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Involvement of μ-opioid receptors in antinociceptive action of botulinum toxin type A
Abstract
Botulinum toxin A (BTX-A) is approved for treatment of chronic migraine and has been investigated in various other painful conditions. Recent evidence demonstrated retrograde axonal transport and suggested the involvement of CNS in antinociceptive effect of BTX-A. However, the mechanism of BTX-A central antinociceptive action is unknown. In this study we investigated the potential role of opioid receptors in BTX-A's antinociceptive activity. In formalin-induced inflammatory pain we assessed the effect of opioid antagonists on antinociceptive activity of BTX-A. Naltrexone was injected subcutaneously (0.02 - 2 mg/kg) or intrathecally (0.07 μg/ 10μl - 350 μg/10 μl), while selective μ-antagonist naloxonazine was administered intraperitoneally (5 mg/kg) prior to nociceptive testing. The influence of naltrexone (2 mg/kg s.c.) on BTX-A antinociceptive activity was examined additionally in an experimental neuropathy induced by partial sciatic nerve transection. To investigate the effects of naltrexone and BTX-A on neuronal activation in spinal cord, c-Fos expression was immunohistochemically examined in a model of formalin-induced pain. Antinociceptive effects of BTX-A in formalin and sciatic nerve transection-induced pain were prevented by non-selective opioid antagonist naltrexone. Similarly, BTX-A-induced pain reduction was abolished by low dose of intrathecal naltrexone and by selective μ-antagonist naloxonazine. BTX-A-induced decrease in dorsal horn c-Fos expression was prevented by naltrexone. Prevention of BTX-A effects on pain and c-Fos expression by opioid antagonists suggest that the central antinociceptive action of BTX-A might be associated with the activity of endogenous opioid system (involving μ-opioid receptor). These results provide first insights into the mechanism of BTX-A's central antinociceptive activity.
... Saline or formalin (10 μl) was administered into the trigeminal ganglion 5 d following peripheral BoNT/A injection into the whisker pad (15 U/kg). N(animals per group)=4 (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) Sensory testing of responsiveness to acute mechanical stimuli in whisker pad area performed using Von-Frey filaments (2 g and 8 g bending force) demonstrated normal sensitivity to mechanical stimuli of vehicle and capsaicin treated animals, while the formalin-induced denervation produced lack of response to mechanical stimuli. Similarly, pin prick test evoked a normal nocifensive behavior, except in formalin-treated animals which did not respond to noxious stimulus. ...
... Similarly to previous findings in spinal cord dorsal horn [2,18,64], in the present experiment, BoNT/A lowered the painevoked neural activation (measured by c-Fos expression) in the TNC. Additionally, BoNT/A reduced the formalin-evoked neural activation in locus coeruleus and periaqueductal gray. ...
... agonists, reduce the nocifensive behavior and mechanical hyperalgesia evoked by capsaicin [4,5,24,32,49,55,59], and thermal hyperalgesia evoked by inflammatory or neuropathic pain [4,5,7,15,34,36,49,56,59,60,66]. -BoNT/A and TRPV1 antagonists reduce the inflammatory and neuropathic mechanical allodynia and hyperalgesia [7,18,21,34,46,49,66]. The results are ambiguous after denervation with high-dose TRPV1 agonists: some studies report the reduction of mechanical allodynia [36,60], while others do not [35]. ...
Background: Botulinum toxin type A (BoNT/A) is an emerging long-acting therapeutic for chronic pain. In contrast to previously assumed local action, novel evidence point to the CNS as the possible site of BoNT/A action on pain after its axonal transport. The aim of this thesis was to characterize the sites and mechanisms of BoNT/A action on central pain transmission. ----- Methods: BoNT/A antinociceptive activity was characterized by behavioral nociceptive assessment, immunodetection of BoNT/A enzymatic product (cleaved synaptosomal-associated protein 25 (SNAP-25)) and c-Fos neuronal activation in different rat sensory regions. Peripheral, intraneural and intraganglionic BoNT/A injections, and microtubule-blocker colchicine were employed to assess BoNT/A axonal transport in peripheral sensory nerves. By employing trigeminal nerve ablation we examined possible transcytosis of BoNT/A in sensory regions. Denervation of trigeminal afferents with capsaicin was employed to examine the potential role of capsaicin-sensitive (vanilloid 1-expressing) neurons. ----- Results: Microtubule-dependent axonal transport of BoNT/A, necessary for its antinociceptive activity, occurred in sensory neurons. Following different toxin peripheral injections, cleaved SNAP-25 has been observed in corresponding sensory nuclei of brainstem (trigeminal nucleus caudalis) and spinal cord dorsal horn, but not in higher level sensory areas. BoNT/A enzyme activity was localized presynaptically in capsaicin-sensitive (vanilloid 1 receptor -expressing) central afferent terminals. BoNT/A reduced the pain-associated neuronal activation in TNC and supramedullary regions involved in descending pain control. ----- Conclusion: After its axonal transport in sensory neurons, BoNT/A modulates pain transmission at the central synapse of primary afferents. Involvement of capsaicin-sensitive neurons is associated with the selectivity of BoNT/A action for pain hypersensitivity. These findings contribute to the explanation of BoNT/A mechanisms of action in pain and possible refinement of its clinical use
... Research on the use of botulinum toxin for myofascial pain is contributing to improve treatments to date for this clinical condition [2]. Myofascial pain is due to regional neuromuscular alteration characterized by the presence of muscular contracture and consequently pain in the musculature of the face [5][6][7][8]. ...
... In addition to potent inhibitor of acetylcholine release, BTX-B may also have an inhibitory action on other neurotransmitters and neuropeptides, with anti-inflammatory and analgesic action [3,4]. Despite this, studies are necessary to better understand the mechanisms involved in the inhibitory action of BTX-B on the nocireceptor, but it is hypothesized that BTX-B can interrupt four painful signs: 1) Normalization of muscular hyperactivity; 2) Normalization of excessive Thus, the inhibition of BTX-B release of acetylcholine occurs in a multifactorial manner [5]. First, BTX-B binds to the presynaptic membrane receptors of the motor nerve terminal irreversibly. ...
... This specificity at the binding site guarantees BTX-B high selectivity for cholinergic synapses. These presynaptic receptors are responsible for endocytosis of the neurotoxin to the motor nerve terminal [5,6]. After internalization of the molecule, it is separated into two polypeptide chains by proteases present in the motor nerve terminal. ...
... 66,67 BoNT seemingly also has an agonistic effect on μ-opioid receptors. 66,68,69 Activation of nociceptive TRP channels is associated with release of CGRP and SP which leads to vasodilatation and release of inflammatory mediators. 70,71 Several members of this receptor family have been linked to headache disorders. ...
... 106,107 While a direct molecular interaction between BoNT and μ-opioid receptors has yet to be established, there are findings suggesting BoNT modulates these receptors agonistically by an unknown mechanism. 66,68,69 As previously mentioned, Drinovac Vlah et al 66 found that application of an u-opioid antagonist inhibited the antinociceptive effect of BoNT/A and has also confirmed these findings in a formalin-induced inflammatory pain model and a partial sciatic nervetransection model. 68 Vacca et al 69 found that BoNT/A can enhance the analgesic effect of morphine. ...
... 66,68,69 As previously mentioned, Drinovac Vlah et al 66 found that application of an u-opioid antagonist inhibited the antinociceptive effect of BoNT/A and has also confirmed these findings in a formalin-induced inflammatory pain model and a partial sciatic nervetransection model. 68 Vacca et al 69 found that BoNT/A can enhance the analgesic effect of morphine. ...
... Recently we have provided evidence of the involvement of endogenous opioid system in BT-A's antinociceptive action. We demonstrated that antinociceptive effect of BT-A can be dose-dependently blocked by opioid antagonists, applied either systemically or intrathecally, in several pathophysiologically different types of experimental pain: inflammatory pain induced by formalin injection into the hind paw-pad, neuropathic pain induced by partial sciatic nerve transection (Drinovac et al., 2013) and bilateral pain induced by intramuscular carrageenan (Drinovac Vlah et al., 2016). On the basis of these results, we propose that under BT-A treatment spinal inhibitory neurotransmitter systems are indirectly activated, thus the central antinociceptive effect might be more complex than simple inhibition of neurotransmitter release from primary afferent terminals. ...
... According to our previous study protocols, BT-A was applied 5 days before nociceptive testing, whereas morphine, naltrexone and methylnaltrexone were injected 40 min prior to the facial formalin test (Matak et al., 2011;Drinovac et al., 2013). Control animals received saline in appropriate volumes. ...
... The role of the endogenous opioid system in neuromodulation and control of pain is well known. It was suggested that spinal opioid system is involved in antinociceptive effects of BT-A (Drinovac et al., 2013;Drinovac Vlah et al., 2016). This assumption was based on the result that intrathecal opioid antagonists, naltrexone or naloxonazine, dosedependently inhibit the antinociceptive effect of Figure 3 Methylnaltrexone does not interfere with BT-A's effects on nociception and dural plasma protein extravasation in orofacial formalin test. ...
Background:
Although botulinum toxin type A (BT-A) is approved for chronic migraine treatment, its site and mechanism of action are still elusive. Recently our group discovered that suppression of CGRP release from dural nerve endings might account for antimigraine action of pericranially injected BT-A. We demonstrated that central antinociceptive effect of BT-A in sciatic region involves endogenous opioid system as well. Here we investigated possible interaction of BT-A with endogenous opioid system within the trigeminal region.
Methods:
In orofacial formalin test we investigated the influence of centrally acting opioid antagonist naltrexone (2 mg/kg, s.c.) versus peripherally acting methylnaltrexone (2 mg/kg, s.c.) on BT-A's (5 U/kg, s.c. into whisker pad) or morphine's (6 mg/kg, s.c.) antinociceptive effect and the effect on dural neurogenic inflammation (DNI). DNI was assessed by Evans blue-plasma protein extravasation.
Results:
Naltrexone abolished the effect of BT-A on pain and dural plasma protein extravasation, whereas peripherally acting methylnaltrexone did not change either BT-A's effect on pain or its effect on dural extravasation. Naltrexone abolished the antinociceptive and anti-inflammatory effects of morphine, as well. However, methylnaltrexone decreased the antinociceptive effect of morphine only partially in the second phase of the test and had no significant effect on morphine-mediated reduction in DNI.
Conclusions:
Morphine acts on pain in trigeminal region both peripherally and centrally, whereas the effect on dural plasma protein extravasation seems to be only centrally mediated. However, the interaction of BT-A with endogenous opioid system, with consequent inhibition of nociceptive transmission as well as the DNI, occurs primarily centrally.
Significance:
Botulinum toxin type A (BT-A)'s axonal transport and potential transcytosis suggest that its antinociceptive effect might involve diverse neurotransmitters at different sites of trigeminal system. Here we discovered that the reduction in pain and accompanying DNI involves the interaction of BT-A with central endogenous opioid system (probably at the level of trigeminal nucleus caudalis).
... The selected studies demonstrated a series of NPs originating from the different kingdoms of the classification of living things, which corroborates the great diversity of these products and their importance in the search for precursors of new analgesic drugs. Studies evaluating Fos protein expression in the spinal cord or dorsal root ganglion (DRG) described the effect of toxins [18][19][20][21][22][23][24][25], animal hormone [26], animal glycoprotein [27], a herbal paste [28], plant extracts [29][30][31], glycosides [32,33], organic salt [34], saponins [35,36], polyphenols [37,38], a flavonoid [39], terpenes [40][41][42], and an alkaloid [43] (Table 1). Studies evaluating the brain described the effect of toxins [44,45], a plant extract [46], essential oils [47,48], a saponin [49], monoterpenes [50][51][52]63], and a peptide [53] ( Table 2). ...
... Drinovac et al. [18] demonstrated the Fos expression reduction in the superficial dorsal horn (SDH; lamina I-II) in visceral pain induced by acetic acid. Drinovac et al. [19] showed a reduction of Fos expression in the SDH and nucleus proprius (NP) (lamina III-IV), probably by an effect on opioid and GABAergic pathways, after nociception induced by formalin. Shin et al. [20], studying hyperalgesia induced by carrageenan, showed a reduction of Fos expression in the L4-L5 segments of the spinal cord, probably by inhibition of the release of substance P and calcitonin generelated peptide (CGRP) from the primary sensory neurons. ...
... SDH was the area of spinal cord most studied, perhaps due to the possibility of being activated by several types of algesic stimuli, such as formalin [19,23,32,35,37] and glutamate [38], and to receive the greatest number of afferents related to superficial pain [12]. This region receives fibers of type Aβ and C, responsible for the transmission of signs of acute and chronic pain, respectively. ...
Pain treatment is still ineffective in many conditions and remains one of the greatest challenges of modern medicine. Historically, due to the incredible variety of pharmacologically promising natural products (NPs) and the chemical complexity of their compounds, scientists have explored their use as a source of treatment for diseases or symptomatology. Fos protein and its precursor, the gene c-Fos, have been the subject of study in relation to the pathophysiology of pain as a possible tool to aid in its understanding. More recently, it has become a useful tool in the study of NPs with analgesic profile. Thus, this systematic review aimed to investigate the analgesic effect of NPs and derivatives through changes in Fos protein or c-Fos expression in nervous system central. The search terms “analgesics,” “Fos,” and “drug effects” were used in the databases PubMed, MEDLINE, Scopus, and Embase. Forty-six articles were identified. Twenty-five articles investigated Fos expression in the spinal cord, 1 in dorsal root ganglion, 11 in brain areas, and 9 investigated the association between the spinal cord and brain areas. Although Fos protein expression has been used as a tool in the studies of the mechanism of action of pain in relation to NPs with analgesic activity, the associations between brain areas and the spinal cord—and the possible pathways involved—have not yet been fully elucidated and deserve further study.
... At central synapses BT-A is proposed to inhibit release of excitatory neurotransmitters from primary afferent terminals in dorsal horn of the spinal cord, such as glutamate, calcitonin generelated polypeptide (CGRP) and substance P (SP) (Pavone and Luvisetto 2010). Our group was the first to show that antinociceptive action of peripheral BT-A can be blocked by intrathecally delivered opioid and GABA A antagonist (Drinovac et al. 2013(Drinovac et al. , 2014, indicating that modulation of spinal inhibitory neurotransmitter systems might be an important component of central antinociceptive activity of BT-A. Still, the exact mechanism, as well as the localization of central antinociceptive effect is far from clear. ...
... Filaments were applied in Chaplan's up-down method (Chaplan et al. 1994). Each filament was applied 3 times, kept in bent position for 2 s, with an inter-stimulus interval of 5-10 s (Drinovac et al. 2013). The lowest filament that elicited a withdrawal response was considered the threshold stimulus. ...
... (b) Intrathecally (i.t.): at the lumbar L4/L5 level to anesthetized animals. A small skin incision (2 cm) was made at the lumbar L4/L5 level, substance or saline was injected (27G Tuberculin syringe) between the vertebrae and the skin was sutured (Drinovac et al. 2013). Correctness of application was verified by the animal's tail or hind limb brisk move. ...
