Alleviation of neuropathic pain by trazodone in rats

Abstract Neuropathic pain is generally characterised by an abnormal sensation (dysesthesia), an increased response to painful stimuli (hyperalgesia), and pain in response to a stimulus that does not normally provoke pain (allodynia). The present study was designed to investigate the effect of trazodone (5mg/kg and 10mg/kg) on peripheral neuropathic pain induced by partial sciatic nerve ligation in rats. Mechanical hyperalgesia, cold allodynia and thermal hyperalgesia were assessed by performing the pinprick, acetone, and hot plate tests, respectively. Biochemically, lipid peroxidation level and total calcium levels were measured. However, trazodone administration (5 and 10 mg/ kg i.p.) for 21days significantly diminished partial sciatic nerve ligation-induced neuropathic pain along with areduction in oxidative stress and calcium levels. The results of the present study suggest that trazodone is effective in attenuating partial sciatic nerve ligation-inducedpainful neuropathic states, which may be attributed to decreased oxidative stress and calcium levels.

Nerve conduction assessment and magnetic resonance imaging for the diagnosis of localized hypertrophic neuropathy of the sciatic nerve and the lumbo-sacral plexus.

Localized hypertrophic neuropathy (LHN) are slowly growing nerve lesions causing progressive nerve deficit and weakness. We present the case of a 32-year old woman with long history of motor and sensory deficit complains along the sciatic nerve territory. The muscles involved were featured by delay in F waves at nerve conduction assessment. Magnetic resonance imaging (MRI) showed specific patterns, low intense on T1 and abnormally hyper intense on short tau inversion recovery (STIR) and T2, with no obvious enhancement, features compatible with either LHN or intraneural perineurioma (IP) of the sciatic nerve and/or the lumbosacral plexus. Focal thickening and hypertrophy of the sciatic nerve with preserved fascicular configuration and progressive enlargement of the right lumbosacral plexus could be noted. A nerve conduction assessment followed by an MRI eventually allowed to diagnose LHN, without performing a nerve biopsy. Although similar, LHN and IP are two distinct lesions which should be diagnosed and differentiated as soon as possible, to avoid potential complications due to delayed diagnosis and/or misdiagnosis.

Assessment of the synergic effect of immunomodulation on nerve repair using multiparametric magnetic resonance imaging.

INTRODUCTION: The immune system plays a pivotal role in nerve injury. The aim of this study was to determine the role of multiparametric magnetic resonance imaging (MRI) in evaluation of the synergic effect of immunomodulation on nerve regeneration in neurotmesis. METHODS: Rats with sciatic nerve neurotmesis and surgical repair underwent serial multiparametric MR examinations over an 8-week period after subepineurial microinjection of lipopolysaccharide (LPS) and subsequent subcutaneous injection of FK506 or subepineurial microinjection of LPS or phosphate-buffered saline (PBS) alone. RESULTS: Nerves treated with immunomodulation showed more prominent regeneration than those treated with LPS or PBS alone and more rapid restoration toward normal T2, fractional anisotropy (FA), and radial diffusivity (RD) values than nerves injected with LPS or PBS. DISCUSSION: Nerves treated with immunomodulation exert synergic beneficial effects on nerve regeneration that can be predicted by T2 measurements and FA and RD values. Muscle Nerve 57: E38-E45, 2018.

Novel technique for intraoperative sciatic nerve assessment in complex primary total hip arthroplasty: a pilot study.

