Morphological and morphometric study of peripheral nerves from rats with streptozotocin-induced diabetes mellitus

Effects of decompression on behavioral, electrophysiologic, and histomorphologic recovery in a chronic sciatic nerve compression model of streptozotocin-induced diabetic rats

Purpose

To determine susceptibility to decompression surgery in diabetic and nondiabetic peripheral neuropathy using a chronic compression neuropathy model.

Materials and methods

Twenty-four streptozotocin-induced diabetic rats were randomly divided into three groups: group I, chronic compression of the left sciatic nerve for 4 weeks with decompression; group II, similar without decompression; and group III, sham exposing the sciatic nerve only. The other 24 nondiabetic rats were assigned to groups IV–VI, which received compression–decompression, compression, and the sham operation, respectively. Mixed-nerve-elicited somatosensory evoked potentials (M-SSEPs) and compound muscle action potentials (CMAPs) were measured to verify the compression neuropathy in the posttreatment follow-up. Behavioral observations in thermal hyperalgesia tests were quantified before electrophysiologic examinations. Treated and contralateral nerves were harvested for histomorphologic analysis.

Results

Chronic compression of sciatic nerve induced significant reduction of amplitude and increment of latency of M-SSEP and CMAP in both diabetic and nondiabetic rats. Diabetic group changes were more susceptible. Decompression surgery significantly improved both sensory and motor conduction, thermal hyperalgesia, and the mean myelin diameter of the rat sciatic nerve in both diabetic and nondiabetic groups. Near full recovery of motor and sensory function occurred in the nondiabetic rats, but not in the diabetic rats 8 weeks postdecompression.

Conclusion

Behavioral, electrophysiologic, and histomorphologic findings indicate that decompression surgery is effective in both diabetic and nondiabetic peripheral neuropathy.

Association of chronic diabetes and hypertension in sural nerve morphometry: an experimental study

BACKGROUND

Prospective studies have shown incidence rates of hypertension in diabetes mellitus to be three times that of subjects without diabetes mellitus. The reverse also applies, with the incidence of diabetes two to three times higher in patients with hypertension. Despite this common clinical association, the contribution of each isolated entity in the development of a neuropathy is still not well understood. The aims of the present study were to investigate the presence of peripheral neuropathy in spontaneously hypertensive rats (SHR) and SHR with chronically induced diabetes, using a morphological and morphometric study of the sural nerves.

METHODS

Female SHR and normotensive Wistar rats (WR), 8 weeks old, received a single intravenous injection of streptozotocin (STZ) through the tail vein. Controls from both strains received vehicle. Twelve weeks after the injection, sural nerves were dissected and prepared for light microscopy. Morphometry of sural nerve fascicles and myelinated fibers was performed with the aid of computer software.

RESULTS

The sural nerve myelinated fibers were highly affected by experimental diabetes in normotensive rats, causing mainly the reduction of the fiber size. Hypertensive rats showed characteristics of small fiber neuropathy and a severe reduction of the number and density or Schwann cells. The association between diabetes and hypertension caused an increase on the average size of the myelinated fibers, pointing to a small fiber loss, associated to axonal atrophy.

CONCLUSIONS

Our study gives morphological support to the existence of a neuropathy due to hypertension, which is among one of the most common risk factors for diabetic neuropathy. The association between the two neuropathies showed to be a complex alteration, involving and including both, large and small fibers neuropathy. Hypertension caused, indeed, an exacerbation of the alterations already observed in experimental models of diabetic neuropathy.

Quercetin alleviates high glucose-induced Schwann cell damage by autophagy

Quercetin can reverse high glucose-induced inhibition of neural cell proliferation, and therefore may have a neuroprotective effect in diabetic peripheral neuropathy. It is difficult to obtain primary Schwann cells and RSC96 cells could replace primary Schwann cells in studies of the role of autophagy in the mechanism underlying diabetic peripheral neuropathy. Here, we show that under high glucose conditions, there are fewer autophagosomes in immortalized rat RSC96 cells and primary rat Schwann cells than under control conditions, the proliferative activity of both cell types is significantly impaired, and the expression of Beclin-1 and LC3, the molecular markers for autophagy, is significantly lower. After intervention with quercetin, the autophagic and proliferative activity of both cell types is rescued. These results suggest that quercetin can alleviate high glucose-induced damage to Schwann cells by autophagy.

