460 research outputs found
Neurobiology of the Axon in Health and Disease
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
A Closer Look at Axon Enterprise
No full textabstract: Axon Enterprise, Inc. is a publicly traded company founded in Scottsdale, Arizona in 1993. The company went public on June 7th, 2001. The inspiration for this topic is our interest in equity research. We believe that understanding how to fundamentally research a company is not only beneficial for our careers, but for our own personal financial learning. One thing that stood out about Axon was its dominant control of the stun gun market. Axon captures around 90%.. Because of this, we wanted to dive deeper. Surely, this has to be a good investment. What company owns almost all of the market share but isn’t a good investment? In our heads, none. But that wasn’t enough. We wanted to dive deeper and examine the fundamental business mechanisms of the firm to determine for ourselves why this is, and why we believe the company really does have tremendous growth potential. By connecting with Axon executives, developing an investment thesis, and understanding the fundamental business drivers behind Axon, we will develop a thorough understanding of Axon’s financial standing. Our goals; fundamental analysis of Axon, determine a one year price target, convince readers that Axon is a rewarding and appealing investment opportunity
Human intraretinal myelination: Axon diameters and axon/myelin thickness ratios
No full textPurpose: Human intraretinal myelination of ganglion cell axons occurs in about 1% of the population. We examined myelin thickness and axon diameter in human retinal specimens containing myelinated retinal ganglion cell axons. Materials and Methods: Two eyes containing myelinated patches were prepared for electron microscopy. Two areas were examined in one retina and five in the second retina. Measurements were compared to normal retinal and optic nerve samples and the rabbit retina, which normally contains myelinated axons. Measurements were made using a graphics tablet. Results: Mean axon diameter of myelinated axons at all locations were significantly larger than unmyelinated axons (P ≤ 0.01). Myelinated axons within the patches were significantly larger than axons within the optic nerve (P < 0.01). The relationship between axon diameter/fiber diameter (the G-ratio) seen in the retinal sites differed from that in the nerve. G-ratios were higher and myelin thickness was positively correlated to axon diameter (P < 0.01) in the retina but negatively correlated to axon diameter in the nerve (P < 0.001). Conclusion: Intraretinally myelinated axons are larger than non-myelinated axons from the same population and suggests that glial cells can induce diameter changes in retinal axons that are not normally myelinated. This effect is more dramatic on intraretinal axons compared with the normal transition zone as axons enter the optic nerve and these changes are abnormal. Whether intraretinal myelin alters axonal conduction velocity or blocks axonal conduction remains to be clarified and these issues may have different clinical outcomes
Embryonic axon guidance: insights from Drosophila and other insects
No full textDuring embryonic development, growing axons are guided by cellular signaling pathways that control a series of individual axon guidance decisions. In Drosophila, two major pathways (Netrin-Frazzled/DCC and Slit-Robo) regulate axon guidance in the embryonic ventral nerve cord, including the critical decision of whether or not to cross the midline. Studies in the fruit fly have revealed a complex picture of precise regulation and cross-talk between these pathways. In addition, Robo receptors in Drosophila have diversified their activities to regulate additional axon guidance decisions in the developing embryo. Here, I discuss recent advances in understanding roles and regulation of the Net-Fra and Slit-Robo signaling pathways in Drosophila, and examine the evolutionary conservation of these signaling mechanisms across insects and other arthropods
HODGKIN–HUXLEY AXON IS MADE OF MEMRISTORS
No full textThis paper presents a rigorous and comprehensive nonlinear circuit-theoretic foundation for the memristive Hodgkin-Huxley Axon Circuit model. We show that the Hodgkin-Huxley Axon comprises a potassium ion-channel memristor and a sodium ion-channel memristor, along with some mundane circuit elements. From this new perspective, many hitherto unresolved anomalous phenomena and paradoxes reported in the literature are explained and clarified. The yet unknown nonlinear dynamical mechanisms which give birth to the action potentials remain hidden within the memristors, and the race is on for uncovering the ultimate truth. [ABSTRACT FROM AUTHOR
Cytolinker Gas2L1 regulates axon morphology through microtubule-modulated actin stabilization
No full textCrosstalk between the actin and microtubule cytoskeletons underlies cellular morphogenesis. Interactions between actin filaments and microtubules are particularly important for establishing the complex polarized morphology of neurons. Here, we characterized the neuronal function of growth arrest-specific 2-like 1 (Gas2L1), a protein that can directly bind to actin, microtubules and microtubule plus-end-tracking end binding proteins. We found that Gas2L1 promotes axon branching, but restricts axon elongation in cultured rat hippocampal neurons. Using pull-down experiments and in vitro reconstitution assays, in which purified Gas2L1 was combined with actin and dynamic microtubules, we demonstrated that Gas2L1 is autoinhibited. This autoinhibition is relieved by simultaneous binding to actin filaments and microtubules. In neurons, Gas2L1 primarily localizes to the actin cytoskeleton and functions as an actin stabilizer. The microtubule-binding tail region of Gas2L1 directs its actin-stabilizing activity towards the axon. We propose that Gas2L1 acts as an actin regulator, the function of which is spatially modulated by microtubules.</p
Squid giant axon contains neurofilament protein mRNA but does not synthesize neurofilament proteins
