Voltage-gated sodium channels are critical for the generation and conduction of nerve impulses. Recent studies show that in primary sensory neurons, the expression and dynamic regulation of several sodium channel subtypes play important roles in neuropathic pain. A number of SCN9A (encoding Nav1.7) gene point mutations are related with human genetic pain disorders. Transgenic and specific knockout techniques have revealed that Nav1.3, Nav1.8, Nav1.9 are important for the development and maintenance of neuropathic pain condition. Specific blockers of these sodium channels have been demonstrated to be effective in alleviating allodynia and hyperalgesia. Here we reviewed the roles of sodium channels in neuropathic pain, which may be applicable for the development of new drugs with enhanced efficacy for neuropathic pain treatment.
Animals ; Humans ; Neuralgia ; genetics ; metabolism ; physiopathology ; Neurons ; metabolism ; physiology ; Sodium Channels ; genetics ; metabolism ; physiology

OBJECTIVETo study the possible mechanisms of chronic nonbacterial prostatitis (CNP) pain.

METHODSCNP models were established in male Wistar rats by the autoimmune method. Then the paw withdrawal threshold (PWT) was detected using the Von Frey filament, prostate pathological examination was conducted, the expressions of substance P (SP) and transient receptor potential vanilloid 1 (TRPV1) in the prostate tissue and L5-S2 spinal segments were determined by immunohistochemistry and their correlations were analyzed.

RESULTSCompared with the control group, the CNP model rats showed markedly decreased PWT (P < 0.05) and obvious inflammation in the prostate tissue, with significant differences in the scope of lesion and interstitial lymphocyte infiltration (P < 0.05). The expressions of SP and TRPV1 in the prostate and spinal cord dorsal horn L5-S2 were remarkably upregulated in the models as compared with the control rats (P < 0.05). However, the expression of SP in the prostate was not correlated with that in the spinal cord (r = 0.099, P = 0.338), nor was that of TRPV1 (r = 0.000, P = 0.5).

CONCLUSIONSP and TRPV1 were involved in the formation and persistence of pain in CNP rats through their upregulated expressions in the L5-S2 spinal segments.

Animals ; Lumbosacral Region ; Male ; Neuralgia ; metabolism ; physiopathology ; Pain ; metabolism ; physiopathology ; Prostate ; metabolism ; Prostatitis ; metabolism ; physiopathology ; Rats ; Rats, Wistar ; Spinal Cord ; metabolism ; Substance P ; metabolism ; TRPV Cation Channels ; metabolism

PURPOSE: The TWIK-related spinal cord K+ channel (TRESK) has recently been discovered and plays an important role in nociceptor excitability in the pain pathway. Because there have been no reports on the TRESK expression or its function in the dorsal horn of the spinal cord in neuropathic pain, we analyzed TRESK expression in the spinal dorsal horn in a spinal nerve ligation (SNL) model. MATERIALS AND METHODS: We established a SNL mouse model by using the L5-6 spinal nerves ligation. We used real-time polymerase chain reaction and immunohistochemistry to investigate TRESK expression in the dorsal horn and L5 dorsal rot ganglion (DRG). RESULTS: The SNL group showed significantly higher expression of TRESK in the ipsilateral dorsal horn under pain, but low expression in L5 DRG. Double immunofluorescence staining revealed that immunoreactivity of TRESK was mostly restricted in neuronal cells, and that synapse markers GAD67 and VGlut2 appeared to be associated with TRESK expression. We were unable to find a significant association between TRESK and calcineurin by double immunofluorescence. CONCLUSION: TRESK in spinal cord neurons may contribute to the development of neuropathic pain following injury.
Animals ; Disease Models, Animal ; Hyperalgesia ; Ligation ; Male ; Neuralgia/*metabolism/physiopathology ; Neurons/metabolism ; Nociceptors ; Pain/metabolism/*physiopathology ; Potassium Channels/*metabolism ; Rats ; Rats, Sprague-Dawley ; Real-Time Polymerase Chain Reaction ; Spinal Cord Dorsal Horn/*metabolism ; Spinal Nerves/*injuries

