Role of neurokinin 3 receptors on responses to colorectal distention in the rat: electrophysiological and behavioral studies

BACKGROUND & AIMS: Tachykinins contribute to the control of gastrointestinal motility and modulation of somatic and visceral pain. The role of neurokinin (NK) B and NK3 receptors in visceral pain and gastrointestinal disorders has not been determined. METHODS: Using electromyographic recordings of both abdominal and colonic muscle and electrophysiological recordings of pelvic nerve afferent fibers, we studied drug effects on responses to colorectal distention. RESULTS: In awake rats, intraperitoneal administration of the NK3-receptor antagonist SR 142,801 reduced, whereas the NK3-receptor agonist senktide increased, both the rectocolonic inhibitory reflex and abdominal contractions produced by colorectal distention. In contrast, intracerebroventricular administration of SR 142,801 increased the number of abdominal contractions without affecting the rectocolonic inhibitory reflex produced by colorectal distention. In a similar manner, intracerebroventricular injection of senktide diminished the number of abdominal contractions. In electrophysiological experiments, SR 142,801 decreased responses of pelvic nerve afferent fibers to colorectal distention. Responses of pelvic nerve fibers to urinary bladder distention, however, were unaffected by SR 142,801. CONCLUSIONS: These results suggest that peripheral NK3 receptors are involved in the mediation of both visceral nociception and gastrointestinal disorders. Also, central NK3 receptors seem to play a role in the modulation of visceral nociception.     

Proteinases and proteinase-activated receptor 2: a possible role to promote visceral hyperalgesia in rats

BACKGROUND & AIMS: PAR-2s are highly expressed throughout the gastrointestinal tract. These receptors are cleaved by trypsin and mast cell tryptase and can be activated by peptides corresponding to the tethered ligand of the receptor (SLIGRL-NH2 for rat). The aim of this study was to determine whether colonic administration of PAR-2 agonists affects visceral sensitivity to rectal distention in conscious rats. METHODS: Abdominal contractions (a criteria of visceral pain) were recorded in rats equipped with intramuscular electrodes. Rectal distention was performed at various times after intracolonic infusion of SLIGRL-NH2 and trypsin. Inflammation parameters and permeability were followed in the colon after the intracolonic injections. Fos expression at a spinal level (L4-L6) was also studied 2 hours after intracolonic injection of SLIGRL-NH2. RESULTS: Rectal distention significantly increased abdominal contractions starting at the RD volume of 0.8 mL. Intracolonic injection of SLIGRL-NH2 (200 microg/rat) and trypsin (200 U/rat), but not vehicle, LRGILS-NH2 (control peptide), boiled trypsin, or SLIGRL-NH2 injected IP, significantly increased (P < 0.05) abdominal contractions for high volumes of distention, 10- and 24-hour postinfusion. SLIGRL-NH2-induced hyperalgesia was inhibited by a NK1 receptor antagonist (SR 140333) but not by indomethacin. Intracolonic injection of SLIGRL-NH2 elevated spinal Fos expression and caused increased intestinal permeability but did not cause detectable inflammation. CONCLUSIONS: Intracolonic infusion of subinflammatory doses of PAR-2 agonists activated spinal afferent neurons and produced a delayed rectal hyperalgesia that involves changes in intestinal permeability and the activation of NK1 receptors. These results identify a possible role for proteinases and PAR-2 in the genesis of visceral hyperalgesia.     

