Percussive injury to peripheral nerve in rats

A pan-caspase inhibitor reduces myocyte apoptosis and neuropathic pain in rats with chronic constriction injury of the sciatic nerve

BACKGROUND

Chronic constriction injury is a widely used model for neuropathic pain in rats. It presents with symptoms resembling human neuropathic pain, such as spontaneous pain, hyperalgesia, and allodynia. Recently, myocyte apoptosis was found in neuropathic rats as a possible promoter of pain and motor dysfunction. Our aim in this study was to demonstrate whether muscle cell apoptosis contributes to neuropathic pain in this animal model.

METHODS

To clarify this issue, we examined pain, nutritive perfusion, and inflammation in muscle tissue as well as myocyte apoptosis in rats with neuropathic pain established by chronic constriction injury of the sciatic nerve. Animals received either the pan-caspase inhibitor zVAD (OMe)-fmk (n = 5) or equivalent volumes of vehicle (n = 6). Sham-operated rats served as controls (n = 6).

RESULTS

At day 4 after nerve ligation, there were no signs of perfusion failure or muscle tissue inflammation in all experimental groups. However, animals treated with the vehicle had marked myocyte apoptosis, which was found almost completely blocked in zVA-Dtreated animals. The zVA-Dtreated animals presented with a significant reduction of pain upon heat, cold, and mechanical stimulation comparable with values found in sham controls.

CONCLUSIONS

Myocyte apoptosis possibly contributes to thermal and mechanical allodynia in this experimental model for neuropathic pain. The development of neuropathic pain symptoms did not depend on disturbances in microcirculation or muscle tissue inflammation.

Blunt cavernous nerve injury: A new animal model mimicking postradical prostatectomy neurogenic impotence

Our goal was to develop an animal model of cavernous nerve injury similar to that encountered among patients having undergone a successful nerve sparing radical prostatectomy and to compare patterns of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase staining to quality of erections using the newly developed model. We studied 50 mature Sprague Dawley rats, which were divided into five equal groups. Animals were either observed (sham), underwent an exploratory laparotomy, underwent moderate or severe percussive injury to both cavernous nerves, or underwent ablation of both cavernous nerves. Between 28 and 30 days later, all animals underwent electrostimulation and simultaneous recording of intracavernosal pressure. After sacrifice, penes were harvested and penile tissue NADPH-diaphorase staining pattern was assessed. Severity of cavernous nerve percussive injury and NADPH-diaphorase staining patterns correlated with the quality of recorded erections. This model is a useful experimental tool for research in the field of erectile dysfunction such as is encountered following a successful nerve sparing radical prostatectomy. Penile biopsy assessing NADPH-diaphorase staining may potentially prove to be a useful minimally-invasive diagnostic modality quantifying neurogenic erectile function among patients following radical prostatectomy.

Effects of insulin-like growth factor-I and platelet-rich plasma on sciatic nerve crush injury in a rat model

OBJECT

Local administration of insulin-like growth factor-I (IGF-I) has been shown to increase the rate of axon regeneration in crush-injured and freeze-injured rat sciatic nerves. Local administration of platelet-rich plasma (PRP) has been also shown to have a measurable effect on facial nerve regeneration after transection in a rat model. The objective of the study was to compare the effects of locally administered IGF-I and PRP on the parameters of the Sciatic Function Index (SFI), sensory function (SF), axon count, and myelin thickness/axon diameter ratio (G-ratio) in a rat model of crush-injured sciatic nerves.

METHODS

The right sciatic nerve of Wistar albino rats (24 animals) was crushed using a Yasargil-Phynox aneurysm clip for 45 minutes. All animals were randomly divided into 3 groups: Group 1 (control group) was treated with saline, Group 2 was treated with IGF-I, and Group 3 was treated with PRP. Injections were performed using the tissue expander's injection port with a connecting tube directed at the crush-injured site. Functional recovery was assessed with improvement in the SFI. Recovery of sensory function was using the pinch test. Histopathological examination was performed 3 months after the injury.