INTRODUCTION: Sciatic nerve injury (SNI) is a potentially devastating complication after total hip arthroplasty (THA). Intraoperative neural monitoring has been found in several studies to be useful in preventing SNI, but can be difficult to implement. In this study, we examine the results of using a handheld nerve stimulator for intraoperative sciatic nerve (SN) monitoring during complex THA requiring limb lengthening and/or significant manipulation of the SN. METHODS: A consecutive series of 11 cases (9 patients, 11 hips) with either severe developmental dysplasia of the hip (Crowe 3-4) or other underlying conditions requiring complex hip reconstruction involving significant leg lengthening and/or nerve manipulation. SN function was monitored intraoperatively by obtaining pre- and post-reduction thresholds during component trialing. The results of nerve stimulation were then used to influence intraoperative decision-making. RESULTS: No permanent postoperative SN complications occurred, with an average increase of 28.5 mm in limb length, range (6-51 mm). In 2 out of 11 cases, a change in nerve response was identified after trial reduction, which resulted in an alternate surgical plan (femoral shortening osteotomy and downsizing femoral head). In the remaining cases, the stimulator demonstrated a response consistent with the baseline assessment, assuring that the appropriate lengthening was achieved without SNI. 1 patient had a transient motor and sensory peroneal nerve palsy, which resolved within 2 weeks. CONCLUSIONS: The intraoperative use of a handheld nerve stimulator facilitates surgical decision-making and can potentially prevent SNI. The real-time assessment of nerve function allows immediate corrective action to be taken before nerve injury occurs.

Mechanical Conflict System: A Novel Operant Method for the Assessment of Nociceptive Behavior.

A new operant test for preclinical pain research, termed the Mechanical Conflict System (MCS), is presented. Rats were given a choice either to remain in a brightly lit compartment or to escape to a dark compartment by crossing an array of height-adjustable nociceptive probes. Latency to escape the light compartment was evaluated with varying probe heights (0, .5, 1, 2, 3, and 4 mm above compartment floor) in rats with neuropathic pain induced by constriction nerve injury (CCI) and in naive control rats. Escape responses in CCI rats were assessed following intraperitoneal administration of pregabalin (10 and 30 mg/kg), morphine (2.5 and 5 mg/kg), and the tachykinin NK1 receptor antagonist, RP 67580 (1 and 10 mg/kg). Results indicate that escape latency increased as a function of probe height in both naive and CCI rats. Pregabalin (10 and 30 mg/kg) and morphine (5 mg/kg), but not RP 67580, decreased latency to escape in CCI rats suggesting an antinociceptive effect. In contrast, morphine (10 mg/kg) but not pregabalin (30 mg/kg) increased escape latency in naive rats suggesting a possible anxiolytic action of morphine in response to light-induced fear. No order effects following multiple test sessions were observed. We conclude that the MCS is a valid method to assess behavioral signs of affective pain in rodents.

Periodical assessment of electrophysiological recovery following sciatic nerve crush via surface stimulation in rats.

When evaluating peripheral nerve regeneration, electrophysiological test is recognized as an optimal assessment, which is a quantitative, objective, and direct evidence reflecting function as compared to morphological examinations. In murine models of nerve regeneration, however, it remains a challenge to record compound muscle action potentials (CMAPs) periodically and non-invasively, i.e., with no insult to the nerve. In the present study, we recorded CMAPs in the gastrocnemius muscle weekly until 8 weeks after sciatic nerve crush by stimulating the nerve in a surface manner, and the electric stimuli were delivered to the skin between ischial tuberosity and major trochanter using bipolar hook electrodes. The CMAPs were reproducibly recorded in this way from 3 weeks post-injury, and both amplitude and latency were well correlated to post-operative time. Furthermore, a strong positive correlation was observed between CMAP amplitude and sciatic function index (SFI), a well-recognized assessment for sciatic nerve function. CMAP recordings by direct nerve stimulation at 8 weeks post-injury showed no significant difference in amplitude compared to surface stimulation, but the peak latency was relatively longer than the latter. This study indicated that non-invasive surface stimulation-based periodical recording of CMAPs was a practical electrophysiological approach to monitor the progression of peripheral nerve regeneration in murine models.

Assessment of sensory thresholds and nociceptive fiber growth after sciatic nerve injury reveals the differential contribution of collateral reinnervation and nerve regeneration to neuropathic pain.