Role of peripheral N-methyl-D-aspartate (NMDA) receptors in visceral nociception in rats

BACKGROUND & AIMS: N-methyl-D-aspartate (NMDA) receptors are ligand-gated ion channels that have an important role in long-term potentiation and memory processing in the central nervous system. The aims in this study were to determine whether NMDA receptors are expressed in the peripheral nervous system and identify their role in mediating behavioral pain responses to colonic distention in the normal gut. METHODS AND RESULTS: Immunohistochemical localization of the NR1 subunit showed that NMDA receptors are expressed on the cell bodies and peripheral terminals of primary afferent nerves innervating the colon. Dorsal root ganglia neurons retrogradely labeled from the colon in short-term culture responded to addition of NMDA with increased intracellular [Ca2+]. Activation of peripheral NMDA receptors in colonic tissue sections caused Ca2+-dependent release of the proinflammatory neuropeptides, calcitonin gene-related peptide and substance P. Behavioral pain responses to noxious mechanical stimulation were inhibited in a reversible, dose-dependent manner by intravenous administration of memantine, a noncompetitive antagonist of the NMDA receptor. Single fiber recordings of decentralized pelvic nerves showed that colorectal distention responsive afferent nerve activity was inhibited by memantine. CONCLUSIONS: Peripheral NMDA receptors are important in normal visceral pain transmission, and may provide a novel mechanism for development of peripheral sensitization and visceral hyperalgesia.     

A role for spinal nitric oxide in mediating visceral hyperalgesia in the rat.

BACKGROUND & AIMS: Intracolonic instillation of zymosan in rats produces hyperalgesia (i.e., facilitates the visceromotor response to colorectal distention) mediated by activity at spinal N-methyl-D-aspartate (NMDA) and non-NMDA receptors. Nitric oxide (NO*) production often increases after NMDA receptor activation; NO* may then function as a further messenger. This study was designed to investigate the role of spinal NO* in this model of visceral hyperalgesia. METHODS: Zymosan or saline was given intracolonically, and the visceromotor response to noxious colorectal distention (80 mm Hg, 20 seconds) was measured 3 hours afterward. RESULTS: There was a significant enhancement of the visceromotor response in zymosan-, but not saline-treated, rats. This hyperalgesia was dose-dependently and reversibly attenuated by intrathecal administration of the nonselective NO* synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (100-800 nmol) as well as by the selective neuronal NOS inhibitor ARL 17477 (30-600 nmol). In support of these observations, there was a significant increase in the number of cells labeled for NADPH diaphorase or neuronal NOS in the lumbosacral spinal cord after intracolonic instillation of zymosan, but not saline. CONCLUSIONS: These data suggest that colonic inflammation induces the expression of neuronal NOS in the spinal cord and that increased production of spinal NO* is necessary for maintenance of zymosan-produced visceral hyperalgesia.     

Postcholecystectomy pain syndrome: pathophysiology of abdominal pain in sphincter of Oddi type III

BACKGROUND & AIMS: Persistent abdominal pain occurs in many patients after cholecystectomy, some of whom are described as having sphincter of Oddi dysfunction (SOD). Pain in SOD type III is thought to be of biliary origin with little objective data, and treatment is often unsatisfactory. Chronic abdominal pain without a biological disease marker is similar to irritable bowel syndrome, in which many patients exhibit visceral hyperalgesia. This study tested the hypothesis that duodenal-specific visceral afferent sensitivity exists in patients with SOD type III. METHODS: Eleven patients with chronic abdominal pain after cholecystectomy and 10 controls underwent duodenal and rectal barostat studies to evaluate visceral pain perception measured with a visual analog scale. All subjects underwent psychological testing. RESULTS: Patients with SOD type III exhibited duodenal but not rectal hyperalgesia compared with controls. There were no differences in duodenal compliance between the groups. Duodenal distention reproduced symptoms in all but 1 patient. Patients showed high levels of somatization, depression, obsessive-compulsive behavior, and anxiety. CONCLUSIONS: Patients with SOD type III exhibited duodenal-specific visceral hyperalgesia, and duodenal distention reproduced symptoms in all but 1 patient. Abdominal pain in these patients may not originate exclusively from the biliary tree.     

