Blockade by tetanus and botulinum A toxin of postganglionic cholinergic nerve endings in the myenteric plexus

Effect of Intragastric Botulinum Type A Injection Combined with a Low-Calorie High-Protein Diet in Adults with Overweight or Obesity

(1) Background/aims: Intragastric botulinum toxin A injection (IGBI) combined with diet control is a new and effective weight loss method for grade 2 obese patients. However, the application of IGIB on overweight or obese adults still needs further research to confirm its efficacy. (2) Methods: We retrospectively collected medical data from 1 July 2021 to 1 January 2022 from a total of 71 patients without diabetes who participated in the bariatric clinic with a body mass index (BMI) > 25 kg/m2. Forty-nine participants opted for intragastric botulinum injection (IGBI) using 300 units of botulinum injected into the antrum, body, and fundus, followed with a low-calorie high-protein diet course. Another 22 people participated only in the low-calorie high-protein diet course as a placebo group. This study analyzes the weight loss percentage of the two groups. Adverse events after IGBI are also reported in a safety assessment. (3) Results: In terms of the characteristics of the two groups, the mean BMI was 29.3 kg/m2 in the IGBI group and 28.0 kg/m in the placebo group (p = 0.63 without significant difference). Comparing the percent weight loss from baseline in the two groups after 12 weeks, the IGBI group lost 11.5% of their body weight and the placebo group lost 1.8%. In terms of group analysis, the percentages of participants with a weight reduction of at least 5% for the IGBI and placebo groups were 95% and 4%, respectively. For weight reduction of at least 10%, these values for the IGBI and placebo groups were 63% and 4%, respectively. In terms of adverse events after IGBI for 12 weeks, 12 participants (24.4%) had constipation, which was the main side effect. No serious adverse events were observed during the study period. (4) Conclusion: The combination of a low-calorie high-protein diet and IGBI is an effective and safe procedure in overweight or obese adults for weight reduction, but further larger studies are needed.

The Positive Effects of a Calorie-Restricting High-Protein Diet Combined with Intragastric Botulinum Toxin Type A Application Among Morbidly Obese Patients: A Prospective, Observational Analysis of Eighty-Seven Grade 2 Obese Patients

PURPOSE

Many studies evaluating the effect of intragastric botulinum toxin type A injection (IG-BTxA) for the treatment of obesity have been published. However, none of these studies combined this procedure with a calorie-restricting high-protein diet. Herein, we aimed to evaluate the effects of IG-BTxA application combined with a calorie-restricting high-protein diet.

MATERIALS AND METHODS

This prospective cohort study is conducted with eighty-seven grade 2 obese patients treated between January 2019 and August 2019. Group 1: IG-BTxA + refused to consult the dietitian; group 2: IG-BTxA + get calorie-restricting high-protein diet; group 3: only get a calorie-restricting high-protein diet. Loss of weight, treatment adaptation (visual analog scale score), the status and changes of comorbid conditions, and changes in eating behaviors (Self-Regulation of Eating Behaviour Questionnaire score) were assessed.

RESULTS

Loss of weight, treatment adaptation, and positive behavioral change in eating preferences were significantly higher in group 2 (p = 0.01; p = 0.001; p < 0.01, respectively). Additionally, the decrease in medication requirement for diabetes and hypertension was higher in group 2 (p < 0.05).

CONCLUSION

IG-BTxA application before calorie-restricting high-protein diet facilitates adaptation to the new diet style and helps to lose weight faster in grade 2 obese patients. Also, more positive results were achieved in terms of controlling comorbid diseases.

