Phrenic nerve diabetic neuropathy in rats: unmyelinated fibers morphometry

Anethole Prevents the Alterations Produced by Diabetes Mellitus in the Sciatic Nerve of Rats

Anethole is a terpenoid with antioxidant, anti-inflammatory, and neuronal blockade effects, and the present work was undertaken to study the neuroprotective activity of anethole against diabetes mellitus (DM)-induced neuropathy. Streptozotocin-induced DM rats were used to investigate the effects of anethole treatment on morphological, electrophysiological, and biochemical alterations of the sciatic nerve (SN). Anethole partially prevented the mechanical hyposensitivity caused by DM and fully prevented the DM-induced decrease in the cross-sectional area of the SN. In relation to electrophysiological properties of SN fibers, DM reduced the frequency of occurrence of the 3rd component of the compound action potential (CAP) by 15%. It also significantly reduced the conduction velocity of the 1st and 2nd CAP components from 104.6 ± 3.47 and 39.8 ± 1.02 to 89.9 ± 3.03 and 35.4 ± 1.56 m/s, respectively, and increased the duration of the 2nd CAP component from 0.66 ± 0.04 to 0.82 ± 0.09 ms. DM also increases oxidative stress in the SN, altering values related to thiol, TBARS, SOD, and CAT activities. Anethole was capable of fully preventing all these DM electrophysiological and biochemical alterations in the nerve. Thus, the magnitude of the DM-induced neural effects seen in this work, and the prevention afforded by anethole treatment, place this compound in a very favorable position as a potential therapeutic agent for treating diabetic peripheral neuropathy.

Effects of aldose reductase inhibitor on microneurographically assessed peripheral sympathetic nerve activity in rats

Autonomic neuropathy, one of the serious complications of diabetes, decreases quality of life. Aldose reductase inhibitor (ARI) blocks sorbitol production, and results in prevention of damage of nerve fibers. Beneficial effects of ARI have usually been confirmed through nerve conduction velocity tests in motor and sensory nerves. On the other hand, few reports have dealt with the effects of ARI on the small fiber activity such as sympathetic nerve one. In the present study, we administered eparlestat, ARI orally for 3weeks, to streptozotocin-induced diabetic (STZ+ARI) rats, and then recorded peripheral sympathetic nervous signal detected with microneurographic technique. Action potentials (APs) and bursts of APs were detected from the recorded signal, and their rates and incidences (=rates/heart rate) were compared with those in non-diabetic control (normal) and ARI-untreated streptozotocin-induced diabetic (STZ) rats. While streptozotocin and/or epalrestat did not influence burst parameters in all the three groups, AP parameters in the STZ+ARI and normal groups were higher than those in the STZ group. However, response of AP parameters to the intravenous glucose administration (IVGA) was not large in the STZ+ARI group, similar to that of the STZ group and different from that of the normal group in which AP parameters increased after IVGA. The results suggest that epalrestat may prevent sympathetic nerve activity (SNA) from reduction under hyperglycemic and insulin-depleted conditions, that enhancement of SNA was not induced after IVGA under that condition, and that AP parameters might be useful to assess the degree of neuropathy.

Impulse magnetic stimulation facilitates synaptic regeneration in rats following sciatic nerve injury

The current studies describing magnetic stimulation for treatment of nervous system diseases mainly focus on transcranial magnetic stimulation and rarely focus on spinal cord magnetic stimulation. Spinal cord magnetic stimulation has been confirmed to promote neural plasticity after injuries of spinal cord, brain and peripheral nerve. To evaluate the effects of impulse magnetic stimulation of the spinal cord on peripheral nerve regneration, we compressed a 3 mm segment located in the middle third of the hip using a sterilized artery forceps to induce ischemia. Then, all animals underwent impulse magnetic stimulation of the lumbar portion of spinal crod and spinal nerve roots daily for 1 month. Electron microscopy results showed that in and below the injuryed segment, the inflammation and demyelination of neural tissue were alleviated, apoptotic cells were reduced, and injured Schwann cells and myelin fibers were repaired. These findings suggest that high-frequency impulse magnetic stimulation of spinal cord and corresponding spinal nerve roots promotes synaptic regeneration following sciatic nerve injury.

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.

Renal nerve ultrastructural alterations in short term and long term experimental diabetes

BACKGROUND

Despite the evidence that renal hemodynamics is impaired in experimental diabetes, associated with glomeruli structural alterations, renal nerves were not yet investigated in experimental models of diabetes and the contribution of nerve alterations to the diabetic nephropathy remains to be investigated. We aimed to determine if ultrastructural morphometric parameters of the renal nerves are affected by short term and/or long term experimental diabetes and if insulin treatment reverses these alterations. Left renal nerves were evaluated 15 days or 12 weeks (N = 10 in each group) after induction of diabetes, with a single injection of streptozotocin (STZ). Control rats (N = 10 in each group) were injected with vehicle (citrate buffer). Treated animals (N = 10 in each group) received a single subcutaneous injection of insulin on a daily basis. Arterial pressure, together with the renal nerves activity, was recorded 15 days (short-term) or 12 weeks (long-term) after STZ injection. After the recordings, the renal nerves were dissected, prepared for light and transmission electron microscopy, and fascicle and fibers morphometry were carried out with computer software.

