Freeze-fracture analysis of myelin membrane changes in Wallerian degeneration

The use of electrical stimulation to enhance recovery following peripheral nerve injury

Peripheral nerve injury is common and can have devastating consequences. In severe cases, functional recovery is often poor despite surgery. This is primarily due to the exceedingly slow rate of nerve regeneration at only 1-3 mm/day. The local environment in the distal nerve stump supportive of nerve regrowth deteriorates over time and the target end organs become atrophic. To overcome these challenges, investigations into treatments capable of accelerating nerve regrowth are of great clinical relevance and are an active area of research. One intervention that has shown great promise is perioperative electrical stimulation. Postoperative stimulation helps to expedite the Wallerian degeneration process and reduces delays caused by staggered regeneration at the site of nerve injury. By contrast, preoperative "conditioning" stimulation increases the rate of nerve regrowth along the nerve trunk. Over the past two decades, a rich body of literature has emerged that provides molecular insights into the mechanism by which electrical stimulation impacts nerve regeneration. The end result is upregulation of regeneration-associated genes in the neuronal body and accelerated transport to the axon front for regrowth. The efficacy of brief electrical stimulation on patients with peripheral nerve injuries was demonstrated in a number of randomized controlled trials on compressive, transection and traction injuries. As approved equipment to deliver this treatment is becoming available, it may be feasible to deploy this novel treatment in a wide range of clinical settings.

Preoperative Cryoneurolysis for Total Knee Arthroplasty: A Case Series

PURPOSE

The purpose of this pilot project case series is to describe the use of preoperative cryoneurolysis for 10 patients presenting for total knee arthroplasty (TKA).

DESIGN

Descriptive research design.

METHODS

Billing codes were used to identify 10 patients who had previously undergone TKA, preoperative cryoneurolysis and physical therapy (PT) at a Midwestern community hospital. Data collected included anesthetic management strategies, multimodal analgesic therapies, postanesthesia care unit pain scores (PACU), pain scores during physical therapy, and achievement of a range of motion during physical therapy.

FINDINGS

Nine of 10 patients who received preoperative cryoneurolysis had PACU pain scores of 0 (0-10 scale) up to 90 minutes postoperatively. Pain scores immediately following cryoneurolysis therapy were reduced in all patients reporting pain greater than 0 (1-10 pain scale) before their treatment. Increased active range of motion trends were noted with reports of decreased pain scores during postoperative physical therapy sessions.

CONCLUSIONS

This pilot project case series demonstrates potential benefits of using preoperative cryoneurolysis to provide postoperative pain control and aid with physical therapy recovery following TKA.

Axonotmesis-evoked plantar vasodilatation as a novel assessment of C-fiber afferent function after sciatic nerve injury in rats

Quantitative assessment of the recovery of nerve function, especially sensory and autonomic nerve function, remains a challenge in the field of nerve regeneration research. We previously found that neural control of vasomotor activity could be potentially harnessed to evaluate nerve function. In the present study, five different models of left sciatic nerve injury in rats were established: nerve crush injury, nerve transection/suturing, nerve defect/autografting, nerve defect/conduit repair, and nerve defect/non-regeneration. Laser Doppler perfusion imaging was used to analyze blood perfusion of the hind feet. The toe pinch test and walking track analysis were used to assess sensory and motor functions of the rat hind limb, respectively. Transmission electron microscopy was used to observe the density of unmyelinated axons in the injured sciatic nerve. Our results showed that axonotmesis-evoked vasodilatation in the foot 6 months after nerve injury/repair recovered to normal levels in the nerve crush injury group and partially in the other three repair groups; whereas the nerve defect/non-regeneration group exhibited no recovery in vasodilatation. Furthermore, the recovery index of axonotmesis-evoked vasodilatation was positively correlated with toe pinch reflex scores and the density of unmyelinated nerve fibers in the regenerated nerve. As C-fiber afferents are predominantly responsible for dilatation of the superficial vasculature in the glabrous skin in rats, the present findings indicate that axonotmesis-evoked vasodilatation can be used as a novel way to assess C-afferent function recovery after peripheral nerve injury. This study was approved by the Ethics Committee for Laboratory Animals of Nantong University of China (approval No. 20130410-006) on April 10, 2013.

Extrinsic cellular and molecular mediators of peripheral axonal regeneration

The ability of injured peripheral nerves to regenerate and reinnervate their original targets is a characteristic feature of the peripheral nervous system (PNS). On the other hand, neurons of the central nervous system (CNS), including retinal ganglion cell (RGC) axons, are incapable of spontaneous regeneration. In the adult PNS, axonal regeneration after injury depends on well-orchestrated cellular and molecular processes that comprise a highly reproducible series of degenerative reactions distal to the site of injury. During this fine-tuned process, named Wallerian degeneration, a remodeling of the distal nerve fragment prepares a permissive microenvironment that permits successful axonal regrowth originating from the proximal nerve fragment. Therefore, a multitude of adjusted intrinsic and extrinsic factors are important for surviving neurons, Schwann cells, macrophages and fibroblasts as well as endothelial cells in order to achieve successful regeneration. The aim of this review is to summarize relevant extrinsic cellular and molecular determinants of successful axonal regeneration in rodents that contribute to the regenerative microenvironment of the PNS.