“Mirror pain” or mirror-image pain (MP) is pain opposite to the side of injury. Mechanism and frequency in humans are not known. There is no consent on therapy. Here we report that unilaterally injected botulinum toxin type A (BT-A) has bilateral effect in experimental MP, thus deserves to be investigated as therapy for this condition. We examined the localization of BT-A’s bilateral antinociceptive action in MP induced by 3 % carrageenan intramuscular injection in Wistar rats. BT-A was applied peripherally (5 U/kg), into ipsilateral or contralateral hind paw pad (i.pl.) and centrally (1 U/kg), at spinal (intrathecally, i.t.) or supraspinal (intracisternally, i.c.) level. Additionally, we examined the involvement of central opioid and GABAergic systems, as well as the contribution of peripheral capsaicin-sensitive neurons to BT-A’s bilateral antinociceptive effect. Ipsilateral i.pl. and i.t. BT-A reduced the bilateral mechanical sensitivity to von Frey filaments, while contralateral i.pl. and i.c. treatments had no effect on either tested side. Bilateral antinociceptive effect of ipsilateral i.pl. BT-A was prevented by μ-opioid antagonist naloxonazine (1.5 μg/10 μl) and GABAA antagonist bicuculline (1 μg/10 μl) if applied at the spinal level, in contrast to supraspinal application of the same doses. Local treatment of sciatic nerve with 2 % capsaicin 5 days following BT-A i.pl. injection caused desensitization of sciatic capsaicin-sensitive fibers, but did not affect bilateral antinociceptive effect of BT-A and the presence of cleaved SNAP-25 at the spinal cord slices. Present experiments suggest segmental actions of peripheral BT-A at spinal level, which are probably not solely dependent on capsaicin-sensitive neurons.
... However, bicuculline injected into the cerebellomedullary cistern had no effect, suggesting that BoNT/A affects GABAergic transmission at the spinal cord and not at the supraspinal level. Similarly, both naloxozanine and naltrexone, selective and non-selective μ-opioid receptor antagonists, prevented the antinociceptive activity of BoNT/A in the formalin test and sciatica nerve transection neuropathy models [87]. These findings also aide in an understanding of previous studies that showed the synergistic activity of morphine and BoNT/A on inflammatory and neuropathic pain as well as the prevention of the development of morphine-induced tolerance by peripheral BoNT/A application [88,89]. ...
... Formalin induced inflammatory pain model [73,87,102] Reduction of enhanced nocifensive behaviors (licking, flinching and shaking) [87,102] Reduction of c-fos early response gene expression [87,102] Reduction of enhanced glutamate release in primary afferent terminals [73] Sciatic nerve transection (CCI) induced neuropathic model [87,91,[102][103][104] Recovery of paw withdrawal response [87,91,[102][103][104] Cleaved cSNAP-25 detected in paw, sciatic nerve, DRG, and L4/L5 spinal cord (dorsal horn) [103] Recovery of thermal hyperalgesia [91,104] L5 ventral root transection (VRT) induced neuropathic model [93,94] Bilateral recovery of decreased paw withdrawal thresholds [93,94] Reduced expression of TRPV1 and P2X3 in dorsal root ganglion [93,94] Carrageenan-induced hyperalgesia [92,105] Recovery of paw withdrawal response [92,105] Recovery of thermal hyperalgesia [105] Reduction of c-fos early response gene expression in spinal cord [105] Paclitaxel-induced peripheral neuropathy model [92] Bilateral recovery of decreased paw withdrawal thresholds [92] Diabetic neuropathy pain model [106] Bilateral recovery of decreased paw withdrawal thresholds [106] Bilateral recovery of mechanical and thermal hypersensitivity [106] Acidic saline induced pain model [90] Bilateral recovery of decreased paw withdrawal thresholds [90] Spinal Cord Sciatic nerve transection (SCI) induced neuropathic model [104] Reduction of mechanical allodynia and thermal hyperalgesia [104] Diabetic neuropathy pain model [106] Bilateral recovery of decreased paw withdrawal thresholds [106] Bilateral recovery of mechanical and thermal hypersensitivity [106] Formalin induced inflammatory pain model [107] Reduction of enhanced nocifensive behaviors (licking, flinching and shaking) [107] Reduction of CGRP in spinal dorsal horn [107] Acetic acid induced abdominal pain [86] Reduced writhes [86] Reduction of increased c-fos expression in dorsal horn of the spinal cord (S2/S3segments) [86] Reduction of mechanical allodynia [86] Face Formalin-induced facial pain (into the whisker pad) [108] Reduction of facial rubbing [108] Cleaved cSNAP-25 detected in trigeminal nucleus caudalis (TNC) [108] Colchicine-sensitive [108] Infraorbital nerve constriction (IoNC) induced trigeminal neuropathy model [95] Reduction of dural extravasation [95] Colchicine-sensitive bilateral analgesic effect in trigeminal ganglion [95] ...
... Formalin induced inflammatory pain model [73,87,102] Reduction of enhanced nocifensive behaviors (licking, flinching and shaking) [87,102] Reduction of c-fos early response gene expression [87,102] Reduction of enhanced glutamate release in primary afferent terminals [73] Sciatic nerve transection (CCI) induced neuropathic model [87,91,[102][103][104] Recovery of paw withdrawal response [87,91,[102][103][104] Cleaved cSNAP-25 detected in paw, sciatic nerve, DRG, and L4/L5 spinal cord (dorsal horn) [103] Recovery of thermal hyperalgesia [91,104] L5 ventral root transection (VRT) induced neuropathic model [93,94] Bilateral recovery of decreased paw withdrawal thresholds [93,94] Reduced expression of TRPV1 and P2X3 in dorsal root ganglion [93,94] Carrageenan-induced hyperalgesia [92,105] Recovery of paw withdrawal response [92,105] Recovery of thermal hyperalgesia [105] Reduction of c-fos early response gene expression in spinal cord [105] Paclitaxel-induced peripheral neuropathy model [92] Bilateral recovery of decreased paw withdrawal thresholds [92] Diabetic neuropathy pain model [106] Bilateral recovery of decreased paw withdrawal thresholds [106] Bilateral recovery of mechanical and thermal hypersensitivity [106] Acidic saline induced pain model [90] Bilateral recovery of decreased paw withdrawal thresholds [90] Spinal Cord Sciatic nerve transection (SCI) induced neuropathic model [104] Reduction of mechanical allodynia and thermal hyperalgesia [104] Diabetic neuropathy pain model [106] Bilateral recovery of decreased paw withdrawal thresholds [106] Bilateral recovery of mechanical and thermal hypersensitivity [106] Formalin induced inflammatory pain model [107] Reduction of enhanced nocifensive behaviors (licking, flinching and shaking) [107] Reduction of CGRP in spinal dorsal horn [107] Acetic acid induced abdominal pain [86] Reduced writhes [86] Reduction of increased c-fos expression in dorsal horn of the spinal cord (S2/S3segments) [86] Reduction of mechanical allodynia [86] Face Formalin-induced facial pain (into the whisker pad) [108] Reduction of facial rubbing [108] Cleaved cSNAP-25 detected in trigeminal nucleus caudalis (TNC) [108] Colchicine-sensitive [108] Infraorbital nerve constriction (IoNC) induced trigeminal neuropathy model [95] Reduction of dural extravasation [95] Colchicine-sensitive bilateral analgesic effect in trigeminal ganglion [95] ...
Botulinum neurotoxins (BoNTs) have been widely used to treat a variety of clinical ailments associated with pain. The inhibitory action of BoNTs on synaptic vesicle fusion blocks the releases of various pain-modulating neurotransmitters, including glutamate, substance P (SP), and calcitonin gene-related peptide (CGRP), as well as the addition of pain-sensing transmembrane receptors such as transient receptor potential (TRP) to neuronal plasma membrane. In addition, growing evidence suggests that the analgesic and anti-inflammatory effects of BoNTs are mediated through various molecular pathways. Recent studies have revealed that the detailed structural bases of BoNTs interact with their cellular receptors and SNAREs. In this review, we discuss the molecular and cellular mechanisms related to the efficacy of BoNTs in alleviating human pain and insights on engineering the toxins to extend therapeutic interventions related to nociception.
... The positive effects of BoNT-A in a variety of chronic pain conditions [5] have been reported by some well-designed clinical trials [7,8,10]. In addition, in vivo and in vitro studies have reported that the antinociceptive effect of BoNT-A is mainly related to a peripheral and central decrease of neurotransmitters such as glutamate, substance P, and calcitoningene-related peptide (CGRP) [14][15][16], and by its axonal transport to sensory regions of the trigeminal ganglion [17,18], the modulation of the spinal opioidergic or GABA-ergic system [19,20], and the prevention of microglia activation [21,22]. However, despite the fact that several clinical trials [23][24][25][26][27][28] have assessed BoNT-A efficacy for myofascial pain relief, its efficacy has not yet been established. ...
... Notwithstanding, it is also known that persistent MFP-TMD patients present a deficit in pain modulation [31]. Considering that BoNT-A modulates the opioidergic and GABA-ergic systems [19,20], its effects on pain modulation could also explain the long-term effects presented in our study, corroborating the later hypothesis. ...
This study assessed the long-term effects of botulinum toxin type A (BoNT-A) in subjective pain, pain sensibility, and muscle thickness in persistent myofascial temporomandibular-disorder pain (MFP-TMD) patients. Fourteen female subjects with persistent MFP received BoNT-A treatment with different doses (10U-25U for temporalis muscle and 30U-75U for masseter muscle). The treatment was injected bilaterally in the masseter and anterior temporalis muscles in a single session. Clinical measurements included: self-perceived pain (VAS), pain sensibility (PPT), and muscles thickness (ultrasonography). Follow-up occurred 1, 3, 6, and 72 months after treatment for VAS and PPT and 1, 3, and 72 months for ultrasonography. For statistical analysis, the Friedman test with the Bonferroni test for multiple comparisons as a post hoc test was used for non-parametric repeated measures comparisons among the evaluation times. A 5% probability level was considered significant in all tests. VAS values presented a significant decrease throughout the study (p < 0.05). Regarding PPT values, a significant increase was found when comparing baseline data with post-treatment follow-ups (p < 0.05), and even though a significant decrease was found in muscle thickness when baseline values were compared with the 1- and 3-months assessments, no differences were found when compared with the 72 months follow-up (p > 0.05). A single injection of BoNT-A presents long-term effects in reducing pain in persistent MFP-TMD patients, and a reversibility of adverse effects on masticatory-muscle thickness.
... Central antinociceptive action of BoNT/A might be associated with the activity of endogenous opioid system via µ-opioid receptor. [27] partial sciatic nerve transection in rats A; 7 U/kg, i.pl. post-injury at day 14 Reduced mechanical allodynia. ...
... Drinovac et al. [27,89], based on several lines of experiments on rats with pain in the sciatic region, suggested that enhancement of the opioid and GABA neurotransmission mediated by their receptors (µ-opioid and GABA-A) is involved in the central antinociceptive effect of BoNT/A. Although the opioid receptor antagonist naltrexone, as well as the GABA-A antagonist bicuculline, reduced BoNT/A effect on pain when applied intraperitoneally or intrathecally, the antagonistic effect was completely absent after their intracisternal and intracerebroventricular injection, thus providing evidence for segmental intraspinal action of BoNT/A on pain [24]. ...
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.
... BoNT-A acts at the neuromuscular junction, reducing the release of acetylcholine and thus decreasing muscle contraction. Although the primary effect of BoNT-A occurs at the neuromuscular junction, resulting in chemodenervation, the toxin may also modify the sensory feedback loop, possibly acting at spinal cord level to induce central antinociceptive activity (Drinovac, Bach-Rojecky, Matak, & Lacković, 2013). ...
... PD), we cannot completely exclude a global inhibitory effect of BoNT-A on the cervical spinal neurons. Such inhibition may be due to a retrograde action of the toxin, which could modify the sensory feedback loop and act at spinal cord level as shown by previous studies (Drinovac et al., 2013). In addition, BoNT-A by blocking <alpha> and <gamma> fibers could modify several sensory afferents and indirectly change the baseline EMG activity and the NWR EMG responses possibly due to plastic changes at spinal level. ...
Objectives
The aims of this study were to evaluate the pattern of the nociceptive withdrawal reflex (NWR) of the upper limb at rest and after injection of Botulinum toxin type A (BoNT‐A) in poststroke subacute hemiparetic patients.
Methods
Fourteen patients with poststroke subacute hemiparesis underwent clinical and instrumental evaluation and BoNT‐A injection. Painful electrical stimulation was applied to induce the NWR. Baseline EMG activity and NWR recordings (EMG and kinematic response) were performed at T0, one month (T1), and three months (T2) after the BoNT‐A injection, as were Modified Ashworth Scale (MAS) and Functional Independence Measure (FIM) scores.
Results
Comparison of results at T0, T1, and T2 revealed significant changes in the MAS score for the elbow (p < 0.001) and wrist joints (p < 0.001) and in the FIM score at T0 and T2. BoNT‐A injection had a significant effect on both NWR amplitude and baseline EMG activity in the posterior deltoid (PD) and flexor carpi radialis (FCR) muscles as well as in all averaged muscles. Analysis of elbow kinematics before and after treatment revealed that the reflex probability rates were significantly higher at T1 and T2 than at T0.
Conclusion
Injection of BoNT‐A in the subacute phase of stroke can modify both the baseline EMG activity and the NWR‐related EMG responses in the upper limb muscles irrespective of the site of injection; furthermore, the reflex‐mediated defensive mechanical responses, that is, shoulder extension and abduction and elbow flexion, increased after treatment. BoNT‐A injection may be a useful treatment in poststroke spasticity with a potential indirect effect on spinal neurons.
... Present data suggest that BoNT/A analgesic effect in mice is dependent on the integrity of SP/NK1R-mediated nociceptive transmission. Along with reduction of pain behavior, BoNT/A antinociceptive action is accompanied by prevention of neuronal activation and c-Fos expression in the dorsal horn (Aoki, 2005;Drinovac et al., 2013). Thus, to support the behavioral findings we assessed the c-Fos expression evoked by formalin-induced pain. ...
... Mika et al., 2011;Vacca et al., 2013). Smaller effect of BoNT/A on nerve injury-induced mechanical hyperalgesia, in comparison to carrageenan or diabetic neuropathy-evoked mechanical hyperalgesia, was observed in rats (Bach-Rojecky et al., 2010;Drinovac et al., 2013;Favre-Guilmard et al., 2017). It was speculated that this might be associated with different neurochemical mediators involved in pain of different origins (Favre-Guilmard et al., 2017). ...
The antinociceptive action of botulinum toxin type A (BoNT/A) has been demonstrated in behavioral animal studies and clinical settings. It was shown that this effect is associated with toxin activity in CNS, however, the mechanism is not fully understood. Substance P (SP) is one of the dominant neurotransmitters in primary afferent neurons transmitting pain and itch. Thus, here we examined association of SP-mediated transmission and BoNT/A antinociceptive action by employing gene knockouts. Antinociceptive activity of intraplantarly (i.pl.)-injected BoNT/A was examined in mice lacking the gene encoding for SP/neurokinin A (tac1(-/-)) or SP-preferred receptor neurokinin 1 (tac1r(-/-)), compared to control C57Bl/6J wild type animals. BoNT/A action was assessed in inflammatory pain induced by formalin and CFA, and neuropathic pain induced by partial sciatic nerve ligation. BoNT/A activity in CNS was examined by c-Fos and BoNT/A-cleaved SNAP-25 immunohistochemistry. In wild type mice, acute (formalin-evoked) and chronic pain (neuropathic and inflammatory) was reduced by peripherally injected BoNT/A. In tac1(-/-) and tac1r(-/-) knockout mice, BoNT/A exerted no analgesic effect. In control animals BoNT/A reduced the formalin-evoked c-Fos expression in lumbar dorsal horn, while in knockout mice the c-Fos expression was not reduced. After peripheral toxin injection, cleaved SNAP-25 occurred in lumbar dorsal horn in all animal genotypes. BoNT/A antinociceptive activity is absent in animals lacking the SP and neurokinin 1 receptor encoding genes, in spite of presence of toxin's enzymatic activity in central sensory regions. Thus, we conclude that the integrity of SP-ergic system is necessary for the antinociceptive activity of BoNT/A.
