Convergence of trigeminal input with visceral and phrenic inputs on primate C1-C2 spinothalamic tract neurons

Subdiaphragmatic phrenic nerve supply: A systematic review

OBJECTIVE

The aim of this systematic review is to study the subdiaphragmatic anatomy of the phrenic nerve.

MATERIALS AND METHODS

A computerised systematic search of the Web of Science database was conducted. The key terms used were phrenic nerve, subdiaphragmat*, esophag*, liver, stomach, pancre*, duoden*, intestin*, bowel, gangli*, biliar*, Oddi, gallbladder, peritone*, spleen, splenic, hepat*, Glisson, falciform, coronary ligament, kidney, suprarenal, and adrenal. The 'cited-by' articles were also reviewed to ensure that all appropriate studies were included.

RESULTS

A total of one thousand three hundred and thirty articles were found, of which eighteen met the inclusion and exclusion criteria. The Quality Appraisal for Cadaveric Studies scale revealed substantial to excellent methodological quality of human studies, while a modified version of the Systematic Review Centre for Laboratory Animal Experimentation Risk of Bias Tool denoted poor methodological quality of animal studies. According to human studies, phrenic supply has been demonstrated for the gastro-esophageal junction, stomach, celiac ganglia, liver and its coronary ligament, inferior vena cava, gallbladder and adrenal glands, with half of the human samples studied presenting phrenic nerve connections with any subdiaphragmatic structure.

CONCLUSIONS

This review provides the first systematic evidence of subdiaphragmatic phrenic nerve supply and connections. This is of interest to professionals who care for people suffering from neck and shoulder pain, as well as patients with peridiaphragmatic disorders or hiccups. However, there are controversies about the autonomic or sensory nature of this supply.

Dietary supplementation with grape seed extract prevents development of trigeminal sensitization and inhibits pain signaling in a preclinical chronic temporomandibular disorder model

BACKGROUND

The risk factors neck muscle tension, prolonged jaw opening, and female gender are associated with developing temporomandibular disorders (TMD), which are characterized by persistent sensitization of trigeminal neurons and enhanced pain signaling. Dietary supplementation with a grape seed extract (GSE) can modulate expression of proteins that decrease neuronal excitability and trigeminal sensitization.

METHODS

Mechanical nocifensive thresholds over the masseter were determined using von Frey filaments in male and female adult Sprague Dawley rats. To promote trigeminal sensitization, animals were injected with complete Freund's adjuvant in the upper trapezius. After 8 days, animals were subjected to near maximal jaw opening and head withdrawal responses were determined for 28 days. Some animals received continuous supplementation with 0.5% GSE in their drinking water two weeks prior to trapezius injections.

RESULTS

Prolonged jaw opening increased the average number of nocifensive responses to mechanical stimuli for 14 days in males and females. However, trapezius inflammation prior to jaw opening promoted persistent mechanical sensitivity up to 28 days post-jaw opening in females, while in males nociceptive levels were still elevated at day 21. Supplementation with GSE, which is enriched in polyphenols and exhibits antioxidant and COX-2 activity, inhibited trigeminal nociception in response to jaw opening in both male and female sensitized animals.

CONCLUSIONS

Our findings provide evidence that multiple risk factors contribute to the development of a prolonged state of trigeminal sensitization that is more severe in females and provide preclinical evidence that supplementation with GSE could be beneficial in the management of TMD.

The receptive field for visceral pain referred orofacially by the vagus nerves

BACKGROUND

The nociceptive receptive field of the vagus nerves in animals includes virtually the entire thoracic, abdominal and laryngopharyngeal regions. However, the role of the vagus nerves in the transmission of visceral pain in humans, with the exception of pain from coronary artery diseases, is believed to be insignificant.

AIM

The purpose of this report is to map out the clinical visceral pain receptive field of the vagus nerves relative to its nociceptive counterpart in animals.

MATERIALS AND METHODS

The PubMed database and PMC were searched for case reports of patients with orofacial pain believed by the author(s) of the article to be referred from underlying non-cardiac thoracic, laryngopharyngeal or abdominal diseases. Reports of diseases for which non-neural explanations for the orofacial spread of pain were suggested were excluded.

