Objective To establish neuropathic pain models, explore the effects and mechanisms of dexmedetomidine on neuropathic pain. Methods Wistar rats were randomly divided into four groups (n=9): 0.9% sodium chloride solution CCI group (N),dexmedetomidine CCI group (D), ZD7288 CCI group (Z) and sham-operated group (Sham). Sciatic nerve ligation was performed in group N, D and Z. The sciatic nerve in group Sham was exposured without ligation. 7 d after surgery, the rats in group D were intraperitoneal injected with dexmedetomidine (40 μg·kg-1), and the rats in group Z were intraperitoneal injected with ZD7288 (10 mg·kg-1)once a day for 3 d.The same volume of 0.9% sodium chloride solution was given at the same time in group N. The behavioral test was performed before and 7 d after operation, as well as 3 d after injection treatment. Mechanical allodynia was assessed by paw withdrawal mechanical threshold (PWMT) to von Frey filaments. Thermal hyperalgesia was assessed by paw thermal withdrawal latency (TWL) to radiant heat. Dexmedetomidine block of HCN channels in dorsal root ganglion (DRG) neurons were confirmed by whole-cell recording. Results 7 d after surgery, the PWMT and TWL of rats in group N, D and Z were decreased significantly (P<0.05). The PWMT and TWL in group Sham were no significant difference before and after operation. Dexmedetomidine significantly increased the levers of PWMT and TWL in group D and Z after treatment for 3 d,and group Z was greater than group D (P<0.05). Dexmedetomidine(0.1,1, 10 μmol·L-1)caused a concentration-dependent decrease in the amplitude of Ih in DRG neurons from (-844.43±386.34)to(-215.99±63.90) pA(P<0.05), and the inhibition rate of Ih was(11.87±1.80)%,(35.26±3.65) % and (52.02±5.56)%, respectively(P<0.05). Dexmedetomidine produced a dose-related shift to the left of the Ih activation, and a negative shift in V1/2 (P<0.05). V1/2 shifted from (-86.21±1.68)to (-103.54±2.01)mV(P<0.05). The slope values were not altered by dexmedetomidine.Conclusion Dexmedetomidine produces a dose-dependently analgesic effect on neuropathic pain after peripheral never injury, which is likely due to the inhibition of Ih and reduction of ectopic spontaneous discharge in DRG neurons.
JENSEN TS,FINNERUP NB.Allodynia and hyperalgesia in neuropathic pain: clinical manifestations and mechanisms[J].Lancet Neurol,2014,13(9):924-935.
Allodynia (pain due to a stimulus that does not usually provoke pain) and hyperalgesia (increased pain from a stimulus that usually provokes pain) are prominent symptoms in patients with neuropathic pain. Both are seen in various peripheral neuropathies and central pain disorders, and affect 15-50% of patients with neuropathic pain. Allodynia and hyperalgesia are classified according to the sensory modality (touch, pressure, pinprick, cold, and heat) that is used to elicit the sensation. Peripheral sensitisation and maladaptive central changes contribute to the generation and maintenance of these reactions, with separate mechanisms in different subtypes of allodynia and hyperalgesia. Pain intensity and relief are important measures in clinical pain studies, but might be insufficient to capture the complexity of the pain experience. Better understanding of allodynia and hyperalgesia might provide clues to the underlying pathophysiology of neuropathic pain and, as such, they represent new or additional endpoints in pain trials.
LANDERHOLM AH, HANSSON PT.Mechanisms of dynamic mechanical allodynia and dysesthesia in patients with peripheral and central neuropathic pain[J]. Eur J Pain,2011,15(5): 498-503.
