Regulation Of Neurotransmission Research Articles

Cannabinoids and Mental Health, Part 1: The Endocannabinoid System and Exogenous Cannabinoids.

The increasing public acceptance of cannabis and the proliferation of cannabis products in the marketplace has coincided with more patients using the drug as a substitute for psychiatric medications or as an adjunctive treatment modality for psychiatric conditions, despite limited evidence of efficacy. With a goal of furthering harm-reduction efforts in psychiatric nursing, the current article reviews the fundamentals of the endocannabinoid system in humans and the exogenous phytocannabinoids that act on this regulatory neurotransmitter system. The basics of cannabis botany are also reviewed to help nurse clinicians understand the heterogeneous nature of cannabis products. This foundational knowledge will help improve clinical interactions with patients who use cannabis and provide the necessary understanding of cannabinoids needed to undertake further scientific query into their purported benefits in psychiatric disease states. [Journal of Psychosocial Nursing and Mental Health Services, 57(9), 7-10.].

Total Polysaccharides of Lily Bulb Ameliorate Menopause-Like Behavior in Ovariectomized Mice: Multiple Mechanisms Distinct from Estrogen Therapy.

Our previous study has demonstrated the effects of aqueous extract of lily bulb in alleviating menopause-related psychiatric symptoms in ovariectomized (OVX) mice. This study sought to further investigate the psychotropic effects of total polysaccharides of lily bulb (TPLB) against anxiety, depression, and cognitive deterioration and the underlying mechanisms in OVX mice using behavioral, neurochemical, molecular, and proteomic approaches in comparison with estrogen therapy. While TPLB and estradiol showed similar effects in reducing OVX-induced anxiety, depression, and cognitive impairment, the psychotropic effects of TPLB were more closely associated with the predominant activation of estrogen receptors (ERs) and regulation of brain regional neurotransmitters and neurotrophins with minor effects on the uterus. Estradiol had similar potencies in binding affinity at ERα and ERβ, which caused widespread genetic and epigenetic effects. In contrast, TPLB displayed a higher affinity at ERβ than ERα, triggering the specific Ras/Akt/ERK/CREB signaling pathway without affecting any epigenetic activity. TPLB additionally modulated multiple proteins associated with mitochondrial oxidative stress, but estradiol did not. These results indicate that TPLB has comparable efficacy in reducing menopause-associated neuropsychological symptoms with a better safety profile compared to estrogen therapy. We suggest that TPLB could serve as a novel agent for menopause syndrome.

Synthesis and characterization of novel radiofluorinated probes for positron emission tomography imaging of monoamine oxidase B.

Monoamine oxidase B (MAO-B), predominantly expressed in glial cells, plays an important role in neurotransmitter regulation, and MAO-B activity relates to several neuronal diseases. Here, we aimed to develop a radiofluorinated MAO-B imaging probe based on the structure of a selective MAO-B inhibitor, MD-230254. We synthesized and evaluated a series of compounds in vitro and in vivo. A series of fluorinated analogs of MD-230254 were synthesized and evaluated for inhibitory potency and selectivity toward MAO-B. 5-[4-(2-[18 F]Fluorobenzyloxy)phenyl]-3-(2-cyanoethyl)-1,3,4-oxadiazol-2(3H)-one (2-[18 F]FBPO) was synthesized from a corresponding tributylstannyl precursor and [18 F]CH3 COOF. Biodistribution after intravenous injection of 2-[18 F]FBPO was evaluated in male ddY mice with or without pretreatment by inhibitors. Among the compounds synthesized and evaluated, 2-FBPO showed high inhibitory potency and selectivity toward MAO-B comparable with MD-230254. 2-[18 F]FBPO was successfully synthesized by an electrophilic reaction with a high radiochemical purity of more than 99%. 2-[18 F]FBPO was efficiently taken up by the brain and showed rapid blood clearance, which provided a brain/blood radioactivity ratio of 3.7 at 90 minutes postinjection. The brain radioactivity was significantly decreased by pretreatment with an MAO-B selective inhibitor. The great potential of 2-[18 F]FBPO as an MAO-B imaging probe, applicable to a variety of diseases, is indicated.