... Indirect evidence based on immunohistochemical detection of the cleaved SNAP-25 has suggested that functional BoNT/A not only reaches the central endings of nociceptor axons, but may also act on neurons in the CNS [68]. It has been suggested that BoNT/A antinociceptive action might be associated with the activity of the endogenous opioid system involving μ-opioid receptors [69,70]. ...
... Elucidating the important role of glial cells in pain [69] has opened up a new possibility for testing non-neuronal effects of BoNT/A in association with its antinociceptive/analgesic efficacy. In fact, it has been shown that satellite glial cells, in the trigeminal ganglion, contain SNAP-25 and release glutamate that is blocked by BoNT/A [71]. ...
Botulinum neurotoxin A (BoNT/A) is a toxin produced by the naturally-occurring Clostridium botulinum that causes botulism. The potential of BoNT/A as a useful medical intervention was discovered by scientists developing a vaccine to protect against botulism. They found that, when injected into a muscle, BoNT/A causes a flaccid paralysis. Following this discovery, BoNT/A has been used for many years in the treatment of conditions of pathological muscle hyperactivity, like dystonias and spasticities. In parallel, the toxin has become a “glamour” drug due to its power to ward off facial wrinkles, particularly frontal, due to the activity of the mimic muscles. After the discovery that the drug also appeared to have a preventive effect on headache, scientists spent many efforts to study the potentially-therapeutic action of BoNT/A against pain. BoNT/A is effective at reducing pain in a number of disease states, including cervical dystonia, neuropathic pain, lower back pain, spasticity, myofascial pain and bladder pain. In 2010, regulatory approval for the treatment of chronic migraine with BoNT/A was given, notwithstanding the fact that the mechanism of action is still not completely elucidated. In the present review, we summarize experimental evidence that may help to clarify the mechanisms of action of BoNT/A in relation to the alleviation of headache pain, with particular emphasis on preclinical studies, both in animals and humans. Moreover, we summarize the latest clinical trials that show evidence on headache conditions that may obtain benefits from therapy with BoNT/A.
... Interestingly, BoNT/A could restore normal opioidergic transmission in the trigeminal nucleus's pars caudalis and the spinal cord's dorsal horn. For example, in sciatic pain models of rats, BoNT/A enhanced GABA-A and µ-opioid receptor transmission, increasing the analgesic response and tolerance to morphine [70][71][72][73]. BoNT/A affects the regeneration of injured peripheral nerves and interferes with neuroinflammation. ...
Trigeminal neuralgia is a neuropathic pain syndrome responsive to botulinum toxin type A therapy. This review had the goal of analyzing the different studies published from 2002 to January 2024 to better define the techniques and the types of botulinum toxin type A used, the doses, the injection routes, and the different populations of trigeminal neuralgia patients treated. We considered only articles in which the therapy was administered to humans to treat trigeminal neuralgia. Case reports, case series, open-label, retrospective, and RCT studies were considered. The research was conducted on MEDLINE and the keywords included (trigeminal neuralgia) and (botulinum). Thirty-five articles were considered suitable for this review. Botulinum toxin type A was shown to be an effective therapy for TN pain in all the articles analyzed, albeit there is a lack of standardization in methods and outcomes. The techniques, the doses, and the injection approaches were very heterogeneous among the studies. Only two botulinum toxin type A formulations have been used in this setting: onabotulinumtoxinA and lanbotulinumtoxinA. There were 300 patients treated with onabotulinumtoxinA and 760 treated with lanbotulinumtoxinA overall (in 42 patients, the formulation was not specified). The distinction between etiological and clinical types of TN has been made by only a small portion of the studies. The main adverse event was transient facial asymmetry. Botulinum toxin type A is indeed a promising therapy that is clearly effective for trigeminal neuralgia. OnabotulinumtoxinA is the most common formulation used in Western countries; however, the meager sample of TN patients treated, and the lack of standardization are not sufficient for this therapy to be approved by the FDA or EMA. Indeed, more studies with standardized methods and larger samples are needed for this purpose.
... These findings suggest that the central analgesic effect of BoNT/A may be associated with endogenous opioid system activity. 152 The interaction between BoNT/A and the opioidergic system was also demonstrated in another study. In a mouse model of neuropathic pain, Intraplantar administration of BoNT/A inhibited morphine-evoked tolerance allodynia and increased the analgesic action of morphine in rats with sciatic nerve lesion-induced neuropathic pain. ...
Botulinum neurotoxins (BoNTs), produced by Clostridium botulinum, have been used for the treatment of various central and peripheral neurological conditions. Recent studies have suggested that BoNTs may also have a beneficial effect on pain conditions. It has been hypothesized that one of the mechanisms underlying BoNTs' analgesic effects is the inhibition of pain-related receptors' transmission to the neuronal cell membrane. BoNT application disrupts the integration of synaptic vesicles with the cellular membrane, which is responsible for transporting various receptors, including pain receptors such as TRP channels, calcium channels, sodium channels, purinergic receptors, neurokinin-1 receptors, and glutamate receptors. BoNT also modulates the opioidergic system and the GABAergic system, both of which are involved in the pain process. Understanding the cellular and molecular mechanisms underlying these effects can provide valuable insights for the development of novel therapeutic approaches for pain management. This review aims 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 by inhibiting the transmission of pain-related receptors.
... In the formalin-induced pain model, cleaved SNAP-25 was found in the trigeminal nucleus caudalis; moreover, the effects of onabo-tulinumtoxinA were completely abolished by colchicine, supporting the hypothesis that BoNT-A follows retrograde axonal transport and cell-to-cell transfer, or transcytosis [62]. The central antinociceptive effects of onabotulinumtoxinA can also rely on the enhancement of the endogenous opioid system, though the exact mechanisms of its action have not been cleared out yet [63]. The clinical counterpart of central sensitization is represented by allodynia, an abnormal sensory state in which an innocuous sensory stimulus is felt as painful and involves second-order neurons located in the caudal trigeminal nucleus. ...
Chronic migraine is a disease with a high burden on patients from both a working and quality of life point of view. The pathophysiology of this subtype of migraine is due to several factors, such as medication overuse. Nevertheless, the detrimental recurring of headache attacks with central and peripheral sensitization plays a central role and explains some additional symptoms complained about by these patients even in the interictal phase. OnabotulinumtoxinA is a therapy indicated for chronic migraine since it has proven to reduce peripheral sensitization, showing even efficacy on central symptoms. The aim of this narrative review is to present the current evidence regarding the effect of OnabotulinumtoxinA on sensitization and interictal symptoms.
... Systemic and central administration of opioid antagonists prevents the peripheral antinociceptive function of BoNT/A, and the analgesic effect is mediated by the µ opioid receptor (Vacca et al., 2013). BoNT/A downregulates c-Fos expression in spinal dorsal horn neurons, and this effect is inhibited by opioid antagonists, suggesting a role of the endogenous opioid system in its analgesic effect (Drinovac et al., 2013). In addition, correlation between the analgesic effect of BoNT/A and the GABA-A receptor have been revealed in some studies. ...
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.
... Our findings showed that patients in the BoNT-A group had more effective CPM in the trigeminal area compared with SS at the 1 month follow-up. Using rat models, Drinovac et al. 16,66 suggested that the modulation of the opioidergic and GABA-ergic systems by BoNT-A is involved in the central antinociceptive effect of BoNT-A. In addition, the analgesic action in the trigeminal region (nucleus caudalis) involves interactions with the central endogenous opioid system 67 , implying that BoNT-A can also have effects in reestablishing effective pain modulation resulting in the reduced pain sensitivity found in the present study. ...
The antinociceptive effect of BoNT-A have been well documented in animal studies; however, results of few but well-designed randomized placebo-controlled clinical trials about BoNT-A efficacy in masticatory myofascial pain (MFP) are inconsistent. Therefore, the present randomized, double-blind, placebo-controlled clinical trial evaluated the efficacy of BoNT-A in patients with refractory MFP. Twenty-eight patients with pain reduction of less than 30% despite conservative treatment and with an average pain intensity of > 50 mm on the visual analogue scale (VAS) participated. Patients were randomly assigned to receive a total of 80 U of BoNT-A or saline solution (SS) injected into the masseter and anterior temporalis muscles. Pain intensity (VAS), quantitative sensory testing (QST), conditioned pain modulation (CPM), and psychosocial status were examined. Follow-up was performed at 1 and 6 months. For repeated-measure comparisons between evaluation times, Friedman test with Bonferroni correction was used for pain and somatosensory variables and the Wilcoxon test for the psychosocial variables. The Mann-Whitney test was used for all comparisons between groups. The BoNT-A group had a significant decrease in pain intensity at follow-ups compared with the SS group (p < 0.001). QST assessment revealed higher pressure pain threshold values in the masseter muscle for BoNT-A group compared to SS (p < 0.03) at all follow-ups. No differences were found for mechanical pain threshold and wind-up ratio values (p > 0.05) in the entire study. The BoNT-A group presented the most efficient CPM effect (p < 0.03) only at the 1 month follow-up in the masseter muscle. There was a significant time effect for BoNT-A in all psychosocial variables (p < 0.05) and a drug effect in the Central Sensitization Inventory (p < 0.01), Pittsburgh Sleep Quality Index (p < 0.004), and Healthy Survey 36 (p < 0.05) at 6 months follow-up. The study demonstrates that a single injection-session of BoNT-A has positive effects on the hall pain spectrum of patients with refractory masticatory myofascial pain. Keywords Temporomandibular disorders, Myofascial pain, Botulinum toxin type A Patients with masticatory myofascial pain (MFP) experience constant and varying degrees of pain and physical disability, neurobiological alterations, psychosocial impairment, and a reduction in well-being (impaired OPEN
... BoNT/A modulates neuropathic pain through the interference with the expression of TRPV1 on the plasma membrane of sensory fibers, dorsal root ganglia, and neurons in the central nervous system (29,32). Moreover, BoNT/A inhibits the release of CGRP and substance P in both the peripheral and central nervous system, interfering with the central and peripheral sensitization mechanisms (33)(34)(35)(36), and enhances the inhibitory opioid and GABA systems located in the dorsal horn and brainstem (37,38). It also attenuates microglia activation (39,40). ...
Genitofemoral neuralgia is an uncommon pain disorder that could be resistant to conventional treatment. A 78-year-old woman with refractory right genitofemoral neuralgia was treated with BoNT/A subcutaneous injections; the treatment was performed three times with significant pain improvement, although temporary, and without adverse events. BoNT/A may be a promising alternative intervention in the setting of genitofemoral neuralgia refractory to oral and/or topical treatment.
... This phenomenon is probably due to the retrograde axonal and trans-synaptic transport of BoNT/A [31][32][33]. Moreover, within the central nervous system, it was demonstrated that BoNT/A also attenuates microglia activation and enhances brainstem and dorsal horn inhibitory endogenous opioid and GABA systems [34][35][36][37]. The evidence of BoNT/A safety and efficacy in neuropathic pain and the lack of effective and evidence-based treatments in ATN, especially in refractory cases, convinced us to perform this treatment in our cohort of patients. ...
Auriculotemporal neuralgia is a rare pain disorder in which anesthetic nerve blockade is usually effective but not always resolutive. Botulinum toxin type A has proven to be effective in treating neuropathic pain, and patients with auriculotemporal neuralgia could also benefit from this treatment. We described nine patients with auriculotemporal neuralgia treated with botulinum toxin type A in the territory of auriculotemporal nerve innervation. We compared the basal NRS and Penn facial pain scale scores with those obtained 1 month after BoNT/A injections. Both Penn facial pain scale (96.67 ± 24.61 vs. 45.11 ± 36.70, p 0.004; mean reduction 52.57 ± 36.50) and NRS scores (8.11 ± 1.27 vs. 4.22 ± 2.95, p 0.009; mean reduction 3.89 ± 2.52) improved significantly at one month after treatment. The mean duration of the effect of BoNT/A on pain was 95.00 ± 53.03 days and no adverse effects were reported.
... These reductions in peripheral sensitization and afferent input to the spinal cord from peripheral nerve endings may indirectly decrease the central sensitization process. Botulinum toxin A may also be transported along the axon in a retrograde manner and modulate neuronal activity in the central nervous system through stimulation of inhibitory gamma-amino butyric acid (GABA)-A receptors and m opioid receptors in the spinal cord 12,39,40 . All of these properties of botulinum toxin A may explain why administration of this toxin is able to reduce pain in patients with knee OA. ...
Unlabelled:
Botulinum toxin A has the potential to be used for analgesia because of its anti-inflammatory effect. The utility of intra-articular injections of botulinum toxin A for knee osteoarthritis remains unclear. The aim of this study was to analyze the utility of such injections in knees with osteoarthritis.
Methods:
We conducted a literature search of 4 databases (Scopus, PubMed, ClinicalTrials.gov, and Europe PMC) up to September 10, 2022, using formulated keywords. Articles were included in the study if they had data on botulinum toxin A injection compared with the control group in patients with osteoarthritis of the knee. Results were summarized using the standardized mean difference (SMD) and accompanying 95% confidence interval (CI).
Results:
Pooled analysis of data from 6 trials involving 446 patients with knee osteoarthritis revealed that, compared with placebo, intra-articular injection of botulinum toxin A was associated with greater reductions in early visual analog scale (VAS) pain (SMD, -0.63 [95% CI, -1.08 to -0.18], p = 0.007, I2 = 79%), late VAS pain (SMD, -0.57 [95% CI, -1.07 to -0.08], p = 0.02, I2 = 81%), early Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) (SMD, -0.84 [95% CI, -1.61 to -0.06], p = 0.03, I2 = 90%), and late WOMAC (SMD, -1.12 [95% CI, -1.91 to -0.32], p = 0.006, I2 = 93%) scores from baseline in patients with knee osteoarthritis.
Conclusions:
Intra-articular injection of botulinum toxin A may offer benefits in reducing pain and improving function in patients with knee osteoarthritis, with a relatively good safety profile. Larger randomized trials are warranted to confirm the results of our study.
Level of evidence:
Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.
... Contrary to its well-known peripheral mechanism of action, the activity of BoNT-A on the central nervous system (CNS) is still debated. There is evidence suggesting that central antinociceptive effects of BoNT-A could be mediated by an increase in opioidergic [50] and GABAergic [51] neurotransmission, which can occur by axonal transport of the toxin via sensory afferents to nociceptive nuclei in the CNS [52][53][54]. These data, however, are contradicted by recent studies denying the possibility of a transsynaptic transfer of BoNT-A [55,56], and supporting the hypothesis that central desensitization, synaptic plasticity, and other CNS effects of BoNT-A are secondary phenomena due to the decreased peripheral inputs rather than to a direct central effect [57]. ...
