Static magnetic field-induced anti-nociceptive effect and the involvement of capsaicin-sensitive sensory nerves in this mechanism

Effect of static magnetic field therapy on diabetic neuropathy and quality of life: a double-blind, randomized trial

BACKGROUND

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes mellitus (DM) that can cause annoying symptoms. To address this condition, several treatment approaches have been proposed, including static magnetic field (SMF) therapy, which has shown promise in treating neurological conditions. Therefore, this study aimed to investigate the effects of SMF therapy on symptomatic DPN and the quality of life (QoL) in patients with type 2 diabetes.

METHODS

A double-blind, randomized, placebo-controlled trial was conducted from April to October 2021. Sixty-four DPN patients (20 males, 44 females) were recruited for the study via invitation. The participants were divided into two groups: the magnet group, which used magnetic ankle bracelets (155 mT) for 12 weeks, and the sham group, which used non-magnetic ankle bracelets for the same duration. Neuropathy Symptom Score (NSS), Neuropathic Disability Score (NDS), and Visual Analogue Scale (VAS) were used to assess neuropathy symptoms and pain. In addition, the Neuropathy Specific Quality of Life Questionnaire (Neuro-QoL) tool was used to measure the patients' quality of life.

RESULTS

Before treatment, there were no significant differences between the magnet and sham groups in terms of the NSS scores (P = 0.50), NDS scores (P = 0.74), VAS scores (P = 0.17), and Neuro-QoL scores (P = 0.82). However, after 12 weeks of treatment, the SMF exposure group showed a significant reduction in NSS scores (P < 0.001), NDS scores (P < 0.001), VAS scores (P < 0.001), and Neuro-QoL scores (P < 0.001) compared to the baseline. The changes in the sham group, on the other hand, were not significant.

CONCLUSION

According to obtained data, SMF therapy is recommended as an easy-to-use and drug-free method for reducing DPN symptoms and improving QoL in diabetic type-2 patients. Trial registration Registered at Iranian Registry of Clinical Trials: IRCT20210315050706N1, 2021/03/16.

Molecular mechanism in trigeminal nerve and treatment methods related to orthodontic pain

BACKGROUND

Orthodontic treatment is the main treatment approach for malocclusion. Orthodontic pain is an inevitable undesirable adverse reaction during orthodontic treatment. It is reported orthodontic pain has become one of the most common reason that patients withdraw from orthodontic treatment. Therefore, understanding the underlying mechanism and finding treatment of orthodontic pain are in urgent need.

AIMS

This article aims to sort out the mechanisms and treatments of orthodontic pain, hoping to provide some ideas for future orthodontic pain relief.

MATERIALS

Tooth movement will cause local inflammation. Certain inflammatory factors and cytokines stimulating the trigeminal nerve and further generating pain perception, as well as drugs and molecular targeted therapy blocking nerve conduction pathways, will be reviewed in this article.

METHOD

We review and summaries current studies related to molecular mechanisms and treatment approaches in orthodontic pain control.

RESULTS

Orthodontics pain related influencing factors and molecular mechanisms has been introduced. Commonly used clinical methods in orthodontic pain control has been evaluated.

DISCUSSION

With the clarification of more molecular mechanisms, the direction of orthodontic pain treatment will shift to targeted drugs.

