Satellite Glial Cells and Astrocytes, a Comparative Review

Satellite glial cell manipulation prior to axotomy enhances developing dorsal root ganglion central branch regrowth into the spinal cord

The central and peripheral nervous systems (CNS and PNS, respectively) exhibit remarkable diversity in the capacity to regenerate following neuronal injury with PNS injuries being much more likely to regenerate than those that occur in the CNS. Glial responses to damage greatly influence the likelihood of regeneration by either promoting or inhibiting axonal regrowth over time. However, despite our understanding of how some glial lineages participate in nerve degeneration and regeneration, less is known about the contributions of peripheral satellite glial cells (SGC) to regeneration failure following central axon branch injury of dorsal root ganglia (DRG) sensory neurons. Here, using in vivo, time-lapse imaging in larval zebrafish coupled with laser axotomy, we investigate the role of SGCs in axonal regeneration. In our studies we show that SGCs respond to injury by relocating their nuclei to the injury site during the same period that DRG neurons produce new central branch neurites. Laser ablation of SGCs prior to axon injury results in more neurite growth attempts and ultimately a higher rate of successful central axon regrowth, implicating SGCs as inhibitors of regeneration. We also demonstrate that this SGC response is mediated in part by ErbB signaling, as chemical inhibition of this receptor results in reduced SGC motility and enhanced central axon regrowth. These findings provide new insights into SGC-neuron interactions under injury conditions and how these interactions influence nervous system repair.

Modulation of sensory input to the spinal cord: Contribution of focal epidural polarization and of GABA released by interneurons and glial cells

Modulation of input from primary afferent fibres has long been examined at the level of the first relays of these fibres. However, recent studies reveal that input to the spinal cord may also be modulated at the level of the very entry of afferent fibres to the spinal grey matter before action potentials in intraspinal collaterals of afferent fibres reach their target neurons. Such modulation greatly depends on the actions of GABA via extrasynaptic membrane receptors. In the reported study we hypothesized that the increase in excitability of afferent fibres following epidural polarization close to the site where collaterals of afferent fibres leave the dorsal columns is due to the release of GABA from two sources: not only GABAergic interneurons but also glial cells. We present evidence, primo, that GABA released from both these sources contributes to a long-lasting increase in the excitability and a shortening of the refractory period of epidurally stimulated afferent fibres and, secondo, that effects of epidural polarization on the release of GABA are more critical for these changes than direct effects of DC on the stimulated fibres. The experiments were carried out in deeply anaesthetized rats in which changes in compound action potentials evoked in hindlimb peripheral nerves by dorsal column stimulation were used as a measure of the excitability of afferent fibres. The study throws new light on the modulation of input to spinal networks but also on mechanisms underlying the restoration of spinal functions.

Mesenchymal Stem Cell Engagement Modulates Neuroma Microenviroment in Rats and Humans and Prevents Postamputation Pain

Postamputation pain is currently managed unsatisfactorily with neuron-targeted pharmacological and interventional therapies. Non-neuronal pain mechanisms have emerged as crucial factors in the development and persistence of postamputation pain. Consequently, these mechanisms offer exciting prospects as innovative therapeutic targets. We examined the hypothesis that engaging mesenchymal stem cells (MSCs) would foster local neuroimmune interactions, leading to a potential reduction in postamputation pain. We utilized an ex vivo neuroma model from a phantom limb pain patient to uncover that the oligodeoxynucleotide IMT504 engaged human primary MSCs to promote an anti-inflammatory microenvironment. Reverse translation experiments recapitulated these effects. Thus, in an in vivo rat model, IMT504 exhibited strong efficacy in preventing autotomy (self-mutilation) behaviors. This effect was linked to a substantial accumulation of MSCs in the neuroma and associated dorsal root ganglia and the establishment of an anti-inflammatory phenotype in these compartments. Centrally, this intervention reduced glial reactivity in the dorsal horn spinal cord, demonstrating diminished nociceptive activity. Accordingly, the exogenous systemic administration of MSCs phenocopied the behavioral effects of IMT504. Our findings underscore the mechanistic relevance of MSCs and the translational therapeutic potential of IMT504 to engage non-neuronal cells for the prevention of postamputation pain. PERSPECTIVE: The present study suggests that IMT504-dependent recruitment of endogenous MSCs within severely injured nerves may prevent post-amputation pain by modifying the inflammatory scenario at relevant sites in the pain pathway. Reinforcing data in rat and human tissues supports the potential therapeutic value of IMT504 in patients suffering postamputation pain.

Molecular Characterization of Nodose Ganglia Development Reveals a Novel Population of Phox2b+ Glial Progenitors in Mice

The vagal ganglia, comprised of the superior (jugular) and inferior (nodose) ganglia of the vagus nerve, receive somatosensory information from the head and neck or viscerosensory information from the inner organs, respectively. Developmentally, the cranial neural crest gives rise to all vagal glial cells and to neurons of the jugular ganglia, while the epibranchial placode gives rise to neurons of the nodose ganglia. Crest-derived nodose glial progenitors can additionally generate autonomic neurons in the peripheral nervous system, but how these progenitors generate neurons is unknown. Here, we found that some Sox10+ neural crest-derived cells in, and surrounding, the nodose ganglion transiently expressed Phox2b, a master regulator of autonomic nervous system development, during early embryonic life. Our genetic lineage-tracing analysis in mice of either sex revealed that despite their common developmental origin and extreme spatial proximity, a substantial proportion of glial cells in the nodose, but not in the neighboring jugular ganglia, have a history of Phox2b expression. We used single-cell RNA-sequencing to demonstrate that these progenitors give rise to all major glial subtypes in the nodose ganglia, including Schwann cells, satellite glia, and glial precursors, and mapped their spatial distribution by in situ hybridization. Lastly, integration analysis revealed transcriptomic similarities between nodose and dorsal root ganglia glial subtypes and revealed immature nodose glial subtypes. Our work demonstrates that these crest-derived nodose glial progenitors transiently express Phox2b, give rise to the entire complement of nodose glial cells, and display a transcriptional program that may underlie their bipotent nature.

Astrocytic GDNF ameliorates anesthesia and surgery-induced cognitive impairment by promoting hippocampal synaptic plasticity in aged mice

BACKGROUND

Perioperative neurocognitive disorders (PND) are common complications after surgery in older patients. However, the specific mechanism of this condition remains unclear. Glial cell line-derived neurotrophic factor (GDNF) is an important neurotrophin that abundantly expressed throughout the brain. It can enhance synaptic plasticity and alleviate learning and memory impairments. Thus, the purpose of this study was to investigate the role of GDNF in PND and the mechanisms involved.