RESULTS

A total of 52 case reports of jaw pain and/or otalgia referred from laryngopharyngeal and noncardiac thoracic sources were discovered. In addition, a multicenter prospective study found that 25.8% of more than 3,000 patients with thoracic aortic dissection experienced pain in the head and neck region. In stark contrast, no case reports of orofacially referred pain from abdominal diseases were found.

DISCUSSION

The results indicate that the laryngopharyngeal and thoracic portions of the vagal receptive field are capable of referring pain orofacially while the abdominal portion is not. The roles of the somatotopic organization of the trigeminal sub nucleus caudalis and neuromodulation in this referral of pain were discussed.

CONCLUSION

Referred orofacial pain can lead to delayed diagnosis and poorer outcome in visceral diseases.

Inhibition of Trigeminal Nociception by Non-invasive Vagus Nerve Stimulation: Investigating the Role of GABAergic and Serotonergic Pathways in a Model of Episodic Migraine

Migraine is a prevalent neurological disease that is characterized by unpredictable episodic attacks of intense head pain. The underlying pathology involves sensitization and activation of the trigeminal system. Although non-invasive vagus nerve stimulation (nVNS) is recommended for the treatment of migraine, the abortive mechanism of action is not well-understood. The goal of this study was to compare the ability of nVNS and sumatriptan to inhibit trigeminal activation in two animal models of episodic migraine and to investigate the receptor mechanism of action of nVNS. Nocifensive head withdrawal response was investigated in adult male Sprague Dawley rats using von Frey filaments. To induce trigeminal nociceptor sensitization, complete Freund's adjuvant was injected in the trapezius muscle and trigeminal neurons were activated by exposure to a pungent odor or injection of the nitric oxide donor sodium nitroprusside. Some animals received nVNS or sumatriptan as treatment. Some animals were injected intracisternally with antagonists of GABAA, 5-HT3 or 5-HT7 receptors prior to nVNS since these receptors are implicated in descending modulation. While unsensitized animals exposed to the pungent odor or nitric oxide alone did not exhibit enhanced mechanical nociception, sensitized animals with neck muscle inflammation displayed increased trigeminal nocifensive responses. The enhanced nociceptive response to both stimuli was attenuated by nVNS and sumatriptan. Administration of antagonists of GABAA, 5-HT3, and 5-HT7 receptors in the upper spinal cord suppressed the anti-nocifensive effect of nVNS. Our findings suggest that nVNS inhibits trigeminal activation to a similar degree as sumatriptan in episodic migraine models via involvement of GABAergic and serotonergic signaling to enhance central descending pain modulation.

Safety and efficacy of percutaneous pulsed radiofrequency treatment at the C1-C2 level in chronic cluster headache: a retrospective analysis of 21 cases

We performed a study of the safety and efficacy of percutaneous pulsed radiofrequency (PRF) treatment directed at C1 and C2 levels as performed at our local pain clinic in refractory chronic cluster headache (CCH) patients. We identified 21 CCH patients treated with PRF (240 s, max. 45 V, max. 42 °C) directed at the ganglion and/or nerve root of C1 and C2. Data were collected through retrospective analysis of patients' files and include demographic variables, onset and duration of the headache, mean attack frequency, and prior pharmacological treatment. Safety and reduction of attack frequency in the first 3 months after a first PRF treatment was the primary outcome parameter of this study. All patients had been treated with at least two prophylactic drugs and 19 (90%) had previously been treated with verapamil, lithium, and topiramate. Ten patients (47.6%) reported no meaningful effect, four patients (19%) reported a meaningful reduction of < 50%, and seven patients (33.3%) reported a reduction in headache burden of at least 50% in the 3 months following treatment. Two patients reported occurrence or increase in frequency of contralateral cluster attacks. No other adverse events were reported or detected at follow-up. Upper cervical PRF treatment appears to be a safe procedure that could prove effective in the treatment of patients with refractory CCH and warrants a prospective study.

Jaw pain and myocardial ischemia: A review of potential neuroanatomical pathways

Cardiac pain is usually manifested as a crushing, squeezing, or sensation of pressure in the center of the chest. The pain can be referred to the left shoulder, neck, jaw, and epigastric region as well as the temporomandibular region, paranasal sinuses, and head in general. Although not well understood, during myocardial ischemia, the process of cardiac referred pain to craniofacial structures can be explained by the convergence of visceral and somatic relays at the trigeminal nucleus in the brain stem. The goal of this article is to review the possible pathways for referred jaw pain due to myocardial ischemia. Clin. Anat. 32:476-479, 2019. © 2019 Wiley Periodicals, Inc.

