Exploring the effects of extracranial injections of botulinum toxin type A on activation and sensitization of central trigeminovascular neurons by cortical spreading depression in male and female rats.

BACKGROUND: OnabotulinumtoxinA (onabotA), is assumed to achieve its therapeutic effect in migraine through blocking activation of unmyelinated meningeal nociceptors and their downstream communications with central dura-sensitive trigeminovascular neurons in the spinal trigeminal nucleus (SPV). The present study investigated the mechanism of action of onabotA by assessing its effect on activation and sensitization of dura-sensitive neurons in the SPV by cortical spreading depression (CSD). It is a follow up to our recent study on onabotA effects on activation and sensitization of peripheral trigeminovascular neurons. METHODS: In anesthetized male and female rats, single-unit recordings were used to assess effects of extracranial injections of onabotA (five injections, one unit each, diluted in 5 µl of saline were made along the lambdoid (two injection sites) and sagittal (two injection sites) suture) vs. vehicle on CSD-induced activation and sensitization of high-threshold (HT) and wide-dynamic range (WDR) dura-sensitive neurons in the SPV. RESULTS: Single cell analysis of onabotA pretreatment effects on CSD-induced activation and sensitization of central trigeminovascular neurons in the SPV revealed the ability of this neurotoxin to prevent activation and sensitization of WDR neurons (13/20 (65%) vs. 4/16 (25%) activated neurons in the control vs. treated groups, p = 0.022, Fisher's exact). By contrast, onabotA pretreatment effects on CSD-induced activation and sensitization of HT neurons had no effect on their activation (12/18 (67%) vs. 4/7 (36%) activated neurons in the control vs. treated groups, p = 0.14, Fisher's exact). Regarding sensitization, we found that onabotA pretreatment prevented the enhanced responses to mechanical stimulation of the skin (i.e. responses reflecting central sensitization) in both WDR and HT neurons. In control but not treated WDR neurons, responses to brush (p = 0.004 vs. p = 0.007), pressure (p = 0.002 vs. p = 0.79) and pinch (p = 0.007 vs. 0.79) increased significantly two hours after CSD. Similarly, in control but not treated HT neurons, responses to brush (p = 0.002 vs. p = 0.79), pressure (p = 0.002 vs. p = 0.72) and pinch (p = 0.0006 vs. p = 0.28) increased significantly two hours after CSD. Unexpectedly, onabotA pretreatment prevented the enhanced responses of both WDR and HT neurons to mechanical stimulation of the dura (commonly reflecting peripheral sensitization). In control vs. treated WDR and HT neurons, responses to dural stimulation were enhanced in 70 vs. 25% (p = 0.017) and 78 vs. 27% (p = 0.017), respectively. CONCLUSIONS: The ability of onabotA to prevent activation and sensitization of WDR neurons is attributed to its preferential inhibitory effects on unmyelinated C-fibers. The inability of onabotA to prevent activation of HT neurons is attributed to its less extensive inhibitory effects on the thinly myelinated Aδ-fibers. These findings provide further pre-clinical evidence about differences and potentially complementary mechanisms of action of onabotA and calcitonin gene-related peptide-signaling neutralizing drugs.

Versatility of OnabotulinumtoxinA in Aesthetic Medicine.

BACKGROUND: OnabotulinumtoxinA is an injectable product that was introduced into medicine in the 1970s and has been the subject of thousands of clinical and nonclinical publications. OBJECTIVE: To review the data related to the versatility of onabotulinumtoxinA in medical aesthetics. METHODS: PubMed was searched to identify literature evaluating the effects of onabotulinumtoxinA, with preference given to randomized, placebo-controlled trials and safety meta-analyses. RESULTS: OnabotulinumtoxinA is effective and safe across multiple facial indications, racial and ethnic groups, age groups, genders, and facial line severities. Patient-reported outcomes have been prioritized in aesthetic clinical trials and indicate high patient satisfaction and appearance-related psychological outcomes. Integrated safety meta-analysis and immunogenicity analyses have documented acceptable adverse event rates and low immunogenicity of onabotulinumtoxinA. CONCLUSION: OnabotulinumtoxinA is a versatile aesthetic product supported by a strong literature base and positive physician and patient-reported outcomes that reflect a meaningful impact on patient's quality of life.

