Neurofilament-histomorphometry comparison in the evaluation of unmyelinated axon regeneration following peripheral nerve injury: An alternative to electron microscopy

Combination of stem cells and nerve guide conduit for the treatment of peripheral nerve injury: A meta-analysis

INTRODUCTION/AIMS

Many small-sized, single-center preclinical studies have investigated the benefits of introducing stem cells into the interior of nerve conduit. The aims of this meta-analysis are to review and contrast the effects of various types of stem cells in in vivo models used to reconstruct peripheral nerve injuries (PNIs) and to assess the reliability and stability of the available evidence.

METHODS

A systematic search was conducted using Cochrane Library, Embase, PubMed, and Web of Science to identify studies conducted from January 1, 2000, to September 21, 2022, and investigate stem cell therapy in peripheral nerve reconstruction animal models. Studies that met the relevant criteria were deemed eligible for this meta-analysis.

RESULTS

Fifty-five preclinical studies with a total of 1234 animals were incorporated. Stem cells demonstrated a positive impact on peripheral nerve regeneration at different follow-up times in the forest plots of five outcome indicators: compound muscle action potential (CMAP) amplitude, latency, muscle mass ratio, nerve conduction velocity, and sciatic functional index (SFI). In most comparisons, stem cell groups showed substantial differences compared with the control groups. The superior performance of adipose-derived stem cells (ADSCs) in terms of SFI, CMAP amplitude, and latency (p < .001) was identified.

DISCUSSION

The findings consistently demonstrated a favorable outcome in the reconstruction process when utilizing different groups of stem cells, as opposed to control groups where stem cells were not employed.

Deletion of CD47 from Schwann cells and macrophages hastens myelin disruption/dismantling and scavenging in Schwann cells and augments myelin debris phagocytosis in macrophages

BACKGROUND

Myelin that surrounds axons breaks in trauma and disease; e.g., peripheral nerve and spinal cord injuries (PNI and SCI) and multiple sclerosis (MS). Resulting myelin debris hinders repair if not effectively scavenged by Schwann cells and macrophages in PNI and by microglia in SCI and MS. We showed previously that myelin debris evades phagocytosis as CD47 on myelin ligates SIRPα (signal regulatory protein-α) on macrophages and microglia, triggering SIRPα to inhibit phagocytosis in phagocytes. Using PNI as a model, we tested the in vivo significance of SIRPα-dependent phagocytosis inhibition in SIRPα null mice, showing that SIRPα deletion leads to accelerated myelin debris clearance, axon regeneration and recovery of function from PNI. Herein, we tested how deletion of CD47, a SIRPα ligand and a cell surface receptor on Schwann cells and phagocytes, affects recovery from PNI.

METHODS

Using CD47 null (CD47-/-) and wild type mice, we studied myelin disruption/dismantling and debris clearance, axon regeneration and recovery of function from PNI.

RESULTS

As expected from CD47 on myelin acting as a SIRPα ligand that normally triggers SIRPα-dependent phagocytosis inhibition in phagocytes, myelin debris clearance, axon regeneration and function recovery were all faster in CD47-/- mice than in wild type mice. Unexpectedly compared with wild type mice, myelin debris clearance started sooner and CD47-deleted Schwann cells displayed enhanced disruption/dismantling and scavenging of myelin in CD47-/- mice. Furthermore, CD47-deleted macrophages from CD47-/- mice phagocytosed more myelin debris than CD47-expressing phagocytes from wild type mice.

CONCLUSIONS

This study reveals two novel normally occurring CD47-dependent mechanisms that impede myelin debris clearance. First, CD47 expressed on Schwann cells inhibits myelin disruption/dismantling and debris scavenging in Schwann cells. Second, CD47 expressed on macrophages inhibits myelin debris phagocytosis in phagocytes. The two add to a third mechanism that we previously documented whereby CD47 on myelin ligates SIRPα on macrophages and microglia, triggering SIRPα-dependent phagocytosis inhibition in phagocytes. Thus, CD47 plays multiple inhibitory roles that combined impede myelin debris clearance, leading to delayed recovery from PNI. Similar inhibitory roles in microglia may hinder recovery from other pathologies in which repair depends on efficient phagocytosis (e.g., SCI and MS).

Donor and Recipient Nerve Axon Counts in Gender-affirming Radial Forearm Phalloplasty: Informing Choice of Nerve Coaptations

A key component of success of a nerve transfer is the innervation density, which is directly affected by the donor nerve axonal density and donor-to-recipient (D:R) axon ratio. Optimal D:R axon ratio for a nerve transfer is quoted at 0.7:1 or greater. In phalloplasty surgery, there are currently minimal data available to help inform selection of donor and recipient nerves, including unavailability of axon counts.

Methods

Five transmasculine people who underwent gender-affirming radial forearm phalloplasty had nerve specimens processed with histomorphometric evaluation to determine axon counts and approximate donor-to-recipient axon ratios.

