Spinal Pathways Research Articles

Phrenic motor outputs in response to bronchopulmonary C-fibre activation following chronic cervical spinal cord injury.

Activation of bronchopulmonary C-fibres, the main chemosensitive afferents in the lung, can induce pulmonary chemoreflexes to modulate respiratory activity. Following chronic cervical spinal cord injury, bronchopulmonary C-fibre activation-induced inhibition of phrenic activity was exaggerated. Supersensitivity of phrenic motor outputs to the inhibitory effect of bronchopulmonary C-fibre activation is due to a shift of phrenic motoneuron types and slow recovery of phrenic motoneuron discharge in cervical spinal cord-injured animals. These data suggest that activation of bronchopulmonary C-fibres may retard phrenic output recovery following cervical spinal cord injury. The alteration of phenotype and discharge pattern of phrenic motoneuron enables us to understand the impact of spinal cord injury on spinal respiratory activity. Cervical spinal injury interrupts bulbospinal pathways and results in cessation of phrenic bursting ipsilateral to the lesion. The ipsilateral phrenic activity can partially recover over weeks to months following injury due to the activation of latent crossed spinal pathways and exhibits a greater capacity to increase activity during respiratory challenges than the contralateral phrenic nerve. However, whether the bilateral phrenic nerves demonstrate differential responses to respiratory inhibitory inputs is unclear. Accordingly, the present study examined bilateral phrenic bursting in response to capsaicin-induced pulmonary chemoreflexes, a robust respiratory inhibitory stimulus. Bilateral phrenic nerve activity was recorded in anaesthetized and mechanically ventilated adult rats at 8-9weeks after C2 hemisection (C2Hx) or C2 laminectomy. Intra-jugular capsaicin (1.5μgkg-1 ) injection was performed to activate the bronchopulmonary C-fibres to evoke pulmonary chemoreflexes. The present results indicate that capsaicin-induced prolongation of expiratory duration was significantly attenuated in C2Hx animals. However, ipsilateral phrenic activity was robustly reduced after capsaicin treatment compared to uninjured animals. Single phrenic fibre recording experiments demonstrated that C2Hx animals had a higher proportion of late-inspiratory phrenic motoneurons that were relatively sensitive to capsaicin treatment compared to early-inspiratory phrenic motoneurons. Moreover, late-inspiratory phrenic motoneurons in C2Hx animals had a weaker discharge frequency and slower recovery time than uninjured animals. These results suggest bilateral phrenic nerves differentially respond to bronchopulmonary C-fibre activation following unilateral cervical hemisection, and the severe inhibition of phrenic bursting is due to a shift in the discharge pattern of phrenic motoneurons.

Effects of novel subtype selective M-current activators on spinal reflexes in vitro: Comparison with retigabine

The activation of Kv7 channels and the resulting M-current is a powerful mechanism to control neuronal excitability with profound effects in pain pathways. Despite the lack of specific data on the expression and role of these channels in nociceptive processing, much attention has been paid at exploring their potential value as targets for analgesia. Here we have characterized the spinal actions of two novel subunit selective Kv7 activators, ICA-069673 and ML213, and compared their effects to those of retigabine that acts with similar affinity on all neuronal Kv7 channels.Spinal reflexes were recorded in a mouse spinal cord in vitro preparation to allow the testing of the compounds on native spinal pathways at known concentrations. As retigabine, novel compounds depressed spinal segmental transmission with particularly strong effects on wind up, showing an adequate pro-analgesic profile. ML213 presented the highest potency. In contrast to retigabine, the effects of ICA-069673 and ML213 were blocked by XE-991 even at the highest concentrations used, suggesting specific effect on Kv7 channels. In addition, the effects of ICA-069673 on repetitive stimulation are consistent with a mode of action involving state or activity dependent interaction with the channels.Compared to retigabine, novel Kv7 openers maintain strong depressant effects on spinal nociceptive transmission showing an improved specificity on Kv7 channels. The differential effects obtained with these Kv7 openers may indicate the existence of several Kv7 conformations in spinal circuits.

Possible Involvement of the Rat Hypothalamo-Neurohypophysial/-Spinal Oxytocinergic Pathways in Acute Nociceptive Responses.

