Diabetic neuropathic pain (DNP) is the most common disabling complication of diabetes. Emerging evidence has linked the pathogenesis of DNP to the aberrant sprouting of sensory axons into the epidermal area; however, the underlying molecular events remain poorly understood. Here we found that an axon guidance molecule, Netrin-3 (Ntn-3), was expressed in the sensory neurons of mouse dorsal root ganglia (DRGs), and downregulation of Ntn-3 expression was highly correlated with the severity of DNP in a diabetic mouse model. Genetic ablation of Ntn-3 increased the intra-epidermal sprouting of sensory axons and worsened the DNP in diabetic mice. In contrast, the elevation of Ntn-3 levels in DRGs significantly inhibited the intra-epidermal axon sprouting and alleviated DNP in diabetic mice. In conclusion, our studies identified Ntn-3 as an important regulator of DNP pathogenesis by gating the aberrant sprouting of sensory axons, indicating that Ntn-3 is a potential druggable target for DNP treatment.
Mice ; Animals ; Diabetes Mellitus, Experimental/metabolism* ; Axons/physiology* ; Diabetic Neuropathies ; Sensory Receptor Cells/metabolism* ; Neuralgia/metabolism*

The voltage-gated Na channel subtype Nav1.7 is important for pain and itch in rodents and humans. We previously showed that a Nav1.7-targeting monoclonal antibody (SVmab) reduces Na currents and pain and itch responses in mice. Here, we investigated whether recombinant SVmab (rSVmab) binds to and blocks Nav1.7 similar to SVmab. ELISA tests revealed that SVmab was capable of binding to Nav1.7-expressing HEK293 cells, mouse DRG neurons, human nerve tissue, and the voltage-sensor domain II of Nav1.7. In contrast, rSVmab showed no or weak binding to Nav1.7 in these tests. Patch-clamp recordings showed that SVmab, but not rSVmab, markedly inhibited Na currents in Nav1.7-expressing HEK293 cells. Notably, electrical field stimulation increased the blocking activity of SVmab and rSVmab in Nav1.7-expressing HEK293 cells. SVmab was more effective than rSVmab in inhibiting paclitaxel-induced mechanical allodynia. SVmab also bound to human DRG neurons and inhibited their Na currents. Finally, potential reasons for the differential efficacy of SVmab and rSVmab and future directions are discussed.
Animals ; Antibodies, Monoclonal ; therapeutic use ; Biotin ; metabolism ; Cells, Cultured ; Disease Models, Animal ; Female ; Ganglia, Spinal ; cytology ; HEK293 Cells ; Humans ; Hybridomas ; chemistry ; Hyperalgesia ; drug therapy ; Male ; Mice ; Mice, Inbred C57BL ; NAV1.5 Voltage-Gated Sodium Channel ; metabolism ; NAV1.7 Voltage-Gated Sodium Channel ; chemistry ; immunology ; metabolism ; Neuralgia ; drug therapy ; metabolism ; Protein Binding ; drug effects ; Recombinant Proteins ; biosynthesis ; therapeutic use ; Sensory Receptor Cells ; drug effects ; physiology

Different physical and chemical stimuli are detected by the peripheral sensory receptors of dorsal root ganglion (DRG) neurons, and the generated inputs are transmitted via afferent fibers into the central nervous system. The gene expression profiles of DRG neurons contribute to the generation, transmission, and regulation of various somatosensory signals. Recently, the single-cell transcriptomes, cell types, and functional annotations of somatosensory neurons have been studied. In this review, we introduce our classification of DRG neurons based on single-cell RNA-sequencing and functional analyses, and discuss the technical approaches. Moreover, studies on the molecular and cellular mechanisms underlying somatic sensations are discussed.
Animals ; Ganglia, Spinal ; cytology ; Gene Regulatory Networks ; Humans ; Pain ; genetics ; metabolism ; pathology ; Sensory Receptor Cells ; metabolism ; Sequence Analysis, RNA ; Transcriptome

Chronic pain and itch are a pathological operation of the somatosensory system at the levels of primary sensory neurons, spinal cord and brain. Pain and itch are clearly distinct sensations, and recent studies have revealed the separate neuronal pathways that are involved in each sensation. However, the mechanisms by which these sensations turn into a pathological chronic state are poorly understood. A proposed mechanism underlying chronic pain and itch involves abnormal excitability in dorsal horn neurons in the spinal cord. Furthermore, an increasing body of evidence from models of chronic pain and itch has indicated that synaptic hyperexcitability in the spinal dorsal horn might not be a consequence simply of changes in neurons, but rather of multiple alterations in glial cells. Thus, understanding the key roles of glial cells may provide us with exciting insights into the mechanisms of chronicity of pain and itch, and lead to new targets for treating chronic pain and itch.
Animals ; Chronic Pain ; pathology ; Humans ; Neuralgia ; metabolism ; Pruritus ; pathology ; Sensory Receptor Cells ; physiology ; Spinal Cord ; pathology