RESULTS

The SFI showed an improved functional recovery in the IGF-I-treated animals (Group 2) compared with the saline-treated animals (Group 1) 30 days after the injury. In IGF-I-treated rats, sensory function returned to the baseline level significantly faster than in saline-treated and PRP-treated rats as shown in values between SF-2 and SF-7. The G-ratios were found to be significantly higher in both experimental groups than in the control group.

CONCLUSIONS

This study suggests that the application of IGF-I to the crush-injured site may expedite the functional recovery of paralyzed muscle by increasing the rate of axon regeneration.

Neuropathological changes in vibration injury: an experimental study

Vibration syndrome, a clinical condition arising from chronic use of vibrating tools, is associated with a spectrum of neurovascular symptoms. To date, only its vascular pathology has been extensively studied; we sought to determine what direct neurologic injury, if any, is caused by vibration. Hindlimbs of anesthetized rats were affixed to a vibrating platform 4 h a day for 7 days. Study animals were vibrated with set parameters for frequency, acceleration, velocity, and amplitude; control animals were not vibrated. On day 7, nerves were studied by light and electron microscopy. While light microscopy showed minimal histologic differences between vibrated (n=12) and control (n=12) nerves, electron microscopic changes were dramatic. Splitting of the myelin sheath and axonal damage (e.g., myelin balls and "finger ring") were consistently seen in both myelinated and nonmyelinated axons. Despite relatively short vibration, definite pathology was demonstrated, suggesting that vibration syndrome has a direct neurologic component.

Upper trunk brachial plexopathy. The stinger syndrome

This study was designed to determine the cause of upper trunk brachial plexopathy, which is referred to as a "stinger" or a "burner." This injury often has been thought to occur secondary to traction when an athlete sustains a lateral flexion injury of the neck. At the United States Military Academy, a 4-phase study was begun with 261 tackle football players (236 intramural- and 25 varsity-level players) to investigate this injury. Electromyography and nerve root stimulation studies were used to delineate the lesion, which was found in a total of 32 players who continued throughout the study. This study demonstrated that a much more common mechanism of injury resulting in the stinger syndrome is probably compression of the fixed brachial plexus between the shoulder pad and the superior medial scapula when the pad is pushed into the area of Erb's point, where the brachial plexus is most superficial. An orthosis was designed to protect the brachial plexus from the compressive force of the shoulder pad. In preliminary trials, this orthosis had been very effective in decreasing the number of episodes in which stinger injuries occurred.

Spinal cord concussion

The hallmark of concussion injuries of the nervous system is the rapid and complete resolution of neurological deficits. Cerebral concussion has been well studied, both clinically and experimentally. In comparison, spinal cord concussion (SCC) is poorly understood. The clinical and radiological features of 19 SCC injuries in the general population are presented. Spinal cord injuries were classified as concussions if they met three criteria: 1) spinal trauma immediately preceded the onset of neurological deficits; 2) neurological deficits were consistent with spinal cord involvement at the level of injury; and 3) complete neurological recovery occurred within 72 hours after injury. Most cases involved young males, injured during athletics or due to falls. Concussion occurred at the two most unstable spinal regions, 16 involving the cervical spinal and three the thoracolumbar junction. Fifteen cases presented with combined sensorimotor deficits, while four exhibited only sensory disturbances. Many patients showed signs of recovery with the first few hours after injury and most had completely recovered within 24 hours. Only one case involved an unstable spinal injury. There was no evidence of ligamentous instability, spinal stenosis, or canal encroachment in the remaining 18 cases. Two patients, both children, suffered recurrent SCC injuries. No delayed deterioration or permanent cord injuries occurred. Spinal abnormalities that would predispose the spinal cord to a compressive injury were present in only one of the 19 cases. This suggests that, as opposed to direct cord compression, SCC may be the result of an indirect cord injury. Possible mechanisms are discussed.

