT-I) functions as one of the receptors of laminin by binding to N-linked oligosaccharides on the laminin E8 domain. In the present study, it was revealed that in rat injured sciatic nerves, the expression of beta-1,4-GalT-I mRNA reached its peak 2-3 d after axotomy in both proximal and distal stumps, and decreased thereafter as demonstrated by Northern blot analysis. In situ hybridization revealed that beta-1,4-GalT-I mRNAmainly localized in Schwann cells of the injured nerves. Moreover the Galbeta1-4GlcNAc (N-acetylglucosamine) group mainly localized in Schwann cells of the injured nerves by Ricinus communis agglutinin-I (RCA-I) lectin histochemistry. However, the changes in abundance of the Galbeta1-4GlcNAc group in injured nerves were not consistent with the expression of beta-1, 4-GalT-I mRNA. These findings indicate that beta-1,4-GalT-I might be involved in the regeneration of injured peripheral nerves at the early injury stage.

Homeobox gene expression in adult dorsal root ganglia during sciatic nerve regeneration: is regeneration a recapitulation of development?

After damage of the sciatic nerve, a regeneration process is initiated. Neurons in the dorsal root ganglion regrow their axons and functional connections. The molecular mechanisms of this neuronal regenerative process have remained elusive, but a relationship with developmental processes has been conceived. This chapter discusses the applicability of the developmental hypothesis of regeneration to the dorsal root ganglion; this hypothesis states that regeneration of dorsal root ganglion neurons is a recapitulation of development. We present data on changes in gene expression upon sciatic nerve damage, and the expression and function of homeobox genes. This class of transcription factors plays a role in neuronal development. Based on these data, it is concluded that the hypothesis does not hold for dorsal root ganglion neurons, and that regeneration-specific mechanisms exist. Cytokines and the associated Jak/STAT (janus kinase/signal transducer and activator of transcription) signal transduction pathway emerge as constituents of a regeneration-specific mechanism. This mechanism may be the basis of pharmacological strategies to stimulate regeneration.

Molecular plasticity of primary nociceptive neurons: relations of the NGF-c-jun system to neurotomy and chronic pain

Neurotomy is widely used as a model of chronic, intractable pain, the proverbial "crux medicorum". Immunohistochemical aspects of this chronic pain model are discussed in this paper, with the aim of shedding new light on the pathomechanism and possible therapeutical consequences. Central terminals of nociceptive neurons contain substance P, somatostatin and calcitonin generelated peptide or exhibit fluoride resistant acid phosphatase and thiamine monophosphatase enzyme reaction in the superficial dorsal horn of the spinal cord and in analogous structures of the brain stem. These neuropeptides and neuroproteins are expressed by the related dorsal root ganglion cells and transported via orthograde axoplasmic transport via dorsal roots to the central nervous system. Transection of the ipsilateral, segmentally related peripheral sensory nerve results in transganglionic degenerative atrophy of central terminals of primary nociceptive neurons. Transganglionic degenerative atrophy is characterized by marked ultrastructural alterations superficially similar to, but essentially differing from the signs of Wallerian degeneration which ensue after dorsal rhizotomy. Transganglionic degenerative atrophy is accompanied by depletion of marker neuropeptides and enzymes, and later by the expression of vicarious neuropeptides such as vasoactive intestinal polypeptide, neuropeptide Y and galanin and of the enzyme choline acetyl transferase. Consequences of blockade of retrograde axoplasmic transport of the nerve growth factor elicited either by perineural application of microtubule inhibitors or by perineural administration of anti-nerve growth factor are similar to peripheral neurotomy. According to recent studies described in this paper, the blockade of nerve growth factor supply to primary nociceptive neurons induces activation of c-jun in nuclei of primary nociceptive neurons probably responsible for the plasticity of the neuropeptide and neuroprotein synthesizing machinery. In contrast, invasion of and formation of pericellular baskets by noradrenergic axons can be elicited only by axotomy and not by blockade of retrograde axoplasmic transport. Involvement of nerve growth factor and the nerve growth factor-dependent immediate early genes in neuroplasticity of neuropeptidergic primary sensory neurons raise the possibility of a gene therapy of chronic intractable pain.