A model of neural cross-talk and irritation in the pelvis: implications for the overlap of chronic pelvic pain disorders

BACKGROUND & AIMS: Irritable bowel syndrome, interstitial cystitis, and other chronic pelvic pain (CPP) disorders often occur concomitantly. Neural cross-talk may play a role in the overlap of CPP disorders via the convergence of pelvic afferents. We investigated the hypothesis that afferent irritation of one pelvic organ may adversely influence and sensitize another via neural interactions. METHODS: We measured pelvic organ smooth muscle and striated muscle reflexes during micturition and colorectal distention (CRD) in urethane-anesthetized rats. The effects of acute cystitis on distal colonic sensory thresholds to CRD and the effects of acute colonic irritation on micturition parameters were assessed. RESULTS: External urethral sphincter (EUS) electromyography (EMG) was typical for the rat, with phasic firing during micturition. External anal sphincter EMG also showed phasic firing during micturition in synchrony with EUS activity but, in addition, showed both tonic bursts and phasic firing independent of EUS activity. Before bladder irritation, graded CRDs to 40 cm H2O produced no notable changes in abdominal wall EMG activity. Following acute bladder irritation, dramatic increases in abdominal wall EMG activity in response to CRD were observed at much lower distention pressures, indicating colonic afferent sensitization. Analogously, following acute colonic irritation, bladder contraction frequency increased 66%, suggesting sensitization of lower urinary tract afferents. CONCLUSIONS: We report compelling evidence of bidirectional cross-sensitization of the colon and lower urinary tract in a novel experimental model. This cross-sensitization may account for the substantial overlap of CPP disorders; however, further studies are needed to fully characterize these pathways.     

Effects of moxibustion on dynorphin and endomorphin in rats with chronic visceral hyperalgesia

AIM:To observe the analgesic effects of moxibustion in rats with chronic visceral hyperalgesia and its influence on the concentration of dynorphin(Dyn) and endomorphin(EM) in spinal cord.METHODS:The rat model of chronic visceral hyperalgesia was established by colorectal distention(CRD).In moxibustion(MX) group,moxibustion was applied once daily for 7 d;in sham moxibustion(SM) group,moxibustion was given to the same acupoints but with the nonsmoldered end of the moxa stick.Model control(MC) group and normal...     

肠道炎症诱导的内脏和躯体痛觉过敏

背景：慢性腹痛是功能性胃肠病患者常见症状之一,此类患者亦可同时具有较明显的躯体症状。内脏和躯体症状并存极大影响了患者的生活质量,并增加就医负担。目的：观察肠道炎症后大鼠内脏和躯体痛觉,探究两者间的联系和可能的共同发病机制。方法：80只雄性Sprague—Dawley大鼠随机分为模型组、溶剂对照组和阴性对照组,分别给予20mgTNBS／乙醇混合液、50％乙醇和0．9％NaCl溶液灌肠。灌肠8周后,行不同压力结直肠扩张（CRD）诱导内脏运动反射（VMR）以评估大鼠内脏痛觉。以机械缩足反射阈值（MWT）和甩尾反射潜伏期（TFL）评估躯体痛觉。结果：造模8周后模型组大鼠结肠黏膜病理表现与两组对照组相比无明显差异,未见明显溃疡和炎性细胞浸润。与两组对照组相比,32．5％的模型组大鼠内脏痛觉阈值明显下降（P〈0．001）,且这部分内脏痛觉高敏感的模型组大鼠MWT和TFL均明显降低（P〈0．001）。结论：本研究建立的动物模型模拟了感染后肠易激综合征状态,TNBS诱导的肠道炎症同时导致了大鼠内脏和躯体痛觉过敏,有助于进一步探究内脏和躯体痛觉过敏的共同发病机制。     

Visceral hyperalgesia and intestinal dysmotility in a mouse model of postinfective gut dysfunction

