Botulinum toxin type A-induced changes in the chemical coding of dorsal root ganglion neurons supplying the porcine urinary bladder

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

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

Therapeutic Applications of Botulinum Neurotoxins in Veterinary Medicine

Botulinum neurotoxins (BoNTs) are emerging as multipurpose therapeutic compounds for the treatment of several different syndromes involving peripheral and central nervous systems, and muscular and musculoskeletal disorders both in human and veterinary medicine. Therefore, the study of BoNTs is rapidly developing and identifying newly produced BoNT variants. Efforts should be made to clarify the biological and pharmacological characteristics of these novel BoNTs as well as the natural ones. The high potential of BoNTs as a therapeutic compound for medical syndromes lies in its ability to reach a specific cell type while bypassing other cells, thus having mild or no side effects. In this paper the recent developments in BoNTs are reviewed with the aim of analyzing the current knowledge on BoNTs' biological mechanisms of action, immunogenicity, formulations, and therapeutic applications in the veterinary field, highlighting advantages and drawbacks and identifying the gaps to be filled in order to address research priorities.

Effect of Bladder Injection of OnabotulinumtoxinA on the Central Expression of Genes Associated with the Control of the Lower Urinary Tract: A Study in Normal Rats

To investigate a possible central mechanism of action of Botulinum toxin A (BoNT/A) following injection in the bladder, complementary to the acknowledged peripheral bladder effect, we studied changes in the expression of neuropeptides and receptors involved in lower urinary tract function in the spinal cord (SC) and dorsal root ganglia (DRG) of normal rats following BoNT/A bladder injection. Thirty-six Sprague-Dawley rats, divided into three groups of n = 12, received bladder injections of 2U or 5U OnabotulinumtoxinA (BOTOX^®), or saline. Six animals from each group were sacrificed on days 7 and 14. Expression of Tachykinin 1 (Tac1), capsaicin receptor (TRPV1), neuropeptide Y (NPY), proenkephalin (PENK) and muscarinic receptors M1, M2, M3, was evaluated in the bladder, L6-S1 DRG, and SC segments using real-time PCR and Western blotting. Real-time PCR revealed increased expression of NPY in all tissues except for SC, and increased TRPV1 and PENK expression in DRG and SC, whereas expression of Tac1, M1 and M2 was decreased. Less significant changes were noted in protein levels. These findings suggest that bladder injections of OnabotulinumtoxinA may be followed by changes in the expression of sensory, sympathetic and cholinergic bladder function regulators at the DRG/SC level.

BoNT/A in the Urinary Bladder-More to the Story than Silencing of Cholinergic Nerves

Botulinum neurotoxin (BoNT/A) is an FDA and NICE approved second-line treatment for overactive bladder (OAB) in patients either not responsive or intolerant to anti-cholinergic drugs. BoNT/A acts to weaken muscle contraction by blocking release of the neurotransmitter acetyl choline (ACh) at neuromuscular junctions. However, this biological activity does not easily explain all the observed effects in clinical and non-clinical studies. There are also conflicting reports of expression of the BoNT/A protein receptor, SV2, and intracellular target protein, SNAP-25, in the urothelium and bladder. This review presents the current evidence of BoNT/A’s effect on bladder sensation, potential mechanisms by which it might exert these effects and discusses recent advances in understanding the action of BoNT in bladder tissue.

The Influence of an Adrenergic Antagonist Guanethidine (GUA) on the Distribution Pattern and Chemical Coding of Dorsal Root Ganglia (DRG) Neurons Supplying the Porcine Urinary Bladder