Overexpression of beta-1,4-galactosyltransferase I in rat Schwann cells promotes the growth of co-cultured dorsal root ganglia

The cell surface beta-1,4-galactosyltransferase I (beta-1,4-GalT-I) functions as one of the receptors of laminin during the neurite outgrowth on basal lamina by binding to N-linked oligosaccharides in the laminin E8 domain. In this study, we demonstrated that the purified rat Schwann cells transfected with the expression plasmid of beta-1,4-GalT-I cDNA transiently promoted outgrowth and elongation of the neurites from co-cultured rat dorsal root ganglia, while those transfected with the antisense expression plasmid of beta-1,4-GalT-I had the opposite effects. These results suggested that the expression of beta-1,4-GalT-I in Schwann cells of peripheral nerve might promote both growth of developmental neuron and regeneration of injured nerve.

Perikaryal surface specializations of neurons in sensory ganglia

Slender projections, similar to microvilli, are the main specialization of the perikaryal surface of sensory ganglion neurons. The extent of these projections correlates closely with the volume of the corresponding nerve cell body. It is likely that the role of perikaryal projections of sensory ganglion neurons, which lack dendrites, is to maintain the surface-to-volume ratio of the nerve cell body above some critical level for adequate metabolic exchange. Satellite cells probably have the ability to promote, or provide a permissive environment for, the outgrowth of these projections. It is not yet known whether the effect of satellite cells is mediated by molecules associated with their plasma membrane or by diffusible factors. Furthermore, receptor molecules for numerous chemical agonists are located on the nerve cell body surface, but it is not known whether certain molecules are located exclusively on perikaryal projections or are also present on the smooth surface between these projections. Further study of the nerve cell body surface and of the influence that satellite cells exert on it will improve our understanding of the interactions between sensory ganglion neurons and satellite neuroglial cells.

Expression of beta-1,4-galactosyltransferase II and V in rat injured sciatic nerves

Beta-1,4-Galactosyltransferases II and V (beta-1,4-GalT II and V) are involved in the biosynthesis of N-linked oligosaccharides as beta-1,4-GalT I which plays important roles in promoting neuron outgrowth. In the present paper, it was illustrated that beta-1,4-GalT II and V were localized mainly in Schwann cells of lesion sciatic nerves by in situ hybridization. Northern blot showed that the expression of beta-1,4-GalT II increased gradually at both stumps of injured nerves, while that of beta-1,4-GalT V decreased at proximal stumps but increased and reached its peak on the third day post-operation at distal stumps, before it declined. The different expression of beta-1,4-GalT II and V in Schwann cells suggested that they would affect the different galactosylation of glycoproteins in injured nerves regeneration.

Trachea enhances neurite regeneration from adult rat nodose ganglia in vitro

Trachea is intensely innervated with vagal afferent nerve fibers, and may play an important role in vagus nerve regeneration after axonal injury caused by trauma and surgical operation. We investigated the effects of tracheal tissue on neuronal cell survival and neurite regeneration in adult rat nodose ganglia (NG) in vitro. Co-culture with trachea significantly increased the average number of neurites regenerated from transected nerve terminals of NG explants, from 73.7 to 154.2 after 3 days, from 68 to 186.7 after 5 days, and from 31 to 101.5 after 7 days in culture. Dissociated NG neurons could continue to survive and extend neurites only in the co-existence with satellite cells in collagen gel. Co-cultured trachea improved the ratios of survival and neurite-bearing cells of NG neurons, from 56.7% and 11.1% to 72.3% and 37.6% after 4 days, and from 41.1% and 20.3% to 56.4% and 47.2% after 7 days in culture, respectively. These results imply that tracheal tissue secretes a factor, which could enhance neuronal cell survival and neurite regeneration in NG in the presence of satellite cells in vitro.

Lymnaea epidermal growth factor promotes axonal regeneration in CNS organ culture