Oxytocin (OXT)-containing neurosecretory cells in the parvocellular divisions of the paraventricular nucleus (PVN), which project to the medulla and spinal cord, are involved in various physiological functions, such as sensory modulation and autonomic processes. In the present study, we examined OXT expression in the hypothalamo-spinal pathway, as well as the hypothalamo-neurohypophysial system, which includes the magnocellular neurosecretory cells in the PVN and the supraoptic nucleus (SON), after s.c. injection of saline or formalin into the hindpaws of transgenic rats that express the OXT and monomeric red fluorescent protein 1 (mRFP1) fusion gene. (i) The numbers of OXT-mRFP1 neurones that expressed Fos-like immunoreactivity (-IR) and OXT-mRFP1 intensity were increased significantly in the magnocellular/parvocellular PVN and SON after s.c. injection of formalin. (ii) OXT-mRFP1 neurones in the anterior parvocellular PVN, which may project to the dorsal horn of the spinal cord, were activated by s.c. injection of formalin, as indicated by a significant increases of Fos-IR and mRFP1 intensity intensity. (iii) Formalin injection caused a significant transient increase in plasma OXT. (iv) OXT, mRFP1 and corticotrophin-releasing hormone mRNAs in the PVN were significantly increased after s.c. injection of formalin. (v) An intrathecal injection of OXT-saporin induced hypersensitivity in conscious rats. Taken together, these results suggest that the hypothalamo-neurohypophysial/-spinal OXTergic pathways may be involved in acute nociceptive responses in rats.

Evidence that some long-lasting effects of direct current in the rat spinal cord are activity-independent.

The effects of trans-spinal direct current (DC) stimulation (tsDCS) on specific neuronal populations are difficult to elucidate, as it affects a variety of neuronal networks. However, facilitatory and depressive effects on neurons processing information from the skin and from muscles can be evaluated separately when weak (0.2-0.3μA) DC is applied within restricted areas of the rat spinal cord. The effects of such local DC application were recently demonstrated to persist for at least 1h, and to include changes in the excitability of afferent fibres and their synaptic actions. However, whether these effects require activation of afferent fibres in spinal neuronal pathways during DC application, i.e. whether they are activity-dependent or activity-independent, remained an open question. The aim of the present study was to address this question by analysing the effects of local DC application on monosynaptic actions of muscle and skin afferents (extracellular field potentials) and afferent fibre excitability. The results revealed that long-lasting post-polarization changes evoked without concomitant activation of afferent fibres replicate changes evoked by stimuli applied during, before and after polarization. The study leads to the conclusion that the reported effects are activity-independent. As this conclusion applies to the local effects of DC application in at least two spinal pathways and to the effects of both cathodal and anodal polarization, it indicates that some of the more widespread effects of trans-spinal and trans-cranial stimulation (both tsDCS and transcranial DC stimulation) may be activity-independent. The results may therefore contribute to the design of more specific DC applications in clinical practice.

Participation of spinal CaMKII-NR2B signal pathway in the development of bone cancer pain in mice

Objective To investigate the effect of KN93, a CaMKII inhibitor, on the spinal NR2B expression in the bone cancer pain mouse and its underlying mechanism. Methods Thirty-six male C3H/HeJ mice were randomly divided into 3 groups: sham group(S, n=8), bone cancer pain group(BP, n=8) and KN93 group(K, n=20). The mouse model of bone cancer pain was established by intra-femur inoculation of osteolytic NCTC 2472 cells in BP and K groups. At 14d post operation, mice in K group received intrathecal injection of 60nmol KN93/5μl in 20%DMSO and mice in BP group and S group received 20% DMSD 5μl respectively.Eight mice were selected randomly from each group at 1d before inoculation, at 1h before administration and at 1, 2, 4, 24h after administration(T0-5) to be measured the paw withdrawal threshold(PWT) stimulated by von Frey filaments. Another 3 mice were sacrificed at the corresponding time point and the spinal cord L3~5 were obtained for determination of NR2B expression by western blot. Results PWT was significantly decreased in group BP((0.50±0.11)g) and K((0.52±0.10)g), except for group K at T3(P>0.05), and NR2B expression up-regulated at T2-5 in BP(1.78±0.34), K groups ((1.11±0.14), (0.73±0.03), (1.11±0.15), (1.89±0.32)) compared with S group((1.78±0.31)g, (0.33±0.04), P 0.05). Conclusion Intrathecal injection of KN93 can attenuate bone cancer pain in mice through inhibiting NR2B with a time-dependent manner and spinal CaMKII-NR2B pathway may participate in the development of bone cancer pain. Key words: Calcium/calmodulin-dependent protein kinase II; NR2B; Bone cancer pain

Changes in H-reflex amplitude to muscle stretch and lengthening in humans.