METHODS

The PND animal model was established by performing left tibial fracture surgery on 18-month-old C57BL/6 mice under sevoflurane anesthesia. Recombinant adeno-associated virus (rAAV)-GDNF or empty vectors were injected bilaterally into the hippocampal CA1 region of aged mice 3 weeks before anesthesia/surgery. The open field and fear conditioning test were used to assess the behavior changes. Golgi staining and electrophysiology were utilized to evaluate the morphological and functional alterations of neuronal synaptic plasticity. Western blot analysis was carried out to measure the proteins expression levels and immunofluorescence staining was performed to probe the cellular localization of GDNF.

RESULTS

Mice with surgery and anesthesia showed a significant decrease in hippocampus-dependent learning and memory, accompanied by a decline in hippocampal synaptic plasticity. Anesthesia/surgery induced a reduction of GDNF, which was colocalized with astrocytes. Overexpression of GDNF in astrocytes could ameliorate the decline in cognitive function by improving hippocampal synaptic plasticity, meanwhile astrocytic GDNF rescued the anesthesia/surgery-induced decrease in GFRα1 and NCAM.

CONCLUSION

The study concludes that astrocytic GDNF may improve anesthesia/surgery-induced cognitive impairment by promoting hippocampal synaptic plasticity in aged mice via the GFRα1/NCAM pathway.

Targeting connexins: possible game changer in managing neuropathic pain?

Neuropathic pain is a chronic debilitating condition caused by nerve injury or a variety of diseases. At the core of neuropathic pain lies the aberrant neuronal excitability in the peripheral and/or central nervous system (PNS and CNS). Enhanced connexin expression and abnormal activation of connexin-assembled gap junctional channels are prominent in neuropathic pain along with reactive gliosis, contributing to neuronal hypersensitivity and hyperexcitability. In this review, we delve into the current understanding of how connexin expression and function contribute to the pathogenesis and pathophysiology of neuropathic pain and argue for connexins as potential therapeutic targets for neuropathic pain management.

Role of fragile X messenger ribonucleoprotein 1 in the pathophysiology of brain disorders: a glia perspective

Fragile X messenger ribonucleoprotein 1 (FMRP) is a widely expressed RNA binding protein involved in several steps of mRNA metabolism. Mutations in the FMR1 gene encoding FMRP are responsible for fragile X syndrome (FXS), a leading genetic cause of intellectual disability and autism spectrum disorder, and fragile X-associated tremor-ataxia syndrome (FXTAS), a neurodegenerative disorder in aging men. Although FMRP is mainly expressed in neurons, it is also present in glial cells and its deficiency or altered expression can affect functions of glial cells with implications for the pathophysiology of brain disorders. The present review focuses on recent advances on the role of glial subtypes, astrocytes, oligodendrocytes and microglia, in the pathophysiology of FXS and FXTAS, and describes how the absence or reduced expression of FMRP in these cells can impact on glial and neuronal functions. We will also briefly address the role of FMRP in radial glial cells and its effects on neural development, and gliomas and will speculate on the role of glial FMRP in other brain disorders.

Satellite glial cells in sensory ganglia play a wider role in chronic pain via multiple mechanisms

Satellite glial cells are unique glial cells that surround the cell body of primary sensory neurons. An increasing body of evidence suggests that in the presence of inflammation and nerve damage, a significant number of satellite glial cells become activated, thus triggering a series of functional changes. This suggests that satellite glial cells are closely related to the occurrence of chronic pain. In this review, we first summarize the morphological structure, molecular markers, and physiological functions of satellite glial cells. Then, we clarify the multiple key roles of satellite glial cells in chronic pain, including gap junction hemichannel Cx43, membrane channel Pannexin1, K channel subunit 4.1, ATP, purinergic P2 receptors, and a series of additional factors and their receptors, including tumor necrosis factor, glutamate, endothelin, and bradykinin. Finally, we propose that future research should focus on the specific sorting of satellite glial cells, and identify genomic differences between physiological and pathological conditions. This review provides an important perspective for clarifying mechanisms underlying the peripheral regulation of chronic pain and will facilitate the formulation of new treatment plans for chronic pain.

Neuron-astrocyte metabolic coupling facilitates spinal plasticity and maintenance of inflammatory pain

Long-lasting pain stimuli can trigger maladaptive changes in the spinal cord, reminiscent of plasticity associated with memory formation. Metabolic coupling between astrocytes and neurons has been implicated in neuronal plasticity and memory formation in the central nervous system, but neither its involvement in pathological pain nor in spinal plasticity has been tested. Here we report a form of neuroglia signalling involving spinal astrocytic glycogen dynamics triggered by persistent noxious stimulation via upregulation of the Protein Targeting to Glycogen (PTG) in spinal astrocytes. PTG drove glycogen build-up in astrocytes, and blunting glycogen accumulation and turnover by Ptg gene deletion reduced pain-related behaviours and promoted faster recovery by shortening pain maintenance in mice. Furthermore, mechanistic analyses revealed that glycogen dynamics is a critically required process for maintenance of pain by facilitating neuronal plasticity in spinal lamina 1 neurons. In summary, our study describes a previously unappreciated mechanism of astrocyte-neuron metabolic communication through glycogen breakdown in the spinal cord that fuels spinal neuron hyperexcitability.

Neurovascular effects of cocaine: relevance to addiction

Cocaine is a highly addictive drug, and its use is associated with adverse medical consequences such as cerebrovascular accidents that result in debilitating neurological complications. Indeed, brain imaging studies have reported severe reductions in cerebral blood flow (CBF) in cocaine misusers when compared to the brains of healthy non-drug using controls. Such CBF deficits are likely to disrupt neuro-vascular interaction and contribute to changes in brain function. This review aims to provide an overview of cocaine-induced CBF changes and its implication to brain function and to cocaine addiction, including its effects on tissue metabolism and neuronal activity. Finally, we discuss implications for future research, including targeted pharmacological interventions and neuromodulation to limit cocaine use and mitigate the negative impacts.

