[Show abstract][Hide abstract]ABSTRACT: The silicone chamber model was used to evaluate peripheral nerve regeneration (PNR) in streptozocin (STZ)-induced diabetic rats. Diabetic and control animals underwent sciatic nerve transection and silicone chamber implantation establishing gaps of various lengths between the transected nerve ends. In animals with 5 and 10 mm gaps, diabetes was induced in experimental rats 1 week before surgery, and the animals were sacrificed 3 weeks after surgery. In animals with 8 mm gaps, diabetes induction occurred 3 days after surgery, and they were sacrificed after 7 weeks. Diabetic rats with 10 mm gaps demonstrated an impaired ability to form bridging cables, the initial step of regeneration through chambers. Morphometric studies of bridging cables between transected nerve ends demonstrated a significant reduction in the mean endoneurial area in diabetic animals with 5 and 8 mm gaps compared to controls. The number of regenerated myelinated axons in the chamber was significantly decreased in diabetic rats with 8 and 10 mm gaps. The mean myelinated fiber area in the regenerated cables of the diabetic group was significantly decreased with 5 mm gaps and significantly increased with 8 mm gaps compared to controls. Size-frequency histograms of regenerated myelinated fiber areas suggest a delay in the maturation of small caliber axons. Schwann cell migration across 5 mm gaps was examined with S-100 immunohistochemistry. The total distance of Schwann cell migration into cables from both proximal and distal ends was significantly reduced in diabetic animals. Characterization of PNR across gaps through silicone chambers in diabetic rats showed impairment in multiple aspects of the regenerative process, including cable formation, Schwann cell migration, and axonal regeneration.
[Show abstract][Hide abstract]ABSTRACT: The ability of extracellular proteins to influence the regenerative process was examined in Sprague-Dawley rats. Silicon chambers, filled with sterile saline solutions of cytochrome-c, fibronectin, laminin, a combination of fibronectin and laminin, or nerve growth factor were surgically implanted between the severed ends of sciatic nerves to form gaps of 18 mm. Four months later, the various groups were examined to determine the success of regeneration. The incidence of cable formation that bridged the gap was similar in all groups. The group of animals that had implants containing the combination of fibronectin/laminin had increased numbers of myelinated axons in the regenerated segment within the chamber and in the distal sciatic tributary nerves. Horseradish peroxidase labelling demonstrated that increased numbers of sensory and motor neurons in the fibronectin/laminin group had regenerated axons across the gap into the distal tributaries of the sciatic nerve.
The effect of the various agents on non-neuronal cells was measured by immunohistochemical staining with S-100 antibodies to determine the effects on Schwann cell migration. Silicon chambers, filled with sterile saline solutions of fibronectin, laminin, fibronectin/laminin, nerve growth factor, or cytochrome-c, were surgically implanted to form 5 mm gaps between severed sciatic nerve ends. Ten days later, Schwann cell migration into the bridging cables was examined in each group. Analysis revealed a greater influx of Schwann cells migrating into the regenerating segments in the fibronectin, the laminin, and the combination fibronectin/laminin groups compared to the control group (cytochrome-c).
[Show abstract][Hide abstract]ABSTRACT: We examined whether the short-term beneficial effects of nerve growth factor (NGF) upon regeneration are sustained over a prolonged period of time across 8-mm gaps within silicone chambers. Rat sciatic nerve regeneration both with and without NGF was examined after 10 weeks. Myelinated counts from the regenerated sciatic and distal tributary nerves were correlated to the numbers of motor and sensory neurons retrogradely labeled with horseradish peroxidase (HRP) applied distal to the regenerated segment. Regenerated sciatic and sural nerves were examined ultrastructurally for morphological analysis. Both regenerated groups by 10 weeks achieved essentially complete counts of myelinated axons in the distal tributary nerves and the regenerated segment of the sciatic nerve compared to the uninjured controls. There were similar numbers of retrogradely labeled sensory and motor neurons in the dorsal root ganglia (DRG) and lumbar spinal cord of both groups and, surprisingly, of the uninjured normal control group. Ultrastructural analysis demonstrated no difference in the distribution of axonal diameters or myelin thickness between the regenerated groups. In evaluating regeneration in experimental silicone chamber models, it is important to determine such parameters as the percentage of neurons that grow across the gap and the incidence of axonal sprouting. One can then make accurate assessments of experimental perturbations and predict whether they improve the naturally occurring regeneration through chambers. These results must ultimately be compared with equivalent determinations in the uninjured nerve. At 10 weeks there was essentially complete regeneration of both the NGF and control regenerative groups.(ABSTRACT TRUNCATED AT 250 WORDS)