(1) Background: OnabotulinumtoxinA (BoNT-A) is a commonly used prophylactic treatment for chronic migraine (CM). Although randomized placebo studies have shown its clinical efficacy, the mechanisms by which it exerts its therapeutic effect are still incompletely understood and debated. (2) Methods: We studied in 15 CM patients the cephalic and extracephalic nociceptive and lemniscal sensory systems using electrophysiological techniques before and 1 and 3 months after one session of pericranial BoNT-A injections according to the PREEMPT protocol. We recorded the nociceptive blink reflex (nBR), the trigemino-cervical reflex (nTCR), the pain-related cortical evoked potential (PREP), and the upper limb somatosensory evoked potential (SSEP). (3) Results: Three months after a single session of prophylactic therapy with BoNT-A in CM patients, we found (a) an increase in the homolateral and contralateral nBR AUC, (b) an enhancement of the contralateral nBR AUC habituation slope and the nTCR habituation slope, (c) a decrease in PREP N-P 1st and 2nd amplitude block, and (d) no effect on SSEPs. (4) Conclusions: Our study provides electrophysiological evidence for the ability of a single session of BoNT-A injections to exert a neuromodulatory effect at the level of trigeminal system through a reduction in input from meningeal and other trigeminovascular nociceptors. Moreover, by reducing activity in cortical pain processing areas, BoNT-A restores normal functioning of the descending pain modulation systems.
... The toxic part, together with non-toxic non-hemagglutinin (NTNHA) protein makes heterodimer called minimally functional progenitor toxin complex (M-PTC) which protects the toxin in the gastrointestinal tract from acidic and proteolytic conditions and make it more stable as a biological material. The remaining non-toxic part of auxiliary proteins is made of hemagglutinin components or OrfX proteins which form higher molecular weight (L-PTC), also sharing a role in stabilizing BoNT complex and preserving it in extracellular space (Drinovac et al., 2013;Rossetto et al., 2014;Matak and Lacković, 2014;Matsui et al., 2014). ...
Botulinum toxins are one of the most potent biological toxins known. They cause botulism in wildlife and livestock, and thus, are regarded as a problem in veterinary medicine. On the other hand, use of purified low dose pharmaceutical grade botulinum toxin serotype A (BoNT-A) in different human clinical implications such as movement, autonomic disorders, pain conditions have expanded in the last 30-40 years based on its long-lasting effects and a good safety profile. However, despite that, its use in veterinary practice is lagging far behind the already well-established use in humans. BoNT-A is not licensed for use in any veterinary medical condition, and overall, there are only few clinical trials and several case studies, the most notable being case reports and limited clinical studies of osteoarthritis and perioperative pain in dogs, lameness in horses, as well as the spasticity treatment in cats. Indications for BoNT-A use in veterinary medicine happen to be very similar when compared to human indications, which is not surprising due to pathophysiological similarities. This warrants further clinical research of novel indications of BoNT-A in veterinary medicine.
... BoNT/A exerts its functions on modulating neuropathic pain by inhibiting the release of neurotransmitters involved in peripheric and central sensitization, in particular CGRP and substance P [23][24][25][26], but not the release of GABA [27]. It interferes with the plasma membrane expression of TRPV1 in sensory fibers, the sensory surface of neuronal ganglia, and beyond the ganglia in the central nervous system [28,29], probably due to axonal retrograde transport and trans-synaptic transport [29][30][31]; BoNT/A has proven to enhance the segmental dorsal horn and brainstem endogenous opioid and GABA inhibitory systems [32,33] and attenuate microglia activation [34,35]. Furthermore, BoNT/A has shown selectivity for TRPV1-expressing afferents, such as nociceptive C fibers [36,37], involved in pain and mechanical stimulation but not in other sensory modalities. ...
We treated a 51-year-old woman with refractory Complex Regional Pain Syndrome type I (CRPS-I) involving her left hand and forearm with subcutaneous injections of BoNT/A. The injections were performed every 3 months, with a total of six treatments. Each treatment was able to effectively improve pain and motor impairment; however, the duration of the effect was limited to only a few months. BoNT/A could improve patients’ quality of life with CRPS; however, extensive clinical studies are needed to determine its role in clinical practice.
... Apart from BoNT-A behavioral antinociceptive activity, we examined its action at the level of central sensory nociceptive nuclei by exploiting c-Fos activation as a reliable marker of neuronal activity [23,30]. Interestingly, we found an occurrence of c-Fos activated neurons in the ipsilateral and contralateral TNC after 0.5% formalin stimulation of the TMJ area (Figure 4), which was not observed in the orofacial or hind paw formalin tests [31][32][33]. The unilateral stimulation of mouse masseter with complete Freund's adjuvant (CFA) similarly induces bilateral expression of c-Fos in the TNC [23]. ...
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.
... It was shown that BoNT A leads to a deactivation of sodium channel conductance in cell cultures of central and peripheral neurons [16]. In addition, BoNT A inhibits afferents to muscle spindles, reduces sympathetic signal transmission, and, at least, leads to µreceptor-mediated pain relief at the spinal level [17][18][19]. In 2008, Antonucci et al. suggested that central effects of peripherally applied BoNT A might be due to retrograde transport of the toxin or, alternatively, due to transcytosis leading to an inhibition of neurotransmitters release onto dorsal horn neurons [20]. ...
There are few reports on the safety and effectiveness of long-term botulinumtoxin A (BoNT A) therapy in severe chronic pain of post-herpetic neuralgia (PHN). The literature was searched with the term “neuropathic pain” and “botulinum” on PubMed (up to 29 February 2020). Pain was assessed with the Visual Analogue Scale (VAS) before and after BoNT A therapy. A total of 10 clinical trials and six case reports including 251 patients with PHN were presented. They showed that BoNT A therapy had significant pain reduction (up to 30–50%) and improvement in quality of life. The effect duration seems to be correlated with BoNT A doses injected per injection site. Intervals between BoNT A injections were 10–14 weeks. No adverse events were reported in cases and clinical studies, even in the two pregnant women, whose babies were healthy. The repeated (≥6 times) intra/subcutaneous injections of incobotulinumtoxin A (Xeomin®, Merz Pharmaceuticals, Germany) over the two years of our three cases showed marked pain reduction and no adverse events. Adjunctive local BoNT A injection is a promising option for severe PHN, as a safe and effective therapy in long-term management for chronic neuropathic pain. Its effect size and -duration seem to be depended on the dose of BoNT A injected per each point.
... Centrally, BTA also effects TRPV-1 expression in central systems [144]. Finally, BTA might have an indirect action on endogenous opioids [148] and GABA [149] by enhancing their neurotransmission in the trigeminal innervation region [150]. Thus, the mechanism of action of BTA still warrants further investigation, but all these effects may be at work at different levels. ...
Cluster headache (CH) is the most common form of trigeminal autonomic cephalalgia. Current treatments have several limitations and new drugs are required. This article first briefly reviews present acute and preventive treatments in CH, their mechanism of action and limitations, then describes the state of the art in recent clinical drug trials since 2015, and ends with a critique of trials in the CH field.
Research is limited by lack knowledge of pathophysiology, lack of animal models. In the past 5 years, no brand‐new treatment has emerged, but promising drugs, such as CGRP(R) antibodies, are under study. According to the literature and guidelines, clinicians and researchers should be aware of many limitations in study protocols: concomitant medication, patient sample size, patients’ protocol compliance, and study designs that tend to restrict patient recruitment.
... Although central modulation of the nociceptive activity of BoNT is largely unknown, several re-search results indicate that neurotransmitter receptors have linked -aminobutyric acid (GABA) and opioid transmission to the central antinociceptive action of the toxin. Both GABA and opioid transmission have a role in the attenuation of sensory input transmitted to the dorsal horn [41,42,43]. The functional block of GABA inhibition by BoNT/A and BoNT/B in spinal cord suggests the central modulation of nociceptive activity. ...
Botulinum toxin is one of the most potent molecule known to mankind. A neurotoxin, with high affinity for cholinergic synapse, is effectively capable of inhibiting the release of acetylcholine. On the other hand, botulinum toxin is therapeutically used for several musculoskeletal disorders. Although most of the therapeutic effect of botulinum toxin is due to temporary skeletal muscle relaxation (mainly due to inhibition of the acetylcholine release), other effects on the nervous system are also investigated. One of the therapeutically investigated areas of the botulinum neurotoxin (BoNT) is the treatment of pain. At present, it is used for several chronic pain diseases, such as myofascial syndrome, headaches, arthritis, and neuropathic pain. Although the effect of botulinum toxin in pain is mainly due to its effect on cholinergic transmission in the somatic and autonomic nervous systems, research suggests that botulinum toxin can also provide benefits related to effects on cholinergic control of cholinergic nociceptive and antinociceptive systems. Furthermore, evidence suggests that botulinum toxin can also affect central nervous system (CNS). In summary, botulinum toxin holds great potential for pain treatments. It may be also useful for the pain treatments where other methods are ineffective with no side effect(s). Further studies will establish the exact analgesic mechanisms, efficacy, and complication of botulinum toxin in chronic pain disorders, and to some extent acute pain disorders.
... At the spinal level, it can first of all impair the release of glutamate, SP, and CGRP in the first synapse of the trigeminal pathway, and, secondly, travel transsynaptically to both the neighboring terminals of the processes of cells of Gasserian ganglion with subsequent transport back to the body and/or peripheral terminals, and in projective neurons and interneurons, and glial cells of the STN [269,285,290]. In the trigeminal ganglion, BAT can suppress sensitization of its cells [272,289] and exert a central anti-nociceptive effect, probably due to the involvement of the opioidergic system [298]. ...
Headache is one of the widespread pain syndromes with polyneurochemical mechanisms. Here, we review the involvement of the cholinergic neurotransmitter system in the pathophysiology of various forms of headaches. Data on the sources of cholinergic and parasympathetic innervations of intracranial structures and distribution of N- and M-cholinoreceptors of various subtypes within the trigeminovascular system and their roles in the acetylcholine (ACh) effects on brain circulation and processing of nociception in headache are reviewed. We present data on the algogenic and anti-nociceptive effects of ACh in the peripheral and central parts of the trigeminal nerve system and its presumably analgesic effects at the supraspinal level of the CNS. We discuss the ACh-dependent mechanisms of the anticephalalgia action of pharmacological and nonpharmacological approaches that are used for the headache treatment and the future perspectives of the use of cholinergic drugs.
... BoNT führt außerdem zu einer Reduktion von Muskelspindelafferenzen [17] und zu einer Reduktion der sympathischen Übertragung [40]. Auch eine Wirkung auf spinale μ-Rezeptoren wurde diskutiert [13]. Es konnte gezeigt werden, dass BoNT die analgetische Wirkung von Opioiden verstärkt und einer Toleranzentwicklung vorbeugt [49]. ...
BACKGROUND
Botulinum neurotoxin (BoNT), a toxin of the anaerobic spore-forming bacterium Clostridium botulinum is used as a drug for alleviating muscle spasticity. Other indications include the cosmetic application in facial muscles, hyperhidrosis and neurogenic bladder disorders. It has been approved since 2010 as the first prophylactic treatment for chronic migraine. The analgesic effect of BoNT was observed early on and is currently the subject of intensive research. Painful postherpetic neuralgia is a common complication of an infection with herpes zoster virus. Despite modern treatment algorithms and medication, satisfactory pain treatment is not achieved in all patients. The use of BoNT could represent a new treatment option.
AIM
The aim of this article is to provide an overview of the current evidence for the use of BoNT for postherpetic neuralgia.
MATERIAL AND METHODS
We conducted a systematic literature search with the keywords "botulinum" and "neuropathic" and included original articles in which BoNT was used subcutaneously or intradermally for the treatment of postherpetic neuralgia.
RESULTS
The initial search yielded 212 results. After a title and abstract screening, the number was reduced to 11 relevant publications (5 case reports or series and 6 prospective studies).
DISCUSSION
The results in the currently available literature show that BoNT is an effective therapeutic option for postherpetic neuralgia. In all studies, a significant effect on the pain and also on relevant patient-oriented secondary variables, such as the quality of life and especially the quality of sleep was shown. The only reported side effect was pain during administration.
... Кроме того, обсуждается центральное антиноцицептивное действие БТА, которое может обеспечиваться ретроградным аксональным транспортом с вовлечением других структур ЦНС. Механизм центрального антиноцицептивного действия БТА остается до конца неизвестным, но экспериментальные данные указывают на вовлечение эндогенных опиоидных систем (включая μ-опиоидный рецептор) [45]. Итак, БТА, блокируя высвобождение альгогенных провоспалительных нейромедиаторов, предотвращает развитие нейрогенного воспаления, что, в свою очередь, подавляет развитие периферической сенситизации, а также приводит к снижению болевой импульсации в ЦНС, что препятствует развитию центральной сенситизации [21,37,38]. ...
The results of controlled investigations suggest that botulinumtoxin type A (BTA) leads to decrease headache intensity and prevent migraine attacks. The antinociceptive mechanisms of BTA action remain unclear. Modern and previous hypothesis of antinociceptive action BTA in chronic migraine (CM) are discussed in details. Recent experimental and clinical evidence strongly suggest that BTA has aspecific antinociceptive effect realized through inhibition of proinflammatory neurotransmitters release not only from the sensory terminals but from muscle nociceptors. The mechanism of the action of BTA in CM has more than one target and is considered to involve different pathophysiological levels CM: neurogenic inflammation, peripheral and central sensitization. The administration of BTA on the PREEMPT principle (paradigm) ensures optimal neurotoxin distribution in the anatomic areas in accordance with their sensory innervation by cervical segments and sensory fibers in the trigeminal system, the terminal branches which are the major target of BTA in the treatment of CM.
... The most commonly accepted theory is that BTA acts at peripheral sites to suppress transmission of nociceptive stimuli (53,(87)(88)(89)(90)(91)(92). However, there are increasing reports that peripherally-administered BTA may be transported to the CNS and that it may be this mechanism that allows BTA to suppress pain (93)(94)(95)(96)(97)(98)(99)(100). ...
Botulinum toxin A (BTA) is currently used to treat a variety of painful disorders, including painful bladder syndrome/interstitial cystitis (PBS/IC). However, BTA is not consistently effective in all patients. This may be due to the disparity of causes of pain, but this may also relate to the processes by which BTA exerts anti-nociceptive effects. This review discusses mechanisms by which BTA may inhibit pain and studies of the use of BTA in PSB/IC patients. It is doubtful that any single treatment will effectively control pain in PBS/IC patients, and it is highly probable that multiple strategies will be required, both within individual patients and across the population of PBS/IC patients. The purpose of this review is to discuss those mechanisms by which BTA acts, with the intent that alternative strategies exploiting these mechanism, or work through alternative pathways, can be identified to more effectively treat pain in PBS/IC patients in the future.
Background
Chronic low back pain (CLBP) is a leading cause of disability. Botulinum neurotoxin type A (BoNT-A) has strong anti-spasmodic and analgesic effects, suggesting that its local muscular injection can reduce CLBP compared to other therapies. In this systematic review and meta-analysis, we investigated the efficacy and safety of BoNT-A on patients with CLBP.
Methods
We searched PubMed, Scopus, Cochrane, and Web of Science databases for studies comparing BoNT-A to other therapies in terms of functional improvement and pain improvement as measured by visual analog scale (VAS) and clinically significant improvement in pain (50% or greater reduction in VAS score). We employed trial sequential analysis (TSA) to confirm the findings. The GRADE approach was employed to assess the overall quality of the evidence.
Results
The search yielded nine studies, seven randomised clinical trials (RCTs), and two prospective observational studies. Compared to the control, BoNT-A increased the incidence of clinically significant improvement in pain (RR = 4.82, 95% CI (3.00, 7.76), p < 0.00001) and functional improvement (RR = 3.81, 95% CI (2.40, 6.04), p < 0.00001) (low-certainty evidence), and reduced VAS score (MD = −1.62, 95% CI (−3.13, −0.11), p = 0.04) (very low-certainty evidence). Subgroup analysis showed that BoNT-A is effective against normal saline (moderate-certainty evidence), and it was comparable to steroids and local anaesthetics (very low-certainty evidence). TSA confirmed the findings regarding clinical improvement in pain and functional improvement.