Eighteen patients with peripheral neuropathic pain (PNeP) and seven patients with central post-stroke pain (CPSP) all suffering from dynamic mechanical allodynia (DMA) in a limb were studied. From recent research it is reasonable to suggest that A-beta fibres constitute the peripheral substrate for DMA in patients with PNeP. The pathophysiological basis for DMA in patients with CPSP is unknown. It is clinically observed that some patients with neuropathic pain report variable intensity of DMA and volunteer that the phenomenon at times is only an unpleasant, i.e., dysesthetic sensation. The pathophysiological basis for dynamic mechanical dysesthesia (DMD) has never been addressed. Based on the aforementioned clinical observations we aimed at investigating if DMA is the hyperbole of DMD both mediated by A-beta fibres in the periphery. A compression/ischemia-induced (differential) nerve block in conjunction with repeated quantitative sensory testing of A-delta and C-fibre function using cold and warm stimuli was used to assess which nerve fibre population that contributes to DMA and DMD, respectively. During the nerve block there was a transition of DMA to DMD in all patients with PNeP and in 3/7 patients with CPSP. The rest of the patients lost DMA without transition to DMD. The transition or loss of DMA without transition occurred early and concurrently in time during the block and was paralleled by a continuous impairment of mainly A-beta fibre function. We therefore suggest DMA to be the hyperbole of DMD, the difference being the number of mechanoreceptive fibres having access to the nociceptive system. (C) 2010 Published by Elsevier Ltd. on behalf of European Federation of International Association for the Study of Pain Chapters.
Dexmedetomidine is a highly selective alpha(2)-receptor agonist with sedative, analgetic and anxiolytic effects. It is chemically related to clonidine and has been an authorized drug in Europe since September 2011. Dexmedetomidine enables a level of sedation in which mechanically ventilated patients may be woken by verbal stimulation (Richmond agitation sedation scale RASS 0--3). In this respect dexmedetomidine achieves the same desired effect as propofol and midazolam; however, in direct comparison to a sedation regime with benzodiazepines, dexmedetomidine reduces the prevalence, duration and severity of delirium in intensive care. Patients sedated by dexmedetomidine can statistically be extubated earlier and an influence on duration of stay in the intensive care unit (ICU) has not been shown. Daily therapy costs are approximately 5 times higher than those of propofol but an objective standpoint in relation to clinical cost efficiency is unattainable.
YANG YC,MENG QT,PANX,et al.Dexmedetomidine produced analgesic effect via inhibition of HCN currents[J]. Eur J Pharmacol,2014,740: 560-564.
The purpose of this study was to investigate the mechanism by which systemic dexmedetomidine exerts analgesic effect and examine effect of dexmedetomidine on hyperpolarization-activated cyclic nucleotide-gated (HCN) channels currents. The experiments were performed on C57BL/6 J and HCN1 knockout mice. The analgesic effects of intraperitoneal dexmedetomidine (10-40 mu g/kg) were measured by a tail-flick test. Whole-cell clamp recordings were used to examine the properties of cloned HCN subunit currents expressed in HEK 293 cells under control condition and dexmedetomidine administration (0.1-10 mu M). Injection of dexmedetomidine caused a clear time and dose-related increase in the tail-flick latency of both wild type and knockout mice. Compared with the wild type group, the MPE (maximum possible effect) of tail-Rick latency induced by 30 mu g/kg and 40 mu g/kg dexmedetomidine in knockout mice was significantly lower. The alpha(2)-adrenergic receptor antagonist yohimbine (5 mu g/kg) reduced the MPE of dexmedetomidine (30 mu g/kg) both in wild type and knockout mice. Dexmedetomidine(0.1-10 mu M) inhibited HCN1 and HCN2 channel currents in HEK 293 cells, caused a decrease of maximal currents, an increase of inhibition rate of hyperpolarization-activated currents (I-h), and a negative shift in V-1/2 We conclude that dexmedetomidine produces a dose-dependently analgesic effect, and the effect is likely clue to the inhibition of HCN currents. (C) 2014 Elsevier B.V. All rights reserved.
BENNETT GJ,XIE YK.A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen-inman[J].Pain,1988,33(1):87-107.