The headache research priorities: Research goals from the American Headache Society and an international multistakeholder expert group.

OBJECTIVE: To identify and disseminate research priorities for the headache field that should be areas of research focus during the next 10 years. BACKGROUND: Establishing research priorities helps focus and synergize the work of headache investigators, allowing them to reach the most important research goals more efficiently and completely. METHODS: The Headache Research Priorities organizing and executive committees and working group chairs led a multistakeholder and international group of experts to develop headache research priorities. The research priorities were developed and reviewed by clinicians, scientists, people with headache, representatives from headache organizations, health-care industry representatives, and the public. Priorities were revised and finalized after receiving feedback from members of the research priorities working groups and after a public comment period. RESULTS: Twenty-five research priorities across eight categories were identified: human models, animal models, pathophysiology, diagnosis and management, treatment, inequities and disparities, research workforce development, and quality of life. The priorities address research models and methods, development and optimization of outcome measures and endpoints, pain and non-pain symptoms of primary and secondary headaches, investigations into mechanisms underlying headache attacks and chronification of headache disorders, treatment optimization, research workforce recruitment, development, expansion, and support, and inequities and disparities in the headache field. The priorities are focused enough that they help to guide headache research and broad enough that they are widely applicable to multiple headache types and various research methods. CONCLUSIONS: These research priorities serve as guidance for headache investigators when planning their research studies and as benchmarks by which the headache field can measure its progress over time. These priorities will need updating as research goals are met and new priorities arise.

Update on Non-Interchangeability of Botulinum Neurotoxin Products.

The growing use of botulinum neurotoxins (BoNTs) for medical and aesthetic purposes has led to the development and marketing of an increasing number of BoNT products. Given that BoNTs are biological medications, their characteristics are heavily influenced by their manufacturing methods, leading to unique products with distinct clinical characteristics. The manufacturing and formulation processes for each BoNT are proprietary, including the potency determination of reference standards and other features of the assays used to measure unit potency. As a result of these differences, units of BoNT products are not interchangeable or convertible using dose ratios. The intrinsic, product-level differences among BoNTs are compounded by differences in the injected tissues, which are innervated by different nerve fiber types (e.g., motor, sensory, and/or autonomic nerves) and require unique dosing and injection sites that are particularly evident when treating complex therapeutic and aesthetic conditions. It is also difficult to compare across studies due to inherent differences in patient populations and trial methods, necessitating attention to study details underlying each outcome reported. Ultimately, each BoNT possesses a unique clinical profile for which unit doses and injection paradigms must be determined individually for each indication. This practice will help minimize unexpected adverse events and maximize efficacy, duration, and patient satisfaction. With this approach, BoNT is poised to continue as a unique tool for achieving individual goals for an increasing number of medical and aesthetic indications.

Early development history of Botox (onabotulinumtoxinA).

The development of Botox (onabotulinumtoxinA) began in the 1970s as Dr. Scott was attempting to identify an injectable substance that would weaken the extraocular eye muscles in patients with strabismus as an alternative to muscle surgery. This search led to botulinum toxin type A, which was tested and developed over the next 15 years. As botulinum toxin type A moved from an experimental drug to a product in need of licensing by the Food and Drug Administration (FDA), the first manufacturing methods and quality control procedures were developed for Oculinum, the botulinum toxin type A product that would eventually be sold to Allergan and become known as Botox.

Botox (onabotulinumtoxinA) mechanism of action.

