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S Thesleff

Publications and source records attributed to S Thesleff.

At least 37 records · Page 2Linked to original sources
PubMed1987

Aminoglycosides and 3,4-diaminopyridine on neuromuscular block caused by botulinum type A toxin.

Impulse-evoked transmitter release was greatly reduced at frog neuromuscular junctions 3-20 days after botulinum type A toxin (BoTx) poisoning. The reduction in transmitter release was accompanied by an increased variability in the latency between the presynaptic spike and the release of transmitter. The aminoglycoside antibiotics amikacin, gentamycin, and bekanamycin, when applied at concentrations within their therapeutic levels, markedly enhanced the blockade of transmitter release in BoTx-poisoned junctions. 3,4-diaminopyridine strongly antagonized the effects of BoTx at early stages of poisoning, and the combined presynaptic effects of BoTx and aminoglycoside antibiotics provided that transmitter release was not completely blocked by the toxin. The antagonism was apparent at all frequencies of stimulation. Since the aminoglycoside antibiotics enhanced the neuromuscular block caused by BoTx, these drugs should be avoided in patients suspected of poisoning by this toxin.

4-Aminopyridine↗
PubMed1986

Effects of botulinum toxin induced muscle paralysis on endocytosis and lysosomal enzyme activities in mouse skeletal muscle.

The effects of botulinum toxin (type A) induced muscle paralysis on endocytosis and lysosomal enzyme activities in skeletal muscle were compared with the effects of surgical denervation. Muscle atrophy, measured as decrease in total muscle protein content, was as large or larger after botulinum toxin treatment as after denervation. Endocytic activity, measured as the in vitro uptake of horseradish peroxidase, and the specific activities of the lysosomal enzymes N-acetyl-beta-D-glucosaminidase and cathepsin D were all increased six days after denervation. Only the specific activity of cathepsin D was increased six days after botulinum toxin poisoning. The uptake of horseradish peroxidase and the specific activity of N-acetyl-beta-D-glucosaminidase were also increased eleven days after poisoning. Transverse sections of eleven days botulinum poisoned muscles from animals injected with horseradish peroxidase showed fibres with dense peroxidase staining similar to those seen in denervated muscle although they seemed to occur less frequently. The results show that increases in endocytic activity and lysosomal enzyme activities may occur in skeletal muscle without the presence of degenerating axons. The differences in effects of surgical denervation and botulinum toxin induced paralysis are discussed in terms of what is known about the mechanism of action of botulinum toxin and the possible functional roles of the two lysosomal enzymes studied.

Animals↗
PubMed1986

An ultrastructural study of the segmental uptake of horseradish peroxidase in the endplate region of denervated skeletal muscle fibres.

The segmental uptake of horseradish peroxidase (HRP) in the endplate region of denervated skeletal muscle fibres has been studied ultrastructurally using a method for selecting single muscle fibres with high segmental peroxidase staining from denervated mouse tibialis anterior muscle. Segments containing large peroxidase positive phagosomes could already be seen 10-15 min after i.v. injection of HRP. Such segments were still present 24 h after HRP injection. The localization of phagosomes, deep in the fibres rather than immediately under the sarcolemma, suggests that the uptake occurs from t-tubuli. Vivid proliferation of t-tubuli, consisting of vesiculation, enlargement and encircling of cytoplasmic components, was also observed. The HRP accumulates in phagosomes of varying size and shape. Similar membrane-limited bodies without or with very weak peroxidase staining were also observed. The peroxidase-positive phagosomes participate in autophagic processes as suggested by their content of undegraded cellular material. Golgi profiles, which occurred deep in the muscle fibres, and enlarged components of the sarcoplasmic reticulum were frequently encountered in the segments. Myofibrillar degeneration occurs in the segments and progresses with time after denervation. The described segments may be related to the increased membrane turnover in denervated muscle fibres and/or they may be related to processes aimed at establishing new synaptic contacts.