The purpose of this study was to establish a model of trigeminal neuralgia (TN) through an approach from lower edge of cheekbone and to observe the functional changes in the voltage-gated potassium currents in the cultured trigeminal ganglion (TG) neurons. Thirty Sprague-Dawley male rats were divided into two groups, the sham-operated (sham) group and the operated group. The TN model was carried out by using a chronic constriction injury of the infraorbital nerve (ION-CCI) from lower edge of cheekbone. Peripheral pain threshold test and whole-cell patch clamp recording were used to determine the difference between sham and ION-CCI rats. The withdrawal threshold of whisker pad in operated side of ION-CCI rat was decreased significantly from 6 d after operation and then maintained until 21 d, with the lowest on the 15th day. The threshold of whisker pad in non-operated side of operated rats was also decreased significantly compared with that in the sham group. Delayed rectifier potassium current (I(K)) in cultured ION-CCI TG neurons was decreased significantly compared with that in the sham group. Transient outward potassium currents (I(A)) in both operated and non-operated sides of TG neurons from ION-CCI rats were also reduced significantly compared with that in the sham group. The present study provided a new method of ION-CCI. In this model, the decrease of I(A) and I(K) might contribute, at least in part, to the decrease in mechanical pain threshold of whisker pad and the subsequent hyperalgia.
Animals ; Cells, Cultured ; Constriction ; Disease Models, Animal ; Hyperalgesia ; Male ; Pain Threshold ; Patch-Clamp Techniques ; Potassium Channels ; metabolism ; Rats ; Rats, Sprague-Dawley ; Trigeminal Ganglion ; metabolism ; Trigeminal Neuralgia ; physiopathology ; Vibrissae

