Mechanisms of referred visceral pain: uterine inflammation in the adult virgin rat results in neurogenic plasma extravasation in the skin

Deep electroacupuncture of neurogenic spots attenuates immobilization stress-induced acute hypertension in rats

Background

Our previous studies proved that neurogenic inflammatory spots (or neurogenic spots) have the same physiological features as acupuncture points and that neurogenic spot stimulation generates therapeutic effects in various animal models. However, it is unclear how deeply the neurogenic spots should be stimulated to generate therapeutic effects.

Methods

The effects of acupuncture at various needle depths below the neurogenic spot were examined in a rat immobilization stress-induced hypertension (IMH) model. Electroacupuncture was applied to a neurogenic spot at depths of 1, 2, or 3 mm using a concentric bipolar electrode.

Results

Electrical stimulation of the neurogenic spot at a 3-mm depth most effectively lowered blood pressure compared with controls and stimulation at 1- and 2-mm depths, which was inhibited by pretreatment with a local anesthetic lidocaine. Electrical stimulation of the neurogenic spot or injection of substance P (SP) at a 3-mm depth significantly excited the rostral ventrolateral medulla (rVLM) compared with superficial stimulation. Electrical stimulation applied at a 3-mm depth on neurogenic spots dominantly caused c-fos expression from rVLM and ventrolateral periaqueductal gray (vlPAG) in IMH rats. Pretreatment with resiniferatoxin (RTX) injection into the neurogenic spot to ablate SP or calcitonin gene-related peptide (CGRP) prevented the effects of 3-mm neurogenic spot stimulation on blood pressure in IMH rats. Conversely, artificial injection of SP or CGRP generated anti-hypertensive effects in IMH rats.

Conclusion

Our data suggest that neurogenic spot stimulation at a 3-mm depth generated anti-hypertensive effects through the local release of SP and CGRP and activation of rVLM and vlPAG.

Bladder Pain Sensitivity Is a Potential Risk Factor for Irritable Bowel Syndrome

BACKGROUND

Although dysmenorrhea is a highly prevalent risk factor for irritable bowel syndrome (IBS), the factors underlying this risk are not fully understood. Prior studies support a hypothesis that repeated distressing menstrual pain promotes cross-organ pelvic sensitization with heightened visceral sensitivity.

AIMS

To further explore cross-organ pelvic sensitization we examined the association of dysmenorrhea, provoked bladder pain, and other putative factors with self-reported IBS-domain pain frequency and new onset after 1-year follow up.

METHODS

We measured visceral pain sensitivity with a noninvasive provoked bladder pain test in a cohort of reproductive-aged women, enriched for those reporting moderate-to-severe menstrual pain intensity but without any prior IBS diagnosis (n = 190). We analyzed the relationship between menstrual pain, provoked bladder pain, pain catastrophizing, anxiety, and depression with primary outcomes: (1) frequency of self-reported IBS-domain pain and (2) new onset of IBS-domain pain after 1-year follow up.

RESULTS

All hypothesized factors correlated with the frequency of IBS-domain pain (p's ≤ 0.038). In a cross-sectional model, only menstrual pain (standardized adjusted odds ratio 2.07), provoked bladder pain (1.49), and anxiety (1.90) were independently associated with IBS-domain pain ≥ 2 days/month (C statistic = 0.79). One year later, provoked bladder pain (3.12) was the only significant predictor of new onset IBS-domain pain (C statistic = 0.87).

CONCLUSION

Increased visceral sensitivity among women with dysmenorrhea could lead to IBS. Because provoked bladder pain predicted subsequent IBS, prospective studies should be performed to see if the early treatment of visceral hypersensitivity mitigates IBS.

Myofascial Pelvic Pain: Best Orientation and Clinical Practice. Position of the European Association of Urology Guidelines Panel on Chronic Pelvic Pain

CONTEXT

Despite the high prevalence of a myofascial pain component in chronic pelvic pain (CPP) syndromes, awareness and management of this component are lacking among health care providers.

OBJECTIVE

To summarize the current state of the art for the management of myofascial pain in chronic primary pelvic pain syndromes (CPPPS) according to scientific research and input from experts from the European Association of Urology (EAU) guidelines panel on CPP.

EVIDENCE ACQUISITION

A narrative review was undertaken using three sources: (1) information in the EAU guidelines on CPP; (2) information retrieved from the literature on research published in the past 3 yr on myofascial pelvic pain; and (3) expert opinion from panel members.

EVIDENCE SYNTHESIS

Studies confirm a high prevalence of a myofascial pain component in CPPPS. Examination of the pelvic floor muscles should follow published recommendations to standardize findings and disseminate the procedure. Treatment of pelvic floor muscle dysfunction and pain in the context of CPP was found to contribute to CPP control and is feasible via different physiotherapy techniques. A multidisciplinary approach is the most effective.

CONCLUSIONS

Despite its high prevalence, the myofascial component of CPP has been underevaluated and undertreated to date. Myofascial pain must be assessed in all patients with CPPPS. Treatment of the myofascial pain component is relevant for global treatment success. Further studies are imperative to reinforce and better define the role of each physiotherapy technique in CPPPS.

PATIENT SUMMARY

Pain and inflammation of the body's muscle and soft tissues (myofascial pain) frequently occurs in pelvic pain syndromes. Its presence must be evaluated to optimize management for each patient. If diagnosed, myofascial pain should be treated.

Advancing the Understanding of Acupoint Sensitization and Plasticity Through Cutaneous C-Nociceptors

Acupoint is the key area for needling treatment, but its physiology is not yet understood. Nociceptors, one of the responders in acupoints, are responsible for acupuncture manipulation and delivering acupuncture signals to the spinal or supraspinal level. Recent evidence has shown that various diseases led to sensory hypersensitivity and functional plasticity in sensitized acupoints, namely, acupoint sensitization. Neurogenic inflammation is the predominant pathological characteristic for sensitized acupoints; however, the underlying mechanism in acupoint sensitization remains unclear. Recent studies have reported that silent C-nociceptors (SNs), a subtype of C nociceptors, can be “awakened” by inflammatory substances released by sensory terminals and immune cells under tissue injury or visceral dysfunction. SNs can transform from mechano-insensitive nociceptors in a healthy state to mechanosensitive nociceptors. Activated SNs play a vital role in sensory and pain modulation and can amplify sensory inputs from the injured tissue and then mediate sensory hyperalgesia. Whether activated SNs is involved in the mechanism of acupoint sensitization and contributes to the delivery of mechanical signals from needling manipulation remains unclear? In this review, we discuss the known functions of cutaneous C nociceptors and SNs and focus on recent studies highlighting the role of activated SNs in acupoint functional plasticity.