Peripheral itch stimuli are transmitted by sensory neurons to the spinal cord dorsal horn, which then transmits the information to the brain. The molecular and cellular mechanisms within the dorsal horn for itch transmission have only been investigated and identified during the past ten years. This review covers the progress that has been made in identifying the peptide families in sensory neurons and the receptor families in dorsal horn neurons as putative itch transmitters, with a focus on gastrin-releasing peptide (GRP)-GRP receptor signaling. Also discussed are the signaling mechanisms, including opioids, by which various types of itch are transmitted and modulated, as well as the many conflicting results arising from recent studies.
Action Potentials ; drug effects ; Analgesics, Opioid ; pharmacology ; Animals ; Humans ; Pruritus ; metabolism ; pathology ; Sensory Receptor Cells ; metabolism ; Spinal Cord ; pathology ; Synaptic Transmission ; physiology

Cutaneous neurogenic inflammation (CNI) is inflammation that is induced (or enhanced) in the skin by the release of neuropeptides from sensory nerve endings. Clinical manifestations are mainly sensory and vascular disorders such as pruritus and erythema. Transient receptor potential vanilloid 1 and ankyrin 1 (TRPV1 and TRPA1, respectively) are non-selective cation channels known to specifically participate in pain and CNI. Both TRPV1 and TRPA1 are co-expressed in a large subset of sensory nerves, where they integrate numerous noxious stimuli. It is now clear that the expression of both channels also extends far beyond the sensory nerves in the skin, occuring also in keratinocytes, mast cells, dendritic cells, and endothelial cells. In these non-neuronal cells, TRPV1 and TRPA1 also act as nociceptive sensors and potentiate the inflammatory process. This review discusses the role of TRPV1 and TRPA1 in the modulation of inflammatory genes that leads to or maintains CNI in sensory neurons and non-neuronal skin cells. In addition, this review provides a summary of current research on the intracellular sensitization pathways of both TRP channels by other endogenous inflammatory mediators that promote the self-maintenance of CNI.
Animals ; Chronic Disease ; Dendritic Cells ; metabolism ; pathology ; Dermatitis ; metabolism ; pathology ; Gene Expression Regulation ; Humans ; Inflammation ; metabolism ; pathology ; Keratinocytes ; metabolism ; pathology ; Mast Cells ; metabolism ; pathology ; Sensory Receptor Cells ; metabolism ; pathology ; TRPA1 Cation Channel ; biosynthesis ; TRPV Cation Channels ; biosynthesis

Voltage-gated sodium channels (VGSCs) in primary sensory neurons play a key role in transmitting pain signals to the central nervous system. BmK I, a site-3 sodium channel-specific toxin from scorpion Buthus martensi Karsch, induces pain behaviors in rats. However, the subtypes of VGSCs targeted by BmK I were not entirely clear. We therefore investigated the effects of BmK I on the current amplitude, gating and kinetic properties of Nav1.8, which is associated with neuronal hyperexcitability in DRG neurons. It was found that BmK I dose-dependently increased Nav1.8 current in small-sized (<25 μm) acutely dissociated DRG neurons, which correlated with its inhibition on both fast and slow inactivation. Moreover, voltage-dependent activation and steady-state inactivation curves of Nav1.8 were shifted in a hyperpolarized direction. Thus, BmK I reduced the threshold of neuronal excitability and increased action potential firing in DRG neurons. In conclusion, our data clearly demonstrated that BmK I modulated Nav1.8 remarkably, suggesting BmK I as a valuable probe for studying Nav1.8. And Nav1.8 is an important target related to BmK I-evoked pain.
Aniline Compounds ; pharmacology ; Animals ; Cell Size ; Cells, Cultured ; Electrophysiological Phenomena ; drug effects ; Furans ; pharmacology ; Ganglia, Spinal ; cytology ; Kinetics ; Male ; NAV1.8 Voltage-Gated Sodium Channel ; metabolism ; Rats ; Rats, Sprague-Dawley ; Scorpion Venoms ; antagonists & inhibitors ; pharmacology ; Scorpions ; Sensory Receptor Cells ; drug effects ; metabolism ; physiology ; Sodium Channel Blockers ; pharmacology ; Voltage-Gated Sodium Channel Agonists ; pharmacology

BACKGROUNDAlthough flunarizine has been widely used for migraine prophylaxis with clear success, the mechanisms of its actions in migraine prophylaxis are not completely understood. The aim of this study was to investigate the effects of flunarizine on tetrodotoxin-resistant Na(+) channels and high-voltage activated Ca(2+) channels of acutely isolated mouse trigeminal ganglion neurons.