Dorsal root ganglion (DRG) neurons have peripheral terminals in skin, muscle, and other peripheral tissues, and central terminals in the spinal cord dorsal horn. Hyperpolarization-activated current (I(h)) of the hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels are present in the DRG. The genes encoding HCN channels have four subtypes named HCN1 to HCN4. HCN channels are permeable to both K(+) and Na(+). They underlie the depolarization that modulates the rhythmic generations of action potentials (APs), contribute to the resting membrane potential, and modify the waveform of propagated synaptic and generator potentials. Neuropathic pain is characterized by spontaneous pain, hyperalgesia and allodynia. After spinal nerve injury, the cell bodies of the primary sensory neurons in segmental DRG become hyperexcitable, characterized for some neurons by the presence of spontaneous firing (or ectopic discharge). In the following, we summarize our observations on the role of HCN channels in DRG neurons in neuropathic pain. 1 HCN subtypes and I(h) in DRG neurons Immunohistochemical staining revealed a subgroup of neurons in the DRG that were stained with rabbit polyclonal antibodies specific for HCN1, 2, 3 and 4. The most prominently expressed HCN subtype was HCN1. HCN1-positive cells in DRG were medium to large in size and doubly labeled with neurofilament-200 (NF-200), and were not labeled with isolectin B4 (IB4), a C fiber marker. In contrast, HCN2, 3 or 4 was expressed in all DRG neurons at a lower level. HCN4 was confined to small neurons. DRG neurons expressed I(h). When membrane was hyperpolarized, the channel was activated, mediating a slowly activated, inward current. I(h) was distributed mainly in large and medium-sized DRG neurons. 2 Changes in expression of HCN in DRG after spinal nerve ligation Western blotting was used to detect the changes in the expression of HCN subtypes in the DRG after spinal nerve ligation. HCN1 mRNA and protein were reduced in the DRG whose spinal nerve had been ligated. HCN1 expression was decreased to the lowest level at day 14 and restored at day 28 after spinal nerve ligation. HCN2 mRNA and medium molecular weight protein was also decreased in spinal-nerve ligated DRG. HCN3 and 4 in the same ganglion remained unchanged as evidenced by immunohistochemical staining, until day 28 when they became significantly decreased. HCN4 mRNA in DRG did not change, and protein expression slightly increased. Interestingly, abundant axonal accumulation of HCN channel protein at the injured sites in chronic constriction injury (CCI) rats. Electron immunomicroscopy showed strong positive immunolabeling on the axolemma of myelinated thick axons. 3 Role of I(h) in neuronal excitability and ectopic discharges after spinal nerve ligation ZD7288, a specific I(h) blocker, inhibited I(h) in a time- and concentration-dependent manner. With patch-clamp recording on acutely isolated DRG neurons, it was found that ZD7288 perfusion resulted in a decrease of both I(h) activity and the activation time constant. ZD7288 decreased the number of repetitive APs and caused an increase in AP rise time, accompanied by a small hyperpolarization of the membrane resting potential. The results demonstrated that I(h) was involved in AP firing, and possessed the physiological functions to facilitate neuronal excitability and ectopic firing. Extracellular electrophysiological recording from dorsal root fibers associated with the spinal nerve-ligated ganglion revealed three different firing patterns of ectopic discharges: tonic or regular, bursting and irregular. The average frequency of ectopic discharges and the proportions of active filaments also changed rapidly, both parameters reaching a peak within 24 h then declining gradually in the following days. It was also found that proportions of three different firing patterns changed dynamically over time. The tonic and bursting types were dominant patterns in the first 24 h, while the irregular became the only pattern at day 14. We found that all three firing patterns (tonic, bursting and irregular) were dose- and time-dependently inhibited by local application of ZD7288 to DRG. The rate of suppression was negatively related to the frequency of firing prior to the application of ZD7288. We also found that, while the tonic firing pattern was gradually transformed to bursting type by application of 100 mumol/L ZD7288, it could be transformed to integer multiples firing by 1000 mumol/L ZD7288. 4 Effects of administration of ZD7288 on mechanical allodynia after spinal nerve ligation or CCI After spinal nerve ligation, i.t. injection of 30 mug ZD7288 significantly increased the 50% paw withdrawal threshold, ipsilateral to the ligated nerve. ZD7288 had no effect if the dose was lower than 15 mug, but resulted in motor deficits if the dose was higher than 60 mug. ZD7288 produced much better effects in the early stage (5 or 14 days after spinal nerve ligation) than that in the late stage (28 days after spinal nerve ligation). In CCI rats, ZD7288 application to the injured sited also significantly suppressed the ectopic discharges from injured nerve fibers with no effect on impulse conduction. Moreover, mechanical allodynia was inhibited. In conclusion, these results demonstrated that I(h) participated in the development and maintenance of peripheral sensitivity associated with neuropathic pain and that it is a potential target for the design of novel analgesics in the future.
Action Potentials ; Animals ; Cyclic Nucleotide-Gated Cation Channels ; metabolism ; Ganglia, Spinal ; physiopathology ; Hyperalgesia ; physiopathology ; Membrane Potentials ; Nerve Fibers ; pathology ; Neuralgia ; physiopathology ; Neurons, Afferent ; pathology ; Rats ; Rats, Sprague-Dawley ; Spinal Nerves ; pathology

