Involvement of substance P in the antinociceptive effect of botulinum toxin type A: Evidence from knockout mice

Neurobiological mechanisms of botulinum neurotoxin-induced analgesia for neuropathic pain

Botulinum neurotoxins (BoNTs) are a family of neurotoxins produced by Clostridia and other bacteria that induce botulism. BoNTs are internalized into nerve terminals at the site of injection and cleave soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins to inhibit the vesicular release of neurotransmitters. BoNTs have been approved for multiple therapeutic applications, including the treatment of migraines. They have also shown efficacies for treating neuropathic pain, such as diabetic neuropathy, and postherpetic and trigeminal neuralgia. However, the mechanisms underlying BoNT-induced analgesia are not well understood. Peripherally administered BoNT is taken up by the nerve terminals and reduces the release of glutamate, calcitonin gene-related peptide, and substance P, which decreases neurogenic inflammation in the periphery. BoNT is retrogradely transported to sensory ganglia and central terminals in a microtubule-dependent manner. BoNTs decrease the expression of pronociceptive genes (ion channels or cytokines) from sensory ganglia and the release of neurotransmitters and neuropeptides from primary afferent central terminals, which likely leads to decreased central sensitization in the dorsal horn of the spinal cord or trigeminal nucleus. BoNT-induced analgesia is abolished after capsaicin-induced denervation of transient receptor potential vanilloid 1 (TRPV1)-expressing afferents or the knockout of substance P or the neurokinin-1 receptor. Although peripheral administration of BoNT leads to changes in the central nervous system (e.g., decreased phosphorylation of glutamate receptors in second-order neurons, reduced activation of microglia, contralateral localization, and cortical reorganization), whether such changes are secondary to changes in primary afferents or directly mediated by trans-synaptic, transcytotic, or the hematogenous transport of BoNT is controversial. To enhance their therapeutic potential, BoNTs engineered for specific targeting of nociceptive pathways have been developed to treat chronic pain. Further mechanistic studies on BoNT-induced analgesia can enhance the application of native or engineered BoNTs for neuropathic pain treatment with improved safety and efficacy.

Cellular and molecular mechanisms involved in the analgesic effects of botulinum neurotoxin: A literature review

Botulinum neurotoxins (BoNTs), derived from Clostridium botulinum, have been employed to treat a range of central and peripheral neurological disease. Some studies indicate that BoNT may be beneficial for pain conditions as well. It has been hypothesized that BoNTs may exert their analgesic effects by preventing the release of pain-related neurotransmitters and neuroinflammatory agents from sensory nerve endings, suppressing glial activation, and inhibiting the transmission of pain-related receptors to the neuronal cell membrane. In addition, there is evidence to suggest that the central analgesic effects of BoNTs are mediated through their retrograde axonal transport. The purpose of this review is to summarize the experimental evidence of the analgesic functions of BoNTs and discuss the cellular and molecular mechanisms by which they can act on pain conditions. Most of the studies reviewed in this article were conducted using BoNT/A. The PubMed database was searched from 1995 to December 2022 to identify relevant literature.

The role of botulinum neurotoxin BoNT-A in the management of oily skin and acne vulgaris: A comprehensive review

Oily skin and acne vulgaris are prevalent dermatological conditions with a significant impact on both physical and emotional well-being. Despite numerous available treatments, there is a pressing need for effective, long-term solutions. Botulinum Neurotoxin (BoNT-A) has emerged as a potential therapeutic option. However, existing reviews in this area are often limited. This review aims to comprehensively assess the use of BoNT-A in managing oily skin and acne vulgaris while addressing gaps in previous publications. It integrates the latest research, clinical trials, and case studies to provide an up-to-date analysis of BoNT-A mechanisms of action, efficacy, safety, and long-term outcomes. The review systematically analyzes existing evidence, critically evaluates study strengths and limitations, and explores potential synergies with other treatments. It also examines the safety profile of BoNT-A and its potential long-term effects. This review uncovers promising insights into how BoNT-A affects oily skin and acne vulgaris, including its ability to regulate sebum production, reduce inflammation, and potentially shrink pore size. It provides a comprehensive overview of relevant studies and clinical trials, detailing their methodologies, protocols, measures, and results. Collectively, these studies show significant reductions in sebum production, increased patient satisfaction, and smaller pores following BoNT-A treatment. In conclusion, this review addresses knowledge gaps and provides a comprehensive analysis of BoNT-A as a therapeutic option for oily skin and acne vulgaris. By consolidating evidence and highlighting areas for further investigation, it guides clinicians and researchers toward more effective, personalized treatments for individuals with these dermatological challenges.

An update on the pharmacotherapeutic options for complex regional pain syndrome

INTRODUCTION

Complex regional pain syndrome (CRPS) is a rare and painful condition that has a wide range of triggering factors, often traumatic, and can present various clinical manifestations. The lack of knowledge about the underlying mechanisms has led to numerous treatment approaches, both conservative and surgical, which work through different mechanisms of action.