Alteration in Activity Patterns of Cows as a Result of Pain Due to Health Conditions

Simple Summary

There are several conditions and diseases considered painful to cattle. One reason for the inconsistency in pain recognition and thus pain relief in cattle is the inadequate ability to identify and assess pain. In fact, both increased and/or reduced daily lying time can be indicative of pain in cattle. This review helps to properly interpret pain in cows through behavioural activity patterns and explores whether pain relief is capable to restore their normal activity.

Abstract

The main conditions and diseases considered painful in dairy cows are mastitis, lameness, calving (including dystocia and caesarean section) and metritis. The cattle literature reports that deviation from normal daily activity patterns (both increased and/or reduced daily lying time) can be indicative of painful conditions and diseases in cows. This narrative review discusses on how pain due to several health conditions in dairy cows modifies its activity pattern and explores if non-steroidal anti-inflammatory drugs (NSAIDs) are capable of restoring it. Divergent outcomes may differ depending upon the painful cause, the severity and the moment, and consequently its interpretation should be properly explained. For instance, cows with clinical mastitis reduced their time lying and increased the number of lying bouts and stepping due to pain caused by the swollen udder when cows are lying. However, lame cows show longer lying times, with a lower number of lying bouts and longer and more variable lying bouts duration, as compared to non-lame cows. When the relationship between painful disorders and daily activity patterns is studied, factors such as parity, bedding type and severity of disease are important factors to take into consideration. The potential benefits of the NSAIDs treatment in painful health disorders depend upon the type of drug administered, its dosage and administration mode, and the time of administration relative to the painful health disorder. This narrative review can be used as a tool to properly interpret and grade pain in cows through behavioural activity patterns and proposes directions for future investigations.

Eliapixant is a selective P2X3 receptor antagonist for the treatment of disorders associated with hypersensitive nerve fibers

ATP-dependent P2X3 receptors play a crucial role in the sensitization of nerve fibers and pathological pain pathways. They are also involved in pathways triggering cough and may contribute to the pathophysiology of endometriosis and overactive bladder. However, despite the strong therapeutic rationale for targeting P2X3 receptors, preliminary antagonists have been hampered by off-target effects, including severe taste disturbances associated with blocking the P2X2/3 receptor heterotrimer. Here we present a P2X3 receptor antagonist, eliapixant (BAY 1817080), which is both highly potent and selective for P2X3 over other P2X subtypes in vitro, including P2X2/3. We show that eliapixant reduces inflammatory pain in relevant animal models. We also provide the first in vivo experimental evidence that P2X3 antagonism reduces neurogenic inflammation, a phenomenon hypothesised to contribute to several diseases, including endometriosis. To test whether eliapixant could help treat endometriosis, we confirmed P2X3 expression on nerve fibers innervating human endometriotic lesions. We then demonstrate that eliapixant reduces vaginal hyperalgesia in an animal model of endometriosis-associated dyspareunia, even beyond treatment cessation. Our findings indicate that P2X3 antagonism could alleviate pain, including non-menstrual pelvic pain, and modify the underlying disease pathophysiology in women with endometriosis. Eliapixant is currently under clinical development for the treatment of disorders associated with hypersensitive nerve fibers.

A novel visceral pain model of uterine cervix inflammation in rat

Treatment of visceral pain originating from the uterine cervix is a substantial clinical problem. The underlying mechanisms of such visceral pain remain unclear mainly due to a lack of reliable model. This study aimed to develop and evaluate the performance of a rat model of pain induced by uterine cervix inflammation. Rats were randomized to six groups according to the solution injected into the uterine cervix: normal saline, vehicle, capsaicin (0.3 mg, 0.6 mg, 0.9 mg), capsaicin 0.9 mg + morphine (n = 15 in each group). Spontaneous behaviors after cervical injection were recorded by a computerized video system and analyzed offline. An equation for calculating a novel pain score was derived from particular behaviors, based on Pearson's correlation analysis and regression analysis. c-Fos expression in the spinal cord was detected. The pain score and c-fos expression in the spinal cord were highest in the 0.9 mg capsaicin group and lowest in the normal saline and vehicle groups (P < 0.05). Intrathecal morphine significantly decreased the pain score (P < 0.05) and c-fos expression in the spinal cord (P < 0.05). Injection of capsaicin into the uterine cervix in rats could be a practical model of inflammatory cervical pain, which can be evaluated using our novel pain score. This model will provide further insight into the mechanism underlying visceral pain originating from the uterine cervix.

Chemotherapeutic Agent-Induced Vulvodynia, an Experimental Model

Vulvodynia is a chronic clinical condition associated with vulvar pain that can impair the sexual, social, and psychological life of women. There is a need for more research to develop novel strategies and therapies for the treatment of vulvodynia. Vulvodynia in experimental animal models induced via infections, allergens, and diabetes are tedious and with lessor induction rate. The objective of the study was to explore the possibility of inducing vulvodynia using a chemotherapeutic agent in a rodent model. Paclitaxel is commonly used in treating breast and ovarian cancer, whose dose-limiting side effect is peripheral neuropathy. Studies have shown that peripheral neuropathy is one of the etiologies for vulvodynia. Following paclitaxel administration (2 mg/kg i.p.), the intensity of vulvar hypersensitivity was assessed using a series of von Frey filaments (0.008 to 1 g) to ensure the induction of vulvodynia. Vulvodynia was induced from day 2 and was well sustained for 11 days. Furthermore, the induced vulvodynia was validated by investigating the potentiation of a flinch response threshold, upon topical application and systemic administration of gabapentin, a commonly used medication for treating neuropathic pain. The results demonstrate that vulvodynia was induced due to administration of paclitaxel. The fact that chemotherapeutic agent-induced vulvodynia was responsive to topical and parenterally administered gabapentin provides validity to the model. The study establishes a new, relatively simple and reliable animal model for screening drug molecules for vulvar hypersensitivity.

