Mechanism of Rhinella icterica (Spix, 1824) toad poisoning using in vitro neurobiological preparations.

The biological activity of Rhinella icterica toxic secretion (RITS) was evaluated on chick neuromuscular junctions, rat heart́s tissue and mice hippocampal slices. At chick biventer cervicis preparation, RITS (5, 10 and 20µg/mL) produced a concentration-independent irreversible neuromuscular blockade, which was preceded by a transitory increase of muscle twitch tension with the lowest concentration, in 120min recordings. In this set of experiments, RITS incubation partially prevented the curare neuromuscular blockade. The assessment of chick biventer cervicis muscle acetylcholinesterase (AChE) in the presence of RITS showed a significant inhibition of the enzyme, similarly to neostigmine. The incubation of muscles with digoxin or ouabain mimicked the poison activity by increasing the amplitude of the twitches followed by a progressive depression of the muscle strength. In addition, RITS demonstrated a digitalic-like activity, by inhibiting significantly the cardiac Na+, K+-ATPase. When the central nervous system was accessed, RITS induced an increase in the cell viability, in the lowest concentration. In addition, the poison protected slices subject to oxygen/glucose deprivation. Altogether, these data indicate that the poisonous extract of R. icterica is able to interfere with peripheral and central neurotransmission, probably due to a direct interaction with AChE, calcium channels and Na+, K+-ATPase. A further investigation upon the poison toxic components will unveil the components involved in such a pharmacological activity and the potential biotechnological application of this poison.

[The effect of phenol on the ion currents of the frog motor nerve ending]. / Vliianie fenola na ionnye toki dvigatel'nogo nervnogo okonchaniia liagushki.

Phenol was shown to enhance the quantum content of the end-plate currents and to increase the duration of the nerve ending response. The effect could be abolished by the potassium channel blockers. The data obtained suggest that alteration of the kinetics of the potential-dependent potassium current of the nerve terminal is one of the mechanisms of the phenol facilitating effect on neuro-muscular transmission.

Neuromuscular pharmacology in rat neonates: development of responsiveness to prototypic blocking and reversal drugs.

The neonatal pharmacology of neuromuscular drugs was studied in vivo in newborn rats and in vitro in neonatal phrenic nerve-hemidiaphragm preparations. Drugs used to probe neuromuscular development in rat neonates were physostigmine, edrophonium, neostigmine, 4-aminopyridine, d-tubocurarine (dTc), and succinylcholine. The prejunctional actions of these drugs were monitored in relation to neonatal age by the appearance of stimulus-evoked repetitive discharge initiated by motor nerve endings and the occurrence and magnitude of the resulting enhancement of twitch tension. The occurrence and incidence of drug-induced fasciculations also served to track the development of functional motor nerve endings. Each of these prejunctional actions was inoperative until the third neonatal week, indicative of incomplete motor nerve development. In contrast, 4-aminopyridine, a nonanticholinesterase, evoked these prejunctional actions in 1-wk-old rat neonates. Neostigmine and edrophonium antagonized dTc as early as the first week; presumably, postsynaptic maturation had reached a functional level. 4-Aminopyridine also antagonized dTc at week 1. Rat neonates showed resistance to dTc blockade when tested by neonatal phrenic nerve-hemidiaphragm preparations in vitro. Relationships between age and 85%-95% transmission block declined to the adult level by week 5. This result indicates that in rat neonates, pharmacodynamic rather than pharmacokinetic mechanisms predominate in the development of responsiveness to dTc.

Antagonism of neuromuscular blockade. The cardiovascular effects in children of the combination of edrophonium and glycopyrronium.

Glycopyrronium 5 or 10 micrograms/kg was administered either simultaneously with, or 1 minute before, edrophonium 1 mg/kg in order to antagonise competitive neuromuscular blockade in 80 children. Both doses of glycopyrronium given before the edrophonium resulted in an initial significant (p less than 0.01) increase in heart rate. Heart rate decreased significantly (p less than 0.01) in all groups after the edrophonium was given, and only glycopyrronium 10 micrograms/kg administered before edrophonium prevented a substantial decrease below baseline. Initial heart rate responses to glycopyrronium or edrophonium are rapid, and measurements at intervals of 30 seconds may be necessary to record these changes.