Astroglial Connexin 43-Mediated Gap Junctions and Hemichannels: Potential Antidepressant Mechanisms and the Link to Neuroinflammation

Major depression disorder (MDD) is a neuropsychiatric disorder associated with a high suicide rate and a higher disability rate than any other disease. Evidence suggests that the pathological mechanism of MDD is related to astrocyte dysfunction. Depression is mainly associated with the expression of connexin 43 (Cx43) and the function of Cx43-mediated gap junctions and hemichannels in astrocytes. Moreover, neuroinflammation has been a hotspot in research on the pathology of depression, and Cx43-mediated functions are thought to be involved in neuroinflammation-related depression. However, the specific mechanism of Cx43-mediated functions in neuroinflammation-related depression pathology remains unclear. Therefore, this review summarizes and discusses Cx43 expression, the role of gap junction intercellular communication, and its relationship with neuroinflammation in depression. This review also focuses on the effects of antidepressant drugs (e.g., monoamine antidepressants, psychotropic drugs, and N-methyl-D-aspartate receptor antagonists) on Cx43-mediated function and provides evidence for Cx43 as a novel target for the treatment of MDD. The pathogenesis of MDD is related to astrocyte dysfunction, with reduced Cx43 expression, GJ dysfunction, decreased GJIC and reduced BDNF expression in the depressed brain. The effect of Cx43 on neuroinflammation-related depression involving inflammatory cytokines, glutamate excitotoxicity, and HPA axis dysregulation. Antidepressant drugs targeting Cx43 can effectively relieve depressive symptoms.

Characterisation of GFAP-Expressing Glial Cells in the Dorsal Root Ganglion after Spared Nerve Injury

Satellite glial cells (SGCs), enveloping primary sensory neurons' somas in the dorsal root ganglion (DRG), contribute to neuropathic pain upon nerve injury. Glial fibrillary acidic protein (GFAP) serves as an SGC activation marker, though its DRG satellite cell specificity is debated. We employed the hGFAP-CFP transgenic mouse line, designed for astrocyte studies, to explore its expression within the peripheral nervous system (PNS) after spared nerve injury (SNI). We used diverse immunostaining techniques, Western blot analysis, and electrophysiology to evaluate GFAP+ cell changes. Post-SNI, GFAP+ cell numbers increased without proliferation, and were found near injured ATF3+ neurons. GFAP+ FABP7+ SGCs increased, yet 75.5% of DRG GFAP+ cells lacked FABP7 expression. This suggests a significant subset of GFAP+ cells are non-myelinating Schwann cells (nmSC), indicated by their presence in the dorsal root but not in the ventral root which lacks unmyelinated fibres. Additionally, patch clamp recordings from GFAP+ FABP7-cells lacked SGC-specific Kir4.1 currents, instead displaying outward Kv currents expressing Kv1.1 and Kv1.6 channels specific to nmSCs. In conclusion, this study demonstrates increased GFAP expression in two DRG glial cell subpopulations post-SNI: GFAP+ FABP7+ SGCs and GFAP+ FABP7- nmSCs, shedding light on GFAP's specificity as an SGC marker after SNI.

Scientific and Regulatory Policy Committee Technical Review: Biology and Pathology of Ganglia in Animal Species Used for Nonclinical Safety Testing

Dorsal root ganglia (DRG), trigeminal ganglia (TG), other sensory ganglia, and autonomic ganglia may be injured by some test article classes, including anti-neoplastic chemotherapeutics, adeno-associated virus-based gene therapies, antisense oligonucleotides, nerve growth factor inhibitors, and aminoglycoside antibiotics. This article reviews ganglion anatomy, cytology, and pathology (emphasizing sensory ganglia) among common nonclinical species used in assessing product safety for such test articles (TAs). Principal histopathologic findings associated with sensory ganglion injury include neuron degeneration, necrosis, and/or loss; increased satellite glial cell and/or Schwann cell numbers; and leukocyte infiltration and/or inflammation. Secondary nerve fiber degeneration and/or glial reactions may occur in nerves, dorsal spinal nerve roots, spinal cord (dorsal and occasionally lateral funiculi), and sometimes the brainstem. Ganglion findings related to TA administration may result from TA exposure and/or trauma related to direct TA delivery into the central nervous system or ganglia. In some cases, TA-related effects may need to be differentiated from a spectrum of artifactual and/or spontaneous background changes.

Scientific and Regulatory Policy Committee Points to Consider: Sampling, Processing, Evaluation, Interpretation, and Reporting of Test Article-Related Ganglion Pathology for Nonclinical Toxicity Studies

Certain biopharmaceutical products consistently affect dorsal root ganglia, trigeminal ganglia, and/or autonomic ganglia. Product classes targeting ganglia include antineoplastic chemotherapeutics, adeno-associated virus-based gene therapies, antisense oligonucleotides, and anti-nerve growth factor agents. This article outlines "points to consider" for sample collection, processing, evaluation, interpretation, and reporting of ganglion findings; these points are consistent with published best practices for peripheral nervous system evaluation in nonclinical toxicity studies. Ganglion findings often occur as a combination of neuronal injury (e.g., degeneration, necrosis, and/or loss) and/or glial effects (e.g., increased satellite glial cell cellularity) with leukocyte accumulation (e.g., mononuclear cell infiltration or inflammation). Nerve fiber degeneration and/or glial reactions may be seen in nerves, dorsal spinal nerve roots, spinal cord, and occasionally brainstem. Interpretation of test article (TA)-associated effects may be confounded by incidental background changes or experimental procedure-related changes and limited historical control data. Reports should describe findings at these sites, any TA relationship, and the criteria used for assigning severity grades. Contextualizing adversity of ganglia findings can require a weight-of-evidence approach because morphologic changes of variable severity occur in ganglia but often are not accompanied by observable overt in-life functional alterations detectable by conventional behavioral and neurological testing techniques.