Translocation and dissemination of botulinum neurotoxin from the intestinal tract

Botulinum neurotoxins (BoNTs) are potent toxins which induce flaccid paralysis by inhibiting the release of acetylcholine at the neuromuscular junctions. They associate with non-toxic proteins (ANTPs or NAPs) to form complexes of various sizes which are resistant to acidic pH and protease degradation. BoNT trafficking from the digestive tract to the target neurons is still a matter of debate. BoNTs use different strategies to pass through the intestinal barrier including passage of BoNT complexes containing hemagglutinins (HAs) via M cells, HA-dependent perturbation of E-cadherin intercellular junctions between enterocytes and paracellular passage of BoNT complexes, and transcytosis of BoNT free of NAPs through certain intestinal epithelial cells. Then, BoNTs target neuronal cells, preferentially cholinergic neurons, in the intestinal mucosa and submucosa. The precise mode of BoNT dissemination until the final target neuro-muscular junctions is still elusive.

Substance P is essential for maintaining gut muscle contractility: a novel role for coneurotransmission revealed by botulinum toxin

Substance P (SP) is commonly coexpressed with ACh in enteric motor neurons, and, according to the classical paradigm, both these neurotransmitters excite smooth muscle via parallel pathways. We hypothesized that, in addition, SP was responsible for maintaining the muscular responsiveness to ACh. We tested this hypothesis by using botulinum toxin (BoNT/A), a known blocker of vesicular release of neurotransmitters including ACh and neuropeptides. BoNT/A was injected into rat pyloric sphincter in different doses; as control we used boiled BoNT/A. At the desired time point, pylorus was dissected out and pyloric contractility was measured ex vivo in an organ bath and by measuring phosphorylation of myosin light chain 20 (MLC20). BoNT/A (10 IU) significantly reduced the response of pyloric muscle to exogenous ACh, an effect that was accompanied by reduced MLC20 phosphorylation in the muscle. Both effects were reversed by exogenous SP. CP-96345, a NK1 receptor antagonist, blocked the ability of exogenous SP to reverse the cholinergic hyporesponsiveness as well as the reduction in MLC20 phosphorylation induced by BoNT/A. In conclusion, we have identified a novel role for SP as a coneurotransmitter that appears to be important for the maintenance of muscular responsiveness to the principal excitatory neurotransmitter, ACh. These results also provide new insight into the effects of botulinum toxin on the enteric nervous system and gastrointestinal smooth muscle.

Preferential entry of botulinum neurotoxin A Hc domain through intestinal crypt cells and targeting to cholinergic neurons of the mouse intestine

Botulism, characterized by flaccid paralysis, commonly results from botulinum neurotoxin (BoNT) absorption across the epithelial barrier from the digestive tract and then dissemination through the blood circulation to target autonomic and motor nerve terminals. The trafficking pathway of BoNT/A passage through the intestinal barrier is not yet fully understood. We report that intralumenal administration of purified BoNT/A into mouse ileum segment impaired spontaneous muscle contractions and abolished the smooth muscle contractions evoked by electric field stimulation. Entry of BoNT/A into the mouse upper small intestine was monitored with fluorescent HcA (half C-terminal domain of heavy chain) which interacts with cell surface receptor(s). We show that HcA preferentially recognizes a subset of neuroendocrine intestinal crypt cells, which probably represent the entry site of the toxin through the intestinal barrier, then targets specific neurons in the submucosa and later (90–120 min) in the musculosa. HcA mainly binds to certain cholinergic neurons of both submucosal and myenteric plexuses, but also recognizes, although to a lower extent, other neuronal cells including glutamatergic and serotoninergic neurons in the submucosa. Intestinal cholinergic neuron targeting by HcA could account for the inhibition of intestinal peristaltism and secretion observed in botulism, but the consequences of the targeting to non-cholinergic neurons remains to be determined.

Botulism is a severe and often fatal disease in man and animals characterized by flaccid paralysis. Clostridium botulinum produces a potent neurotoxin (botulinum neurotoxin) responsible for all the symptoms of botulism. Botulism is most often acquired by ingesting preformed botulinum neurotoxin in contaminated food or after intestinal colonization by C. botulinum under certain circumstances, such as in infant botulism, and toxin production in the intestine. The first step of the disease consists in the passage of the botulinum neurotoxin through the intestinal barrier, which is still poorly understood. We investigated the trafficking of the botulinum neurotoxin in a mouse intestinal loop model, using fluorescent HcA (half C-terminal domain of the heavy chain). We observed that HcA preferentially recognizes neuroendocrine intestinal crypt cells, which likely represent the entry site of the toxin through the intestinal barrier, then targets specific neurons, mainly cholinergic neurons, in the submucosa, and later (90–120 min) in the musculosa leading to local paralytic effects such as inhibition of intestinal peristaltism. These results represent an important advance in the understanding of the initial steps of botulism intoxication and can be the basis for the development of new specific countermeasures against botulism.

