Method for morphometric analysis of axons in experimental peripheral nerve reconstruction

Calibration of the stereological estimation of the number of myelinated axons in the rat sciatic nerve: a multicenter study

Several sources of variability can affect stereological estimates. Here we measured the impact of potential sources of variability on numerical stereological estimates of myelinated axons in the adult rat sciatic nerve. Besides biological variation, parameters tested included two variations of stereological methods (unbiased counting frame versus 2D-disector), two sampling schemes (few large versus frequent small sampling boxes), and workstations with varying degrees of sophistication. All estimates were validated against exhaustive counts of the same nerve cross sections to obtain calibrated true numbers of myelinated axons (gold standard). In addition, we quantified errors in particle identification by comparing light microscopic and electron microscopic images of selected consecutive sections. Biological variation was 15.6%. There was no significant difference between the two stereological approaches or workstations used, but sampling schemes with few large samples yielded larger differences (20.7+/-3.7% SEM) of estimates from true values, while frequent small samples showed significantly smaller differences (12.7+/-1.9% SEM). Particle identification was accurate in 94% of cases (range: 89-98%). The most common identification error was due to profiles of Schwann cell nuclei mimicking profiles of small myelinated nerve fibers. We recommend sampling frequent small rather than few large areas, and conclude that workstations with basic stereological equipment are sufficient to obtain accurate estimates. Electron microscopic verification showed that particle misidentification had a surprisingly variable and large impact of up to 11%, corresponding to 2/3 of the biological variation (15.6%). Thus, errors in particle identification require further attention, and we provide a simple nerve fiber recognition test to assist investigators with self-testing and training.

Theory and practice of combining coagulant fixation and microwave histoprocessing

The German, F. Blum, introduced formalin as a fixative in 1893. Formalin rapidly became popular for hardening and preserving gross human and animal specimens. As a result, microscopy for diagnostic pathology by combining paraffin embedding and formalin fixation was developed. Alcohol-based fixatives have coagulation of proteins as their main preservative effect. Because there is no cross-linking, immunostaining is not compromised, and DNA and RNA is not damaged. Ethyl alcohol was used by Dutch scientists of the 18th century, but was replaced by the cheaper formalin. Addition of low molecular weight polyethylene glycol (PEG) optimized the coagulant fixative, Kryofix. The polyethylene glycol prevents excessive hardening and enhances the speed of coagulation of proteins. Kryofix was used on a large scale for skin biopsies in Leiden between 1987 and 2001. DNA preservation by the formulated coagulant fixative, BoonFix, is related to the concentration of ethyl alcohol, PEG and acetic acid. BoonFix has been used since 2004 in Leiden for over 40,000 diagnostic skin biopsies and more than 100,000 cervical samples. A literature review and three decades of experience with coagulant, formalin-free fixatives in pathology suggest that when health authorities realize that formalin invalidates expensive tests, it might eventually be eliminated legislatively from diagnostic pathology. Finally, coagulant fixation is optimal for microwave histoprocessing where ethyl alcohol is followed by isopropanol.

Peripheral nerve regeneration using a three dimensionally cultured schwann cell conduit

The use of artificial nerve conduit containing viable Schwann cells is one of the most promising strategies to repair peripheral nerve injury. To fabricate an effective nerve conduit whose microstructure and internal environment are more favorable in nerve regeneration than those currently existing, a new three-dimensional (3D) Schwann cell culture technique using Matrigel and dorsal root ganglion (DRG) was developed. Nerve conduit of 3D arranged Schwann cells was fabricated using direct seeding of freshly harvested DRG into Matrigel-filled silicone tubes (inner diameter 1.98 mm, 14 mm length) and in vitro rafting culture for 2 weeks. The nerve regeneration efficacy of 3D cultured Schwann cell conduit (3D conduit group, n = 6) was assessed using an Sprague-Dawley rat sciatic nerve defect of 10 mm and compared with that of a silicone conduit filled with Matrigel and Schwann cells prepared with the conventional plain culture method (two-dimensional [2D] conduit group, n = 6). After 12 weeks, sciatic function was evaluated with sciatic function index (SFI) and gait analysis, and histomorphology of nerve conduit and the innervated tissues of sciatic nerve were examined using image analyzer and electromicroscopic methods. The SFI and ankle stance angle in the functional evaluation were -60.1 +/- 13.9, 37.9 degrees +/- 5.4 degrees in the 3D conduit group (n = 5) and -87.0 +/- 12.9, 32.2 degrees +/- 4.8 degrees in the 2D conduit group (n = 4). The myelinated axon was 44.91% +/- 0.13% in the 3D conduit group and 13.05% +/- 1.95% in the 2D conduit group. In the transmission electron microscope study, the 3D conduit group showed more abundant myelinated nerve fibers with well-organized and thickened extracellular collagen than the 2D conduit group, and the gastrocnemius muscle and biceps femoris tendon in the 3D conduit group were less atrophied and showed decreased fibrosis with less fatty infiltration than the 2D conduit group. A new 3D Schwann cell culture technique was established, and nerve conduit fabricated using this technique showed much improved nerve regeneration capacity than the silicone tube filled with Matrigel and Schwann cells prepared from the conventional plain culture method.