Following traumatic peripheral nerve injury reinnervation of denervated targets may be achieved by regeneration of injured axons and by collateral sprouting of neighbor undamaged axons. Experimental models commonly use sciatic nerve injuries to assess nerve regeneration and neuropathic pain, but behavioral tests for evaluating sensory recovery often disregard the pattern of hindpaw innervation. This may lead to confounding attribution of recovery of sensory responses to improvement in sciatic nerve regeneration instead of collateral reinnervation by the undamaged saphenous nerve. We used a standardized methodology to assess the separate contribution of collateral and regenerative skin reinnervation on sensory responses. Section and suture of the sciatic nerve induced loss of sensibility in the lateral and central areas of the injured paw, but nociceptive responses rapidly recovered by expansion of the intact saphenous innervation territory. We used electronic Von Frey and Plantar test devices to measure mechanical and thermal withdrawal thresholds in specific sites of the injured paw: lateral site innervated by the sciatic nerve, medial site that remained innervated by the saphenous nerve, and central site originally innervated by the sciatic nerve but affected by saphenous sprouting. After sciatic section, signs of early hyperalgesia developed in medial and central paw areas due to saphenous sprouting and expansion. The regenerating sciatic nerve fibers reached the paw at 3-4weeks and a late mechanical hyperalgesia was observed at the lateral site. Immunohistochemical staining of sensory fibers innervating the medial and lateral areas revealed a different pattern of skin reinnervation. Hypersensitivity in the intact saphenous nerve area was paralleled by early fiber sprout growth in the subepidermal plexus, but not entering the epidermis. On the other side, late sciatic hyperalgesia was accompanied by gradual skin reinnervation after 4weeks. The standardization of algesimetry testing in sciatic nerve injury models, as proposed in this study, provides a suitable model for studying in parallel neuropathic pain and sensory nerve regeneration processes. Our results also indicate that collateral sprouting and axonal regeneration contribute differently in the initiation and maintenance of neuropathic pain.

[Pain assessment of biological conduit small gap tubulization in rat sciatic nerve multilation model].

OBJECTIVE: To explore the pain sensation recovery discipline of 2 mm small gap biological conduit tubulization and epineurial neurorrhaphy in rat sciatic nerve multilation model. METHODS: Based on the rat sciatic nerve multilation model, 2 mm small gap biological conduit tubulization and epineurial neurorrhaphy were applied and the 50% paw withdrawal threshold was observed after 2, 4, 5, 6, 8 and 12 weeks. The data were analyzed by two-way ANOVA and chi-square criterion. RESULTS: Obvious hyperalgesia was observed in week 2 in both experimental group and control group, and 50% paw withdrawal threshold was improved significantly even to 15 g. The 50% paw withdrawal threshold began to decline week 4 and the 50% paw withdrawal threshold of small gap tubulization group was obviously lower than that of control group, which may imply that the pain sensation recovery of small gap tubulization group was earlier than that of control group. The 50% paw withdrawal threshold of small gap tubulization group began to increase to the plateau period [week 5: (12.70 ± 5.64) g; week 6: (12.20 ± 3.26) g; week 8: (12.31 ± 4.19) g; week 12: (13.95 ± 2.58) g]. The 50% paw withdrawal threshold of control group declined gradually [week 5: (10.47 ± 7.02) g; week 6: (9.42 ± 6.86) g; week 8: (8.50 ± 7.15) g; week 12: (8.06 ± 5.93) g]. The difference was statistical significant between small gap tubulization group and control group in 12th week. CONCLUSION: Compared with the traditional epineurial neurorrhaphy for peripheral nerve multilation, 2 mm small gap biological conduit tubulization can improve the 50% paw withdrawal threshold during peripheral nerve regeneration process and reduce the pain incidence.

Comparison of CatWalk analysis and von Frey testing for pain assessment in a rat model of nerve crush plus inflammation.