The Analgesic Effects of Static Magnetic Fields

Pain is one of the most common reasons why people seek medical care, which is related to most disease states. Magnetic fields (MFs) can be applied locally to specific parts of human bodies with high penetration and temporal control, which have a long-debated history in folk therapy. The purpose of this review is to collect and analyze experimental data about the analgesic effects of static magnetic fields (SMFs) so that we can have a scientific understanding regarding this topic. We collected 28 studies (25 English and 3 Chinese papers) with proper sham controls that investigated the effects of SMFs on pain relief in humans or mice. We found that 64% of the human studies and all mice studies in the literature showed positive analgesic effects of SMFs, which are related to factors including SMF intensity, treatment time, and pain types. Higher intensity and/or longer treatment time, as well as some specific pain types, may have better pain relief effects. Initial mechanistic studies indicated that membrane receptors, such as capsaicin receptor VR1/TRPV1, opioid receptors, and P2X3 receptors, might be involved. By describing experimental evidence and analysis, we found that SMFs actually hold considerable promise for managing some specific types of pain if proper SMF parameters are used. More studies comprehensively evaluating the parameters of SMF and its corresponding analgesic effects on different pain types, as well as the underlying molecular mechanisms, will be necessary to further validate its therapeutic potential in pain management in the future. Bioelectromagnetics. 00:00-00, 2021. © 2021 Bioelectromagnetics Society.

Hemokinin-1 is an important mediator of pain in mouse models of neuropathic and inflammatory mechanisms

The Tac4 gene-derived hemokinin-1 (HK-1) is present in pain-related regions and activates the tachykinin NK1 receptor, but with binding site and signaling pathways different from Substance P (SP). NK1 receptor is involved in nociception, but our earlier data showed that it has no role in chronic neuropathic hyperalgesia, similarly to SP. Furthermore, NK1 antagonists failed in clinical trials as analgesics due to still unknown reasons. Therefore, we investigated the role of HK-1 in pain conditions of distinct mechanisms using genetically modified mice. Chronic neuropathic mechanical and cold hyperalgesia after partial sciatic nerve ligation (PSL) were determined by dynamic plantar aesthesiometry and withdrawal latency from icy water, motor coordination on the accelerating Rotarod. Peripheral nerve growth factor (NGF) production was measured by ELISA, neuronal and glia cell activation by immunohistochemistry in pain-related regions. Acute somatic and visceral chemonocifensive behaviors were assessed after intraplantar formalin or intraperitoneal acetic-acid injection, respectively. Resiniferatoxin-induced inflammatory mechanical and thermal hyperalgesia by aesthesiometry and increasing temperature hot plate. Chronic neuropathic mechanical and cold hypersensitivity were significantly decreased in HK-1 deficient mice. NGF level in the paw homogenates of intact mice were significantly lower in case of HK-1 deletion. However, it significantly increased under neuropathic condition in contrast to wildtype mice, where the higher basal concentration did not show any changes. Microglia, but not astrocyte activation was observed 14 days after PSL in the ipsilateral spinal dorsal horn of wildtype, but not HK-1-deficient mice. However, under neuropathic conditions, the number of GFAP-positive astrocytes was significantly smaller in case of HK-1 deletion. Acute visceral, but not somatic nocifensive behavior, as well as neurogenic inflammatory mechanical and thermal hypersensitivity were significantly reduced by HK-1 deficiency similarly to NK1, but not to SP deletion. We provide evidence for pro-nociceptive role of HK-1, via NK1 receptor activation in acute inflammation models, but differently from SP-mediated actions. Identification of its targets and signaling can open new directions in pain research.

Static magnetic field enhances the anticancer efficacy of capsaicin on HepG2 cells via capsaicin receptor TRPV1

Static magnetic field (SMF) has shown some possibilities for cancer therapies. In particular, the combinational effect between SMF and anti-cancer drugs has drawn scientists’ attentions in recent years. However, the underlying mechanism for the drug-specific synergistic effect is far from being understood. Besides, the drugs used are all conventional chemotherapy drugs, which may cause unpleasant side effects. In this study, our results demonstrate for the first time that SMF could enhance the anti-cancer effect of natural compound, capsaicin, on HepG2 cancer cells through the mitochondria-dependent apoptosis pathway. We found that the synergistic effect could be due to that SMF increased the binding efficiency of capsaicin for the TRPV1 channel. These findings may provide a support to develop an application of SMF for cancer therapy. The present study offers the first trial in combining SMF with natural compound on anti-cancer treatment, which provides additional insight into the interaction between SMF and anti-cancer drugs and opens the door for the development of new strategies in fighting cancer with minimum cytotoxicity and side effects.