Intragastric injection of botulinum toxin A for the treatment of obesity

BACKGROUND

Botulinum toxin A (BTX-A) is a powerful and long-acting inhibitor of muscular contractions in both striated and smooth muscles. Hypothetically, BTX-A should inhibit the acetylcholine-mediated peristalsis, which is mainly responsible for gastric motility, and thereby induce slowed gastric emptying, earlier satiety and weight loss. The aim of this study was to observe the effects of endoscopic intragastric injections of BTX-A in obese patients.

METHODS

After approval by the University Ethics Committee, 10 female patients with class I obesity (body mass index 30-35) were double-blind randomized into 2 groups (BTX-A and 0.9% Saline). In Group 1, 200 U BTX-A were injected endoscopically into the antrum and the distal gastric body. In Group 2, 0.9% saline was injected endoscopically into the antrum and the distal gastric body. Body weight and feeling of satiety were recorded monthly over a period of 6 months.

RESULTS

Both groups (BTX-A and 0.9% Saline) showed no significant weight reduction (P>0.05). One patient in Group 1 and two patients in Group 2 reported a feeling of early satiety. No adverse effects related to BTX-A or complications resulting from the endoscopic procedure were observed.

CONCLUSION

Intragastric injection of BTX-A for the treatment of obesity does not seem to reduce body weight.

Effect of botulinum toxin antral injection on gastric emptying and weight reduction in obese patients: a pilot study

BACKGROUND

A potential approach to the treatment of morbid obesity is reduction of gastric emptying to achieve satiety. Botulinum toxin A (Btx-A) is a long-acting inhibitor of acetylcholine-mediated peristalsis, which is mainly responsible for gastric motility.

AIM

To investigate whether botulinum toxin A, injected in the antrum of obese patients, delays gastric emptying.

METHODS

In a double_blind study, 18 healthy obese subjects (body mass index >30) were randomized into three groups (BTX133, BTX200 and Saline); they received Btx-A133U, Btx-A200U, or saline under endoscopic control. Gastric emptying was tested by scintigraphy before and 10 days after treatment. Body weight variations and appetite sensation were recorded after 5 weeks.

RESULTS

Fourteen patients completed the study. The botulinum toxin A-treated groups showed weight reduction, which was not statistically significant. The effects on gastric emptying were variable. Most of the botulinum toxin A treated patients reported a reduced appetite.

CONCLUSION

This pilot clinical trial suggests potential activity of botulinum toxin A for the manipulation of appetite.

Emerging role of botulinum toxin in the management of voiding dysfunction

PURPOSE

In recent years there has been tremendous excitement over the use of botulinum neurotoxin (BTX) to treat various urethral and bladder dysfunctions. BTX is the most potent, naturally occurring toxin known to mankind. Why, then, would a urologist want to use this agent to poison the bladder or urethral sphincter?

MATERIALS AND METHODS

We reviewed the recent literature on the mechanisms underlying the effects of BTX treatment and discuss current use of this agent within the urological community, as well as provide perspective on future targets of BTX. The information was gathered from MEDLINE, abstracts from recent urological meetings and personal experience.

RESULTS

Injection of BTX appears to have a positive therapeutic effect in multiple urological conditions, including detrusor hyperreflexia and detrusor external sphincter dyssynergia, and nonneurogenic conditions such as pelvic floor spasticity, refractory overactive bladder and, possibly, benign prostatic hyperplasia. Interstitial cystitis may even be potentially helped with bladder BTX injection.