Although guanethidine (GUA) was used in the past as a drug to suppress hyperactivity of the sympathetic nerve fibers, there are no available data concerning the possible action of this substance on the sensory component of the peripheral nervous system supplying the urinary bladder. Thus, the present study was aimed at disclosing the influence of intravesically instilled GUA on the distribution, relative frequency, and chemical coding of dorsal root ganglion neurons associated with the porcine urinary bladder. The investigated sensory neurons were visualized with a retrograde tracing method using Fast Blue (FB), while their chemical profile was disclosed with single-labeling immunohistochemistry using antibodies against substance P (SP), calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase activating polypeptide (PACAP), galanin (GAL), neuronal nitric oxide synthase (nNOS), somatostatin (SOM), and calbindin (CB). After GUA treatment, a slight decrease in the number of FB⁺ neurons containing SP was observed when compared with untreated animals (34.6 ± 6.5% vs. 45.6 ± 1.3%), while the number of retrogradely traced cells immunolabeled for GAL, nNOS, and CB distinctly increased (12.3 ± 1.0% vs. 7.4 ± 0.6%, 11.9 ± 0.6% vs. 5.4 ± 0.5% and 8.6 ± 0.5% vs. 2.7 ± 0.4%, respectively). However, administration of GUA did not change the number of FB⁺ neurons containing CGRP, PACAP, or SOM. The present study provides evidence that GUA significantly modifies the sensory innervation of the porcine urinary bladder wall and thus may be considered a potential tool for studying the plasticity of this subdivision of the bladder innervation.

Somatostatin immunoreactivity within the urinary bladder nerve fibers and paracervical ganglion urinary bladder projecting neurons in the female pig

The study was designed to examine the distribution and chemical coding of somatostatin-immunoreactive (SOM-IR) nerve fibers supplying the urinary bladder wall and to establish the distribution and immunohistochemical characteristics of the subpopulation of paracervical ganglion (PCG) SOM-IR neurons projecting to this organ in female pigs. The PCG-urinary bladder projecting neurons (PCG-UBPN) were visualized with retrograde neuronal tracer Fast Blue (FB). Double-labeling immunohistochemistry performed on cryostat sections from the urinary bladder wall revealed that the greatest density of SOM-IR nerve fibers was found in the muscle layer and around blood vessels, a moderate number of these nerve terminals supplied the submucosa and only single SOM-IR axons were encountered beneath the urothelium. In all the investigated sections the vast majority of SOM-IR nerve fibers were immunopositive to vesicular acetylcholine transporter (VAChT) and many SOM-IR axons contained immunoreactivity to neuropeptide Y (NPY). Approximately 65 % of FB-positive (FB+) PCG-UBPN were immunoreactive to SOM. Moreover, PCG FB+/SOM + nerve cells were simultaneously immunoreactive to choline acetyltransferase (ChAT; 64.6 ± 0.6 %), NPY (59.7 ± 1.2 %), neuronal nitric oxide synthase (nNOS; 46.1 ± 0.7 %), vasoactive intestinal polypeptide (VIP; 29.9 ± 2.2 %), Leu⁵-enkephalin (L-ENK; 19.5 ± 6.3 %), dopamine β-hydroxylase (DβH; 14.9 ± 1.9 %) or pituitary adenylate cyclase-activating polypeptide (PACAP; 14.8 ± 2.4 %). The present study reveals the extensive expression of SOM in both the nerve fibres supplying the porcine urinary bladder wall and the PCG neurons projecting to this organ, indicating an important regulatory role of SOM in the control of the urinary bladder function.

The Influence of an Adrenergic Antagonist Guanethidine on the Distribution Pattern and Chemical Coding of Caudal Mesenteric Ganglion Perikarya and Their Axons Supplying the Porcine Bladder

This study was aimed at disclosing the influence of intravesically instilled guanethidine (GUA) on the distribution, relative frequency and chemical coding of both the urinary bladder intramural sympathetic nerve fibers and their parent cell bodies in the caudal mesenteric ganglion (CaMG) in juvenile female pigs. GUA instillation led to a profound decrease in the number of perivascular nerve terminals. Furthermore, the chemical profile of the perivascular innervation within the treated bladder also distinctly changed, as most of axons became somatostatin-immunoreactive (SOM-IR), while in the control animals they were found to be neuropeptide Y (NPY)-positive. Intravesical treatment with GUA led not only to a significant decrease in the number of bladder-projecting tyrosine hydroxylase (TH) CaMG somata (94.3 ± 1.8% vs. 73.3 ± 1.4%; control vs. GUA-treated pigs), but simultaneously resulted in the rearrangement of their co-transmitters repertoire, causing a distinct decrease in the number of TH⁺/NPY⁺ (89.6 ± 0.7% vs. 27.8 ± 0.9%) cell bodies and an increase in the number of SOM-(3.6 ± 0.4% vs. 68.7 ± 1.9%), calbindin-(CB; 2.06 ± 0.2% vs. 9.1 ± 1.2%) or galanin-containing (GAL; 1.6 ± 0.3% vs. 28.2 ± 1.3%) somata. The present study provides evidence that GUA significantly modifies the sympathetic innervation of the porcine urinary bladder wall, and thus may be considered a potential tool for studying the plasticity of this subdivision of the bladder innervation.