Neurotransmitter regulation of luteinizing hormone and prolactin secretion

Neurotransmitter regulation of luteinizing hormone and prolactin secretion

Proteomics of the mediodorsal thalamic nucleus of rats with stress-induced gastric ulcer.

BACKGROUNDStress-induced gastric ulcer (SGU) is one of the most common visceral complications after trauma. Restraint water-immersion stress (RWIS) can cause serious gastrointestinal dysfunction and has been widely used to study the pathogenesis of SGU to identify medications that can cure the disease. The mediodorsal thalamic nucleus (MD) is the centre integrating visceral and physical activity and contributes to SGU induced by RWIS. Hence, the role of the MD during RWIS needs to be studied.AIMTo screen for differentially expressed proteins in the MD of the RWIS rats to further elucidate molecular mechanisms of SGU.METHODSMale Wistar rats were selected randomly and divided into two groups, namely, a control group and an RWIS group. Gastric mucosal lesions of the sacrificed rats were measured using the erosion index and the proteomic profiles of the MD were generated through isobaric tags for relative and absolute quantitation (iTRAQ) coupled with two-dimensional liquid chromatography and tandem mass spectrometry. Additionally, iTRAQ results were verified by Western blot analysis.RESULTSA total of 2853 proteins were identified, and these included 65 dysregulated (31 upregulated and 34 downregulated) proteins (fold change ratio ≥ 1.2). Gene Ontology (GO) analysis showed that most of the upregulated proteins are primarily related to cell division, whereas most of the downregulated proteins are related to neuron morphogenesis and neurotransmitter regulation. Ingenuity Pathway Analysis revealed that the dysregulated proteins are mainly involved in the neurological disease signalling pathways. Furthermore, our results indicated that glycogen synthase kinase-3 beta might be related to the central mechanism through which RWIS gives rise to SGU.CONCLUSIONQuantitative proteomic analysis elucidated the molecular targets associated with the production of SGU and provides insights into the role of the MD. The underlying molecular mechanisms need to be further dissected.

Role of ketogenic diet in pediatric epilepsy

Pediatric epileptic seizures occupy a significant place in the current nosology of neurological syndromes. Most effected population with seizures is children and elderly and less affected are adults. Role of diet is plays an important part in reducing the severity of symptoms, most significant diet is ketogenic, which has been used from 1921 as a best treatment option. Composition of ketogenic diet (KD) includes highest ratio of fat, moderate ratio of protein and lowest ratio of carbohydrates. Combination of energy giving nutrients in this ratio induces the ketosis which leads to reduction in the initiation of seizures. Ketogenic diet participates in various mechanisms i.e. regulation of neurotransmitters, limiting glycolysis pathway, tri-carboxylic-acid cycle and oxidation of polyunsaturated fatty acid; induces the anti-seizures responses. Numerous nutrients also showing the positive potential against epileptic seizures. But continues and very strict adherence to ketogenic diet causes some adverse effects on human body disrupting the normal mechanism of body. The focus of this review is on the pediatric epilepsy and modification in symptoms with the application of the ketogenic diet