Animals↗
PubMed1986

Pharmacological characterization of the calcium-insensitive, intermittent acetylcholine release at the rat neuromuscular junction.

A variety of pharmacologically active compounds was surveyed for effects on the Ca2+-insensitive miniature end-plate potentials (slow mepps) induced by botulinum toxin type A (Botx) poisoning in rat muscle. The purpose was to gain insight into the release process responsible for this type of acetylcholine secretion. It was found that caffeine and dibutyryl cyclic adenosine 3',5'-monophosphate increased significantly the frequency of slow mepps in Botx-poisoned muscles, but had no effect on slow mepps in control muscles. Vinblastine and cytochalasin B significantly increased the slow mepp frequency in Botx-poisoned as well as in normal control muscles. Inhibitors of oxidative metabolism reduced the frequency of slow mepps by 90%, indicating a high energy requirement for this type of release. No agent was found to augment the slow mepp frequency above 1-2 Hz, suggesting that an upper limit exists for this type of packaging and release of acetylcholine.

Acetylcholine↗
PubMed1986

The nature and origin of calcium-insensitive miniature end-plate potentials at rodent neuromuscular junctions.

1. To study the nature and origin of slow-rising, Ca2+-insensitive miniature end-plate potentials (m.e.p.p.s) in mammalian muscle we used intracellular recording techniques and drugs which block acetylcholine (ACh) synthesis or the uptake of ACh into synaptic vesicles. Slow m.e.p.p.s were induced in vivo by paralysing the extensor digitorum longus muscle of the rat with botulinum toxin type A or in vitro by the application of 4-aminoquinoline to the mouse diaphragm nerve-muscle preparation. 2. Hemicholinium-3, which blocks ACh synthesis, reduced the amplitude of all synaptic potentials including slow m.e.p.p.s, but only if the nerve was stimulated. 3. 2(4-phenylpiperidino)cyclohexanol (AH-5183), which blocks the active uptake of ACh into synaptic vesicles, reduced both the frequency and the amplitude of slow m.e.p.p.s and did so without requiring nerve stimulation. 4. No correlation was observed between the molecular leakage of ACh from the motor nerve and the frequency and amplitude of slow m.e.p.p.s. 5. We conclude that slow m.e.p.p.s are caused by the release of ACh from the nerve terminal, possibly from a small pool of synaptic vesicle-like structures.

Acetylcholine↗
PubMed1984

Studies on the mode of action of botulinum toxin type A at the frog neuromuscular junction.

In frogs poisoned with botulinum toxin type A the quantal content of endplate potentials is greatly reduced. Lowering the temperature of the preparation increases quantum content; between 14 and 4 degrees C the mean Q10 for this effect is 6.3. Facilitation of synaptic transmission is marked with pairs of stimuli and cooling further enhances facilitation. The time constant of decay of facilitation is 34 ms at 20 degrees C and 116 ms at 4 degrees C. The increase in facilitation and in its time constant of decay at low temperature are presumably not a result of a prolongation of the duration of the nerve terminal action potential since such changes are not seen in the presence of K+-channel blockade by 3,4-diaminopyridine. Electrotonic depolarization of nerve terminals in the presence of tetrodotoxin and 3,4-diaminopyridine induces all-or-none endplate currents. Such endplate currents, at a holding potential of -50 mV, show that the amount of charge entry is about 1/3 of that in unpoisoned junctions but still corresponds to 5-10 X 10(3) transmitter quanta. Transmitter release at this level is maintained during repetitive stimulation even in the presence of 82 mM Ca2+ in the extracellular solution. We speculate that the blockade of transmitter release in BoTx -poisoned muscles results from a stimulatory effect of the toxin on metabolic systems of Ca2+ disposal in the nerve terminal.

Animals↗
PubMed1984

Miniature end-plate potentials in rat skeletal muscle poisoned with botulinum toxin.