AREAS COVERED

In this review, the authors explore the key aspects of CRPS, including definition, diagnostic criteria, pitfalls, pathogenic hypotheses, and treatment strategies with a focus on pharmacotherapy. The review was based on a comprehensive search of the literature using PubMed, while also considering international guidelines for managing CRPS.

EXPERT OPINION

Based on the available evidence, pharmacological interventions appear to be effective in treating CRPS, especially when they target peripheral mechanisms, specifically nociceptive inflammatory pain, and when administered early in the course of the disease. However, there is still a lack of reliable evidence regarding the effects of drugs on central mechanisms of chronic pain in CRPS. In our expert opinion, drug therapy should be initiated as soon as possible, particularly in warm CRPS patient clusters, to prevent significant functional limitations, psychological distress, and negative impacts on individuals' social and economic well-being.

Botulinum toxin type a antinociceptive activity in trigeminal regions involves central transcytosis

OBJECTIVE

Botulinum toxin type A (BoNT-A) provides lasting pain relief in patients with craniofacial pain conditions but the mechanisms of its antinociceptive activity remain unclear. Preclinical research revealed toxin axonal transport to the central afferent terminals, but it is unknown if its central effects involve transsynaptic traffic to the higher-order synapses. To answer this, we examined the contribution of central BoNT-A transcytosis to its action in experimental orofacial pain.

MATERIAL AND METHODS

Male Wistar rats, 3-4 months old, were injected with BoNT-A (7 U/kg) unilaterally into the vibrissal pad. To investigate the possible contribution of toxin's transcytosis, BoNT-A-neutralizing antiserum (5 IU) was applied intracisternally. Antinocicepive BoNT-A action was assessed by duration of nocifensive behaviors and c-Fos activation in the trigeminal nucleus caudalis (TNC) following bilateral or unilateral formalin (2.5%) application into the vibrissal pad. Additionally, cleaved synaptosomal-associated protein of 25 kDa (cl-SNAP-25) immunoreactivity was analyzed in the bilateral TNC.

RESULTS

Unilaterally injected BoNT-A reduced the nocifensive behaviors and bilateral c-Fos activation induced by formalin, which was accompanied by the toxin's enzymatic activity on both sides of the TNC. BoNT-A antinociceptive or enzymatic activities were prevented by the specific neutralizing antitoxin. BoNT-A contralateral action occurred independently from ipsilateral side nociception or contralateral trigeminal nerve-mediated axonal traffic.

CONCLUSION

Herein, we demonstrate that antinociceptive action of pericranially administered BoNT-A involves transsynaptic transport to second order synapses and contralateral trigeminal nociceptive nuclei. These results reveal more complex central toxin activity, necessary to explain its clinical effectiveness in the trigeminal region-related pain states.

Botulinum Toxin Treatment for Cancer-Related Disorders: A Systematic Review

This systematic review investigates the effect of botulinum neurotoxin (BoNT) therapy on cancer-related disorders. A major bulk of the literature is focused on BoNT's effect on pain at the site of surgery or radiation. All 13 published studies on this issue indicated reduction or cessation of pain at these sites after local injection of BoNTs. Twelve studies addressed the effect of BoNT injection into the pylorus (sphincter between the stomach and the first part of the gut) for the prevention of gastroparesis after local resection of esophageal cancer. In eight studies, BoNT injection was superior to no intervention; three studies found no difference between the two approaches. One study compared the result of intra-pyloric BoNT injection with preventive pyloromyotomy (resection of pyloric muscle fibers). Both approaches reduced gastroparesis, but the surgical approach had more serious side effects. BoNT injection was superior to saline injection in the prevention of esophageal stricture after surgery (34% versus 6%, respectively, p = 0.02) and produced better results (30% versus 40% stricture) compared to steroid (triamcinolone) injection close to the surgical region. All 12 reported studies on the effect of BoNT injection into the parotid region for the reduction in facial sweating during eating (gustatory hyperhidrosis) found that BoNT injections stopped or significantly reduced facial sweating that developed after parotid gland surgery. Six studies showed that BoNT injection into the parotid region prevented the development of or healed the fistulas that developed after parotid gland resection-parotidectomy gustatory hyperhidrosis (Frey syndrome), post-surgical parotid fistula, and sialocele. Eight studies suggested that BoNT injection into masseter muscle reduced or stopped severe jaw pain after the first bite (first bite syndrome) that may develop as a complication of parotidectomy.

Prolonged Antipruritic Effect of Botulinum Toxin Type A on Cowhage-induced Itch: A Randomized, Single-blind, Placebo-controlled Trial

Botulinum toxin type A (Botox) is thought to have antipruritic effects through inhibition of pruritic factors, including acetylcholine, substance P, and glutamate. The aim of this randomized, single-blind, placebo-controlled trial was to test the effect of botulinum toxin type A on cowhage, a non-histaminergic model for chronic itch. Botulinum toxin type A was injected into the arm of 35 healthy subjects, with a saline control injected into the contralateral arm. Thermal sensory parameters (warmth and heat thresholds and heat pain intensity) and itch intensity after cowhage application were examined on test areas. Botulinum toxin type A reduced itch intensity, overall perceived itch (area under the curve (AUC); percentage change from baseline), and peak itch intensity compared with the control at 1 week, 1 month, and 3 months. Botulinum toxin type A had no effect on thermal thresholds or heat pain intensity. In conclusion, botulinum toxin type A reduced cowhage itch for at least 3 months, which suggests that botulinum toxin type A is a potential long-lasting treatment for localized, non-histaminergic itch.