Spinal reflex excitability is traditionally assessed to investigate neural adjustments that occur during human movement. Different experimental procedures are known to condition spinal reflex excitability. Among these, lengthening movements and static stretching the human triceps have been investigated over the last 50 years. The purpose of this review is to shed light on several apparent incongruities in terms of magnitude and duration of the reported results. In the present review dissimilarities in neuro-spinal changes are examined in relation to the methodologies applied to condition and measure them. Literature that investigated three different conditioning procedures was reviewed: passive dorsiflexion, active dorsiflexion through antagonists shortening and eccentric plantar-flexors contractions. Measurements were obtained before, during and after lengthening or stretching. Stimulation intensities and time delays between conditioning procedures and stimuli varied considerably. H-reflex decreases immediately as static stretching is applied and in proportion to the stretch degree. During dorsiflexions the inhibition is stronger with greater dorsiflexion angular velocity and at lower nerve stimulation intensities, while it is weaker if any concomitant muscle contraction is performed. Within 2 s after a single passive dorsiflexion movement, H-reflex is strongly inhibited, and this effect disappears within 15 s. Dorsiflexions repeated over 1 h and prolonged static stretching training induce long-lasting inhibition. This review highlights that the apparent disagreement between studies is ascribable to small methodological differences. Lengthening movements and stretching can strongly influence spinal neural pathways. Results interpretation, however, needs careful consideration of the methodology applied.

Activation of glial glutamate transporter via MAPK p38 prevents enhanced and long-lasting non-evoked resting pain after surgical incision in rats

Pain after surgery has recently become a major issue not only due to lack of treatment success in the acute phase; even more alarming is the large number of patients developing prolonged pain after surgery. Because spinal glutamate as well as spinal glia plays a major role in acute incisional pain, we investigated the role of the spinal glial glutamate transporters (GT), GLAST, GLT-1, for acute and prolonged pain and hyperalgesia caused by an incision. Spinal administration of the GT-inhibitor DL-TBOA increased non-evoked pain but not evoked pain behavior (hyperalgesia) up to 2 weeks after incision. In accordance, spinal GLAST (and to a lesser degree GLT-1) were upregulated after incision for several days. Long-term incision induced GT upregulation was prevented by long-lasting p38-inhibitor administration but not by long-lasting ERK1/2-inhibition after incision. In accordance, daily treatment with the p38-inhibitor (but not the ERK1/2 inhibitor) prolonged non-evoked but not evoked pain behavior after incision. In electrophysiological experiments, spontaneous activity of high threshold (HT) (but not wide dynamic range (WDR)) neurons known to transmit incision induced non-evoked pain was increased after prolonged treatment with the p38-inhibitor. In conclusion, our findings indicate a new spinal pathway by which non-evoked pain behavior after incision is modulated. The pathway is modality (non-evoked pain) and neuron (HT) specific and disturbance contributes to prolonged long-term pain after surgical incision. This may have therapeutic implications for the treatment of acute and – even more relevant – for prevention of chronic pain after surgery in patients.