The present study aimed to investigate the role of spinal p38 mitogen-activated protein kinase (p38 MAPK) activation in chronic constriction injury (CCI) of the sciatic nerve induced neuropathic pain. CCI model was produced by loosely ligating the left sciatic nerve proximal to the sciatica's trifurcation with 4-0 silk thread in male Sprague-Dawley rat. SB203580, a specific inhibitor of the p38 MAPK, was intrathecally administered on day 5 post-CCI. Thermal and mechanical nociceptive thresholds were assessed with the paw withdrawal lantency (PWL) to radiant heat and the paw withdrawal threshold (PWT) to von Frey filaments respectively. The protein levels of the phosphorylated p38 MAPK (p-p38 MAPK) and phosphorylated cAMP response element binding protein (pCREB) were assessed by Western blot analysis. The results showed that CCI significantly increased the expressions of cytosolic and nuclear p-p38 MAPK in the spinal cord. Intrathecal administration of SB203580 dose-dependently reversed the established mechanical allodynia and thermal hyperalgesia induced by CCI. Correlated with behavior results, SB203580 dose-dependently inhibited the CCI-induced increase of the expressions of cytosolic and nuclear p-p38 MAPK and nuclear pCREB in the spinal cord. Taken together, these findings suggest that the activation of p38 MAPK pathway contributes to the development of neuropathic pain induced by CCI, and that the function of p-p38 MAPK may partly be accomplished via the CREB-dependent gene expression.
Animals ; Female ; Ligation ; Male ; Neuralgia ; enzymology ; etiology ; physiopathology ; Rats ; Rats, Sprague-Dawley ; Sciatic Nerve ; injuries ; Spinal Cord ; enzymology ; p38 Mitogen-Activated Protein Kinases ; metabolism

OBJECTIVETo investigate the changes of GABA-activated currents in isolated dorsal root ganglion neurons in rats with neuropathic pain.

METHODSThe neuropathic pain model was established by chronic constriction injury (CCI) 7 days before electrophysiological-recording. The rat DRG neurons were enzymatically dissociated. Whole-cell patch clamp technique was used to record GABA-activated currents. The changes of currents of injured side and opposite side were expected to compare with control group.

RESULTS(1) The currents of injured side of CCI group were notablely decreased compared with control group (GABA concentration, 0.1-1000 micromol/L). (2) By the contrast, opposite side currents of CCI group increased significantly compared with those in injured side and control group (GABA concentration, 0.01-1000 micromol/L).

CONCLUSIONThe data indicates that the chronic constriction injury change both the function of GABAA receptors of injury side and opposite side. The decrease of pre-synaptic inhibition of GABA may be the possible reason of neuropathic pain.

Animals ; Cell Separation ; Constriction ; Ganglia, Spinal ; pathology ; physiopathology ; Male ; Neuralgia ; etiology ; physiopathology ; Neurons ; metabolism ; physiology ; Patch-Clamp Techniques ; Rats ; Rats, Sprague-Dawley ; Receptors, GABA-A ; metabolism ; physiology ; Sciatic Nerve ; injuries

To observe the effect of multiple electroacupuncture (EA) on the pain threshold and the regulation of N-methyl-D-aspartate (NMDA) receptor in dorsal root ganglia (DRG) of neuropathic pain rats. Rats were prepared with a unilateral chronic constriction injury (CCI) to the sciatic nerve. EA was done in acupoints "Huan Tiao" and "Yang Ling Quan" for 30 min every day and the thermal thresholds were detected after EA at 3, 5, 7, 10, 14 days after operation. On day 14 after nerve injury, the in situ hybridization method was used to investigate the change of NMDA R1 mRNA in L4-L5 DRG. The thermal threshold reduced significantly from day 3 after operation in CCI rats. After multiple EA treatment, the ipsilateral thermal hyperalgesia relieved gradually and the thermal threshold had no difference with control side after day 5 (P > 0.05). From Day 7 after operation, the thermal threshold at each time point were significantly different compared with CCI group respectively (P > 0.05). Moreover the EA had accumulative effect. On Day 14 after operation, the NMDAR1 mRNA positive neurons and the mean optic density in ipsilateral L4-5 DRG were less than that of control side (P < 0.05), mainly in medium and small neurons. After EA treatment, the NMDAR1 mRNA positive neurons in ipsilateral DRG had no considerable difference comparing with those of control side, significantly increased comparing with CCI group (P < 0.05). It's concluded that the NMDA receptors in DRG relate closely with the generation and development of neuropathic pain. The multiple EA treatment can attenuate the thermal hyperlagesia of neuropathic pain rats and regulate the NMDA receptor.
Animals ; Electroacupuncture ; Ganglia, Spinal ; metabolism ; Hyperalgesia ; physiopathology ; Male ; Neuralgia ; metabolism ; physiopathology ; Pain Measurement ; Pain Threshold ; RNA, Messenger ; biosynthesis ; genetics ; Rats ; Rats, Sprague-Dawley ; Receptors, N-Methyl-D-Aspartate ; biosynthesis ; genetics ; Sciatic Nerve

