Myocardial ischemia (MI) causes somatic referred pain and sympathetic hyperactivity, and the role of sensory inputs from referred areas in cardiac function and sympathetic hyperactivity remain unclear. Here, in a rat model, we showed that MI not only led to referred mechanical hypersensitivity on the forelimbs and upper back, but also elicited sympathetic sprouting in the skin of the referred area and C8-T6 dorsal root ganglia, and increased cardiac sympathetic tone, indicating sympathetic-sensory coupling. Moreover, intensifying referred hyperalgesic inputs with noxious mechanical, thermal, and electro-stimulation (ES) of the forearm augmented sympathetic hyperactivity and regulated cardiac function, whereas deafferentation of the left brachial plexus diminished sympathoexcitation. Intradermal injection of the α₂ adrenoceptor (α₂AR) antagonist yohimbine and agonist dexmedetomidine in the forearm attenuated the cardiac adjustment by ES. Overall, these findings suggest that sensory inputs from the referred pain area contribute to cardiac functional adjustment via peripheral α₂AR-mediated sympathetic-sensory coupling.
Animals ; Ganglia, Spinal ; Hyperalgesia/etiology* ; Myocardial Ischemia/complications* ; Pain, Referred/complications* ; Rats ; Sympathetic Nervous System

The excitability of nociceptive neurons increases in the intact dorsal root ganglion (DRG) after a chronic compression, but the underlying mechanisms are still unclear. The aim of this study was to investigate the ionic mechanisms underlying the hyperexcitability of nociceptive neurons in the compressed ganglion. Chronic compression of DRG (CCD) was produced in adult rats by inserting two rods through the intervertebral foramina to compress the L4 DRG and the ipsilateral L5 DRG. After 5-7 d, DRG somata were dissociated and placed in culture for 12-18 h. In sharp electrode recording model, the lower current threshold and the depolarized membrane potential in the acutely dissociated CCD neurons were detected, indicating that hyperexcitability is intrinsic to the soma. Since voltage-gated K(+) (Kv) channels in the primary sensory neurons are important for the regulation of excitability, we hypothesized that CCD would alter K(+) current properties in the primary sensory neurons. We examined the effects of 4-aminopyridine (4-AP), a specific antagonist of A-type potassium channel, on the excitability of the control DRG neurons. With 4-AP in the external solution, the control DRG neurons depolarized (with discharges in some cells) and their current threshold decreased as the CCD neurons demonstrated, indicating the involvement of decreased A-type potassium current in the hyperexcitability of the injured neurons. Furthermore, the alteration of A-type potassium current in nociceptive neurons in the compressed ganglion was investigated with the whole-cell patch-clamp recording model. CCD significantly decreased A-type potassium current density in nociceptive DRG neurons. These data suggest that a reduction in A-type potassium current contributes, at least in part, to the increase in neuron excitability that may lead to the development of pain and hyperalgesia associated with CCD.
Animals ; Female ; Ganglia, Spinal ; physiopathology ; Hyperalgesia ; etiology ; physiopathology ; Neurons, Afferent ; physiology ; Nociceptors ; physiology ; Pain ; physiopathology ; Potassium Channels ; physiology ; Radiculopathy ; physiopathology ; Rats ; Rats, Sprague-Dawley

OBJECTIVETo determine the effects of the autologous nucleus pulposus on the pain-related behaviors of hind paws in rats.

METHODSThe nucleus pulposus harvested from autologous coccygeal vertebra was applied beside the unilateral L4 and L5 nerve roots without compression. The mechanical withdrawal threshold of both paws were measured in different times after surgery. And hematoxylin and eosin (HE) staining was applied to observe the changes of nucleus pulposus and nerve roots.

RESULTSMechanical sensitivity of the operated side in paws obviously increased after application of autologous nucleus pulposus beside the lumbar nerve roots without compression. And HE staining showed obviously inflammatory changes in the nucleus pulposus and vacuolation in the nerve roots.

CONCLUSIONSInflammation resulted from nucleus pulposus may contribute to the development of mechanical hyperalgesia. The results suggest that in addition to mechanical compression, inflammation may be an important factor in the pathogenesis of sciatica.