Analysis of the effect of locally applied inhomogeneous static magnetic field-exposure on mouse ear edema--a double blind study

The effect static magnetic field (SMF)-exposure may exert on edema development has been investigated. A 6 h long whole-body (WBSMF) or local (LSMF), continuous, inhomogeneous SMF-exposure was applied on anesthetized mice in an in vivo model of mustard oil (MO)-induced ear edema. LSMF was applied below the treated ear, below the lumbar spine, or below the mandible. Ear thickness (v) was checked 8 times during the exposure period (at 0, 0.25, 1, 2, 3, 4, 5, and 6 h). The effect size of the applied treatment (η) on ear thickness was calculated by the formula η = 100% × (1–v_j/v_i), where group i is the control group and j is the treated group. Results showed that MO treatment in itself induced a significant ear edema with an effect of 9% (p<0.001). WBSMF or LSMF on the spine in combination with MO treatment increased ear thickness even further resulting in an effect of η>11% in both cases compared to SMF-exposure alone (p<0.001). In these cases SMF-exposure alone without MO treatment reduced ear thickness significantly (p<0.05), but within estimated experimental error. In cases of LSMF-exposure on the head, a significant SMF-exposure induced ear thickness reduction was found (η = 5%, p<0.05). LSMF-exposure on the spine affected ear thickness with and without MO treatment almost identically, which provides evidence that the place of local SMF action may be in the lower spinal region.

Influence of inhomogeneous static magnetic field-exposure on patients with erosive gastritis: a randomized, self- and placebo-controlled, double-blind, single centre, pilot study

This pilot study was devoted to the effect of static magnetic field (SMF)-exposure on erosive gastritis. The randomized, self- and placebo-controlled, double-blind, pilot study included 16 patients of the 2nd Department of Internal Medicine, Semmelweis University diagnosed with erosive gastritis. The instrumental analysis followed a qualitative (pre-intervention) assessment of the symptoms by the patient: lower heartburn (in the ventricle), upper heartburn (in the oesophagus), epigastric pain, regurgitation, bloating and dry cough. Medical diagnosis included a double-line upper panendoscopy followed by 30 min local inhomogeneous SMF-exposure intervention at the lower sternal region over the stomach with peak-to-peak magnetic induction of 3 mT and 30 mT m(-1) gradient at the target site. A qualitative (post-intervention) assessment of the same symptoms closed the examination. Sham- or SMF-exposure was used in a double-blind manner. The authors succeeded in justifying the clinically and statistically significant beneficial effect of the SMF- over sham-exposure on the symptoms of erosive gastritis, the average effect of inhibition was 56% by p = 0.001, n = 42 + 96. This pilot study was aimed to encourage gastroenterologists to test local, inhomogeneous SMF-exposure on erosive gastritis patients, so this intervention may become an evidence-based alternative or complementary method in the clinical use especially in cases when conventional therapy options are contraindicated.

Exposure to inhomogeneous static magnetic field beneficially affects allergic inflammation in a murine model

Previous observations suggest that static magnetic field (SMF)-exposure acts on living organisms partly through reactive oxygen species (ROS) reactions. In this study, we aimed to define the impact of SMF-exposure on ragweed pollen extract (RWPE)-induced allergic inflammation closely associated with oxidative stress. Inhomogeneous SMF was generated with an apparatus validated previously providing a peak-to-peak magnetic induction of the dominant SMF component 389 mT by 39 T m(-1) lateral gradient in the in vivo and in vitro experiments, and 192 mT by 19 T m(-1) in the human study at the 3 mm target distance. Effects of SMF-exposure were studied in a murine model of allergic inflammation and also in human provoked skin allergy. We found that even a single 30-min exposure of mice to SMF immediately following intranasal RWPE challenge significantly lowered the increase in the total antioxidant capacity of the airways and decreased allergic inflammation. Repeated (on 3 consecutive days) or prolonged (60 min) exposure to SMF after RWPE challenge decreased the severity of allergic responses more efficiently than a single 30-min treatment. SMF-exposure did not alter ROS production by RWPE under cell-free conditions, while diminished RWPE-induced increase in the ROS levels in A549 epithelial cells. Results of the human skin prick tests indicated that SMF-exposure had no significant direct effect on provoked mast cell degranulation. The observed beneficial effects of SMF are likely owing to the mobilization of cellular ROS-eliminating mechanisms rather than direct modulation of ROS production by pollen NAD(P)H oxidases.