Family of protein fragments promises fresh view of Alzheimer's disease

Neuroscientist Joris de Wit was pretty sure he was on the right track as he homed in on a receptor for a potentially beneficial brain molecule. Known as sAPPalpha (soluble amyloid precursor protein alpha), the molecule is a seemingly benevolent sibling to amyloid beta, the peptide that forms clumps in the brains of people with Alzheimer's disease. De Wit's confidence grew when he received a call from his structural biologist collaborators. “Something is actually happening,” they told him. sAPPalpha (red), expressed here in mice, seems to have beneficial effects on the brain. In experiments in mouse models of Alzheimer’s disease, sAPPalpha expression improves memory (dendritic neuron processes shown in green). Image credit: Heidelberg University Institute of Pharmacy and Molecular Biotechnology/Max Richter and Ulrike Muller. For months, the group had been stymied—the receptor motif they were trying to characterize was floppy and unstructured. Then they decided to add a short peptide corresponding to a region of sAPPalpha. The receptor motif and peptide zipped together, and a model of the structure emerged. The resulting study, recently published in Science (1), shows that sAPPalpha binds to a receptor for the neurotransmitter glutamate, modulating the transmission of neural signals across synapses. The findings suggest that sAPPalpha can quell excess neurotransmission and thereby contribute to brain health. They also offer further clues of the part a special class of protein fragments plays in the development of Alzheimer’s disease. A hardy cadre of researchers is looking to understand the precise inner workings of amyloid precursor protein (APP) and its assorted fragments, including sAPPalpha—and what happens to those fragments when things go awry. Progress is slow and piecemeal in this potentially key subfield of Alzheimer’s research—and has been for years. Slowly, the picture is becoming clearer. One idea is that APP is a regulator of neurotransmission, explains …

Development of chimeric and bifunctional antagonists for CLR/RAMP receptors.

CGRP, adrenomedullin (ADM), and adrenomedullin 2 (ADM2) family peptides are important neuropeptides and hormones for the regulation of neurotransmission, vasotone, cardiovascular morphogenesis, vascular integrity, and feto‒placental development. These peptides signal through CLR/RAMP1, 2 and 3 receptor complexes. CLR/RAMP1, or CGRP receptor, antagonists have been developed for the treatment of migraine headache and osteoarthritis pain; whereas CLR/RAMP2, or ADM receptor, antagonists are being developed for the treatment of tumor growth/metastasis. Based on the finding that an acylated chimeric ADM/ADM2 analog potently stimulates CLR/RAMP1 and 2 signaling, we hypothesized that the binding domain of this analog could have potent inhibitory activity on CLR/RAMP receptors. Consistent with this hypothesis, we showed that acylated truncated ADM/ADM2 analogs of 27–31 residues exhibit potent antagonistic activity toward CLR/RAMP1 and 2. On the other hand, nonacylated analogs have minimal activity. Further truncation at the junctional region of these chimeric analogs led to the generation of CLR/RAMP1-selective antagonists. A 17-amino-acid analog (Antagonist 2–4) showed 100-fold selectivity for CLR/RAMP1 and was >100-fold more potent than the classic CGRP receptor antagonist CGRP8-37. In addition, we showed (1) a lysine residue in the Antagonist 2–4 is important for enhancing the antagonistic activity, (2) an analog consisted of an ADM sequence motif and a 12-amino-acid binding domain of CGRP exhibits potent CLR/RAMP1-inhibitory activity, and (3) a chimeric analog consisted of a somatostatin analog and an ADM antagonist exhibits dual activities on somatostatin and CLR/RAMP receptors. Because the blockage of CLR/RAMP signaling prevents migraine pain and suppresses tumor growth/metastasis, further studies of these analogs, which presumably have better access to the tumor microenvironment and nerve endings at the trigeminal ganglion and synovial joints as compared to antibody-based therapies, may lead to the development of better anti-CGRP therapy and alternative antiangiogenesis therapy. Likewise, the use of bifunctional somatostatin-ADM antagonist analogs could be a promising strategy for the treatment of high-grade neuroendocrine tumors by targeting an antiangiogenesis agent to the neuroendocrine tumor microenvironment.

Phenotypic distinctions between the nodose and jugular TRPV1-positive vagal sensory neurons in the cynomolgus monkey.