Electroacupuncture at Neurogenic Spots in Referred Pain Areas Attenuates Hepatic Damages in Bile Duct-Ligated Rats

Visceral pain frequently produces referred pain at somatic sites due to the convergence of somatic and visceral afferents. In skin overlying the referred pain, neurogenic spots characterized by hyperalgesia, tenderness and neurogenic inflammation are found. We investigated whether neurogenic inflammatory spots function as acupoints in the rat model of bile duct ligation-induced liver injury. The majority of neurogenic spots were found in the dorsal trunk overlying the referred pain and matched with locations of acupoints. The spots, as well as acupoints, showed high electrical conductance and enhanced expression of the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP). Electroacupuncture at neurogenic spots reduced serum hepatocellular enzyme activities and histological patterns of acute liver injury in bile duct ligation (BDL) rats. The results suggest that the neurogenic spots have therapeutic effects as acupoints on hepatic injury in bile-duct ligated rats.

The role of substance P in acupuncture signal transduction and effects

BACKGROUND

Acupuncture has been used to treat a wide variety of diseases, disorders, and conditions for more than 2500 years. While the anatomical structures of acupuncture points (or acupoints) are largely unknown, our previous studies have suggested that many acupoints can be identified as cutaneous neurogenic inflammatory spots (neurogenic spots or Neuro-Sps), arising from the release of neuropeptides from activated small diameter sensory afferents at topographically distinct body surfaces due to the convergence of visceral and somatic afferents. In turn, the neuropeptides released during neurogenic inflammation may play important roles in the effects of acupuncture as well as the formation of active acupoints. Thus, the present study has focused on the role of substance P (SP) in acupuncture signal transduction and effects.

METHODS

Neuro-Sps were detected by using in vivo fluorescence imaging after intravenous injection of Evans blue dye (EBD) and compared with traditional acupoints. Stimulatory effects of the Neuro-Sps were examined in a rat model of immobilization-induced hypertension (IMH). The roles of increased SP in Neuro-Sps were also investigated by using immunohistochemistry, in vivo single-fiber peripheral nerve recordings, and in vivo midbrain extracellular recordings.

RESULTS

Neurogenic inflammation quickly appeared at acupoints on the wrist and was fully developed within 15 min in IMH model. The Neuro-Sps showed an increased release of SP from afferent nerve terminals. Mechanical stimulation of these Neuro-Sps increased cell excitability in the midbrain (rostral ventrolateral medulla) and alleviated the development of hypertension, which was blocked by the local injection of the SP receptor antagonist CP-99994 into Neuro-Sps prior to acupuncture and mimicked by the local injection of capsaicin. Single fiber recordings of peripheral nerves showed that increased SP into the Neuro-Sps elevated the sensitivity of A- and C-fibers in response to acupuncture stimulation. In addition, the discharge rates of spinal wide dynamic response (WDR) neurons significantly increased following SP or acupuncture treatment in Neuro-Sps in normal rats, but decreased following the injection of CP-99994 into Neuro-Sps in IMH rats.

CONCLUSIONS

Our findings suggest that SP released during neurogenic inflammation enhances the responses of sensory afferents to the needling of acupoints and triggers acupuncture signaling to generate acupuncture effects.

Pharmacological modulation of voltage-gated sodium (NaV) channels alters nociception arising from the female reproductive tract

Dyspareunia, also known as vaginal hyperalgesia, is a prevalent and debilitating symptom of gynaecological disorders such as endometriosis and vulvodynia. Despite this, the sensory pathways transmitting nociceptive information from female reproductive organs remain poorly characterised. As such, the development of specific treatments for pain associated with dyspareunia is currently lacking. Here, we examined, for the first time, (1) the mechanosensory properties of pelvic afferent nerves innervating the mouse vagina; (2) the expression profile of voltage-gated sodium (NaV) channels within these afferents; and (3) how pharmacological modulation of these channels alters vaginal nociceptive signalling ex vivo, in vitro, and in vivo. We developed a novel afferent recording preparation and characterised responses of pelvic afferents innervating the mouse vagina to different mechanical stimuli. Single-cell reverse transcription-polymerase chain reaction determined mRNA expression of NaV channels within vagina-innervating dorsal root ganglia neurons. Vagina-innervating dorsal root ganglia neuroexcitability was measured using whole-cell patch-clamp electrophysiology. Nociception evoked by vaginal distension was assessed by dorsal horn neuron activation within the spinal cord and quantification of visceromotor responses. We found that pelvic afferents innervating the vagina are tuned to detect various mechanical stimuli, with NaV channels abundantly expressed within these neurons. Pharmacological modulation of NaV channels (with veratridine or tetrodotoxin) correspondingly alters the excitability and mechanosensitivity of vagina-innervating afferents, as well as dorsal horn neuron activation and visceromotor responses evoked by vaginal distension. This study identifies potential molecular targets that can be used to modulate vaginal nociceptive signalling and aid in the development of approaches to manage endometriosis and vulvodynia-related dyspareunia.

Enhanced spinal neuronal responses as a mechanism for increased number and size of active acupoints in visceral hyperalgesia

Acupuncture has been used to treat a variety of illness and involves the insertion and manipulation of needles into specific points on the body (termed “acupoints”). It has been suggested that acupoints are not merely discrete, static points, but can be dynamically changed according to the pathological state of internal organs. We investigated in a rat model of mustard oil (MO)-induced visceral hyperalgesia whether the number and size of acupoints were modified according to the severity of the colonic pain, and whether the changes were associated with enhanced activity of the spinal dorsal horn. In MO-treated rats, acupoints showing neurogenic inflammation (termed “neurogenic spots” or Neuro-Sps) were found both bilaterally and unilaterally on the leg. The number and size of these acupoints increased along with increasing doses of MO. Electroacupuncture of the acupoints generated analgesic effects on MO-induced visceral hypersensitivity. The MO-treated rats showed an increase in c-Fos expression in spinal dorsal horn neurons and displayed increased evoked activity and a prolonged after-discharge in spinal wide dynamic response (WDR) neurons in response to colorectal distension. Increased number and size of neurogenic inflammatory acupoints following MO treatment were reduced by inhibiting AMPA and NMDA receptors in the spinal cord. Our findings suggest that acupoints demonstrate increased number and size along with severity of visceral pain, which may be associated with enhanced neuronal responses in spinal dorsal horn neurons.

