Mirror-Image Pain Update: Complex Interactions Between Central and Peripheral Mechanisms.

The appearance of contralateral effects after unilateral injury has been shown in various experimental pain models, as well as in clinics. They consist of a diversity of phenomena in contralateral peripheral nerves, sensory ganglia, or spinal cord: from structural changes and altered gene or protein expression to functional consequences such as the development of mirror-image pain (MP). Although MP is a well-documented phenomenon, the exact molecular mechanism underlying the induction and maintenance of mirror-like spread of pain is still an unresolved challenge. MP has generally been explained by central sensitization mechanisms leading to facilitation of pain impulse transfer through neural connections between the two sides of the central nervous system. On the contrary, the peripheral nervous system (PNS) was usually regarded unlikely to evoke such a symmetrical phenomenon. However, recent findings provided evidence that events in the PNS could play a significant role in MP induction. This manuscript provides an updated and comprehensive synthesis of the MP phenomenon and summarizes the available data on the mechanisms. A more detailed focus is placed on reported evidence for peripheral mechanisms behind the MP phenomenon, which were not reviewed up to now.

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

OBJECTIVE: Botulinum toxin type A (BoNT-A) provides lasting pain relief in patients with craniofacial pain conditions but the mechanisms of its antinociceptive activity remain unclear. Preclinical research revealed toxin axonal transport to the central afferent terminals, but it is unknown if its central effects involve transsynaptic traffic to the higher-order synapses. To answer this, we examined the contribution of central BoNT-A transcytosis to its action in experimental orofacial pain. MATERIAL AND METHODS: Male Wistar rats, 3-4 months old, were injected with BoNT-A (7 U/kg) unilaterally into the vibrissal pad. To investigate the possible contribution of toxin's transcytosis, BoNT-A-neutralizing antiserum (5 IU) was applied intracisternally. Antinocicepive BoNT-A action was assessed by duration of nocifensive behaviors and c-Fos activation in the trigeminal nucleus caudalis (TNC) following bilateral or unilateral formalin (2.5%) application into the vibrissal pad. Additionally, cleaved synaptosomal-associated protein of 25 kDa (cl-SNAP-25) immunoreactivity was analyzed in the bilateral TNC. RESULTS: Unilaterally injected BoNT-A reduced the nocifensive behaviors and bilateral c-Fos activation induced by formalin, which was accompanied by the toxin's enzymatic activity on both sides of the TNC. BoNT-A antinociceptive or enzymatic activities were prevented by the specific neutralizing antitoxin. BoNT-A contralateral action occurred independently from ipsilateral side nociception or contralateral trigeminal nerve-mediated axonal traffic. CONCLUSION: Herein, we demonstrate that antinociceptive action of pericranially administered BoNT-A involves transsynaptic transport to second order synapses and contralateral trigeminal nociceptive nuclei. These results reveal more complex central toxin activity, necessary to explain its clinical effectiveness in the trigeminal region-related pain states.

The safety of botulinum neurotoxin type A's intraarticular application in experimental animals.

In vivo studies of botulinum neurotoxin type A (BoNT-A) enabled characterization of its activity in the nociceptive sensory system separate from its preferred action in motor and autonomic nerve terminals. However, in the recent rodent studies of arthritic pain which employed high intra-articular (i.a.) doses (expressed as a total number of units (U) per animal or U/kg), possible systemic effects have not been conclusively excluded. Herein we assessed the effect of two pharmaceutical preparations, abobotulinumtoxinA (aboBoNT-A, 10, 20, and 40 U/kg corresponding to 0.05, 0.11, and 0.22 ng/kg neurotoxin) and onabotulinumtoxinA (onaBoNT-A, 10 and 20 U/kg corresponding to 0.09 and 0.18 ng/kg, respectively) injected into the rat knee, on safety-relevant readouts: digit abduction, motor performance and weight gain during 14 days post-treatment. The i. a. toxin produced dose-dependent impairment of the toe spreading reflex and rotarod performance, which was moderate and transient after 10 U/kg onaBoNT-A and ≤20 U/kg aboBoNT-A doses, and severe and long-lasting (examined up to 14 days) after ≥20 U/kg of onaBoNT-A and 40 U/kg aboBoNT-A. In addition, lower toxin doses prevented the normal weight gain compared to controls, while higher doses induced marked weight loss (≥20 U/kg of onaBoNT-A and 40 U/kg aboBoNT-A). Commonly employed BoNT-A formulations, depending on the doses, cause local relaxation of the surrounding muscles and systemic adverse effects in rats. Thus, to evade possible toxin unwanted local or systemic spread, careful dosing and motor testing should be mandatory in preclinical behavioral studies, irrespective of the sites and doses of toxin application.