Measurement of ultrasonic attenuation in diabetic neuropathic sciatic nerves for diagnostic and therapeutic applications

Measurements of ultrasonic attenuation in the sciatic nerves of rats were performed to verify the feasibility of ultrasound diagnosis of peripheral neuropathy and to avoid damage to the nerves caused by overheating in pain management applications. A rat model of diabetic peripheral neuropathy was established. The proximal-segment and middle-segment sciatic nerves of control and neuropathic rats were dissected for the attenuation measurement. Two commercial ultrasound transducers and a self-developed experimental platform were used in the measurements. Using H&E staining and transmission electron (TE) microscopy, morphological analysis of the control and neuropathic nerves was performed to determine the relationship between attenuation and the histology of the nerves. The experimental results showed that the attenuation coefficients of the control, second-week, fourth-week, and eighth-week neuropathic nerves were -6.68 ± 0.50, -5.61 ± 0.34, -6.27 ± 0.40, and -7.10 ± 0.35 dB/cm at 2.68 MHz, respectively. The respective values at 7.50 MHz were -14.96 ± 0.79, -12.65 ± 0.28, -13.98 ± 1.07, and -16.00 ± 0.54 dB/cm. The changes in the attenuation coefficients were significantly different among the second-week, fourth-week, and eighth-week DN nerves. Additionally, the ultrasonic attenuation coefficient of the rat sciatic nerve was fourfold that of the cat brain and cow liver and twofold that of human muscle.

The impact of low-dose insulin on peripheral nerve insulin receptor signaling in streptozotocin-induced diabetic rats

BACKGROUND

The precise mechanisms of the neuroprotective effects of insulin in streptozotocin (STZ)-induced diabetic animals remain unknown, but altered peripheral nerve insulin receptor signaling due to insulin deficiency might be one cause.

METHODOLOGY AND PRINCIPAL FINDINGS

Diabetes was induced in 10-week-old, male Wistar rats by injecting them with STZ (45 mg/kg). They were assigned to one group that received half of an insulin implant (∼1 U/day; I-group, n = 11) or another that remained untreated (U-group, n = 10) for 6 weeks. The controls were age- and sex-matched, non-diabetic Wistar rats (C-group, n = 12). Low-dose insulin did not change haemoglobin A1c, which increased by 136% in the U-group compared with the C-group. Thermal hypoalgesia and mechanical hyperalgesia developed in the U-group, but not in the I-group. Sensory and motor nerve conduction velocities decreased in the U-group, whereas sensory nerve conduction velocity increased by 7% (p = 0.0351) in the I-group compared with the U-group. Western blots showed unaltered total insulin receptor (IR), but a 31% decrease and 3.1- and 4.0-fold increases in phosphorylated IR, p44, and p42 MAPK protein levels, respectively, in sciatic nerves from the U-group compared with the C-group. Phosphorylated p44/42 MAPK protein decreased to control levels in the I-group (p<0.0001).

CONCLUSIONS AND SIGNIFICANCE

Low-dose insulin deactivated p44/42 MAPK and ameliorated peripheral sensory nerve dysfunction in rats with STZ-induced diabetes. These findings support the notion that insulin deficiency per se introduces impaired insulin receptor signaling in type 1 diabetic neuropathy.

Quantitative histological analysis of the mandibular branch of the facial nerve in rats

PURPOSE

To establish a model to quantitative histological analysis of the mandibular branch of the facial nerve in rats.

METHODS

Eleven Wistar rats had their right and left mandibular branches of the facial nerve surgically removed and were sacrificed afterwards. Quantitative histological analysis was performed with: a) partial number of axons; b) partial area of the transversal cut of the nerve (9000 μm(2)); c) partial density. The averages of partial density were obtained. The statistical study was established by Wilcoxon test (p=0.05).