BACKGROUND & AIMS: We established the concept that transient enteric infection may lead to persistent gut dysfunction, evident in vitro, in nematode-infected mice. The present study determined whether gut dysfunction in this model involves motor and sensory changes reminiscent of changes found in patients with postinfective irritable bowel syndrome (PI-IBS) and investigated underlying mechanisms. METHODS: Mice infected up to 70 days previously with Trichinella spiralis (Tsp) underwent videofluoroscopy with image analysis to assess upper gastrointestinal motility. Pseudoaffective responses to colorectal distention (CRD) were assessed using a barostat and validated by single fiber recordings from spinal nerves during CRD. Tissues were examined at different time points for histology, immunohistochemistry, and cytokine analysis. Some mice received dexamethasone intraperitoneally on days 23-25 PI or Tsp antigen orally on days 29, 43, and 57 PI. RESULTS: From day 28 PI, no discernible inflammation was present in the gut. Frequency and propagation velocity of intestinal contractions decreased, and retroperistalsis increased at days 28 to 42 PI. CRD induced an allodynic and hyperalgesic response in PI mice, which was accompanied by increased single unit discharge. Gavage of Tsp antigen induced T-cell responses and sustained gut dysfunction for 70 days PI. Administration of dexamethasone postinfection normalized dysmotility and visceral hyperalgesia. CONCLUSIONS: Long-lasting gut dysmotility and hyperalgesia develop in mice after transient intestinal inflammation. These changes are maintained by luminal exposure to antigen and reversed by corticosteroid treatment. The findings prompt consideration of this as a model of PI-IBS.     

Facilitation and attenuation of a visceral nociceptive reflex from the rostroventral medulla in the rat

BACKGROUND & AIMS: Noxious inputs from somatic tissue are subject to biphasic descending modulation from the rostroventral medulla (RVM). In the present study, we investigated descending facilitatory and inhibitory influences from the RVM on a visceral nociceptive reflex. METHODS: The visceromotor response (VMR), a contraction of peritoneal musculature during noxious colorectal distention (80 mm Hg, 20 seconds), was quantified as the integrated electromyogram. RESULTS: At 22 sites in the RVM, electrical stimulation produced biphasic effects, facilitating the VMR at low (5, 10, and 25 microA) and inhibiting it at greater (>50 microA) intensities of stimulation. Electrical stimulation at all intensities tested (5-200 microA) in other sites in the RVM only inhibited (30 sites) or only facilitated (12 sites) the VMR to colorectal distention. Activation of glutamatergic receptors in the RVM replicated the effects of electrical stimulation. Reversible blockage (intraspinal lidocaine injection) or irreversible transection of spinal funiculi revealed that descending facilitatory influences from the RVM were conveyed in the ventrolateral/ventral funiculus, whereas descending inhibitory influences were contained in the dorsolateral funiculi. CONCLUSIONS: Spinal visceral nociceptive reflexes are subject to facilitatory modulation from the RVM, providing the basis for a mechanism by which visceral sensations can be enhanced from supraspinal sites.     

炎症后内脏高敏感大鼠前扣带回皮质NR2A、NR2B表达变化

背景:研究显示N-甲基-D-天冬氨酸(NMDA)受体参与了伤害性信号的传递,中枢前扣带回皮质(ACC)在内脏高敏感大鼠内脏疼痛反应的调节中起重要作用,该作用是由NMDA受体活性增强介导的。目的:检测炎症后内脏痛觉过敏大鼠ACC区域NMDA受体亚基NR2A、NR2B的表达变化,探讨两者在炎症后内脏高敏感形成中的作用。方法:以去氧胆酸结肠灌注建立炎症后内脏痛觉过敏大鼠模型。造模3周后观察实验组和对照组结肠组织病理学改变,以对结直肠扩张(CRD)的内脏运动反射(VMR)幅值为指标评价内脏痛敏感性的变化,以免疫荧光法和蛋白质印迹法检测ACC区域NR2A、NR2B表达情况。结果:实验组和对照组大鼠结肠组织均未见明显病理学改变。CRD压力为60 mm Hg(伤害性刺激)时,实验组VMR幅值显著高于对照组(P0.05)。与对照组相比,实验组ACC区域NR2A、NR2B荧光强度和蛋白表达量均显著上调(P0.05)。结论:ACC区域NMDA受体亚基NR2A、NR2B表达上调在炎症后内脏高敏感的形成中发挥重要作用。     