A peripheral mononeuropathy was produced in adult rats by placing loosely constrictive ligatures around the common sciatic nerve. The postoperative behavior of these rats indicated that hyperalgesia, allodynia and, possibly, spontaneous pain (or dysesthesia) were produced. Hyperalgesic responses to noxious radiant heat were evident on the second postoperative day and lasted for over 2 months. Hyperalgesic responses to chemogenic pain were also present. The presence of allodynia was inferred from the nocifensive responses evoked by standing on an innocuous, chilled metal floor or by innocuous mechanical stimulation, and by the rats' persistence in holding the hind paw in a guarded position. The presence of spontaneous pain was suggested by a suppression of appetite and by the frequent occurrence of apparently spontaneous nocifensive responses. The affected hind paw was abnormally warm or cool in about one-third of the rats. About one-half of the rats developed grossly overgrown claws on the affected side. Experiments with this animal model may advance our understanding of the neural mechanisms of neuropathic pain disorders in humans.
RUAN JP, ZHANG HX, LU XF,et al.EphrinBs/EphBs signaling is involved in modulation of spinal nociceptive processing through a mitogen-activated protein kinases-dependent mechanism[J].Anesthesiology, 2010, 112(5): 1234-1249.
Abstract BACKGROUND: Our previous studies have demonstrated that EphBs receptors and ephrinBs ligands were involved in modulation of spinal nociceptive information. However, the downstream mechanisms that control this process are not well understood. The aim of this study was to further investigate whether mitogen-activated protein kinases (MAPKs), as the downstream effectors, participate in modulation of spinal nociceptive information related to ephrinBs/EphBs. METHODS: Thermal hyperalgesia and mechanical allodynia were measured using radiant heat and von Frey filaments test. Immunofluorescence staining was used to detect the expression of p-MAPKs and of p-MAPKs/neuronal nuclei, or p-MAPKs/glial fibrillary acidic protein double label. C-Fos expression was determined by immunohistochemistry. The expression of p-MAPKs was also determined by Western blot assay. RESULTS: Intrathecal injection of ephrinB1-Fc produced a dose- and time-dependent thermal and mechanical hyperalgesia, accompanied by the increase of spinal p-MAPKs and c-Fos expression. Immunofluorescence staining revealed that p-MAPKs colocalized with the neuronal marker (neuronal nuclei) and the astrocyte marker (glial fibrillary acidic protein). Inhibition of MAPKs prevented and reversed pain behaviors and the increase of spinal c-Fos expression induced by intrathecal injection of ephrinB1-Fc. Inhibition of EphBs receptors by intrathecal injection of EphB1-Fc reduced formalin-induced inflammation and chronic constrictive injury-induced neuropathic pain behaviors accompanied by decreased expression of spinal p-MAPKs and c-Fos protein. Furthermore, pretreatment with MK-801, an N-methyl-d-aspartate receptor antagonist, prevented behavioral hyperalgesia and activation of spinal MAPKs induced by intrathecal injection of ephrinB1-Fc. CONCLUSIONS: These results demonstrated that activation of MAPKs contributed to modulation of spinal nociceptive information related to ephrinBs/EphBs.
JIANG YQ, XING GG, WANG SL, et al.Axonal accumulation of hyperpolarization-activated cyclic nucleotide-gated cation channels contributes to mechanical allodynia after peripheral nerve injury in rat[J]. Pain, 2008, 137(3): 495-506.
Peripheral nerve injury causes neuropathic pain including mechanical allodynia and thermal hyperalgesia due to central and peripheral sensitization. Spontaneous ectopic discharges derived from dorsal root ganglion (DRG) neurons and from the sites of injury are a key factor in the initiation of this sensitization. Numerous studies have focused primarily on DRG neurons; however, the injured axons themselves likely play an equally important role. Previous studies of neuropathic pain rats with spinal nerve ligation (SNL) showed that the hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channel in DRG neuronal bodies is important for the development of neuropathic pain. Here, we investigate the role of the axonal HCN channel in neuropathic pain rats. Using the chronic constriction injury (CCI) model, we found abundant axonal accumulation of HCN channel protein at the injured sites accompanied by a slight decrease in DRG neuronal bodies. The function of these accumulated channels was verified by local application of ZD7288, a specific HCN blocker, which significantly suppressed the ectopic discharges from injured nerve fibers with no effect on impulse conduction. Moreover, mechanical allodynia, but not thermal hyperalgesia, was relieved significantly by ZD7288. These results suggest that axonal HCN channel accumulation plays an important role in ectopic discharges from injured spinal nerves and contributes to the development of mechanical allodynia in neuropathic pain rats.