Conclusion
BoNT-A is a tolerable and effective treatment for CLBP with a longer duration of action. Future high-quality studies are needed to confirm our findings.
Significance
This paper provides good evidence that BoNT-A may be employed in patients suffering from resistant chronic low back pain not responding to normal saline injection due to its higher efficacy and longer duration of action. Compared to steroids and local anaesthetics injections, there is not enough data to draw a firm conclusion and future studies are needed.
Objective
To systematically examine the literature on the clinical consequences of inadvertent delays in scheduled onabotulinumtoxin A (OTA) therapy for chronic migraine during the COVID-19 pandemic and assess recommendations when access to OTA is limited.
Background
The coronavirus (COVID-19) pandemic was unprecedented in its impact on the global medical community. Most healthcare institutions in the United States (US) and the world had begun significantly limiting elective procedures, undermining management of many debilitating chronic conditions. OTA injections, were similarly involuntarily postponed, leading to significant setbacks in symptom control.
Methods
A comprehensive literature search was conducted on databases of Medline and Embase with search timeframe defined as the point of database inception to March 1st, 2024, and the search was performed on March 2nd, 2024. The search strategy was independently formulated by two authors (QR and CR) and was reviewed and approved by all authors of the article after appropriate amendments.
Results
A total of nine articles met the defined inclusion criteria. They collectively demonstrated marked delays in OTA treatment with decline in migraine symptom control measured in the form of migraine intensity, frequency, as well as patient satisfaction in disease management. Quality of care in the form of follow-ups also appeared compromised. Alternative strategies of telemedicine and the administration of calcitonin gene-related peptide monoclonal antibodies (CGRP mAb) were adopted in place of conventional treatment.
Conclusion
The COVID-19 pandemic had caused marked clinical deterioration in the migraine patient populations across US, Europe, and the Middle East. Strategies employed to circumvent this limitation included the adoption of remote consultation via telemedicine as well as the use of pharmacological agents such as CGRP antagonists. In the event of a reoccurrence of a worldwide pandemic, strategies should be implemented to prevent the cessation of needed treatment for those suffering from chronic migraine.
Background
Knee osteoarthritis (KOA) is the most common cause of chronic knee pain causing functional disability and dependency. Multiple interventions have been used in reducing pain and improving functionality. We intend to compare the efficacy of intra-articular platelet-rich plasma (PRP) and hyaluronic acid (HA) with botulinum toxin type A and HA in bilateral Grade 3 and 4 KOA.
Methods
Prospective single-blinded randomized controlled trial conducted for 6 months. Among 54 participants, 27 received intra-articular botulinum toxin type A with HA (Group A), and the other 27 received intra-articular PRP with HA (Group B), single session. Pain (Numerical Rating Scale [NRS]) and functional limitation (Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC]) were assessed at 2, 4, 12, and 24 weeks postintervention. Effect of weight and physiotherapy on NRS and WOMAC score were assessed. P <0.05 was considered statistically significant. Data were analyzed by statistical software R version 4.2.3.
Results
Fifty-four participants were enrolled. There was no loss to follow-ups. Except for age ( P < 0.001) and mean height ( P = 0.013), other demographic data were insignificant. Preprocedural NRS was significantly high in Group A ( P = 0.04). Overall NRS postprocedure was significantly lesser in Group B, P < 0.001. The mean WOMAC score postprocedure was significantly low in Group B, P < 0.001. Group B had increased heart rate which was statistically significant ( P = 0.051). The mean reduction in WOMAC score was observed with regular physiotherapy in Group B ( P = 0.023). Reduction in weight was directly proportional to reduction in NRS ( P = 0.015).
Conclusion
Intra-articular PRP with HA, single session, is effective in improving pain, functionality, and safe in Grade 3 and 4 KOA.
Driven by the clinical success of botulinum toxin serotype A (BoNT/A) and the need for improved chronic pain management, researchers attempted to develop re-designed botulinum toxin (BoNT)-based molecules as novel analgesics. Various recombinant protein expression strategies including retargeted binding domains, and chimeric toxins combining different serotypes were tested to improve BoNT/A therapeutic safety margin and expand its efficacy. The aim of this review is to re-evaluate the current design strategies for recombinant BoNT-based molecules for pain treatment, compares their analgesic profile against the native BoNT/A, as well as to discuss the main strengths and potential weaknesses of reported approaches.
Botulinum toxin (BoNT), a presynaptic inhibitor of acetylcholine (Ach) release at the neuromuscular junction (NMJ), is a successful and safe drug for the treatment of several neurological disorders. However, a wide and recent literature review has demonstrated that BoNT exerts its effects not only at the “periphery” but also within the central nervous system (CNS). Studies from animal models, in fact, have shown a retrograde transport to the CNS, thus modulating synaptic function. The increasing number of articles reporting efficacy of BoNT on chronic neuropathic pain (CNP), a complex disease of the CNS, demonstrates that the central mechanisms of BoNT are far from being completely elucidated. In this new light, BoNT might interfere with the activity of spinal, brain stem, and cortical circuitry, modulating excitability and the functional organization of CNS in healthy conditions. Botulinum toxins efficacy on CNP is the result of a wide and complex action on many and diverse mechanisms at the basis of the maladaptive plasticity, the core of the pathogenesis of CNP. This systematic review aims to discuss in detail the BoNT's mechanisms and effects on peripheral and central neuroplasticity, at the basis for the clinical efficacy in CNP syndromes.
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 regionrelated
pain states.
The purpose of this study was to investigate the efficacy and safety of intra-articular Botulinum Toxin type A (BTA) injection in the management of patients with knee osteoarthritis (KOA). The literature retrieval was conducted based on PRISMA guidelines. Databases including Pubmed, Web of science, EMBASE, and Cochrane Library were searched to identify RCTs that comparing the effects of intra-articular BTA injection with control interventions on patients with KOA. The primary outcomes involved pain and function improvements as well as the occurrence of adverse events. Seven RCTs comprising 548 participants were included in this meta-analysis. Compared with the control group, BTA injection exhibited greater pain reduction at 4 weeks posttreatment (SMD = -0.86, 95% CI [-1.52, -0.19], p = 0.011), but not 8-24 weeks posttreatment (wk 8, SMD = -0.53, 95% CI [-1.21, 0.15], p = 0.127; wk 12, SMD = -0.34, 95% CI [-0.73, 0.04], p = 0.081; wk 24, SMD = -0.65, 95% CI [-1.52, 0.22], p = 0.144). Additionally, no differences were found between BTA injection versus control intervention on functional improvement at all time points assessed (wk 4, WMD = -5.16, 95% CI [-12.31, 2.00], p = 0.158; wk 8, WMD = -0.98, 95% CI [-5.66, 3.71], p = 0.683; wk 12, WMD = -2.52, 95% CI [-7.54, 2.50], p = 0.325); wk 24, WMD = -3.66, 95% CI [-14.09, 6.76], p = 0.491). There was no significant difference in adverse event rate between the BTA and control group (OR = 0.88, 95% CI [0.24, 3.18], p = 0.843). This meta-analysis suggests that intra-articular BTA injection could be an efficious and safe strategy for analgesic treatment of KOA. However, evidence is limited due to the small number and heterogeneity of included studies, this urges further and stronger trials to confirm our findings.
Recent discoveries of the new pain receptors and channels as well as pain modulators and transmitters have improved our knowledge of pain pathophysiology. Animal data on botulinum neurotoxins (BoNTs) indicate that application of this toxin via injection can modify and diminish the function of several mechanisms that generate or maintain pain. The first part of this chapter describes the pathophysiology of pain in light of the new knowledge recently gained in this area. The second part provides a brief review of the literature on how treatment with BoNTs can improve pain behavior in animals and lower perception of pain in asymptomatic human volunteers; the therapeutic impact of BoNTs on pain receptors, channels, and mediators is also discussed.
Prospective, double-blind and placebo-controlled studies (PREEMPT) have demonstrated the efficacy of onabotulinumtoxinA (onaA) in chronic migraine (class A evidence). Follow-up of patients included in PREEMPT studies with 5 cycles of onaA injections (over 56 weeks) has shown good tolerability and safety of OnaA injections in chronic migraine along with improvement of patients’ quality of life. Studies using onaA in management of episodic migraine and chronic daily headaches, however, have shown disappointing results. Most blinded studies of botulinum neurotoxins (BoNTs) in management of tension-type headache have also provided negative results, but the results are confounded by selection of low dose, suboptimal technique, and selection of rigid primary outcome criteria. Emerging data from investigation of efficacy of botulinum toxins in cluster headaches and posttraumatic headaches are encouraging, but blinded studies of larger cohorts are needed in these areas. An alternative injection protocol, based on the author’s experience at Walter Reed Medical Center and Yale University, that differs from PREEMPT and uses fewer number of injection sites compared to PREEMPT protocol for treatment of chronic migraine, is described and discussed.
The use of botulinum toxin type A (BoNT-A) in pain conditions is continuously growing largely because of its long-lasting effect after local application and safety profile. These unique features distinguish BoNT-A from other conventional and adjuvant analgesic drugs. Furthermore, BoNT-A diminishes only the pathological pain, without affecting the normal pain threshold. Preclinical data from several complex pain models suggested the central site of its action on pain after retrograde axonal transport from the peripheral site of application. Further investigations of the mechanism of BoNT-A antinociceptive action are ongoing as well as experiments on new recombinant BoNTs with higher selectivity for nociceptive neurons.
Botulinum toxins are a large family of proteins produced by a gram-positive anaerobic bacterium, Clostridium botulinum. They are largely used in the clinical practice to treat a number of pathologic conditions characterized by the spasticity of striated muscles. Moreover, the neurotoxin is also used, in an off label setting, in the treatment of pain related disorders, such as chronic pelvic pain. Interstitial cystitis/bladder painful syndrome, category III, nonbacterial chronic prostatitis/chronic pelvic pain syndrome, vaginismus and vulvodynia, are actually fields of application and research of botulinum toxins in the affected patients. Some robust evidences exist on the efficacy and safety of botulinum toxin type A in patients affected by interstitial cystitis/bladder painful syndrome, but no consistent data are available on the use of the neurotoxin in the other pelvic pain conditions. To date, there is the urgent need to have adequate randomized, controlled studies to definitively establish the role of botulinum toxins in treating pelvic pain conditions.
Tremendous progress has been made in the past decades for the treatment of headache disorders. Chronic migraine is the most disabling type of headache and requires the use of acute and preventive medications, many of which are associated with adverse events that limit patient adherence. Botulinum toxin (BoNT) serotype A, a neurotoxin derived from certain strains of Clostridium, disrupts neuropeptide secretion and receptor translocation related to trigeminal nociception, thereby preventing pain sensitization through peripheral and possibly central mechanisms. Ever since the first randomized controlled trial on onabotulinumtoxinA (onabotA) for migraine was published two decades ago, onabotA has been the only BoNT formulation approved for use in the prevention of chronic migraine. Superior tolerability and efficacy have been demonstrated on multiple migraine endpoints in many controlled trials and real-life studies. OnabotA is a safe and efficacious treatment for chronic migraine and possibly high-frequency episodic migraine. Further research is still needed to understand its mechanism of action to fully develop its therapeutic potential.
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.
Migraine is a highly prevalent and disabling disorder accounted among the primary headaches. It is the expression of a complex, and not yet fully understood, pathophysiology involving the sensitization of peripheral and central nociceptive pathways. In this review we succinctly illustrate the molecular, anatomical, and functional abnormalities underlying the migraine attack that are relevant for understanding in more depth the neurobiology behind the therapeutic effect of Botulinum Toxin Type A (BoNT-A). BoNT-A has proved effective in several neurological conditions and, more recently, also in chronic migraine. Its antimigraine mechanism of action was initially thought to be limited to the periphery and interpreted as an inhibitory activity on the processes associated to the local release of neuropeptides, with subsequent induction of peripheral sensitization. Increasing experimental evidence has become available to suggest that additional mechanisms are possibly involved, including the direct/indirect inhibition of sensitization processes in central nociceptive pathways.
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.
To clarify the analgesic effect in neuropathic pain of bot-ulinum toxin type A (BoNT/A), a study regarding intrath-ecal administration of BoNT/A in a neuropathic pain model was performed. 0.15 units of intrathecal BoNT/A was administered 2 days after sciatic ligation (Seltzer method). Allodynia was examined using the von Frey test, and the effect of BoNT/A on excitatory synaptic transmission in the spinal dorsal horn was evaluated using patch clamp whole-cell recording. The attenuation of allodynia was observed in the BoNT/A treatment group after ligation with the von-Frey test after the sciatic nerve ligation (p<0.05). Patch clamp whole cell recording of spinal slice was performed 7 days after BoNT/A treatment, and miniature excitatory postsynaptic currents (mEPSCs) were observed. The frequency of mEP-SCs was significantly reduced compared with the vehicle group (p<0.05) with no effect on amplitude. The amplitude of evoked excitatory postsynaptic currents (eEPSCs) induced by single stimulation was also inhibited by intrathecal BoNT/A. These results suggested that the increasing of excitatory synaptic transmission in the spinal cord dorsal horn might be suppressed by intrathecal administration of BoNT/A, which is likely to produce presynaptic suppression underlying these analgesic effects.
Infraorbital nerve constriction (IoNC) is an experimental model of trigeminal neuropathy. We investigated if IoNC is accompanied by dural extravasation and if botulinum toxin type A (BoNT/A) can reduce pain and dural extravasation in this model.
Rats which developed mechanical allodynia 14 days after the IoNC were injected with BoNT/A (3.5 U/kg) into vibrissal pad. Allodynia was tested by von Frey filaments and dural extravasation was measured as colorimetric absorbance of Evans blue-plasma protein complexes. Presence of dural extravasation was also examined in orofacial formalin-induced pain. Unilateral IoNC, as well as formalin injection, produced bilateral dural extravasation. Single unilateral BoNT/A injection bilaterally reduced IoNC induced dural extravasation, as well as allodynia (lasting more than 2 weeks). Similarly, BoNT/A reduced formalin-induced pain and dural extravasation. Effects of BoNT/A on pain and dural extravasation in IoNC model were dependent on axonal transport through sensory neurons, as evidenced by colchicine injections (5 mM, 2 µl) into the trigeminal ganglion completely preventing BoNT/A effects.
Two different types of pain, IoNC and formalin, are accompanied by dural extravasation. The lasting effect of a unilateral injection of BoNT/A in experimental animals suggests that BoNT/A might have a long-term beneficial effect in craniofacial pain associated with dural neurogenic inflammation. Bilateral effects of BoNT/A and dependence on retrograde axonal transport suggest a central site of its action.
The action of botulinum neurotoxins (BoNTs) at the neuromuscular junction has been extensively investigated and knowledge gained in this field laid the foundation for the use of BoNTs in human pathologies characterized by excessive muscle contractions. Although much more is known about the action of BoNTs on the peripheral system, growing evidence has demonstrated several effects also at the central level. Pain conditions, with special regard to neuropathic and intractable pain, are some of the pathological states that have been recently treated with BoNTs with beneficial effects. The knowledge of the action and potentiality of BoNTs utilization against pain, with emphasis for its possible use in modulation and alleviation of chronic pain, still represents an outstanding challenge for experimental research. This review highlights recent findings on the effects of BoNTs in animal pain models.