On sampling and sampling errors in histomorphometry of peripheral nerve fibers

Histomorphometrical assessment of regenerated peripheral nerves is a very common goal of many studies in experimental microsurgery. In this paper, the main critical issues in nerve fiber sampling for quantitative morphological assessment are addressed. The equal opportunity rule, i.e., the basic paradigm of random sampling, is described, together with an explanation of how sampling errors, in the selection of histologic fields and of the nerve fibers inside them, can produce a bias in quantitative estimates. Finally, some practical suggestions on how to cope with the most common sampling errors are provided, in order to help researchers obtain reliable histomorphometrical data on peripheral nerve fibers.

Silicone rubber tubulization in peripheral sensory nerve reconstruction: an experimental study in rabbits

Silicone rubber (polydimethyl siloxane) tubes are used clinically in peripheral nerve reconstruction. A disadvantage of this procedure is that the material often has to be removed owing to its mechanical properties. The aim of our study was to investigate the healing of reconstructed sensory nerves tubulized by silicone rubber in an animal model. In our experiments, we reconstructed the saphenous nerves in 27 rabbits. In series 1 (n = 12), silicone rubber tubes were slid over a nerve suture without a gap. In series 2 (n = 12), silicone rubber tubes were slid over a 10-mm nerve gap. In series 3 (n = 12), conventional suturing was performed in the collateral saphenous nerves of the animals of the series 1. Epineurial suturing was performed. Three other collateral nonoperated saphenous nerves served as controls. The healing was studied after 3, 6, and 12 months. Morphometric analysis of the regenerating axons was performed by using our new method for quantification of nerve fibers in cross sections stained by immunohistochemistry and using confocal laser scanning microscopy. Data analysis was carried out using a software program especially developed for this purpose. Our results showed in the silicone procedures that at 12 months significantly fewer axons per fascicle area were present compared with conventional suturing. However, mean axon diameters in the distal nerve stump of the silicone procedures did not differ significantly compared with the conventional suturing procedure. The ratio of total axon area to total fascicle area in the distal nerve stumps of the silicone procedure without gap was significantly smaller compared with the conventionally sutured nerve. The percentage outgrowing axons from the proximal nerve stump into the distal one in the silicone rubber procedure without gap was 57%. This was significantly higher than in the silicone rubber procedure with 10-mm gap (48%). However, in conventional suturing, the percentage of outgrowing axons (99%) was significantly higher than in both tubulization procedures. It appeared that tubulization by silicone rubber of sutured nerves without gap did not enhance axon regeneration. Conventional suturing gave significantly better results. If a gap was present, the use of a silicone rubber tube was preferable to non-suturing.

Processed porcine collagen tubulization versus conventional suturing in peripheral nerve reconstruction: An experimental study in rabbits

In peripheral nerve reconstruction, various procedures are used. One of the procedures that received the most interest in the past decade is the tubulization technique for small nerve gaps. A disadvantage in the use of non-biodegradable tubes is that the material often has to be removed owing to its mechanical properties. Some investigators, in exploring the use of collagen tubes, being a natural biodegradable material, found either allogenicity or xenogenicity and immune responses that may inhibit nerve regeneration. Processed porcine collagen (PPC) is a new inert and biodegradable material that has a favorable effect on wound healing, as demonstrated by experiments on other tissues. The aim of our study was to compare the healing of nerve sutures with PPC tubes with conventional end-to-end sutures. In our experiments, we reconstructed the saphenous nerves of 27 rabbits. In series 1 (n = 12) and 2 (n = 12), PPC tubes were slid over an end-to-end nerve suture without or with a 10-mm nerve gap, respectively. In series 3 (n = 12), conventional suturing was performed in the collateral saphenous nerves of the animals of series 1. Epineurial suturing was performed. Three other non-operated saphenous nerves served as controls. The healing was studied after 3, 6, and 12 months in sections stained by monoclonal antibodies and by conventional histologic staining. Morphometric analysis of the regenerating axons was done by using confocal scanning laser microscopy (CLSM). Data analysis was carried out using a software program especially developed for this purpose. All results were evaluated statistically. Our results showed that during the healing period in the distal nerve stump, the number of axons of the PPC procedure with a 10-mm gap was significantly higher than that in the procedure without a gap. At 12 months, the mean number of axons of all procedures was significantly lower than in the non-operated nerve, and the mean axon diameter in all distal stumps did not differ significantly from that of the non-operated nerve. In the distal nerve stump, the ratio of total axon area to total fascicle area in the PPC procedure with a gap was significantly higher than that in the conventional suturing procedure. After 12 months, there was no significant difference between the percentages of axon outgrowth of the PPC procedure without a gap, the conventional suturing procedure, and the non-operated nerve (100%). The percentage of axon outgrowth in PPC with a gap was significantly higher than in the other procedures.