CONCLUSIONS

Botulinum toxin is a novel and promising treatment for a variety of lower urinary tract dysfunctions. The basic science behind its mechanism of action and physiology, and published clinical results are impressive. However, since application of BTX in the lower urinary tract has not been approved by the Food and Drug Administration, caution should be used until future properly designed, multicenter randomized studies are completed to assess the safety and efficacy of BTX in urological diseases.

Inhibitory effects of botulinum toxin on pyloric and antral smooth muscle

Botulinum toxin injection into the pylorus is reported to improve gastric emptying in gastroparesis. Classically, botulinum toxin inhibits ACh release from cholinergic nerves in skeletal muscle. The aim of this study was to determine the effects of botulinum toxin on pyloric smooth muscle. Guinea pig pyloric muscle strips were studied in vitro. Botulinum toxin type A was added; electric field stimulation (EFS) was performed every 30 min for 6 h. ACh (100 microM)-induced contractile responses were determined before and after 6 h. Botulinum toxin caused a concentration-dependent decrease of pyloric contractions to EFS. At a low concentration (2 U/ml), botulinum toxin decreased pyloric contractions to EFS by 43 +/- 9% without affecting ACh-induced contractions. At higher concentrations (10 U/ml), botulinum toxin decreased pyloric contraction to EFS by 75 +/- 7% and decreased ACh-induced contraction by 79 +/- 9%. In conclusion, botulinum toxin inhibits pyloric smooth muscle contractility. At a low concentration, botulinum toxin decreases EFS-induced contractile responses without affecting ACh-induced contractions suggesting inhibition of ACh release from cholinergic nerves. At higher concentrations, botulinum toxin directly inhibits smooth muscle contractility as evidenced by the decreased contractile response to ACh.

Review article: botulinum toxin in the therapy of gastrointestinal motility disorders

Since 1980, botulinum toxin has been employed for the treatment of various voluntary muscle spastic disorders in the fields of neurology and ophthalmology. More recently, botulinum toxin has been proved to be effective in the therapy of dyskinetic smooth muscle disorders of the gastrointestinal tract. Achalasia and anal fissure are the gastrointestinal disorders in which botulinum toxin therapy has been most extensively investigated. Botulinum toxin is the best treatment option for achalasia in patients whose condition makes them unfit for pneumatic dilation or surgery. In anal fissure, botulinum toxin is highly effective and may become the treatment of choice. In the future, botulinum toxin application in the gastrointestinal tract will be extended to many other gastrointestinal disorders, such as non-achalasic motor disorders of the oesophagus, dysfunction of Oddi's sphincter, achalasia of the internal anal sphincter and others. This article describes the mechanism of action, rationale of employment, indications and side-effects of botulinum toxin application in smooth muscle disorders of the gastrointestinal tract, and compares the results of different techniques of botulinum toxin therapeutic application.

Emerging role of botulinum toxin in the treatment of neurogenic and non-neurogenic voiding dysfunction

Botulinum toxin (BTX) is the most lethal naturally occurring toxin known to mankind. Why, then, would an urologist want to use this agent to poison the bladder or urethral sphincter? This article reviews the mechanisms underlying the effects of BTX treatment, summarizes the current usage of this agent within the urologic community, and provides perspectives on future targets of this therapy.

Achalasia: a review of therapeutic options and outcomes

Advances in achalasia has led to the development of new therapeutic options. This review will focus on methodology and outcomes of two established techniques; pneumatic dilation and surgical myotomy; and one new technique, LES injection of botulinum A toxin.