ZD 7288,an HCN channel blocker,attenuates chronic visceral pain in irritable bowel syndrome-like rats

AIM:To investigate the effects of ZD 7288,a hyperpolarization-activated cyclic nucleotide-gated(HCN)channel blocker,on rats with chronic visceral pain.METHODS:Rats with visceral hypersensitivity were generated using neonatal colon irritation during postnatal days 8-15 as described previously.Visceral hypersensitivity was evaluated using electromyographic(EMG)responses of abdominal external oblique muscles to 20-80 mmHg colorectal distentions(CRD).Abdominal withdrawal reflex(AWR)scores and pain thresholds were also detected in adult rats.Different doses of ZD7288(25,50,and 100 nmol/L)were intrathecally administered in rats to study the role of spinal HCN channel in chronic visceral hypersensitivity.RESULTS:EMG responses to 20-80 mmHg CRD and AWR scores under 20-60 mmHg CRD significantly increased in rats with visceral hypersensitivity compared to control rats(P<0.05).The pain threshold in rats with visceral hypersensitivity significantly decreased compared to control rats(P<0.05).Treatment with50-100 nmol/L ZD 7288 significantly inhibited EMG responses(16%-62%,80-20 mmHg CRD,P<0.05)and AWR scores(24%-37%,40-20 mmHg CRD,P<0.05;12%-61%,80-20 mmHg CRD,P<0.05,respectively),and significantly increased pain thresholds(32%-77%,P<0.05).CONCLUSION:Spinal HCN channels may play an important role in chronic visceral hypersensitivity.     

PKCγ在内脏高敏感状态下跨器官敏化中的作用

背景：内脏-内脏之间存在广泛的伤害性传人会聚和相互作用．在跨器官痛觉过敏的发生中起重要作用。目的：在内脏高敏感状态下建立跨器官敏化大鼠模型,探讨蛋白激酶C1（PKCγ）对跨器官内脏敏感性的调控作用．方法：Sprague-Dawlev大鼠随机分为4组．其中3组在鸡卵清蛋白（OVA）基础致敏联合结直肠芥子油（MO）灌注建立结直肠-膀胱跨器官敏化模型的基础上,分别鞘内注射PKC叫特异性抑制剂GF109203X、0．9％NaCl溶液（NS）或不予鞘内注射,另一组为正常对照组。各组大鼠行梯度结直肠扩张／膀胱扩张（CRD／UBD）．根据腹壁肌电活动曲线下面积（AUC）评估内脏敏感性的变化。结果：各组UBD梯度扩张刺激体积均与腹壁肌电活动AUC显著相关（P〈0．05）。UBD扩张体积为1．0、1．5、2．0m1以及CRD扩张压力为40、60、80mmHg时,OVA＋MO组AUC显著高于正常对照组（P〈0．05）;UBD扩张体积为1．5、2．0ml以及CRD扩张压力为60、80mmHg时,OVA＋MO＋GF109203X组AUC较OVA＋MO＋NS组显著降低（P〈0．05）。结论：鞘内注射PKC吖特异性抑制剂能逆转跨器官交叉内脏高敏感性,提示PKC7在跨器官敏化的产生和维持中起重要作用。     