METHODSSodium currents and calcium currents in trigeminal ganglion neurons were monitored using whole-cell patch-clamp recordings. Paired Student's t test was used as appropriate to evaluate the statistical significance of differences between two group means.

RESULTSBoth tetrodotoxin-resistant sodium currents and high-voltage activated calcium currents were blocked by flunarizine in a concentration-dependent manner with the concentration producing half-maximal current block values of 2.89 µmol/L and 2.73 µmol/L, respectively. The steady-state inactivation curves of tetrodotoxin-resistant sodium currents and high-voltage activated calcium currents were shifted towards more hyperpolarizing potentials after exposure to flunarizine. Furthermore, the actions of flunarizine in blocking tetrodotoxin-resistant sodium currents and high-voltage activated calcium currents were use-dependent, with effects enhanced at higher rates of channel activation.

CONCLUSIONBlockades of these currents might help explain the peripheral mechanism underlying the preventive effect of flunarizine on migraine attacks.

Animals ; Calcium ; metabolism ; Cells, Cultured ; Female ; Flunarizine ; pharmacology ; Male ; Mice ; Patch-Clamp Techniques ; Sensory Receptor Cells ; drug effects ; metabolism ; Sodium ; metabolism ; Trigeminal Ganglion ; cytology ; drug effects ; metabolism

The cytoplasmic polyadenylation element (CPE)-binding protein (CPEB) binds to CPE containing mRNAs on their 3' untranslated regions (3'UTRs). This RNA binding protein comes out many important tasks, especially in learning and memory, by modifying the translational efficiency of target mRNAs via poly (A) tailing. Overexpressed CPEB has been reported to induce the formation of stress granules (SGs), a sort of RNA granule in mammalian cell lines. RNA granule is considered to be a potentially important factor in learning and memory. However, there is no study about RNA granule in Aplysia. To examine whether an Aplysia CPEB, ApCPEB1, forms RNA granules, we overexpressed ApCPEB1-EGFP in Aplysia sensory neurons. Consistent with the localization of mammalian CPEB, overexpressed ApCPEB1 formed granular structures, and was colocalized with RNAs and another RNA binding protein, ApCPEB, showing that ApCPEB1 positive granules are RNA-protein complexes. In addition, ApCPEB1 has a high turnover rate in RNA granules which were mobile structures. Thus, our results indicate that overexpressed ApCPEB1 is incorporated into RNA granule which is a dynamic structure in Aplysia sensory neuron. We propose that ApCPEB1 granule might modulate translation, as other RNA granules do, and furthermore, influence memory.
Animals ; Aplysia/genetics/*metabolism ; Fluorescence Recovery After Photobleaching ; RNA/genetics/metabolism ; Sensory Receptor Cells/*metabolism ; mRNA Cleavage and Polyadenylation Factors/genetics/metabolism/*physiology

A subset of patients of amyotrophic lateral sclerosis (ALS) present with mutation of Cu/Zn superoxide dismutase 1 (SOD1), and such mutants caused an ALS-like disorder when expressed in rodents. These findings implicated SOD1 in ALS pathogenesis and made the transgenic animals a widely used ALS model. However, previous studies of these animals have focused largely on motor neuron damage. We report herein that the spinal cords of mice expressing a human SOD1 mutant (hSOD1-G93A), besides showing typical destruction of motor neurons and axons, exhibit significant damage in the sensory system, including Wallerian-like degeneration in axons of dorsal root and dorsal funiculus, and mitochondrial damage in dorsal root ganglia neurons. Thus, hSOD1-G93A mutation causes both motor and sensory neuropathies, and as such the disease developed in the transgenic mice very closely resembles human ALS.
Amyotrophic Lateral Sclerosis/enzymology/*pathology ; Animals ; Axons/*pathology ; Disease Models, Animal ; Ganglia, Spinal/pathology ; Humans ; Mice ; Mice, Transgenic ; Mitochondria/pathology ; Motor Neurons/metabolism/pathology ; Mutation ; Nerve Degeneration/*pathology ; Sensory Receptor Cells/*pathology ; Spinal Cord/*pathology ; Superoxide Dismutase/genetics/*physiology