RESULTS

In relation to density of axons, comparison between sides shows no statistically significant difference (p=0.248; p=0.533). Mean partial density of distal and proximal samples was, respectively, 0.18 ± 0.02 and 0.19 ± 0.02 axons/μm(2). Comparison between proximal and distal samples shows no statistically significant difference (p=0.859; p=0.182).

CONCLUSION

This study has successfully established a model to histological quantitative analysis of the mandibular branch of the facial nerve in rats.

Rosuvastatin positively changes nerve electrophysiology in diabetic rats

OBJECTIVE

To examine the effect of rosuvastatin on peripheral nerve function in diabetic rats using electrophysiological measurements.

BACKGROUND

Diabetes was induced in 5-day-old male Wistar rats by intraperitoneal (i.p.) injection of streptozotocin (STZ). As many as 45 diabetic rats were randomized to three groups: one treated with rosuvastatin (group R), another with rosuvastatin and mevalonate (group MR) and the other was untreated (group U). The data were compared with a group of normal age-matched rats i.e. control rats (group C).

METHODS

Neurophysiological measurements were performed at the age of 3 months (T1) and again at the age of 8 months (T2), after 3 months of treatment.

RESULTS

At T1, there was a trend to lower amplitude of compound motor action potential (CMAP) in the three diabetic groups as compared to controls, and no difference for motor nerve conduction velocity (MNCV), amplitude of sensory nerve action potential (SNAP), sensory nerve conduction velocity (SNCV) between diabetic groups and controls. At T2, the amplitude of CMAP was significantly lower in groups R and MR versus group U and control rats. MNCV was significantly and similarly decreased in the three diabetic groups; the latency of the first sensory peak (fastest sensory fibres) was significantly increased in group U but was normal in groups R and MR.

CONCLUSIONS

This study shows that: 1.rosuvastatin exerts a beneficial effect on the conduction of the fastest sensory fibres;2.these effects are independent of blood pressure and lipid changes.

Effect of cerivastatin on peripheral capillary permeability to albumin and peripheral nerve function in diabetic rats

OBJECTIVE

To examine the effect of cerivastatin on capillary permeability to albumin and peripheral nerve function in diabetic rats.

ANIMALS

Diabetes was induced in male Wistar rats by i.p. injection of streptozotocin (STZ) at the age of 5 days. Forty diabetic rats were randomized in two groups: one treated by cerivastatin (diabetic treated group, DT) and the other untreated (diabetic untreated group, DU). The data were compared to a group of normal rats.

MEASUREMENTS

The peripheral capillary filtration of albumin (CFA) was studied on a limb by a non-invasive isotopic method, and nerve electrophysiological measurements were performed. Rats were followed-up until 6 months. In group DU albumin retention (AR) increased by 3 months and lymphatic uptake of interstitial albumin was impaired at 6 months. None of these disorders was observed in group DT. Motor and sensory nerve conduction velocities (MNCV and SNCV) were significantly slower at 6 months in group DU but not in group DT as compared to control rats. The duration of the sensory nerve action potential (SNAP) was significantly longer in group DU than in control rats at 6 months whereas it did not differ in group DT and in control animals.

CONCLUSIONS

This study shows that cerivastatin may prevent the peripheral increase in CFA and lymphatic dysfunction induced by diabetes. These beneficial effects on microcirculation may be involved in the prevention of nerve function deterioration. The underlying mechanisms are likely to be independent of a lipid-lowering effect, but their clarification needs further investigations.