Distribution and chemical coding of phoenixin-immunoreactive nerve structures in the spinal cord of the pig

Phoenixin (PNX) is a newly described peptide found in both neural and non-neural tissues. Until now, no attempts have been made to investigate the expression of PNX in the nervous system of animals other than laboratory rodents, in which an enzyme immunoassay revealed the highest quantity of the substance in the spinal cord. Since the domestic pig, due to its anatomical and histological resemblance to humans, is often used as an animal model in biomedical investigations, the present study was designed to examine PNX-immunoreactivity in the spinal cords of female pigs (n=5). The spinal cords were dissected and divided into the cervical, thoracic, lumbar, sacral and coccygeal segments, which were sectioned transversally into 10-μm-thick serial sections. The sections from each spinal cord segment were processed for double-labelling immunohistochemistry using antibodies against PNX in a mixture with those against calcitonin gene-related peptide (CGRP), substance P (SP) or choline acetyltransferase (CHAT). The PNX-immunoreactivity had a similar distribution in the grey matter of all the spinal cord sections examined and was mainly observed in varicose nerve fibres (NF) that formed a dense plexus in laminae I and II of the dorsal horn. Nearly all of the PNX-immunoreactive NF stained also for CGRP or SP and, interestingly, many of them were CHAT-positive. The present study has provided for the first time the detailed information on the arrangement and chemical features of nerve structures expressing PNX-immunoreactivity in the spinal cord of a large mammal. The exact function of PNX in the spinal cord is not known yet. However, the distribution pattern and immunohistochemical characteristics of PNX-IR NF clearly suggest that this peptite most likely plays a role in spinal noxious signalling.

Botulinum toxin A for refractory OAB and idiopathic urinary retention: Can phenotyping improve outcome for patients: ICI-RS 2019?

AIMS

Botulinum toxin A (BTX-A) is a well-established treatment for refractory idiopathic overactive bladder (OAB). It has also been used with short-term success in treating idiopathic urinary retention. However, efficacy and complication rates are variable and predicting those likely to benefit most from treatment would enable personalization of therapy and optimization of outcomes. At the International Consultation on Incontinence-Research Society (ICI-RS) meeting in 2019 a Think Tank addressed the question of how we can improve the way we phenotype patients undergoing BTX-A treatment.

METHODS

The Think Tank conducted a literature review and expert consensus meeting focussing on how advances in basic science research of the mechanism of action of BTX-A, as well as assessment of psychological comorbidity, can be translated into clinical practice to improve patient selection for therapy.

RESULTS

Idiopathic OAB and idiopathic urinary retention are heterogenous conditions encompassing several phenotypes with multiple potential pathophysiological mechanisms. Animal models have demonstrated a central nervous system mechanism of action of intravesically injected BTX-A and this has been confirmed in human functional MRI studies, but whether this tool can be used to predict outcome from treatment remains to be determined. Phenotyping based on psychological comorbidity using validated screening tools should be studied as a way to potentially optimize patient selection for therapy.

CONCLUSIONS

Advances in basic science research into the mechanism of action of BTX-A have improved our understanding of the pathophysiology of OAB and may lead to novel ways to phenotype patients. Psychological assessment is another way in which phenotyping may be improved. Areas for further research are proposed.