[Clinical use of botulinum toxin type A in pain medicine]

Botulinum toxin has been used for decades in the treatment of a variety of painful diseases. Botulinum toxin not only blocks neuromuscular transmission, but also the secretion of neuropeptides, such as substance P, glutamate and calcitonin gene-related peptide (CGRP) and thus inhibits neurogenic inflammation. In addition, it has a modulatory pain-relieving effect via retrograde transport into the central nervous system. In addition to approval for the treatment of dystonia or spasticity, onabotulinum toxin A is also approved for the prophylaxis of chronic migraine if the oral prophylactic migraine medication has had an insufficient effect or has not been tolerated. In addition, botulinum toxin is also recommended in guidelines as a third-line treatment for neuropathic pain, but in Germany this is an off-label application. This article provides an overview of the current clinically relevant areas of application of botulinum toxin in the field of pain medicine.

Novel botulinum neurotoxin-A tibial nerve perineural injection to alleviate overactive bladder symptoms in male rats

Although tibial nerve modulation has shown to induce positive changes in the overactive bladder (OAB), prolonged therapeutic effects using percutaneous stimulation have not yet been achieved. Intradetrusor onabotulinum toxin A injection can provide prolonged therapeutic effects; however, its delivery requires invasive measures. By applying local relief of tibial nerve neural entrapment with onabotulinum toxin A injection, this study investigated the feasibility and efficacy of combining the abovementioned two therapeutic strategies. An OAB animal model was developed using 12 adult Sprague-Dawley rats with cyclophosphamide intraperitoneal injection. A perineural injection site comparable to the tibial nerve perineural injection site and corresponding to that in humans was identified and developed in rats. The toxin was injected five days after establishing the OAB. The incision was made in the skin on the lateral surface of the thigh. The biceps femoris muscle was cut across, exposing the sciatic nerve and its three terminal branches: the sural, common peroneal, and tibial nerves, and 100 units of onabotulinum toxin A was injected into the surrounding tissue. Five days following injection, cystometry was performed. Inter-contraction time, contraction pressure, and interval of the disease state improved with statistical significance. The OAB animal model showed significant improvement with the tibial nerve perineural injection of botulinum toxin, thereby suggesting the possibility of a comparable treatment adaptation in humans.

The effect of intraarticular botulinum toxin-A injection on symptoms of temporomandibular joint disorder

INTRODUCTION

Application of arthrocentesis in temporomandibular joint disorders preferred and suggested therapeutic treatment option in recent years. This study was designed to investigate and compare the effect of intra-articular injection of botulinum toxin-A (Btx-A) on pain and mouth opening after arthrocentesis in nonreduction disc displacement.

MATERIALS AND METHODS

This restrospective study was conducted on 30 patients with a visual analogue scale is higher than five and limited mouth opening. Patients were divided into 2 groups as conventional arthrocentesis group (group A) and intra-articular Btx-A injection following arthrocentesis group (group B). Maximum mouth openining and temporomandibular joint pain were measured in preoperative (t0) and at postoperative 1^st-week (t1), 1^st-month (t2) and 6^th-month (t3).

RESULTS

When VAS scores of group A and group B were examined, no statistical difference was observed at t0 and t1 time intervals; an increased in mouth opening values and decreased VAS score values were observed in both groups in the 1^st month (t2) and 6^{th (}t3) months, mostly in group A.

CONCLUSION

İntra-articular injection of Btx-A following arthrocentesis can induce mouth opening and reduce the pain and dysfunction in patients with anterior disc displacement.

Evaluation of Recombinant Botulinum Neurotoxin Type A1 Efficacy in Peripheral Inflammatory Pain in Mice