STUDY DESIGN: Assessment of pain-related behavior and immunohistology of the dorsal root ganglion in a rat model. OBJECTIVE: To investigate pain-related behavior in a rat model of nerve crush plus inflammation using the CatWalk system. SUMMARY OF BACKGROUND DATA: A definitive method for evaluating animal models of lumbar disease has not been established. Von Frey testing has often been used in this type of study, but the reliability remains in question. The CatWalk system is a computer-assisted apparatus for analyzing gait that provides an automated way to assess gait function during pain. However, there have been few reports using this system for models of lumbar disease. METHODS: Fourteen rats were divided into 2 groups: a treatment group and a sham group. For the treatment group, nucleus pulposus was applied to the sciatic nerve and the sciatic nerve was pinched. Two different methods for assessment of pain-related behavior, von Frey testing and CatWalk analysis, were used before surgery and at 4 and 7 days after surgery. Immunohistochemistry was used to examine calcitonin gene-related peptide expression in L4 to L6 dorsal root ganglia. RESULTS: No significant differences were found between the treatment and sham control groups using von Frey testing. However, significant differences in 4 parameters were found between the 2 groups using the CatWalk system (P < 0.05). The proportion of calcitonin gene-related peptide-immunoreactive neurons was higher in the treatment group than in the control group (P < 0.05). CONCLUSION: Our results demonstrate that the CatWalk system is useful for the measurement of pain-related behavioral change in our rat model in which nociception was indicated at a cellular level. Although further studies are needed, we think that this system is a valid alternative method for the evaluation of models of lumbar disease in rodents.

Peripheral neuropathy: assessment of proximal nerve integrity by diffusion tensor imaging.

INTRODUCTION: We investigated the utility of diffusion tensor imaging (DTI) for detecting neuropathic changes in proximal nerve segments in patients with peripheral neuropathy. METHODS: Twenty-one individuals with (n = 11) and without (n = 10) peripheral neuropathy underwent DTI of a defined sciatic nerve segment. Patients and controls were evaluated by clinical examination and nerve conduction studies at baseline and 6 months after the initial DTI scan. RESULTS: The mean fractional anisotropy (FA) value was significantly lower in sciatic nerves from patients with peripheral neuropathy as compared with controls. Sciatic nerve FA values correlated with clinical disability scores and electrophysiological parameters of axonal damage at baseline and 6 months after MRI scan. CONCLUSIONS: DTI-derived FA values are a sensitive measure to discriminate healthy from functionally impaired human sciatic nerve segments. DTI of proximal nerve segments may be useful for estimating the proximal axonal degeneration burden in patients with peripheral neuropathies.

Multimodal assessment of painful peripheral neuropathy induced by chronic oxaliplatin-based chemotherapy in mice.

BACKGROUND: A major clinical issue affecting 10-40% of cancer patients treated with oxaliplatin is severe peripheral neuropathy with symptoms including cold sensitivity and neuropathic pain. Rat models have been used to describe the pathological features of oxaliplatin-induced peripheral neuropathy; however, they are inadequate for parallel studies of oxaliplatin's antineoplastic activity and neurotoxicity because most cancer models are developed in mice. Thus, we characterized the effects of chronic, bi-weekly administration of oxaliplatin in BALB/c mice. We first studied oxaliplatin's effects on the peripheral nervous system by measuring caudal and digital nerve conduction velocities (NCV) followed by ultrastructural and morphometric analyses of dorsal root ganglia (DRG) and sciatic nerves. To further characterize the model, we examined nocifensive behavior and central nervous system excitability by in vivo electrophysiological recording of spinal dorsal horn (SDH) wide dynamic range neurons in oxaliplatin-treated mice RESULTS: We found significantly decreased NCV and action potential amplitude after oxaliplatin treatment along with neuronal atrophy and multinucleolated DRG neurons that have eccentric nucleoli. Oxaliplatin also induced significant mechanical allodynia and cold hyperalgesia, starting from the first week of treatment, and a significant increase in the activity of wide dynamic range neurons in the SDH. CONCLUSIONS: Our findings demonstrate that chronic treatment with oxaliplatin produces neurotoxic changes in BALB/c mice, confirming that this model is a suitable tool to conduct further mechanistic studies of oxaliplatin-related antineoplastic activity, peripheral neurotoxicity and pain. Further, this model can be used for the preclinical discovery of new neuroprotective and analgesic compounds.