Paired mechanical and electrical acupuncture of neurogenic spots induces opioid-mediated suppression of hypertension in rats

While our recent studies have suggested that effective acupoints display neurogenic inflammation and can be identified as neurogenic spots (Neuro-Sps), the optimal stimulation conditions and the underlying mechanisms remain uncharacterized. We developed a combined mechano-electrical acupuncture device (MEA) and examined the effects of acupuncture at Neuro-Sps on systolic blood pressure (BP) in a rat model of immobilization-induced hypertension (IMH) and the mediation of endogenous opioid systems in its effect. Cutaneous neurogenic spots were found mostly in the forelimb. Electrical and mechanical acupuncture of Neuro-Sps increased 22-kHz ultrasonic vocalizations (USVs), c-Fos expression and cell excitability in the midbrain and synergistically alleviated the development of hypertension following immobilization stress, which was prevented by administration of the opioid antagonist naloxone into the rostral ventrolateral medulla (rVLM). These findings suggest that mechanical and electrical stimulation at Neuro-Sps suppresses the development of hypertension via mediation of the endogenous opioid system.

Electroacupuncture relieved visceral and referred hindpaw hypersensitivity in colitis rats by inhibiting tyrosine hydroxylase expression in the sixth lumbar dorsal root ganglia

Irritable bowel syndrome patients frequently complain of pain in body regions somatotopically distinct from the gut, suggesting the involvement of an exaggerated signaling process in both visceral and somatic sensory pathways. Increasing evidence has shown that sprouting of tyrosine hydroxylase immunoreactive (TH-IR) fibers toward sensory neurons in dorsal root ganglia maintains and exacerbates the neuropathic and inflammatory pain, as well as colonic inflammation. The aim of the present study was to determine whether electroacupuncture could alleviate the visceral and secondary somatic hyperalgesia in colitis rats by suppressing the TH-IR expression in related dorsal root ganglia. After trinitrobenzene sulfonic acid irritation, rats developed inflammatory tissue damage in the distal colon, which was accompanied by visceral hypersensitivity and secondary hind paw hyperalgesia, as indicated by enhanced visceromotor response to colorectal distension and decreased mechanical and thermal withdrawal latency of the hind paw. Additionally, excessive TH-IR fibers sprouted toward calcitonin gene-related peptide immunoreactive sensory neurons, and TH-IR neurons also increased in the sixth lumbar dorsal root ganglia of colitis rats. Both electroacupuncture and guanethidine attenuated visceral and referred hind paw hyperalgesia by inhibiting the over-expression of TH-IR neurons and fibers in the sixth lumbar dorsal root ganglia. Moreover local inflammatory damage in the distal colon was restored after 7 days of electroacupuncture intervention. These results suggest that electroacupuncture relieved visceral and referred hind paw hypersensitivity in colitis rats by inhibiting TH expression in the sixth lumbar dorsal root ganglia.

Pathophysiology and Management of Abdominal Myofascial Pain Syndrome (AMPS): A Three-Year Prospective Audit of a Management Pathway in 120 Patients

Background

Chronic abdominal wall pain arising from the myofascial structures is termed abdominal myofascial pain syndrome and is an important cause of refractory abdominal pain that utilizes significant health care costs. The current literature is vague on its management.

Design

The author presents a prospective audit of a structured management pathway and discusses the pathophysiology of abdominal myofascial pain syndrome. The objective was to identify an effective and durable treatment for the individual patient and evaluate patient satisfaction with the management pathway.

Methods

Over a three-year period, 120 patients diagnosed with abdominal myofascial pain syndrome were included in a structured management pathway and were prospectively audited at a tertiary care university hospital.

Results

Patient satisfaction with the pathway was high. Trigger point injection with local anesthetic was useful in diagnosis but ineffective in providing durable relief. Trigger point injection with steroids and pulsed radiofrequency treatment of trigger point(s) were effective therapeutic interventions, providing durable relief lasting six months in 32% and 60%, respectively. There was improvement reported in pain intensity scores, quality of life, anxiety, and depression scores following the interventional management of abdominal myofascial pain syndrome.

Conclusions

Abdominal myofascial pain syndrome is often unrecognized, especially in patients with a history of visceral inflammation. The suggested pathway may be an option in its management. Trigger point injection with steroids may have a role in the differential diagnosis of chronic abdominal pain.

Neuropeptides SP and CGRP Underlie the Electrical Properties of Acupoints

Electrical skin measurements at acupuncture points (acupoints) have been utilized as a diagnostic and therapeutic aid for more than 50 years. Although acupoints are described as having distinct electrical properties, such as high conductance and low impedance, the underlying mechanisms are currently unknown. The present study investigated in a rat model of hypertension whether the high conductance at acupoints is a result of the release of the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) during neurogenic inflammation in the referred pain area. When plasma extravasation from neurogenic inflammation was examined by exploring the leakage of intravenously injected Evans blue dye (EBD) to the skin, extravasated EBD was found most frequently in acupoints on the wrist. The increased conductance and temperature at these acupoints occurred during the development of hypertension. The increase in conductance and plasma extravasation at acupoints in hypertensive rats was ablated by cutting median and ulnar nerves, blocking small diameter afferent fibers with resiniferatoxin (RTX) injection into median and ulnar nerves, or antagonizing SP or CGRP receptors in acupoints. In turn, intradermal injection of SP or CGRP resulted in increased conductance and plasma extravasation in naïve rats. Elevated levels of SP and CGRP were found in the acupoints of hypertensive rats. These findings suggest that the high conductance at acupoints is due to vascular leakage following local release of SP and CGRP during neurogenic inflammation.