Chest pain in patients with COPD: the fascia's subtle silence

COPD is a progressive condition that leads to a pathological degeneration of the respiratory system. It represents one of the most important causes of mortality and morbidity in the world, and it is characterized by the presence of many associated comorbidities. Recent studies emphasize the thoracic area as one of the areas of the body concerned by the presence of pain with percentages between 22% and 54% in patients with COPD. This article analyzes the possible causes of mediastinal pain, including those less frequently taken into consideration, which concern the role of the fascial system of the mediastinum. The latter can be a source of pain especially when a chronic pathology is altering the structure of the connective tissue. We conclude that to consider the fascia in daily clinical activity may improve the therapeutic approach toward the patient.

An Unusual Cause of Ear Pain. A Life Threatening Disease Revealed by a Common Symptom

A 40-year-old woman presented to the emergency department (ED) for bilateral otalgia as her sole complaint. The physician's otoscopic examination was normal and the rest of the examination was unremarkable except for previously unknown high blood pressure. The patient had no chest pain or dyspnea. She was discharged from the ED with antihypertensive therapy, pain-relief medications, and an appointment with a cardiologist. Twelve days later, transthoracic echocardiography revealed pericardial effusion and dilated ascending aorta. Computed tomography scan finally diagnosed an aortic dissection (AD) type A (Stanford classification) which necessitated emergency surgery.

Anatomy and physiology of phrenic afferent neurons

Large-diameter myelinated phrenic afferents discharge in phase with diaphragm contraction, and smaller diameter fibers discharge across the respiratory cycle. In this article, we review the phrenic afferent literature and highlight areas in need of further study. We conclude that 1) activation of both myelinated and nonmyelinated phrenic sensory afferents can influence respiratory motor output on a breath-by-breath basis; 2) the relative impact of phrenic afferents substantially increases with diaphragm work and fatigue; 3) activation of phrenic afferents has a powerful impact on sympathetic motor outflow, and 4) phrenic afferents contribute to diaphragm somatosensation and the conscious perception of breathing. Much remains to be learned regarding the spinal and supraspinal distribution and synaptic contacts of myelinated and nonmyelinated phrenic afferents. Similarly, very little is known regarding the potential role of phrenic afferent neurons in triggering or modulating expression of respiratory neuroplasticity.

Occipital Nerve Field Transcranial Direct Current Stimulation Normalizes Imbalance Between Pain Detecting and Pain Inhibitory Pathways in Fibromyalgia

Occipital nerve field (OCF) stimulation with subcutaneously implanted electrodes is used to treat headaches, more generalized pain, and even failed back surgery syndrome via unknown mechanisms. Transcranial direct current stimulation (tDCS) can predict the efficacy of implanted electrodes. The purpose of this study is to unravel the neural mechanisms involved in global pain suppression, mediated by occipital nerve field stimulation, within the realm of fibromyalgia. Nineteen patients with fibromyalgia underwent a placebo-controlled OCF tDCS. Electroencephalograms were recorded at baseline after active and sham stimulation. In comparison with healthy controls, patients with fibromyalgia demonstrate increased dorsal anterior cingulate cortex, increased premotor/dorsolateral prefrontal cortex activity, and an imbalance between pain-detecting dorsal anterior cingulate cortex and pain-suppressing pregenual anterior cingulate cortex activity, which is normalized after active tDCS but not sham stimulation associated with increased pregenual anterior cingulate cortex activation. The imbalance improvement between the pregenual anterior cingulate cortex and the dorsal anterior cingulate cortex is related to clinical changes. An imbalance assumes these areas communicate and, indeed, abnormal functional connectivity between the dorsal anterior cingulate cortex and pregenual anterior cingulate cortex is noted to be caused by a dysfunctional effective connectivity from the pregenual anterior cingulate cortex to the dorsal anterior cingulate cortex, which improves and normalizes after real tDCS but not sham tDCS. In conclusion, OCF tDCS exerts its effect via activation of the descending pain inhibitory pathway and de-activation of the salience network, both of which are abnormal in fibromyalgia.

