Fluoxetine is neuroprotective in slow-channel congenital myasthenic syndrome

Antagonistic postsynaptic and presynaptic actions of cyclohexanol on neuromuscular synaptic transmission and function

Intentional ingestion of agricultural organophosphorus insecticides is a significant public health issue in rural Asia, causing thousands of deaths annually. Some survivors develop a severe, acute or delayed myasthenic syndrome. In animal models, similar myasthenia has been associated with increasing plasma concentration of one insecticide solvent metabolite, cyclohexanol. We investigated possible mechanisms using voltage and current recordings from mouse neuromuscular junctions (NMJs) and transfected human cell lines. Cyclohexanol (10-25 mM) reduced endplate potential (EPP) amplitudes by 10-40% and enhanced depression during repetitive (2-20 Hz) stimulation by up to 60%. EPP decay was prolonged more than twofold. Miniature EPPs were attenuated by more than 50%. Cyclohexanol inhibited whole-cell currents recorded from CN21 cells expressing human postjunctional acetylcholine receptors (hnAChR) with an IC₅₀ of 3.74 mM. Cyclohexanol (10-20 mM) also caused prolonged episodes of reduced-current, multi-channel bursting in outside-out patch recordings from hnAChRs expressed in transfected HEK293T cells, reducing charge transfer by more than 50%. Molecular modelling indicated cyclohexanol binding (-6 kcal/mol) to a previously identified alcohol binding site on nicotinic AChR α-subunits. Cyclohexanol also increased quantal content of evoked transmitter release by ∼50%. In perineurial recordings, cyclohexanol selectively inhibited presynaptic K⁺ currents. Modelling indicated cyclohexanol binding (-3.8 kcal/mol) to voltage-sensitive K⁺ channels at the same site as tetraethylammonium (TEA). TEA (10 mM) blocked K⁺ channels more effectively than cyclohexanol but EPPs were more prolonged in 20 mM cyclohexanol. The results explain the pattern of neuromuscular dysfunction following ingestion of organophosphorus insecticides containing cyclohexanol precursors and suggest that cyclohexanol may facilitate investigation of mechanisms regulating synaptic strength at NMJs. KEY POINTS: Intentional ingestion of agricultural organophosphorus insecticides is a significant public health issue in rural Asia, causing thousands of deaths annually. Survivors may develop a severe myasthenic syndrome or paralysis, associated with increased plasma levels of cyclohexanol, an insecticide solvent metabolite. Analysis of synaptic transmission at neuromuscular junctions in isolated mouse skeletal muscle, using isometric tension recording and microelectrode recording of endplate voltages and currents, showed that cyclohexanol reduced postsynaptic sensitivity to acetylcholine neurotransmitter (reduced quantal size) while simultaneously enhancing evoked transmitter release (increased quantal content). Patch recording from transfected cell lines, together with molecular modelling, indicated that cyclohexanol causes selective, allosteric antagonism of postsynaptic nicotinic acetylcholine receptors and block of presynaptic K⁺ -channel function. The data provide insight into the cellular and molecular mechanisms of neuromuscular weakness following intentional ingestion of agricultural organophosphorus insecticides. Our findings also extend understanding of the effects of alcohols on synaptic transmission and homeostatic synaptic function.

Worsening of myasthenia due to antiepileptic, antipsychotic, antidepressant, and sedative medication: An estimation of risk based on reporting frequency

BACKGROUND AND PURPOSE

Many drugs can worsen myasthenia symptoms. The clinician usually relies on cautionary lists compiled according to case reports. We intended to provide a quantitative basis for a risk comparison within the groups of antiepileptic, antidepressant, neuroleptic, and sedative drugs.

METHODS

We extracted adverse drug reaction (ADR) counts (total and myasthenia related) for drugs from these groups and calculated the reporting odds ratio (ROR) within the drug groups from the World Health Organization pharmacovigilance database. For a given drug, the ROR was increased above 1 if the proportion of myasthenia-related ADRs for this drug was larger than the same proportion for the rest of drugs in that same group. If the 95% confidence interval of ROR was >1, this was taken as a signal for a higher risk of the given drug as compared to the average of the respective group.