The effect of whole-body, repetitive, inhomogeneous static magnetic field-exposure on the symptoms of experimental autoimmune encephalomyelitis in mice

Experimental autoimmune encephalomyelitis (EAE) is a model for human multiple sclerosis (MS) in rodents. Static magnetic field (SMF)-exposure was shown to be beneficial in specific cases of inflammatory background, where it suppresses symptoms. The null-hypothesis was that animals with induced EAE exposed to SMF would show different seriousness of symptoms, than those in the sham-exposed control group. Three replicated series of repetitive, 30 min/day whole-body exposure to SMF with 477 mT peak-to-peak magnetic induction and 48 T/m lateral induction gradient was tested on female CSJLF1 mice with a mild, mouse spinal cord homogenate emulsion-induced EAE. Conventional scores of the animal response to EAE were compared between sham- and SMF-exposed groups of animals. Following pilot test we used 18 animals per group. Primary outcome measure was the daily group average of standard EAE scores. Results show that SMF-exposure has a strong, reproducible, and significantly beneficial effect up to 51.82% (p<0.001) over sham-exposure on the symptoms of EAE in the course of the 25 days of the experiment. This study aimed to build experimental research foundation for a later therapy option by applying SMF-exposure in the clinical management of MS.

In vitro analysis of the anti-inflammatory effect of inhomogeneous static magnetic field-exposure on human macrophages and lymphocytes

The effect of inhomogeneous static magnetic field (SMF)-exposure on the production of different cytokines from human peripheral blood mononuclear cells (PMBC), i.e., lymphocytes and macrophages, was tested in vitro. Some cultures were activated with lipopolysaccharide (LPS) at time point −3 h and were either left alone (positive control) or exposed to SMF continuously from 0 until 6, 18, or 24 h. The secretion of interleukin IL-6, IL-8, tumor necrosis factor TNF-α, and IL-10 was tested by ELISA. SMF-exposure caused visible morphological changes on macrophages as well as on lymphocytes, and also seemed to be toxic to lymphocytes ([36.58; 41.52]%, 0.308≤p≤0.444), but not to macrophages (<1.43%, p≥0.987). Analysis of concentrations showed a significantly reduced production of pro-inflammatory cytokines IL-6, IL-8, and TNF-α from macrophages compared to negative control ([56.78; 87.52]%, p = 0.031) and IL-6 compared to positive control ([45.15; 56.03]%, p = 0.035). The production of anti-inflammatory cytokine IL-10 from macrophages and from lymphocytes was enhanced compared to negative control, significantly from lymphocytes ([−183.62; −28.75]%, p = 0.042). The secretion of IL-6 from lymphocytes was significantly decreased compared to positive control ([−115.15; −26.84]%, p = 0.039). This massive in vitro evidence supports the hypotheses that SMF-exposure (i) is harmful to lymphocytes in itself, (ii) suppresses the release of pro-inflammatory cytokines IL-6, IL-8, and TNF-α, and (iii) assists the production of anti-inflammatory cytokine IL-10; thus providing a background mechanism of the earlier in vivo demonstrated anti-inflammatory effects of SMF-exposure.