Blockade of the spinal BDNF-activated JNK pathway prevents the development of antiretroviral-induced neuropathic pain

Although antiretroviral agents have been used successfully in suppressing viral production, they have also been associated with a number of side effects. The antiretroviral toxic neuropathy induces debilitating and extremely difficult to treat pain syndromes that often lead to discontinuation of antiretroviral therapy. Due to the critical need for the identification of novel therapeutic targets to improve antiretroviral neuropathic pain management, we investigated the role of the JNK signalling pathway in the mechanism of antiretroviral painful neuropathy. Mice were exposed to zalcitabine (2′,3′-dideoxycytidine, ddC) and stavudine (2′,3′-didehydro-3′-deoxythymidine, d4T) that induced a persistent mechanical allodynia and a transient cold allodynia. Treatment with the JNK blocker SP600125 before antiretroviral administration abolished mechanical hypersensitivity with no effect on thermal response. A robust spinal JNK overphosphorylation was observed on post-injection day 1 and 3, along with a JNK-dependent increase in p-c-Jun and ATF3 protein levels. Co-immunoprecipitation experiments showed the presence of a heterodimeric complex between ATF3 and c-Jun indicating that these transcription factors can act together to regulate transcription through heterodimerization. A rise in BDNF and caspase-3 protein levels was detected on day 1 and BDNF sequestration prevented both caspase-3 and p-JNK increase. These data suggest that BDNF plays a role in the early stages of ddC-induced allodynia by promoting apoptotic events and the activation of a hypernociceptive JNK-mediated pathway. We illustrated the activation of a BDNF-mediated JNK pathway involved in the early events responsible for the promotion of neuropathic pain, leading to a better knowledge of the mechanisms involved in the antiretroviral neuropathy. SummaryJNK blockade prevents antiretroviral-induced pain hypersensitivity. This may represent a potential prophylactic treatment of neuropathic pain to improve antiretroviral tolerability.

Longitudinal Evaluation of Residual Cortical and Subcortical Motor Evoked Potentials in Spinal Cord Injured Rats.

We have applied transcranial electrical stimulation to rats with spinal cord injury and selectively tested the motor evoked potentials (MEPs) conveyed by descending motor pathways with cortical and subcortical origin. MEPs were elicited by electrical stimulation to the brain and recorded on the tibialis anterior muscles. Stimulation parameters were characterized and changes in MEP responses tested in uninjured rats, in rats with mild or moderate contusion, and in animals with complete transection of the spinal cord. All injuries were located at the T8 vertebral level. Two peaks, termed N1 and N2, were obtained when changing from single pulse stimulation to trains of 9 pulses at 9 Hz. Selective injuries to the brain or spinal cord funiculi evidenced the subcortical origin of N1 and the cortical origin of N2. Animals with mild contusion showed small behavioral deficits and abolished N1 but maintained small amplitude N2 MEPs. Substantial motor deficits developed in rats with moderate contusion, and these rats had completely eliminated N1 and N2 MEPs. Animals with complete cord transection had abolished N1 and N2 and showed severe impairment of locomotion. The results indicate the reliability of MEP testing to longitudinally evaluate over time the degree of impairment of cortical and subcortical spinal pathways after spinal cord injuries of different severity.

Effect of spinal monoaminergic neuronal system dysfunction on pain threshold in rats, and the analgesic effect of serotonin and norepinephrine reuptake inhibitors

Dysfunction in the central serotonin (5-HT) and norepinephrine (NE) systems cause depression and pain. Descending spinal pain modulatory pathways are important in the analgesic mechanisms of antidepressants, particularly serotonin and norepinephrine reuptake inhibitors (SNRIs). While many non-clinical studies have demonstrated the roles of central monoaminergic systems in pain, there is little evidence to illuminate the direct contribution of spinal descending pain modulatory systems independently of depressive-like behavior. To examine the effects of dysfunction of spinal monoaminergic systems on pain sensitivity, we established a rat chronic pain model by administering lumbar-intrathecal reserpine to minimize its influence on brain. Lumbar-intrathecal reserpine evoked persistent mechanical hypersensitivity and corresponding reductions in spinal 5-HT and NE concentrations (from 767.2 to 241.6ng/g and from 455.9 to 41.7ng/g, respectively after reserpine 30nmol). Lumbar-intrathecal reserpine did not deplete brain monoamines or bring about depressive-like behavior in the forced swim test. Spinal monoamines depletion-induced pain sensitivity was ameliorated by lumbar-intrathecal administration of the SNRIs (duloxetine and milnacipran) in dose-dependent manners. These suggest that increased pain sensitivity could be induced by dysfunction solely of the descending pain modulatory system, regardless of depressive-like behavior, and lumbar-intrathecal administration of SNRIs could ameliorate the pain sensitivity which might be mediated by affecting the descending pain modulatory system in the spinal cord, not via their antidepressant effects.