旋毛虫感染后肠易激综合征大鼠内脏敏感性及CD4^＋/CD25^＋T细胞的变化特征

[目的]观察旋毛虫感染后肠易激综合征（PI-IBS）不同造模时间点小鼠内脏敏感性的变化及调节T细胞的变化特征,探讨两者在PI-IBS发病机制中的作用及相关性。[方法]旋毛虫幼虫囊泡（350～400条）感染成年SD大鼠,分别于感染后2、8周后行结直肠扩张（CRD）,记录腹壁肌电图（EMG）,评价内脏感觉功能的变化。取大鼠外周血经流式细胞仪检测CD4＋CD25＋细胞比例,评价不同时间点调节T细胞比例变化特征。[结果]①CRD联合EMG腹外斜肌放电次数可以反映内脏感觉功能。②3组不同扩张压力（20、40、60mmHg）下,旋毛虫急性感染2、8周后（以相同年龄及相同饲养环境的大鼠为对照）腹壁肌电放电次数均显著增加,80mmHg组差异无统计学意义;提示旋毛虫急性感染后可导致内脏高敏感性,该效应可持续至少8周。③在急性感染后2周,外周血CD4＋CD25＋/CD4＋明显减少,而至模型诱导成功8周后,血CD4＋CD25＋/CD4＋比例趋于正常。[结论]旋毛虫PI-IBS早期存在内脏敏感性增高及调节性T细胞下调增高,晚期调节性T细胞趋于正常,而内脏高敏感性持续存在。     

Corticotropin-releasing hormone receptor 1 antagonist blocks brain-gut activation induced by colonic distention in rats

BACKGROUND & AIMS: The corticotropin-releasing hormone receptor 1 mediates stress-induced changes in colonic motor activity and emotion. We tested the hypothesis that pretreatment with JTC-017, a specific corticotropin-releasing hormone receptor 1 antagonist, blocks colorectal distention-induced hippocampal noradrenaline release and visceral perception in rats. We also investigated whether pretreatment with JTC-017 blocks acute or chronic colorectal distention-induced adrenocorticotropic hormone release, anxiety, and stress-induced changes in colonic motility. METHODS: Rats were pretreated intrahippocampally with alpha-helical corticotropin-releasing hormone (1.25 microg/kg; vehicle), a nonspecific corticotropin-releasing hormone receptor antagonist, or intraperitoneally with JTC-017 (10 mg/kg). Hippocampal noradrenaline release after microdialysis and the frequency of abdominal contractions were measured in response to acute colorectal distention. Plasma adrenocorticotropic hormone levels, anxiety-related behavior, and stress-induced changes in colonic motility were evaluated after acute or chronic colorectal distention followed by exposure to an elevated plus maze. RESULTS: Administration of alpha-helical corticotropin-releasing hormone or JTC-017 significantly attenuated hippocampal noradrenaline release and reduced the frequency of abdominal contractions induced by acute distention. In addition, JTC-017 significantly reduced plasma adrenocorticotropic hormone and anxiety after acute distention. After chronic distention, changes in plasma adrenocorticotropic hormone and anxiety were not significant because of habituation. In contrast, a significant increase in fecal pellet output during the elevated plus maze was observed after chronic distention. This increase in fecal pellet output was blocked by pretreatment with JTC-017. CONCLUSIONS: Our results suggest that JTC-017, a specific corticotropin-releasing hormone receptor 1 antagonist, attenuates hippocampal noradrenaline release, visceral perception, adrenocorticotropic hormone release, and anxiety after acute colorectal distention in rats. In addition, JTC-017 blocks stress-induced changes in colonic motility after chronic colorectal distention in rats.     