Visceral pain

Modeling visceral pain requires an appreciation of the underlying neurobiology of visceral sensation, including characteristics of visceral pain that distinguish it from pain arising from other tissues, the unique sensory innervation of visceral organs, the functional basis of visceral pain, and the concept of viscero-somatic and viscero-visceral convergence. Further, stimuli that are noxious when applied to the viscera are different than stimuli noxious to skin, muscle, and joints, thus informing model development and assessment. Visceral pain remains an important and understudied area of pain research and basic science knowledge and mechanisms acquired using animal models can translate into approaches that can be applied to the study and development of future therapeutics.

Vagal afferent modulation of spinal trigeminal neuronal responses to dural electrical stimulation in rats

Vagus nerve stimulation (VNS) is an approved antiepileptic and antidepressant treatment, which has recently shown promise as a therapy for drug-resistant primary headaches. Specific neurobiological mechanisms underlying its anticephalgic action are not elucidated, partly because of the deficiency of research-related findings. The spinal trigeminal nucleus (STN) plays a prominent role in pathophysiology of headaches by modulating pain transmission from intracranial structures to higher centers of the brain. To determine whether vagal stimulation may affect trigeminovascular nociception, we investigated the effects of VNS on the STN neuronal activity in the animal model of headache. In anesthetized rats the spike activity of the STN neurons with convergent orofacial and meningeal inputs was monitored, and the changes in neuronal responses to electrical stimulation of the dura mater under preconditioning or under continuous electrical stimulation of the left cervical vagus nerve were studied. Preconditioning vagal afferent stimulation (200-ms train of pulses at 30 Hz applied before each dural stimulus) did not produce substantial changes in the STN spike activity. However, continuous VNS with frequency of 10 Hz in 48% of cases significantly suppressed trigeminal neuronal responses to dural electrical stimulation. In line with the decrease in evoked activity, the VNS-induced depression of ongoing neuronal firing was observed. Although the inhibitory effect was prevailing, 29.5% of STN neurons were facilitated by VNS, whereas 22.5% were unresponsive to the stimulation. These results provide an evidence of VNS-induced modulation of trigeminovascular nociception, and therefore contribute to a deeper understanding of neurophysiological mechanisms underlying effects of vagal stimulation in chronic drug-resistant headaches.

Orofacial pain of cardiac origin: review literature and clinical cases

The most common types of orofacial pain originate at the dental or periodontal level or in the musculoskeletal structures. However, the patient may present pain in this region even though the source is located elsewhere in the body. One possible source of heterotopic pain is of cardiac origin. Objectives: Report two cases of orofacial pain of cardiac origin and review the clinical cases described in the literature. Study Design: Description of clinical cases and review of clinical cases. Results and conclusions: Nine cases of atypical pain of cardiac origin are recorded, which include 5 females and 4 males. In craniofacial structures, pain of cardiac origin is usually bilateral. At the craniofacial level, the most frequent location described is in the throat and jaw. Pain of cardiac origin is considered atypical due to its location, although roughly 10% of the cases of cardiac ischemia manifest primarily in craniofacial structures. Finally, the differential diagnosis of pain of odontogenic origin must be taken into account with pain of non-odontogenic origin (muscle, psychogenic, neuronal, cardiac, sinus and neurovascular pain) in order to avoid diagnostic errors in the dental practice as well as unnecessary treatments.

Key words:Orofacial pain, ischemic heart disease, heterotopic pain, odontalgia.

Quality Difference in Craniofacial Pain of Cardiac vs. Dental Origin

Craniofacial pain, whether odontogenic or caused by cardiac ischemia, is commonly referred to the same locations, posing a diagnostic challenge. We hypothesized that the validity of pain characteristics would be high in assessment of differential diagnosis. Pain quality, intensity, and gender characteristics were assessed for referred craniofacial pain from dental (n = 359) vs. cardiac (n = 115) origin. The pain descriptors “pressure” and “burning” were statistically associated with pain from cardiac origin, while “throbbing” and “aching” indicated an odontogenic cause. No gender differences were found. These data should now be added to those craniofacial pain characteristics already known to point to acute cardiac disease rather than dental pathology, i.e., pain provocation/aggravation by physical activity, pain relief at rest, and bilateralism. To initiate prompt and appropriate treatment, dental and medical clinicians as well as the public should be alert to those clinical characteristics of craniofacial pain of cardiac origin.