Microscopic anatomy of brachial plexus branches in Wistar rats

In the present study, we analyze the morphology and morphometry of the lateral proper digital nerve of the third finger, and of the proximal and distal segments of the ulnar, median, and radial nerves, in Wistar rats 4 or 7 weeks old. The fascicular area and diameter were generally significantly greater in the proximal compared to distal segments and tended to be larger in 7-week-old compared to 4-week-old rats (e.g., median nerve area of 0.13 mm(2) for the proximal and 0.07 mm(2) for distal segments in 4-week-old rats, and 0.17 and 0.10 mm(2), respectively, for the proximal and distal segments of 7-week-old rats). The number of fascicles was significantly greater while the number of myelinated fibers was significantly less in the distal segments (e.g., 1,359 and 509 myelinated fibers, respectively, in the proximal and distal segments of the radial nerve 4-week-old rats). There was no significant difference in these parameters between the two age groups. The diameter of the myelinated fibers and their respective axons increased from 4 to 7 weeks of age (e.g., myelinated fiber diameter of 4.10 microm in 4-week-old animals and 4.7 microm in the ulnar nerve proximal segment of 7-week-old rats). The g-ratio regression line (axon diameter vs. fiber diameter quotient) was outlined for all the nerves studied here. Differences in myelinated fiber density were detected between the segments of the radial nerve, accompanying the number of myelinated fibers. Detailed knowledge of the microscopic anatomy of rat forelimb nerves provides control data for comparison with studies of experimentally induced neuropathies, which can shed more light on human neuropathies.

Effect of various nerve decompression procedures on the functions of distal limbs in streptozotocin-induced diabetic rats: further optimism in diabetic neuropathy

It is known that diabetic neuropathy is the result of endoneurial edema caused by various biochemical reactions triggered by hyperglycemia. This sequence of events can cause cessation of circulation at the perineurial level, or the tough layer, which is not resilient enough to spread intraneural pressure. Internal and external limiting structures create a double crush phenomenon to the nerve structure. Decompression of the nerve trunk at separate levels is one of the adjuncts to the overall treatment plan for diabetic neuropathy. In this study, the right sciatic nerves of 30 rats with streptozotocin-induced diabetes were used; three groups were created. In the control group, the sciatic nerves were explored and dissected only. In group II, tarsal tunnel release was performed and accompanied by epineurotomy of the sciatic nerve and its peroneal and tibial extensions. In group III, in addition to the procedures performed in group II, perineural sheaths, exposed through the epineurotomy sites at both the peroneal and tibial nerves, were incised for decompression of the fascicles. Improvement in diabetic neuropathy was evaluated by using footprint parameters. The last print length values, estimated according to the 38-month measurements, were 26.1 +/- 0.12 mm in the control group, 23.2 +/- 0.07 mm in group II, and 22.2 +/- 0.1 mm in group III. The toe spread and intermediate toe spread values of the groups were parallel to improvements in print lengths throughout the study. The best improvement was observed in the perineurotomy group. Finally, an electron microscopic study revealed variable degenerative changes in all groups, but they were milder in groups II and III. This experimental study reveals that adding internal decompression to external release doubled the effect in reducing derangement in the sciatic nerves of the rats and, in the authors' opinion, offers cause for further optimism in the treatment of diabetic neuropathy.

Reduced Ia-afferent-mediated Hoffman reflex in streptozotocin-induced diabetic rats

In addition to reduced nerve conduction velocity, diabetic neuropathic patients often exhibit a reduction in the amplitude of the compound muscle action potential elicited by stimulation of the Ia-afferent-mediated reflex pathway (Hoffman or H wave) that can contribute to diminished or absent tendon reflexes. In contrast to nerve conduction velocity deficits, changes in H-wave amplitudes have not been reproduced in diabetic animal models. Using electrophysiological techniques developed for repeated recordings in individual animals, we report H-wave deficits in streptozotocin (STZ)-treated insulin-dependent diabetic rats. After 4 weeks of diabetes induced by STZ treatment, a 47% reduction in the H-wave amplitude was demonstrated by recording compound muscle action potentials in foot muscles after stimulation of Ia afferents. Interestingly, we also demonstrate that the H-wave amplitude gradually recovers to a 26% deficit after 12 weeks of experimental diabetes. The recovery of the H wave in STZ-treated rats distinguishes this deficit mechanistically from other STZ-induced electrophysiological changes and may model a similar recovery of the H wave reported in diabetic patients.