Effect of a single 30 min UMTS mobile phone-like exposure on the thermal pain threshold of young healthy volunteers

One of the most frequently investigated effects of radiofrequency electromagnetic fields (RF EMFs) on the behavior of complex biological systems is pain sensitivity. Despite the growing body of evidence of EMF-induced changes in pain sensation, there is no currently accepted experimental protocol for such provocation studies for the healthy human population. In the present study, therefore, we tested the effects of third generation Universal Mobile Telecommunications System (UMTS) RF EMF exposure on the thermal pain threshold (TPT) measured on the surface of the fingers of 20 young adult volunteers. The protocol was initially validated with a topical capsaicin treatment. The exposure time was 30 min and the genuine (or sham) signal was applied to the head through a patch antenna, where RF EMF specific absorption rate (SAR) values were controlled and kept constant at a level of 1.75 W/kg. Data were obtained using randomized, placebo-controlled trials in a double-blind manner. Subjective pain ratings were tested blockwise on a visual analogue rating scale (VAS). Compared to the control and sham conditions, the results provide evidence for intact TPT but a reduced desensitization effect between repeated stimulations within the individual blocks of trials, observable only on the contralateral side for the genuine UMTS exposure. Subjective pain perception (VAS) data indicated marginally decreased overall pain ratings in the genuine exposure condition only. The present results provide pioneering information about human pain sensation in relation to RF EMF exposure and thus may contribute to cover the existing gap between safety research and applied biomedical science targeting the potential biological effects of environmental RF EMFs.

Role of Pituitary Adenylate-Cyclase Activating Polypeptide and Tac1 gene derived tachykinins in sensory, motor and vascular functions under normal and neuropathic conditions

Pituitary Adenylate-Cyclase Activating Polypeptide (PACAP) and Tac1 gene-encoded tachykinins (substance P: SP, neurokinin A: NKA) are expressed in capsaicin-sensitive nerves, but their role in nociception, inflammation and vasoregulation is unclear. Therefore, we investigated the function of these neuropeptides and the NK1 tachykinin receptor (from Tacr1 gene) in the partial sciatic nerve ligation-induced traumatic mononeuropathy model using gene deficient (PACAP(-/-), Tac1(-/-), and Tacr1(-/-)) mice. Mechanonociceptive threshold of the paw was measured with dynamic plantar aesthesiometry, motor coordination with Rota-Rod and cutaneous microcirculation with laser Doppler imaging. Neurogenic vasodilation was evoked by mustard oil stimulating sensory nerves. In wildtype mice 30-40% mechanical hyperalgesia developed one week after nerve ligation, which was not altered in Tac1(-/-) and Tacr1(-/-) mice, but was absent in PACAP(-/-) animals. Motor coordination of the PACAP(-/-) and Tac1(-/-) groups was significantly worse both before and after nerve ligation compared to their wildtypes, but it did not change in Tacr1(-/-) mice. Basal postoperative microcirculation on the plantar skin of PACAP(-/-) mice did not differ from the wildtypes, but was significantly lower in Tac1(-/-) and Tacr1(-/-) ones. In contrast, mustard oil-induced neurogenic vasodilation was significantly smaller in PACAP(-/-) mice, but not in Tacr1(-/-) and Tac1(-/-) animals. Both PACAP and SP/NKA, but not NK1 receptors participate in normal motor coordination. Tachykinins maintain basal cutaneous microcirculation. PACAP is a crucial mediator of neuropathic mechanical hyperalgesia and neurogenic vasodilation. Therefore identifying its target and developing selective, potent antagonists, might open promising new perspectives for the treatment of neuropathic pain and vascular complications.

Exposure to static magnetic field delays induced preterm birth occurrence in mice

OBJECTIVE

The purpose of this study was to demonstrate that daily 40-minute whole body exposure to an inhomogeneous static magnetic field (SMF) prolongs induced preterm birth (PTB) in mice.

STUDY DESIGN

The murine model for PTB induction was performed by the administration of 25 μg/animal lipopolysaccharide (LPS) intraperitoneally. The applied SMF was an inhomogeneous gradient field with 2.8-476.7 millitesla peak-to-peak magnetic induction range by 10 mm lateral periodicity. During SMF exposure, mice were free to move in their cage.