Botulinum neurotoxin type A (BoNT/A) is a metalloprotease that blocks synaptic transmission via the cleavage of SNAP-25 (synaptosomal-associated protein of 25 kDa). BoNT/A is successfully used in clinical neurology for the treatment of several neuromuscular pathologies and pain syndromes. Despite its widespread use, relatively little is known on BoNT/A intracellular trafficking in neurons. Using the visual pathway as a model system, here we show that catalytically active BoNT/A is capable of undergoing anterograde axonal transport and transcytosis. Following BoNT/A injection into the rat eye, significant levels of BoNT/A-cleaved SNAP-25 appeared in the retinorecipient layers of the superior colliculus (SC). Anterograde propagation of BoNT/A effects required axonal transport, ruling out a systemic spread of the toxin. Cleaved SNAP-25 was present in presynaptic structures of the tectum, but retinal terminals were devoid of the immunoreactivity, indicative of transcytosis. Experiments based on sequential administration of BoNT/A and BoNT/E showed a persistent catalytic activity of BoNT/A in tectal cells following its injection into the retina. Our findings demonstrate that catalytically active BoNT/A is anterogradely transported from the eye to the SC and transcytosed to tectal synapses. These data are important for a more complete understanding of the mechanisms of action of BoNT/A.
Botulinum (BoNT) toxin has been used for its muscle-paralyzing action in conditions such as treatment of wrinkles, cervical dystonia and blephrospasm. There is preclinical and emerging clinical evidence of another mechanism of action of BoNT, namely, an antinociceptive action. In this review, we provide an evidence-based review of clinical studies of BoNT in osteoarticular conditions, such as osteoarthritis, tennis elbow, low back pain, and hand pain. Many randomized controlled trials (RCTs) found evidence of short-term efficacy of an injection of BoNT in relief of pain, and in some cases, improvement of function and quality of life. However, more clinical trials are needed to better define the clinical use of BoNT for treatment of refractory osteoarticular pain.
Mammalian cells synthesize morphine and the respective biosynthetic pathway has been elucidated. Human neutrophils release this alkaloid into the media after exposure to morphine precursors. However, the exact role of endogenous morphine in inflammatory processes remains unclear. We postulate that morphine is released during infection and can be determined in the serum of patients with severe infection such as sepsis.
The presence and subcellular immunolocalization of endogenous morphine was investigated by ELISA, mass spectrometry analysis and laser confocal microscopy. Neutrophils were activated with Interleukin-8 (IL-8) or lipopolysaccharide (LPS). Morphine secretion was determined by a morphine-specific ELISA. mu opioid receptor expression was assessed with flow cytometry. Serum morphine concentrations of septic patients were determined with a morphine-specific ELISA and morphine identity was confirmed in human neutrophils and serum of septic patients by mass spectrometry analysis. The effects of the concentration of morphine found in serum of septic patients on LPS-induced release of IL-8 by human neutrophils were tested.
We confirmed the presence of morphine in human neutrophil extracts and showed its colocalisation with lactoferrin within the secondary granules of neutrophils. Morphine secretion was quantified in the supernatant of activated human polymorphonuclear neutrophils in the presence and absence of Ca(2+). LPS and IL-8 were able to induce a significant release of morphine only in presence of Ca(2+). LPS treatment increased mu opioid receptor expression on neutrophils. Low concentration of morphine (8 nM) significantly inhibited the release of IL-8 from neutrophils when coincubated with LPS. This effect was reversed by naloxone. Patients with sepsis, severe sepsis and septic shock had significant higher circulating morphine levels compared to patients with systemic inflammatory response syndrome and healthy controls. Mass spectrometry analysis showed that endogenous morphine from serum of patient with sepsis was identical to poppy-derived morphine.
Our results indicate that morphine concentrations are increased significantly in the serum of patients with systemic infection and that morphine is, at least in part, secreted from neutrophils during sepsis. Morphine concentrations equivalent to those found in the serum of septic patients significantly inhibited LPS-induced IL-8 secretion in neutrophils.
beta-Endorphin, a 31-amino-acid peptide, is primarily synthesised in the anterior pituitary gland and cleaved from pro-opiomelanocortin, its larger precursor molecule. beta-Endorphin can be released into the circulation from the pituitary gland or can project into areas of the brain through nerve fibres. Exercise of sufficient intensity and duration has been demonstrated to increase circulating beta-endorphin levels. Previous reviews have presented the background of opioids and exercise and discussed the changes in beta-endorphin levels in response to aerobic and anaerobic exercise. The present review is to update the response of beta-endorphin to exercise. This review suggests that exercise-induced beta-endorphin alterations are related to type of exercise and special populations tested, and may differ in individuals with health problems. Additionally, some of the possible mechanisms which may induce beta-endorphin changes in the circulation include analgesia, lactate or base excess, and metabolic factors. Based on the type of exercise, different mechanisms may be involved in the regulation of beta-endorphin release during exercise.
To test antinociceptive properties of botulinum toxin type A (BTX-A) in rats with carrageenan- and capsaicin-induced pain and inflammation.
Pain was provoked with carrageenan (1%) or capsaicin (0.1%) injection into the plantar surface of the rat paw-pad. The effect of BTX-A 5 U/kg on carrageenan- and capsaicin-induced mechanical and thermal hypersensitivity, as well as the size of carrageenan-induced paw edema were tested 24 hours and 6 days following the toxin injection into the rat paw-pad. In the dose-response experiment, the effect of different doses of BTX-A (2, 3, 3.5, 5, and 7 U/kg) on carrageenan-induced mechanical hypersensitivity was investigated on day 5 after BTX-A application.
Pretreatment with 5 U/kg BTX-A significantly reduced or completely abolished the enhanced sensitivity to mechanical and thermal stimuli provoked by peripheral carrageenan or capsaicin injections. This reduction was significant when BTX-A was applied 6 days before the induction of pain and inflammation, but the toxin was ineffective when applied 24 hours before the challenge. In the dose-response experiment, the lowest effective dose was 3.5 U/kg, but apparently the effect was not dose-dependent. In contrast to the antinociceptive effect, 5 U/kg BTX-A had no effect on the carrageenan-induced paw edema.
The study demonstrated the efficacy of peripherally applied BTX-A pretreatment on the pain component of inflammatory process in experimental animals.
Reductions in pain ratings when administered a placebo with expected analgesic properties have been described and hypothesized to be mediated by the pain-suppressive endogenous opioid system. Using molecular imaging techniques, we directly examined the activity of the endogenous opioid system on mu-opioid receptors in humans in sustained pain with and without the administration of a placebo. Significant placebo-induced activation of mu-opioid receptor-mediated neurotransmission was observed in both higher-order and sub-cortical brain regions, which included the pregenual and subgenual rostral anterior cingulate, the dorsolateral prefrontal cortex, the insular cortex, and the nucleus accumbens. Regional activations were paralleled by lower ratings of pain intensity, reductions in its sensory and affective qualities, and in the negative emotional state of the volunteers. These data demonstrate that cognitive factors (e.g., expectation of pain relief) are capable of modulating physical and emotional states through the site-specific activation of mu-opioid receptor signaling in the human brain.
Botulinum neurotoxins (designated BoNT/A-BoNT/G) are bacterial enzymes that block neurotransmitter release by cleaving essential components of the vesicle fusion machinery. BoNT/A, which cleaves SNAP-25 (synaptosomal-associated protein of 25 kDa), is extensively exploited in clinical medicine to treat neuromuscular pathologies, facial wrinkles, and various types of pain. It is widely assumed that BoNT/A remains at the synaptic terminal and its effects are confined to the injection site. Here we demonstrate that catalytically active BoNT/A is retrogradely transported by central neurons and motoneurons and is then transcytosed to afferent synapses, in which it cleaves SNAP-25. SNAP-25 cleavage by BoNT/A was observed in the contralateral hemisphere after unilateral BoNT/A delivery to the hippocampus. Appearance of cleaved SNAP-25 resulted in blockade of hippocampal activity in the untreated hemisphere. Injections of BoNT/A into the optic tectum led to the appearance of BoNT/A-truncated SNAP-25 in synaptic terminals within the retina. Cleaved SNAP-25 also appeared in the facial nucleus after injection of the toxin into rat whisker muscles. Experiments excluded passive spread of the toxin and demonstrated axonal migration and neuronal transcytosis of BoNT/A. These findings reveal a novel pathway of BoNT/A trafficking in neurons and have important implications for the clinical uses of this neurotoxin.
β-Endorphin, a 31-amino-acid peptide, is primarily synthesised in the anterior pituitary gland and cleaved from pro-opiomelanocortin, its larger precursor molecule. β-Endorphin can be released into the circulation from the pituitary gland or can project into areas of the brain through nerve fibres. Exercise of sufficient intensity and duration has been demonstrated to increase circulating β-endorphin levels. Previous reviews have presented the background of opioids and exercise and discussed the changes in β-endorphin levels in response to aerobic and anaerobic exercise. The present review is to update the response of β-endorphin to exercise. This review suggests that exercise-induced β-endorphin alterations are related to type of exercise and special populations tested, and may differ in individuals with health problems. Additionally, some of the possible mechanisms which may induce β-endorphin changes in the circulation include analgesia, lactate or base excess, and metabolic factors. Based on the type of exercise, different mechanisms may be involved in the regulation of β-endorphin release during exercise.
The analgesic effect of Botulinum toxin A has been already demonstrated in different experimental models of pain. The aim of the present study was to compare the efficacy of Dysport® and Botox® on inflammatory pain induced in rats by a sub-plantar (s.p.) injection of carrageenan (2 mg/0.1 ml) in the right hind paw. Hyperalgesia was assessed by measurement of the withdrawal threshold of each hind paw in response to mechanical stimulus (Randall & Selitto pressure test). In this model, Dysport® and Botox® elicited a comparable analgesic effect (ED50: 22 and 28 U/kg, respectively) when administered (s.p.) in the right hind paw 3 days before carrageenan administration. In this model, intraperitoneal injection of morphine induced a dose-dependent analgesic effect with an ED50 of 0.6 mg/kg. When a non-active dose of morphine (0.3 mg/kg) was tested in animals pre-treated 3 days before with a non-active dose of Dysport® (10 U/kg), a significant analgesic effect was observed. Considering that large doses of morphine result in side effects and tolerance, this result suggests that Botulinum toxin A may have morphine sparing effects.
Over the recent years compelling evidence has accumulated indicating that botulinum neurotoxin serotype A (BoNT/A) results in analgesic effects on neuropathic as well as inflammatory pain, both in humans and in animal models. In the present study, the pharmacological interaction of BoNT/A with morphine in fighting inflammatory pain was investigated in mice using the formalin test. Moreover, the effects of BoNT/A on the tolerance-induced by chronic administration of morphine were tested and the behavioral effects were correlated with immunofluorescence staining of glial fibrillary acidic protein, the specific marker of astrocytes, at the spinal cord level. An ineffective dose of BoNT/A (2 pg/paw) combined with an ineffective dose of morphine (1 mg/kg) exerted a significant analgesic action both during the early and the late phases of formalin test. A single intraplantar injection of BoNT/A (15 pg/paw; i.pl.), administered the day before the beginning of chronic morphine treatment (7 days of s.c. injections of 20 mg/kg), was able to counteract the occurrence of tolerance to morphine. Moreover, BoNT/A reduces the enhancement of the expression of astrocytes induced by inflammatory formalin pain. Side effects of opiates, including the development of tolerance during repeated use, may limit their therapeutic use, the possibility of using BoNT/A for lowering the effective dose of morphine and preventing the development of opioid tolerance would have relevant implications in terms of potential therapeutic perspectives.
The present work aimed to investigate the effects of acute sucrose treatment on the perception of painful stimuli. Specifically, we sought to determine the involvement of the endogenous opioid peptide-mediated system as well as the role of the μ(1)-opioid receptor in antinociception organisation induced by acute sucrose intake. Nociception was assessed with the tail-flick test in rats (75, 150 and 250 g) of different ages acutely pre-treated with 500 μL of a sucrose solution (25, 50, 150 and 250 g/L) or tap water. Young and Adult rats (250 g) showed antinociception after treatment with 50 g/L (during 5 min) and 150 g/L and 250 g/L (during 20 min) sucrose solutions. Surprisingly, this antinociception was more consistent in mature adult rodents than in pups. To evaluate the role of opioid systems, mature adult rodents were pre-treated with different doses (0.25, 1 or 4 mg/kg) of the non-selective opioid receptor antagonist naloxone, the selective μ(1)-opioid receptor antagonist naloxonazine or vehicle followed by 250 g/L sucrose solution treatment. Sucrose-induced antinociception was reduced by pre-treatment with both naloxone and naloxonazine. The present findings suggest that sweet substance-induced hypo-analgesia is augmented by increasing sucrose concentrations in young and adult rodents. Acute oral sucrose treatment inhibits pain in laboratory animal by mediating endogenous opioid peptide and μ(1)-opioid receptor actions.
To provide updated information on the role of botulinum toxins in the treatment of refractory pain based on prospective, randomized, double-blind, placebo-controlled studies. DESIGN OF THE REVIEW: Class I and class II articles were searched online through PubMed (1966 to the end of January 2011) and OvidSP including ahead-of-print manuscripts.
Level A evidence (two or more class I studies-established efficacy): pain of cervical dystonia, chronic migraine, and chronic lateral epicondylitis. Level B evidence (one class I or two class II studies-probably effective and recommended): post-herpetic neuralgia, post-traumatic neuralgia, pain of plantar fasciitis, piriformis syndrome, and pain in total knee arthroplasty. Level C evidence (one class II study-possibly effective, may be used at discretion of clinician): allodynia of diabetic neuropathy, chronic low back pain, painful knee osteoarthritis, anterior knee pain with vastus lateralis imbalance, pelvic pain, post-operative pain in children with cerebral palsy after adductor hip release surgery, post-operative pain after mastectomy, and sphincter spasms and pain after hemorrhoidectomy. Level U evidence (efficacy not proven due to diverse class I and II results): myofascial pain syndrome and chronic daily headaches. Studies in episodic migraine and tension headaches have shown treatment failure (level A-negative).
Evidence-based data indicate that administration of botulinum toxin in several human conditions can alleviate refractory pain. The problems with some study designs and toxin dosage are critically reviewed.
Botulinum toxin A (BTX-A) is approved for treatment of different cholinergic hyperactivity disorders, and, recently, migraine headache. Although suggested to act only locally, novel observations demonstrated bilateral reduction of pain after unilateral toxin injection, and proposed retrograde axonal transport, presumably in sensory neurons. However, up to now, axonal transport of BTX-A from periphery to CNS was identified only in motoneurons, but with unknown significance. We assessed the effects of low doses of BTX-A injected into the rat whisker pad (3.5 U/kg) or into the sensory trigeminal ganglion (1 U/kg) on formalin-induced facial pain. Axonal transport was prevented by colchicine injection into the trigeminal ganglion (5 mM, 2 μl). To find the possible site of action of axonally transported BTX-A, we employed immunohistochemical labeling of BTX-A-truncated synaptosomal-associated protein 25 (SNAP-25) in medullary dorsal horn of trigeminal nucleus caudalis after toxin injection into the whisker pad. Both peripheral and intraganglionic BTX-A reduce phase II of formalin-induced pain. Antinociceptive effect of BTX-A was prevented completely by colchicine. BTX-A-truncated SNAP-25 in medullary dorsal horn (spinal trigeminal nucleus) was evident 3 days following the peripheral treatment, even with low dose applied (3.5 U/kg). Presented data provide the first evidence that axonal transport of BTX-A, obligatory for its antinociceptive effects, occurs via sensory neurons and is directed to sensory nociceptive nuclei in the CNS.