What have we learned about antinociceptive effect of botulinum toxin type A from mirror-image pain models?

Mirror pain represents pain with complex pathophysiological background experienced at both sides of the body, usually after unilateral injury. Although observed almost 10 years ago, the phenomenon of bilateral antinociceptive effect of botulinum toxin type A (BoNT/A) following its unilateral administration in experimental mirror-image pain (MP) models remains challenging and intriguing task to explain. Data generated so far using MP models and mechanisms behind this unique feature of BoNT/A might influence the overall understanding of its mechanism of antinociceptive action. Here we review the effects contributing to BoNT/A's bilateral antinociceptive action observed in experimental MP models.

Resolving Issues About Efficacy and Safety of Low-Dose Codeine in Combination Analgesic Drugs: A Systematic Review.

INTRODUCTION: The objective of this systematic review is to reflect on assumptions in relation to codeine use in combination with other analgesics. METHODS: MEDLINE was searched according to the predetermined keywords and criteria. Only English language studies were taken into consideration and the outcome data of the final studies were extracted by two reviewers independently from each other and were checked by the third reviewer. Additionally, the available codeine-related Individual Case Safety Reports (ICSRs) retrieved from EudraVigilance were reviewed. RESULTS: Sixteen placebo-controlled studies that involved 3378 subjects suffering from acute pain were analyzed for the efficacy of low-dose codeine (≤ 30 mg) combination products. Twelve of them found low-dose codeine combinations more efficient in relieving pain than the assigned comparator. According to 20 randomized clinical trials which included at least one dose of codeine (from 30 to 240 mg daily), the vast majority of reported side-effects were mild or moderate in severity. A total of 20 ICSRs for dependence were identified in the EudraVigilance database with codeine as a suspect drug for the 10-year time period for the European region. CONCLUSIONS: Low-dose codeine combinations are effective after a single application in treating acute pain. Codeine in doses ≤ 30 mg and higher was considered safe since only mild to moderate side-effects were observed. There is no indication in the available sources which clearly links low doses of codeine to substance use disorder in non-dependent subjects.

Pharmacogenomics at the center of precision medicine: challenges and perspective in an era of Big Data.

Pharmacogenomics (PGx) is one of the core elements of personalized medicine. PGx information reduces the likelihood of adverse drug reactions and optimizes therapeutic efficacy. St Catherine Specialty Hospital in Zagreb/Zabok, Croatia has implemented a personalized patient approach using the RightMed® Comprehensive PGx panel of 25 pharmacogenes plus Facor V Leiden, Factor II and MTHFR genes, which is interpreted by a special counseling team to offer the best quality of care. With the advent of significant technological advances comes another challenge: how can we harness the data to inform clinically actionable measures and how can we use it to develop better predictive risk models? We propose to apply the principles artificial intelligence to develop a medication optimization platform to prevent, manage and treat different diseases.

Challenges in anesthesia personalization: resolving the pharmacogenomic puzzle.

Clinicians are witnessing differences in the doses required for induction and maintenance of anesthesia, as well as prolonged recovery in some patients. Predictable factors like patient characteristics, factors related to the procedure, pharmacological characteristics of anesthetics and adjunctive drugs, might explain some of the observed differences. However, the role of various polymorphisms of genes encoding for drugs' molecular targets, transporters and metabolic enzymes can have a significant impact on anesthesia outcome, too. In the present paper, we critically discuss pharmacological characteristics of the most common drugs used in anesthesia, with a focus on the possible genetic background of unpredictable diversities in anesthesia outcomes.

Mechanisms of Botulinum Toxin Type A Action on Pain.

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

Continuing war on pain: a personalized approach to the therapy with nonsteroidal anti-inflammatory drugs and opioids.

Successful pain management requires the delivery of analgesia with minimal risk of adverse drug reactions. Nonsteroidal anti-inflammatory drugs and opioids remain the mainstay of treatment for the majority of patients. Unfortunately, almost 50% of all patients experience inadequate pain relief and serious side effects. Allelic variants in genes coding for target proteins, transporters and enzymes, which govern analgesic drugs action and their fate in the organism, might explain inter-individual variability in pain severity and in drug-induced pain relief and toxicities. Additionally, it seems that epigenetic changes contribute to the highly variable response to pain treatment. Therefore, pharmacogenomic testing might be a valuable tool for personalization of pain treatment, with a multidisciplinary team approach involved.

Antinociceptive effect of botulinum toxin type A on experimental abdominal pain.