Well-established efficacy of botulinum neurotoxin type A (BoNT/A) in aesthetic dermatology and neuromuscular hyperactivity disorders relies on canonical interruption of acetylcholine neurotransmission at the neuromuscular junction at the site of the injection. The mechanisms and the site of activity of BoNT/A in pain, on the other hand, remain elusive. Here, we explored analgesic activity of recombinant BoNT/A1 (rBoNT/A1; IPN10260) in a mouse model of inflammatory pain to investigate the potential role of peripheral sensory afferents in this activity. After confirming analgesic efficacy of rBoNT/A1 on CFA-induced mechanical hypersensitivity in C57Bl6J mice, we used GCaMP6s to perform in vivo calcium imaging in the ipsilateral dorsal root ganglion (DRG) neurons in rBoNT/A1 vs. vehicle-treated mice at baseline and following administration of a range of mechanical and thermal stimuli. Additionally, immunohisochemical studies were performed to detect cleaved SNAP25 in the skin, DRGs and the spinal cord. Injection of CFA resulted in reduced mechanical sensitivity threshold and increased calcium fluctuations in the DRG neurons. While rBoNT/A1 reduced mechanical hypersensitivity, calcium fluctuations in the DRG of rBoNT/A1- and vehicle-treated animals were similar. Cleaved SNAP25 was largely absent in the skin and the DRG but present in the lumbar spinal cord of rBoNT/A1-treated animals. Taken together, rBoNT/A1 ameliorates mechanical hypersensitivity related to inflammation, while the signal transmission from the peripheral sensory afferents to the DRG remained unchanged. This strengthens the possibility that spinal, rather than peripheral, mechanisms play a role in the mediation of analgesic efficacy of BoNT/A in inflammatory pain.

Antinociceptive Actions of Botulinum Toxin A1 on Immunogenic Hypersensitivity in Temporomandibular Joint of Rats

Botulinum neurotoxin type A1 (BoNT-A) reduces the peripheral peptide and cytokine upregulation in rats with antigen-evoked persistent immunogenic hypersensitivity (PIH) of the temporomandibular joint (TMJ). Herein, we examined the effects of two preparations of BoNT-A, abobotulinumtoxinA (aboBoNT-A; Dysport) and onabotulinumtoxinA (onaBoNT-A; Botox), on spontaneous and evoked nociceptive behaviors, as well as on central neuronal and astroglial activation. The antigen-evoked PIH was induced in rats via repeated systemic and unilateral intra-articular (i.a.) injections of methylated bovine serum albumin (mBSA). Rats were subsequently injected with unilateral i.a. aboBoNT-A (14 U/kg), onaBoNT-A (7 U/kg), or the vehicle (saline). After i.a. treatments, spontaneous and mechanically evoked nocifensive behaviors were assessed before and after the low-dose i.a. formalin (0.5%) challenge. The central effects of BoNT-A were assessed by an immunohistochemical analysis of cleaved synaptosomal-associated protein 25 (cSNAP-25) presence, c-Fos, GFAP, and CGRP expression in the trigeminal nucleus caudalis (TNC). Both BoNT-A preparations similarly reduced the formalin-induced spontaneous pain-related behaviors and mechanical allodynia of the hypernociceptive rats. Likewise, their effects were associated with the central occurrence of cSNAP-25 and reduction of c-Fos and GFAP upregulation in the TNC. BoNT-A antinociceptive activity on the PIH is associated with the toxin axonal transport to trigeminal sensory areas and reduction of neuronal and glial activation in central nociceptive regions.

Botulinum toxin for scalp dysesthesia

Scalp dysesthesia is characterized by abnormal cutaneous sensations such as burning, stinging, or itching of the scalp. This condition is particularly challenging to manage as there is a lack of well-established treatments. By limiting release of neurotransmitters such as substance P, glutamate, and calcitonin gene-related peptide, botulinum toxin may have a role in ameliorating neuropathic pain. We report a unique case in which botulinum toxin was used in the management of scalp dysesthesia.

Botulinum Neurotoxin Type A in the Treatment of Facial Seborrhea and Acne: Evidence and a Proposed Mechanism

Intradermal injection of botulinum neurotoxin is a frequently performed procedure in aesthetic dermatology to improve facial skin tone, texture, fine wrinkles, and enlarged pores. In practice, botulinum neurotoxin type A is also used to reduce skin oiliness of the face. There is increasing evidence that acetylcholine plays specific roles in sebum production, suggesting that botulinum neurotoxin type A may reduce sebum production by interfering with cholinergic transmission between sebaceous glands and autonomic nerve terminals. Botulinum neurotoxins can also inhibit several pathogenetic components of acne development, suggesting that botulinum neurotoxins can be used as a safe and effective treatment modality for acne and other skin disorders related to overactivity of sebaceous glands. This review aims to explore the current evidence behind the treatment of facial seborrhea and acne with botulinum neurotoxin type A.

Efficacy of botulinum toxin type A in the management of masticatory myofascial pain: A retrospective clinical study

BACKGROUND

Muscular pain is the main cause of disability worldwide. Myofascial pain of orofacial origin is a frequent condition, the treatment of which is not always accomplished with traditional treatment. Botulinum toxin type A (BTA) is being studied for the treatment of this type of pain with contradicting results. Thus, the objective of this study was to assess the efficacy of BTA in the therapeutic management of masticatory myofascial pain (MFP).

CASE DESCRIPTION

A retrospective study of 100 patients with a diagnosis of MFP was conducted. The control group (50 patients) received conventional treatment (prescription of a muscle relaxant and craniocervical physical therapy). The BTA group (50 patients) received this same treatment and the infiltration of 100 units of BTA in the masticatory musculature. Subjective and objective pain ratings and range of mandibular movements were recorded before and after the treatment. No differences were found between groups in the baseline values. Statistically significant improvements were found in both groups compared with baseline values in all studied parameters. Moreover, BTA improved the subjective pain ratings compared with the control group. The administration of BTA added to the conventional treatment does not seem to improve objective pain ratings and functional measurements, but it improves the subjective pain ratings.