Structural abnormalities do not explain the early functional abnormalities in the peripheral nerves of the streptozotocin diabetic rat

The streptozotocin (STZ)-diabetic rat, the most commonly employed model of experimental diabetic neuropathy, is characterised by a reduction in nerve conduction velocity, pain threshold and blood flow. Whether or not structural abnormalities underlie these functional abnormalities is unclear. 10 adult male Sprague-Dawley STZ-diabetic rats (diabetes duration 27 d) and 10 age-matched (23 wk) control animals were studied. Motor nerve conduction velocity (m s(-1)) was significantly reduced in diabetic (41.31 +/- 0.8) compared with control (46.15 +/- 1.5) animals (P < 0.001). The concentration of sciatic nerve glucose (P < 0.001), fructose (P < 0.001) and sorbitol (P < 0.001) was elevated, and myoinositol (P < 0.001) was reduced in diabetic compared with control animals. Detailed morphometric studies demonstrated no significant difference in fascicular area, myelinated fibre density, fibre and axon areas as well as unmyelinated fibre density and diameter. Endoneurial capillary density, basement membrane area and endothelial cell profile number did not differ between diabetic and control animals. However, luminal area (P < 0.03) was increased and endothelial cell area (P < 0.08) was decreased in the diabetic rats. We conclude there is no detectable structural basis for the reduction in nerve conduction velocity, pain threshold or blood flow, observed in the streptozotocin diabetic rat.

Quantitative analysis of myelinated nerve fibers of peripheral nerve in streptozotocin-induced diabetes mellitus

The purpose of this study was to examine morphometric changes of myelinated fibers in early stages of experimental diabetes mellitus. Adult male Wistar rats aged 17 wk were used in this study. Diabetes mellitus was induced by streptozotocin. Samples of common peroneal nerve from diabetic rats (4 and 8 wk after induction of diabetes mellitus) and age-matched control animals were removed and processed. The semithin cross sections were stained with toluidine blue and used for myelinated fiber computer-aided morphometric analysis. There were no significant changes in diabetic animals after 4 wk duration of the disease. There was significant reduction in myelinated nerve fiber caliber in diabetic rats 8 wk after induction of diabetes as compared to age-matched controls. There was no significant reduction of axonal area in this group of diabetic rats, so diminution of fiber area was caused predominantly by reduction of myelin sheath area. The study demonstrates that the induction of diabetes mellitus in rat by streptozotocin is accompanied by early changes of the morphometric indices of myelinated nerve fibers of peripheral nerve.

Nerve conduction changes and fine structural alterations of extra- and intrafusal muscle and nerve fibers in streptozotocin diabetic rats

Streptozotocin-induced diabetes mellitus is known to cause a reduction of both conduction velocity and axon caliber in sciatic nerves and also a decrease in muscle fiber size. The present study investigates whether the distal parts of the peripheral nervous system, including extra- and intrafusal muscle fibers, are more severely affected than the proximal segments in the diabetic state. Proximal and distal sensory nerve conduction velocities were monitored during a period of 3 months in rats rendered diabetic by injection of streptozotocin. Segments of the sciatic and ventral coccygeal nerves, and of the biceps femoris and lumbrical muscles, were studied by light and electron microscopy, including morphometric analysis. In contrast to previous studies, daily suboptimal insulin injections were given to prevent acute metabolic complications. Sensory conduction velocity in the ventral coccygeal nerve was significantly (P < 0.05) decreased in the diabetic rats compared to controls. Proximal and distal nerve segments were equally affected. Mean cross-sectional axon area of the sciatic nerve was moderately, but significantly (P < 0.05), smaller in insulin-treated diabetic rats than in controls. In both the sciatic nerve and the terminal, intrafusal nerve segments, occasional axons showed moderate dystrophic changes. Fibers of the intrafusal nerve segments appeared to be equally affected compared to the fibers in the sciatic nerve, although no quantitative comparison was made. The increase of small caliber skeletal muscle fibers in experimental streptozotocin-induced diabetes was confirmed. These findings indicate that proximal and distal segments of peripheral nerves are affected equally in the early stages of experimental diabetic neuropathy.

