Real-time visualisation of peripheral nerve trauma during subepineural injection in pig brachial plexus using micro-ultrasound

BACKGROUND

Nerve damage is consistently demonstrated after subepineural injection in animal studies, but not after purposeful injection in patients participating in clinical studies. There is a need to better visualise nerves in order to understand the structural changes that occur during subepineural injection.

METHODS

We scanned the brachial plexuses of three anaesthetised pigs using micro-ultrasound imaging (55-22 MHz probe), inserted 21 gauge block needles into the radial, median, and axillary nerves, and injected two 0.5 ml boluses of saline into nerves at a rate of 12 ml min^-1. Our objectives were to measure the area and diameter of nerves and fascicles, and to describe changes in nerve anatomy, comparing our findings with histology.

RESULTS

Images were acquired at 42 sites across 18 nerves in three pigs and compared dimensions (geometric ratio; 95% confidence interval; P value). As expected, the nerve cross-sectional area was greater in the proximal brachial plexus compared with the mid-plexus (2.10; 1.07-4.11; P<0.001) and the distal plexus (2.64; 1.42-4.87; P<0.001). Nerve area expanded after 0.5 ml injection (2.13; 1.48-3.08; P<0.001). Using microultrasound, subepineural injection was characterised by nerve and fascicle rotation, uniform, or localised swelling and epineural rupture. Micro-ultrasound revealed a unique pattern suggestive of subperineural injection after a median nerve injection, and good face validity with histology. Histology showed epineural trauma and inflammation to the perineurium.

CONCLUSION

We accurately identified fascicles and real-time structural changes to peripheral nerves using micro-ultrasound. This is the first study to visualise in vivo and in real-time the motion of nerves and fascicles in response to anaesthetic needle insertion and fluid injection.

Multiple steps characterise ventricular layer attrition to form the ependymal cell lining of the adult mouse spinal cord central canal

The ventricular layer of the spinal cord is remodelled during embryonic development and ultimately forms the ependymal cell lining of the adult central canal, which retains neural stem cell potential. This anatomical transformation involves the process of dorsal collapse; however, accompanying changes in tissue organisation and cell behaviour as well as the precise origin of cells contributing to the central canal are not well understood. Here, we describe sequential localised cell rearrangements which accompany the gradual attrition of the spinal cord ventricular layer during development. This includes local breakdown of the pseudostratified organisation of the dorsal ventricular layer prefiguring dorsal collapse and evidence for a new phenomenon, ventral dissociation, during which the ventral‐most floor plate cells separate from a subset that are retained around the central canal. Using cell proliferation markers and cell‐cycle reporter mice, we further show that following dorsal collapse, ventricular layer attrition involves an overall reduction in cell proliferation, characterised by an intriguing increase in the percentage of cells in G1/S. In contrast, programmed cell death does not contribute to ventricular layer remodelling. By analysing transcript and protein expression patterns associated with key signalling pathways, we provide evidence for a gradual decline in ventral sonic hedgehog activity and an accompanying ventral expansion of initial dorsal bone morphogenetic protein signalling, which comes to dominate the forming the central canal lining. This study identifies multiple steps that may contribute to spinal cord ventricular layer attrition and adds to increasing evidence for the heterogeneous origin of the spinal cord ependymal cell population, which includes cells from the floor plate and the roof plate as well as ventral progenitor domains.

Thiel embalming: Quantifying histological changes in skeletal muscle and tendon and investigating the role of boric acid

Cadaver preservation methods impact their utilization in anatomical research and teaching. Thiel-embalmed cadavers show flexibility, however, the cause remains poorly understood. This study aimed to (1) describe qualitative and quantitative histological differences between Thiel-embalmed and formalin-fixed skeletal muscle and tendon tissue; (2) investigate whether boric acid in Thiel solution is solely responsible for modification of tissues; and (3) explore whether the modifications observed could potentially explain the mechanisms underpinning flexibility of Thiel cadavers. Skeletal muscle and tendon samples were harvested from mice preserved using formalin, Thiel solution, or modified-Thiel solution (without boric acid). Using standard H&E and Gomori's trichrome histological methods, tissues were examined to determine whether differences were apparent between the preservative treatments. Differences were present between the Thiel and formalin-fixed tissues; formalin-fixed samples remained substantially more intact while Thiel-embalmed samples showed fiber fragmentation and lack of nuclei. The mean cell diameter of Thiel-embalmed muscle (24.4 μm) was significantly smaller (P < 0.005) than formalin-fixed muscle (40.7 μm). There was significantly greater (P < 0.005) fragmentation in Thiel-embalmed muscle (631.5 per 1 mm² ) compared to formalin-fixed muscle (75.4 per 1 mm² ). Samples embalmed using modified-Thiel showed a severe lack of integrity within internal tissue structure. This suggests that Thiel solution significantly alters tissue structure at cellular level, with quantitative data demonstrating measurable differences between Thiel and formalin-fixed specimens. While the precise mechanism for these alterations remains unknown, it is shown that boric acid is not the only component of Thiel responsible for degradation of internal tissue structure. Clin. Anat., 33:696-704, 2020. © 2019 Wiley Periodicals, Inc.