Spontaneous transmitter release, recorded as miniature end-plate potentials (m.e.p.p.s), was studied in rat extensor digitorum longus (e.d.l.) and soleus muscles partially or completely paralysed by botulinum toxin type A (BoTx). Normal unpoisoned muscles were examined for comparison. Analysis of m.e.p.p.s in both normal and BoTx-poisoned muscles confirmed the presence of two populations of potentials. One population, which comprised about 96% of the m.e.p.p.s recorded at non-poisoned end-plates, was characterized by a uniform time course and a mean time-to-peak of 0.5-0.7 ms. These potentials had a shape and time-to-peak similar to that of quantal end-plate potentials (e.p.p.s) evoked by nerve stimuli. These were designated 'fast m.e.p.p.s'. The other population of m.e.p.p.s was characterized by a slower, more variable rise-time, the time-to-peak exceeding 1.1 ms, and generally a larger amplitude. These were designated 'slow m.e.p.p.s'. In both partial and complete paralysis by BoTx the frequency of fast m.e.p.p.s was reduced by more than 90% and the reduction lasted several weeks. After 6-10 days of poisoning the frequency of slow m.e.p.p.s gradually increased. The highest frequency of slow m.e.p.p.s (0.4 Hz) was recorded in the partially paralysed soleus muscle, the frequency being about ten times that at unpoisoned end-plates. In both partially paralysed muscles slow m.e.p.p. frequency returned towards normal 28 days after poisoning. A significant correlation (r = 0.67) was observed between the quantal content of e.p.p.s and the frequency of fast m.e.p.p.s in partially paralysed e.d.l. muscles. No significant correlation was observed between quantal content of e.p.p.s and the frequency of slow m.e.p.p.s. To further study if muscle activity influenced the appearance of slow m.e.p.p.s, partially paralysed soleus muscles were directly stimulated in vivo during the first 11-13 days following BoTx poisoning, using a stimulation pattern which inhibits nerve terminal sprouting and the appearance of denervation changes. This procedure did not alter the frequency of slow m.e.p.p.s as compared to unstimulated poisoned controls. It is concluded that enhancement of slow m.e.p.p. frequency in muscles poisoned with BoTx is related to the blockade of evoked Ca2+-dependent quantal transmitter release. However, additional factors influence this type of spontaneous and Ca2+-insensitive release of acetylcholine since there is a great variability between fibres and a time lag between the disappearance of fast m.e.p.p.s and the activation of slow m.e.p.p. frequency.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1984

Local anaesthesia and immunomodulatory effects of antithyroid drugs.

Propylthiouracil (PTU) and propranolol can suppress, while methimazole (MMI) can enhance, mitogenic activation of lymphocytes. The present study investigated whether this effect of PTU, as has been shown for propranolol, relates to local anaesthetic activity. MMI (1 mM) but not PTU (1 mM) reduced the action potential in rat skeletal muscle. Thus, PTU seems to lack local anaesthetic activity. Moreover, the recorded local anaesthetic capacity of MMI hardly explains the stimulatory influence of MMI on lymphocyte activation. Apparently, the interference of MMI and PTU with lymphocyte activation seems to be due to another mechanism than local anaesthetic activity.

Action Potentials↗
PubMed1984

Transmitter release in botulinum-poisoned muscles.

Examination of miniature end-plate potentials (m.e.p.ps) in rat skeletal muscle poisoned in vivo by botulinum toxin type A reveals the presence of two populations of potentials. One population which corresponds to m.e.p.ps in unpoisoned muscles and to quantal end-plate potentials. The frequency of these m.e.p.ps is greatly reduced by botulinum toxin. The second population of m.e.p.ps has quite different characteristics. These m.e.p.ps have a more variable, but generally much larger amplitude, and their time to peak is longer than normal m.e.p.ps. The frequency of these m.e.p.ps increases during poisoning and reaches 0.3-1 Hz after 10-14 days. In addition to the variability in amplitude and time-to-peak these m.e.p.ps differ from those at unpoisoned junctions by being unaffected by procedures which alter extra- or intracellular Ca2+ concentrations. The appearance of this Ca2+-insensitive spontaneous quantal secretion of acetylcholine is apparently not a direct effect of the toxin but secondary to blockade of impulse transmission since it also appears at unpoisoned end-plates when transmission is impaired for other reasons. Procedures which increase the intracellular Ca2+ concentration in nerve terminals restore transmitter release from botulinum toxin poisoned nerves. Furthermore, the block caused by the toxin is very temperature-dependent, a reduction in temperature relieving the block. Since presynaptic Ca2+ currents are unaltered by the toxin it is proposed that the block of transmission is due to a reduction in the calcium content of the nerve terminal to a level where the amount of Ca2+, which normally enters, is insufficient to activate transmitter release.