Are Human Digit Muscles Devoid of Recurrent Inhibition?

Are Human Digit Muscles Devoid of Recurrent Inhibition?

Effect of cannabinoids on CGRP release in the isolated rat lumbar spinal cord

Cannabinoids produce analgesia through a variety of mechanisms. It has been proposed that one mechanism is by modulating the release of CGRP in the spinal cord pain pathways. Previous studies have reported that cannabinoids, particularly CB2 receptor agonists, can modulate CGRP release in the isolated rat spinal cord. In our experiments, the TRPV1 agonist capsaicin evoked CGRP release and this was supressed by the TRPV1 antagonist capsazepine and by the opioid receptor agonist DAMGO. However, none of the cannabinoid receptor agonists that we tested were able to modulate evoked CGRP release; including WIN 55,212-2, methanandamide, and GW405833. These results question the role of spinal cord cannabinoid receptors in the regulation of CGRP signaling.

Acting Out of the Ordinary: A Case of Sudden Death after Abnormal Behavior Due to a Craniopharyngioma

Introduction: We report a patient who initially presented with behavioral changes for a short period and then succumbed to unexpected death while on psychiatric treatment. The cause of death was found to be a craniopharyngioma at medico-legal autopsy. Case report: A previously apparently healthy, 52-year old female, started showing disinhibited behavior such as removing clothes in public and was consequently treated with antipsychotics for two weeks. Behavioral symptoms improved gradually but she complained of intermittent difficulty in maintaining balance. A week later she was found dead at home in her bed. Medico-legal autopsy and subsequent investigations revealed severe cerebral edema resulting from a well formed craniopharyngioma with surrounding cystic degeneration at pituitary gland. The optic chiasma was partially displaced by the tumor. Moderate pulmonary edema was seen. Examination of other systems, toxicology and microbiological investigations were unremarkable. The cause of death was given as cerebral edema due to craniopharyngioma. Discussion: The patient was initially treated as having a mental illness. This reflects the importance of excluding organic causes early and considering neurological assessment in previously well patients who suddenly presented with psychiatric symptoms. Autopsy findings are consistent with acute hydrocephalus due to growing brain tumor. The enlarged gland had encroached on the basal cisterna, obstructing the cerebral spinal fluid pathway, and causing acute hydrocephalus. This was speculated to have resulted in sudden death. Conclusion: This case exemplifies the medico-legal autopsy role in determining causes of death.

A latent serotonin-1A receptor-gated spinal afferent pathway inhibiting breathing.

Spinal afferents such as nociceptive afferents and group III-IV muscle afferents are known to exert an acute excitatory effect on breathing when activated. Here, we report the surprising existence of latent spinal afferents which exerted tonic inhibitory influence on breathing subliminally in anesthetized rats, an effect which was reversed upon activation of serotonin-1A receptors (5-HT1ARs) in lumbar spinal cord, lesion of pontine lateral parabrachial nucleus or suppression of the adjacent Kölliker-Fuse nucleus with NMDA receptor blockade. Small-interfering RNA knockdown of 5-HT1ARs in lumbar spinal cord unequivocally localized the site of 5-HT1AR-mediated gating of these respiratory-inhibiting interoceptive afferents to relay neurons in the spinal superficial dorsal horn at the lumbar level and not cervical spinal or supraspinal levels. Our results reveal a novel somatosensory/viscerosensory mechanism which exerts tonic inhibitory influence on homeostatic regulation of breathing independent from the classical chemoreflex excitatory pathways, and suggest a hitherto unrecognized therapeutic target in spinal dorsal horn for 5-HT1AR-based treatment of a variety of respiratory abnormalities.