Treatment of achalasia with botulinum A toxin

Achalasia is an idiopathic neuromuscular disorder of the esophagus which is associated with absence of esophageal peristalsis and incomplete relaxation of a normal or raised lower esophageal sphincter (LES). Dysphagia is the most commonly associated symptom. Conventional therapeutic approaches are directed to reducing LES pressure and include orally-administered smooth muscle relaxants, forceful sphincter dilation with balloon dilators, and open or laparoscopic-assisted myotomy of the LES. Pharmacologic therapies have a low success rate. Forceful dilation has a perforation complication rate of 2% to 5%, and myotomies may precipitate significant gastroesophageal reflux, a complication minimized when a partial fundal wrap is employed simultaneously. In recent years, botulinum toxin, utilized widely as a striated muscle relaxant in managing blepharospasm, anal sphincter spasm, and muscle spasm complicating CVAs, and in smoothening facial wrinkles, has been extended to the management of achalasia on the basis that it impairs smooth muscle responsiveness to acetylcholine. Eighty units of Botox (botulinum toxin) are injected directly into the endoscopically (endoscopic ultrasound techniques may facilitate localization) located LES region (20 units into each of 4 quadrants). Symptom relief lasting 6 months on average is experienced in more than 65% of treated patients, and the complication rate is negligible. This therapeutic option is reserved for patients too ill to undergo any surgical procedure and is most effective when the lower esophageal region is hypertonic.

Botulinum toxin as a therapeutic agent

Botulinum toxin is a presynaptic neuromuscular blocking agent that, when injected intramuscularly in minute quantities, can produce selective muscle weakness. This property is employed therapeutically to provide symptomatic relief in conditions related to excessive muscle activities in strabismus, blepharospasm, hemifacial spasm, cervical dystonia, spasmodic dysphonia (adductor type), and jaw closing dystonia. It is investigational for a long list of medical conditions. It is a marketed drug in a number of countries in the world, but its use has only been approved by different regulatory agencies for use in a limited number of conditions. The long-term effects, appropriate dose for children, and in pregnancy, and maximum dose without causing toxicity remain unclear.

Effects of intrasphincteric botulinum toxin on the lower esophageal sphincter in piglets

BACKGROUND

The toxin of Clostridium botulinum (BoTx) inhibits the release of acetylcholine from nerve terminals and causes paralysis of skeletal muscle. The present study examined the hypothesis that BoTx may have a similar effect on gastrointestinal smooth muscle.

METHODS

Baseline lower esophageal sphincter (LES) pressures were obtained in five piglets, and normal saline was injected endoscopically into the LES. One week later, LES pressure was measured again, followed by injection of BoTx into the LES. After another week, LES pressure was measured again.

RESULTS

Compared with a baseline LES pressure of 8.2 +/- 1.5 mm Hg, LES pressure decreased to 3.2 +/- 1.0 mm Hg after BoTx injection, a reduction of about 60% (P < 0.01). By contrast, LES pressure did not change significantly after normal saline injection. The animals showed no evidence of toxicity. Data from other experiments showed that after injection with toxin, the LES responds normally to bethanechol and pentagastrin but displays a paradoxical response to edrophonium and cholecystokinin.

CONCLUSIONS

BoTx is a potent inhibitor of resting LES tone. Its relatively specific anticholinergic effect may help clarify the role of cholinergic and noncholinergic pathways in the regulation of gastrointestinal sphincters.

Molecular structure of tetanus neurotoxin as revealed by Fourier transform infrared and circular dichroic spectroscopy