Central role of purinergic receptors with inflammation in neuropathic pain-related macrophage-SGC-neuron triad

Adenosine triphosphate (ATP) acts on P2 purinergic receptors as an extracellular signaling molecule. P2 purinergic receptors include P2X ionotropic receptors and P2Y metabotropic receptors. Satellite glial cells (SGCs) and macrophages express P2X and P2Y receptors. Inflammatory cytokines and pro-nociceptive mediators are released by activated macrophages and SGCs, which can act on neurons to promote excitability and firing. In the primary sensory ganglia, in response to signals of injury, SGCs and macrophages accumulate around primary sensory neurons, forming a macrophage-SGC-neuron triad. In addition to affecting the pathological alterations of inflammation-related neuropathic pain, inflammatory cytokines and pro-nociceptive mediators are released by the action of ATP on P2X and P2Y receptors in macrophages and SGCs. Macrophages and SGCs work together to enhance and prolong neuropathic pain. The macrophage-SGC-neuron triad communicates with each other through ATP and other inflammatory mediators and maintains and promotes the initiation and development of inflammation related-neuropathic pain. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

A richer and more diverse future for microglia phenotypes

Microglia are the only resident innate immune cells derived from the mesoderm in the nerve tissue. They play a role in the development and maturation of the central nervous system (CNS). Microglia mediate the repair of CNS injury and participate in endogenous immune response induced by various diseases by exerting neuroprotective or neurotoxic effects. Traditionally, microglia are considered to be in a resting state, the M0 type, under physiological conditions. In this state, they perform immune surveillance by constantly monitoring pathological responses in the CNS. In the pathological state, microglia undergo a series of morphological and functional changes from the M0 state and eventually polarize into classically activated microglia (M1) and alternatively activated microglia (M2). M1 microglia release inflammatory factors and toxic substances to inhibit pathogens, while M2 microglia exert neuroprotective effects by promoting nerve repair and regeneration. However, in recent years, the view regarding M1/M2 polarization of microglia has gradually changed. According to some researchers, the phenomenon of microglia polarization is not yet confirmed. The M1/M2 polarization term is used for a simplified description of its phenotype and function. Other researchers believe that the microglia polarization process is rich and diverse, and consequently, the classification method of M1/M2 has limitations. This conflict hinders the academic community from establishing more meaningful microglia polarization pathways and terms, and therefore, a careful revision of the concept of microglia polarization is required. The present article briefly reviews the current consensus and controversy regarding microglial polarization typing to provide supporting materials for a more objective understanding of the functional phenotype of microglia.

The Similar and Distinct Roles of Satellite Glial Cells and Spinal Astrocytes in Neuropathic Pain

Preclinical studies have identified glial cells as pivotal players in the genesis and maintenance of neuropathic pain after nerve injury associated with diabetes, chemotherapy, major surgeries, and virus infections. Satellite glial cells (SGCs) in the dorsal root and trigeminal ganglia of the peripheral nervous system (PNS) and astrocytes in the central nervous system (CNS) express similar molecular markers and are protective under physiological conditions. They also serve similar functions in the genesis and maintenance of neuropathic pain, downregulating some of their homeostatic functions and driving pro-inflammatory neuro-glial interactions in the PNS and CNS, i.e., "gliopathy". However, the role of SGCs in neuropathic pain is not simply as "peripheral astrocytes". We delineate how these peripheral and central glia participate in neuropathic pain by producing different mediators, engaging different parts of neurons, and becoming active at different stages following nerve injury. Finally, we highlight the recent findings that SGCs are enriched with proteins related to fatty acid metabolism and signaling such as Apo-E, FABP7, and LPAR1. Targeting SGCs and astrocytes may lead to novel therapeutics for the treatment of neuropathic pain.

Integrative Analysis Reveals the Expression Pattern of SOX9 in Satellite Glial Cells after Sciatic Nerve Injury

BACKGROUND

Several complex cellular and gene regulatory processes are involved in peripheral nerve repair. This study uses bioinformatics to analyze the differentially expressed genes (DEGs) in the satellite glial cells of mice following sciatic nerve injury.

METHODS

R software screens differentially expressed genes, and the WebGestalt functional enrichment analysis tool conducts Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomics (KEGG) pathway analysis. The Search Tool for the Retrieval of Interacting Genes/Proteins constructs protein interaction networks, and the cytoHubba plug-in in the Cytoscape software predicts core genes. Subsequently, the sciatic nerve injury model of mice was established and the dorsal root ganglion satellite glial cells were isolated and cultured. Satellite glial cells-related markers were verified by immunofluorescence staining. Real-time polymerase chain reaction assay and Western blotting assay were used to detect the mRNA and protein expression of Sox9 in satellite glial cells.

RESULTS

A total of 991 DEGs were screened, of which 383 were upregulated, and 508 were downregulated. The GO analysis revealed the processes of biosynthesis, negative regulation of cell development, PDZ domain binding, and other biological processes were enriched in DEGs. According to the KEGG pathway analysis, DEGs are primarily involved in steroid biosynthesis, hedgehog signaling pathway, terpenoid backbone biosynthesis, American lateral skeleton, and melanoma pathways. According to various cytoHubba algorithms, the common core genes in the protein-protein interaction network are Atf3, Mmp2, and Sox9. Among these, Sox9 was reported to be involved in the central nervous system and the generation and development of astrocytes and could mediate the transformation between neurogenic and glial cells. The experimental results showed that satellite glial cell marker GS were co-labeled with Sox9; stem cell characteristic markers Nestin and p75NTR were labeled satellite glial cells. The mRNA and protein expression of Sox9 in satellite glial cells were increased after sciatic nerve injury.

CONCLUSIONS

In this study, bioinformatics was used to analyze the DEGs of satellite glial cells after sciatic nerve injury, and transcription factors related to satellite glial cells were screened, among which Sox9 may be associated with the fate of satellite glial cells.

Satellite glial cells drive the transition from acute to chronic pain in a rat model of hyperalgesic priming

Chronic pain is one of the most common clinical syndromes affecting patients' quality of life. Regulating the transition from acute to chronic pain is a novel therapeutic strategy for chronic pain that presents a major clinical challenge. However, the mechanism underlying pain transitions remains poorly understood. A rat hyperalgesic priming (HP) model, which mimics pain transition, was established decades ago. Here, this HP model and RNA sequencing (RNA-seq) were used to study the potential role of neuroinflammation in pain transition. In this study, HP model rats developed prolonged hyperalgesia in the hind paw after carrageenan (Car) and PGE2 injection, accompanied by obvious satellite glial cell (SGC) activation in the dorsal root ganglion (DRG), as indicated by upregulation of GFAP. RNA-Seq identified a total of differentially expressed genes in the ipsilateral DRG in HP model rats. The expression of several representative genes was confirmed by real-time quantitative PCR (qPCR). Functional analysis of the differentially expressed genes indicated that genes related to the inflammatory and neuroinflammatory response showed the most significant changes in expression. We further found that the expression of the chemokine CXCL1 was significantly upregulated in the rat DRG. Pharmacological blockade of CXCL1 reduced protein kinase C epsilon overproduction as well as hyperalgesia in HP rats but did not prevent the upregulation of GFAP in the DRG. These results reveal that neuroinflammatory responses are involved in pain transition and may be the source of chronic pain. The chemokine CXCL1 in the DRG is a pivotal contributor to chronic pain and pain transition in HP model rats. Thus, our study provides a putative novel target for the development of effective therapeutics to prevent pain transition.