Vagal capsaicin-sensitive afferent C-fibers play an important role in the maintenance of visceral homeostasis and contribute to symptoms in visceral diseases. Based on their developmental origin two functionally distinct types of vagal C-fibers are recognized: those with neurons in the vagal nodose ganglia (derived from epibranchial placodes) and in the vagal jugular ganglia (from neural crest). Studies in nonprimate species demonstrated that the vagal nodose and jugular C-fibers differ in activation profile, neurotrophic regulation, and expression of neurotransmitters. We hypothesized that the expression of selected markers related to key phenotypic properties of vagal C-fibers in the cynomolgus monkey is similar to that reported in nonprimate species. We performed single-cell RT-PCR on nodose and jugular putative C-fiber (TRPV1-positive) neurons isolated from the cynomolgus monkey. We found that the expression of purinergic P2X receptors that underlie selective responsiveness of nodose C-fiber terminals to ATP was conserved in that P2X2 and P2X3 subunits were expressed in nodose, but only P2X3 subunit was expressed in jugular TRPV1-positive neurons. Also conserved was the preferential expression of neurotrophic receptor TrkB in the nodose and preprotachykinin-A in the jugular TRPV1-positive neurons. Several key distinctions in gene expression between nodose and jugular TRPV1-positive (C-fiber) neurons that have been noted in mice, rats, and guinea pigs, are conserved in the cynomolgus monkey. Our results support the translatability of distinct vagal C-fiber phenotypes to primates.

Lipid Metabolism Crosstalk in the Brain: Glia and Neurons.

Until recently, glial cells have been considered mainly support cells for neurons in the mammalian brain. However, many studies have unveiled a variety of glial functions including electrolyte homeostasis, inflammation, synapse formation, metabolism, and the regulation of neurotransmission. The importance of these functions illuminates significant crosstalk between glial and neuronal cells. Importantly, it is known that astrocytes secrete signals that can modulate both presynaptic and postsynaptic function. It is also known that the lipid compositions of the pre- and post-synaptic membranes of neurons greatly impact functions such as vesicle fusion and receptor mobility. These data suggest an essential lipid-mediated communication between glial cells and neurons. Little is known, however, about how the lipid metabolism of both cell types may interact. In this review, we discuss neuronal and glial lipid metabolism and suggest how they might interact to impact neurotransmission.

Elevated synaptic vesicle release probability in synaptophysin/gyrin family quadruple knockouts.

This article has been through an editorial process in which the authors decide how to respond to the issues raised during peer review. The Reviewing Editor's assessment is that all the issues have been addressed (see decision letter).

Loss of Neurogenesis in Aging Hydra.

In Hydra the nervous system is composed of neurons and mechanosensory cells that differentiate from interstitial stem cells (ISCs), which also provide gland cells and germ cells. The adult nervous system is actively maintained through continuous de novo neurogenesis that occurs at two distinct paces, slow in intact animals and fast in regenerating ones. Surprisingly Hydra vulgaris survive the elimination of cycling interstitial cells and the subsequent loss of neurogenesis if force‐fed. By contrast, H. oligactis animals exposed to cold temperature undergo gametogenesis and a concomitant progressive loss of neurogenesis. In the cold‐sensitive strain Ho_CS, this loss irreversibly leads to aging and animal death. Within four weeks, Ho_CS animals lose their contractility, feeding response, and reaction to light. Meanwhile, two positive regulators of neurogenesis, the homeoprotein prdl‐a and the neuropeptide Hym‐355, are no longer expressed, while the “old” RFamide‐expressing neurons persist. A comparative transcriptomic analysis performed in cold‐sensitive and cold‐resistant strains confirms the downregulation of classical neuronal markers during aging but also shows the upregulation of putative regulators of neurotransmission and neurogenesis such as AHR, FGFR, FoxJ3, Fral2, Jagged, Meis1, Notch, Otx1, and TCF15. The switch of Fral2 expression from neurons to germ cells suggests that in aging animals, the neurogenic program active in ISCs is re‐routed to germ cells, preventing de novo neurogenesis and impacting animal survival.