PRACTICAL IMPLICATIONS

The addition of BTA could be beneficial in the treatment of MFP in addition to conventional treatment, but further studies are needed to elucidate the mechanisms underlying this positive effect.

Comparative Effectiveness of Injection Therapies for Hemiplegic Shoulder Pain in Stroke: A Systematic Review and Network Meta-Analysis

Hemiplegic shoulder pain (HSP) hampers post-stroke functional recovery and is not well managed with conservative treatments. This systematic review aimed to examine the various injection therapies for HSP and investigate their effectiveness at different time points. The protocol of this meta-analysis was registered on INPLASY with a registration number of INPLASY202180010. PubMed, EMBASE, and Scopus were searched from their inception to 4 August 2021 for the clinical studies investigating comparative effectiveness of different injection regimens for treating hemiplegic shoulder pain in patients with stroke. The primary outcome was the weighted mean difference (WMD) on the visual analog scale (VAS) of pain reduction in the fourth-week and between the fourth and twenty-fourth weeks. Ranking probabilities of the WMD for each treatment were obtained using simulations. Seventeen studies with 595 participants were included. The network meta-analysis showed that at the fourth-week, intra-muscular botulinum toxin (BoNT) injections and suprascapular nerve blocks (SSNB) were superior to a placebo, with WMDs of 1.55 (95% CI, 0.09 to 3.01) and 1.44 (95% CI, 0.07 to 2.80), respectively. SSNB possessed the highest probability (53.3%) and appeared to be the best treatment in the fourth-week, followed by intra-muscular BoNT injections (42.6%). Intramuscular BoNT injections were better than the placebo, with a WMD of 1.57 (95% CI, 0.30 to 2.84) between the 4th and 24th weeks. Intramuscular BoNT injections had the highest probability (79.8%) as the best treatment between the 4th and 24th weeks. SSNB was likely to rank first in relieving HSP at the fourth post-treatment week, whereas intra-muscular BoNT injections had the highest probability to achieve the best treatment effectiveness in the post-injection period between the fourth and twenty-fourth weeks. However, as some of the included studies used a non-randomized controlled design, more randomized controlled trials are needed in the future to validate and better understand the short- and long-term efficacy of different injection therapies for management of HSP.

The Mechanisms of Action of Botulinum Toxin Type A in Nociceptive and Neuropathic Pathways in Cancer Pain

BACKGROUND

Botulinum toxin type A (BoNT-A) is widely employed for cosmetic purposes and in the treatment of certain diseases such as strabismus, hemifacial spasm and focal dystonia among others. BoNT-A effect mainly acts at the muscular level by inhibiting the release of acetylcholine at presynaptic levels consequently blocking the action potential in the neuromuscular junction. Despite the great progress in approval and pharmaceutical usage, improvement in displacing BoNT-A to other pathologies has remained very limited. Patients under diagnosis of several types of cancer experience pain in a myriad of ways; it can be experienced as hyperalgesia or allodynia, and the severity of the pain depends, to some degree, on the place where the tumor is located. Pain relief in patients diagnosed with cancer is not always optimal, and as the disease progresses, transition to more aggressive drugs, like opioids is sometimes unavoidable. In recent years BoNT-A employment in cancer has been explored, as well as an antinociceptive drug; experiments in neuropathic, inflammatory and acute pain have been carried out in animal models and humans. Although its mechanism has not been fully known, evidence has shown that BoNT-A inhibits the secretion of pain mediators (substance P, Glutamate, and calcitonin gene related protein) from the nerve endings and dorsal root ganglion, impacting directly on the nociceptive transmission through the anterolateral and trigeminothalamic systems.

AIM

The study aimed to collect available literature regarding molecular, physiological and neurobiological evidence of BoNT-A in cancer patients suffering from acute, neuropathic and inflammatory pain in order to identify possible mechanisms of action in which the BoNT-A could impact positively in pain treatment.

CONCLUSION

BoNT-A could be an important neo-adjuvant and coadjuvant in the treatment of several types of cancer, to diminish pro-tumor activity and secondary pain.

Pain complications of oral implants: Is that an issue?

The use of oral implants as a form of replacing missing teeth in partial or total edentulous patients is considered the gold standard in oral rehabilitation. Although considered a history of success in contemporary dentistry, surgical complications may occur, as excessive bleeding, damage to the adjacent teeth and mandibular fractures. Persistent pain and abnormal somatosensory responses after the surgery ordinary healing time are also potential problems and may lead to the development of a condition named posttraumatic trigeminal neuropathic pain (PTNP). Though relatively rare, PTNP has a profound impact on patient's quality of life. Appropriated previous image techniques, effective anaesthetic procedures and caution during the surgical procedure and implant installation are recommended for the prevention of this condition. In case of the PTNP, different management modalities, including antidepressant and membrane stabilizer medications, as well as peripheral strategies, as the use of topical medication and the botulin toxin are presented and discussed.