Members of the epidermal growth factor (EGF) family are frequently implicated in the injury response of the mammalian nervous system. Although this implication is supported by extensive molecular evidence, it is not underpinned by conclusive functional data. Recently, we found that expression of an EGF homolog from the pond snail Lymnaea stagnalis (L-EGF) is upregulated after axotomy in the adult CNS, suggesting a role for this molecule in the injury response of the CNS. In the present study we asked whether L-EGF can promote axonal regeneration of three types of identified neurons in organ-cultured CNS. Treatment with purified L-EGF substantially enhanced axonal regeneration of all three types of neurons, an effect inhibited by submicromolar doses of PD153035, a specific EGF receptor (EGFR) tyrosine kinase inhibitor. In addition, PD153035 and K252a, a nonspecific kinase inhibitor, also reduced the degree of axonal regeneration that occurs without L-EGF supplementation, indicating that L-EGF or other EGFR ligands synthesized in the CNS participate in the regenerative response. An intriguing aspect of these results is that axonal regeneration of different, intrinsically L-EGF responsive and unresponsive neurons occurred in a coordinated manner. This observation suggests that indirect in addition to direct actions contribute to the beneficial effect of L-EGF. In conclusion, we provide functional evidence that an EGF homolog can promote axonal regeneration, substantiating existing molecular evidence implicating the EGF family in peripheral nerve regeneration and emphasizes the therapeutic potential of these molecules.

Lack of effects of transforming growth factor-alpha gene knockout on peripheral nerve regeneration may result from compensatory mechanisms

Transforming growth factor-alpha (TGF-alpha), previously identified as a major member of the epidermal growth factor (EGF) family of growth factors, plays a role in proliferation, differentiation, and survival of neuronal and glial precursors and is implicated in development of the nervous system. However, its roles in nerve injury-induced responses remain obscure. The current study examined roles of endogenous TGF-alpha in peripheral nerve regeneration using sciatic nerve injury models with TGF-alpha knockout mice. Three weeks after a sciatic nerve crush, no significant differences were found between TGF-alpha wild-type and mutant mice in the number of retrogradely labeled L5 dorsal root ganglion (DRG) sensory neurons and L5 spinal cord motor neurons and in the morphology of myelinated regenerating nerve fibers, indicating that TGF-alpha is not essential for sensory and motor nerve regeneration. To assess a possible functional redundancy among TGF-alpha-related ligands in response to a nerve injury, mRNA expression of the EGF family was analyzed by RT-PCR in L4/L5 DRG pools and distal degenerating sciatic nerve segments after sciatic nerve ligation. Prior to and 1 day after ligation, there was a higher level of EGF-R mRNA in DRGs and in nerve in TGF-alpha null mice compared to wild types, and there was an induction of ligand amphiregulin mRNA in DRGs in mutant mice in place of the TGF-alpha upregulation present in wild types. These results indicate that TGF-alpha gene knockout does not affect peripheral nerve regeneration, probably due to a functional redundancy within the EGF family through a compensatory expression mechanism at both the receptor and ligand levels in TGF-alpha knockout mice.

Pericellular Griffonia simplicifolia I isolectin B4-binding ring structures in the dorsal root ganglia following peripheral nerve injury in rats

Patients with a peripheral nerve injury often suffer from persistent chronic pain, but the underlying mechanism remains largely unknown. The persistent nature of the pain suggests injury-induced profound structural changes along the sensory pathways. In the present study, using the plant Griffonia simplicifolia I isolectin B4 (IB4) as a marker for nonpeptidergic small sensory neurons, we sought to examine whether these neurons sprout in the dorsal root ganglia (DRG) in response to peripheral nerve injury. The lumbar 5 (L5) spinal nerve was transected, and rats were allowed to survive for varying lengths of time before IB4 histology was performed. We found that a subpopulation of IB4-positive sensory neurons sprouted robustly after spinal nerve injury. Twelve weeks after spinal nerve injury, the IB4-positive ring structures became dramatic and encircled both large and small neurons in the DRG. The aberrant sprouting of small sensory neurons was also demonstrated by retrograde labeling. The processes of satellite cells surrounding large sensory neurons also became IB4 positive, and 87.8% of perineuronal IB4-positive ring structures intermingled and/or coexpressed with glial fibrillary acidic protein-positive satellite cells. Thus, the sprouting axons of IB4-positive neurons were intermingled with IB4-positive satellite cells, forming perineuronal ring structures surrounding large-diameter neurons. Ultrastructural examinations further confirmed that IB4-positive nerve terminals were entangled with satellite cells and IB4-negative unmyelinated sprouting fibers around sensory neurons. These studies have provided the first evidence that a subpopulation of IB4-binding small sensory neurons sprouts and forms perineuronal ring structures together with IB4-positive satellite cells in response to nerve injury. The significance of the sprouting of IB4-positive neurons remains to be determined.