Nonsteroidal antiinflammatory drug resistance in dysmenorrhea: epidemiology, causes, and treatment

Although nonsteroidal antiinflammatory drugs can alleviate menstrual pain, about 18% of women with dysmenorrhea are unresponsive, leaving them and their physicians to pursue less well-studied strategies. The goal of this review is to provide a background for treating menstrual pain when first-line options fail. Research on menstrual pain and failure of similar drugs in the antiplatelet category suggested potential mechanisms underlying nonsteroidal antiinflammatory drug resistance. Based on these mechanisms, alternative options may be helpful for refractory cases. This review also identifies key pathways in need of further study to optimize menstrual pain treatment.

Acupuncture points can be identified as cutaneous neurogenic inflammatory spots

Acupuncture, a traditional medical procedure practised for over 2000 years in Asia, stimulates specific but poorly defined sites called acupoints. To date, no unique anatomical acupoint structures have been found. However, noxious sensory signals from visceral organs produce hypersensitive spots on the skin (neurogenic spots), caused by cutaneous neurogenic inflammation, in the dermatome that overlaps with visceral afferent innervations. Here, we show that an acupoint is one form of neurogenic inflammation on the skin. Various studies have demonstrated that acupoints show mechanical hypersensitivity and have high electrical conductance. Stimulation of acupoints produces needling sensations caused by the activation of small diameter afferent nerve fibres and therapeutic effects on the associated visceral organs, which is likely due to the release of endogenous opioids. The present study provides experimental evidence that neurogenic spots exhibit all the characteristics of the acupoints listed above. In addition, the stimulation of neurogenic spots by electrical, mechanical, or chemical means alleviated pathological conditions in rat colitis and hypertension models via the endogenous opioid system. Our results suggest that acupoints associated with internal organs may be identical to neurogenic inflammatory spots on the skin, which are produced by activation of somatic afferents in abnormal conditions of visceral organs.

The Effects of Platelet-Activating Factor on Uterine Contractility, Perfusion, Hypoxia, and Pain in Mice

It is widely hypothesized that menstrual pain is triggered by prostaglandin synthesis that evokes high-pressure uterine contractions and ischemia. However, the effects of molecules implicated in menstrual pain on uterine contractility, perfusion, and oxygenation in vivo have been rarely demonstrated. Studies in women that do not respond to nonsteroidal anti-inflammatory drugs (NSAIDs) have reported elevated levels of platelet-activating factor (PAF). To establish in vivo evidence of PAF's capability to impair uterine homeostasis and to elicit visceral pain, we examined the effects of the PAF receptor agonist (carbamyl PAF [CPAF]) in comparison to other molecules hypothesized to play a role in uterine pain in mice. Uterine pressure was increased by oxytocin, prostaglandin F2α (PGF2α), and CPAF. Even in the absence of inflammatory molecules, uterine contractions reduced uterine oxygenation by 38%. CPAF reduced uterine perfusion by 40% ± 8% and elicited further oxygen desaturation approaching hypoxia (9.4 ± 3.4 mm Hg Pao₂). Intraperitoneal injections of CPAF and PGF2α evoked visceral pain and pelvic hyperalgesia in awake wild-type mice. However, pain was not observed in identically injected PAF-receptor knockout mice. Thus, our model provides a demonstration that a molecule implicated in NSAID-resistant dysmenorrhea has a detrimental effect on uterine homeostasis and is capable of causing visceral pain. Our results support the general hypothesis that menstrual cramps are caused by uterine contractions, impaired perfusion, and reduced oxygenation. Since this study was limited to mice, confirmation of these results in humans would be valuable for development of novel therapeutics targeted at inflammatory precursors, contractility, perfusion, and tissue oxygenation.

Cutaneous neurogenic inflammation in the sensitized acupoints induced by gastric mucosal injury in rats

BACKGROUND

In acupuncture practice, the most important step is to confirm the location of a sensitized acupoint which reflects a diagnosis and can be stimulated with a specialized needle to treat the disease. Abnormal symptoms such as hyperalgesia or allodynia at the sensitized acupoints in patients with visceral disorders are considered to be in relation with referred pain and neurogenic inflammation. Yet, limited study has investigated the cutaneous neurochemical changes of the sensitized acuponits.

METHODS

The resent study developed an animal model of gastric mucosal injury (GMI) by HCl administered into the stomach of the rats. Evans Blue (EB) dye was applied by injection of tail vein after mucosal damage to observe the neurogenic plasma extravasation dots in the skin of the rats. The EB dots extravagated in the skin were compared with locations of acupoints. Immnohistochemistry analysis was used to detect the expression of calcitonin gene-related peptide (CGRP)- or substance P (SP)-labeled nerve fibers, histamine (HA)-, serotonin (5-HT)-, and tryptase-labeled cells in EB dots. Images were recorded and analyzed by Confocal imaging system and Olympus Image Processing Software.

RESULTS

The results showed that GMI resulted in neurogenic plasma extravasation in the skin of the acupoints over the back and abdomen, which mostly occurred in the T9-11 dermatomere. The EB extravasation dots appeared after GMI and disappeared gradually during the natural self-recovery of the gastric mucosa. More SP and CGRP positive nerve fibers were distributed in EB dots than that in regions beside EB dots and in the control, mostly distributed in the nerve fibers around both the vessels and root of hair follicle. Mast cells also aggregated and degranulated to release algogenic substances of 5-HT and HA around the vessels in areas of the EB dots.

CONCLUSIONS

Our results indicates that the mechanism of EB extravasation in the skin of the acupoints induced by GMI are closely related to neurogenic inflammation, and that the high expression of local allergic substances and nociceptive neuropeptides in the local skin including SP, CGRP, HA, 5-HT, and mast cell tryptase may be the underlying mechanism of the acupoint sensitization.