A study on preganglionic connections and possible viscerofugal projections from urinary bladder intramural ganglia to the caudal mesenteric ganglion in the pig

The present study was designed to (1) ascertain the distribution and immunohistochemical characteristics of sympathetic preganglionic neurons supplying the caudal mesenteric ganglion (CaMG) and (2) verify the existence of viscerofugal projections from the urinary bladder trigone intramural ganglia (UBT-IG) to the CaMG in female pigs (n = 6). Combined retrograde tracing and immunofluorescence methods were used. Injections of the neuronal tracer Fast Blue (FB) into the right CaMG revealed no retrogradely labelled (FB-positive; FB⁺ ) nerve cells in the intramural ganglia; however, many FB⁺ neurons were found in the spinal cord sympathetic nuclei. Double-labelling immunohistochemistry revealed that nearly all (99.4 ± 0.6%) retrogradely labelled neurons were cholinergic (choline acetyltransferase-positive; ChAT⁺ ) in nature. Many FB⁺ /ChAT⁺ perikarya stained positive for vesicular acetylcholine transporter (63.11 ± 5.34%), neuronal nitric oxide synthase (53.48 ± 9.62%) or cocaine- and amphetamine-regulated transcript peptide (41.13 ± 4.77%). A small number of the retrogradely labelled cells revealed immunoreactivity for calcitonin gene-related peptide (7.60 ± 1.34%) or pituitary adenylate cyclase-activating polypeptide (4.57 ± 1.43%). The present study provides the first detailed information on the arrangement and chemical features of preganglionic neurons projecting to the porcine CaMG and, importantly, strong evidence suggesting the absence of viscerofugal projections from the UBT-IG.

Therapeutic use of botulinum toxin in pain treatment

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.

The efficacy of botulinum toxin A and sacral neuromodulation in the management of interstitial cystitis (IC)/bladder pain syndrome (BPS), what do we know? ICI-RS 2017 think thank, Bristol

AIMS

This manuscript aims to address the evidence availale in the literature on the efficacy of Botulinum Toxin A (BoNT-A) and sacral neuromodulation (SNM) in patients suffering from Interstitial Cystitis (IC)/BPS and propose further research to identify mechanisms of action and establish the clinical efficacy of either therapy.

METHODS

At the International Consultation on Incontinence-Research Society (ICI-RS) in 2017, a panel of Functional Urologists and Urogynaecologists participated in a Think Tank (TT) discussing the management of IC/BPS by BoNT-A and SNM, using available data from both PubMed and Medicine literature searches.

RESULTS

The role of BoNT-A and SNM in the treatment of IC/BPS are discussed and mechanisms of actions are proposed. Despite the available randomized trial data on the effect of intravesical BoNT-A treatment on symptoms of IC/BPS, a consistent conclusion of a positive effect cannot be drawn at the moment, as the published studies are small and heterogeneous in design. There is substantive evidence for the positive effects of SNM on symptoms of IC/BPS patients however, during patient selection, it is important to distinguish the degree and the location of pain in order to tailor the best therapy to the right patients.

CONCLUSIONS

Both intravesical BoNT-A treatment and SNM have been shown to have positive effects in patients with IC/BPS. However, firm conclusions cannot yet be drawn. Patient-reported outcomes and quality of life should be assessed in addition to urinary and pain symptoms. Since current treatments mainly focus on symptomatic relief, future research should also focus on clarifying the pathogenic mechanisms involved in IC/BPS.

The Influence of Resiniferatoxin (RTX) and Tetrodotoxin (TTX) on the Distribution, Relative Frequency, and Chemical Coding of Noradrenergic and Cholinergic Nerve Fibers Supplying the Porcine Urinary Bladder Wall