Charcot-Marie-Tooth disease (CMT) is the most common inherited motor and sensory neuropathy. Previous studies have found that, according to CMT patients, neuropathic pain is an occasional symptom of CMT. However, neuropathic pain is not considered to be a significant symptom associated with CMT and, as a result, no studies have investigated the pathophysiology underlying neuropathic pain in this disorder. Thus, the first animal model of neuropathic pain was developed by our laboratory using an adenovirus vector system to study neuropathic pain in CMT. To this end, glycyl-tRNA synthetase (GARS) fusion proteins with a FLAG-tag (wild type [WT], L129P and G240R mutants) were expressed in spinal cord and dorsal root ganglion (DRG) neurons using adenovirus vectors. It is known that GARS mutants induce GARS axonopathies, including CMT type 2D (CMT2D) and distal spinal muscular atrophy type V (dSMA-V). Additionally, the morphological phenotypes of neuropathic pain in this animal model of GARS-induced pain were assessed using several possible markers of pain (Iba1, pERK1/2) or a marker of injured neurons (ATF3). These results suggest that this animal model of CMT using an adenovirus may provide information regarding CMT as well as a useful strategy for the treatment of neuropathic pain.
Animals ; Charcot-Marie-Tooth Disease/*diagnosis/*physiopathology ; *Disease Models, Animal ; Glycine-tRNA Ligase/*genetics/metabolism ; Male ; Mice ; Mice, Inbred C57BL ; Mice, Transgenic ; Mutagenesis, Site-Directed ; Mutation/genetics ; Neuralgia/*diagnosis/*physiopathology

Charcot-Marie-Tooth disease (CMT) is the most common inherited motor and sensory neuropathy. Previous studies have found that, according to CMT patients, neuropathic pain is an occasional symptom of CMT. However, neuropathic pain is not considered to be a significant symptom associated with CMT and, as a result, no studies have investigated the pathophysiology underlying neuropathic pain in this disorder. Thus, the first animal model of neuropathic pain was developed by our laboratory using an adenovirus vector system to study neuropathic pain in CMT. To this end, glycyl-tRNA synthetase (GARS) fusion proteins with a FLAG-tag (wild type [WT], L129P and G240R mutants) were expressed in spinal cord and dorsal root ganglion (DRG) neurons using adenovirus vectors. It is known that GARS mutants induce GARS axonopathies, including CMT type 2D (CMT2D) and distal spinal muscular atrophy type V (dSMA-V). Additionally, the morphological phenotypes of neuropathic pain in this animal model of GARS-induced pain were assessed using several possible markers of pain (Iba1, pERK1/2) or a marker of injured neurons (ATF3). These results suggest that this animal model of CMT using an adenovirus may provide information regarding CMT as well as a useful strategy for the treatment of neuropathic pain.
Animals ; Charcot-Marie-Tooth Disease/*diagnosis/*physiopathology ; *Disease Models, Animal ; Glycine-tRNA Ligase/*genetics/metabolism ; Male ; Mice ; Mice, Inbred C57BL ; Mice, Transgenic ; Mutagenesis, Site-Directed ; Mutation/genetics ; Neuralgia/*diagnosis/*physiopathology