Modelling the effect of ephaptic coupling on spike propagation in peripheral nerve fibres

Experimental and theoretical studies have shown that ephaptic coupling leads to the synchronisation and slowing down of spikes propagating along the axons within peripheral nerve bundles. However, the main focus thus far has been on a small number of identical axons, whereas realistic peripheral nerve bundles contain numerous axons with different diameters. Here, we present a computationally efficient spike propagation model, which captures the essential features of propagating spikes and their ephaptic interaction, and facilitates the theoretical investigation of spike volleys in large, heterogeneous fibre bundles. The spike propagation model describes an action potential, or spike, by its position on the axon, and its velocity. The velocity is primarily defined by intrinsic features of the axons, such as diameter and myelination status, but it is also modulated by changes in the extracellular potential. These changes are due to transmembrane currents that occur during the generation of action potentials. The resulting change in the velocity is appropriately described by a linearised coupling function, which is calibrated with a biophysical model. We first lay out the theoretical basis to describe how the spike in an active axon changes the membrane potential of a passive axon. These insights are then incorporated into the spike propagation model, which is calibrated with a biophysically realistic model based on Hodgkin-Huxley dynamics. The fully calibrated model is then applied to fibre bundles with a large number of axons and different types of axon diameter distributions. One key insight of this study is that the heterogeneity of the axonal diameters has a dispersive effect, and that with increasing level of heterogeneity the ephaptic coupling strength has to increase to achieve full synchronisation between spikes. Another result of this study is that in the absence of full synchronisation, a subset of spikes on axons with similar diameter can form synchronised clusters. These findings may help interpret the results of noninvasive experiments on the electrophysiology of peripheral nerves.

Differential adhesion regulates neurite placement via a retrograde zippering mechanism

During development, neurites and synapses segregate into specific neighborhoods or layers within nerve bundles. The developmental programs guiding placement of neurites in specific layers, and hence their incorporation into specific circuits, are not well understood. We implement novel imaging methods and quantitative models to document the embryonic development of the C. elegans brain neuropil, and discover that differential adhesion mechanisms control precise placement of single neurites onto specific layers. Differential adhesion is orchestrated via developmentally-regulated expression of the IgCAM SYG-1, and its partner ligand SYG-2. Changes in SYG-1 expression across neuropil layers result in changes in adhesive forces, which sort SYG-2-expressing neurons. Sorting to layers occurs, not via outgrowth from the neurite tip, but via an alternate mechanism of retrograde zippering, involving interactions between neurite shafts. Our study indicates that biophysical principles from differential adhesion govern neurite placement and synaptic specificity in vivo in developing neuropil bundles.

Myelin Basic Protein and Cardiac Sympathetic Neurodegeneration in Nonhuman Primates

Minimal myelination is proposed to be a contributing factor to the preferential nigral neuronal loss in Parkinson’s disease (PD). Similar to nigral dopaminergic neurons, sympathetic neurons innervating the heart have long, thin axons which are unmyelinated or minimally myelinated. Interestingly, cardiac sympathetic loss in PD is heterogeneous across the heart, yet the spatial relationship between myelination and neurodegeneration is unknown. Here, we report the mapping of myelin basic protein (MBP) expression across the left ventricle of normal rhesus macaques (n = 5) and animals intoxicated with systemic 6-OHDA (50 mg/kg iv) to model parkinsonian cardiac neurodegeneration (n = 10). A subset of 6-OHDA-treated rhesus received daily dosing of pioglitazone (5 mg/kg po; n = 5), a PPARγ agonist with neuroprotective properties. In normal animals, MBP-immunoreactivity (-ir) was identified surrounding approximately 14% of axonal fibers within nerve bundles of the left ventricle, with more myelinated nerve fibers at the base level of the left ventricle than the apex p < 0.014 . Greater MBP-ir at the base was related to a greater number of nerve bundles at that level relative to the apex p < 0.05 , as the percent of myelinated nerve fibers in bundles was not significantly different between levels of the heart. Cardiac sympathetic loss following 6-OHDA was associated with decreased MBP-ir in cardiac nerve bundles, with the percent decrease of MBP-ir greater in the apex (84.5%) than the base (52.0%). Interestingly, cardiac regions and levels with more MBP-ir in normal animals showed attenuated sympathetic loss relative to areas with less MBP-ir in 6-OHDA + placebo (r = −0.7, p < 0.014 ), but not in 6-OHDA + pioglitazone (r = −0.1) subjects. Our results demonstrate that myelination is present around a minority of left ventricle nerve bundle fibers, is heterogeneously distributed in the heart of rhesus macaques, and has a complex relationship with cardiac sympathetic neurodegeneration and neuroprotection.

Bovine bilateral mesenchymal hamartomas on the upper eyelid: A case report

A 2-day-old calf was presented with a bilateral mass in the medial canthus of the upper eyelid. The masses were removed surgically. The morphological diagnosis was a bilateral hamartoma characterised by an abnormal mixture of tissue indigenous to that area including blood vessels, striated muscle bundles, adipose tissue, isolated cartilage and nerve bundles. No recurrence developed in the 6 months following the surgical removal. Overall, although this congenital defect is relatively rare, it should be differentiated from eyelid tumours such as haemangiomas, squamous cell carcinomas, Meibomian gland tumours, dermoid cysts and teratomas in cattle.