Anti-curare action of stannous ion in the frog neuromuscular junction.

For the purpose of elucidating the mechanism of action of stannous ion (Sn2+), we investigated effects of stannous chloride (SnCl2) on the twitch and on the electrical phenomena in the muscle fiber. Sciatic nerve-sartorius muscle preparations from the bullfrog were used as the material. Effect of SnCl2 was examined on the twitch partially inhibited by pretreatment with d-tubocurarine. SnCl2 (1-100 microM) antagonized d-tubocurarine and enhanced the twitch dose-dependently. Tartaric acid, which is the solvent used for SnCl2 solution, had no augmentative effect on the twitch, even at a concentration as high as 250 microM. SnCl2 (1-50 microM) increased the amplitude of the endplate potential; that is, it exerted an anti-curare action. The resting potential and the membrane resistance of the muscle fiber were not altered by 30 microM SnCl2. These findings lead to the conclusion that Sn2+ enhances the twitch by increasing the endplate potential of the muscle fibers.

Effects of anticurare agents produced in Bulgaria on the smooth muscles of the gastro-intestinal tract.

The effect of nivalin-P (nivalin:pymadin/4-aminopiridine hydrochloride ratio--1:1) on the smooth muscles of the gastro-intestinal tract was studied. The experiments were carried out on guinea-pig ileum, rabbit jejunum using the method of Magnus, and on isolated strips of guinea-pig stomach and taenia coli by the modified method of Golenhofen. The agents studied were added to the incubation medium in the following concentrations: acetylcholine--1 X 10(-7) g/ml to 2 X 10(-6) g/ml, pymadin--up to 2 X 10(-6) g/ml, nivalin--up to 2 X 10(-6) g/ml, nivalin-P--up to 2 X 10(-6) g/ml, pancuronium, diadonii and galamine--from 2 X 10(-5) to 4 X 10(-4) g/ml, isoptin--from 1 X 10(-5) to 2 X 10(-5) g/ml and sodium nitroprusside--2 X 10(-5) to 4 X 10(-5) g/ml. Nivalin was found to increase mainly the tone of the smooth muscles, while pymadin increases predominantly the amplitude of the contractions. The combined agent nivalin-P stimulates both the phasical and the tonic activity. The role played by calcium ions in the mechanisms of the stimulating effect of nivalin-P on the smooth muscles is discussed.

The first reversal of curare. A translation of Pal's original paper, 'Physostigmine, an antidote to curare', 1900.

This paper describes an experiment performed by J. Pal of Vienna in 1900, which showed that physostigmine reverses the neuromuscular blocking properties of curare. Pal's original article is translated from the German.

Synaptic facilitatory and depressant actions of 3,4-diaminopyridine: correlation with anticurare properties.

This study aimed to define the complete concentration-effect relationship for anticurare effects of 3,4-diaminopyridine (3,4-DAP) in the isolated sympathetic ganglion of the bullfrog. Synaptic transmission was monitored by extracellular and intracellular recordings of the postganglionic response to preganglionic stimulation. A previous study showed that in the bullfrog sympathetic ganglion 3,4-DAP caused stimulus-bound repetitive postganglionic responses (SBR) to each single preganglionic stimulus. The concentration-effect relationship for 3,4-DAP-induced SBR was bell-shaped, and the descending limb of the curve reflected progressive suppression of SBR while normal synaptic transmission was maintained. In the present study a detailed concentration-effect analysis of 3,4-DAP's anticurare action also resulted in a bell-shaped curve nearly congruent with that for SBR. SBR and anticurare effects of 3,4-DAP therefore occupy a common concentration-effect domain, and this suggests that a common mechanism (increased transmitter release) may account for both effects.

[Neostigmine and dehiscence of intestinal anastomoses (author's transl)]. / Neostigmin und Insuffizienz intestinaler Anastomosen.