RESULTS

Gabapentin, sertraline, citalopram, lithium, and amisulpride had a signal for the ROR to be increased above 1 within their respective groups. Bupropion, desvenlafaxine, duloxetine, escitalopram, and paroxetine had ROR values <1. For all other drugs, 1 was within the ROR confidence interval.

CONCLUSIONS

For gabapentin and lithium, the analysis of RORs confirmed case reports and cautionary lists. For a number of antidepressant drugs associated with a higher-than-average risk, no case reports exist substantiating our results. For these drugs, special attention should be paid to this risk. The remarkable difference between citalopram and escitalopram could prompt experimental work to confirm differential influence of the two preparations on neuromuscular transmission.

Utility of Rapid Exome Sequencing in the Diagnosis of a Rare Congenital Myasthenic Syndromes in a Preterm Infant

Congenital myasthenic syndromes (CMS) are rare and challenging diagnoses in preterm neonates. We presented in this case report a preterm infant with recurrent extubation failures. An exhaustive workup to rule out common etiologies of chronic ventilator dependence was negative including a neostigmine trial, acetylcholine receptor antibodies, and chromosomal microarray. Electromyography (EMG) showed features of a neuromuscular junction defect. After ruling out metabolic, inflammatory, and immune mediated causes, a rapid exome sequencing demonstrated CHRNB1 gene mutation diagnostic of autosomal dominant slow channel CMS. The patient was started on fluoxetine and nebulized salbutamol with a gradual improvement in her respiratory function over time with minimal ventilator support.

A rare mutation in the COLQ gene causing congenital myasthenic syndrome with remarkable improvement to fluoxetine: A case report

Congenital myasthenic syndromes (CMS) are genetically determined heterogenous disorders of neuromuscular transmission. We report a rare mutation of COLQ causing CMS in an Asian man that remarkably improved with fluoxetine. A 51-year-old Sri Lankan man with slowly progressive fatigable muscle weakness since eight years of age, presented with type 2 respiratory failure that required mechanical ventilation in the acute crisis and subsequent home-based non-invasive ventilation. His birth and family histories were unremarkable. On examination, he had limb girdle type of muscle weakness with fatigability and normal tendon reflexes with no ocular or bulbar involvement. DNA sequencing revealed a pathogenic homozygous mutation in COLQ gene: ENST00000383788.10:exon16:c.1228C>T:p.R410W, the first report in an Asian. Treatment with fluoxetine resulted in remarkable improvement and regain of muscle power and independence from assisted ventilation.

Fluoxetine-mediated inhibition of endoplasmic reticulum stress is involved in the neuroprotective effects of Parkinson's disease

Background: Accumulating evidence suggests that Fluoxetine (FLX), an anti-depressant drug, has broad neurobiological functions and neuroprotective effects in central nervous system injury, but its roles in Parkinson's disease (PD) remain unclear. In this study, we aimed to evaluate whether fluoxetine attenuates rotenone-induced neurodegeneration in PD.

Methods: Male Sprague-Dawley rats were randomly allocated to control, rotenone-treated, rotenone + FLX-treated and FLX-treated groups. Behavioral tests including open field behavioral test and catalepsy measurement were taken to evaluate neurological behavioral measurements. Apoptosis was detected by TUNEL assay. Endoplasmic reticulum (ER)-related gene expressions were detected by qRT-PCR and western blot. Immunohistochemistry was performed to assess dopaminergic neuronal degeneration.

Results: We demonstrated that pretreatment with FLX (10.0 mg/kg, i.p.) significantly ameliorated the catalepsy symptom and increased locomotor activity. In addition, FLX markedly reversed the loss of dopaminergic neurons and suppressed the X‑box‑binding protein 1 (XBP1)/caspase-3-activated ER stress. Furthermore, FLX inhibited rotenone-mediated neurodegeneration through caspase-3-mediated neuronal apoptosis.

Conclusion: Taken together, our findings indicate that FLX has beneficial neuroprotective effects in PD and FLX might be a potential therapeutic agent for the treatment of PD. In light of its favorable properties, FLX should be evaluated in the treatment of PD as well as related neurologic disorders.