Studies in the 1920s found that botulinum neurotoxin type A (BoNT/A) inhibited the activity of motor and parasympathetic nerve endings, confirmed several decades later to be due to decreased acetylcholine release. The 1970s were marked by studies of cellular mechanisms aided by use of neutralizing antibodies as pharmacologic tools: BoNT/A disappeared from accessibility to neutralizing antibodies within minutes, although it took several hours for onset of muscle weakness. The multi-step mechanism was experimentally confirmed and is now recognized to consist broadly of binding to nerve terminals, internalization, and lysis or cleavage of a protein (SNAP-25: synaptosomal associated protein-25 kDa) that is part of the SNARE (Soluble NSF Attachment protein REceptor) complex needed for synaptic vesicle docking and fusion. Clinical use of the BoNT/A product onabotulinumtoxinA was based on its ability to reduce muscle contractions via inhibition of acetylcholine from motor terminals. Sensory mechanisms of onabotulinumtoxinA have now been identified, supporting its successful treatment of chronic migraine and urgency in overactive bladder. Exploration into migraine mechanisms led to anatomical studies documenting pain fibers that send axons through sutures of the skull to outside the head-a potential route by which extracranial injections could affect intracranial processes. Several clinical studies have also identified benefits of onabotulinumtoxinA in major depression, which have been attributed to central responses induced by feedback from facial muscle and skin movement. Overall, the history of BoNT/A is distinguished by basic science studies that stimulated clinical use and, conversely, clinical observations that spurred basic research into novel mechanisms of action.

The pluripotential evolution and journey of Botox (onabotulinumtoxinA).

Clinical use of onabotulinumtoxinA evolved based on strategic, hypothesis-driven applications, as well as serendipitous observations by physicians and patients. The success of onabotulinumtoxinA in blepharospasm and strabismus led to its study in other head and neck dystonias, followed by limb dystonia, tremor, and spasticity. The aesthetic use of onabotulinumtoxinA followed initial reports from patients of improved facial lines after injections for facial dystonias and hemifacial spasm. Although patients with dystonias and spasticity regularly reported that their local pain improved after injections, onabotulinumtoxinA was not systematically explored for chronic migraine until patients began reporting headache improvements following aesthetic injections. Clinicians began assessing onabotulinumtoxinA for facial sweating and hyperhidrosis based on its inhibition of acetylcholine from sympathetic cholinergic nerves. Yet another line of research grew out of injections for laryngeal dystonia, whereby clinicians began to explore other sphincters in the gastrointestinal tract and eventually to treatment of pelvic sphincters; many of these sphincters are innervated by autonomic nerves. Additional investigations in other autonomically mediated conditions were conducted, including overactive bladder and neurogenic detrusor overactivity, achalasia, obesity, and postoperative atrial fibrillation. The study of onabotulinumtoxinA for depression also grew out of the cosmetic experience and the observation that relaxing facial muscle contractions associated with negative emotions may improve mood. For approved indications, the safety profile of onabotulinumtoxinA has been demonstrated in the formal development programs and post-marketing reports. Over time, evidence has accumulated suggesting clinical manifestations of systemic effects, albeit uncommon, particularly with high doses and in vulnerable populations. Although onabotulinumtoxinA is approved for approximately 26 indications across multiple local regions, there are 15 primary indication uses that have been approved in most regions, including the United States, Europe, South America, and Asia. This review describes many uses for which AbbVie has not sought and/or received regulatory approval and are mentioned for historical context only.

Treatment of strabismus and blepharospasm with Botox (onabotulinumtoxinA): Development, insights, and impact.

Strabismus, deviation of the ocular alignment, can adversely affect quality of life and activities of daily living. Surgery was the prior standard of care for strabismus, but up to 40% of patients required additional surgeries. This need for more effective and less invasive treatment, along with the convergence of other events such as the development of electromyography, purification of botulinum toxin A, and the finding that injection of botulinum toxin type A could paralyze the hind limbs of chicks, led Dr. Alan Scott to investigate injection of his formulation for strabismus. The positive results of initial trials in monkeys segued to human trials with observations of alignment improvements and few adverse events. The success of botulinum toxin type A in the treatment of strabismus led to interest in its use to treat other skeletal muscles, particularly in blepharospasm, a type of focal dystonia involving eyelid spasms and involuntary eye closure that lacked an effective pharmacological treatment. Patient groups helped to increase awareness of this novel treatment, and results from clinical trials confirmed its effectiveness. Dr. Scott's formulation, then known as Oculinum, received its first Food and Drug Administration approvals in 1989 for strabismus and blepharospasm. Allergan acquired Oculinum in 1991, renaming it Botox. These initial uses led to its application in a myriad of other indications as outlined in other articles of this supplement.