The present study investigated the influence of intravesically instilled resiniferatoxin (RTX) or tetrodotoxin (TTX) on the distribution, number, and chemical coding of noradrenergic and cholinergic nerve fibers (NF) supplying the urinary bladder in female pigs. Samples from the bladder wall were processed for double-labelling immunofluorescence with antibodies against cholinergic and noradrenergic markers and some other neurotransmitter substances. Both RTX and TTX caused a significant decrease in the number of cholinergic NF in the urinary bladder wall (in the muscle coat, submucosa, and beneath the urothelium). RTX instillation resulted in a decrease in the number of noradrenergic NF in the submucosa and urothelium, while TTX treatment caused a significant increase in the number of these axons in all the layers. The most remarkable changes in the chemical coding of the NF comprised a distinct decrease in the number of the cholinergic NF immunoreactive to CGRP (calcitonin gene-related peptide), nNOS (neuronal nitric oxide synthase), SOM (somatostatin) or VIP (vasoactive intestinal polypeptide), and an increase in the number of noradrenergic NF immunopositive to GAL (galanin) or nNOS, both after RTX or TTX instillation. The present study is the first to suggest that both RTX and TTX can modify the number of noradrenergic and cholinergic NF supplying the porcine urinary bladder.

The Influence of Tetrodotoxin (TTX) on the Distribution and Chemical Coding of Caudal Mesenteric Ganglion (CaMG) Neurons Supplying the Porcine Urinary Bladder

The treatment of micturition disorders creates a serious problem for urologists. Recently, new therapeutic agents, such as neurotoxins, are being considered for the therapy of urological patients. The present study investigated the chemical coding of caudal mesenteric ganglion (CaMG) neurons supplying the porcine urinary bladder after intravesical instillation of tetrodotoxin (TTX). The CaMG neurons were visualized with retrograde tracer Fast blue (FB) and their chemical profile was disclosed with double-labeling immunohistochemistry using antibodies against tyrosine hydroxylase (TH), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), calbindin (CB), galanin (GAL) and neuronal nitric oxide synthase (nNOS). It was found that in both the control (n = 6) and TTX-treated pigs (n = 6), the vast majority (92.6% ± 3.4% and 88.8% ± 2%, respectively) of FB-positive (FB+) nerve cells were TH+. TTX instillation caused a decrease in the number of FB+/TH+ neurons immunopositive to NPY (88.9% ± 5.3% in the control animals vs. 10.6% ± 5.3% in TTX-treated pigs) or VIP (1.7% ± 0.6% vs. 0%), and an increase in the number of FB+/TH+ neurons immunoreactive to SOM (8.8% ± 1.6% vs. 39% ± 12.8%), CB (1.8% ± 0.7% vs. 12.6% ± 2.7%), GAL (1.7% ± 0.8% vs. 10.9% ± 2.6%) or nNOS (0% vs. 1.1% ± 0.3%). The present study is the first to suggest that TTX modifies the chemical coding of CaMG neurons supplying the porcine urinary bladder.

Botulinum toxin type A induces changes in the chemical coding of substance P-immunoreactive dorsal root ganglia sensory neurons supplying the porcine urinary bladder

Botulinum toxin (BTX) is a potent neurotoxin which blocks acetylcholine release from nerve terminals, and therefore leads to cessation of somatic motor and/or parasympathetic transmission. Recently it has been found that BTX also interferes with sensory transmission, thus, the present study was aimed at investigating the neurochemical characterization of substance P-immunoreactive (SP-IR) bladder-projecting sensory neurons (BPSN) after the toxin treatment. Investigated neurons were visualized with retrograde tracing method and their chemical profile was disclosed with double-labelling immunohistochemistry using antibodies against SP, calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase activating polypeptide (PACAP), neuronal nitric oxide synthase (nNOS), galanin (GAL), calbindin (CB), and somatostatin (SOM). In the control group (n = 6), 45% of the total population of BPSN were SP-IR. Nearly half of these neurons co-expressed PACAP or CGRP (45% and 35%, respectively), while co-localization of SP with GAL, nNOS, SOM or CB was found less frequently (3.7%, 1.8%, 1.2%, and 0.7%, respectively). In BTX-treated pigs (n = 6), toxin-injections caused a decrease in the number of SP-IR cells containing CGRP, SOM or CB (16.2%, 0.5%, and 0%, respectively) and a distinct increase in these nerve cells immunopositive to GAL (27.2%). The present study demonstrates that BTX significantly modifies the chemical phenotypes of SP-IR BPSN.