Convergence of cutaneous, musculoskeletal, dural and visceral afferents onto nociceptive neurons in the first cervical dorsal horn

The convergence of cutaneous, musculoskeletal, dural and visceral afferents onto nociceptive neurons in the first cervical dorsal horn was investigated in urethane/chloralose-anesthetized rats. Electrical stimulation was applied to facial, neck, shoulder and forepaw skin, cornea (COR), dura, second cervical (C2) nerve, hypoglossal nerve, temporomandibular joint, masseter (MAS) muscle and superior laryngeal nerve. In addition, acetic acid was injected intraperitoneally and microinjection of glutamate was applied to the tongue, MAS muscle, splenius cervicis muscle, dura and intrapericardial area. A total of 52 nociceptive neurons classified as wide dynamic range (n = 28) or nociceptive-specific (n = 24) was studied. All nociceptive neurons received afferent input from the skin and at least one COR, musculoskeletal, dural or visceral afferent source in the trigeminal (V) or cervical area but input from afferent sources caudal to the C2 innervation territory was sparse. The proportion of neurons responding to COR, dural, C2 nerve, hypoglossal nerve, temporomandibular joint, MAS muscle and superior laryngeal nerve stimulations was 87, 54, 85, 52, 73, 64 and 31%, respectively. Electrical stimulation of all tested sites showed a double logarithmic stimulus-response relation, and cluster analysis of the excitability to COR, musculoskeletal, dural and visceral stimulations revealed two groups of neurons, one mainly containing wide dynamic range neurons and one mainly containing nociceptive-specific neurons. These findings indicate that afferent convergence in first cervical dorsal horn nociceptive neurons may be limited to the craniofacial area and that they may play an important role in the integration of craniofacial and upper cervical nociceptive inputs.

N-Methyl-D-Aspartate (NMDA) and non-NMDA receptor antagonists suppress the superior sagittal sinus-evoked activity of C1 spinal neurons responding to tooth pulp electrical stimulation in rats

The aim of the present study was to determine whether there is a convergence of inputs from tooth pulp (TP) and the superior sagittal sinus (SSS) on rat C1 spinal neurons, and to examine the effects of iontophoretically applied N-methyl-D: -aspartate (NMDA) and non-NMDA receptor antagonists on the SSS-evoked activity of C1 neurons. Extracellular single unit-recordings were made from 20 C1 units responding to TP electrical stimulation with a constant temporal relationship to a digastric electromyogram signal, using a multibarrel electrode in pentobarbital-anesthetized rats. Ninety percent of C1 neurons (18/20) responding to TP stimulation also responded to the SSS stimulation. These neurons were considered to be SSS-afferent inputs from Adelta-fibers (5.8 +/- 0.6 m/s; n = 18), based on the calculation of nerve conduction velocity. After the iontophoretic application (30, 50, and 70 nA) of an NMDA receptor blocker (5R-10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cycloheptene-5,10-imine hydrogen maleate (MK801) or a non-NMDA receptor blocker (6-cyano-7-nitroquinoxaline-2,3-dione) (CNQX), the mean number of spikes responding to the SSS stimulation significantly decreased (30, 50, and 70 nA; P < 0.05). These results suggest that there is a convergence of inputs from SSS and TP afferents on C1 neurons; it is possible that both NMDA and non-NMDA receptors located on C1 neurons may be targets for the treatment of the trigeminal referred pain associated with migraine.

Role of capsaicin-sensitive primary afferent inputs from the masseter muscle in the C1 spinal neurons responding to tooth-pulp stimulation in rats