Central neuromechanisms underlying control of intragastric pressure through acupuncture at Zusanli (ST36) in rats: the upper cervical cord is the key link between the ascending and descending pathways

Sensory inputs stimulated by Zusanli (ST36) acupuncture in the abdomen are known to converge in the upper cervical cord. However, it is unclear whether these inputs are subsequently conveyed to the hypothalamic paraventricular nucleus and what kind of afferent fibers are involved. We focused on the upper cervical cord, where afferent inputs converge, and detected c-fos expression in oxytocinergic neurons. We found that Zusanli acupuncture therapy effectively elevated intragastric pressure, but inhibited expression of c-fos in oxytocinergic neurons of the paraventricular nucleus in upper cervical cord injured rats. These Zusanli acupuncture effects remained even after complete dorsal cord transection. However, after complete transection of the spinal cord or dorsolateral funiculus, the effects were significantly attenuated and even disappeared. These findings suggest that the paraventricular nucleus is responsible for pooling and integrating signals from the Zusanli acupuncture and sensory information from the intragastric pressure variation, thereby contributing to the regulation of intragastric pressure. The upper cervical cord serves as the key link between ascending and descending pathways, which conveys afferent inputs to the paraventricular nucleus through the dorsolateral funiculus.

Spontaneous extracranial hemorrhagic phenomena in primary headache disorders: A systematic review of published cases

Background Head pain is a cardinal feature of primary headache disorders (PHDs) and is often accompanied by autonomic and vasomotor symptoms and/or signs. Spontaneous extracranial hemorrhagic phenomena (SEHP), including epistaxis, ecchymosis, and hematohidrosis (a disorder of bleeding through sweat glands), are poorly characterized features of PHDs. Aim To critically appraise the association between SEHP and PHDs by systematically reviewing and pooling all reports of SEHP associated with headaches. Methods Advanced searches using the PubMed/MEDLINE, Web of Science, Cochrane Library, Google Scholar, and ResearchGate databases were carried out for clinical studies by combining the terms "headache AND ecchymosis", "headache AND epistaxis", and "headache AND hematohidrosis" spanning all medical literature prior to October 10, 2015. Preferred Reporting Items for Systematic Reviews and Meta-analyses and Meta-analysis of Observational Studies in Epidemiology guidelines were applied. Results A total of 105 cases of SEHP associated with PHDs (83% migraine and 17% trigeminal autonomic cephalgias) were identified (median age 27 years, male to female ratio 1:2.3); 63% had epistaxis, 33% ecchymosis, and 4% hematohidrosis. Eighty-three percent of studies applied the International Classification of Headache Disorders diagnostic criteria. Eighty percent of the reported headaches were episodic and 20% were chronic. Twenty-four percent of studies reported recurrent episodes of SEHP. Conclusions Our results suggest that SEHP may be rare features of PHDs. Future studies would benefit from the systematic characterization of these phenomena.

Animal Models for the Study of Female Sexual Dysfunction

INTRODUCTION

Significant progress has been made in elucidating the physiological and pharmacological mechanisms of female sexual function through preclinical animal research. The continued development of animal models is vital for the understanding and treatment of the many diverse disorders that occur in women.

AIM

To provide an updated review of the experimental models evaluating female sexual function that may be useful for clinical translation.

METHODS

Review of English written, peer-reviewed literature, primarily from 2000 to 2012, that described studies on female sexual behavior related to motivation, arousal, physiological monitoring of genital function and urogenital pain.

MAIN OUTCOMES MEASURES

Analysis of supporting evidence for the suitability of the animal model to provide measurable indices related to desire, arousal, reward, orgasm, and pelvic pain.

RESULTS

The development of female animal models has provided important insights in the peripheral and central processes regulating sexual function. Behavioral models of sexual desire, motivation, and reward are well developed. Central arousal and orgasmic responses are less well understood, compared with the physiological changes associated with genital arousal. Models of nociception are useful for replicating symptoms and identifying the neurobiological pathways involved. While in some cases translation to women correlates with the findings in animals, the requirement of circulating hormones for sexual receptivity in rodents and the multifactorial nature of women's sexual function requires better designed studies and careful analysis. The current models have studied sexual dysfunction or pelvic pain in isolation; combining these aspects would help to elucidate interactions of the pathophysiology of pain and sexual dysfunction.

CONCLUSIONS

Basic research in animals has been vital for understanding the anatomy, neurobiology, and physiological mechanisms underlying sexual function and urogenital pain. These models are important for understanding the etiology of female sexual function and for future development of pharmacological treatments for sexual dysfunctions with or without pain. Marson L, Giamberardino MA, Costantini R, Czakanski P, and Wesselmann U. Animal models for the study of female sexual dysfunction. Sex Med Rev 2013;1:108-122.

Assessment of visceral pain associated with metritis in dairy cows

Metritis is a common disease in dairy cattle, but to our knowledge, no work has assessed pain associated with this disease. Tissue palpation is commonly used to assess pain in human and veterinary medicine. The objective of this study was to evaluate visceral pain responses during rectal palpation, with and without uterine palpation, in healthy cows and in cows diagnosed with metritis. A total of 49 Holstein dairy cows (mean ± standard deviation parity of 2.8±1.8) were subjected to systematic health checks every 3 d after parturition for 21 d, scoring for vaginal discharge (0 to 4); 13 cows showed a discharge score ≥2 during at least 1 health check and were classified as metritic, whereas 29 cows were classified as healthy and showed no sign of this or any other disease (including mastitis and lameness). Back arch and heart rate variability before examination and during palpation were recorded using video and heart rate monitors. Back arch (cm(2)) on the day of diagnosis was greater in metritic versus healthy cows (1,034±72 vs. 612±48cm(2)), and greater during rectal palpation with uterine palpation versus rectal palpation without uterine palpation (869±45 vs. 777±45cm(2)). Heart rate frequency domain analysis showed that the low-frequency portion was higher in cows with metritis versus healthy cows (16.5±1.2 vs. 12.9±1.0). Time domain analysis showed that the standard deviation between normal to normal interbeat intervals and the root mean square of successive differences both decreased during rectal palpation with uterine palpation versus rectal palpation without uterine palpation (1.9±0.1 vs. 2.5±0.1 and 1.3±0.1 vs. 1.7±0.1, respectively). Together, these results indicate that the inflammation associated with metritis is painful, and that the pain response can be detected during rectal palpation with and without uterine palpation. Rectal palpation with uterine palpation appears to be more aversive than rectal palpation without uterine palpation, suggesting that the former should be avoided when possible.