Secondary structure contents of tetanus neurotoxin have been estimated at neutral and acidic pH using circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy. An analysis of the far-ultraviolet CD spectra of the neurotoxin dissolved in 50 mM citrate-phosphate buffer (pH 7.0) revealed 20.0 +/- 2.1% alpha-helix, 50.5 +/- 2.1% beta-pleated sheets, no beta-turns, and 29.5% random coils, which is at considerable variance with results from an earlier detailed study of tetanus neurotoxin's secondary structures (J.P. Robinson, L.A. Holladay, J.H. Hash and D. Puett, J. Biol. Chem. 257 (1982) 407). However, the alpha-helix content estimated in this study is consistent with the earlier studies of Robinson et al. (J.P. Robinson, L.A. Holladay, J.B. Picklesimer and D. Puett, Mol. Cell. Biochem. 5 (1974) 147; J.P. Robinson, J.B. Picklesimer and D. Puett, J. Biol. Chem. 250 (1975) 7435) and with the study by Lazarovici et al. (P. Lazarovici, P. Yanai and E. Yavin, J. Biol. Chem. 262 (1986) 2645), although other secondary structural features do not agree with those of the previous studies. Secondary structure estimation from Fourier transform infrared spectra in both amide I and amide III frequency regions revealed 22-23% alpha-helix, 49-51% beta-pleated sheets and 27-28% random coils, indicating a good correlation with the secondary structure content estimated from CD analysis. Lowering of the pH of the neurotoxin to 5.5 or 4.0 did not result in any noticeable change in the overall secondary structures. However, there were significant pH-induced variations observed in the individual curve-fitted FT-IR bands in the amide III frequency region. For example, the 1302 cm-1 band (relative area, 4.2%) observed at pH 7.0 was shifted to 1297 cm-1 (relative area, 2.2%) at pH 5.5, and the relative area of the band at 1316-1317 cm-1 (alpha-helix) increased by approx. 40%. This study suggests that contrary to earlier reports, tetanus neurotoxin is a beta-pleated sheet dominated structure, and although lower pH does not change the overall contents of the secondary structures, significant conformational alterations are observed.

Tetanus toxin and botulinum A and C neurotoxins inhibit noradrenaline release from cultured mouse brain

Primary nerve cell cultures from the brainstem of embryonic mice take up [3H]noradrenaline. Release can be evoked by high K+ or sea anemone toxin II and depends on Ca2+. The cultures allow neurochemical studies on the long-term actions of clostridial neurotoxins. Tetanus and botulinum A and C neurotoxins partially inhibit the absolute and fractional release evoked by high K+, as well as the fractional basal release. The detection limit for the toxins is below 5 pM. Total radioactivity is higher in the poisoned cultures, although the initial velocity of uptake is not measurably influenced by tetanus or botulinum A toxin. Pretreatment with neuraminidase prevents the effects of botulinum A toxin and diminishes those of botulinum C and tetanus toxins. Within 6 days, the cultures partially recover from tetanus toxin poisoning. Antitoxin prevents the actions of the toxin, but only slightly promotes recovery. The data indicate close pharmacological analogies between the clostridial neurotoxins.

Tetanus and botulinum toxins block the release of acetylcholine from slices of rat striatum and from the isolated electric organ of Torpedo at different concentrations

Tetanus toxin, like botulinum toxin type A, blocks cholinergic synaptic transmission at the central and peripheral nervous systems. Nevertheless, the diseases induced by the two toxins are different since tetanus toxin induces a spastic paralysis and botulinum toxin elicits a flaccid paralysis. Thus, we have investigated the sensitivity of a central and a peripheral cholinergic synapse to these two toxins. We have studied the action of both poison on the release of acetylcholine from slices of the rat striatum and from the isolated electric organ of Torpedo, which is homologous to the neuromuscular junction. Acetylcholine release from the rat striatum was continuously monitored by a chemiluminescent method. The secretion of acetylcholine from the electric organ was estimated both by measuring the amplitude of the evoked electrical discharge from stacks of electroplaques, and by continuously monitoring the neurotransmitter release from isolated nerve terminals. Tetanus toxin blocks the electrical discharge of electric organ prisms, and also impairs the release of acetylcholine from the Torpedo electric organ nerve endings. Our results on acetylcholine release show that tetanus toxin is more potent than botulinum toxin type A at the central cholinergic synapse (tetanus/botulinum toxins potency ratio about 100-200) whereas botulinum toxin is the most potent at the peripheral cholinergic synapse (botulinum/tetanus toxins potency ratio about 100).