The aim of the present study was to demonstrate the convergence of inputs from masseter muscle (MM) and tooth pulp (TP) onto C1 spinal neurons and to determine whether the afferent fibers express the functional vanilloid receptor (VR1). Extracellular single-unit recordings were made from 61 C1 units responding to TP electrical stimulation with a constant temporal relationship to a digastric electromyogram signal in pentobarbital anesthetized rats. Eighty-four percent of C1 neurons responding to TP stimulation also responded to the ipsilateral MM stimulation. Of these neurons, 61% were considered to be afferent inputs from Adelta-fibers and the remaining units (39%) were C-fibers, based on calculation of the nerve conduction velocity. Intramuscular injection of capsaicin (0.05 and 0.1%) produced a reduction in a MM-induced C1 neuronal activity in a dose-dependent manner and this effect was antagonized by pretreatment with an antagonist of VR1, capsazepine. Some of these units were also excited by noxious heat stimulation (> 43 degrees C). The trigeminal root ganglion (TRG) neurons that innervated the MM were retrogradely labeled with Fluorogold (FG) and the small-diameter FG-labeled TRG neurons expressed the immunoreactivity for VR1. After intramuscular mustard oil injection (noxious chemical stimulation), the C1 neuronal activity induced by both touch and pinch stimuli was enhanced and their receptive field sizes were significantly expanded. These changes were reversed within 15-20 min. These results suggest that there may be the convergence of noxious afferents inputs from the MM and TP afferents on the same C1 neurons in rats, and that the afferent fibers expressing the functional VR1 may contribute to the hyperalgesia and/or referred pain associated with temporomandibular joint disorder.

Craniofacial inputs to upper cervical dorsal horn: implications for somatosensory information processing

The aim of this study was to characterize the properties of somatosensory neurons in the first 2 cervical spinal dorsal horns (C1 and C2 DHs) and compare them with those previously described for the rostral subnucleus caudalis (rVc). A total of 74 nociceptive neurons classified as wide-dynamic-range (WDR) or nociceptive-specific (NS), as well as 72 low-threshold mechanoreceptive (LTM) neurons, was studied in urethane/chloralose-anesthetized rats. The majority of LTM neurons were located in laminae III/IV and had a small mechanoreceptive field (RF) that included the posterior face and cervical tissues. In contrast, the nociceptive neurons were located in laminae I/II or V/VI, and the RF of each C1 and C2 DH nociceptive neuron included a part of the face and in 47% of them the RF included a region supplied by upper cervical afferents. There was a gradual caudal shift in the neuronal RF from nasal/intraoral tissues towards the neck as recording sites progressed from rVc to C1 and C2 DHs. In contrast to LTM neurons, many C1 and C2 DH nociceptive neurons received mechanosensitive convergent afferent inputs from cervical and craniofacial deep tissues (e.g., tongue muscles or temporomandibular joint), and over 50% could be activated by hypoglossal (XII) nerve electrical stimulation. We propose that C1 and C2 DHs represent part of the caudal extension of the Vc, and that Vc and C1 and C2 DHs may act together as one functional unit to process nociceptive information from craniofacial and cervical tissues, including that from deep craniofacial tissues.

Convergence of nociceptive information from temporomandibular joint and tooth pulp afferents on C1 spinal neurons in the rat

The aim of the present study was to test the hypothesis that there is a convergence of afferent inputs from the temporomandibular joint (TMJ) on C1 spinal neurons responding to electrical stimulation of the tooth pulp (TP). In 14 pentobarbital anesthetized rats, the extracellular single unit activity of 31 C1 spinal neurons and the amplitude in a digastric muscle electromyogram (n = 31) increased proportionally during 1.0-3.5 times the threshold for the jaw-opening reflex (JOR). Of 31 C1 spinal neurons responsive to TP afferents, 28 (approximately 90%) were also excited by electrical stimulation of the ipsilateral TMJ capsule. All neurons tested were divided into three categories of nociceptive specific, wide dynamic range and non-responsive as to their responsiveness to mechanical stimuli (pin prick and touch) of the somatic receptive field (skin of the face, neck, jaw and upper forearm) and TMJ capsule. Nineteen (68%) of 28 C1 spinal neurons received nociceptive information from C fibers of the TMJ capsule. These results suggest that there is a convergence of noxious information from the TMJ and TP afferents on the same C1 spinal neurons, which importantly contribute to pain perception from the TMJ region.

Integration of viscerosomatic sensory input at the spinal level

The major point of this chapter is that there is evidence to support the idea that cervical headache might not only result from injured somatic structures in the neck but also occur because of interactions with visceral organs. The complex arrangement of convergent inputs from somatic and visceral afferent fibers and of the propriospinal pathways in the upper cervical segments may create an environment to precipitate such headaches (Fig. 8). It is possible that the soreness experienced in the muscles innervating the neck may not be due to direct injury but may occur as muscle hyperalgesia that is often associated with visceral pain (Giamberardino, et al., 1993). Much more research is required to understand these complex interactions before patients who suffer pain of cervical headache can be treated satisfactorily.