Assessment of alterations in the electrical impedance of muscle after experimental nerve injury via finite-element analysis.

The surface measurement of electrical impedance of muscle, incorporated as the technique of electrical impedance myography (EIM), provides a noninvasive approach for evaluating neuromuscular diseases, including amyotrophic lateral sclerosis. However, the relationship between alterations in surface impedance and the electrical properties of muscle remains uncertain. In order to investigate this further, a group of healthy adult rats, a group of rats two weeks postsciatic crush, and a group of animals six months postcrush underwent EIM of the gastrocnemius-soleus complex. The animals were then killed and the conductivity and permittivity of the extracted muscle measured. Finite-element models based on MRI data were then constructed for each group. The characteristic EIM parameter, 50 kHz phase (±standard error), obtained with surface impedance measurements was 17.3° ± 0.3° for normal animals, 13.8° ± 0.7° for acutely injured animals, and 16.1° ± 0.5° for chronically injured animals. The models predicted parallel changes with phase values of 24.3°, 18.8°, and 21.2° for the normal, acute, and chronic groups, respectively. Other multifrequency impedance parameters showed similar alterations. These results confirm that surface impedance measurements taken in conjunction with anatomical data and finite-element models may offer a noninvasive approach for assessing biophysical alterations in muscle in neuromuscular disease states.

Allopregnanolone prevents and suppresses oxaliplatin-evoked painful neuropathy: multi-parametric assessment and direct evidence.

Oxaliplatin (OXAL) is a platinum-based drug used for the treatment of colorectal, lung, breast and ovarian cancers. OXAL does not cause renal or hematologic toxicity. However, OXAL induces neuropathic pain which hampers the chemotherapy success. Attempts with neuroprotective agents including anticonvulsivants and antidepressants were made to prevent OXAL-induced painful neuropathy but the clinical data are controversial and the tested neuroprotectors are able to evoke themselves undesirable effects. Here, we demonstrated that the natural neurosteroid allopregnanolone (3α,5α-THP), known to be devoid of toxic side-effects in humans and experimental models, prevented and suppressed OXAL-induced painful neuropathic symptoms. Indeed, 3α,5α-THP repaired OXAL-evoked neurochemical and functional alterations in peripheral nerves and intra-epidermal nerve fibers (IENF). Behavioral analyses showed that prophylactic or corrective 3α,5α-THP treatment (4mg/kg/2days) respectively prevented or abolished OXAL-induced cold allodynia, mechanical allodynia and hyperalgesia by reversing to normal decreased thermal and mechanical pain thresholds of OXAL-treated rats. Electrophysiological investigations revealed that 3α,5α-THP restored control values of sciatic nerve conduction velocity and action potential peak amplitude drastically reduced by OXAL-treatment. Furthermore, immunohistochemistry and confocal microscopic quantifications demonstrated that 3α,5α-THP repaired OXAL-induced neurochemical/cellular alterations by restoring IENF control density and normal level of neurofilament 200kDa that was strongly repressed by OXAL in dorsal root ganglion neurons and sciatic nerve axons. OXAL showed no toxicity for the non-compact myelin protein 2',3'-cyclic-nucleotide-3'-phosphodiesterase whose expression level was similarly increased by 3α,5α-THP in controls and OXAL-treated rat nerves. Together, these results may be interesting for the development of natural or safe neurosteroid-based neuroprotective strategy against anticancer drug-evoked painful neuropathy.

Assessment of 3-nitropropionic acid-evoked peripheral neuropathy in rats: neuroprotective effects of acetyl-l-carnitine and resveratrol.