In a study from 1968, anastomotic leakage was reported to be nine times as frequent if neostigmine was used for reversal of curare action than in control patients. Subsequent studies did not confirm this finding although it is not disputed that neostigmine activates bowel peristalsis. Both animal experiments and clinical observations indicate that anastomoses in undamaged bowel, if properly done, withstand all kinds of hyperperistalsis. However, it cannot entirely be excluded that coincident pathologic conditions (cachexia, damaged bowel, chronic steroid medication, anaemia etc.) may occur, in which neostigmine administration is unsafe. Appropriate anaesthesiological techniques to avoid the need for neostigmine include titration of the individual relaxant requirement by means of a peripheral nerve stimulator, preference of intermediate or short-acting nondepolarizing muscle relaxants and primary postoperative mechanical ventilation. If nevertheless reversal of residual nondepolarizing block is decided, it should be performed with deep halothane anaesthesia still maintained and by means of an anticholinesterase agent with little muscarinic side effect such as edrophonium (0.5-1.0 mg/kg).

[Pymadine, a new type of non-depolarizing muscle-relaxant antagonist]. / Pymadine, un nou tip de antagonist al miorelaxantelor nedepolarizante.

The paper presents the author's experience in post-anesthetic decurarization with a new antagonist of competitive curare. Presented for the first time in 1970, 4-amino-pyridine was found o tbe a substance with a different mode of action than that of reversible inhibitors of cholinesterase, without parasympaticomimetic effects, and without untoward effects on the cardio-circulatory function. It also has a central analeptic effect. This is why the authors consider the new drug as a powerful means for reversing the competitive neuromuscular blockage.

Regulation of acetylcholinesterase appearance at neuromuscular junctions in vitro.

The appearance of acetylcholinesterase (AChE) at newly formed nerve-muscle synapses depends on synaptic transmission. Synapses form when cultures are grown in the presence of acetylcholine receptor antagonists, but AChE does not accumulate at these synapses. The important component of transmission seems to be muscle activity. Treatment with dibutyryl cyclic GMP mimics muscle activity, directly inducing synaptic AChE appearance.

[Comparison of 2-aminopyridine, 3-aminopyridine and 4-aminopyridine hydrochlorides and iodomethylates by the degree of decrease in curare toxicity]. / Sravniavane na khidrokhloridite i iodmetilatite na 2-aminopiridina, 3-aminopiridina i 4-aminopiridina po stepenta na ponizhavane na kurarinovata toksichnost.

The authors carried out studies on rats with apnoea, indiced by (+)-tubucurarine and found protective action, due to galantamine, neostigmine, hydrochlorides and jodometilates of 2-aminopyridine, 3-aminopyridine and 4-aminopyridine. Jodmethylates had protective action in larger doses in comparison with the respective hydrochlorides of nonsubstituted pyridilamines. The authors proposed a method for determination and comparison of the effect of compounds, eliminating the action of antidepolarizating myorelaxants, on tubocurarine toxicity.

Amitriptyline therapy increases electrocardiographic changes during reversal of neuromuscular blockade.

Induction of anesthesia is associated with an increased incidence of cardiac arrhythmias in patients maintained on amitriptyline medication. This study presents additional evidence showing that, in experimental animals (cats), amitriptyline treatment also produces significant ST-T wave and conduction abnormalities during neostigmine reversal of neuromuscular blockade.

Nerve, muscle, and serotonin.

Effects of serotonin one neuromuscular transmission and muscle contraction were studied in the tibialis anterior of rabbits. Serotonin antagonised the Mg++-induced block of transmission, and also provided dual effects on the curare-induced block, anti-curare phase followed by curare-potentiating phase. Independent of transmission processes, serotonin caused a reduction in twitch tension, mainly associated with decreased acceleration of twitch development. These serotonin actions were independent of vascular changes; pharmacological mechanisms are discussed in comparison with those of adrenaline and isoprenaline. A possible role of serotonin in causing a myopathy is proposed.