Nerve growth factor modulates the activation status and fast axonal transport of ERK 1/2 in adult nociceptive neurones

Mature dorsal root ganglion cells respond to neurotrophins, and the intracellular signalling pathways activated by neurotrophins have been characterized in vitro. We have now used immunocytochemistry and Western blots to examine the expression and activation of extracellular signal-regulated protein kinase-1/2 (ERK) in rat dorsal root ganglion cells in vivo, using antisera to total (tERK) and phosphorylated (pERK) forms. This has revealed a number of novel findings. tERK immunoreactivity is present in most dorsal root ganglion cells but is expressed most strongly in small (nociceptive) cells and, surprisingly, is absent in a population of large cells that expressed trkB or trkC but mainly lack p75(NTR) immunoreactivity. In contrast pERK is prominent in a few trkA cells and in satellite glial cells, and is further increased by NGF treatment. tERK and pERK both undergo fast anterograde and retrograde axonal transport, indicated by accumulation at a sciatic nerve ligature, and NGF reduces the level of retrograde pERK transport.

In vivo expression and localization of the fibroblast growth factor system in the intact and lesioned rat peripheral nerve and spinal ganglia

Basic fibroblast growth factor (FGF-2) is involved in several cellular processes of the nervous system during development, maintenance, and regeneration. In the central nervous system, FGF-2 has been shown to be expressed in neurons and glial cells, depending on the developmental stage and brain area. In the present study, a comprehensive analysis was performed of the cellular distribution of the transcripts of FGF-2 and of the FGF high-affinity receptors (R) 1-4 in intact and lesioned sciatic nerve and spinal ganglia. In the adult rat sciatic nerve FGF-2, FGFR1-3 were expressed at low levels as revealed by reverse transcriptase-polymerase chain reaction (RT-PCR). Sciatic nerve crush resulted in an increase of these transcript levels. FGFR4 expression was not detected in the intact and crushed nerve as revealed by RT-PCR and RNase protection assay. In situ hybridization using riboprobes for FGF-2, FGFR1-3 displayed staining in diverse cell types. Immunocytochemical staining of consecutive sections with cell markers for myelin, macrophages, and neurons revealed colocalization of the transcripts with Schwann cells and macrophages. In addition to FGF-2 and FGFR1, the transcripts of FGFR2-4 were expressed in neurons of spinal ganglia. Crush lesion of the sciatic nerve resulted in no alterations of the FGFR1-4 transcripts, whereas FGF-2 and FGFR3 mRNAs were up-regulated in spinal ganglia. The expression of FGFRs and FGF-2 in Schwann cells and macrophages at the lesion site of the sciatic nerve and in sensory neurons suggests that FGF-2 is involved in specific functions of these cells during regeneration.

Adult rat otic placode-derived neurons and sensory epithelium express all four erbB receptors: a role in regulating vestibular ganglion neuron viability

The erbB receptor family consists of erbB1/epidermal growth factor receptor, erbB2/neu, erbB3, and erbB4, all of which have been implicated in cell proliferation, differentiation, and survival in several tissues. In the nervous system, these family members can function in a trophic capacity for certain subpopulations of neurons and some types of non-neuronal cells. Vestibular sensory epithelial cells and vestibular ganglion neurons are derived from ectodermal otic placode and are essential components of the peripheral vestibular system, the sensory system for balance. Recent studies in mammals suggest that certain ligands of the epidermal growth factor receptor can induce proliferation of vestibular sensory epithelial cells. We now show that vestibular ganglion neurons and vestibular sensory epithelial cells express all four erbB receptors in adult rats. Cultured vestibular ganglion neurons also expressed all four erbB family members and were therefore used to analyze the effects of modulating erbB signaling on differentiated vestibular ganglion neurons. Transforming growth factor-alpha (a ligand for epidermal growth factor receptor) and sensory and motor neuron-derived factor (a ligand for erbB3 and erbB4) promoted vestibular ganglion neuron viability, whereas epidermal growth factor (another ligand for epidermal growth factor receptor) did not. Glial growth factor 2 (another ligand for erbB3 and erbB4) and an antibody that blocks erbB2/neu-mediated signaling inhibited vestibular ganglion neuron viability. Collectively, these observations indicate that erbB signaling regulates the viability of differentiated otic placode-derived cells in mammals and suggest that exogenous modulation of erbB signaling in peripheral vestibular tissues may prove therapeutically useful in peripheral vestibular disorders.