A case report of palmar xanthoma with xanthomatous neuropathy

Xanthomas are plaques or nodules consisting of an accumulation of excess lipids, resulting in the formation of foam cells in the skin or tendons. Typically, xanthomas are not accompanied by other symptoms. Here, we report a patient with a presentation of painful palmar xanthomas and subsequent diagnosis of metabolic and cardiovascular morbidities. A 44-year-old man presented with multiple yellowish, firm, and painful nodules on his right palm and fingers. Lipid panel and medical examination revealed a diagnosis of type III hyperlipoproteinemia and diabetes mellitus type II. Histopathological examination of the lesions revealed numerous lipid-laden foamy cells surrounding the nerve bundles through the dermis. This unique presentation of painful xanthomas prior to the manifestation of more significant underlying conditions suggested that xanthomas might be used as early diagnostic indicators. Based on this case, we propose more thorough examinations of palmar xanthomas in patients for earlier detection of potentially lethal diseases.

The doctrine of neurons before the court of the newest researchers

The modern doctrine of neurons penetrated very quickly into the scientific consciousness of neurologists because of the clarity and definiteness of the basic provisions that clarify the pathways and methods of transmitting irritation in the nervous system. Based mainly on the Golgi method, it was, however, also consistent with the facts obtained using the methods of Gooden, Fleksig, Weigert, Marka as far as they concerned the course of nerve bundles; but the Golgi method had the advantage over the previous methods that it clarified the relationship of the nerve fiber to the cell and made it possible to follow the course and development of a particular fiber. In addition, the main provisions of this study were consistent with the development of nervous cells according to the research of Giss, with experimental physiology and clinical medicine, as well as with experimental pathology.

Posterior superior alveolar nerves contribute to sensation in the anterior teeth

There is no available data on the occurrence rate of a converged alveolar canal, the detailed three-dimensional (3D) courses of alveolar canals/grooves (ACGs), or the contribution of each superior alveolar nerve to each area in the maxilla. This study aimed to clarify the 3D courses of ACGs, the relationship between ACGs and superior alveolar nerves, and the contribution of posterior superior alveolar nerves (PSANs) using computed tomography (CT) with histological analysis. During the gross anatomy course at Niigata University, we investigated nine human cadavers. All anterior and posterior ACGs converged into the common alveolar canal, which contained blood vessels and several nerve bundles surrounded by perineurium, located at the nasal floor near the pyriform aperture. Histometrical analysis clarified that 16.3% of the nerve bundles in this canal were derived from PSANs, and 67% of the bundles were dispersed while they coursed down to the nasal floor. There seems to be no relationship between the density of nerve bundles in the canal and the number of remaining anterior teeth. Data obtained from observing the detailed 3D courses of anterior and posterior ACGs, and their relationship with superior alveolar nerves, suggests that PSANs partially contribute to the nociception of the anterior teeth.

Abstract 15228: Role of Sympathetic Innervation in the Pathogenesis of Abdominal Aortic Aneurysm

Introduction: The objective of this study is to understand the role of neurological factors, specifically those from the perivascular sympathetic nervous system (SNS), on the initiation and development of Abdominal Aortic Aneurysm (AAA). Hypothesis: We hypothesize that the formation of AAA is associated with the loss of perivascular SNS-induced vasoconstriction specific to the aneurysm region. Methods: We developed a rat Abdominal Aortic Denervation (AAD) model, where the infrarenal aorta of Spauge Dawley rats was denervated with surgical removal of nerve fibers and chemical denervation with 10% phenol ( Figure. A ). A sham control group was included where the infrarenal aorta was treated with PBS. The arteries were harvested at 1 month after the surgeries for histological assessment. Results: The denervated aortas exhibited significant thinning of the aortic wall including the media and the adventitia, compared to the sham controls ( Figure. B ). Moreover, degradation of elastin, demonstrated by the fragmentation of elastic fibers and the decreased number of lamellar units, was also observed in the dennervated aortas in comparison to the sham controls. While the control aortas were well innervated with perivascular nerve bundles adjacent to the adventitia, no nerves were found surrounding the denervated aortas, suggesting successful denervation. Conclusions: We generated an AAD model that could be used for mechanistic understanding and therapeutic development of AAA. The preliminary data suggest a direct link between the lack of aortic sympathetic innervation and AAA formation. Long-term studies are currently underway to further characterize changes in the aortic walls after sympathetic denervation. Figure. (A) Illustration of the denervated region on the rat infrarenal aorta. ( B ) Histological staining of control and denervated rat abdominal aortas at 1 month after surgery. Yellow stars: para-aortic nerve bundles. Scale bar = 200 μm.

Application of Cryopreservation Technique in the Preservation of Rat Limbs

Objective: This study aims to observe the physiological and pathological changes of severed fingers (limbs) under different storage conditions through animal experiments, and to screen out the best preservation conditions. Medthods: Sixty healthy adult male Sprague-Dawley rats were selected and evenly divided into 4 preservation groups, including conventional low-temperature dry (CLTD), the university of wisconsin (UW) solution, cryopreservation and cryopreservation + UW solution preservation group. After harvesting the limbs, were preservated for 72 h and 7 days, respectively. Then the limbs were thawed and replanted in situ. Sciatic nerves were collected for hematoxylin and eosin (HE) staining, and observed the changes in tissue morphology. Results: Replantation was successful in 11 out of 15 rats (73%) in cryopreservation + UW group, and the walking function of the 9 (82%) rats in cryopreservation + UW group were significantly better than that of the cryopreservation preservation group. In addition, the HE staining results shown that the CLTD group nerve bundles were morphologically damaged, and there were more acellular structures and tissue fragments; the UW group nerve bundles were less injured and the perineurium was more complete and orderly; The nerve bundles in the cryopreservation group and cryopreservation + UW group are tightly arranged and the tissue morphology is regular; Compared with the cryopreservation + UW group, the complete of the cryopreservation group is not well. Conclusions: The cryopreservation technology combined with UW solution is a new and effective method for the severed limbs preserving.