Histology, vascularity and innervation of the glenoid labrum

BACKGROUND

Although the glenoid labrum has an important role in shoulder stability, little is known about its composition, vascularity and innervation. The aims of this study were therefore to evaluate the histology, vascularity and innervation of the glenoid labrum.

MATERIALS AND METHODS

Ten glenoid labrum specimens (three male, two female: mean age 81.2 years, range 76-90 years) were detached at the glenoid neck. Following decalcification, sections were cut through the whole thickness of each specimen perpendicular to the glenoid labrum at 12 radii corresponding to a clock face superimposed on the glenoid fossa. Then they were stained using haematoxylin and eosin, a silver nitrate protocol or subjected to immunohistochemistry using anti-protein gene protein 9.5 to demonstrate neuronal processes.

RESULTS

The labrum was fibrocartilaginous, being more fibrous in its free margin. There was a variable distribution of blood vessels, being more vascular in its periphery, with many originating from the fibrous capsule and piercing the glenoid labrum. Immunohistochemistry revealed positive staining of nerve fibres within the glenoid labrum.

CONCLUSION

The glenoid labrum is fibrocartilaginous, being more fibrous in its periphery, and is vascularized, with the anterosuperior aspect having a rich blood supply. Free sensory nerve fibres were also present; no encapsulated mechanoreceptors were observed. The presence of sensory nerve fibres in the glenoid labrum could explain why tears induce pain. It is postulated that these sensory fibres could play a role in glenohumeral joint proprioception.

Blood supply and vascularity of the glenoid labrum: Its clinical implications

BACKGROUND

Tears of the glenoid labrum are common after dislocation of the glenohumeral joint. The outcome for healing or surgical reconstruction of the glenoid labrum relies on the extent of its vascularization. This study aims to evaluate the glenoid labrum blood supply and to determine its regional vascularity.

MATERIALS AND METHODS

A total of 140 shoulders (30 male and 40 female cadavers) were examined: mean age 81.5 years, range 53-101 years. All blood vessels around the glenohumeral joint were dissected and recorded. Ten specimens with the glenoid labrum and fibrous capsule attached were randomly selected and detached at the glenoid neck and subjected to decalcification. Sections (10-20 μm) were cut through the whole thickness of each specimen from the centre of the glenoid fossa perpendicular to the glenoid labrum at 12 radii corresponding to a clock face superimposed on the glenoid. Sections were stained using haematoxylin and eosin and then examined.

RESULTS

The blood supply to the glenoid labrum is by direct branches from the second part of the axillary artery, subscapular, circumflex scapular and anterior circumflex humeral and posterior circumflex humeral arteries, as well as branches of muscular arteries supplying the surrounding muscles.

CONCLUSION

This study shows that the glenoid labrum has a rich blood supply suggesting that, regardless of the types of the glenoid labrum lesions or their management, an excellent outcome for glenoid labrum healing and joint stability is possible. The observations also suggest that the blood supply to the glenoid labrum is sufficient, enabling its reattachment.

Quantification of Osteon Morphology Using Geometric Histomorphometrics

Many histological methods in forensic anthropology utilize combinations of traditional histomorphometric parameters which may not accurately describe the morphology of microstructural features. Here, we report the novel application of a geometric morphometric method suitable when considering structures without anatomically homologous landmarks for the quantification of complete secondary osteon size and morphology. The method is tested for its suitability in the measurement of intact secondary osteons using osteons digitized from transverse femoral diaphyseal sections prepared from two human individuals. The results of methodological testing demonstrate the efficacy of the technique when applied to intact secondary osteons. In providing accurate characterization of micromorphology within the robust mathematical framework of geometric morphometrics, this method may surpass traditional histomorphometric variables currently employed in forensic research and practice. A preliminary study of the intersectional histomorphometric variation within the femoral diaphysis is made using this geometric histomorphometric method to demonstrate its potential.