TAKASUK,ONOH,TANABEM.Spinal hyperpolarization-activated cyclic nucleotide-gated cation channels at primary afferent terminals contribute to chronic pain[J].Pain, 2010,151(1):87-96.
Abstract Hyperpolarization-activated cyclic nucleotide-gated cation channels (HCN channels) have large influences upon neuronal excitability. However, the participation of spinal HCN channels in chronic pain states, where pathological conditions are related to altered neuronal excitability, has not been clarified. Intraperitoneally (i.p.) or intrathecally (i.t.) administered ZD7288, a selective blocker of Ih channels, reduced thermal and mechanical hypersensitivity in mice under neuropathic conditions induced by the partial ligation of the sciatic nerve, while no analgesic effect was observed in na茂ve animals. Moreover, in the mouse formalin test, ZD7288 (i.p. and i.t.) reduced the licking/biting behavior observed during the second phase without affecting the first phase. To further explore the pain-modulatory action of spinal HCN channels, whole-cell patch clamp recordings were made from the visually identified substantia gelatinosa neurons in adult mouse spinal cord slices with an attached dorsal root, and A-fiber- and/or C-fiber-mediated monosynaptic excitatory postsynaptic currents (EPSCs) were evoked by electrical stimulation of the L4 or L5 dorsal root using a suction electrode. Bath-applied ZD7288 reduced A-fiber- and C-fiber-mediated monosynaptic EPSCs more preferentially in slices prepared from mice after peripheral nerve injury. In addition, ZD7288 reduced the frequency of miniature EPSCs without affecting their amplitude in cells receiving monosynaptic afferent inputs, indicating that it inhibits EPSCs via presynaptic mechanisms. The present behavioral and electrophysiological data suggest that spinal HCN channels, most likely at the primary afferent terminals, contribute to the maintenance of chronic pain. Copyright 2010 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.
WENGX,SMITHT,SATHISHJ,et al.Chronic inflammatory pain is associated with increased excitability and hyperpolarization-activated current(Ih) in C- but not Adelta- nociceptors[J]. Pain, 2012, 153(4): 900-914.
Inflammatory pain hypersensitivity results partly from hyperexcitability of nociceptive (damage-sensing) dorsal root ganglion (DRG) neurons innervating inflamed tissue. However, most of the evidence for this is derived from experiments using acute inflammatory states. Herein, we used several approaches to examine the impact of chronic or persistent inflammation on the excitability of nociceptive DRG neurons and on their expression of I-h and the underlying hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, which regulate neuronal excitability. Using in vivo intracellular recordings of somatic action potentials from L4/L5 DRG neurons in normal rats and rats with hindlimb inflammation induced by complete Freund's adjuvant (CFA), we demonstrate increased excitability of C- but not A delta-nociceptors, 5 to 7 days after CFA. This included an afterdischarge response to noxious pinch, which may contribute to inflammatory mechanohyperalgesia, and increased incidence of spontaneous activity (SA) and decreased electrical thresholds, which are likely to contribute to spontaneous pain and nociceptor sensitization, respectively. We also show, using voltage clamp in vivo, immunohistochemistry and behavioral assays that (1) the inflammation-induced nociceptor hyperexcitability is associated, in C- but not A delta-nociceptors, with increases in the mean I-h amplitude/density and in the proportion of I-h expressing neurons, (2) increased proportion of small DRG neurons (mainly IB4-negative) expressing HCN2 but not HCN1 or HCN3 channel protein, (3) increased HCN2- immunoreactivity in the spinal dorsal horn, and (4) attenuation of inflammatory mechanoallodynia with the selective I-h antagonist, ZD7288. Taken together, the findings suggest that C- but not A delta-nociceptors sustain chronic inflammatory pain and that I-h/HCN2 channels contribute to inflammation-induced C-nociceptor hyperexcitability. (C) 2012 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.
Axonal accumulation of hyperpolarization-activated cyclic nucleotide-gated cation channels contributes to mechanical allodynia after peripheral nerve injury in rat
, 刘康, 周芳, 孟庆涛, 夏中元