The association of resting state heart rate variability and 24-hour blood pressure variability in spinal cord injury

Patients with high cervical complete spinal cord injuries (tetraplegia) sustain damage to the autonomic neural pathways that influence cardiovascular functioning and produce variability in the heart rate (HR) and blood pressure (BP). In non-injured individuals, an inverse relationship exists between resting autonomic control of the heart (as evidenced by HR variability (HRV)) and BP variability (BPV). This study examined the relationship between HRV, BP and BPV in individuals with tetraplegic (n=10) and paraplegic (n=10) spinal cord injuries, and a group of healthy controls (n=14). Resting HRV at baseline and 24-hour ambulatory BP measurements were collected from electrocardiogram measures of each participant. HRV was quantified using time- and frequency-domain measures. The standard deviation of the BP measurements was used as an index of BPV. Multivariate analyses of variance were performed to examine group differences for laboratory-based and 24-h dependent variables. The MANOVAs for HRV parameters (λ(14,50)=.352, p=.010, η2=.407) and for BP indices and HR (λ(16,48)=.318, p=.013, η2=.436) were significant. Furthermore, in line with existing evidence, we found that vagally mediated HRV was inversely related to BPV in healthy controls. However, this relationship did not hold for the tetraplegia group (ρ<|.42|), and mixed results were found for the paraplegia group (e.g., ρ<|.29| for time domain HRV, ρ>|.65| for low-frequency power). These results support the conclusion that the damage to the spinal sympathetic pathways to the heart found in people with tetraplegia causes a significant disruption in baroreflex control of BP.

Patient safety in spinal surgery: from scene of injury to discharge

Abstract In 1999 the Institute of Medicine (IOM) report To Err is Human. Building a Safer Health System, was a landmark publication that identified adverse events associated with surgery. The IOM report was effectively a wakeup call for a safer healthcare system for patients. Fourteen years later, much has been achieved, but patient safety still remains an important issue. The IOM report categorized incidents as nonsurgical and surgical, although nothing was specifically directed at spinal surgery. Some of the broad topics of concern that may relate to the spine were medication errors , infection , and technical problems of surgery. Almost 50% of adverse events identified in the IOM report were surgical in origin. Technical errors constituted the most frequent adverse events within surgery- however, the IOM did not specify what these were. According to other studies, we can deduce some of the most frequent technical issues in spine surgery; these include: wrong-level surgery, incomplete decompression, dural tears, battered root syndrome, and development of instability. We review the spinal patient pathway of the trauma patient, including pre-hospital and peri-operative care, and focus on strategies and campaigns to improve patient safety such as the WHO surgical safety checklist.

Ultrafast traveling wave dominates the electric organ discharge of Apteronotus leptorhynchus: an inverse modelling study.

Identifying and understanding the current sources that give rise to bioelectric fields is a fundamental problem in the biological sciences. It is very difficult, for example, to attribute the time-varying features of an electroencephalogram recorded from the head surface to the neural activity of specific brain areas; model systems can provide important insight into such problems. Some species of fish actively generate an oscillating (c. 1000 Hz) quasi-dipole electric field to communicate and sense their environment in the dark. A specialized electric organ comprises neuron-like cells whose collective signal underlies this electric field. As a step towards understanding the detailed biophysics of signal generation in these fish, we use an anatomically-detailed finite-element modelling approach to reverse-engineer the electric organ signal over one oscillation cycle. We find that the spatiotemporal profile of current along the electric organ constitutes a travelling wave that is well-described by two spatial Fourier components varying in time. The conduction velocity of this wave is faster than action potential conduction in any known neuronal axon (>200 m/s), suggesting that the spatiotemporal features of high-frequency electric organ discharges are not constrained by the conduction velocities of spinal neuron pathways.

The Periaqueductal Gray Orchestrates Sensory and Motor Circuits at Multiple Levels of the Neuraxis.

Neural circuits that coordinate survival behaviors remain poorly understood. We demonstrate in rats that the periaqueductal gray (PAG) affects motor systems at the following multiple levels of the neuraxis: (1) through altering transmission in spino-olivary pathways that forward sensory signals to the cerebellum, reducing and enhancing transmission of nociceptive and proprioceptive information, respectively; (2) by alterations in cerebellar output; and (3) through enhancement of spinal motor reflex pathways. The sensory and motor effects occurred at the same time and were present in both anesthetized animals and behavioral experiments in which fear conditioning naturally activated the PAG. The results provide insights into the neural circuits that enable an animal to be ready and able to react to danger, thus assisting in survival.