Animals ; Disease Models, Animal ; Hyperalgesia ; etiology ; pathology ; physiopathology ; Intervertebral Disc Displacement ; complications ; pathology ; physiopathology ; Male ; Radiculopathy ; complications ; pathology ; physiopathology ; Rats ; Rats, Sprague-Dawley

To investigate the role of spinal interleukin-6-Janus kinase 2 (IL-6-JAK2) signaling transduction pathway in regulating astrocytes activation during the maintenance of bone cancer pain (BCP).
 Methods: NCTC 2472 fibrosarcoma cells were injected into the femur marrow cavity in C3H/HeNCrlVr male mice to establish BCP model and they were replaced by the equal volume of α-MEM in the sham model. The paw withdrawal latency (PWL) was measured after inoculation of tumor cells. The lumbar enlargement of spinal cord (L3-L5) was isolated, and Real-time RT-PCR and Western blot were used to detect the expression of spinal glial fibrillary acidic protein (GFAP) and JAK2 mRNA and protein, respectively. The expression level of spinal GFAP mRNA indirectly reflect astrocytes activation level. Pain behaviors and spinal cord GFAP mRNA and protein expression were observed at the given time points after intrathecal administration of JAK2 antagonist AG-490.
 Results: The PWL at 10, 14, 21 d after operation in BCP model group were significantly shorter than that in the sham group (P<0.05); the spinal GFAP and JAK2 mRNA and protein levels were higher in the BCP model group in comparison to mice in the sham group (P<0.05); intrathecal injection of JAK2 agonist AG-490 (30 or 90 nmol) significantly alleviated PWL, and downregulated the expression of spinal GFAP mRNA and protein (P<0.05).
 Conclusion: The IL-6-JAK2 signaling pathway plays an important role in maintaining the BCP by regulating the expression of GFAP in the spinal cord. Intrathecal injection of AG-490 can reduce the BCP, and inhibit the activation of IL-6-JAK2 signaling pathway, which may be one of the mechanisms for spinal astrocyte activation.
Animals ; Astrocytes ; pathology ; Bone Neoplasms ; complications ; Hyperalgesia ; drug therapy ; etiology ; Injections, Spinal ; Male ; Mice ; Mice, Inbred C3H ; Rats, Sprague-Dawley ; Spinal Cord ; cytology ; pathology ; Tyrphostins ; administration & dosage

Post-amputation pain causes great suffering to amputees, but still no effective drugs are available due to its elusive mechanisms. Our previous clinical studies found that surgical removal or radiofrequency treatment of the neuroma at the axotomized nerve stump effectively relieves the phantom pain afflicting patients after amputation. This indicated an essential role of the residual nerve stump in the formation of chronic post-amputation pain (CPAP). However, the molecular mechanism by which the residual nerve stump or neuroma is involved and regulates CPAP is still a mystery. In this study, we found that nociceptors expressed the mechanosensitive ion channel TMEM63A and macrophages infiltrated into the dorsal root ganglion (DRG) neurons worked synergistically to promote CPAP. Histology and qRT-PCR showed that TMEM63A was mainly expressed in mechanical pain-producing non-peptidergic nociceptors in the DRG, and the expression of TMEM63A increased significantly both in the neuroma from amputated patients and the DRG in a mouse model of tibial nerve transfer (TNT). Behavioral tests showed that the mechanical, heat, and cold sensitivity were not affected in the Tmem63a^-/- mice in the naïve state, suggesting the basal pain was not affected. In the inflammatory and post-amputation state, the mechanical allodynia but not the heat hyperalgesia or cold allodynia was significantly decreased in Tmem63a^-/- mice. Further study showed that there was severe neuronal injury and macrophage infiltration in the DRG, tibial nerve, residual stump, and the neuroma-like structure of the TNT mouse model, Consistent with this, expression of the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β all increased dramatically in the DRG. Interestingly, the deletion of Tmem63a significantly reduced the macrophage infiltration in the DRG but not in the tibial nerve stump. Furthermore, the ablation of macrophages significantly reduced both the expression of Tmem63a and the mechanical allodynia in the TNT mouse model, indicating an interaction between nociceptors and macrophages, and that these two factors gang up together to regulate the formation of CPAP. This provides a new insight into the mechanisms underlying CPAP and potential drug targets its treatment.
Animals ; Mice ; Amputation, Surgical ; Chronic Pain/pathology* ; Disease Models, Animal ; Ganglia, Spinal/pathology* ; Hyperalgesia/etiology* ; Ion Channels/metabolism* ; Macrophages ; Neuroma/pathology*