The effects of purified botulinum neurotoxin type A on cholinergic, adrenergic and non-adrenergic, atropine-resistant autonomic neuromuscular transmission

The twitch response observed during low frequency electrical stimulation of postganglionic cholinergic neurones supplying the longitudinal smooth muscle of the guinea-pig ileum was markedly reduced by incubation with an homogeneous preparation of botulinum type A neurotoxin (4.3-8.6 nM). This intoxication of the autonomic cholinergic neurones was long-lasting, irreversible by washing, but readily reversed by 4-aminopyridine (50-1000 microM). The noradrenergic motor response of the rat anococcygeus following field stimulation was partially antagonised by the neurotoxin. The non-adrenergic inhibitory response of the guinea-pig taenia coli, elicited by field stimulation, was not antagonised by botulinum toxin, suggesting that a source of a non-adrenergic inhibitory transmitter exists, other than intramural cholinergic neurones. However, the neurogenic excitatory responses of the guinea-pig bladder, elicited by field stimulation in the presence of atropine and guanethidine, were virtually abolished by botulinum toxin. It is suggested that the parasympathetic neurones which supply the smooth muscle of the guinea-pig urinary bladder co-release acetylcholine and a non-cholinergic excitatory transmitter; ATP or polypeptides are possible candidates.

Botulinum toxin type A: kinetics of calcium dependent paralysis of the neuromuscular junction and antagonism by drugs and animal toxins

The effect of botulinum Toxin (BoTx), which blocks the mechanism of release of acetylcholine at neuromuscular junctions and induces paralysis of muscles stimulated by nerves, is known to be Ca2+-dependent. Amplitude of muscular contractions evoked by nerve impulse was studied in BoTx poisoned preparations. The present report notes that an increase in Ca2+ concentration in vitro delays paralysis of muscular contractions of the frog evoked by nerve impulse. The restorative effect of different drugs on this paralysis has been tested: 4-aminopyridine, ATXII (toxin isolated and purified from the sea anemone Anemonia sulcata tentacles) and a crude venom isolated from the scorpion Androctonus australis antagonize the BotX induced paralysis at physiological concentrations of Ca2+ (Cao2+ = 2 mM), whereas the restorative effect observed with tetra-ethylammonium or guanidine occurs at higher concentrations of Ca2+ (Cao2+ = 4 mM), as in mammals. ATXII restores in vivo the activity of a BoTx paralysed muscle of guinea pig and this effect is more efficient if the interval between the injection of BoTx and ATXII is shortened. These results on the frog and guinea pig are in agreement with those obtained on other biological preparations by several investigators. Moreover it is suggested that the antagonism of BoTx induced paralysis is a consequence of the increase in Ca2+ at the nerve ending. The efficiency of 4-aminopyridine and animal toxins is explained by an action on the nerve ending, by increasing Ca2+ from an interval compartment of the cell, whereas antagonism produced by guanidine and tetraethylammonium involves uptake of Ca2+ from the external medium. The bathing medium must be at a higher concentration of Ca2+ than usual. This explains the differences in antagonism obtained by these drugs and toxins in vitro and in vivo.

Tetanus toxin and botulinum A toxin inhibit acetylcholine release from but not calcium uptake into brain tissue

Slices or particles from rat forebrain cortex were preloaded with [3H]choline, and the release of [3H]acetylcholine was evoked with potassium ions in a superfusion system. Release depended on the presence of calcium. 1. Incubation of the preloaded tissue preparation for 2 h with tetanus or botulinum A toxin did not change the [3H]acetylcholine content or the ratio [3H]acetylcholine/[3H]choline. Tetanus toxin diminished, dependent on dose and time, the release of [3H]acetylcholine evoked by 25 mM K+. It was about ten times more potent than botulinum A toxin. The effect of botulinum toxin was due to its neurotoxin content. Raising the potassium concentration partially overcame the inhibition by the toxins. Hemicholinium-3, applied to preloaded slices, left the subsequent [3H]acetylcholine release unchanged. Pretreatment of particles with neuraminidase diminished the content of long-chain gangliosides to the detection limit. Such particles remained fully sensitive to tetanus toxin, and at least partially sensitive to botulinum A toxin. 2. The potassium or sea anemone toxin II stimulated uptake of 45Ca2+ into cortex synaptosomes or particles was not inhibited by either toxin. Both toxins appear to impede the Ca2+-dependent mobilization of an easily releasable acetylcholine pool, without inhibiting the transmembranal calcium fluxes.