Wallerian degeneration: the innate-immune response to traumatic nerve injury

Traumatic injury to peripheral nerves results in the loss of neural functions. Recovery by regeneration depends on the cellular and molecular events of Wallerian degeneration that injury induces distal to the lesion site, the domain through which severed axons regenerate back to their target tissues. Innate-immunity is central to Wallerian degeneration since innate-immune cells, functions and molecules that are produced by immune and non-immune cells are involved. The innate-immune response helps to turn the peripheral nerve tissue into an environment that supports regeneration by removing inhibitory myelin and by upregulating neurotrophic properties. The characteristics of an efficient innate-immune response are rapid onset and conclusion, and the orchestrated interplay between Schwann cells, fibroblasts, macrophages, endothelial cells, and molecules they produce. Wallerian degeneration serves as a prelude for successful repair when these requirements are met. In contrast, functional recovery is poor when injury fails to produce the efficient innate-immune response of Wallerian degeneration.

Deep-etch EM reveals that the early poxvirus envelope is a single membrane bilayer stabilized by a geodetic "honeycomb" surface coat

Three-dimensional "deep-etch" electron microscopy (DEEM) resolves a longstanding controversy concerning poxvirus morphogenesis. By avoiding fixative-induced membrane distortions that confounded earlier studies, DEEM shows that the primary poxvirus envelope is a single membrane bilayer coated on its external surface by a continuous honeycomb lattice. Freeze fracture of quick-frozen poxvirus-infected cells further shows that there is only one fracture plane through this primary envelope, confirming that it consists of a single lipid bilayer. DEEM also illustrates that the honeycomb coating on this envelope is completely replaced by a different paracrystalline coat as the poxvirus matures. Correlative thin section images of infected cells freeze substituted after quick-freezing, plus DEEM imaging of Tokuyasu-type cryo-thin sections of infected cells (a new application introduced here) all indicate that the honeycomb network on immature poxvirus virions is sufficiently continuous and organized, and tightly associated with the envelope throughout development, to explain how its single lipid bilayer could remain stable in the cytoplasm even before it closes into a complete sphere.

Early myelin breakdown following sural nerve crush: a freeze-fracture study

In this study we describe the early changes of the myelin sheath following surgical nerve crush. We used the freeze-fracture technique to better evaluate myelin alterations during an early stage of Wallerian degeneration. Rat sural nerves were experimentally crushed and animals were sacrificed by transcardiac perfusion 30 h after surgery. Segments of the nerves were processed for routine transmission electron microscopy and freeze-fracture techniques. Our results show that 30 h after the lesion there was asynchrony in the pattern of Wallerian degeneration, with different nerve fibers exhibiting variable degrees of axon disruption. This was observed by both techniques. Careful examination of several replicas revealed early changes in myelin membranes represented by vacuolization and splitting of consecutive lamellae, rearrangement of intramembranous particles and disappearance of paranodal transverse bands associated or not with retraction of paranodal myelin terminal loops from the axolemma. These alterations are compatible with a direct injury to the myelin sheath following nerve crush. The results are discussed in terms of a similar mechanism underlying both axon and myelin breakdown.

Septohippocampal cholinergic axonal regeneration through peripheral nerve bridges: quantification and temporal development

Axons of the adult mammalian CNS have been shown to regrow vigorously into peripheral nerve grafts. Using a cholinergic septohippocampal model for adult CNS regeneration, involving complete denervation of the hippocampal formation from its basal forebrain cholinergic afferents, this study has established quantitative parameters and a temporal baseline of cholinergic fiber regeneration into the dorsal hippocampal tissue through a peripheral sciatic nerve graft. In nerve-implanted animals (i) the nerve grafts are maximally invaded by AChE-positive fibers between 2 weeks and 1 month postlesion, (ii) the fibers entering the hippocampal formation from the graft show a peak numerical increase and rate of elongation around the first month and/or in the proximal hippocampal region, (iii) an apparently normal innervation pattern and fiber density in the most rostral 1.5 mm of the dorsal hippocampal formation is reached by 6 months postlesion. The present study provides a basis for future quantitative comparisons of manipulations of different components of the system, e.g., the contributing neurons, the bridging material, and the receiving central nervous tissue. The temporal/spatial pattern of fiber regeneration suggests that the hippocampal CNS tissue can be a good axonal growth-promoting environment, albeit with temporal and/or spatial limitations, and is therefore not an immutably restrictive environment for axonal regeneration.

Lysophosphatidyl choline-induced demyelination. A freeze-fracture study

Focal demyelination was produced in the rat sciatic nerve by microinjection of lysophosphatidyl choline (LPC). The demyelinating lesion was examined over the following 48 h using the freeze-fracture technique to examine myelin, Schwann cell and axonal membranes. Myelin lamellae were replaced by myriad spherical or oval membranous vesicles. The axonal and Schwann cell plasma membranes remained intact and the latter showed a large increase in caveolae-associated pores in some nerve fibres. The lysis of myelin lamellae and membranous vesicle formation are related to the known action of LPC on myelin and its membrane fusogenic properties. The importance of calcium ion influx and membrane protein aggregation and depletion in vesiculation are discussed.