Far from home: the role of glial mRNA localization in synaptic plasticity

Neurons and glia are highly polarized cells, whose distal cytoplasmic functional subdomains require specific proteins. Neurons have axonal and dendritic cytoplasmic extensions containing synapses whose plasticity is regulated efficiently by mRNA transport and localized translation. The principles behind these mechanisms are equally attractive for explaining rapid local regulation of distal glial cytoplasmic projections, independent of their cell nucleus. However, in contrast to neurons, mRNA localization has received little experimental attention in glia. Nevertheless, there are many functionally diverse glial subtypes containing extensive networks of long cytoplasmic projections with likely localized regulation that influence neurons and their synapses. Moreover, glia have many other neuron-like properties, including electrical activity, secretion of gliotransmitters and calcium signaling, influencing, for example, synaptic transmission, plasticity and axon pruning. Here, we review previous studies concerning glial transcripts with important roles in influencing synaptic plasticity, focusing on a few cases involving localized translation. We discuss a variety of important questions about mRNA transport and localized translation in glia that remain to be addressed, using cutting-edge tools already available for neurons.

Glial Cells and Itch: Possible Targets for Novel Antipruritic Therapies

Glial cells, which are the non-neuronal cells of the nervous system, play essential roles in brain development, homeostasis, and diseases. Glial cells have attracted attention because of their active involvement in many neurological disorders. In recent years, substantial progress has been made in our understanding of the roles of glial cells in the pathogenesis of itch. Mechanistically, central and peripheral glial cells modulate acute and chronic pruritus via different mechanisms. In this review, we present the current knowledge about the involvement of glial cells in the modulation of itch processing and the mechanism of glial cell activation under itch stimuli. Targeting glial cells may provide novel approaches for itch therapy.

Involvement of interferon gamma signaling in spinal trigeminal caudal subnucleus astrocyte in orofacial neuropathic pain in rats with infraorbital nerve injury

Background: Trigeminal nerve injury causes orofacial pain that can interfere with activities of daily life. However, the underlying mechanism remains unknown, and the appropriate treatment has not been established yet. This study aimed to examine the involvement of interferon gamma (IFN-γ) signaling in the spinal trigeminal caudal subnucleus (Vc) in orofacial neuropathic pain. Methods: Infraorbital nerve (ION) injury (IONI) was performed in rats by partial ION ligation. The head-withdrawal reflex threshold (HWT) to mechanical stimulation of the whisker pad skin was measured in IONI or sham rats, as well as following a continuous intracisterna magna administration of IFN-γ and a mixture of IFN-γ and fluorocitrate (inhibitor of astrocytes activation) in naïve rats, or an IFN-γ antagonist in IONI rats. The IFN-γ receptor immunohistochemistry and IFN-γ Western blotting were analyzed in the Vc after IONI or sham treatment. The glial fibrillary acid protein (GFAP) immunohistochemistry and Western blotting were also analyzed after administration of IFN-γ and the mixture of IFN-γ and fluorocitrate. Moreover, the change in single neuronal activity in the Vc was examined in the IONI, sham, and IONI group administered IFN-γ antagonist. Results: The HWT decreased after IONI. The IFN-γ and IFN-γ receptor were upregulated after IONI, and the IFN-γ receptor was expressed in Vc astrocytes. IFN-γ administration decreased the HWT, whereas the mixture of IFN-γ and fluorocitrate recovered the decrement of HWT. IFN-γ administration upregulated GFAP expression, while the mixture of IFN-γ and fluorocitrate recovered the upregulation of GFAP expression. IONI significantly enhanced the neuronal activity of the mechanical-evoked responses, and administration of an IFN-γ antagonist significantly inhibited these enhancements. Conclusions: IFN-γ signaling through the receptor in astrocytes is a key mechanism underlying orofacial neuropathic pain associated with trigeminal nerve injury. These findings will aid in the development of therapeutics for orofacial neuropathic pain.

Blocking Cx43 alleviates neuropathic pain in rats with chronic constriction injury via the P2X4 and P38/ERK-P65 pathways

Neuropathic pain is a growing concern in the medical community, and studies on new analgesic targets for neuropathic pain have become a new hot spot. Whether Connexin43 (Cx43) has a key role in neuropathic pain mediated by the purinergic 2X4 (P2X4) receptor in rats with chronic constriction injury (CCI) was explored in this study. Our experimental results show that blockade of Cx43 could attenuate neuropathic pain in rats suffering from CCI via the P2X4, p38, ERK, and NF-kB signalling pathways. These results suggest that Cx43 may be a promising therapeutic target for the development of novel pharmacological agents in the management of neuropathic pain.

Neuron-glia interaction at the receptor level affects olfactory perception in adult Drosophila

Some types of glia play an active role in neuronal signaling by modifying their activity although little is known about their role in sensory information signaling at the receptor level. In this research, we report a functional role for the glia that surround the soma of the olfactory receptor neurons (OSNs) in adult Drosophila. Specific genetic modifications have been targeted to this cell type to obtain live individuals who are tested for olfactory preference and display changes both increasing and reducing sensitivity. A closer look at the antenna by Ca²⁺ imaging shows that odor activates the OSNs, which subsequently produce an opposite and smaller effect in the glia that partially counterbalances neuronal activation. Therefore, these glia may play a dual role in preventing excessive activation of the OSNs at high odorant concentrations and tuning the chemosensory window for the individual according to the network structure in the receptor organ.