Female reproductive tract pain: targets, challenges, and outcomes

Pain from the female reproductive tract (FRT) is a significant clinical problem for which there are few effective therapies. The complex neuroanatomy of pelvic organs not only makes diagnosis of pelvic pain disorders difficult but represents a challenge to development of targeted therapies. A number of potential therapeutic targets have been identified on sensory neurons supplying the FRT but our knowledge on the basic neurophysiology of these neurons is limited compared with other viscera. Until this is addressed we can only guess if the new experimental therapies proposed for somatic, gastrointestinal, or bladder pain will translate to the FRT. Once suitable therapeutic targets become clear, the next challenge is drug delivery. The FRT represents a promising system for topical drug delivery that could be tailored to act locally or systemically depending on formulation. Development of these therapies and their delivery systems will need to be done in concert with more robust in vivo and in vitro models of FRT pain.

Animal models of pancreatitis: Can it be translated to human pain study?

Chronic pancreatitis affects many individuals around the world, and the study of the underlying mechanisms leading to better treatment possibilities are important tasks. Therefore, animal models are needed to illustrate the basic study of pancreatitis. Recently, animal models of acute and chronic pancreatitis have been thoroughly reviewed, but few reviews address the important aspect on the translation of animal studies to human studies. It is well known that pancreatitis is associated with epigastric pain, but the understanding regarding to mechanisms and appropriate treatment of this pain is still unclear. Using animal models to study pancreatitis associated visceral pain is difficult, however, these types of models are a unique way to reveal the mechanisms behind pancreatitis associated visceral pain. In this review, the animal models of acute, chronic and un-common pancreatitis are briefly outlined and animal models related to pancreatitis associated visceral pain are also addressed.

The Possible Neuronal Mechanism of Acupuncture: Morphological Evidence of the Neuronal Connection between Groin A-Shi Point and Uterus

Somatovisceral reflex suggested that the somatic stimulation could affect visceral function like acupuncture which treats diseases by stimulating acupoints. The neuronal connection between somatic point and visceral organ was not clear. Uterine pain referred to the groin region has long been recognized clinically. Wesselmann, using neurogenic plasma extravasation method, showed that uterine pain was referred to the groin region through a neuronal mechanism (Wesselmann and Lai 1997). This connection could be considered through the somatovisceral reflex pathway. However, the relay center of this pathway is still not clearly identified. In the present study, bee venom was injected in the groin region to induce central Fos expression to map the sensory innervation of groin region. Pseudorabies virus (PrV), a transneuronal tracer, was injected in the uterus to identify the higher motor control of the uterus. Immunohistochemistry staining revealed the Fos expression and PrV-infected double-labeled neurons in the nucleus of solitary tract (NTS), the dorsal motor nucleus of vagus (DMX), and the paraventricular hypothalamic nucleus (PVN). These results suggest a somatoparasympathetic neuronal connection (groin-spinal dorsal horn-NTS/DMX-uterus) and a somatosympathetic neuronal connection (groin-spinal dorsal horn-NTS-PVN-uterus). These two neuronal connections could be the prerequisites to the neuronal basis of the somatovisceral reflex and also the neuronal mechanism of acupuncture.

Abdominal migraine reviewed from both central and peripheral aspects

Despite the 2%-5% prevalence of abdominal migraine (AM) during childhood, the precise mechanism remains unknown. In this review, we present recent studies on AM and speculate its mechanism from both peripheral and central nervous system aspects. Although the main symptoms of AM exist at the peripheral level, previous studies have reported possible dysfunction of central nervous system, including photophobia, phonophobia and abnormal visual evoked responses. Recently, a case has been reported with AM combined with “Alice in Wonderland” syndrome with visual and/or bodily distortions, which serves as another piece of evidence of central dysfunction. Another case reported an AM patient having peculiar stereotypical ecchymosis in the legs and buttocks associated with pain attack, which implied possible involvement of peripheral nervous system. Although further investigations and accumulation of AM cases are still needed, we believe that the schema hypothesized here is helpful to plan further experimental approach to clarify the mechanism of this peculiar disease.

Endometriosis and abdominal myofascial pain in adults and adolescents

Endometriosis and myofascial pain are common disorders with significant impact on quality of life. Increasingly, these conditions are being recognized as highly interconnected through processes that have been described for more than a century. This review is directed to this interconnection through a description of the relationships of endometriosis to proposed mechanisms of pain and chronic pain physiology; the clinical assessment of myofascial representations of this pain; and an approach to the management of these interconnected disorders.

The immediate effects of sigmoid colon manipulation on pressure pain thresholds in the lumbar spine

Visceral manual therapy is increasingly used by UK osteopaths and manual therapists, but there is a paucity of research investigating its underlying mechanisms, and in particular in relation to hypoalgesia. The aim of this study was to investigate the immediate effects of osteopathic visceral mobilisation on pressure pain thresholds. A single-blinded, randomised, within subjects, repeated measures design was conducted on 15 asymptomatic subjects. Pressure pain thresholds were measured at the L1 paraspinal musculature and 1st dorsal interossei before and after osteopathic visceral mobilisation of the sigmoid colon. The results demonstrated a statistically significant improvement in pressure pain thresholds immediately after the intervention (P<0.001). This effect was not observed to be systemic, affecting only the L1 paraspinal musculature. This novel study provides new experimental evidence that visceral manual therapy can produce immediate hypoalgesia in somatic structures segmentally related to the organ being mobilised, in asymptomatic subjects.

Neurogenic inflammation in the upper digestive tract of the mule duck: effect of a chemical algogen and force-feeding

1.The objectives were to quantify the presence of neurogenic inflammation in 4 regions of the upper digestive tract of anaesthetised ducks (post-pharynx, pseudo-crop, transition between the pseudo-crop and the proventriculus, and proventriculus) after application of HCl stimulation of up to 4 M in the pseudo-crop. 2.The second objective was to quantify the presence of neurogenic inflammation in the same digestive tract regions as mentioned above during 4 feeding periods of foie gras production (rearing, preparation to force-feeding, and second and last meals of the force-feeding period). 3. Extravasation increased above a HCl stimulation threshold of 2 M. Furthermore, more extravasation was observed in the proventriculus compared to the other regions (P < 0·001). 4.Highest extravasation responses were observed in the proventriculus and the pseudo-crop at the end of the preparation period, and in the proventriculus after the second forced meal, compared with the rearing period (P < 0·01), with a return to rearing level at the end of force-feeding. 5.Such a kinetic could be indicative of a relative mildness of the irritant components associated with this feeding practice.