Central sensitization is essential in maintaining chronic pain induced by chronic pancreatitis (CP), but cortical modulation of painful CP remains elusive. Here, we examined the role of the anterior cingulate cortex (ACC) in the pathogenesis of abdominal hyperalgesia in a rat model of CP induced by intraductal administration of trinitrobenzene sulfonic acid (TNBS). TNBS treatment resulted in long-term abdominal hyperalgesia and anxiety in rats. Morphological data indicated that painful CP induced a significant increase in FOS-expressing neurons in the nucleus tractus solitarii (NTS) and ACC, and some FOS-expressing neurons in the NTS projected to the ACC. In addition, a larger portion of ascending fibers from the NTS innervated pyramidal neurons, the neural subpopulation primarily expressing FOS under the condition of painful CP, rather than GABAergic neurons within the ACC. CP rats showed increased expression of vesicular glutamate transporter 1, and increased membrane trafficking and phosphorylation of the N-methyl-D-aspartate receptor (NMDAR) subunit NR2B and the α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) subunit GluR1 within the ACC. Microinjection of NMDAR and AMPAR antagonists into the ACC to block excitatory synaptic transmission significantly attenuated abdominal hyperalgesia in CP rats, which was similar to the analgesic effect of endomorphins injected into the ACC. Specifically inhibiting the excitability of ACC pyramidal cells via chemogenetics reduced both hyperalgesia and comorbid anxiety, whereas activating these neurons via optogenetics failed to aggravate hyperalgesia and anxiety in CP rats. Taken together, these findings provide neurocircuit, biochemical, and behavioral evidence for involvement of the ACC in hyperalgesia and anxiety in CP rats, as well as novel insights into the cortical modulation of painful CP, and highlights the ACC as a potential target for neuromodulatory interventions in the treatment of painful CP.
Animals ; Anxiety/etiology* ; Chronic Pain/etiology* ; GABAergic Neurons ; Gyrus Cinguli/metabolism* ; Hyperalgesia/metabolism* ; Pancreatitis, Chronic/pathology* ; Rats ; Rats, Sprague-Dawley ; Receptors, N-Methyl-D-Aspartate/metabolism* ; Trinitrobenzenesulfonic Acid/toxicity*

Painful diabetic neuropathy (PDN) is a diabetes mellitus complication. Unfortunately, the mechanisms underlying PDN are still poorly understood. Adenosine triphosphate (ATP)-gated P2X7 receptor (P2X7R) plays a pivotal role in non-diabetic neuropathic pain, but little is known about its effects on streptozotocin (STZ)-induced peripheral neuropathy. Here, we explored whether spinal cord P2X7R was correlated with the generation of mechanical allodynia (MA) in STZ-induced type 1 diabetic neuropathy in mice. MA was assessed by measuring paw withdrawal thresholds and western blotting. Immunohistochemistry was applied to analyze the protein expression levels and localization of P2X7R. STZ-induced mice expressed increased P2X7R in the dorsal horn of the lumbar spinal cord during MA. Mice injected intrathecally with a selective antagonist of P2X7R and P2X7R knockout (KO) mice both presented attenuated progression of MA. Double-immunofluorescent labeling demonstrated that P2X7R-positive cells were mostly co-expressed with Iba1 (a microglia marker). Our results suggest that P2X7R plays an important role in the development of MA and could be used as a cellular target for treating PDN.
Acetamides/pharmacology* ; Animals ; Diabetes Mellitus, Experimental/complications* ; Diabetes Mellitus, Type 1/complications* ; Diabetic Neuropathies/etiology* ; Hyperalgesia/etiology* ; Male ; Mice ; Mice, Inbred C57BL ; Quinolines/pharmacology* ; Receptors, Purinergic P2X7/physiology* ; Spinal Cord/physiology* ; Streptozocin/pharmacology*

Patients with diabetic peripheral neuropathy experience debilitating pain that significantly affects their quality of life (Abbott et al., 2011), by causing sleeping disorders, anxiety, and depression (Dermanovic Dobrota et al., 2014). The primary clinical manifestation of painful diabetic neuropathy (PDN) is mechanical hypersensitivity, also known as mechanical allodynia (MA) (Callaghan et al., 2012). MA's underlying mechanism remains poorly understood, and so far, based on symptomatic treatment, it has no effective therapy (Moore et al., 2014).
Animals ; CX3C Chemokine Receptor 1/physiology* ; Chemokine CX3CL1/physiology* ; Diabetes Mellitus, Experimental/complications* ; Diabetes Mellitus, Type 1/complications* ; Diabetic Neuropathies/etiology* ; Hyperalgesia/etiology* ; Mice ; Mice, Inbred C57BL ; Spinal Cord/physiology* ; Streptozocin/pharmacology*