Functional differences and interactions between phenotypic subpopulations of olfactory ensheathing cells in promoting CNS axonal regeneration

We demonstrate that there are significantly more p75 neurotrophin receptor- (NTR)-expressing cells in olfactory ensheathing cell (OEC) primary cultures from olfactory nerve rootlets (ONR), but a greater proportion of O4 antigen- and PSA-NCAM-expressing cells in parallel cultures from the nerve fibre layer of the olfactory bulb (OB). By co-culturing adult rat retinal ganglion cells (RGCs) with OECs derived from either ONR or OB tissue, we compared their neurite regrowth-promoting properties. In phenotypically unsorted cultures, there is greater RGC neurite regrowth on ONR OECs compared to OB OECs. Following immunoselection of ONR cells for p75 NTR, there is increased RGC neurite regrowth on the enriched population compared to the unselected cell population or the p75 NTR depleted population. When p75 NTR-enriched cells from ONR and OB cultures are compared directly, tissue source-related differences are no longer observed. Our previous work implicated a pertussis toxin (PTx)-sensitive G protein-linked signalling pathway in OEC regulation of neurite regrowth. We show that this pathway probably operates in interactions between the p75 NTR-positive and -negative cells; separated populations lose the PTx-mediated enhancement of neurite regrowth-promoting properties seen in mixed cultures. Optimum neurite regrowth is observed when both phenotypes are present in cultures from either ONR or OB, and where glial G-protein signalling is disabled by PTx before co-culture with neurons. We thus propose that p75 NTR-positive cells, whilst being the more effective neurite regrowth promoting subpopulation in isolation, cooperate with negative cells to provide optimum support for axonal regrowth.

Down-regulation of transcripts for Na channel alpha-SNS in spinal sensory neurons following axotomy

Spinal sensory (dorsal root ganglion; DRG) neurons display slowly inactivating, tetrodotoxin-resistant (TTX-R), and rapidly inactivating, TTX-sensitive (TTX-S) Na currents. Attenuation of the TTX-R Na current and enhancement of TTX-S Na current have been demonstrated in cutaneous afferent DRG neurons in the adult rat after axotomy and may underlie abnormal bursting. We show here that steady-state levels of transcripts encoding the alpha-SNS subunit, which is associated with a slowly inactivating, TTX-R current when expressed in oocytes, are reduced significantly 5 days following axotomy of DRG neurons, and continue to be expressed at reduced levels, even after 210 days. Steady-state levels of alpha-III transcripts, which are present at low levels in control DRG neurons, show a pattern of transiently increased expression. In situ hybridization using alpha-SNS- and alpha-III-specific riboprobes showed a decreased signal for alpha-SNS, and an increased signal for alpha-III, in both large and small DRG neurons following axotomy. Reduced levels of alpha-SNS may explain the selective loss of slowly inactivating, TTX-R current. The abnormal electrophysiological properties of DRG neurons following axonal injury thus appear to reflect a switch in Na channel gene expression.

Distribution of sodium channels in chronically demyelinated spinal cord axons: immuno-ultrastructural localization and electrophysiological observations

The immuno-ultrastructural localization of voltage-sensitive sodium channels was demonstrated within a central demyelinating lesion induced in the rat spinal cord by ethidium bromide/irradiation using polyclonal antibody 7493. Antibody 7493 has previously been shown to immunostain intensely axon membrane at nodes of Ranvier, and also perinodal astrocyte processes. At 25-35 days post injection/irradiation, the central portion of the demyelinating lesion is populated with chronically demyelinated axons and there is an absence of glial processes. Sodium channel immunoreactivity was not observed on the chronically demyelinated axolemma within this central portion of the lesion. Within the peripheral portion of the lesion demyelinated axons were occasionally abutted by astrocyte and Schwann cell processes. At these focal sites of apposition, the axon membrane displayed intense sodium channel immunoreactivity, while the abutting astrocyte and Schwann cell processes did not exhibit immunostaining. Also in the periphery of the lesion, some axons become ensheathed and myelinated by oligodendrocytes and Schwann cells. The axon membrane of circumferentially ensheathed axons displayed antibody 7493 immunostaining, and this immunoreactivity persisted on the axolemma until the ensheathing cytoplasmic processes compacted into myelin. Internodal axon membrane beneath the myelin sheath did not display sodium channel immunoreactivity, though (putative) developing nodal axon membrane adjacent to terminal paranodal loops exhibited robust sodium channel staining. Electrophysiological recordings within the ethidium bromide/irradiation lesion demonstrated that at least some axons conducted action potentials within the lesion, while others exhibited conduction block. These results indicate that there is a reorganization of sodium channels within the axon membrane of chronically demyelinated central axons.

Diazoxide modification of streptozotocin-induced diabetes in rats

Diazoxide was found to modify streptozotocin-induced diabetes in rats when given twelve hours and one hour before streptozotocin. In contrast to rats treated with streptozotocin alone, rats treated with diazoxide, 15 or 30 mg./kg., plus streptozotocin, 30 mg./kg., did not become clinically diabetic and had fasting blood glucose levels within the normal range. Diazoxide pretreatment protected against streptozotocin-induced glucose intolerance as defined by response to intraperitoneal glucose. Further, the immunoreactive insulin response to intraperitoneal glucose in the rats treated with both diazoxide and streptozotocin differed from the control value only at sixty minutes. It is possible that the protective effect of diazoxide is mediated through the adrenergic-like activity of diazoxide on the β-cell.