Visceral pain, especially in the abdominal region, represents one of the most common types of pain. Its chronic form is usually very hard to treat by conventional analgesic agents and adjuvants. We investigated the antinociceptive effect of botulinum toxin type A (BTX-A) in male Wistar rats in two models of visceral pain: peritonitis induced by intraperitoneal injection of 1% acetic acid and colitis induced by intracolonic instillation of 0.1% capsaicin. Pain was measured as the number of abdominal writhes. Additionally, referred mechanical sensitivity in the ventral abdominal area was evaluated by von Frey test and the extent of spinal c-Fos expression was immunohistochemically examined. BTX-A significantly reduced the number of abdominal writhes in both models of visceral pain after intrathecal application in a dose of 2 U/kg. In the experimental colitis model, BTX-A (2 U/kg) reduced both referred mechanical allodynia and c-Fos expression in the dorsal horn of the spinal cord (S2/S3 segments). In contrast to intrathecal administration, BTX-A (2 U/kg) administered into the cisterna magna had no effect on pain suggesting that the primary site of its action is a spinal cord.

Central action of peripherally applied botulinum toxin type A on pain and dural protein extravasation in rat model of trigeminal neuropathy.

BACKGROUND: 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. METHODOLOGY/PRINCIPAL FINDINGS: 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. CONCLUSIONS/SIGNIFICANCE: 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.

Botulinum toxin type A reduces pain supersensitivity in experimental diabetic neuropathy: bilateral effect after unilateral injection.

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.

Lasting reduction of postsurgical hyperalgesia after single injection of botulinum toxin type A in rat.

A single injection of low doses of botulinum toxin type A (3.5 U/kg) completely abolished secondary mechanical hyperalgesia throughout its duration in a model of post surgical pain after gastrocnemius incision in rat.

Central origin of the antinociceptive action of botulinum toxin type A.

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.

Lack of anti-inflammatory effect of botulinum toxin type A in experimental models of inflammation.

Botulinum toxin type A (BTX-A) has a long-lasting antinociceptive activity and less clear effect on inflammation. It was proposed that these two effects share the same mechanism--the inhibition of neurotransmitter exocytosis from peripheral nerve endings. However, till now possible anti-inflammatory action of BTX-A did not evoke much attention. In the present paper, we investigate possible anti-inflammatory action of the toxin in carrageenan and capsaicin models of inflammation in rats. BTX-A (5 and 10 U/kg) was injected into the plantar surface of the rat right hind-paw pad 5 days before the injection of the carrageenan (1%) or capsaicin (0.1%) at the same site. Carrageenan-induced paw oedema and capsaicin-induced protein extravasation were measured. Control, inflamed and BTX-A pretreated inflamed paws were photographed and histopathological analysis (haematoxylin & eosin) was performed. Pretreatment with BTX-A had no effect on the size of carrageenan-induced paw oedema, measured as paw volume and weight or capsaicin-induced plasma extravasations, measured by Evans blue as a marker of protein leakage. Neither macroscopic nor microscopic analysis showed a significant difference between BTX-A pretreated and control inflamed tissue. Results show dissociation between the effect of BTX-A on pain and inflammation thus questioning the validity of the suggested assumption about the common peripheral mechanism of action.

Reduced brain antioxidant capacity in rat models of betacytotoxic-induced experimental sporadic Alzheimer's disease and diabetes mellitus.

It is believed that oxidative stress (OS) plays a central role in the pathogenesis of metabolic diseases like diabetes mellitus (DM) and its complications (like peripheral neuropathy) as well as in neurodegenerative disorders like sporadic Alzheimer's disease (sAD). Representative experimental models of these diseases are streptozotocin (STZ)-induced diabetic rats and STZ-intracerebroventricularly (STZ-icv) treated rats, in which antioxidant capacity (AC) against peroxyl (ORAC(-ROO) (*)) and hydroxyl (ORAC(-OH) (*)) free radicals (FR) was measured in three different brain regions: the hippocampus (HPC), the cerebellum (CB), and the brain stem (BS) by means of oxygen radical absorbance capacity (ORAC) assay. In the brain of both STZ-induced diabetic and STZ-icv treated rats decreased AC has been found demonstrating regionally specific distribution. In the diabetic rats these abnormalities were not associated with the development of peripheral diabetic neuropathy (PDN). Also, these abnormalities were not prevented by the intracerebroventricularly (icv) pretreatment of glucose transport inhibitor 5-thio-D: -glucose (TG) in the STZ-icv treated rats, suggesting different mechanism of STZ-induced central effects from those at the periphery. Similarities of the OS alterations in the brain of STZ-icv rats and humans with sAD could be useful in the search for the new drugs in the treatment of sAD that have antioxidant activity. In the STZ-induced diabetic animals the existence of PDN was tested by the paw pressure test, 3 weeks following the diabetes induction. Mechanical nociceptive thresholds were measured three times at 10-min intervals by applying increased pressure to the hind paw until the paw-withdrawal or overt struggling was elicited. Only those diabetic animals which demonstrated decreased withdrawal threshold values in comparison with the control non-diabetic animals (C) were considered to have developed the PDN.