Sciatic nerve morphology and morphometry in mature rats with streptozocin-induced diabetes

Controversy exists as to the morphological and morphometric changes seen in experimental diabetic neuropathy (EDN). Most previous studies have utilized immature animals, with controversy as to whether the observed changes are due to maturational delays induced by hyperglycemia, or to diabetes per se. This study utilizes mature 9-month-old Sprague-Dawley rats. Six control and six hyperglycemic rats were examined 24 weeks after streptozocin injection. No morphological abnormalities were seen in the sciatic nerve at the light microscopy level. Total fascicular area and myelinated fiber density showed no significant differences (ANOVA, P > 0.05). No significant differences [ANOVA, P > 0.05 and Kolmogorov-Smirnoff (K-S), P > 0.05] between control and diabetic groups were shown for fiber, axon, and myelin areas, fiber and axon diameters, and myelin thickness. Fiber index of circularity, axon index of circularity, and g ratio were not significantly different with ANOVA (P > 0.05), but the diabetic group showed significantly lower values (P < 0.001) with K-S testing. Regression analyses of axonal area and log(n) axonal area plotted against myelin thickness showed no significant differences between the control and diabetic animals. This study in mature rats confirms the relative lack of morphological and morphometric changes in EDN which have previously been reported in studies involving immature rats. It highlights the difficulties in trying to extrapolate from EDN to human diabetic neuropathy where severe morphological and morphometric abnormalities may be present.

Ultrastructural abnormalities of myelinated fibres in the tibial nerve of streptozotocin-diabetic rats

In this paper we have examined the ultrastructural changes in myelinated fibre structure after the administration of streptozotocin to Sprague-Dawley rats which had passed the rapid growth period. Myelinated fibre size in the tibial nerve was found to be less in diabetic animals 4 and 6 months after the induction of diabetes, when compared to age-matched controls, but not less than onset. The relative contributions of axon and myelin to this reduction in fibre dimensions were examined. When myelin area was plotted against axon area (derived from perimeter) it showed that the pathological insult of diabetes had a greater effect on the rate of myelin production. The incidence of axonal glycogenosomes was also assessed. These results are discussed in detail.

Relative growth and maturation of axon size and myelin thickness in the tibial nerve of the rat. 2. Effect of streptozotocin-induced diabetes

The relative changes in the growth and maturation of axon size and myelin thickness were studied in the medial plantar division of the tibial nerve in the lower leg and in the motor branches of the tibial nerve to the calf muscles in rats in which diabetes mellitus had been induced with streptozotocin at the time of weaning. Observations were made at 6 weeks and 3, 6, 9 and 12 months of diabetes for comparison with age-matched controls. Similar changes were observed in both nerves. Growth in body weight and skeletal growth was severely retarded from the time of induction of diabetes but at the 6-week stage axon size was not reduced, suggesting that neural growth may initially be relatively protected. At later stages axon size was consistently reduced in the diabetic animals as compared with the controls and showed an absolute reduction at 12 months, as compared with 9 months, that was greater than in the controls. Myelin thickness became reduced earlier and was more severely affected than axon size so that the fibers were relatively hypomyelinated. The myelin changes were greater in larger than in smaller fibers. The index of circularity of axons was reduced in the diabetic nerves. These results show that induction of diabetes in prepubertal rats produces effects on peripheral nerve fibers which differ from those resulting from diabetes induced in adult animals. The effects also differ between large and small nerve fibres. These observations may explain some of the disparate findings obtained in previous studies on experimental diabetes in rats.