Animal Models of the Neuromuscular Junction, Vitally Informative for Understanding Function and the Molecular Mechanisms of Congenital Myasthenic Syndromes

The neuromuscular junction is the point of contact between motor nerve and skeletal muscle, its vital role in muscle function is reliant on the precise location and function of many proteins. Congenital myasthenic syndromes (CMS) are a heterogeneous group of disorders of neuromuscular transmission with 30 or more implicated proteins. The use of animal models has been instrumental in determining the specific role of many CMS-related proteins. The mouse neuromuscular junction (NMJ) has been extensively studied in animal models of CMS due to its amenability for detailed electrophysiological and histological investigations and relative similarity to human NMJ. As well as their use to determine the precise molecular mechanisms of CMS variants, where an animal model accurately reflects the human phenotype they become useful tools for study of therapeutic interventions. Many of the animal models that have been important in deconvolving the complexities of neuromuscular transmission and revealing the molecular mechanisms of disease are highlighted.

Gonorazky H, Cohn RD, Campbell C. Treating pediatric neuromuscular disorders: The future is now

Pediatric neuromuscular diseases encompass all disorders with onset in childhood and where the primary area of pathology is in the peripheral nervous system. These conditions are largely genetic in etiology, and only those with a genetic underpinning will be presented in this review. This includes disorders of the anterior horn cell (e.g., spinal muscular atrophy), peripheral nerve (e.g., Charcot-Marie-Tooth disease), the neuromuscular junction (e.g., congenital myasthenic syndrome), and the muscle (myopathies and muscular dystrophies). Historically, pediatric neuromuscular disorders have uniformly been considered to be without treatment possibilities and to have dire prognoses. This perception has gradually changed, starting in part with the discovery and widespread application of corticosteroids for Duchenne muscular dystrophy. At present, several exciting therapeutic avenues are under investigation for a range of conditions, offering the potential for significant improvements in patient morbidities and mortality and, in some cases, curative intervention. In this review, we will present the current state of treatment for the most common pediatric neuromuscular conditions, and detail the treatment strategies with the greatest potential for helping with these devastating diseases.

Effects of the antidepressant mirtazapine and zinc on nicotinic acetylcholine receptors

Nicotinic acetylcholine receptors (nAChRs) and zinc are associated with regulation of mood and related disorders. In addition, several antidepressants inhibit muscle and neuronal nAChRs and zinc potentiates inhibitory actions of them. Moreover, mirtazapine (a noradrenergic, serotonergic and histaminergic antidepressant) inhibits muscarinic AChRs and its effects on nAChRs are unknown. Therefore, we studied the modulation of muscle α1β1γd nAChRs expressed in oocytes and native α7-containing nAChRs in hippocampal interneurons by mirtazapine and/or zinc, using voltage-clamp techniques. The currents elicited by ACh in oocytes (at -60 mV) were similarly inhibited by mirtazapine in the absence and presence of 100 μM zinc (IC₅₀ ∼15 μM); however, the ACh-induced currents were stronger inhibited with 20 and 50 μM mirtazapine in the presence of zinc. Furthermore, the potentiation of ACh-induced current by zinc in the presence of 5 μM mirtazapine was 1.48 ± 0.06, and with 50 μM mirtazapine zinc potentiation did not occur. Interestingly, in stratum radiatum interneurons (at -70 mV), 20 μM mirtazapine showed less inhibition of the current elicited by choline (Ch) than at 10 μM (0.81 ± 0.02 and 0.74 ± 0.02 of the Ch-induced current, respectively). Finally, the inhibitory effects of mirtazapine depended on membrane potential: 0.81 ± 0.02 and 0.56 ± 0.05 of the control Ch-induced current at -70 and -20 mV, respectively. These results indicate that mirtazapine interacts with muscle and neuronal nAChRs, possibly into the ion channel; that zinc may increase the sensitivity of nAChRs to mirtazapine; and that mirtazapine decreases the sensitivity of nAChRs to zinc.