Nano-integrated cascade antioxidases opsonized by albumin bypass the blood-brain barrier for treatment of ischemia-reperfusion injury

Potent antioxidative drugs are urgently needed to treat ischemia-reperfusion (I/R) induced reactive oxygen species (ROS)-mediated cerebrovascular and neural injury during ischemia strokes. However, current antioxidative agents have limited application in such disease due to low blood-brain barrier (BBB) penetration. We herein designed a "neutrophil piggybacking" strategy based on albumin opsonized nanoparticles co-encapsulated with antioxidases catalase (CAT) and superoxide dismutase 1 (SOD1). The system utilized the natural potential of neutrophils to target inflamed tissues to deliver antioxidases to injured sites in the brain. In addition, the system was integrated with a selenium (Se)-containing crosslinker to inhibit ferroptosis. We showed that the nanoparticles opsonized in the hybrid form rather than with an albumin-shell structure exhibited enhanced neutrophil targeting and efficient BBB penetration in vitro and in vivo. We further showed that the neutrophil-mediated delivery of antioxidases effectively reduced oxidative damage and apoptosis of neurons in brain tissue in a transient middle cerebral artery occlusion (tMCAO) mouse model. Moreover, the successful delivery of Se with the nanoparticles increased the expression of glutathione peroxidase 4 (GPX4) and effectively inhibited neuronal ferroptosis, achieving a satisfactory neuroprotective effect in I/R injury mice. Our study demonstrated that the rationally designed nanomedicines using the "neutrophil piggybacking" strategy can efficiently penetrate the BBB, greatly expanding the application of nanomedicines in the treatment of central nervous system (CNS) diseases.

Profiling the molecular signature of satellite glial cells at the single cell level reveals high similarities between rodents and humans

ABSTRACT

Peripheral sensory neurons located in dorsal root ganglia relay sensory information from the peripheral tissue to the brain. Satellite glial cells (SGCs) are unique glial cells that form an envelope completely surrounding each sensory neuron soma. This organization allows for close bidirectional communication between the neuron and its surrounding glial coat. Morphological and molecular changes in SGC have been observed in multiple pathological conditions such as inflammation, chemotherapy-induced neuropathy, viral infection, and nerve injuries. There is evidence that changes in SGC contribute to chronic pain by augmenting the neuronal activity in various rodent pain models. Satellite glial cells also play a critical role in axon regeneration. Whether findings made in rodent model systems are relevant to human physiology have not been investigated. Here, we present a detailed characterization of the transcriptional profile of SGC in mice, rats, and humans at the single cell level. Our findings suggest that key features of SGC in rodent models are conserved in humans. Our study provides the potential to leverage rodent SGC properties and identify potential targets in humans for the treatment of nerve injuries and alleviation of painful conditions.

Glia from the central and peripheral nervous system are differentially affected by paclitaxel chemotherapy via modulating their neuroinflammatory and neuroregenerative properties

Glia are critical players in defining synaptic contacts and maintaining neuronal homeostasis. Both astrocytes as glia of the central nervous system (CNS), as well as satellite glial cells (SGC) as glia of the peripheral nervous system (PNS), intimately interact with microglia, especially under pathological conditions when glia regulate degenerative as well as regenerative processes. The chemotherapeutic agent paclitaxel evokes peripheral neuropathy and cognitive deficits; however, the mechanisms underlying these diverse clinical side effects are unclear. We aimed to elucidate the direct effects of paclitaxel on the function of astrocytes, microglia, and SGCs, and their glia-glia and neuronal-glia interactions. After intravenous application, paclitaxel was present in the dorsal root ganglia of the PNS and the CNS of rodents. In vitro, SGC enhanced the expression of pro-inflammatory factors and reduced the expression of neurotrophic factor NT-3 upon exposure to paclitaxel, resulting in predominantly neurotoxic effects. Likewise, paclitaxel induced a switch towards a pro-inflammatory phenotype in microglia, exerting neurotoxicity. In contrast, astrocytes expressed neuroprotective markers and increasingly expressed S100A10 after paclitaxel exposure. Astrocytes, and to a lesser extent SGCs, had regulatory effects on microglia independent of paclitaxel exposure. Data suggest that paclitaxel differentially modulates glia cells regarding their (neuro-) inflammatory and (neuro-) regenerative properties and also affects their interaction. By elucidating those processes, our data contribute to the understanding of the mechanistic pathways of paclitaxel-induced side effects in CNS and PNS.

Stellate Ganglia and Cardiac Sympathetic Overactivation in Heart Failure

Heart failure (HF) is a major public health problem worldwide, especially coronary heart disease (myocardial infarction)-induced HF with reduced ejection fraction (HFrEF), which accounts for over 50% of all HF cases. An estimated 6 million American adults have HF. As a major feature of HF, cardiac sympathetic overactivation triggers arrhythmias and sudden cardiac death, which accounts for nearly 50–60% of mortality in HF patients. Regulation of cardiac sympathetic activation is highly integrated by the regulatory circuitry at multiple levels, including afferent, central, and efferent components of the sympathetic nervous system. Much evidence, from other investigators and us, has confirmed the afferent and central neural mechanisms causing sympathoexcitation in HF. The stellate ganglion is a peripheral sympathetic ganglion formed by the fusion of the 7th cervical and 1st thoracic sympathetic ganglion. As the efferent component of the sympathetic nervous system, cardiac postganglionic sympathetic neurons located in stellate ganglia provide local neural coordination independent of higher brain centers. Structural and functional impairments of cardiac postganglionic sympathetic neurons can be involved in cardiac sympathetic overactivation in HF because normally, many effects of the cardiac sympathetic nervous system on cardiac function are mediated via neurotransmitters (e.g., norepinephrine) released from cardiac postganglionic sympathetic neurons innervating the heart. This review provides an overview of cardiac sympathetic remodeling in stellate ganglia and potential mechanisms and the role of cardiac sympathetic remodeling in cardiac sympathetic overactivation and arrhythmias in HF. Targeting cardiac sympathetic remodeling in stellate ganglia could be a therapeutic strategy against malignant cardiac arrhythmias in HF.