Resistance to axonal degeneration after nerve compression in experimental diabetes

To determine the effect of diabetes on the development of axonal degeneration after acute nerve compression, the mobilized peroneal nerves of rats with streptozotocin-induced diabetes and of control rats were compressed at 150 mmHg (1 mmHg = 133 Pa) for 30 min by using specially devised cuffs. At three intervals after compression--3 days, rats diabetic for 31 wk; 14 days, diabetic for 6 wk; and 24 days, diabetic for 31 wk--groups of nerves were studied to assess numbers and sizes of fibers above, at, and below the cuff and to assess frequency of fiber degeneration in teased fibers from nerve distal to the cuff. Teased fibers with pathologic abnormalities were more frequent in nerves from controls than in nerves from diabetic rats in all three groups but the difference was statistically significant only at 3 and 14 days after compression. The lack of significant difference at 24 days may be explained by higher rates of disappearance of degenerating products and of fiber regeneration at 24 than at 3 and 14 days. This study provides evidence that in addition to delaying the reported functional deficit of vibratory detection threshold and conduction block during nerve compression, diabetes also may partially prevent axonal injury. Low nerve myo-inositol concentration did not predispose diabetic nerve to acute compression injury. If these results also apply to human diabetes and if repeated acute compression is involved in the genesis of fiber degeneration in entrapment, then a higher frequency of entrapment neuropathy among diabetics might be due to mechanisms other than increased susceptibility of fibers to acute compression--e.g., possibly to greater constriction of nerve due to pathologic alterations of the carpal ligament.

De- and regeneration of axons after minor lesions in the rat sciatic nerve. Effects of microneurography electrode penetrations

The structural effects of microneurography electrode penetrations were examined in the rat sciatic nerve. Such penetrations always produced restricted peri- and endoneurial lesions, resulting in degeneration of myelinated and unmyelinated axons, as well as in demyelination. The regenerative response was vigorous, and the regenerating axons usually formed a separate region of fascicle. However, restitution was not complete after 9 weeks survival, and in some cases not even after 16 weeks.

Functional consequences of experimental nerve lesions: effects of time, location, and extent of damage

The purpose of this experiment was to investigate the part played by each of the four fundamental components of a nerve in functional recovery from injury. In order to single out the role of cellular elements (the neurites), tissular elements (the Schwann cells), structural elements (the basal lamina tubes), and the blood-nerve barrier, various crush lesions were made on sciatic nerves of rats and functional recovery was studied. I examined the effects of the location and number of damaged sites and of the time elapsed between successive injuries. Results were assessed for a post-operative period of 2.5 months by studying tracks obtained from walking rats. This study suggested that (a) as far as neurites were concerned, the location of injury influenced the recovery pattern but the extent of damage did not; (b) the extent of damage to the Schwann cells had no measurable influence; (c) long-lasting deficits could be attributed to disruption of the basal lamina tubes, and (d) damage of the blood-nerve barrier could be responsible for slight and temporary disruption of the recovery pattern. I did not observe any of the possible beneficial effects of conditioning lesions described by some authors. This study emphasized the role of the basal lamina tubes in nerve injury and regeneration.

Functional consequences of experimental nerve lesions: effects of reinnervation blend

In spite of a constant and irrepressible growth of sprouts from the proximal stump of peripheral nerves that have been injured, functional recovery varies greatly from one case to another. To try and understand the reasons for this variability, I have proposed a novel view of the events occurring in a regenerating nerve; based on this view, a probability model was designed that could represent all situations observed after nerve injury. This model, described elsewhere, is based on the assumptions that the guidance role of basal lamina tubes is fundamentally important and that when this guidance fails, regrowth is random. In the present study, this model was tested; behavioral results were measured after various procedures on rat sciatic nerve, and these data were compared with results predicted for similar injuries through the probability model. A good correlation was observed between theoretical and experimental results, indicating that the probability model was reliable. Using this model as the basis for my conclusions, the inconsistent results of current surgical techniques of nerve repair were tentatively explained.

Pathophysiological mechanisms of intraoperative and postoperative hearing deficits in cerebellopontine angle surgery: an experimental study