Botulinum neurotoxin serotype A (BoNT/A) acts by cleaving synaptosome-associated-protein-25 (SNAP-25) in nerve terminals to inhibit neuronal release and shows long-lasting antinociceptive action in neuropathic pain. However, its precise mechanism of action remains unclear. Our study aimed to characterize BoNT/A-induced neuroimmunological changes after chronic constriction injury (CCI) of the sciatic nerve. In the ipsilateral lumbar spinal cords of CCI-exposed rats, the mRNA of microglial marker (complement component 1q, C1q), astroglial marker (glial fibrillary acidic protein, GFAP), and prodynorphin were upregulated, as measured by reverse transcription-polymerase chain reaction (RT-PCR). No changes appeared in mRNA for proenkephalin, pronociceptin, or neuronal and inducible nitric oxide synthase (NOS1 and NOS2, respectively). In the dorsal root ganglia (DRG), an ipsilateral upregulation of prodynorphin, pronociceptin, C1q, GFAP, NOS1 and NOS2 mRNA and a downregulation of proenkephalin mRNA were observed. A single intraplantar BoNT/A (75 pg/paw) injection induced long-lasting antinociception in this model. BoNT/A diminished the injury-induced ipsilateral spinal upregulation of C1q mRNA. In the ipsilateral DRG a significant decrease of C1q-positive cell activation and of the upregulation of prodynorphin, pronociceptin and NOS1 mRNA was also observed following BoNT/A admistration. BoNT/A also diminished the injury-induced upregulation of SNAP-25 expression in both structures. We provide evidence that BoNT/A impedes injury-activated neuronal function in structures distant from the injection site, which is demonstrated by its influence on NOS1, prodynorphin and pronociceptin mRNA levels in the DRG. Moreover, the silence of microglia/macrophages after BoNT/A administration could be secondary to the inhibition of neuronal activity, but this decrease in neuroimmune interactions could be the key to the long-lasting BoNT/A effect on neuropathic pain.
Botulinum neurotoxin (BoNT) is an effective treatment for conditions associated with overactivity of glandular, smooth or skeletal muscle, and this toxin can also ameliorate certain painful conditions. Electromyography, endoscopy and imaging techniques such as ultrasonography and fluoroscopy have been used to increase the accuracy of BoNT injections. This Review assesses the mechanisms of action of BoNT, and examines the use of BoNT injections in numerous neurological conditions, including dystonia, spasticity, headaches and other painful disorders, hemifacial spasm, essential tremor, motor tics, hyperhidrosis, and sialorrhea and drooling. Important practical aspects, such as the reconstitution of BoNT, dosing, and methods of administration, are also addressed.
To assess the efficacy, safety, and tolerability of onabotulinumtoxinA (BOTOX) as headache prophylaxis in adults with chronic migraine.
Chronic migraine is a prevalent, disabling, and undertreated neurological disorder. Few preventive treatments have been investigated and none is specifically indicated for chronic migraine.
The 2 multicenter, pivotal trials in the PREEMPT: Phase 3 REsearch Evaluating Migraine Prophylaxis Therapy clinical program each included a 24-week randomized, double-blind phase followed by a 32-week open-label phase (ClinicalTrials.gov identifiers NCT00156910, NCT00168428). Qualified patients were randomized (1:1) to onabotulinumtoxinA (155-195 U) or placebo injections every 12 weeks. Study visits occurred every 4 weeks. These studies were identical in design (eg, inclusion/exclusion criteria, randomization, visits, double-blind phase, open-label phase, safety assessments, treatment), with the only exception being the designation of the primary and secondary endpoints. Therefore, the predefined pooling of the results was justified and performed to provide a complete overview of between-group differences in efficacy, safety, and tolerability that may not have been evident in individual studies. The primary endpoint for the pooled analysis was mean change from baseline in frequency of headache days at 24 weeks. Secondary endpoints were mean change from baseline to week 24 in frequency of migraine/probable migraine days, frequency of moderate/severe headache days, total cumulative hours of headache on headache days, frequency of headache episodes, frequency of migraine/probable migraine episodes, frequency of acute headache pain medication intakes, and the proportion of patients with severe (> or =60) Headache Impact Test-6 score at week 24. Results of the pooled analyses of the 2 PREEMPT double-blind phases are presented.
A total of 1384 adults were randomized to onabotulinumtoxinA (n = 688) or placebo (n = 696). Pooled analyses demonstrated a large mean decrease from baseline in frequency of headache days, with statistically significant between-group differences favoring onabotulinumtoxinA over placebo at week 24 (-8.4 vs -6.6; P < .001) and at all other time points. Significant differences favoring onabotulinumtoxinA were also observed for all secondary efficacy variables at all time points, with the exception of frequency of acute headache pain medication intakes. Adverse events occurred in 62.4% of onabotulinumtoxinA patients and 51.7% of placebo patients. Most patients reported adverse events that were mild to moderate in severity and few discontinued (onabotulinumtoxinA, 3.8%; placebo, 1.2%) due to adverse events. No unexpected treatment-related adverse events were identified.
The pooled PREEMPT results demonstrate that onabotulinumtoxinA is an effective prophylactic treatment for chronic migraine. OnabotulinumtoxinA resulted in significant improvements compared with placebo in multiple headache symptom measures, and significantly reduced headache-related disability and improved functioning, vitality, and overall health-related quality of life. Repeat treatments with onabotulinumtoxinA were safe and well tolerated.
The endogenous opioids mediate the analgesic effects of celecoxib in a model of mechanical hyperalgesia in rats. As responses to thermal stimuli may differ from those to mechanical stimuli, we have here assessed celecoxib in a rat model of thermal hyperalgesia and the possible involvement of endogenous opioids and their corresponding receptors in these effects.
Injection of carrageenan (CG) into one hind paw induced a dose-related hyperalgesia (decreased time for paw withdrawal) to thermal stimuli (infra-red light beam), over 6h.
Celecoxib (sc) 30 min before CG (250 microg per paw) induced a dose-dependent reversal of hyperalgesia, with withdrawal times well above basal levels, characterizing development of hypoalgesia. Indomethacin (sc) reversed CG-induced hyperalgesia only to basal levels (an anti-hyperalgesic effect). Naltrexone (sc) prevented hypoalgesia after celecoxib but did not change the response to indomethacin. Local (intraplantar) injection of either a selective antagonist of mu-(beta-funaltrexamine), kappa-(nor-binaltorphimine) or of delta-(naltrindole) opioid receptors also reversed the hypoalgesic effects of celecoxib, without modifying the hyperalgesia due to CG or affecting the nociceptive thresholds in the non-injected paw.
Our data show that celecoxib, unlike indomethacin, was hypoalgesic in this model of thermal hyperalgesia, and that this effect was mediated by peripheral mu-, kappa- and delta-opioid receptors.
We investigated antinociceptive activity of botulinum toxin type A (BTX-A) in a model of diabetic neuropathic pain in rats. Male Wistar rats were made diabetic by a single intraperitoneal injection of streptozotocin (80mg/kg). Sensitivity to mechanical and thermal stimuli was measured with the paw-pressure and hot-plate test, respectively. The formalin test was used to measure sensitivity to chemical stimuli. Diabetic animals with pain thresholds lower for at least 25% compared to the non-diabetic group were considered neuropathic and were injected with BTX-A either subcutaneously (3, 5 and 7U/kg) or intrathecally (1U/kg). Mechanical and thermal sensitivity was measured at several time-points. After peripheral application, BTX-A (5 and 7U/kg) reduced mechanical and thermal hypersensitivity not only on ipsilateral, but on contralateral side, too. The antinociceptive effect started 5days following BTX-A injection and lasted at least 15days. Formalin-induced hypersensitivity in diabetic animals was abolished as well. When applied intrathecally, BTX-A (1U/kg) reduced diabetic hyperalgesia within 24h supporting the assumption of retrograde axonal transport of BTX-A from the peripheral site of injection to central nervous system. The results presented here demonstrate the long-lasting pain reduction after single BTX-A injection in the animals with diabetic neuropathy. The bilateral pain reduction after unilateral toxin application and the effectiveness of lower dose with the faster onset after the intrathecal injection suggest the involvement of the central nervous system in the antinociceptive action of BTX-A in painful diabetic neuropathy.
Here we provide behavioural evidence for an axonal transport and the central origin of the antinociceptive effect of botulinum toxin type A (BTX-A). In rats we investigated the effectiveness of BTX-A on "mirror pain" induced by unilateral repeated intramuscular acidic saline injections (pH 4.0). Since experimental evidence suggest that bilateral pain induced by acidic saline is of central origin, peripheral application of BTX-A should have no effect on this type of pain. However, here we demonstrated that the unilateral subcutaneous BTX-A (5U/kg) application diminished pain on the ipsilateral, and on the contralateral side too. When injected into the proximal part of a distally cut sciatic nerve, BTX-A still reduced pain on the contralateral side. Colchicine, an axonal transport blocker, when injected into the ipsilateral sciatic nerve, prevented the effect of the peripheral BTX-A injection on both sides. Additionally, when BTX-A (1U/kg) was applied intrathecally in the lumbar cerebrospinal fluid, the bilateral hyperalgesia was also reduced. The results demonstrate the necessity of retrograde axonal transport and involvement of the central nervous system for the antinociceptive activity of BTX-A.
Placebo analgesia involves the endogenous opioid system, as administration of the opioid antagonist naloxone decreases placebo analgesia. To investigate the opioidergic mechanisms that underlie placebo analgesia, we combined naloxone administration with functional magnetic resonance imaging. Naloxone reduced both behavioral and neural placebo effects as well as placebo-induced responses in pain-modulatory cortical structures, such as the rostral anterior cingulate cortex (rACC). In a brainstem-specific analysis, we observed a similar naloxone modulation of placebo-induced responses in key structures of the descending pain control system, including the hypothalamus, the periaqueductal gray (PAG), and the rostral ventromedial medulla (RVM). Most importantly, naloxone abolished placebo-induced coupling between rACC and PAG, which predicted both neural and behavioral placebo effects as well as activation of the RVM. These findings show that opioidergic signaling in pain-modulating areas and the projections to downstream effectors of the descending pain control system are crucially important for placebo analgesia.
In addition to inhibition of acetylcholine release in the neuromuscular junction botulinum toxin type A (BoNT-A) also inhibits the release of mediators involved in pain perception. We have investigated the effect of two types of BoNT-A on mechanical hyperalgesia in the rat models of carrageenan-induced hyperalgesia and of paclitaxel-induced peripheral neuropathy. A subplantar (s.p.) injection of BoNT-A in the ipsilateral hindpaw 3 days before carrageenan administration reduced hypersensitivity. Dysport and Botox elicited comparable antihyperalgesic effects. Dysport up to 30 U/kg and Botox up to 20 U/kg did not impair the rat withdrawal nociceptive reflex or the locomotor performance as assessed by the rotarod test. Intraperitoneal administration of the skeletal muscle relaxant dantrolene produced, in contrast to BoNT-A, more motor impairment than analgesia. Paclitaxel treatment resulted in a peripheral neuropathy that affected the two hindpaws. Injection of 20 U/kg (s.p.) Dysport produced a significant antihyperalgesic effect in the injected paw of neuropathic animals 3 days after administration. Unexpectedly, a similar analgesic effect was observed in the contralateral paw. The same results were also observed when Botox was used instead of Dysport. In contrast, a contralateral administration of Dysport in the carrageenan test was ineffective. We conclude that BoNT-A elicits antinociceptive effects independent of the effects on muscular relaxation. Our results suggest that different mechanisms of action are responsible for the effect of BoNT-A in inflammatory and peripheral polyneuropathic rat models.
The disposition of naltrexone during acute and chronic administration of 100-mg oral dose was studied in 4 subjects. Following an acute dose the mean (X) peak naltrexone plasma level was 43.6 +/- 29.9 ng/ml at 1 hr and for the major biotransformation product, beta-naltrexol, was 87.2 +/- 25.0 ng/ml at 2 hr. Twenty-four hours after the dose the X levels of naltrexone and beta-naltrexol declined to 2.1 +/- 0.47 and 17.6 +/- 5.0 ng/ml, respectively. Following chronic administration and X peak plasma levels of naltrexone and beta-naltrexol rose to 46.4 +/- 18.5 and 158.4 +/- 89.9 ng/ml at 1 hr, but by 24 hr both compounds declined to levels of the same order as in the acute state at 24 hr. Plasma levels of naltrexone and beta-naltrexol measured 24 hr after the daily doses of naltrexone throughout the study indicated that steady-state equilibrium was rapidly attained and that there was no accumulation of naltrexone and beta naltrexol in the plasma after chronic treatment on 100 mg oral doses. Biexponential kinetics were observed for naltrexone and beta-naltrexol in the first 24 hr. The half-life of naltrexone and beta-naltrexol decreased slightly from the acute to thechronic study from 10.3 +/- 3.3 to 9.7 +/- 1.1 hr and from 12.7 +/- 2.6 to 11.4 +/- 2.0 hr. The plasma levels of naltrexone declined slowly from 24 through 72 hr from 2.4 to 1.7 ng/ml, with an apparent half-life of 96 hr. The renal clearance data indicate that naltrexone is partially reabsorbed while beta naltrexol is actively secreted by the kidney. During acute and chronic naltrexone administration the mean fecal excretion was 2.1% and 3.6% while urinary excretion was 38% and 70% of the dose in a 24-hr period. Opiate antagonism to 25 mg heroin challenges was nearly complete through 48 hr after naltrexone. At 72 hr the objective responses reappeared to a greater extent than the subjective ones. Correlation coefficient (r) between naltrexone plasma levels and opiate antagonism was 0.91 and between individual half-life of naltrexone and opiate antagonism it was 0.99.
The formalin test for nociception, which is predominantly used with rats and mice, involves moderate, continuous pain generated by injured tissue. In this way it differs from most traditional tests of nociception which rely upon brief stimuli of threshold intensity. In this article we describe the main features of the formalin test, including the characteristics of the stimulus and how changes in nociceptive behaviour may be measured and interpreted. The response to formalin shows an early and a late phase. The early phase seems to be caused predominantly by C-fibre activation due to the peripheral stimulus, while the late phase appears to be dependent on the combination of an inflammatory reaction in the peripheral tissue and functional changes in the dorsal horn of the spinal cord. These functional changes seem to be initiated by the C-fibre barrage during the early phase. In mice, the behavioural response in the late phase depends on the ambient temperature. We argue that the peripheral tissue temperature as well as other factors influencing the peripheral inflammation may affect the response, possibly confounding the results obtained with the test. Furthermore, we discuss the methods of recording the response and the value of observing more than one aspect of behaviour. Scoring of several behavioural variables provides a means of assessing motor or sensorimotor function as possible causes for changes in behaviour. In conclusion, the formalin test is a valuable addition to the battery of methods available to study nociception.