The effects of sorbinil on peripheral nerve conduction velocity, polyol concentrations and morphology in the streptozotocin-diabetic rat

This study examined the effects of an aldose reductase inhibitor, Sorbinil, on neuropathy over a 6-month period in streptozotocin-diabetic rats. Sorbinil treatment prevented the 10-fold increase in nerve sorbitol found with diabetes. It produced a 60% improvement in tibial nerve motor conduction velocity after 6 months. Morphometric profiles of nerves were also normalized. Axon area was reduced by 14% in untreated diabetic rats compared to age-matched controls, whereas Sorbinil-treated animals showed normal age-related axon growth. Myelin area was increased by 28% in untreated diabetic animals, but was the same as age-matched controls with Sorbinil treatment. Nerve myo-inositol levels were reduced by 45% after three months of untreated diabetes, but were normal after six months. Sorbinil treatment tended to restore myo-inositol levels toward normal over the shorter time period. It was concluded that axon growth retardation is the most likely cause of the conduction deficit seen in long-term experimental diabetes.

Skin biopsy as a beneficial procedure for morphological evaluation of diabetic neuropathy

In an attempt to evaluate the morphological abnormalities of dermal non-myelinated nerve fibers of diabetics and elucidate the pathogenesis of diabetic peripheral neuropathy, the terminal part of peripheral nerve in the upper dermis was observed on electron microscopy using skin samples biopsied in 10 diabetics with symptomatic neuropathy and 6 age-matched controls. In diabetics, the density of nerve fibers was significantly lower than in controls. In addition, swelling, lytic change and vacuolation in the axon, multiplication of basement membrane of the Schwann cell and Schwann cell cluster devoid of axon were more frequently observed in diabetics. The Schwann cell did not show significant structural alterations. These findings suggest that the axon is primarily involved, at least in the terminal region of nerve fiber, in diabetic peripheral neuropathy. It is also concluded that the skin biopsy technique is harmless, cosmetically not troublesome and might be beneficial for studying peripheral neuropathies including diabetic neuropathy.

Peripheral nerve axonal dwindling with concomitant myelin sheath hypertrophy in experimentally induced diabetes

Axons of the peripheral nervous system (PNS) are reduced in caliber in response to the experimental diabetic state. The cause of this reduced axonal size is disputed. Various theories include (a) axonal dwindling, (b) inhibition of growth, and (c) shrinkage due to serum hyperosmolarity. This study was designed to directly address these conflicting theories and to provide additional information on the character of the peripheral neuropathy resulting from an experimentally induced diabetic state. Four weeks, 6 and 12 months after establishing a streptozotocin-induced diabetic condition in rats, a morphometric evaluation of randomly selected cross sections of myelinated nerve fibers in the common peroneal nerve was performed on diabetic and age and weight-matched control animals. A reduction in the cross-sectional area of axons with a concomitant increase in the width of myelin sheaths was detected following 6 months of exposure to the diabetic state. Axons in rats diabetic for 12 months showed smaller cross-sectional areas than those seen in rats diabetic for only 6 months; hence, a dwindling in axonal caliber had occurred during this period. These findings indicate the presence of an axonopathy, associated with a myelin sheath alteration in the common peroneal nerve of the chronically diabetic rat.

Experimental thalidomide neuropathy: the morphological correlate of reduced conduction velocity

Morphological studies of experimental thalidomide neuropathy have thus far failed to show any significant structural changes. The present investigation was performed on sural nerves of female New Zealand white rabbits showing a reduction of sensory conduction velocity after oral treatment with thalidomide (100 mg/kg b. wt. per day) for a period of 33 weeks. Rabbits of the same strain and equal sex, weight, and number served as controls. Very few nerve fibers were undergoing Wallerian degeneration in both groups, experimental animals and controls. Morphometry, however, revealed a statistically significant reduction of the mean myelin thickness of sural nerve fibers in the thalidomide group of rabbits as compared to controls. The mean myelin thickness of the largest nerve fibers was also significantly smaller than in the control group. On the other hand, axonal diameters were not significantly altered. The association between the decrease of the sensory conduction velocity, the reduction of the myelin sheath thickness, and the chronic thalidomide application is discussed.