The influence of intravesical administration of resiniferatoxin (RTX) on the chemical coding of sympathetic chain ganglia (SChG) neurons supplying the porcine urinary bladder

Resiniferatoxin (RTX) is used as an experimental drug in therapy of neurogenic urinary bladder disorders. The present study investigated the chemical coding of sympathetic chain ganglia (SChG) neurons supplying porcine urinary bladder after intravesical RTX instillation. The SChG neurons were visualized with retrograde tracing method and their chemical profile was disclosed with double-labeling immunohistochemistry using antibodies against dopamine β-hydroxylase (DβH; marker of noradrenergic neurons), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), galanin, Leu(5)-enkephalin and neuronal nitric oxide synthase (nNOS). It was found that in both the control (n = 5) and RTX-treated pigs (n = 5), the vast majority (90.4 ± 2.8 and 89.7 ± 2.3%, respectively) of FB-positive (FB+) nerve cells were DβH+. RTX instillation caused a decrease in the number of FB+/DβH+ neurons immunopositive to NPY (71.1 ± 12.1 vs 43.2 ± 6.7%), VIP (21.3 ± 10.7 vs 5.3 ± 4.3%) or SOM (16.5 ± 4.6 vs 2.3 ± 2.6%) and a distinct increase in the number of FB+/DβH+ neurons immunoreactive to nNOS (0.8 ± 1 vs 5.3 ± 1.9 %). The present study for the first time has provided some information that therapeutic effects of RTX on the mammalian urinary bladder can be partly mediated by SChG neurons.

Botulinum neurotoxin type A: Actions beyond SNAP-25?

Botulinum neurotoxin type A (BoNT/A), the most potent toxin known in nature which causes botulism, is a commonly used therapeutic protein. It prevents synaptic vesicle neuroexocytosis by proteolytic cleavage of synaptosomal-associated protein of 25 kDa (SNAP-25). It is widely believed that BoNT/A therapeutic or toxic actions are exclusively mediated by SNAP-25 cleavage. On the other hand, in vitro and in vivo findings suggest that several BoNT/A actions related to neuroexocytosis, cell cycle and apoptosis, neuritogenesis and gene expression are not necessarily mediated by this widely accepted mechanism of action. In present review we summarize the literature evidence which point to the existence of unknown BoNT/A molecular target(s) and modulation of unknown signaling pathways. The effects of BoNT/A apparently independent of SNAP-25 occur at similar doses/concentrations known to induce SNAP-25 cleavage and prevention of neurotransmitter release. Accordingly, these effects might be pharmacologically significant. Potentially the most interesting are observations of antimitotic and antitumor activity of BoNT/A. However, the exact mechanisms require further studies.

Retrograde transport of radiolabelled botulinum neurotoxin type A to the CNS after intradetrusor injection in rats

OBJECTIVE

To investigate the potential distribution of radiolabelled botulinum neurotoxin type A (BoNT/A) in the CNS after bladder injection in normal rats, by using the gamma-emitting radionuclide technetium-99 m ((99m) Tc).

MATERIALS AND METHODS

BoNT/A was radiolabelled by pretreatment with 2-iminothiolane and incubation with (99m) Tc-gluconate. The labelled toxin (99m) Tc-BoNT/A was purified using size exclusion HPLC. Twenty-four female Wistar rats were evenly injected in the bladder wall with either (99m) Tc-ΒοΝΤ/Α (n = 12) or free (99m) Tc (n = 12). Four rats from each group were killed at 1, 3 and 6 h after injection, respectively. The bladder, L6-S1 spinal cord segment and L6-S1 dorsal root ganglia (DRG) were harvested and their radioactivity counted in a gamma scintillation detector. Results were calculated as % injected dose (I.D.) per gram of tissue. The paired t-test was used for comparison of means of (99m) Tc-ΒοΝΤ/Α radioactivity vs free (99m) Tc in the tissues of interest.