Treatment of cervical dystonia with Botox (onabotulinumtoxinA): Development, insights, and impact.

Cervical dystonia (CD), the most common focal dystonia encountered in neurologic practice, is a chronic disorder in which the muscles of the neck involuntarily contract and cause abnormal postures and movements of the head, neck, and shoulders. Treatment of CD prior to botulinum toxin was unsatisfactory, as existing therapies often did not improve symptoms. The use of botulinum toxin for CD grew out of its success in treating blepharospasm, another type of focal dystonia. On the basis of results from a double-blind, placebo-controlled trial, onabotulinumtoxinA was approved in 2000 in the US for the treatment of CD in adults in order to alleviate abnormal head position and neck pain. A subsequent large observational trial further demonstrated the effectiveness of onabotulinumtoxinA for CD, showing improvements in various rating scales, physician-reported measures, and profound positive effects on patient quality of life, including in amelioration of pain and improvements in work productivity. In addition, onabotulinumtoxinA treatment also reduced the complications of CD, as patients no longer develop contractures (permanent muscle and tendon shortening from prolonged untreated dystonia), which markedly limited the range of neck motion. The onset of onabotulinumtoxinA treatment also accompanied advances in understanding the functional anatomy of neck muscles, basal ganglia physiology, and video and other recording technology. Following the success of onabotulinumtoxinA in the treatment of CD, its use has been expanded into numerous other therapeutic indications, and these advances stimulated educational and training programs by various neurologic and other medical societies.

Treatment of glabellar lines with Botox (onabotulinumtoxinA): Development, insights, and impact.

OnabotulinumtoxinA is an injectable medication that produces muscle relaxation through local chemical denervation at the neuromuscular junction. Discovery of onabotulinumtoxinA's aesthetic benefits occurred serendipitously in the 1980s at the intersection of several medical disciplines, including ophthalmology, neurology, otolaryngology, and dermatology. Patients receiving onabotulinumtoxinA for blepharospasm, hemifacial spasm, and dystonia noticed their periorbital wrinkles disappearing, particularly frown lines between the eyebrows called glabellar lines (GL). Aesthetic use of onabotulinumtoxinA necessitated rigorous training programs and vigilant monitoring by Allergan. Approval for the GL indication was based on 2 similarly designed, double-blind, randomized, multicenter clinical studies. Subjects with moderate to severe GL receiving onabotulinumtoxinA achieved significantly greater improvement in GL severity than those receiving placebo. In subsequent studies, more than 80% of subjects were satisfied with onabotulinumtoxinA treatment through day 60, and many reported looking approximately 4 years younger at weeks 4 and 12 than at baseline. OnabotulinumtoxinA has a rapid onset of action, and peak effect occurs between 30 and 60 days. The median duration of response for dynamic GL in the initial studies was 120 days and response progressively improved with subsequent treatments. OnabotulinumtoxinA was well tolerated, and the 2 most common adverse events, headache and blepharoptosis, tended to decrease in frequency with repeat treatment. The novel use of onabotulinumtoxinA for treating GL was an important step in addressing the clinical need for a noninvasive, straightforward, office-based procedure for facial lines that also left patients extremely satisfied with its treatment effects and represented the beginning of its widespread use for numerous aesthetic indications.

Treatment of crow's feet lines and forehead lines with Botox (onabotulinumtoxinA): Development, insights, and impact.

Extrinsic and age-related intrinsic factors contribute to the development of facial lines, including lateral canthal lines (called crow's feet lines [CFL]) and horizontal forehead lines (FHL). OnabotulinumtoxinA is a highly effective treatment for facial lines that inhibits acetylcholine release at the neuromuscular junction. This temporary chemical denervation leads to localized muscle relaxation and subsequent wrinkle reduction. Early studies of onabotulinumtoxinA treatment for facial neuronal disorders such as dystonia documented improvements in FHL and CFL. After the neurotoxin was approved for treating frown lines (glabellar lines [GL]), individuals requested treatment for other rhytids, and physicians continued assessing use in new areas. Once onabotulinumtoxinA was in clinical trial development, its efficacy and safety for CFL and FHL were successively evaluated as required by the US Food and Drug Administration and by key global health authorities, including those in the European Union, Japan, and China. Allergan, collaborating with leading physicians, established clinical programs that included novel safety and efficacy measures to meet regulatory requirements. Global, phase 3, randomized, controlled studies of CFL and FHL met rigorous primary endpoints. Some countries mandated clinical trial data beyond US and European regulations, and Allergan conducted 11 studies in total, fulfilling diverse regulatory and study population data requirements. Adverse events associated with local spread, including brow and eyelid ptosis, diplopia, headache, and eyelid sensory disorder, were infrequent and well tolerated. Consequently, onabotulinumtoxinA treatment of upper facial lines is now established globally as a highly effective, minimally invasive treatment for patients to achieve a natural appearance and look younger.