The formalin test in mice is a valid and reliable model of nociception and is sensitive for various classes of analgesic drugs. The noxious stimulus is an injection of dilute formalin (1% in saline) under the skin of the dorsal surface of the right hindpaw. The response is the amount of time the animals spend licking the injected paw. Two distinct periods of high licking activity can be identified, an early phase lasting the first 5 min and a late phase lasting from 20 to 30 min after the injection of formalin. In order to elucidate the involvement of inflammatory processes in the two phases, we tested different classes of drugs in the two phases independently. Morphine, codeine, nefopam, and orphenadrine, as examples of centrally acting analgesics, were antinociceptive in both phases. In contrast, the non-steroid anti-inflammatory drugs indomethacin and naproxen and the steroids dexamethasone and hydrocortisone inhibited only the late phase, while acetylsalicylic acid (ASA) and paracetamol were antinociceptive in both phases. The results demonstrate that the two phases in the formalin test may have different nociceptive mechanisms. It is suggested that the early phase is due to a direct effect on nociceptors and that prostaglandins do not play an important role during this phase. The late phase seems to be an inflammatory response with inflammatory pain that can be inhibited by anti-inflammatory drugs. ASA and paracetamol seem to have actions independent of their inhibition of prostaglandin synthesis and they also have effects on non-inflammatory pain.
Neurotransmitter release is potently blocked by a group of structurally related toxin proteins produced by Clostridium botulinum. Botulinum neurotoxin type B (BoNT/B) and tetanus toxin (TeTx) are zinc-dependent proteases that specifically cleave synaptobrevin (VAMP), a membrane protein of synaptic vesicles. Here we report that inhibition of transmitter release from synaptosomes caused by botulinum neurotoxin A (BoNT/A) is associated with the selective proteolysis of the synaptic protein SNAP-25. Furthermore, isolated or recombinant L chain of BoNT/A cleaves SNAP-25 in vitro. Cleavage occurred near the carboxyterminus and was sensitive to divalent cation chelators. In addition, a glutamate residue in the BoNT/A L chain, presumably required to stabilize a water molecule in the zinc-containing catalytic centre, was required for proteolytic activity. These findings demonstrate that BoNT/A acts as a zinc-dependent protease that selectively cleaves SNAP-25. Thus, a second component of the putative fusion complex mediating synaptic vesicle exocytosis is targeted by a clostridial neurotoxin.
Botulinum toxin is widely used for the treatment of focal movement disorders, where chemodenervation is used to decrease hyperactivity in selected muscles. Beside a focal paresis, widespread effects on neuromuscular synaptic function have been demonstrated. However, reactions of motoneurons after neuromuscular chemodenervation without gross morphological lesions are largely unknown. Peripheral axotomy, in contrast, leads to profound changes in the expression of several genes, including those encoding neurotransmitters, in motoneurons. We therefore examined the expression of neurotransmitter genes in rat motoneurons six days after intramuscular botulinum toxin application in the right gastrocnemius muscle. Similar doses of botulinum toxin as used in human where injected. A focal bilateral increase in expression of the choline acetyltransferase gene and a widespread bilateral increase of the beta-calcitonin-gene-related peptide and the enkephalin genes was measured in motoneurons after botulinum toxin injection. Cholecystokinin had a lower expression after botulinum toxin injections. Growth-associated protein 43, nitric oxide synthase, somatostatin and proopiomelanocortin messenger RNA were not found in motoneurons of both groups. Our results demonstrate that changes in the expression of neurotransmitter genes in motoneurons also occur after chemodenervation but with different patterns to those found after mechanical nerve lesioning. These changes reflect focal and widespread modulative events. The knowledge of these events should lead to a better understanding of the focal paralysis and of the more widespread effects found in human after intramuscular injection of botulinum toxin.
The effect of neuropeptide FF in the periaqueductal gray on pain behaviour was studied in rats with a chronic neuropathy induced by unilateral ligation of two spinal nerves. Neuropeptide FF produced in a non-monotonic fashion a significant attenuation of tactile allodynia. The antiallodynic effect was not significantly modulated by naloxone administered systemically or intracerebrally. The dose of neuropeptide FF producing a significant antiallodynic effect was not antinociceptive in a test of mechanical or thermal nociception. The thermal antinociceptive effect induced by morphine administered in the periaqueductal gray was significantly attenuated by neuropeptide FF, whereas that induced by systemically administered morphine was not. The interaction of neuropeptide FF with intracerebrally or systemically administered morphine in a test of tactile allodynia was not significant. The results indicate that neuropeptide FF in the periaqueductal gray may produce a selective attenuation of tactile allodynia in neuropathic rats. This antiallodynic effect is at least partly independent of naloxone-sensitive opioid receptors. Furthermore, neuropeptide FF in the periaqueductal gray attenuates antinociception induced by intracerebrally but not systemically administered morphine.
Botulinum toxin is used to induce transient graded paresis by chemodenervation in the treatment of focal hyperkinetic movement disorders. While the molecular events occurring in motoneurons after mechanical nerve lesioning leading to muscle paresis are well known, they have been investigated to a lesser extent after chemodenervation. We therefore examined the expression of enkephalin (ENK), acidic fibroblast growth factor (aFGF), neurotensin (NT), galanin (GAL), substance P (SP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) in rat spinal motoneurons after chemodenervation of the gastrocnemius. In order to precisely localize the motoneurons targeting the injection site, retrograde tracing was performed in additional rats by using Fluorogold injections. ENK expression was upregulated in the region corresponding to the Fluorogold positive motoneurons, but also on the contralateral side and in more distant parts of the spinal cord. The highest upregulation occurred 7 to 14 days after injections and decreased over a period of three months. At 8 days, aFGF was slightly downregulated in all regions studied, single motoneurons showed NT expression, while expression of GAL, SP, VIP, and NPY could be detected neither in controls nor in toxin-treated animals. These alterations in gene expression were strikingly different from those described after axotomy. Our present findings give additional demonstration of the considerable plasticity of the adult spinal cord after botulinum toxin treatment.
One of the most commonly used experimental animal models for neuropathic pain is the chronic constriction injury (CCI) where four loose ligatures are tied around the sciatic nerve. One disadvantage of this model is the introduction of foreign material into the wound, which causes a local inflammatory reaction. Thus the distinction between the neuropathic and the inflammatory component of pain is difficult in this model. In order to produce a pure nerve lesion, we performed a partial sciatic nerve transection (PST; a modification of the Seltzer model) in female Sprague-Dawley rats and compared behavior and nerve pathology. These rats developed thermal hyperalgesia and mechanical allodynia comparable to the CCI model. Recovery of these symptoms was found between days 40 and 60 after the nerve lesion. Some animals still showed symptoms on day 101, which was associated with a neuroma formation. The main pathological findings in the endoneurium in nerve segments distal to the lesion were edema, loss of myelinated fibers and increase in endoneurial cells, especially macrophages. In the epineurium the number of macrophages was strikingly increased after CCI compared with PST, indicating that the response of the immune system is different in a structural lesion with and without foreign material. In conclusion, PST is a pure nerve injury model without an epineurial inflammatory component due to foreign material and is therefore well suited for studying the role of local endoneurial processes in the development and maintenance of neuropathic pain. Also, the importance of regeneration in the termination of hyperalgesia can convincingly be shown in this model.
Botulinum toxin type A (BoNT-A) produced by the bacterium Clostridium botulinum is a potent inhibitor of acetylcholine release in the neuromuscular junction and has been used to treat many disorders related to excessive muscle contraction. However, BoNT-A has recently been used in pain therapy to treat myofascial pain, low back pain and various types of headaches, including migraine. The purpose of this study is to investigate the antinociceptive effect of BoNT-A and its underlying mechanism in the rat formalin inflammatory pain model. BoNT-A (3.5, 7, 15 and 30 U/kg) or vehicle was administered to the plantar surface of the right hindpaw of male Sprague-Dawley rats. BoNT-A dose-dependently (P<0.05) inhibited formalin-induced nociceptive behavior during phase 2 but not during phase 1 when administered 5 h to 12 days before formalin challenge. The onset of the antinociceptive effect started at 5 h after pre-treatment and this effect lasted for at least 12 days. BoNT-A (7 U/kg) also reduced edema. Consistent with the lack of effect in the formalin phase 1, BoNT-A, at 15 U/kg, had no effect on acute thermal nociception; no local muscle weakness was observed at this dose. Pre-treatment of rats with BoNT-A (3.5, 7 or 15 U/kg) all significantly reduced formalin-evoked glutamate (Glu) release. These results demonstrate that local peripheral injection of BoNT-A significantly reduces formalin-induced nociceptive behaviors with the absence of obvious muscle weakness. Such an antinociceptive effect of BoNT-A is associated with the inhibition of formalin-induced release of Glu (and/or neuropeptides) from primary afferent terminals.
We evaluated a putative inhibitory effect of intravesical botulinum toxin A (BTX-A) on afferent pathways in conditions of chronic bladder inflammation.
Female Sprague-Dawley rats were divided into 4 groups, namely group 1-saline treated, group 2-BTX-A treated, group 3-cyclophosphamide (CYP) treated and group 4-BTX-A and CYP treated. At the beginning of the treatment period all animals received intravesical protamine sulfate (1%), followed by intravesical BTX-A or saline. Subsequently CYP or saline was injected intraperitoneally every 3 days for 10 days. The rats then underwent cystometrogram evaluation prior to spinal cord harvest. Sections from the L6 and S1 spinal cord segments were examined for the total number of Fos immunoreactive cells.
Comparisons of the L6 and S1 sections showed a significant difference among groups (p <0.05). CYP treated animals had a significant increase in L6 and S1 (78% and 107%, respectively) c-fos expression compared with saline controls (p <0.001). Comparison of the CYP and BTX-A/CYP groups showed a significant decrease in L6 and S1 in c-fos expression (50% and 52%, respectively) in the BTX-A/CYP treated group (p <0.001). No significant difference was present between the saline and BTX-A alone groups. Cystometrogram studies revealed that the nonvoiding intercontractile interval increased by more than 10-fold in BTX-A/CYP treated animals compared with CYP treated rats (p <0.01).
In a CYP model of chronic bladder inflammation intravesical BTX-A significantly inhibits the afferent neural response without impairing efferent bladder function.
A peripheral application of botulinum toxin type A (7 U/kg) has significantly reduced thermal and mechanical hypersensitivity in rats with the partial sciatic nerve transection as a classical model of surgical neuropathy.
Botulinum toxin type A (BOTOX) has been used to treat pathological pain conditions although the mechanism is not entirely understood. Subcutaneous (s.c.) BOTOX also inhibits inflammatory pain in the rat formalin model, and the present study examined whether this could be due to a direct action on sensory neurons. BOTOX (3.5-30 U/kg) was injected s.c. into the subplantar surface of the rat hind paw followed 1-5 days later by 50 mL of 5% formalin. Using microdialysis, we found that BOTOX significantly inhibited formalin-induced glutamate release (peak inhibitions: 35%, 41%, and 45% with 3.5, 7, and 15 U/kg, respectively). BOTOX also dose dependently reduced the number of formalin-induced Fos-like immunoreactive cells in the dorsal horn of the spinal cord and significantly (15 and 30 U/kg) inhibited the excitation of wide dynamic range neurons of the dorsal horn in Phase II but not Phase I of the formalin response. These results indicate that s.c. BOTOX inhibits neurotransmitter release from primary sensory neurons in the rat formalin model. Through this mechanism, BOTOX inhibits peripheral sensitization in these models, which leads to an indirect reduction in central sensitization.
The endogenous opioid system is one of the most studied innate pain-relieving systems. This system consists of widely scattered neurons that produce three opioids: beta-endorphin, the met- and leu-enkephalins, and the dynorphins. These opioids act as neurotransmitters and neuromodulators at three major classes of receptors, termed mu, delta, and kappa, and produce analgesia. Like their endogenous counterparts, the opioid drugs, or opiates, act at these same receptors to produce both analgesia and undesirable side effects. This article examines some of the recent findings about the opioid system, including interactions with other neurotransmitters, the location and existence of receptor subtypes, and how this information drives the search for better analgesics. We also consider how an understanding of the opioid system affects clinical responses to opiate administration and what the future may hold for improved pain relief. The goal of this article is to assist clinicians to develop pharmacological interventions that better meet their patient's analgesic needs.
The protooncogene c-fos is rapidly activated after noxious stimuli to express the protein Fos in spinal dorsal horn neurons that are in the 'correct' locations for nociceptive information transfer. As such, therefore, mapping Fos expression in these neurons is at present the best global marker for efficiently locating populations of neurons in the awake animal that respond to nociceptive input. This allows, among other things, precise behavioral measurements to be correlated with Fos expression. Two arenas where mapping dorsal horn Fos expression has made a major impact are in the anatomy of nociceptive systems and as a useful assay for the analgesic properties of various therapeutic regimens. Also Fos expression is the only way to map populations of neurons that are responding to non-localized input such as withdrawal after addiction and vascular occlusion. Another insight is that it shows a clear activation of neurons in superficial 'pain-processing' laminae by innocuous stimuli after nerve lesions, a finding that presumably bears on the allodynia that often accompanies these lesions. It is to be understood, however, that the Fos localizations are not sufficient unto themselves, but the major function of these studies is to efficiently locate populations of cells in nociceptive pathways so that powerful anatomic and physiologic techniques can be brought to bear efficiently. Thus, the purpose of this review is to summarize the studies whose numbers are geometrically expanding that deal with Fos in the dorsal horn and the conclusions therefrom.
Botulinum toxin type A (BoNT-A) has been used to treat many disorders related to excessive muscle contraction, but there are few studies evaluating its effects on neuropathic pain. The aim of this study was to evaluate the analgesic effects of BoNT-A in a rat model of neuropathic pain.
Male Sprague-Dawley rats were prepared by ligating the left L5 and L6 spinal nerves to produce neuropathic pain. Seventy neuropathic rats were randomly assigned into seven groups. Either normal saline or BoNT-A (10, 20, 30 and 40 U.kg(-1)) was administered to the plantar surface of the affected left hind paw, and BoNT-A (30 and 40 U.kg(-1)) was administered into the unaffected right paw in order to determine the drug-induced systemic effect. Mechanical and cold allodynia were observed at pre-administration, one, three, five, seven and 15 days after drug administration, and were quantified by measuring withdrawal frequencies to stimuli with von Frey filament and 100% acetone, respectively. Rotarod performance was measured to detect drug-induced adverse motor effects.
The mean minimum withdrawal frequencies to mechanical and cold stimuli were 77 +/- 11 and 90 +/- 4.5%, 46 +/- 5 and 66 +/- 7%, 33 +/- 7 and 62 +/- 7%, 12 +/- 2.9 and 54 +/- 7.3% with 10, 20, 30 and 40 U.kg(-1) BoNT-A respectively (P < 0.05). Doses of 30 and 40 U.kg(-1) BoNT-A resulted in reduced rotarod performance time.
We conclude that peripherally administered BoNT-A reduces mechanical and cold allodynia in a rat model of neuropathic pain.
In southern Africa there are 130 species of scorpions and only a few species' venom have been investigated to date. This review gives an overview of the research done on the venom of southern African scorpions and the toxins and peptides identified up to date. It also aims to highlight the enormous potential that lies in this field of research. Southern African scorpion toxins include four long-chain Na(+)-channel toxins, four short-chain alpha-K(+)-channel toxins (alpha-KTx), three Ca(2+)-channel toxins and also an insect-selective peptide active on K(+) and Cl(-) channels. Three antimicrobial peptides have also been isolated and characterized. All of these peptides are diverse not only in function and target but also in the species they are isolated from.
A method for measurement of analgesic activity on inflamed tissue Botulinum toxin therapy for osteoarticular pain: an evidence-based review
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Fos, nociception and the dorsal horn Peripheral mu-, kappa-and delta-opioid re-ceptors mediate the hypoalgesic effect of celecoxib in arat model of thermal hyperalgesia
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The endogenous opioid system and clinical pain management Enkephalin and aFGF are differentially regulated in rat spinal motoneurons after chemodenervation with botulinum toxin
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