RESULTS

The major diabetic alteration on the renal nerves was a small myelinated fibers loss since their number was smaller on chronic diabetic animals, the average morphometric parameters of the myelinated fibers were larger on chronic diabetic animals and distribution histograms of fiber diameter was significantly shifted to the right on chronic diabetic animals. These alterations began early, after 15 days of diabetes induction, associated with a severe mitochondrial damage, and were not prevented by conventional insulin treatment.

CONCLUSIONS

The experimental diabetes, induced by a single intravenous injection of STZ, in adult male Wistar rats, caused small fiber loss in the renal nerves, probably due to the early mitochondrial damage. Conventional treatment with insulin was able to correct the weight gain and metabolic changes in diabetic animals, without, however, correcting and / or preventing damage to the thin fibers caused by STZ-induced diabetes. The kidney innervation is impaired in this diabetic model suggesting that alterations of the renal nerves may play a role in the development of the diabetic nephropathy.

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.

Ultrastructural and morphometric alterations in the aortic depressor nerve of rats due to long term experimental diabetes: effects of insulin treatment

Most of the reports about an altered baroreflex attribute this condition to the diabetic efferent neuropathy of the aortic depressor nerve (ADN) (afferent arm of the baroreflex less explored). We evaluated the ADN ultrastructural alterations caused by long term experimental diabetes and the effects of insulin treatment. Wistar rats (N=14) received a single intravenous injection of streptozotocin (40 mg/kg) 12 weeks before the experiment. Control animals (N=9) received vehicle (citrate buffer). Insulin treated animals (N=8) received a single subcutaneous injection of insulin daily. Under pentobarbital anesthesia the ADNs were isolated and had their spontaneous activity recorded. Afterwards, proximal and distal segments of the nerves were prepared for transmission electron microscopy study. Morphometry of the unmyelinated fibers was carried out with the aid of computer software. ADN of the diabetic animals showed axonal atrophy for myelinated fibers, with more pronounced alterations of the myelin sheath, such as myelin infolding and out folding, presence of myelin balls and very thin myelin sheath in relation to the axonal size, particularly for the small myelinated fibers becoming evident. No differences were observed in myelinated fiber number and their density, as well as on the fascicular area. Unmyelinated fiber number was significantly larger in the diabetic group while fiber diameter was significantly smaller compared to control. This result suggests axonal atrophy or, if associated to the larger number of fibers present in this group, could indicate fiber sprouting. These alterations were more evident in the distal segments of the nerves and were moderated by insulin treatment.

Neurovascular proximity in the diaphragm muscle of adult mice

OBJECTIVE

Regional blood flow to the diaphragm muscle varies with the workload of inspiration. To provide anatomical insight into coupling between muscle fiber recruitment and oxygen supply, we tested whether arterioles are physically associated with motor nerve branches of the diaphragm.

METHODS

Following vascular casting, intact diaphragm muscles of C57BL/6 and CD-1 mice were stained for motor innervation. Arteriolar networks and nerve networks were mapped (~2 μm resolution) to evaluate their physical proximity.

RESULTS

Neurovascular proximity was similar between muscle regions and mouse strains. Of total mapped nerve lengths (C57BL/6, 70 ± 15 mm; CD-1, 87 ± 13 mm), 80 ± 14% and 67 ± 10% were ≤250 μm from the nearest arteriole and associated predominantly with arterioles ≤45 μm in diameter. Distances to the nearest arteriole encompassing 50% of total nerve length (D(50)) were consistently within 200 μm. With nerve networks repositioned randomly within muscle borders, D(50) values nearly doubled (p < 0.05). Reference lines within anatomical boundaries reduced proximity to arterioles (p < 0.05) as they deviated from the original location of motor nerves.

CONCLUSION

Across two strains of mice, motor nerves and arterioles of the diaphragm muscle are more closely associated than can be explained by chance. We hypothesize that neurovascular proximity facilitates local perfusion upon muscle fiber recruitment.

Sural nerve involvement in experimental hypertension: morphology and morphometry in male and female normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR)

Background

The sural nerve has been widely investigated in experimental models of neuropathies but information about its involvement in hypertension was not yet explored. The aim of the present study was to compare the morphological and morphometric aspects of different segments of the sural nerve in male and female spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. Rats aged 20 weeks (N = 6 in each group) were investigated. After arterial pressure and heart rate recordings in anesthetized animals, right and left sural nerves were removed and prepared for epoxy resin embedding and light microscopy. Morphometric analysis was performed with the aid of computer software, and took into consideration the fascicle area and diameter, as well as myelinated fiber number, density, area and diameter.

Results

Significant differences were observed for the myelinated fiber number and density, comparing different genders of WKY and SHR. Also, significant differences for the morphological (thickening of the endoneural blood vessel walls and lumen reduction) and morphometric (myelinated fibers diameter and G ratio) parameters of myelinated fibers were identified. Morphological exam of the myelinated fibers suggested the presence of a neuropathy due to hypertension in both SHR genders.

Conclusions

These results indicate that hypertension altered important morphometric parameters related to nerve conduction of sural nerve in hypertensive animals. Moreover the comparison between males and females of WKY and SHR allows the conclusion that the morphological and morphometric parameters of sural nerve are not gender related. The morphometric approach confirmed the presence of neuropathy, mainly associated to the small myelinated fibers. In conclusion, the present study collected evidences that the high blood pressure in SHR is affecting the sural nerve myelinated fibers.