Results

Mean axon counts for recipient nerves were 6957 ± 1098 [the lateral antebrachial (LABC)], 1866 ± 590 [medial antebrachial (MABC)], and 1712 ± 121 [posterior antebrachial cutaneous (PABC)]. Mean axon counts for donor nerves were 2301 ± 551 [ilioinguinal (IL)] and 5140 ± 218 [dorsal nerve of the clitoris (DNC)]. D:R axon ratios using mean axon counts were DNC:LABC 0.739 (0.61-1.03), DNC:MABC 2.754 (1.83-5.91), DNC:PABC 3.002 (2.71-3.53), IL:LABC 0.331 (0.24-0.46), IL:MABC 1.233 (0.86-1.17), and IL:PABC 1.344 (0.85-1.82).

Conclusions

The DNC is the more powerful donor nerve with greater than two times the axon count of the IL. The IL nerve may be under-powered to re-innervate the LABC based on an axon ratio consistently less than 0.7:1. All other mean D:R are more than 0.7:1. DNC axon counts may be excessive for re-innervation of the MABC or PABC alone with D:R of more than 2.5:1, potentially increasing risk of neuroma formation at the coaptation site.

THE EFFECTS OF CURCUMIN AND BLUEBERRY ON AXONAL REGENERATION AFTER PERIPHERAL NERVE INJURY

The purpose of this study was to analyze the axonal regeneration and therapeutic effects of curcumin and blueberry administration following peripheral nerve injury using stereological, electron microscopic and electrophysiological methods. Animals in were assigned into one of four groups - control (Cont), injury (Inj), injury+curcumin (Cur) and injury+blueberry (Blue). Following the induction of sciatic nerve crush injury (75 Newtons for 5sec) in the Inj, Cur, and Blue groups, the rats in the Cur group received intraperitoneal injection of 30mg/kg curcumin (Sigma C1386) and the rats in the Blue group received 4g/kg blueberry by gavage over a four-week period. The rats in the Cont and Inj groups were not exposed to any substance. All animals were given standard chow. Sciatic functional index analyses were performed on the 14^th and 28^th days after injury, and electromyography (EMG) results were recorded. Stereological analysis of the nerve was performed under light microscopy. Light and electron microscopies were used for the histopathological evaluation of the sciatic nerve. Analysis of myelinated axon numbers revealed no significant differences between the Inj group and the Cur and Blue groups. However, a significant difference was observed between the Blue and Inj groups in terms of axonal areas. EMG test results differed between the Blue and the Inj groups (p<0.05), but no significant difference was observed between the Inj and Cur groups. Electron microscopic analysis revealed protective effects of curcumin and blueberry treatment after injury. The use of the curcumin and blueberry may represent a supportive approach to the protection of nerve fibers after peripheral nerve crush injury.

How many nerve fibers innervate the human glans clitoris: a histomorphometric evaluation of the dorsal nerve of the clitoris

INTRODUCTION

It is frequently quoted in mainstream media that the clitoris has "8000 nerve endings." However, no study has yet quantified the number of nerve fibers (axons) innervating the human clitoris. The dorsal nerves of the clitoris (DNCs) are the primary source of sensation and somatic clitoral innervation. Therefore, reporting the number of axons in the DNCs is an important step in our understanding of clitoral innervation and sexual response with implications for many fields of medical practice. The purpose of this study is to quantify the mean number of axons in the human DNCs and to report the approximate mean number of nerve fibers that innervate the human glans clitoris.

METHODS

DNC samples were obtained from 7 transmasculine patients undergoing gender-affirming phalloplasty surgery. At the time of nerve coaptation, a small excess of the DNC (5 mm) was collected for analysis at the proximal level of the clitoral body, just distal of the emergence of the DNCs from underneath the pubic symphysis. Samples were placed into 3% glutaraldehyde fixative, postfixed in 1% osmium tetroxide, and serially dehydrated in ethanol and toluene. Samples were then embedded in araldite, sectioned on an ultramicrotome into 1-μm cross sections, and counterstained with 1% toluidine blue. Histomorphometric evaluation was performed at 1000x magnification with a Leitz Laborlux S microscope and image analysis software (Clemex Vision Professional) to obtain an axon counts. Descriptive statistics were performed to yield a mean and standard deviation of the number of axons in the DNCs. Assuming anatomic symmetry between bilateral DNCs, mean total number of somatic nerve fibers innervating the human glans clitoris was obtained by doubling the mean count of the DNCs.

RESULTS

Seven sample DNCs were collected. Of those, 5 were analyzed as 2 did not have sufficient nerve tissue present. The mean number of nerve fibers in the human DNCs was 5140 (SD = 218.4). The mean number of myelinated nerve fibers innervating the human clitoris was 10,281 (SD = 436.8).

CONCLUSION

This study is the first to report the number of axons in the human DNC, at a mean 5140. Given the bilateral nature of clitoral innervation and symmetry of anatomic structures, the approximate mean number of myelinated axons that innervate the human glans clitoris is 10,280. When the uncaptured unmyelinated fibers and contributions from the cavernosal innervation are accounted for, it is clear that far Moree than 8000 axons innervate the human clitoris.