Acetylcholine↗
PubMed1983

Botulinum toxin and 4-aminoquinoline induce a similar abnormal type of spontaneous quantal transmitter release at the rat neuromuscular junction.

Intracellular recordings from botulinum toxin type A (BoTx)-poisoned extensor digitorum longus muscles from adult rats have shown that the toxin initially reduced the frequency of miniature endplate potentials (m.e.p.ps) to about 1/200 of normal. After a few days the m.e.p.p. frequency rose and was subsequently maintained at a level of about 1/3 of that at normal endplates. Depolarization of the nerve terminals with 20-30 mM KCl-Ringer initially failed to affect the frequency of m.e.p.ps and later caused only a 2-3--fold increase in their frequency. The temperature dependence of m.e.p.p. frequency at BoTx-poisoned endplates had a Q10 of about 12 compared to 2-3 for normal junctions. The time to peak of a population of m.e.p.ps at Botx-poisoned junctions was prolonged as compared to normal and fast- and slow-rising m.e.p.ps originated within the same post-synaptic membrane field area. M.e.p.ps in BoTx-poisoned muscles resembled the m.e.p.ps which 4-aminoquinoline (4-AQ) has been shown to induce in normal muscle, and we therefore examined and compared these two release processes for acetylcholine. Procedures known to markedly affect m.e.p.p. frequency at normal junctions, such as nerve terminal depolarization or changes in extra- and intracellular Ca2+ concentrations, failed to affect m.e.p.p. frequency in BoTx-poisoned muscles and similarly the frequency of m.e.p.ps induced by 4-AQ in normal muscle. Tonicity changes in the extracellular medium altered m.e.p.p. frequency in both the experimental conditions, but in a direction opposite to that at normal junctions. The temperature dependence of the frequency of 4-AQ-induced m.e.p.ps was similar to that of m.e.p.ps at BoTx-poisoned junctions. It is concluded that BoTx poisoning induces an abnormal type of spontaneous quantal transmitter release, characterized by being insensitive to nerve terminal depolarization and to transmembrane Ca2+ fluxes. This transmitter release has characteristics similar to that previously described for the release induced, at normal junctions, by 4-AQ.

Aminoquinolines↗
PubMed1983

A new type of transmitter release at the neuromuscular junction.

Examination of spontaneous miniature endplate potentials (MEPPs) in murine skeletal muscle has revealed that in conditions such as botulinum poisoning, during nerve terminal regeneration or in the presence of the drug 4-aminoquinoline, two types of acetylcholine release are responsible for the MEPPs. In addition to the MEPPs which correspond to the quantal component of a nerve impulse-evoked endplate potential a second type of acetylcholine release occurs. The latter type of transmitter release gives rise to MEPPs with a more prolonged time-to-peak and frequently a larger than normal amplitude. It is unaffected by nerve terminal depolarization and transmembrane Ca2+ fluxes. The relationship between MEPP frequency and temperature has a Q10 of about 12 compared to 2-3 for normal MEPPs. In botulinum-poisoned muscles this secretory type of transmitter release dominates, being exclusively present in muscles where nerve stimulation fails to release transmitter. In normal muscle such a release is induced by 4-aminoquinoline which may cause up to 45% of all the spontaneous MEPPs to be of that kind. It is suggested that the described spontaneous secretion of acetylcholine serves in inductory and neurotrophic function.