Regional cerebral blood flow during gastric balloon distention in functional dyspepsia

BACKGROUND & AIMS: Hypersensitivity to proximal gastric distention as a result of abnormal central nervous system processing of visceral stimuli is a possible pathophysiologic mechanism in functional dyspepsia (FD). Increasing evidence suggests involvement of both lateral and medial pain systems in normal visceral sensitivity and aberrant brain activation patterns in visceral hypersensitivity. We hypothesized that there is involvement of aberrant brain activation in FD with hypersensitivity to gastric distention. Our aim was to investigate regional cerebral blood flow during painful proximal gastric distention in hypersensitive FD. METHODS: Brain (15)O-water positron emission tomography was performed in 13 FD patients with symptoms of gastric hypersensitivity during 3 conditions: no distention, sham distention, and isobaric distention to unpleasant or painful sensation. Pain, discomfort, nausea, and bloating during maximal distention were rated on visual analogue scales. Data were analyzed using statistical parametric mapping. RESULTS: The threshold for painful distention was 6.6 +/- 3.8 mm Hg greater than the minimal distending pressure. At the corrected P level of less than .05, subtraction analysis (painful distention - no distention) showed activations in bilateral gyrus precentralis, bilateral gyrus frontalis inferior, bilateral gyrus frontalis medialis, bilateral gyrus temporalis superior, bilateral cerebellar hemisphere, and left gyrus temporalis inferior. Sham distention minus no distention showed no activations. CONCLUSIONS: Similar to healthy volunteers, proximal stomach distention in FD activates components of the lateral pain system and bilateral frontal inferior gyri, putatively involved in regulation of hunger and satiety. In hypersensitive FD, these activations occur at significantly lower distention pressures. In contrast to findings in normosensitivity, none of the components of the medial pain system were significantly activated.     

Acupuncture inhibition on neuronal activity of spinal dorsal horn induced by noxious colorectal distention in rat

AIM: To observe how acupuncture stimulation influences the visceral nociception in rat and to clarify the interactions between acupuncture or somatic input and visceral nociceptive inputs in the spinal dorsal horn. These will provide scientific base for illustrating the mechanism of acupuncture on visceral pain. METHODS: Experiments were performed on Sprague-Dawley rats and the visceral nociceptive stimulus was generated by colorectal distention (CRD). Unit discharges from individual single neuron were recorded extracellularly with glass-microelectrode in L1-3 spinal dorsal horn. Acupuncture stimulation was applied at contralateral heterotopic acupoint and ipsilateral homotopic acupoint, both of which were innervated by the same segments that innervate also the colorectal-gut. RESULTS: The visceral nociception could be inhibited at the spinal level by the heterotopic somatic mechanical stimulation and acupuncture. The maximal inhibition was induced by acupuncture or the somatic noxious stimulation at spinal dorsal horn level with inhibiting rate of 68.61% and 60.79%, respectively (P<0.01 and <0.001). In reversible spinalized rats (cervical-thoracic cold block) both spontaneous activity and responses to CRD increased significantly in 16/20 units examined, indicating the existence of tonic descending inhibition. The inhibition of acupuncture on the noxious CRD disappeared totally in the reversible spinalized rats (P<0.001). CONCLUSION: The inputs of noxious CRD and acupuncture may interact at the spinal level. The nociceptive visceral inputs could be inhibited by acupuncture applied to hetero-topic acupoint. The effect indicates that the spinal dorsal horn plays a significant role in mediating the inhibition of acupuncture and somatic stimulation on the neuronal response to the noxious visceral stimulation and the inhibition is modulated by upper cervical cord and/or supra-spinal center.     

Electroacupuncture alleviates stress-induced visceral hypersensitivity through an opioid system in rats