TISSUE EXPRESSION OF NEURONAL PROTEINS DURING SCIATIC NERVE REGENERATION AND INFLUENCE OF DIFFERENT SPECTRUM LASER RADIATION

OBJECTIVE

Aim: To determine the effect of laser irradiation of different spectrum on the expression of neuronal proteins (GFAP, S100, NSE and NF-L) in the sciatic nerve during its regeneration after crossing and surgical suturing.

PATIENTS AND METHODS

Materials and methods: The experiment was performed on 60 laboratory rats of the Wistar line (200-250 g) with crossing of the left sciatic nerve and sutur¬ing with an epineural suture end to end 30 minutes after neurotomy. 90 days later, an immunohistochemical study was performed using specific antibodies (Thermo Fisher Scientific; USA).

RESULTS

Results: A study of the marker of non-myelin Schwann GFAP cells showed their pronounced activation with germination in nerve thickness and the formation of weaves of processes around regenerated nerve fibers. The number of S-100-positive myelin Schwann cells decreased, the heterogeneity of their color and the loss of processes were determined. It showed a general decrease in the intensity of NSE- and NF-L-positive staining of nerve fibers regenerated after neurotomy, which was less pronounced when irradiated with a laser with a wavelength of 450-480 nm and 520 nm.

CONCLUSION

Conclusions: In general, the use of laser radiation had a positive effect on the repair of nerve fibers after neurotomy. According to the immunohistochemical study of neuromarkers, the effect of laser irradiation of the blue spectrum was the most effective.

Anatomic Comparison of Recipient Nerves for Deep Inferior Epigastric Perforator Flap Neurotization: A Randomized Control Trial

INTRODUCTION

Although neurotization has the potential to improve sensory outcomes after autologous breast reconstruction, this technique remains controversial. There is debate regarding the clinical outcomes and the recipient nerve of choice. This histoanatomical study aims to quantitatively compare the sensory components of the recipient nerves involved in neurotization of the deep inferior epigastric perforator flap.

METHODS

Subjects undergoing bilateral autologous breast reconstruction were enrolled. Transected nerve specimens underwent immunohistochemical staining with antibodies against neurofilament 1 and choline acetyltransferase for total and motor neurons within the axons, respectively. Photomicrographs were captured, and axons were analyzed using ImageJ. Sensory axons were calculated as equal to the difference between the total and cholinergic axonal counts.

RESULTS

Thirty-eight nerves from 19 subjects were included. The overall mean sensory axon count was 1246.3 (±1171.9) in the lateral cutaneous branch (LCB) of the fourth intercostal nerve and 1123.8 (±1213.0) in the anterior cutaneous branch (ACB) of the third intercostal nerve.The fourth LCB presented with an additional 10.9% sensory axonal count (P > 0.05). On average, sensory fibers constituted 36.7% and 31.7% of all fibers in the third ACBs and fourth LCBs, respectively.

CONCLUSIONS

This study provides anatomic and histological evidence that the fourth LCB and third ACB contain comparable mean numbers of sensory axons. Both constitute adequate recipient nerves for coaptation in deep inferior epigastric perforator reinnervation to achieve optimal sensory return after breast reconstruction. The fourth LCB should be preferable when the third ACB remains intact to preserve any native breast flap sensation.

Long-gap peripheral nerve repair through sustained release of a neurotrophic factor in nonhuman primates

Severe injuries to peripheral nerves are challenging to repair. Standard-of-care treatment for nerve gaps >2 to 3 centimeters is autografting; however, autografting can result in neuroma formation, loss of sensory function at the donor site, and increased operative time. To address the need for a synthetic nerve conduit to treat large nerve gaps, we investigated a biodegradable poly(caprolactone) (PCL) conduit with embedded double-walled polymeric microspheres encapsulating glial cell line–derived neurotrophic factor (GDNF) capable of providing a sustained release of GDNF for >50 days in a 5-centimeter nerve defect in a rhesus macaque model. The GDNF-eluting conduit (PCL/GDNF) was compared to a median nerve autograft and a PCL conduit containing empty microspheres (PCL/Empty). Functional testing demonstrated similar functional recovery between the PCL/GDNF-treated group (75.64 ± 10.28%) and the autograft-treated group (77.49 ± 19.28%); both groups were statistically improved compared to PCL/Empty-treated group (44.95 ± 26.94%). Nerve conduction velocity 1 year after surgery was increased in the PCL/GDNF-treated macaques (31.41 ± 15.34 meters/second) compared to autograft (25.45 ± 3.96 meters/second) and PCL/Empty (12.60 ± 3.89 meters/second) treatment. Histological analyses included assessment of Schwann cell presence, myelination of axons, nerve fiber density, and g-ratio. PCL/GDNF group exhibited a statistically greater average area occupied by individual Schwann cells at the distal nerve (11.60 ± 33.01 μm2) compared to autograft (4.62 ± 3.99 μm2) and PCL/Empty (4.52 ± 5.16 μm2) treatment groups. This study demonstrates the efficacious bridging of a long peripheral nerve gap in a nonhuman primate model using an acellular, biodegradable nerve conduit.