Treatment of chronic migraine with Botox (onabotulinumtoxinA): Development, insights, and impact.

Chronic migraine (CM) is a neurological disease characterized by frequent migraine attacks that prevent affected individuals from performing daily activities of living, significantly diminish quality of life, and increase familial burden. Before onabotulinumtoxinA was approved for CM, there were few treatment options for these seriously disabled patients and none had regulatory approval. The terminology and recognition of CM evolved in parallel with the onabotulinumtoxinA clinical development program. Because there were no globally accepted classification criteria for CM when onabotulinumtoxinA was in development, the patient populations for the trials conducted by Allergan were determined by the Allergan migraine team in collaboration with headache scientists and clinicians. These trials and collaborations ultimately led to improvements in CM classifications. In 2010, onabotulinumtoxinA became the first medication and first biologic approved specifically to prevent headaches in patients with CM. Approval was based on 2 similarly designed phase 3, double-blind, randomized, placebo-controlled, multicenter clinical studies. Both studies showed significantly greater improvements in mean change from baseline in headache-day frequency in patients with CM receiving onabotulinumtoxinA compared with those receiving placebo. The safety and effectiveness of onabotulinumtoxinA have been established globally in >5000 patients with CM with or without medication overuse treated in clinical and observational studies. Benefits also include improvements in quality of life, fewer psychiatric comorbidities, and reduced healthcare resource utilization. Across studies, onabotulinumtoxinA was well tolerated; adverse events tended to be mild or moderate in severity and to decline over subsequent treatment cycles.

Treatment of pediatric spasticity, including children with cerebral palsy, with Botox (onabotulinumtoxinA): Development, insights, and impact.

Spasticity is a velocity-dependent increase in muscle tone that has a negative effect on quality of life and hinders the ability of others to provide care. In children, most cases are caused by cerebral palsy. Traditionally, many children are treated with surgery, sometimes performed before their limbs had grown sufficiently to permit long-term success. Nonsurgical treatment comprises oral pharmacological options, but their efficacy is limited and side effects such as drowsiness and decreased short-term memory are common; nerve block procedures can cause painful dysesthesias and muscle scarring. OnabotulinumtoxinA was first approved for the treatment of pediatric lower limb spasticity in Europe in the 1990s and is now licensed for use in pediatric patients in over 80 countries worldwide, based on a large body of clinical evidence demonstrating its efficacy and safety. In 2019 the U.S. Food and Drug Administration approved onabotulinumtoxinA for the treatment of pediatric patients with upper or lower limb spasticity. This approval represents 3 decades of work to refine the dose, measurements, patient selection, and muscle selection. The availability of onabotulinumtoxinA as a treatment for pediatric spasticity can have a substantial impact on a patient's quality of life. The use of onabotulinumtoxinA in combination with orthoses and occupational/physical therapy can postpone corrective surgery until growth is nearly complete and minimize the number of corrective surgeries.

Botulinum neurotoxins: Future innovations.