No full textAuthor Posting. © The Author(s), 2016. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Cellular and Molecular Neurobiology 37 (2017): 475-486, doi:10.1007/s10571-016-0382-z.When isolated squid giant axons are incubated in radioactive amino acids, abundant newly synthesized proteins are found in the axoplasm. These proteins are translated in the adaxonal Schwann cells and subsequently transferred into the giant axon. The question as to whether any de novo protein synthesis occurs in the giant axon itself is difficult to resolve because the small contribution of the proteins possibly synthesized intra-axonally is not easily distinguished from the large amounts of the proteins being supplied from the Schwann cells. In this paper we reexamine this issue by studying the synthesis of endogenous neurofilament (NF) proteins in the axon. Our laboratory previously showed that NF mRNA and protein is present in the squid giant axon, but not in the surrounding adaxonal glia. Therefore, if the isolated squid axon could be shown to contain newly synthesized NF protein de novo, it could not arise from the adaxonal glia. The results of experiments in this paper show that abundant 3H-labeled NF protein is synthesized in the squid giant fiber lobe containing the giant axon’s neuronal cell bodies, but despite the presence of NF mRNA in the giant axon, no labeled NF protein is detected in the giant axon. This lends support to the Glia-Axon Protein Transfer Hypothesis which posits that the squid giant axon obtains newly synthesized protein by Schwann cell transfer and not through intra-axonal protein synthesis, and further suggests that the NF mRNA in the axon is in a translationally repressed state.This research was supported by the Intramural Research Program of the NIH2017-05-2
Regulation of axon growth by the JIP1-AKT axis
No full textThe polarisation of developing neurons to form axons and dendrites is required for the establishment of neuronal connections leading to proper brain function. The protein kinase AKT and the MAP kinase scaffold protein JNK-interacting protein-1 (JIP1) are important regulators of axon formation. Here we report that JIP1 and AKT colocalise in axonal growth cones of cortical neurons and collaborate to promote axon growth. The loss of AKT protein from the growth cone results in the degradation of JIP1 by the proteasome, and the loss of JIP1 promotes a similar fate for AKT. Reduced protein levels of both JIP1 and AKT in the growth cone can be induced by glutamate and this coincides with reduced axon growth, which can be rescued by a stabilized mutant of JIP1 that rescues AKT protein levels. Taken together, our data reveal a collaborative relationship between JIP1 and AKT that is required for axon growth and can be regulated by changes in neuronal activity. © 2014. Published by The Company of Biologists Ltd
Hydrogen with water addition: an exergy analysis of the internal combustion engine
No full textData availability statement:
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.The internal combustion engine is likely to be used for on- and off-road vehicles for many years yet, but the push to cease using fossil fuels is strong. Hydrogen is a possible alternative fuel with both advantages and disadvantages, so understanding and quantifying the efficiency losses of burning hydrogen are important. The limits to efficiency and the compromises needed to reduce losses can be investigated using exergy analysis. This analysis of a boosted lean-burn neat hydrogen spark ignition engine investigates exergetic processes under real-world engine operating conditions. Using a two-zone combustion model to study in-cylinder processes, the results suggest exergy transfer to work improves with increasing air dilution by diverting exhaust exergy to reversible work. Injecting water could potentially control emissions through in-cylinder thermo-physical property changes. For an equivalence ratio of 0.45 with 5% water addition, the exergy transfers to heat and work decrease by 12% and 7%, respectively. Conversely, the exergy transfers to combustion-related irreversibility and exhaust rise by 2% and 81%, respectively. However, it was shown that increasing manifold air pressures and compression ratios increases the quantity of exergy directed to work and heat, while reducing exergy expelled to exhaust. This exergy analysis of a hydrogen-fueled spark ignition engine operating under real-world parameters shows the need to optimize water injection as the trade-off between engine performance and emission reductions. Understanding the fundamentals of the thermodynamic mechanisms of work loss may inform engineering improvements to minimize exergy losses and increase efficiency and work output.The author(s) declare that no financial support was received for the research and/or publication of this article
Postnatal development of vibrissae motor output following neonatal infraorbital nerve manipulation
No full textUsing the model of infraorbital nerve (IoN) injury, we have studied the role IoN signals have on the developing vibrissal motor system. To this end, in ten rats, the IoN was severed on the day of birth: in five rats, the IoN was repaired to promote axon regeneration (Reinnervated group) while axon regeneration was prevented in the remaining five rats (Deafferented group). In another five rats, the isolated IoN was left intact (Sham group) and still another group of five rats was left untouched (Control group). After these rats had reached adulthood, the compound muscle action potential (MAP) was recorded from the vibrissa muscle and intracortical microstimulation (ICMS)-evoked movements were mapped in the frontal cortex contralateral to the operated side. We found: (i) no difference between Control, Sham and Reinnervated groups in the integrated MAPs and in the size and excitability of the M1 vibrissal representation. (ii) the Deafferented group showed a 42.9% decrease in the integrated MAP plus a 47.2% and 36.9% reduction, respectively, in the size and excitability of the M1 vibrissae representation. We conclude that, during perinatal life, IoN signals regulate the development of both the peripheral and central vibrissal motor system and that IoN reinnervation restores sensory signals able to stabilize normal development of the vibrissal motor system
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