RESULTS

The fetal development and the delivery were normal in animals that were exposed to SMF but not treated with LPS. SMF in these cases did not influence the term of delivery. In LPS-challenged animals, SMF exposure prolonged the time of PTB occurrence from 17.43 h (n = 7) to 21.93 h (n = 15) after the challenge (P < .05).

CONCLUSION

Exposure to inhomogeneous SMF may have a valuable effect in the prevention of PTB and may have clinical relevance to humans.

Impaired nocifensive behaviours and mechanical hyperalgesia, but enhanced thermal allodynia in pituitary adenylate cyclase-activating polypeptide deficient mice

Pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) and its receptors (PAC1 and VPAC) have been shown in the spinal dorsal horn, dorsal root ganglia and sensory nerve terminals. Data concerning the role of PACAP in central pain transmission are controversial and we have recently published its divergent peripheral effects on nociceptive processes. The aim of the present study was to investigate acute somatic and visceral nocifensive behaviours, partial sciatic nerve ligation-evoked chronic neuropathic, as well as resiniferatoxin-induced inflammatory thermal and mechanical hyperalgesia in PACAP deficient (PACAP(-/-)) mice to elucidate its overall function in pain transmission. Neuronal activation was investigated with c-Fos immunohistochemistry. Paw lickings in the early (0-5 min) and late (20-45 min) phases of the formalin test were markedly reduced in PACAP(-/-) mice. Acetic acid-evoked abdominal contractions referring to acute visceral chemonociception was also significantly attenuated in PACAP knockout animals. In both models, the excitatory role of PACAP was supported by markedly greater c-Fos expression in the periaqueductal grey and the somatosensory cortex. In PACAP-deficient animals neuropathic mechanical hyperalgesia was absent, while c-Fos immunopositivity 20 days after the operation was significantly higher. In this chronic model, these neurons are likely to indicate the activation of secondary inhibitory pathways. Intraplantarly injected resiniferatoxin-evoked mechanical hyperalgesia involving both peripheral and central processes was decreased, but thermal allodynia mediated by only peripheral mechanisms was increased in PACAP(-/-) mice. These data clearly demonstrate an overall excitatory role of PACAP in pain transmission originating from both exteroceptive and interoceptive areas, it is also involved in central sensitization. This can be explained by the signal transduction mechanisms of its identified receptors, both PAC1 and VPAC activation leads to neuronal excitation. In contrast, it is an inhibitory mediator at the level of the peripheral sensory nerve endings and decreases their sensitization to heat with presently unknown mechanisms.

Static magnetic field exposure fails to affect the viability of different bacteria strains

The viability of the microbes Saccharomyces cerevisiae, Bacillus circulans, Escherichia coli, Micrococcus luteus, Pseudomonas fluorescens, Salmonella enteritidis, Serratia marcescens, and Staphylococcus aureus was tested under static magnetic field exposure up to 24 h in either a homogeneous (159.2 +/- 13.4 mT) or three types of inhomogeneous static magnetic fields: (i) peak-to-peak magnetic flux density 476.7 +/- 0.1 mT with a lateral magnetic flux density gradient of 47.7 T/m, (ii) 12.0 +/- 0.1 mT with 1.2 T/m, or (iii) 2.8 +/- 0.1 mT with 0.3 T/m. Even the longest period of exposure failed to produce any effect in the growth of bacteriae that could be correlated with static magnetic field exposure.

Pain-inhibiting inhomogeneous static magnetic field fails to influence locomotor activity and anxiety behavior in mice: no interference between magnetic field- and morphine-treatment

OBJECTIVES

We wanted to demonstrate (i) in the writhing test in mice, whether there was a prolonged analgesic effect induced by an inhomogeneous static magnetic field (SMF) exposure; (ii) whether SMF had an effect on the analgesic effect induced by 0.5mg/kgs.c. administered morphine, on the behavioral patterns, and on the hyperlocomotion-inducing effect of morphine.