Role of spinal AMPK signaling pathway in reduction of neuropathic pain by dexmedetomidine in rats

Objective To evaluate the role of spinal AMP-activated protein kinase (AMPK) signaling pathway in reduction of neuropathic pain (NP) by dexmedetomidine in rats. Methods One hundred twenty adult male Sprague-Dawley rats, weighing 180–220 g, were randomly divided into 4 groups (n= 30 each) using a random number table: sham operation group (group S); group NP; dexmedetomidine group (group Dex) and AMPK inhibitor group (group AI). The animals were anesthetized with intraperitoneal 10% chloral hydrate 350 mg/kg.The right sciatic nerve was exposed, and 4 loose ligatures were placed on the sciatic nerve at 1 mm intervals with 4-0 silk thread in NP and Dex groups.In group Dex, dexmedetomidine 50 μg/kg was injected intraperitoneally once a day starting from the end of operation until the animals were sacrificed.In group AI, AMPK inhibitor Compound C 20 mg/kg was injected intraperitoneally at the end of operation, and the other treatments were similar to those previously described in group Dex.The equal volume of normal saline was given instead of dexmedetomidine in S and NP groups.The mechanical paw withdrawal threshold to von Frey filament stimulation (MWT) and thermal paw withdrawal latency (TWL) were measured at 1 day before operation (baseline) and 2, 8 and 14 days after operation (T0-3). Results Compared with group S, the MWT was significantly decreased, and the TWL was shortened at T1-3 in NP, Dex and AI groups (P 0.05). Conclusion Spinal AMPK signaling pathway is involved in reduction of NP by dexmedetomidine in rats. Key words: Protein-serine-threonine kinases; Dexmedetomidine; Neuralgia; Spinal cord

Role of spinal ERK signaling pathway in reduction of remifentanil-induced hyperalgesia by electro-acupuncture at Zusanli in rats with incisional pain

Objective To evaluate the role of spinal extracellular signal-regulated kinase (ERK) signaling pathway in reduction of remifentanil-induced hyperalgesia by electro-acupuncture (EA) at Zusanli in rats with incisional pain. Methods Fifty male adult Sprague-Dawley rats, weighing 250–280 g, in which the intrathecal catheter was successfully placed without complications, were randomly divided into 5 groups (n= 10 each) using a random number table: control group (group C), remifentanil + incisional pain group (group RI), EA at acupoint group (group E), EA at non-acupoint group (group NE), and 1/2 ERK inhibitor U0126 + EA at acupoint group (group UE). Normal saline 0.1 ml· kg–1· min–l was infused intravenously for 60 min in group C. In RI, E, NE and UE groups, after the model of incisional pain was established, remifentanil 1.0 μg · kg–1· min–l was infused for 60 min, and in addition, EA (intensity 10 mA, frequency 4 Hz) of Zusanli lasting for 60 min was performed at the same time in E and UE groups, and EA was performed at the points 5 mm lateral to the acupoints of Zusanli on the operated side simultaneously in group NE.ERK1/2 inhibitor U0126 5 μg (in 5% dimethyl sulfoxide 10 μl) was injected intrathecally in group UE, and 5% dimethyl sulfoxide 10 μl was injected intrathecally in the other groups.The mechanical paw withdrawal threshold (MWT) was measured before remifentanil or normal saline infusion (T1), and at 2 h, 1, and 2 days after the end of infusion (T2-4). After MWT was measured at T4, the expression of ERK1/2 and phosphorylated ERK1/2 (p-ERK1/2) in spinal cord dorsal horns was measured by Western blot. Results Compared with group C, the MWT was significantly decreased at T2-4 in RI, E, NE and UE groups, and the expression of p-ERK1/2 was up-regulated in RI, E and NE groups (P 0.05). Compared with group E, the MWT was significantly increased at T2-4, and the expression of p-ERK1/2 was down-regulated in group UE (P<0.05). Conclusion The mechaism by which EA at Zusanli reduces hyperalgesia induced by remifentanil in rats with incisional pain is related to inhibited activation of ERK signaling pathway in the spinal cord . Key words: Extracellular signal-regulated MAP kinases; Spinal cord; Electric stimulation therapy; POINT ST36 (ZUSANLI); Piperidines; Pain, postoperative; Hyperalgesia