New trends in the treatment and management of myofascial pain syndrome

Myofascial pain syndrome presents a significant physical and financial burden to society. In view of the aging demographics, myofascial pain promises to be an even greater challenge to health care in the future. Myofascial trigger points have been identified as important anatomic and physiologic phenomena in the pathophysiology of myofascial pain. While their pathophysiologic mechanisms are still unclear, emerging research suggests that trigger points may be initiated by neurogenic mechanisms secondary to central sensitization, and not necessarily by local injury. A variety of treatments are employed in the management of trigger points, including manual therapy, electrotherapy, exercise, and needle therapy. Therapeutic ultrasound demonstrates significant potential as a safe, cost-effective, and relatively noninvasive therapeutic alternative in the treatment and management of this modern day medical enigma.

Sciatic nerve injury induces functional pro-nociceptive chemokine receptors in bladder-associated primary afferent neurons in the rat

Visceral sensory afferents during disease or following injury often produce vague, diffuse body sensations, and pain referred to somatic targets. Alternatively, injury due to trauma or disease of somatic nerve targets can also lead to referred pain in visceral targets via a somatovisceral reflex. Both phenomenons are thought to be due to convergence of visceral and somatic afferents within the spinal cord. To investigate a potential peripheral influence for referred pain in visceral targets following somatic nerve injury, we examined whether a sciatic nerve injury known to produce hindpaw tactile hyperalgesia alters the frequency of micturition and the sensitivity of bladder-associated sensory neurons to pro-nociceptive chemokines. Adult female Sprague-Dawley rats received injections of cholera toxin B subunit conjugated to 555 into urinary bladder wall to retrogradely label visceral primary afferent neurons. After 7 days, the right sciatic nerve of these animals was subjected to a lysophosphatidylcholine (LPC)-induced focal demyelination injury. Pre- and post-injury tactile sensitivity in the hind paw and micturition frequency were assayed. Animals were allowed to survive for 14-28 days. Lumbosacral and lumbar dorsal root ganglia (DRG) ipsilateral to the nerve injury were acutely dissociated from sham and nerve injured animals. Bladder wall-associated sensory neurons identified via the retrograde marker were assayed for fluxes in intracellular calcium following administration of pro-nociceptive chemokines. The assayed chemokines included monocyte chemoattractant protein-1 (MCP1/CCL2) and stromal cell derived factor-1 alpha (SDF1/CXCL12). LPC nerve injured animals exhibited tactile hyperalgesia and increased micturition frequency for at least 28 days. Focal demyelination of the sciatic nerve also increased the number of injured L₄L₅ and non-injured L₆-S₂ bladder-associated sensory neurons that responded to MCP1 and SDF1 when compared with sensory neurons derived from uninjured naïve and sham-injured control animals. Taken together, these data suggest that some visceral hypersensitivity states may have a somatic origin. More importantly, nociceptive somatovisceral sensation may be mediated by upregulation of chemokine signaling in visceral sensory neurons.

[Anatomy and physiology of chronic pelvic and perineal pain]

OBJECTIVE

To determine the mechanisms involved in the regulation of pelvic and perineal pain.

MATERIAL AND METHODS

Description of the anatomical pathways mediating nociceptive transmission and the physiological mechanisms of pain control.

RESULTS

The pelvis and perineum do not have the same innervation. The pelvis is innervated by the sympathetic nervous system, while the perineum is innervated by the somatic nervous system via sacral nerve roots (and the pudendal nerve) and the thoracolumbar sympathetic nervous system. Systems of regulation of nociceptive messages are present at all levels of the nervous system. Two of these systems are essential: one situated in the dorsal horns of the spinal cord (gate control) and another supraspinal system (descending inhibitory system). Via a series of filters and amplifiers, the nociceptive message is integrated and analysed in the cerebral cortex, with interconnections with various areas, especially involving memory and emotion.

CONCLUSION

Excessive nociceptive stimulation must be clearly distinguished from dysfunction of pain control systems (for example neuropathic pain). The definition of pain: "unpleasant sensory and emotional experience related to a real or potential tissue lesion or described in terms of such a lesion" clearly indicates that not all pain is inevitably related to a persistent and visible cause. Convergence phenomena identified between nerve pathways of the various systems and pelvic organs account for the possible diffusion of visceral nociceptive messages and interactions between organs. A good knowledge of anatomy is essential to understand the patient's description of the pain, and a good knowledge of the modalities of pain control is essential to correctly adapt treatment strategies (drugs, neurostimulation, psycho-behavioural therapy, etc.).

Abdominal migraine associated with ecchymosis of the legs and buttocks: does the symptom imply an unknown mechanism of migraine?

Abdominal migraine is one subcategory of migraine-related syndromes. Migraine is sometimes associated with facial ecchymosis, which may be accounted for by trigeminovascular activation. However, the precise mechanism of this concurrence remains unknown. Here, we describe a 9-year-old girl, who presented ecchymosis of the legs and buttock associated with recurrent, severe, non-localized midline abdominal pain. The patient has positive family history of migraine. Investigations during an attack revealed no obvious abnormalities. According to the International Classification of Headache Disorders (Second Edition), she was diagnosed with abdominal migraine. Her abdominal pain was relieved with sumatriptan, a migraine-specific serotonin(1B/1D) agonist. The ecchymosis always occurred in conjunction with abdominal pain and tended to regress after pain relief. In contrast to the local trigeminovascular activation theory that explains the ecchymosis in a migraine-related condition, the findings gained from the presented patient suggest a mechanism that involves the initial activation of the visceral nerves responsible for abdominal nociception under the predisposition of visceral hypersensitivity associated with abdominal migraine. Subsequently, ecchymosis developed in the skin region innerved by the activated nerves, possibly involving dichotomizing afferent fibers and afferent-afferent interactions via sacral spinal cord pathway or a sympathetic reflex. Taken together with the probable common mechanism of migraine and abdominal migraine, we suggest that the skin changes in migraine are associated with somatic referral of migraine headache via the trigeminal nerve pathway.