Botulinum toxin A alleviates orofacial nociception induced by orthodontic tooth movement through nociceptin/orphanin-FQ pathway in rats

OBJECTIVES

To investigate the effect and mechanism of botulinum neurotoxin type A (BoNT/A) in the modulation of orofacial nociception induced by orthodontic tooth movement in rats.

METHODS

An orofacial nociception model was established in male Sprague-Dawley rats by ligating closed-coil springs between incisors and ipsilateral molars. There were two group sets of animals. For the first group set, 120 rats were randomly divided into four groups: no-force group (n = 30), force + saline group (n = 30), force + low dose BoNT/A group (1U/6 μL, n = 30), and force + high dose BoNT/A group (1U/6 μL, n = 30). BoNT/A and saline were injected into periodontal ligament to explore the nociceptive effect of BoNT/A. Ipsilateral trigeminal ganglia (TG) were harvested for detecting the expression levels of nociceptin/orphanin-FQ (N/OFQ). For the second group set, 36 rats were randomly divided into three force groups: BoNT/A + saline group (n = 12), BoNT/A + UFP-101 group (n = 12), and saline + UFP-101 group (n = 12). A potent N/OFQ receptor (NOP) antagonist (UFP-101) was used to examine the role of N/OFQ in BoNT/A-induced antinociception. Tooth-movement nociception level of all groups was evaluated by bite force and rat grimace scale (RGS) at baseline, day 1, day 3, day 5, day 7, day 14.

RESULTS

The behavioral assessments showed the orofacial nociception level in the force + low dose BoNT/A group and force + high dose BoNT/A group were lower than that in the force + saline group. No significant difference was observed in orofacial nociception among no-force group, force + low dose and force + high dose group. The expression levels of N/OFQ in TG were elevated from day 1 and maintained a high level, presenting in descending order among the force + high dose, force + low dose, force + saline and no-force group, respectively. The nociception level of the BoNT/A + UFP-101 group was higher than that of the BoNT/A + saline group. No significant difference was observed between the BoNT/A + UFP-101 group and the saline + UFP-101 group.

CONCLUSIONS

BoNT/A can exert an antinociceptive effect on orofacial nociception induced by tooth movement by stimulating the expression of N/OFQ in TG.

Novelty in Inflammation and Immunomodulation in Migraine

BACKGROUND

Migraine is a diffuse and disabling disease. Its pathophysiology is complex and involves both central and peripheral dysfunctions.

OBJECTIVE

This review will discuss the pathogenesis of migraine from the origin of the neuro-inflammatory theory, to the modern pathophysiological model and the latest therapies.

METHODS

PUBMED and EMBASE (up to May 2019) were searched for: migraine, inflammation, immunomodulation. An additional search was carried out from the bibliography of previous review articles.

RESULTS

Migraine was thought to be mainly a vascular disorder, according to the so-called "vascular theory". Based on animal models, a new hypothesis called "the neuro-inflammatory" was conceived at the end of the 20th century. The growing knowledge about the trigeminovascular system and its role in the inflammatory-pain pathway, allowed to identify other specific neurotransmitters, such as the Calcitonin Gene-Related Peptide and Pituitary Adenylate Cyclase-Activating Peptide. Evidence was provided that the inflammatory-pain system could become sensitised and, due to this sensitisation, the pain could also perpetuate, even in the absence of any triggers of the migraine attack. At last, brain immune cells modification during cortical spreading depression in migraine was demonstrated, along with the existence and function of the glymphatic system. The better comprehension of the immune system abnormalities allowed the development of new immunomodulating drugs: the monoclonal antibodies against the CGRP or the CGRP receptor. Moreover, new insights into the molecular mechanism of CGRP, and the function of C-fibres and Aδ-fibres, highlighted the mechanism of action of Botulinum Toxin type A in the treatment of chronic migraine.

New analgesic: Focus on botulinum toxin

In 2010, Kissin concluded pessimistically that of the 59 new drugs introduced in the fifty-year period between 1960 and 2009 and still in use, only seven had new molecular targets. Of these, only one, sumatriptan, was effective enough to lead to the introduction of multiple drugs targeting the same target molecules (triptans) (Kissin, 2010). Morphine and acetylsalicylic acid (aspirin), introduced for the treatment of pain more than a century ago, continue to dominate biomedical publications despite their limited effectiveness in many areas (e.g., neuropathic pain) and serious adverse effects. Today, are we really closer to ideal analgesics that would work hard enough, long enough, and did not have unwanted side effects? The purpose of the present article is to analyze where we are now. Several drugs, like long-acting opioids or botulinum toxins open some hope. Advantage of botulinum toxin A is unique duration of action (months). New discoveries showed that after peripheral application botulinum toxin by axonal transport reaches the CNS. Major analgesic mechanism of action seems to be of central origin. Will botulinum toxin in the CNS bring new indications and or/adverse effects? Much more basic and clinical research should be in front of us. Although relatively safe as a drug, botulinum toxin is not without adverse effect. Policy makers, clinicians and all those applying botulinum toxin should be aware of that. Unfortunately the life without the pain is still not possible.