Pathophysiological mechanisms responsible for intraoperative and postoperative hearing deficits associated with cerebellopontine (CP) angle operations were explored experimentally in dogs. The CP angle operative manipulations performed were the same as those experienced by human patients, and auditory evoked potentials were monitored intraoperatively. As a result of the operative manipulations, petechial or confluent hemorrhages occurred at the compressed portions of the cochlear nerve, and intravascular clots were often observed. Disintegration of the nerve fibers was verified by ultrastructural examination. Moreover, rupture of the microvasculature within the cochlear nerve occurred at locations remote from the operative site, due to stretching of the nerve trunk. The Obersteiner-Redlich zone, the Schwann-glial junction of the cochlear nerve, was a locus minoris resistentiae in CP angle surgery; the vasa nervorum easily bled at this zone and the peripheral and central myelins easily separated at their junctional zones ("central" avulsion injury). Intracochlear hemorrhages were identified as the most probable cause of the sudden loss of all components of the auditory evoked potentials, a frequent predictor of postoperative hearing loss, although rupture, occlusion, or vasospasm of the main trunk of the internal auditory artery have also been implicated as possible causes of such hearing losses. The results of this study show that hearing preservation is highly dependent on preserving not only the nerve at the operative site but also the remote O-R zone and intracochlear structures.

Nerve fibres in spinal cord impact injuries. Part 1. Changes in the myelin sheath during the initial 5 weeks

The spinal cords of cats were subjected to an impact injury using a "weight dropping" technique and sequential changes in the sheaths of non-degenerate myelinated fibres studied over a 3-week period. By 1 1/2 h after impact fibres showed retraction of some lateral loops from one paranode. The extent and severity of this change increased over the first week so that partial and full thickness demyelination were seen frequently. Partial demyelination most commonly resulted from the internodal termination of the innermost lamellae at an internodal location often associated with a Schmidt-Lantermann incisure. Remyelination by both Schwann cells and oligodendroglia occurred at the end of the second week. Oligodendroglial myelin showed many features of immaturity, similar to those found during development. It is suggested that the very earliest myelin damage is mechanical but is aggravated by other factor(s) one of which is probably ischaemia. Within the most severely injured areas there is death of oligodendroglia and any surviving axons are remyelinated principally by Schwann cells. In intermediate and minimally damaged areas of white matter oligodendroglial remyelination predominates.

Ultrastructural changes in rat peripheral nerve following pneumatic tourniquet compression

The sciatic nerves of 12 male rats were examined in the electron microscope 14 days after pneumatic tourniquet compression. Tourniquet pressure was maintained at 300 mmHg for varied lengths of time (30 minutes to 3 hours). Nerves compressed for 30 minutes showed very mild fissuring of the myelin without axonal degeneration. Examination of nerves compressed for 1 to 3 hours showed progressively more varied and extensive damage. Changes included splaying of myelin lamellae, axonal shrinkage with periaxonal edema. Schwann cell hypertrophy, and an increase in the number of microtubules and mitochondria per unit area. The myelin sheaths of some fibers, compressed for more than 2 hours, were completely ruptured. These changes resemble nerve lesions which could be induced by a variety of experimental procedures. Ultrastructural changes produced by tourniquet compression are apparently time-related and affect large-diameter nerves more profoundly than smaller-diameter nerves. The data reported provide an explanation for delayed muscle rehabilitation experienced by patients who have undergone extremity surgery with pneumatic tourniquet application. The evidence presented suggests that the incidence of tourniquet palsy may be far greater than previously recognized.

Spinal cord concussion

A reliable experimental model using decerebrate frogs has been developed by which a measured cutaneous stimulus to the right forelimb produces a single electrical response from the left sciatic nerve. Using this model, the minimal concussing force necessary to abolish the propagation of the nerve impulse down the spinal cord was established by trial and error. The mean recovery time was 31.2 seconds, with a standard deviation of 1.32 seconds. Recovery of function of the spinal cord, as measured this method, was complete following single and multiple concussions.

Acute nerve compression during limb ischaemia--an experimental study

In 6 baboons the deep peroneal nerve was compressed for 1 hr by a weighted cord laid over the leg just above the ankle. The procedure was carried out on both sides in a single experiment. On one side the whole leg was rendered ischaemic by a cuff round the thigh which was maintained for 3 or 4 hr before and during the period of nerve compression at the ankle. As judged by the severity of the conduction block at the ankle 24 hr later, and its subsequent recovery, the compressed nerves which were also made ischaemic fared no worse than those subjected to compression alone. Histological studies showed evidence of selective damage to large myelinated fibres during the compression; this damage was not increased on the ischaemic side. There is thus no evidence that ischaemia increased the susceptibility of nerve fibres to mechanical damage in these experiments.