Botulinum neurotoxins (BoNTs) are multi-domain proteins whose potent and selective actions on nerve endings have led to innovations in both basic and clinical science. The various BoNT domains are responsible for binding to gangliosides and proteins associated with nerve cell membranes, internalization into the cell, and cleavage of one or more SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) proteins necessary for vesicle docking and fusion. Novel modifications to BoNT molecules, such as the creation of chimeras, helped identify the protein domains responsible for various aspects of BoNT action, such as localized effects. Other molecular modifications have been introduced in attempts to increase the specificity of BoNTs for autonomic or sensory neurons, with the ultimate goal of optimizing therapeutic selectivity. This research, in turn, has led to the development of BoNT-based proteins that can target non-SNARE substrates such as phosphatase and tensin homolog (PTEN). Still others are developing different BoNT serotypes, subtypes, or variants that are longer- or shorter-acting or have faster onset for various clinical purposes. New formulations of BoNTs that provide convenience for both patients and physicians are under investigation. Novel clinical uses are being evaluated for onabotulinumtoxinA, including in the prevention of post-operative atrial fibrillation. All these innovations capitalize on the unique properties of BoNTs, which continue to intrigue scientists and clinicians across numerous fields of study.

Pregnancy Outcomes in Patients Exposed to OnabotulinumtoxinA Treatment: A Cumulative 29-Year Safety Update.

BACKGROUND AND OBJECTIVES: A previous publication of pregnancy outcomes in onabotulinumtoxinA-exposed mothers demonstrated that the prevalence of major fetal defects (0.9%, 1/110) was comparable with background rates in the general population. There is continued interest to better understand the safety of onabotulinumtoxinA during pregnancy. This analysis evaluated pregnancy outcomes after onabotulinumtoxinA exposure to provide a cumulative 29-year update. METHODS: The Allergan Global Safety Database was searched from January 1, 1990, to December 31, 2018. Data from women (younger than 65 years or unknown) during pregnancy or ≤3 months before conception treated with onabotulinumtoxinA were assessed to estimate birth defect prevalence rates of live births only from prospective pregnancies. RESULTS: Of 913 pregnancies, 397 (43.5%) were eligible with known outcomes. Maternal age was known in 215 pregnancies: 45.6% were 35 years or older. Indication was known in 340 pregnancies: most frequent were aesthetic (35.3%) and migraine/headache (30.3%). The timing of exposure was known in 318 pregnancies: 94.6% were before conception or during the first trimester. OnabotulinumtoxinA dose information was known in 242 pregnancies; most (83.5%) were exposed to <200 U. Of 195 prospective pregnancies with 197 fetuses, there were 152 (77.2%) live births and 45 (22.8%) fetal losses (32 spontaneous, 13 elective). Of 152 live births, 148 (97.4%) had normal outcomes and 4 had abnormal outcomes. Among the 4 abnormal outcomes, there were 1 major birth defect, 2 minor fetal defects, and 1 birth complication. The prevalence rate for overall fetal defects was 2.6% (4/152, 95% CI 1.0%-6.6%) and 0.7% (1/152, 95% CI 0.1%-3.6%) for major fetal defects (3%-6% in the general population). Among cases of live births and known determinable exposure times, there was 1 birth defect with preconception exposure and 2 with first-trimester exposure. DISCUSSION: Although subject to reporting bias due to the nature of the postmarketing database review, this 29-year retrospective analysis of safety data in pregnant women exposed to onabotulinumtoxinA demonstrates that the prevalence rate of major fetal defects among live births is consistent with the rates reported in the general population. Although there are limited data available for second-trimester and third-trimester exposure, this updated and expanded safety analysis provides important real-world evidence to health care providers and their patients. CLASSIFICATION OF EVIDENCE: This analysis provides Class III data that demonstrate that the prevalence rate of major fetal defects among live births subsequent to in utero onabotulinumtoxinA exposure is comparable with the reported background rates.

Neutralizing Antibody Formation with OnabotulinumtoxinA (BOTOX®) Treatment from Global Registration Studies across Multiple Indications: A Meta-Analysis.