Quantification of surviving neurons after contusion, dislocation, and distraction spinal cord injuries using automated methods

This study proposes and validates an automated method for counting neurons in spinal cord injury (SCI) and then uses it to examine and compare the surviving cells in common types of SCI mechanisms. Moderate contusion, dislocation, and distraction SCIs were surgically induced in Sprague Dawley male rats (n = 6 for each type of injury). Their spinal cords were harvested 8 weeks post injury with 5 normal weight-matched rats. The spinal cords were cut, stained with anti-NeuN antibody and fluorescent Nissl, and imaged in the dorsal and ventral horns at various distances to the epicenter. Neurons in the images were automatically counted using an algorithm that was designed to filter non-soma-like objects based on morphological characteristics (size, solidity, circular pattern) and check the remaining objects for the double-stained nucleus/cell body features (brightness variation, brightness distribution, color). To validate the automated method, some of the images were randomly selected for manual counting. The number of surviving cells that were automatically measured by the algorithm was found to be correlated with the values that were manually measured by 2 observers (P < .001) with similar differences (P > .05). Neurons in the dorsal and ventral horns were reduced after the SCIs (P < .05). Dislocation and distraction, respectively, caused the most severe damage to the ventral horn neurons especially near the epicenter and the most extensive and uniform damage to the dorsal horn neurons (P < .05). Our method was proved to be reliable, which is suitable for studying different types of SCI.

Mechanisms of Botulinum Toxin Type A Action on Pain

Already a well-established treatment for different autonomic and movement disorders, the use of botulinum toxin type A (BoNT/A) in pain conditions is now continuously expanding. Currently, the only approved use of BoNT/A in relation to pain is the treatment of chronic migraines. However, controlled clinical studies show promising results in neuropathic and other chronic pain disorders. In comparison with other conventional and non-conventional analgesic drugs, the greatest advantages of BoNT/A use are its sustained effect after a single application and its safety. Its efficacy in certain therapy-resistant pain conditions is of special importance. Novel results in recent years has led to a better understanding of its actions, although further experimental and clinical research is warranted. Here, we summarize the effects contributing to these advantageous properties of BoNT/A in pain therapy, specific actions along the nociceptive pathway, consequences of its central activities, the molecular mechanisms of actions in neurons, and general pharmacokinetic parameters.

Pharmacotherapeutic options for complex regional pain syndrome

INTRODUCTION

Complex regional pain syndromes (CRPS) are rare painful conditions characterized by considerable variability in possible triggering factors, usually traumatic, and in the clinical scenario. The limited knowledge of the pathophysiological mechanisms has led to countless treatment attempts with multiple conservative and surgical options that act by different mechanisms of action.

AREAS COVERED

In this narrative review, the authors discuss key points about CRPS definitions, diagnostic criteria and pitfalls, pathophysiological hypotheses, and treatment strategies with particular reference to pharmacotherapy. The article was based on a literature search using PubMed while the available guidelines for the management of CRPS were also examined.

EXPERT OPINION

According to the quality of evidence, pharmacological interventions for CRPS seem to be more effective all the more so when they act on peripheral mechanisms, particularly on nociceptive pain, and when applied early in the disease, while reliable evidence about central mechanisms of chronic pain in CRPS is lacking. In our opinion, drug therapy should be preferred as early as possible, particularly in warm forms of CRPS to prevent significant functional limitation, psychological distress, and social and economic fallout.

Botulinum toxin type A applications for masticatory myofascial pain and trigeminal neuralgia: what is the evidence regarding adverse effects?

OBJECTIVES

The objective of the study was to conduct a systematic review of literature assessing botulinum toxin type A (BoNT-A) safety and adverse effects in the treatment of myofascial pain (MFP) and trigeminal neuralgia (TN).

MATERIALS AND METHODS

The search for articles by two specific researchers involved the PubMed, EMBASE, Web of Science, and Scopus databases. Specific terms were used, and no publication time and language restrictions were applied. Clinical trials that investigated the effects of BoNT-A among participants with myofascial pain in masticatory muscles or trigeminal neuralgia were considered eligible for this systematic review. Data for each study were extracted and analyzed according to a PICO-like structured reading.

RESULTS

The search strategy provided 436 citations. After analysis, 16 citations were included, seven for MFP and nine for TN. In all studies, BoNT-A was well tolerated and improved pain. The most common adverse effects were temporary regional weakness, tenderness over the injection sites, and minor discomfort during chewing. Most studies reported a spontaneous resolution of adverse effect.

CONCLUSIONS

It can be concluded that BoNT-A treatment is well tolerated, since minor adverse effects were the most frequently reported; however, it is recommended that future studies aim to assess the safety and possible adverse effects of multiples applications or high doses of this treatment.

