High-frequency electrical stimulation can be a complementary therapy to promote nerve regeneration in diabetic rats

Abstract

The purpose of this study was to evaluate whether 1 mA of percutaneous electrical stimulation (ES) at 0, 2, 20, or 200 Hz augments regeneration between the proximal and distal nerve stumps in streptozotocin diabetic rats. A10-mm gap was made in the diabetic rat sciatic nerve by suturing the stumps into silicone rubber tubes. Normal animals were used as the controls. Starting 1 week after transection, ES was applied between the cathode placed at the distal stump and the anode at the proximal stump every other day for 3 weeks. At 4 weeks after surgery, the normal controls and the groups receiving ES at 20, and 200 Hz had a higher success percentage of regeneration compared to the ES groups at 0 and 2 Hz. In addition, quantitative histology of the successfully regenerated nerves revealed that the groups receiving ES at a higher frequency, especially at 200 Hz, had a more mature structure with more myelinated fibers compared to those in the lower-frequency ES groups. Similarly, electrophysiology in the ES group at 200 Hz showed significantly shorter latency, larger amplitude, larger area of evoked muscle action potentials and faster conduction velocity compared to other groups. Immunohistochemical staining showed that ES at a higher frequency could significantly promote calcitonin gene-related peptide expression in lamina I-II regions in the dorsal horn and recruit a higher number of macrophages in the diabetic distal sciatic nerve. The macrophages were found that they could stimulate the secretion of nerve growth factor, platelet-derived growth factor, and transforming growth factor-β in dissected sciatic nerve segments. The ES at a higher frequency could also increase cutaneous blood flow in the ipsilateral hindpaw to the injury. These results indicated that a high-frequency ES could be necessary to heal severed diabetic peripheral nerve with a long gap to be repaired.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. Success rates of regenerated nerves across the 10-mm gaps.

Figure 2. Temporal profile of morphologic changes of a normal control from an animal of (a) group A, and the diabetic sciatic nerves after ES treatment four weeks postoperatively from (b) group B (0 Hz), (c) group C (2 Hz), (d) group D (20 Hz), and (e) group E (200 Hz).

The nerves in groups B and C showed less mature structures with mostly Schwann cells and few myelinated axons dispersed randomly over the endoneurium. It was noted that the nerves in groups A, D, and E had numerous myelinated axons distributed in a more compact neural connective tissue structure. Bar = 30 µm.

Figure 3. Photomicrographs demonstrating CGRP-IR (arrows) in dorsal horn in the lumbar spinal cord after injury of a normal control from an animal of (a) group A, and the diabetic sciatic nerves after ES treatment from (b) group B (0 Hz), (c) group C (2 Hz), (d) group D (20 Hz), and (e) group E (200 Hz).

(f) Note the significantly increased CGRP-IR area ratios in diabetic animals receiving a higher frequency of ES. Each data point represents the mean ± SEM. Bar = 200 µm.

Figure 4. Photomicrographs demonstrating anti-rat CD68 immunoreactivity in macrophages (arrows) from cross sections of distal nerve cables of (a) group A, (b) group B, (c) group C, (d) group D, (e) and group E.

(f) Note the significantly increased density of macrophages in diabetic animals receiving a higher frequency of ES. Each data point represents the mean ± SEM. Bar = 25 µm.

Figure 5. Changes in mRNA levels of FGF, NGF, PDGF, and TGF-β of rat sciatic nerve segments conditioned by IL-1β.

*p<0.05 versus control.