[Botulinum toxin type A and cholinergic system]. / Botulinum toksin tipa A i kolinergicni sustav.

Anaerobic bacterium Clostridium botulinum produces seven different serotypes of botulinum neurotoxins (A-G), which specifically act at the peripheral cholinergic nerve terminals blocking the release of acethylcholine. Primary site of action of botulinum toxin type A (BT-A) is neuromuscular end plate where it specifically cleaves SNAP-25, one of the proteins necessary for neuroegzocytosis. The consequence is long-lasting muscle paralysis. Although BT-A is one of the most potent toxins in nature, over the last 20 years, intramuscular injections of nanogram quantities of BT-A have been used to treat various conditions characterized by increased muscle contraction, like dystonias, spasticity related to cerebral palsy etc but also for autonomic nervous system disorders, like hyperhydrosis. Long duration of action (several months) after peripheral application is the most prominent feature of the toxin's action. Although the acute mechanism of action on neuromuscular junction is largely investigated, there are still some unknowns related to: the passage of BT-A through epithelial barriers, specific recognition of peripheral cholinergic neurons. The mechanism of long duration of action, which is the base of therapeutic use of BT-A, is poorly understood.

Influence of ethanol on the myorelaxant effect of diazepam in rats.

Interaction of ethanol with benzodiazepines can lead to enhanced therapeutic anxyolytic, sedative and hypnotic effects but can also augment unwanted effects such as drowsiness, confusion, amnesia and impaired coordination. In this study we investigated the interaction between ethanol and diazepam and its influence on muscle strength in rats using the grip-strength meter. Three doses of ethanol (0.4, 0.6 and 0.8 g kg(-1) of body mass) and diazepam (0.75, 1.5 and 7.5 mg kg(-1) b.m.) were used in experiments. Single substances and their combinations were tested. The myorelaxant effect of ethanol, measured as grip force (expressed in grams), was dose-dependent. The lowest dose (0.4 g kg(-1) b.m.) failed to affect muscle strength while the strongest effect was observed with the highest dose of ethanol (0.8 g kg(-1) b.m.) and it lasted for 75 min. Diazepam dose-dependently reduced muscle strength too. However, when ethanol was combined with diazepam (1.5 mg kg(-1) b.m.), more enhanced muscle relaxation occurred than by either drug alone. Namely, two lower doses of ethanol (0.4 and 0.6 g kg(-1) b.m) enhanced the myorelaxant effect of diazepam by additional 26 and 46%, respectively, when measured after 15 min. The most pronounced myorelaxation was recorded when the highest dose of ethanol (0.8 g kg(-1) b.m.) was combined with diazepam: from complete muscle relaxation observed after 15 min, it gradually decreased to 91% at the 45th min and to 24% at the 105th min after the beginning of the treatment. The results of this preclinical investigation showed that ethanol enhanced the muscle relaxant effect of diazepam in rats. This enhancement as well as duration of the effect was dependent on the applied dose of ethanol.

Antinociceptive effect of botulinum toxin type a in rat model of carrageenan and capsaicin induced pain.

AIM: To test antinociceptive properties of botulinum toxin type A (BTX-A) in rats with carrageenan- and capsaicin-induced pain and inflammation. METHODS: 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. RESULTS: 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. CONCLUSION: The study demonstrated the efficacy of peripherally applied BTX-A pretreatment on the pain component of inflammatory process in experimental animals.

The antidepressant activity of Hypericum perforatum L. measured by two experimental methods on mice.

The pharmacological approach to the treatment of depression includes a long-term employment of antidepressants, either in the form of monotherapy or as a combination of several antidepressants with various mechanisms of action. Hypericum perforatum L. (St. John's wort) is the only natural antidepressant. Several constituents of the extract, such as hypericin and hyperforin, seem to be important for this effect. H. perforatum is considered to be an effective alternative to other therapeutic agents in the treatment of mild to moderate depression. The paper describes the investigation of the antidepressant effect of H. perforatum (doses 7, 35 and 70 mg kg(-1) b. m.) on mice using the forced-swimming and tail-suspension methods. As an indicator of the antidepressant effect, it was shown that the immobility time of animals in the forced-swimming and tail-suspension experiments was shorter, i.e. the activity of the animals was higher. With single doses of extract suspension increasing from 7 over 35 to 70 mg kg(-1) the antidepressant effect increased in proportion by 10.1%, 25.8% and 38.6% in the swimming method, and by 12.7%, 16.5% and 24.5% in the tail-suspension method compared to controls. H. perforatum extract displays dose-dependent antidepressant effect at a dose as low as 7 mg kg(-1). Both models have proved to be equally valuable for demonstration of substances with a potential antidepressant effect.