Systematic Review of Basic Research on Alzheimer's Disease with Shen Zhi Ling Oral Liquid.

Objective The present report systematically reviewed the basic research of Shen Zhi Ling oral liquid (Tiao Xin preparation) treatment on Alzheimer's disease (AD). Methods CNKI, Wanfang, and VIP were searched, and the literature was selected according to inclusion and exclusion criteria. Data were extracted, and descriptive analysis was used. Results Twenty-four articles were included, all of which were published as “Tiao Xin preparation.” There were seven types of AD models involved. The mechanism of action of Shen Zhi Ling oral liquid in the treatment of AD primarily included suppression of Aβ deposition and tau hyperphosphorylation, regulation of multiple neurotransmitters, improvement in energy metabolism, and promotion of the expression of autophagy-related and learning-memory-associated proteins. Conclusions AD is a complex disease caused by multiple factors. Shen Zhi Ling oral liquid exhibited multiple and multitarget effects and great potential for treating AD. The continuous development of molecular biology and related disciplines will further elucidate the mechanism of Shen Zhi Ling oral liquid intervention in AD.

Loss of DmGluRA exacerbates age-related sleep disruption and reduces lifespan

Declines in sleep amount and quality—characterized by excessive daytime sleepiness and an inability to sleep at night—are common features of aging. Sleep dysfunction is also associated with age-related ailments and diseases, suggesting that sleep is functionally relevant to the aging process. Metabotropic glutamate receptors (mGluRs)—which are critical regulators of neurotransmission and synaptic plasticity—have been implicated in both age-related disease and sleep regulation. Therefore, in this study, we examined the sleep and aging effect of complete genetic loss of mGluR signaling in Drosophila melanogaster. Genetic knockdown of the sole Drosophila mGluR—known as DmGluRA—reduced daytime wakefulness and nighttime sleep, recapitulating age-related sleep changes that occur across species. Furthermore, loss of DmGluRA significantly reduced lifespan and exacerbated age-related sleep loss in older flies. Thus, we identify DmGluRA as a novel regulator of sleep whose loss results in an age-relevant sleep phenotype that is associated with shortened lifespan. This is the first evidence that mGluR signaling regulates sleep/wake in a manner that is relevant to the aging process.

Antidepressant Effects of Crocin‐1 from Saffron in Mice with Chronic Unpredictable Mild Stress‐Induced Depression

AimDepression is a severe disorder that has enormous consequences for the individual's quality of life, and it is among the most prevalent forms of mental illness. Saffron, a famous herb medicine and spice in the world, has been suggested as a potential efficacious and tolerable treatment for depression and anxiety, while there is no study about the effect of crocin‐1 on depression and a few studies about the mechanism of saffron. So the aim of this study was to investigate the effects of crocin‐1, one of the most important active compounds in saffron, on chronic unpredictable mild stress (CUMS) induced depression in mice.MethodsThe effects of crocin‐1 were examined using CUMS induced depression ICR mice and factors including depressant‐like behaviors, neurotransmitters, the expression of MKP‐1, CREB and BDNF.ResultsOur data showed that crocin‐1 significantly prevented reduction of body weight induced by CUMS. Oral administration of crocin‐1 (10, 20, and 40mg/kg) markedly improved depressant‐like behaviors, increasing the latency and reducing the immobility time in both the tail suspension test and forced swimming tests, compared with the CUMS mice. Enzyme‐linked immunosorbent (Elisa) assay were performed on serum and it showed that crocin‐1 treatment not only restored the decreased neurotransmitter concentrations of dopamine (DA) and serotonin (5‐HT), but also increased the level of mBDNF and decreased proBDNF. The results of reverse transcription‐polymerase chain reaction and Elisa assay showed that crocin‐1 decreased the level of MKP‐1 mRNA and MKP‐1 expression in hippocampus, moreover, it also increased the level of BDNF mRNA expression and CREB mRNA expression.ConclusionTaken together, our study confirmed that crocin‐1 might have an antidepressant‐like effect in the CUMS model of depression in mice, and suggest it might be mediated by regulation of neurotransmitters, activation MKP‐1/CREB/BDNF pathway and balanced the ratio of proBDNF and mBDNF.Support or Funding InformationThis work was supported by Natural Science Foundation of China (81703688), China Postdoctoral Science Foundation (2016M592016) and Key Project of Science and Technology Department of Zhejiang Province (2015C02032).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Regulation of SNARE‐Dependent Membrane Fusion by Alpha‐Synuclein