AIM:To investigate whether stress-induced visceral hypersensitivity could be alleviated by electroacupuncture(EA) and whether EA effect was mediated by endogenous opiates.METHODS:Six to nine week-old male SpragueDawley rats were used in this study.Visceral hypersensitivity was induced by a 9-d heterotypic intermittent stress(HIS) protocol composed of 3 randomly stressors,which included cold restraint stress at 4?℃ for 45 min,water avoidance stress for 60 min,and forced swimming stress for 20 min,in adult male rats.The extent of visceral hypersensitivity was quantified by electromyography or by abdominal withdrawal reflex(AWR) scores of colorectal distension at different distention pressures(20 mmHg,40 mmHg,60 mmHg and 80 mmHg).AWR scores either 0,1,2,3 or 4 were obtained by a blinded observer.EA or sham EA was performed at classical acupoint ST-36(Zu-San-Li) or BL-43(Gao-Huang) in both hindlimbs of rats for 30 min.Naloxone(NLX) or NLX methiodide(m-NLX) was administered intraperitoneally to HIS rats in some experiments.RESULTS:HIS rats displayed an increased sensitivity to colorectal distention,which started from 6 h(the first measurement),maintained for 24 h,and AWR scores returned to basal levels at 48 h and 7 d after HIS compared to pre-HIS baseline at different distention pressures.The AWR scores before HIS were 0.6 ± 0.2,1.3 ± 0.2,1.9 ± 0.2 and 2.3 ± 0.2 for 20 mmHg,40 mmHg,60 mmHg and 80 mmHg distention pressures,respectively.Six hours after termination of the last stressor,the AWR scores were 2.0 ± 0.1,2.5 ± 0.1,2.8 ± 0.2 and 3.5 ± 0.2 for 20 mmHg,40 mmHg,60 mmHg and 80 mmHg distention pressures,respectively.EA given at classical acupoint ST-36 in both hindlimbs for 30 min significantly attenuated the hypersensitive responses to colorectal distention in HIS rats compared with sham EA treatment [AWRs at 20 mmHg:2.0 ± 0.2 vs 0.7 ± 0.1,P = 4.23 711 E-4;AWRs at 40 mmHg:2.6 ± 0.2 vs 1.5 ± 0.2,P = 0.00 163;AWRs at 60 mmHg:3.1 ± 0.2 vs 1.9 ± 0.1,P = 0.003;AWRs at 80 mmHg:3.6 ± 0.1 vs 2.4 ± 0.2,P = 0.0023;electromyographic(EMG) at 20 mmHg:24 ± 4.7 vs 13.8 ± 3.5;EMG at 40 mmHg:60.2 ± 6.6 vs 30 ± 4.9,P = 0.00 523;EMG at 60 mmHg:83 ± 10 vs 39.8 ± 5.9,P = 0.00 029;EMG at 80 mmHg:94.3 ± 10.8 vs 49.6 ± 5.9,P = 0.00 021].In addition,EA at the acupuncture point BL-43 with same parameters did not alleviate visceral hypersensitivity in HIS rats.EA in healthy rats also did not have any effect on AWR scores to colorectal distention at distention pressuresof 20 and 40 mmHg.The EA-mediated analgesic effect was blocked by pretreatment with NLX in HIS rats [AWR scores pretreated with NLX vs normal saline(NS) were 2.0 vs 0.70 ± 0.20,2.80 ± 0.12 vs 1.50 ± 0.27,3 vs 2.00 ± 0.15 and 3.60 ± 0.18 vs 2.60 ± 0.18 for 20 mmHg,40 mmHg,60 mmHg and 80 mmHg;P = 0.0087,0.0104,0.0117 and 0.0188 for 20,40,60 and 80 mmHg,respectively].Furthermore,EA-mediated analgesic effect was completely reversed by administration of m-NLX,a peripherally restricted opioid antagonist(EMG pretreated with m-NLX vs NS were 30.84 ± 4.39 vs 13.33 ± 3.88,74.16 ± 9.04 vs 36.28 ± 8.01,96.45 ± 11.80 vs 50.19 ± 8.28,and 111.59 ± 13.79 vs 56.42 ± 8.43 for 20 mmHg,40 mmHg,60 mmHg and 80 mmHg;P = 0.05 026,0.00 034,0.00 005,0.000 007 for 20 mmHg,40 mmHg,60 mmHg and 80 mmHg,respectively).CONCLUSION:EA given at classical acupoint ST-36 alleviates stress-induced visceral pain,which is most likely mediated by opioid pathways in the periphery.