Nerve Na+-K+-ATPase, conduction, and myo-inositol in the insulin-deficient BB rat

Nerve conduction slowing in acute diabetes in animals has been associated with both a diminished axolemmal transmembrane Na+ potential and a myo-inositol-related defect in nerve Na+-K+-ATPase activity. The interaction between these two potentially related defects, their reversibility, and their possible role in the nerve conduction slowing and axonopathy of diabetes are not well defined. Therefore, the effects of rigorous insulin replacement on peripheral nerve conduction velocity, myoinositol content, and Na+-K+-ATPase activity were studied in the spontaneously diabetic BB-Wistar rat, an animal model that manifests both conduction slowing and a characteristic progressive axonopathy. Twelve weeks of sustained hyperglycemia reduced both motor conduction velocity and Na+-K+-ATPase activity in sciatic nerve. Six weeks of subsequent vigorous insulin replacement normalized the enzymatic defect but only partially corrected diminished nerve conduction velocity. Hence, nerve conduction slowing in diabetic animals may be partly attributable to reduced nerve Na+-K+-ATPase activity, but a less readily reversible component of conduction slowing probably reflects structural alterations that occur in nerve within the first 3 mo of diabetes.

Morphometric analysis of the vagus nerve in non-diabetic and ketonuric diabetic Chinese hamsters

Morphometric analysis of axons from the ventral division of the vagus nerve of ketonuric diabetic Chinese hamsters and age-sex matched non-diabetic controls was performed to determine the frequency distribution and numerical and volume density. Myelinated fibres of diabetics displayed a significant reduction in diameter (P less than 0.001) compared with controls, which was correlated inversely with progressive ketonuria (P less than 0.05). The reduced calibre of myelinated fibres was the result of thin myelin sheaths rather than a reduction in axon diameter. A marked decrease in numerical density (P less than 0.05) and volume density (P less than 0.005) was found in the myelinated fibres of diabetics compared with controls. Non-myelinated axons showed a significant shift to smaller diameter (P less than 0.001) in diabetics, which was correlated inversely with duration of ketonuria (P less than 0.05). Numerical density of non-myelinated axons was increased (P less than 0.01) in diabetic hamsters whereas volume density was comparable in diabetic and control animals. These data provide morphological evidence of impairment in the parasympathetic nervous system which may be a major factor underlying previously reported gastrointestinal and pancreatic islet dysfunction in the diabetic Chinese hamster.

Glycogen accumulation in tibial nerves of experimentally diabetic and aging control rats

Tibial nerves of streptozotocin-diabetic, alloxan-diabetic, and age-matched control rats were examined at 2 weeks and 2, 4, 8, and 12 months following the induction of diabetes. Glycogen-like granules accumulated within perineurial and Schwann cells of only the diabetic animals. This accumulation may reflect a metabolic abnormality in these cells which could account for the reduced conduction velocities seen in the peripheral nerves of these same diabetic rats (Moore et al. 1980a). Glycogen-like granules were also present and increased with age in myelinated axons of both diabetic and control rats. Quantitative data suggest that axonal accumulation of glycogen-like granules is related to aging or injury related phenomena to which diabetic axons may be more susceptible.

Changes in peripheral nerves of rats four months after induction of streptozotocin diabetes. A qualitative and quantitative study

Eight streptozotocin-injected Wistar rats and eight controls were fixed by whole-body perfusion 4 months after beginning of the experiment, the nervus radialis was dissected and processed for light and electron microscopy. After light-microscopic study standard photographs of nerve cross sections were measured by means of a semiautomatic image analyzer. The following measurements were obtained: (1) surface of fibers, axons, and myelin sheaths, (2) ratio of myelin to axon surface, and (3) percent of endoneural space. Group means and standard deviations were calculated, and cumulated size class distributions were made. Representative nerve specimens from all animals were also studied by electron microscopy. The quantitative study revealed in the diabetics a severe reduction of the average myelin surface, a mild increase of axonal cross section and of endoneural space, a reduction of myelin/axon ratio and a mild reduction in cross section of the nerve. Ultrastructural lesions of minor degree were found in the cytoplasm of Schwann and mesenchymal cells, no lesion was observed in axons. These findings demonstrate the presence of neuropathy 4 months after induction of diabetes and support the pathogenetic role of the Schwann cell in our experimental model.