DESIGN

A magnetic exposure system developed by the present authors was used with peak-to-peak flux densities in the 2-754mT range. The writhing test was used for the assessment of pain. An elevated plus maze and a Conducta System was used for studying the anxiogenic or anxyolitic effect in mice, and the locomotor activity, respectively.

OUTCOME MEASURES

We looked for the difference in the number of writhings and in the behavioral patterns between treated (s.c. morphine and/or SMF exposure) and control animals, respectively.

RESULTS

(i) The antinociceptive effect could be identified 10-30min following SMF exposition in the writhing test in mice. (ii) SMF failed to affect the morphine-induced antinociception, the behavioral patterns in either type of tests, and the hyperlocomotion-inducing effect of morphine.

CONCLUSIONS

(i) The long-lasting antinociceptive effect of SMF allows experiments under conditions, when in situ application of the SMF-producing device would be technically difficult or impossible; or where it would disturb the experiments. (ii) The results of behavioral tests with freely moving mice in or in the vicinity of inhomogeneous SMFs are not affected by the SMF in the applied flux density range. (iii) Morphine in treated subjects is not interacting with the inhomogeneous SMFs in the applied flux density range.

3 T homogeneous static magnetic field of a clinical MR significantly inhibits pain in mice

AIMS

In recent years nuclear magnetic resonance (MR) systems have proliferated worldwide. This imaging/spectroscopy technique utilizes a strong homogeneous static magnetic field, much smaller time-varying gradient magnetic fields, and radiofrequency radiation. Many studies addressed the question of potential adverse side effects induced by MR, but less attention has been paid to its potential beneficial, therapeutical effects. The present study shows that whole body exposure of mice to the 3 T homogeneous static magnetic field of a clinical MR resulted in a statistically significant antinociceptive activity.

MAIN METHODS

Antinociceptive activity was studied in the writhing test, where pain was elicited by the intraperitoneal injection of 0.6% acetic acid in the mouse. No imaging sequence of the MR was used during the experiments. Mice could freely move in their cage without any restraint.

KEY FINDINGS

An antinociceptive activity of 68+/-2% (p<0.001, n=18) was found. Subcutaneous injection of naloxone (0.2 mg/kg) in the mice reversed the magnetic field-induced antinociceptive activity. The effect of noise, vibration and lighting stimuli could be neglected. Although motion-induced effects generated in the body of the mice could not be completely excluded, their influence on pain perception was estimated to be below threshold.

SIGNIFICANCE

MR's static magnetic field should be regarded as a potential therapeutical tool.

Antinoceptive effect of triterpenoid alpha,beta-amyrin in rats on orofacial pain induced by formalin and capsaicin

The effects of alpha,beta-amyrin, a pentacyclic triterpene isolated from Protium heptaphylum was investigated on rat model of orofacial pain induced by formalin or capsaicin. Rats were pretreated with alpha,beta-amyrin (10, 30, and 100mg/kg, i.p.), morphine (5mg/kg, s.c.) or vehicle (3% Tween 80), before formalin (20 microl, 1.5%) or capsaicin (20 microl, 1.5 microg) injection into the right vibrissa. In vehicle-treated controls, formalin induced a biphasic nociceptive face-rubbing behavioral response with an early first phase (0-5 min) and a late second phase (10-20 min) appearance, whereas capsaicin produced an immediate face-rubbing (grooming) behavior that was maximal at 10-20 min. Treatment with alpha,beta-amyrin or morphine significantly inhibited the face-rubbing response in both test models. While morphine produced significant antinociception in both phases of formalin test, alpha,beta-amyrin inhibited only the second phase response, more prominently at 30 mg/kg, in a naloxone-sensitive manner. In contrast, alpha,beta-amyrin produced much greater antinociceptive effect at 100mg/kg in the capsaicin test, which was also naloxone-sensitive. These results provide first time evidence to show that alpha,beta-amyrin attenuates orofacial pain at least, in part, through a peripheral opioid mechanism but warrants further detailed study for its utility in painful orofacial pathologies.