Acetylcholine↗
PubMed1983

Different effects of types A and B botulinum toxin on transmitter release at the rat neuromuscular junction.

Blockade of neuromuscular transmission was produced in the lower hind limb of the rat by local injection of either crystalline type A botulinum toxin or purified type B botulinum neurotoxin. At 1, 3, 5 and 7 days after injection, the extensor digitorum longus nerve-muscle preparation was excised and analyzed in vitro for alterations in spontaneous and nerve stimulus-evoked quantal transmitter release. Muscles receiving type A toxin were paralyzed up to and including 7 days after injection. Muscles treated with type B toxin, although completely paralyzed at 1 and 3 days, twitched in response to nerve stimulation at 5 and 7 days after injection. Both toxins induced a marked decrease in the frequency of miniature endplate potentials but type A did so to a greater extent. The remaining population of miniature endplate potentials contained a greater frequency of potentials with small or large amplitudes and prolonged rise times compared to normal muscle. These changes were more pronounced with type A toxin than with type B toxin. In the presence of alpha-dinitrophenol (1 mM), high frequency, fast-rising miniature endplate potentials of uniform size reappeared. High K+ (20 mM) was less effective in this respect. At 3 days after toxin injection nerve impulse evoked transmitter release was reduced more for type A treated muscles than for type B. However, 3,4-diaminopyridine, an agent which increases nerve-evoked transmitter release by increasing Ca2+ influx, was more effective in reversing the paralysis in type A than in type B-treated muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Aminopyridine↗
PubMed1982

Discrepancies between spontaneous and evoked synaptic potentials at normal, regenerating and botulinum toxin poisoned mammalian neuromuscular junctions.

Amplitudes and times to peak of spontaneous miniature endplate potentials (m.e.p.ps) and evoked quantal endplate potentials (e.p.ps) were compared at normal, regenerating and botulinum toxin poisoned neuromuscular junctions of the extensor digitorum longus muscle of the rat. At normal junctions the mean time to peak of m.e.p.ps was longer and more variable than that of similar-sized e.p.ps. At endplates where nerve regeneration was induced by mechanical crushing of the motor nerve the frequency of m.e.p.ps was reduced and their amplitude distribution was broader than normal. The distribution of times to peak of m.e.p.ps was considerably broader than that of quantal e.p.ps recorded at the same endplates. At neuromuscular junctions poisoned with botulinum toxin type A, spontaneous and evoked transmitter release were greatly reduced. The amplitude distribution of m.e.p.ps was wider than that of e.p.ps and the time to peak of e.p.ps was about twice as fast as and less variable than that of m.e.p.ps. To explain the observed differences in time to peak among m.e.p.ps and between m.e.p.ps and quantal e.p.ps we suggest that some m.e.p.ps, but not e.p.ps, originate from transmitter quanta released from sites at a greater distance from postsynaptic receptors or that the release or diffusion process for acetylcholine is more prolonged when producing some of the m.e.p.ps. Such mechanisms produce at normal junctions a small population of m.e.p.ps with prolonged times to peak, at regenerating junctions a greater proportion of such m.e.p.ps and in botulinum toxin poisoning a majority.

Animals↗
PubMed1982

4-aminoquinoline-induced 'giant' miniature endplate potentials at mammalian neuromuscular junctions.