Morphological and phenotypical characteristics of porcine satellite glial cells of the dorsal root ganglia

Satellite glial cells (SGCs) of the dorsal root ganglia (DRG) ensure homeostasis and proportional excitability of sensory neurons and gained interest in the field of development and maintenance of neuropathic pain. Pigs represent a suitable species for translational medicine with a more similar anatomy and physiology to humans compared to rodents, and are used in research regarding treatment of neuropathic pain. Knowledge of anatomical and physiological features of porcine SGCs is prerequisite for interpreting potential alterations. However, state of knowledge is still limited. In the present study, light microscopy, ultrastructural analysis and immunofluorescence staining was performed. SGCs tightly surround DRG neurons with little vascularized connective tissue between SGC-neuron units, containing, among others, axons and Schwann cells. DRG were mainly composed of large sized neurons (∼59%), accompanied by fewer medium sized (∼36%) and small sized sensory neurons (∼6%). An increase of neuronal body size was concomitant with an increased number of surrounding SGCs. The majority of porcine SGCs expressed glutamine synthetase and inwardly rectifying potassium channel Kir 4.1, known as SGC-specific markers in other species. Similar to canine SGCs, marked numbers of porcine SGCs were immunopositive for glial fibrillary acidic protein, 2',3'-cyclic-nucleotide 3'-phosphodiesterase and the transcription factor Sox2. Low to moderate numbers of SGCs showed aquaporin 4-immunoreactivity (AQP4) as described for murine SGCs. AQP4-immunoreactivity was primarily found in SGCs ensheathing small and medium sized neuronal somata. Low numbers of SGCs were immunopositive for ionized calcium-binding adapter molecule 1, indicating a potential immune cell character. No immunoreactivity for common leukocyte antigen CD45 nor neural/glial antigen 2 was detected. The present study provides essential insights into the characteristic features of non-activated porcine SGCs, contributing to a better understanding of this cell population and its functional aspects. This will help to interpret possible changes that might occur under activating conditions such as pain.

Satellite Glial Cells: Morphology, functional heterogeneity, and role in pain

Neurons in the somatic, sympathetic, and parasympathetic ganglia are surrounded by envelopes consisting of satellite glial cells (SGCs). Recently, it has become clear that SGCs are highly altered after nerve injury, which influences neuronal excitability and, consequently, the development and maintenance of pain in different animal models of chronic pain. However, the exact mechanism underlying chronic pain is not fully understood yet because it is assumed that SGCs in different ganglia share many common peculiarities, making the process complex. Here, we review recent data on morphological and functional heterogeneity and changes in SGCs in various pain conditions and their role in response to injury. More research is required to decipher the role of SGCs in diseases, such as chronic pain, neuropathology, and neurodegenerative diseases.

Sodium Danshensu protects against oxygen glucose deprivation/reoxygenation-induced astrocytes injury through regulating NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome and tuberous sclerosis complex-2 (TSC2)/mammalian target of rapamycin (mTOR) pathways

BACKGROUND

Cerebral ischemic stroke is a serious condition with high incidence, mortality, and associated disability. Currently, effective therapeutic options are available for ischemic stroke are limited. Accumulating evidence indicates that sodium Danshensu, mono sodium compound derived from Salvia miltiorrhiza, plays protective roles in ischemic stroke. However, the underlying protective mechanism of sodium Danshensu in cerebral ischemic stroke remains unknown.

METHODS

In the current study, we explored the role and mechanism of sodium Danshensu on astrocytes exposed to oxygen-glucose deprivation/reoxygenation (OGD/R), which mimics the process of ischemia-reperfusion. The impact of sodium Danshensu on cell viability and apoptosis after OGD/R were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-dophenyl tetrazolium bromide (MTT) assay and flow cytometry. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blot were used to detect the expression of target messenger RNA (mRNA) and proteins associated with apoptosis and autophagy. The release of lactate dehydrogenase (LDH) was determined, and the production of proinflammatory cytokines were detected using enzyme-linked immunosorbent assay (ELISA) kits.

RESULTS

It was found that sodium Danshensu could significantly increase cell viability and decrease LDH release and apoptosis. Besides, it inhibited the production of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6. Sodium Danshensu also dose-dependently decreased protein and mRNA levels of nucleotide binding oligomerization NOD-like receptor pyrin domain containing 3 (NLRP3) and high mobility group box 1 (HMGB1), which play a crucial role in promoting ischemic stroke-induced cell injury. Moreover, sodium Danshensu dose-dependently upregulated Beclin 1 expression, downregulated P62 protein expression, and further increased LC3B-II/LC3B-I ratio through inducing autophagy in astrocytes. Additionally, we noticed that sodium Danshensu dose-dependently increased tuberous sclerosis complex-2 (TSC2) protein expression, while significantly reduced the levels of mammalian target of rapamycin (mTOR) in the presence of OGD/R insult.

CONCLUSIONS

These findings suggest that sodium Danshensu protects against OGD/R-induced injury by modulating the NLRP3 inflammasome and TSC2/mTOR pathways.

Satellite glia modulate sympathetic neuron survival, activity, and autonomic function

Satellite glia are the major glial cells in sympathetic ganglia, enveloping neuronal cell bodies. Despite this intimate association, the extent to which sympathetic functions are influenced by satellite glia in vivo remains unclear. Here, we show that satellite glia are critical for metabolism, survival, and activity of sympathetic neurons and modulate autonomic behaviors in mice. Adult ablation of satellite glia results in impaired mTOR signaling, soma atrophy, reduced noradrenergic enzymes, and loss of sympathetic neurons. However, persisting neurons have elevated activity, and satellite glia-ablated mice show increased pupil dilation and heart rate, indicative of enhanced sympathetic tone. Satellite glia-specific deletion of Kir4.1, an inward-rectifying potassium channel, largely recapitulates the cellular defects observed in glia-ablated mice, suggesting that satellite glia act in part via K⁺-dependent mechanisms. These findings highlight neuron–satellite glia as functional units in regulating sympathetic output, with implications for disorders linked to sympathetic hyper-activity such as cardiovascular disease and hypertension.

Society of Toxicologic Pathology Neuropathology Interest Group Article: Neuropathologic Findings in Nonhuman Primates Associated With Administration of Biomolecule-Based Test Articles

The increasing specificity of novel druggable targets coupled with the complexity of emerging therapeutic modalities for treating human diseases has created a growing need for nonhuman primates (NHPs) as models for translational drug discovery and nonclinical safety assessment. In particular, NHPs are critical for investigating potential unexpected/undesired on-target and off-target liabilities associated with administration of candidate biotherapeutics (nucleic acids, proteins, viral gene therapy vectors, etc.) to treat nervous system disorders. Nervous system findings unique to or overrepresented in NHPs administered biomolecule-based ("biologic") test articles include mononuclear cell infiltration in most neural tissues for all biomolecule classes as well as neuronal necrosis with glial cell proliferation in sensory ganglia for certain viral vectors. Such test article-related findings in NHPs often must be differentiated from procedural effects (e.g., local parenchymal or meningeal reactions associated with an injection site or implanted catheter to administer a test article directly into the central nervous system) or spontaneous background findings (e.g., neuronal autophagy in sensory ganglia).