Nefopam has a pharmacologic profile distinct from that of opioids or other anti-inflammatory drugs. Several recent studies demonstrate that nefopam has a mechanism of action similar to those of anti-depressants and anticonvulsants for treating neuropathic pain. The present study investigates the mechanical antiallodynic effect of nefopam using immunohistochemical study and western blot analysis in a rat neuropathic pain model. Twenty-eight male Sprague-Dawley rats were subjected to left fifth lumbar (L5) spinal nerve ligation and intrathecal catheter implantation, procedures which were not performed on the 7 male Sprague-Dawley rats in the sham surgery group (group S). Nefopam, either 10 or 100 microg/kg (group N10 or N100, respectively), and normal saline (group C) were intrathecally administered into the catheter every day for 14 days. The mechanical allodynic threshold of intrathecal nefopam was measured using a dynamic plantar aesthesiometer. Immunohistochemistry targeting cluster of differentiation molecule 11b (CD11b) and glial fibrillary acidic protein (GFAP) was performed on the harvested spinal cord at the level of L5. Extracellular signal-regulated kinase 1/2 (ERK 1/2) and cyclic adenosine monophosphate response element binding protein (CREB) were measured using western blot analysis. The N10 and N100 groups showed improved mechanical allodynic threshold, reduced CD11b and GFAP expression, and attenuated ERK 1/2 and CREB in the affected L5 spinal cord. In conclusion, intrathecal nefopam reduced mechanical allodynia in a rat neuropathic pain model. Its mechanical antiallodynic effect is associated with inhibition of glial activation and suppression of the transcription factors' mitogen-activated protein kinases in the spinal cord.
Analgesics, Non-Narcotic/administration & dosage ; Animals ; Dose-Response Relationship, Drug ; Hyperalgesia/*drug therapy/etiology/*physiopathology ; Injections, Spinal ; Male ; Nefopam/*administration & dosage ; Neuralgia/complications/*drug therapy/*physiopathology ; Pain Measurement/drug effects ; Pain Perception/*drug effects ; Rats ; Rats, Sprague-Dawley ; Treatment Outcome

OBJECTIVETo explore the effect of food allergy (FA) on the development of visceralgia sensibility and the substance P (SP) expression in colon of developing rats with FA.

METHODThree-week old female Sprague-Dawley (SD) rats were randomly divided into two groups (n = 10 in each). The rats in FA group were sensitized with ovalbumin (OVA) 40 µg and Al(OH)3 1 mg suspension solution (0.2 ml) intraperitoneal (i.p.) injection on day 0, only OVA 40 µg solution i.p. on day 2, 4, 7, 9, 11, respectively, and the rats were challenged by gavage with OVA solution 30 mg (2 ml) on day 20, 24, 28, 30. The rats in non-sensitized (NS) group were not challenged except handled in the same ways. The serum OVA-IgE were determined by enzyme-linked immuno sorbent assay (ELISA) on day 0, 30. Jejunum segments were used to observe morphological structure, the expression of eosinophils, and the density and the percentage of degranulation of mast cells (MC). The rats were appraised for the pain sensibility of intestinal tract under colorectal distension irritation by the electrophysiological method on external oblique in the 18-24 hr after the last challenge. Colons were used to analyze the expression of SP through immunohistochemical staining and computer image analyzing system.

RESULTThe serum OVA-IgE concentration and the eosinophils, mast cell, the percentage of mast cells degranulation in FA group were more than NS group (P < 0.01). The amplitudes of spike external oblique muscle of abdomen (EOMA, µV) of the FA group under the colorectal distension (CRD) pressures at 0, 15, 30, 45, 60, 75 mm Hg were (17.74 ± 0.72), (18.63 ± 1.72), (22.55 ± 1.70), (28.63 ± 7.00), (33.97 ± 7.34), (37.26 ± 8.40), and (17.43 ± 1.18), (17.27 ± 1.16), (17.73 ± 1.42), (19.55 ± 3.54), (23.29 ± 5.46), (25.20 ± 4.75) in NS group. With the CRD pressure increased, the amplitudes of spike EOMA increased significantly. There were significant differences between groups under the CRD pressures at 30, 45, 60, 75 mm Hg (F = 47.470, 13.367, 13.317, 15.390, P < 0.01). The expressions of colons SP in FA group and NS group are 247.12 ± 90.83 and 103.90 ± 58.94, respectively (t = 4.183, P < 0.01).

CONCLUSIONSensitization through i.p. pathway and challenge by gavage with OVA in early life could result in FA in young SD rats. FA in early life enabled the amplitudes of spike EOMA and the expression of colons SP increase significantly. It may be related to increase in amount and degranulation of MC and SP abnormal expression in colon, which could lead to the development of visceralgia sensibility.

Animals ; Colonic Diseases, Functional ; metabolism ; Disease Models, Animal ; Electrophysiology ; Female ; Food Hypersensitivity ; complications ; metabolism ; Hyperalgesia ; etiology ; metabolism ; physiopathology ; Intestinal Mucosa ; metabolism ; pathology ; Mast Cells ; metabolism ; Ovalbumin ; adverse effects ; Pain Threshold ; Rats ; Rats, Sprague-Dawley ; Stress, Psychological ; Substance P ; metabolism