117 research outputs found
âCalcium bombs' as harbingers of synaptic pathology and their mitigation by magnesium at murine neuromuscular junctions
Excitotoxicity is thought to be an important factor in the onset and progression of amyotrophic lateral sclerosis (ALS). Evidence from human and animal studies also indicates that early signs of ALS include degeneration of motor nerve terminals at neuromuscular junctions (NMJs), before degeneration of motor neuron cell bodies. Here we used a model of excitotoxicity at NMJs in isolated mouse muscle, utilizing the organophosphorus (OP) compound omethoate, which inhibits acetylcholinesterase activity. Acute exposure to omethoate (100 ÎŒM) induced prolonged motor endplate contractures in response to brief tetanic nerve stimulation at 20â50 Hz. In some muscle fibers, Fluo-4 fluorescence showed association of these contractures with explosive increases in Ca(2+) (âcalcium bombsâ) localized to motor endplates. Calcium bombs were strongly and selectively mitigated by increasing Mg(2+) concentration in the bathing medium from 1 to 5 mM. Overnight culture of nerve-muscle preparations from Wld(S) mice in omethoate or other OP insecticide components and their metabolites (dimethoate, cyclohexanone, and cyclohexanol) induced degeneration of NMJs. This degeneration was also strongly mitigated by increasing [Mg(2+)] from 1 to 5 mM. Thus, equivalent increases in extracellular [Mg(2+)] mitigated both post-synaptic calcium bombs and degeneration of NMJs. The data support a link between Ca(2+) and excitotoxicity at NMJs and suggest that elevating extracellular [Mg(2+)] could be an effective intervention in treatment of synaptic pathology induced by excitotoxic triggers
Donepezil inhibits neuromuscular junctional acetylcholinesterase and enhances synaptic transmission and function in isolated skeletal muscle
BACKGROUND AND PURPOSE: Donepezil, a piperidine inhibitor of acetylcholinesterase (AChE) prescribed for treatment of Alzheimer's disease, has adverse neuromuscular effects in humans, including requirement for higher concentrations of nonâdepolarising neuromuscular blockers during surgery. Here, we examined the effects of donepezil on synaptic transmission at neuromuscular junctions (NMJs) in isolated nerveâmuscle preparations from mice. EXPERIMENTAL APPROACH: We measured effects of therapeutic concentrations of donepezil (10ânM to 1âÎŒM) on AChE enzymic activity, muscle force responses to repetitive stimulation, and spontaneous and evoked endplate potentials (EPPs) recorded intracellularly from flexor digitorum brevis muscles from CD01 or C57BlWld(S) mice. KEY RESULTS: Donepezil inhibited muscle AChE with an approximate IC(50) of 30ânM. Tetanic stimulation in subâmicromolar concentrations of donepezil prolonged postâtetanic muscle contractions. Preliminary Fluo4âimaging indicated an association of these contractions with an increase and slow decay of intracellular Ca(2+) transients at motor endplates. Donepezil prolonged spontaneous miniature EPP (MEPP) decay time constants by about 65% and extended evoked EPP duration almost threefold. The mean frequency of spontaneous MEPPs was unaffected but the incidence of âgiantâ MEPPs (gMEPPs), some exceeding 10âmV in amplitude, was increased. Neither mean MEPP amplitude (excluding gMEPPs), mean EPP amplitude, quantal content or synaptic depression during repetitive stimulation were significantly altered by concentrations of donepezil up to 1âÎŒM. CONCLUSION AND IMPLICATIONS: Adverse neuromuscular signs associated with donepezil therapy, including relative insensitivity to neuromuscular blockers, are probably due to inhibition of AChE at NMJs, prolonging the action of ACh on postsynaptic nicotinic acetylcholine receptors but without substantively impairing evoked ACh release
Difficulty accessing data from randomised trials of drugs for heart failure: a call for action
âCalcium bombsâ as harbingers of synaptic pathology and their mitigation by magnesium at murine neuromuscular junctions
Excitotoxicity is thought to be an important factor in the onset and progression of amyotrophic lateral sclerosis (ALS). Evidence from human and animal studies also indicates that early signs of ALS include degeneration of motor nerve terminals at neuromuscular junctions (NMJs), before degeneration of motor neuron cell bodies. Here we used a model of excitotoxicity at NMJs in isolated mouse muscle, utilizing the organophosphorus (OP) compound omethoate, which inhibits acetylcholinesterase activity. Acute exposure to omethoate (100 ÎŒM) induced prolonged motor endplate contractures in response to brief tetanic nerve stimulation at 20â50 Hz. In some muscle fibers, Fluo-4 fluorescence showed association of these contractures with explosive increases in Ca2+ (âcalcium bombsâ) localized to motor endplates. Calcium bombs were strongly and selectively mitigated by increasing Mg2+ concentration in the bathing medium from 1 to 5 mM. Overnight culture of nerve-muscle preparations from WldS mice in omethoate or other OP insecticide components and their metabolites (dimethoate, cyclohexanone, and cyclohexanol) induced degeneration of NMJs. This degeneration was also strongly mitigated by increasing [Mg2+] from 1 to 5 mM. Thus, equivalent increases in extracellular [Mg2+] mitigated both post-synaptic calcium bombs and degeneration of NMJs. The data support a link between Ca2+ and excitotoxicity at NMJs and suggest that elevating extracellular [Mg2+] could be an effective intervention in treatment of synaptic pathology induced by excitotoxic triggers
Synaptic withdrawal following nerve injury is influenced by postnatal maturity, muscle-specific properties, and the presence of underlying pathology in mice
Altered mitochondrial bioenergetics are responsible for the delay in Wallerian degeneration observed in neonatal mice
The construction and evaluation of a device for mechanomyography in anaesthetized Göttingen minipigs
OBJECTIVE: To devise a method for assessing evoked muscle strength on nerve stimulation [mechanomyography (MMG)] in the anaesthetized minipig. STUDY DESIGN: Prospective observational. ANIMALS: Sixty male Göttingen minipigs weighing 10.5â26.0 kg. METHODS: After cadaveric studies, a limb fixation device was constructed which allowed the twitch responses of the pelvic limb digital extensor muscles to be measured by force-displacement transduction in response to supramaximal train-of-four (TOF) stimulation of the common peroneal nerve. The device was tested in 60 minipigs weighing 10.5â26.0 kg positioned in dorsal recumbency. RESULTS: The technique recorded the MMG of the common peroneal-pelvic limb digital extensor nerve-muscle unit for up to 12 hours during which twitch height remained constant in 18 animals in which single twitch duration was <300â500 ms. In 42, in which twitch duration was >300â500 ms, 2 Hz nerve stimulation caused progressive baseline elevation (reverse fade) necessitating a modified signal capture method for TOF ratio (TOFR) computation. However, T1 was unaffected. The mean (range) of the TOFR in pigs with reverse fade was 1.2 (1.1â1.3). CONCLUSIONS AND CLINICAL RELEVANCE: The technique allowed MMG recording in unparalysed pigs in response to TOF nerve stimulation and revealed a hitherto unreported complication of MMG monitoring using TOF in animals: reverse fade. This complicated TOFR calculation
Modest and variable efficacy of pre-exposure hydroxocobalamin and dicobalt edetate in a porcine model of acute cyanide salt poisoning
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