CLINICAL RELEVANCE

BoNT-A has been increasingly diffused in dentistry, being used for the management of masticatory myofascial pain and trigeminal neuralgia. Nonetheless, there is no consensus about its efficacy and adverse effects that could occur when this treatment is applied.

OnabotulinumtoxinA Reduces Temporal Pain Processing at Spinal Level in Patients with Lower Limb Spasticity

Spasticity is a muscle tone disorder associated with different neurological conditions. Spasticity could be associated with pain, high disability, poor functional recovery, and reduced quality of life. Botulinum neurotoxin type A (BoNT-A) is considered a first-line treatment for spasticity and, more recently, it also represents a therapeutic option for various chronic pain conditions. In this open label study, we aim to evaluate the effect of the BoNT-A on the spinal nociception in patients affected by spasticity of the lower limbs with associated pain with predominantly neuropathic features. Ten patients with stroke, 10 with multiple sclerosis and 5 with spinal cord injury were enrolled in the study. They were tested with clinical scales (neuropathic pain scale inventory (NPSI), numerical rating scale (NRS), modified Ashworth scale (MAS) and with the nociceptive withdrawal reflex at lower limbs to explore the spinal temporal summation threshold at baseline and 30 day after BoNT-A injection. OnabotulinumtoxinA (50 to 200 units per site) was injected in the lower limb muscles according to the distribution of spasticity. No significant differences were found at baseline for neurophysiological features across groups. After the BoNT-A injection, we recorded a significant reduction in MAS and NRS scores. Regarding the neurophysiological parameters, we described a significant increase in the temporal summation threshold after the BoNT-A injection. Our data supports the hypothesis that peripherally injected OnabotulinumtoxinA modulates the excitability of spinal cord nociceptive pathways. This activity may take place irrespective of the effect of the drug on spasticity.

Neurokinin-1 receptor-based bivalent drugs in pain management: The journey to nowhere?

Hybrid compounds (also known as chimeras, designed multiple ligands, bivalent compounds) are chemical units where two active components, usually possessing affinity and selectivity for distinct molecular targets, are combined as a single chemical entity. The rationale for using a chimeric approach is well documented as such novel drugs are characterized by their enhanced enzymatic stability and biological activity. This allows their use at lower concentrations, increasing their safety profile, particularly when considering undesirable side effects. In the group of synthetic bivalent compounds, drugs combining pharmacophores having affinities toward opioid and neurokinin-1 receptors have been extensively studied as potential analgesic drugs. Indeed, substance P is known as a major endogenous modulator of nociception both in the peripheral and central nervous systems. Hence, synthetic peptide fragments showing either agonism or antagonism at neurokinin 1 receptor were both assigned with analgesic properties. However, even though preclinical studies designated neurokinin-1 receptor antagonists as promising analgesics, early clinical studies revealed a lack of efficacy in human. Nevertheless, their molecular combination with enkephalin/endomorphin fragments has been considered as a valuable approach to design putatively promising ligands for the treatment of pain. This paper is aimed at summarizing a 20-year journey to the development of potent analgesic hybrid compounds involving an opioid pharmacophore and devoid of unwanted side effects. Additionally, the legitimacy of considering neurokinin-1 receptor ligands in the design of chimeric drugs is discussed.

Anti-allodynic effect of interleukin 10 in a mouse model of complex regional pain syndrome through reduction of NK1 receptor expression of microglia in the spinal cord

Background

To date, there has been no study on the effects of interleukin-10 (IL-10) on complex regional pain syndrome (CRPS) rodent models, despite the anti-allodynic effect of IL-10 in previous studies. Thus, the aim of this study was to investigate the effect of IL-10 in a CRPS mouse model and find whether early inhibition of neuro-inflammation by IL-10 administration, which is considered to be one of the important mechanisms in the generation of central sensitization, could prevent the transition from the acute stage to the chronic stage of CRPS.

Method

A mouse model of CRPS (n=6/group) involving tibia fracture/cast immobilization to test the efficacy of intrathecal IL-10 (0.3 μg/5 μL^-1 day^-1 for 7 days) or vehicle during the acute (3 weeks after fracture) stage of CRPS.

Results

Intrathecal recombinant IL-10 (rIL-10) administration was anti-allodynic in the acute stage of the CRPS mouse model, and these anti-allodynic effects of IL-10 developed by modulating microglial activation and decreasing NK1 receptor expression in the spinal cord. However, intrathecal rIL-10 administration in the acute stage of the CRPS mouse model cannot prevent the transition to the chronic stage of CRPS in the acute stage of CRPS.

Conclusion

Collectively, these results demonstrate that intrathecally administered rIL-10 attenuates mechanical allodynia in the CRPS mouse model. However, this effect of IL-10 on allodynia in the acute stage of CRPS was not sufficient to prevent the transition to the chronic stage of CRPS. In the future, further studies about the mechanisms of central sensitization in CRPS will be necessary.