4-Aminoquinoline (4-AQ) in concentrations around 200 micrometers induces, within minutes of its application to isolated mouse or rat neuromuscular junctions, the appearance of a population of miniature endplate potentials (m.e.p.ps) with a larger than normal amplitude, so-called giant m.e.p.ps (g.m.e.p.ps). With amplitudes 2-12 times the modal value of m.e.p.p. amplitude, the population of g.m.e.p.ps varied between 15 and 45% of the total population of m.e.p.ps. There was no increase in the frequency of m.e.p.ps but a positive correlation between the frequency of g.m.e.p.ps and the total frequency of m.e.p.ps. In many instances the rise time and decay time of g.m.e.p.ps were prolonged compared to normal. Elevated extracellular calcium concentrations increased the frequency of m.e.p.ps but had no effect on g.m.e.p.p. frequency. High extracellular potassium concentrations markedly increased m.e.p.p. frequency but failed to influence g.m.e.p.p. frequency. Similar observations were made with ethanol 0.1 M, ouabain 200 micrometers or black widow spider venom. Botulinum toxin type A markedly reduced total m.e.p.p. frequency but 4-AQ still induced g.m.e.p.ps. Nerve stimulation failed to release quanta corresponding to the g.m.e.p.ps. G.m.e.p.ps seemed to originate from quantal acetylcholine release from the nerve terminal since they were abolished by surgical denervation and by the addition of d-tubocurarine to the medium. Blockade of voltage-sensitive calcium or sodium channels by, respectively, manganese ions or tetrodotoxin failed to affect the appearance and the frequency of g.m.e.p.ps. The electrophysiological findings and a statistical analysis of the characteristics of the m.e.p.ps indicate that they belong to two populations. One population is accelerated by the depolarization-release coupling mechanism responsible for evoked transmitter release and is characterized by an amplitude distribution and a process in time that indicate that they correspond to releases occurring at 'active zones' in the nerve terminal. The second population of m.e.p.ps is uninfluenced by nerve terminal depolarization and transmembrane calcium fluxes. This population apparently originates from sites dispersed in the nerve terminal membrane and outside the 'active zones'. 4-AQ increases the frequency of this second m.e.p.p. population without affecting the first population.

Aminoquinolines↗
PubMed1982

Electronic properties of motor nerve terminals.

To obtain information about the electric membrane properties of frog motor nerve terminals we examined how depolarizing or hyperpolarizing current pulses of 2-8 ms duration to the preterminal, by electrotonic spread of potential, affected depolarization induced transmitter release. Sodium channels were blocked by tetrodotoxin. Under this condition a hyperpolarizing current pulse produced inhibition of release, followed by potentiation of release. Inhibition lasted more than 100 ms with a time constant of 50-150 ms. When, in addition, potassium channels were blocked by 3,4-diaminopyridine or tetraethylammonium a depolarizing current pulse potentiated transmitter release for a period up to 50 ms. The results imply that inward currents in the nerve terminal are carried mainly by sodium and calcium ions and outward currents by potassium ions while "leak" conductances are negligible. A low "leak" conductance and therefore a high specific membrane resistance facilitates the spread of electronic potentials and thereby explains the longlasting effects on transmitter release of brief current pulses to the preterminal.

4-Aminopyridine↗
PubMed1982

Giant miniature endplate potentials induced by 4-aminoquinoline.

In experiments on the isolated extensor digitorum longus muscle of the rat it was shown that 4-aminoquinoline (125-250 micro M) altered the amplitude distribution of spontaneous miniature endplate potentials to include a large portion of giant miniature endplate potentials with slow rise and decay times. Similar, slow-rising giant miniature endplate potentials were induced by the drug at neuromuscular junctions with regenerating nerve terminals, i.e. in a condition where spontaneous as well as evoked transmitter release is depressed. The appearance of giant miniature endplate potentials was not correlated with inhibition of cholinesterase since neostigmine (3 micro M) failed to induce such potentials. Nerve impulse evoked endplate potentials of amplitudes similar to the spontaneous giant miniature endplate potentials had a faster and more uniform rise time. The results suggest that 4-amino-quinoline, by a direct action on the nerve terminal, causes the release of larger than normal quanta of acetylcholine. Quantitative assays of acetylcholine released before and in the presence of 4-aminoquinoline gave similar values showing that the amounts of acetylcholine which give rise to the giant miniature potentials contribute little to the total amount of acetylcholine liberated.

Action Potentials↗