Effects of endogenous neurotrophins on sympathetic sprouting in the dorsal root ganglia and allodynia following spinal nerve injury

Peripheral nerve injury is often complicated by a chronic pain syndrome that is difficult to treat. In animal models of peripheral nerve injury, sympathetic nerve terminals in the dorsal root ganglia (DRG) sprout to form baskets around large diameter neurons, an anatomical change that has been implicated in the induction of neuropathic pain. In the present study, we have investigated whether neurotrophins derived from peripheral sources play any roles in sympathetic sprouting and neuropathic pain in a rat model of peripheral nerve injury. After transection of the left lumbar (L) 5 spinal nerve, antisera specific to neurotrophins were injected intraperitoneally twice a week for 2 weeks. The foot withdrawal response to von Frey hairs was examined on days 1, 3, 7, 10, and 14 postlesion. After completion of behavioral tests, sympathetic sprouting in DRG was examined by tyrosine hydroxylase (TH) immunohistochemistry. The number of TH-immunoreactive (ir) fibers and baskets around large neurons within the lesioned DRG was dramatically increased in the rats treated with control normal sheep serum. Antisera specific to nerve growth factor (NGF), neurotrophin-3 (NT3), and brain-derived neurotrophic factor (BDNF) significantly reduced the sympathetic sprouting and the formation of baskets. L5 spinal nerve lesion induced a significant increase in foot withdrawal responses to von Frey hair stimuli, which was attenuated by treatment of antisera to neurotrophins with a different time sequential. The effect of BDNF antiserum occurred earlier and lasted longer than those of NGF and NT3 antisera. These results implicate that peripherally derived neurotrophins are involved in the induction of sympathetic sprouting and neuropathic pain following peripheral nerve injury.

Neurotrophins from dorsal root ganglia trigger allodynia after spinal nerve injury in rats

Injury to peripheral nerves often results in chronic pain which is difficult to relieve. The mechanism underlying the pain syndrome remains largely unknown. In previous studies we showed that neurotrophins are up-regulated in satellite cells around sensory neurons following sciatic nerve lesion. In the present study, we have examined whether the neurotrophins in the dorsal root ganglia play any role in allodynia after nerve injury. Antibodies to different neurotrophins, directly delivered to injured dorsal root ganglia, significantly reduced (with different time sequences) the percentage of foot withdrawal responses evoked by von Frey hairs. The antibodies to nerve growth factor acted during the early phase but antibodies to neurotrophin-3 and brain-derived neurotrophic factor were effective during the later phase. Exogenous nerve growth factor or brain-derived neurotrophic factor, but not neurotrophin-3, directly delivered to intact dorsal root ganglia, trigger a persistent mechanical allodynia. Our results showed that neurotrophins within the dorsal root ganglia after peripheral nerve lesion are involved in the generation of allodynia at different stages. These studies provide the first evidence that ganglia-derived neurotrophins are a source of nociceptive stimuli for neuropathic pain after peripheral nerve injury.

Roles of transforming growth factor-alpha and related molecules in the nervous system

The epidermal growth factor (EGF) family of polypeptides is regulators for tissue development and repair, and is characterized by the fact that their mature forms are proteolytically derived from their integral membrane precursors. This article reviews roles of the prominent members of the EGF family (EGF, transforming growth factor-alpha [TGF-alpha] and heparin-binding EGF [HB-EGF]) and the related neuregulin family in the nerve system. These polypeptides, produced by neurons and glial cells, play an important role in the development of the nervous system, stimulating proliferation, migration, and differentiation of neuronal, glial, and Schwann precursor cells. These peptides are also neurotrophic, enhancing survival and inhibiting apoptosis of post-mitotic neurons, probably acting directly through receptors on neurons, or indirectly via stimulating glial proliferation and glial synthesis of other molecules such as neurotrophic factors. TGF-alpha, EGF, and neuregulins are involved in mediating glial-neuronal and axonal-glial interactions, regulating nerve injury responses, and participating in injury-associated astrocytic gliosis, brain tumors, and other disorders of the nerve system. Although the collective roles of the EGF family (as well as those of the neuregulins) are shown to be essential for the nervous system, redundancy may exist among members of the EGF family.