RESULTS

Radiolabelled BoNT/A had a high radiochemical stability of 70% after 24 h. Gradual accumulation of (99m) Tc-ΒοΝΤ/Α was observed in the DRG up to 6 h after injection (P = 0.04 and P = 0.029 compared with 1 h and 3 h, respectively), while no accumulation was detected for free (99m) Tc. Consequently, (99m) Tc-ΒοΝΤ/Α radioactivity in the DRG was higher than free (99m) Tc radioactivity (3.18 ± 0.67% I.D./g vs 0.19 ± 0.10% I.D./g [P = 0.002] 6 h after injection). Values for (99m) Tc-ΒοΝΤ/Α radioactivity in the spinal cord were higher than those for free (99m) Tc, but not significantly. The bladder retained higher dosages of (99m) Tc-ΒοΝΤ/Α than free (99m) Tc at all time points.

CONCLUSIONS

Significant accumulation of the radiolabelled toxin in the lumbosacral DRG, together with a less significant uptake in the respective spinal cord segment as opposed to free radioactivity provide first evidence of the retrograde transport of BoNT/A to the CNS after bladder injection in rats.

Changes in chemical coding of sympathetic chain ganglia (SChG) neurons supplying porcine urinary bladder after botulinum toxin (BTX) treatment

Botulinum toxin (BTX) is a neurotoxin used in medicine as an effective drug in experimental therapy of neurogenic urinary bladder disorders. We have investigated the influence of BTX on the chemical coding of sympathetic chain ganglia (SChG) neurons supplying the porcine urinary bladder. The toxin was injected into the wall of the bladder. SChG neurons were visualized by a retrograde tracing method with fluorescent tracer fast blue (FB) and their chemical coding was investigated by double-labelling immunohistochemistry with antibodies against dopamine β-hydroxylase (DβH; a marker of noradrenergic neurons), neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP), somatostatin (SOM), galanin (GAL), Leu⁵-enkephalin (L-ENK) and neuronal nitric oxide synthase (nNOS). In both the control (n = 5) and BTX-treated pigs (n = 5), the vast majority (91 ± 2.3 % and 89.8 ± 2.5 %, respectively) of FB-positive (FB+) nerve cells were DβH+. BTX injections caused a decrease in the number of FB+/DβH+ neurons that were immunopositive to NPY (39.5 ± 4.5 % vs 74.5 ± 11.9 %), VIP (8.9 ± 5.3 % vs 22.3 ± 8.8 %), SOM (5.8 ± 2.3 % vs 17.4 ± 3.7 %) or GAL (0.9 ± 1.2 % vs 5.4 ± 4.4 %) and a distinct increase in the number of FB+/DβH+ neurons that were immunoreactive to L-ENK (3.7 ± 2.9 % vs 1.1 % ± 0.8 %) or nNOS (7.7 ± 3.5 % vs 0.8 ± 0.6 %). Our study provides novel evidence that the therapeutic effects of BTX on the mammalian urinary bladder are partly mediated by SChG neurons.

Botulinum toxin A, brain and pain

Botulinum neurotoxin type A (BoNT/A) is one of the most potent toxins known and a potential biological threat. At the same time, it is among the most widely used therapeutic proteins used yearly by millions of people, especially for cosmetic purposes. Currently, its clinical use in certain types of pain is increasing, and its long-term duration of effects represents a special clinical value. Efficacy of BoNT/A in different types of pain has been found in numerous clinical trials and case reports, as well as in animal pain models. However, sites and mechanisms of BoNT/A actions involved in nociception are a matter of controversy. In analogy with well known neuroparalytic effects in peripheral cholinergic synapses, presently dominant opinion is that BoNT/A exerts pain reduction by inhibiting peripheral neurotransmitter/inflammatory mediator release from sensory nerves. On the other hand, growing number of behavioral and immunohistochemical studies demonstrated the requirement of axonal transport for BoNT/A's antinociceptive action. In addition, toxin's enzymatic activity in central sensory regions was clearly identified after its peripheral application. Apart from general pharmacology, this review summarizes the clinical and experimental evidence for BoNT/A antinociceptive activity and compares the data in favor of peripheral vs. central site and mechanism of action. Based on literature review and published results from our laboratory we propose that the hypothesis of peripheral site of BoNT/A action is not sufficient to explain the experimental data collected up to now.