Disrupted Association of Sensory Neurons With Enveloping Satellite Glial Cells in Fragile X Mouse Model

Among most prevalent deficits in individuals with Fragile X syndrome (FXS) is hypersensitivity to sensory stimuli and somatosensory alterations. Whether dysfunction in peripheral sensory system contributes to these deficits remains poorly understood. Satellite glial cells (SGCs), which envelop sensory neuron soma, play critical roles in regulating neuronal function and excitability. The potential contributions of SGCs to sensory deficits in FXS remain unexplored. Here we found major structural defects in sensory neuron-SGC association in the dorsal root ganglia (DRG), manifested by aberrant covering of the neuron and gaps between SGCs and the neuron along their contact surface. Single-cell RNAseq analyses demonstrated transcriptional changes in both neurons and SGCs, indicative of defects in neuronal maturation and altered SGC vesicular secretion. We validated these changes using fluorescence microscopy, qPCR, and high-resolution transmission electron microscopy (TEM) in combination with computational analyses using deep learning networks. These results revealed a disrupted neuron-glia association at the structural and functional levels. Given the well-established role for SGCs in regulating sensory neuron function, altered neuron-glia association may contribute to sensory deficits in FXS.

Astrocytes in cocaine addiction and beyond

Drug addiction remains a key biomedical challenge facing current neuroscience research. In addition to neural mechanisms, the focus of the vast majority of studies to date, astrocytes have been increasingly recognized as an "accomplice." According to the tripartite synapse model, astrocytes critically regulate nearby pre- and postsynaptic neuronal substrates to craft experience-dependent synaptic plasticity, including synapse formation and elimination. Astrocytes within brain regions that are implicated in drug addiction exhibit dynamic changes in activity upon exposure to cocaine and subsequently undergo adaptive changes themselves during chronic drug exposure. Recent results have identified several key astrocytic signaling pathways that are involved in cocaine-induced synaptic and circuit adaptations. In this review, we provide a brief overview of the role of astrocytes in regulating synaptic transmission and neuronal function, and discuss how cocaine influences these astrocyte-mediated mechanisms to induce persistent synaptic and circuit alterations that promote cocaine seeking and relapse. We also consider the therapeutic potential of targeting astrocytic substrates to ameliorate drug-induced neuroplasticity for behavioral benefits. While primarily focusing on cocaine-induced astrocytic responses, we also include brief discussion of other drugs of abuse where data are available.

Neuroglia in Psychiatric Disorders

In the twentieth century, neuropsychiatric disorders have been perceived solely from a neurone-centric point of view, which considers neurones as the key cellular elements of pathological processes. This dogma has been challenged thanks to the better comprehension of the brain functioning, which, even if far from being complete, has revealed the complexity of interactions that exist between neurones and neuroglia. Glial cells represent a highly heterogeneous population of cells of neural (astroglia and oligodendroglia) and non-neural (microglia) origin populating the central nervous system. The variety of glia reflects the innumerable functions that glial cells perform to support functions of the nervous system. Aberrant execution of glial functions contributes to the development of neuropsychiatric pathologies. Arguably, all types of glial cells are implicated in the neuropathology; however, astrocytes have received particular attention in recent years because of their pleiotropic functions that make them decisive in maintaining cerebral homeostasis. This chapter describes the multiple roles of astrocytes in the healthy central nervous system and discusses the diversity of astroglial responses in neuropsychiatric disorders suggesting that targeting astrocytes may represent an effective therapeutic strategy.

Phenotypical changes of satellite glial cells in a murine model of GM1 -gangliosidosis

Satellite glial cells (SGCs) of dorsal root ganglia (DRG) react in response to various injuries in the nervous system. This study investigates reactive changes within SGCs in a murine model for G_M1‐gangliosidosis (G_M1). DRG of homozygous β‐galactosidase‐knockout mice and homozygous C57BL/6 wild‐type mice were investigated performing immunostaining on formalin‐fixed, paraffin‐embedded tissue. A marked upregulation of glial fibrillary acidic protein (GFAP), the progenitor marker nestin and Ki67 within SGCs of diseased mice, starting after 4 months at the earliest GFAP, along with intracytoplasmic accumulation of ganglioside within neurons and deterioration of clinical signs was identified. Interestingly, nestin‐positive SGCs were detected after 8 months only. No changes regarding inwardly rectifying potassium channel 4.1, 2, 3‐cyclic nucleotide 3‐phosphodiesterase, Sox2, doublecortin, periaxin and caspase3 were observed in SGCs. Iba1 was only detected in close vicinity of SGCs indicating infiltrating or tissue‐resident macrophages. These results indicate that SGCs of DRG show phenotypical changes during the course of G_M1, characterized by GFAP upregulation, proliferation and expression of a neural progenitor marker at a late time point. This points towards an important role of SGCs during neurodegenerative disorders and supports that SGCs represent a multipotent glial precursor cell line with high plasticity and functionality.

Discrepancy in the Usage of GFAP as a Marker of Satellite Glial Cell Reactivity

Satellite glial cells (SGCs) surrounding the neuronal somas in peripheral sensory ganglia are sensitive to neuronal stressors, which induce their reactive state. It is believed that such induced gliosis affects the signaling properties of the primary sensory neurons and is an important component of the neuropathic phenotype leading to pain and other sensory disturbances. Efforts to understand and manipulate such gliosis relies on reliable markers to confirm induced SGC reactivity and ultimately the efficacy of targeted intervention. Glial fibrillary acidic protein (GFAP) is currently the only widely used marker for such analyses. However, we have previously described the lack of SGC upregulation of GFAP in a mouse model of sciatic nerve injury, suggesting that GFAP may not be a universally suitable marker of SGC gliosis across species and experimental models. To further explore this, we here investigate the regulation of GFAP in two different experimental models in both rats and mice. We found that whereas GFAP was upregulated in both rodent species in the applied inflammation model, only the rat demonstrated increased GFAP in SGCs following sciatic nerve injury; we did not observe any such GFAP upregulation in the mouse model at either protein or mRNA levels. Our results demonstrate an important discrepancy between species and experimental models that prevents the usage of GFAP as a universal marker for SGC reactivity.