Neurotransmitter release is a foundation of all thoughts in central nervous system. Communication between these neurons is mediated by the release and uptake of neurotransmitters through vesicle fusion at the synapses. The SNARE (Soluble N-ethylmaleimide-sensitive factor Attachment Protein Receptor) proteins are believed to mediate neurotransmitter release by promoting fusion of neurotransmitter laden presynaptic vesicle with the presynaptic membrane. Defects in the regulation of neurotransmission are believed to be the primary cause for many neurological diseases. The key to a better understanding of neurological diseases may lie in a more complete understanding of the molecular machine responsible for synaptic vesicle fusion. Alpha-synuclein (αS) has long been a protein of great interest because of its pathological aggregation in neuronal plaque and Lewy bodies which are associated with Parkinson's Disease and Lewy Bodies Dementia, respectively. Despite its medical significance, the normal function of αS has been elusive. αS is a 14 kDa soluble protein, abundantly present (several μM) in the presynapse. Thus, not surprisingly, αS has been found to play roles in various aspects of vesicle recycling. Very interestingly, however, αS has emerged as an important regulator for SNARE-dependent vesicle fusion. We used an in vitro single-vesicle fusion assay which allowed for the precise variation of the αS concentration. This assay provided the opportunity to dissect the impact of αS on individual vesicle fusion steps such as docking and lipid mixing along the membrane fusion pathway. The assay is effective in analyzing single fusion events in a natural, millisecond timescale between vesicle and a supported-bilayer. Using this assay, we have found that αS enhances vesicle docking by a factor of 10 at excessive 20 μM which is as much as 4 times higher than a normal cellular concentration. Detailed analysis reveals that the effect of αS on SNARE-dependent membrane fusion is largely on vesicle docking with no significant changes in lipid mixing observed. It also suggests that αS plays a role in accelerating and stabilizing large fusion pore formation. αS may be pathologically involved in neurological diseases, but it also is a crucial SNARE regulator by enhancing presynaptic vesicle docking and stabilizing the membrane fusion pore. αS may be pathologically involved in neurological diseases, but it also is a crucial SNARE regulator This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Electroceutical Residue-Free Graphene Device for Dopamine Monitoring and Neural Stimulation.

The simultaneous neural signal monitoring and stimulation can allow accurate neurotransmitter regulation for patients in various degrees of neural degeneration disorders. Here, we developed a residue-free graphene device as an effective electrical neural interface for dopamine sensing and secretion. We demonstrated the ultrasensitive dopamine sensing of residue-free graphene devices cultured with PC12 cells and the on-demand functional electrical stimulation for electroceutical applications. The doping effect of graphene by the released dopamine from living cells was confirmed from the electrical current change. The dopamine release could be also quantitatively analyzed by ELISA. Then, Ca2+ ion-dependent dopamine release was optically observed by fluorescence microscopy during the stimulation. Taken together, this study confirms the feasibility of graphene surface as a neural interface for electroceutical applications to various central nerve system disorders.