Though the formation of neutralizing antibodies (NAbs) during treatment with botulinum neurotoxin is rare, their presence may nonetheless affect the biological activity of botulinum toxin and negatively impact clinical response. The goal of this updated meta-analysis was to evaluate and characterize the rate of NAb formation using an expanded dataset composed of 33 prospective placebo-controlled and open-label clinical trials with nearly 30,000 longitudinal subject records prior to and following onabotulinumtoxinA treatment in 10 therapeutic and aesthetic indications. Total onabotulinumtoxinA doses per treatment ranged from 10 U to 600 U administered in ≤15 treatment cycles. The NAb formation at baseline and post-treatment was tested and examined for impact on clinical safety and efficacy. Overall, 27 of the 5876 evaluable subjects (0.5%) developed NAbs after onabotulinumtoxinA treatment. At study exit, 16 of the 5876 subjects (0.3%) remained NAb positive. Due to the low incidence of NAb formation, no clear relationship was discernable between positive NAb results and gender, indication, dose level, dosing interval, treatment cycles, or the site of injection. Only five subjects who developed NAbs post-treatment were considered secondary nonresponders. Subjects who developed NAbs revealed no other evidence of immunological reactions or clinical disorders. This comprehensive meta-analysis confirms the low NAb formation rate following onabotulinumtoxinA treatment across multiple indications, and its limited clinical impact on treatment safety and efficacy.

Modulation of amygdala activity for emotional faces due to botulinum toxin type A injections that prevent frowning.

According to the facial feedback hypothesis, when we see an angry or happy face, we contract or flex the relevant muscles to recreate the expression to assist in identifying and experiencing the emotion reflected. We investigated the facial feedback hypothesis by using botulinum toxin type A (onabotulinumtoxinA; onabotA) injections to induce temporary paralysis in the glabellar muscles (responsible for frowning) and measured functional brain activity during the processing of emotional faces. Ten females viewed pictures of happy and angry faces during two functional magnetic resonance imaging (fMRI) scan sessions: one prior (Pre) to onabotA and one following (Active) onabotA injections. We found Pre vs. Active onabotA modulation of activity in the amygdala for both happy and angry faces, as well as modulation of activity in the fusiform gyrus for happy faces. Consistent with our predictions, preventing frowning through inhibition of glabellar muscle contraction altered amygdala processing for emotional faces. The modulation of amygdala and fusiform gyrus activity following onabotA may reflect compensatory processes in a neuroanatomical circuit involved in emotional processing that is engaged when facial feedback is impaired. These data contribute to a growing literature suggesting that inhibition of glabellar muscle contraction alters neural activity for emotional processing.Clinical Trials.gov registration number: NCT03373162.

OnabotulinumtoxinA effects on trigeminal nociceptors.

BACKGROUND: OnabotulinumtoxinA (onabotA) is approved globally for prevention of chronic migraine; however, the classical mechanism of action of onabotA in motor and autonomic neurons cannot fully explain the effectiveness of onabotulinumtoxinA in this sensory neurological disease. We sought to explore the direct effects of onabotulinumtoxinA on mouse trigeminal ganglion sensory neurons using an inflammatory soup-based model of sensitization. METHODS: Primary cultured trigeminal ganglion neurons were pre-treated with inflammatory soup, then treated with onabotulinumtoxinA (2.75 pM). Treated neurons were used to examine transient receptor potential vanilloid subtype 1 and transient receptor potential ankyrin 1 cell-surface expression, calcium influx, and neuropeptide release. RESULTS: We found that onabotulinumtoxinA cleaved synaptosomal-associated protein-25 kDa in cultured trigeminal ganglion neurons; synaptosomal-associated protein-25 kDa cleavage was enhanced by inflammatory soup pre-treatment, suggesting greater uptake of toxin under sensitized conditions. OnabotulinumtoxinA also prevented inflammatory soup-mediated increases in TRPV1 and TRPA1 cell-surface expression, without significantly altering TRPV1 or TRPA1 protein expression in unsensitized conditions. We observed similar inhibitory effects of onabotulinumtoxinA on TRP-mediated calcium influx and TRPV1- and TRPA1-mediated release of calcitonin gene-related peptide and prostaglandin 2 under sensitized, but not unsensitized control, conditions. CONCLUSIONS: Our data deepen the understanding of the sensory mechanism of action of onabotulinumtoxinA and support the notion that, once endocytosed, the cytosolic light chain of onabotulinumtoxinA cleaves synaptosomal-associated protein-25 kDa to prevent soluble N-ethylmaleimide-sensitive factor attachment protein receptor-mediated processes more generally in motor, autonomic, and sensory neurons.