The human-microbiome superorganism and its modulation to restore health

Microbiome is the community of microorganism that co-live with a host. The human being is the result of the integration of its genome and the coexistence with millions of microorganisms throughout its evolutionary history. Human-microbiome association can be considered a step of integration in evolution, constituting a superorganism. Many emergent diseases are related to the loss of part of this microbiome and its restoration can be achieved by different strategies. Gut microbiome imbalance is particularly associated with numerous inflammatory, immune and nervous system-related diseases by a communication pathway called microbiome–brain axis. Modulation of microbiome by administering prebiotics, like arabinoxylans, and synbiotics is a plausible treatment for dysbiosis, the regulation of neurotransmitters and alleviation of neurological manifestations.

Usefulness of COMT gene polymorphisms in North African populations

The COMT gene encodes for catechol-O-methyl-transferase, an enzyme playing a major role in regulation of synaptic catecholamine neurotransmitters. Investigating 4 markers of the COMT gene (rs2020917, rs4818, rs4680, rs9332377) in 6 Tunisian populations and a pool of Libyans. Our objective was to determine the distribution of allelic, genotypic and haplotypic frequencies by comparison to other populations of the 1000 genomes project and 59 populations from the Kidd Lab dataset.The allelic frequencies established for these SNPs in the North African populations are similar to those of Europeans and South Asians. Linkage disequilibrium between these SNPs and haplotypes frequencies are different between populations whose clustering in principal components analysis (PCA) according to their geographic origin was more significant using haplotypic frequencies.COMT activity prediction by haplotypes genotyping could be limited to rs4818-rs4680 micro-haplotypes. The Low activity haplotype (CG) displays the highest frequency in African populations (55%), in the 59 Kidd Lab populations we found also that Sub-Saharan Africans, Native Americans, and some East Asian and Pacific Island populations all have frequencies in the 50–81% range for (CG) where as its lowest frequency was found in Europeans (10%), this results have been also confirmed for Southwest Asians. North Africans and South Asians with intermediate frequencies have approximately similar values (20% and 25%). Europeans show the highest frequencies of haplotypes with predicted High and Medium activity in contrast to Africans. North Africans and South Asians present similar results for all the category of the COMT activity prediction by haplotypes genotyping.The high level of genetic diversity of COMT haplotypes, not only allows distinction between populations according to their history settlement, origin and ethnicity, it constitutes a basis for studies of association of the COMT gene polymorphism with pathologies, drugs response and for forensic investigation in North African populations.

Reorganization of Septins Modulates Synaptic Transmission at Neuromuscular Junctions

Septins (Sept) are highly conserved Guanosine-5'-triphosphate (GTP)-binding cytoskeletal proteins involved in neuronal signaling in the central nervous system but their involvement in signal transmission in peripheral synapses remains unclear. Sept5 and Sept9 proteins were detected in mouse peripheral neuromuscular junctions by immunofluorescence with a greater degree of co-localization with presynaptic than postsynaptic membranes. Preincubation of neuromuscular junction preparations with the inhibitor of Sept dynamics, forchlorfenuron (FCF), decreased co-localization of Sept with presynaptic membranes. FCF introduced ex vivo or in vivo had no effect on the amplitude of the spontaneous endplate currents (EPCs), indicating the absence of postsynaptic effects of FCF. However, FCF decreased acetylcholine (ACh) quantal release in response to nerve stimulation, reduced the amplitude of evoked quantal currents and decreased the number of quanta with long synaptic delays, demonstrating the presynaptic action of FCF. Nevertheless, FCF had no effect on the amplitude of calcium transient in nerve terminals, as detected by calcium-sensitive dye, and slightly decreased the ratio of the second response amplitude to the first one in paired-pulse experiments. These results suggest that FCF-induced decrease in ACh quantal secretion is not due to a decrease in Ca2+ influx but is likely related to the impairment of later stages occurring after Ca2+ entry, such as trafficking, docking or membrane fusion of synaptic vesicles. Therefore, Sept9 and Sept5 are abundantly expressed in presynaptic membranes, and disruption of Sept dynamics suppresses the evoked synchronous and delayed asynchronous quantal release of ACh, strongly suggesting an important role of Sept in the regulation of neurotransmission in peripheral synapses.