Oxidative stress and secondary excitotoxicity, due to cellular energy deficit, are major factors playing roles in 3-nitropropionic acid (3-NPA) induced mitochondrial dysfunction. Acute or chronic exposure to 3-NPA also leads to neuronal degeneration in different brain regions. The present study quantitatively assessed peripheral neuropathy induced by chronic exposure to 3-NPA in rats. The neuroprotective abilities of two antioxidants, acetyl-l-carnitine and resveratrol, were investigated as well. Rats were exposed for up to four weeks to 3-NPA alone or 3-NPA combined with acetyl-l-carnitine or resveratrol, administered peripherally. The experimental outcome was evaluated by neurophysiological, histological, and morphometric analyses. Rats exposed to 3-NPA developed hind limb paresis. Furthermore, a significant decrease in motor nerve conduction velocity (MCV) was detected in tail nerves and axonal degeneration in sciatic nerves (p<0.05). Treatment with resveratrol prevented the functional effects of 3-NPA exposure, whereas treatment with acetyl-l-carnitine, preventing paresis, was not effective to MCV and morphological changes. These data suggest that resveratrol is a good candidate for treatment of metabolic neuropathy. The experimental outcome of this study shows that chronic treatment with 3-NPA in rats is relevant in development of an experimental model of toxic neuropathy.

Functional assessment after sciatic nerve injury in a rat model.

The aim of this study is to evaluate the effectiveness of Sciatic Function Index (SFI) and Basso, Beattie, and Bresnahan (BBB) Locomotor Rating in assessing peripheral nerve injuries. SFI is a standard method for evaluating crush and transected peripheral nerve injuries, likewise BBB for spinal cord injury. Models of chronic nerve compression (CNC), crush, and transection injury were created on Sprague-Dawley rats and functional outcomes were measured using BBB and SFI at 1-week interval for 6 weeks. All injury models showed high correlation between SFI and BBB scores. With crush injury, the SFI showed near complete recovery while BBB showed residual deficits 6 weeks after injury. Both the BBB and SFI were unable to detect motor deficits in 6-week CNC animals. The BBB score should be considered as an adjunct in evaluating peripheral nerve recovery and may be more sensitive in detecting residual deficits than SFI after crush-type injuries.

The CatWalk method: assessment of mechanical allodynia in experimental chronic pain.

The CatWalk gait analysis system has recently been suggested as a rapid and objective alternative method over the von Frey test to assess mechanical allodynia in chronic neuropathic pain models. Our results demonstrate that no correlation exists between the development of mechanical allodynia and changes in CatWalk-gait parameters in a chronic inflammatory pain model. Hence, the use of the CatWalk in assessment of experimental chronic pain is discussed.

Assessment of long- and short-term neurotoxic effects of glass ionomer bone cement by electromyography and histopathologic examination: experimental study.

OBJECTIVE: The objective of this study was to investigate the possible neurotoxic effects of bone cement on the peripheral nerves. STUDY DESIGN: Experimental study. SETTING: Teaching and research hospital. METHODS: Twenty New Zealand rabbits were included in this study. The sciatic nerves of both legs of the 10 rabbits were exposed surgically under general anesthesia and closed primarily without any intervention and constituted the control group (group 1). Following surgical exploration, glass ionomer cement (GIC) was applied to the left sciatic nerves of the 10 rabbits for 10 seconds and then aspirated (group 2). GIC material was also applied to the right sciatic nerves of these rabbits but without aspiration (group 3). OUTCOME MEASURES: All rabbits were sacrificed at the end of 8 weeks postoperatively following electromyographic investigation. The sections were stained with hematoxylin-eosin and Immune Olig 2 staining technique for histopathologic examination under light microscopy. RESULTS: There was no statistically significant difference in distal latency, which indicates the conduction speed of the nerve, between all groups by electromyography. Histopathologic examination of all specimens revealed no demyelinization or axonal degeneration, and all had an intact myelin structure. There was no statistically significant difference in inflammation of the specimens between groups. (p>.05). CONCLUSION: GIC has no neurotoxic effects on the nerves in short- and long-term applications.

A new approach to assess function after sciatic nerve lesion in the mouse - adaptation of the sciatic static index.

Among the numerous ways of assessing regeneration after peripheral nerve lesions, the analysis of gait is one of the most important, because it shows the recovery of function, which is the ultimate goal of the repair machinery. The sciatic function index was introduced as a method to assess reinnervation after an experimental sciatic nerve lesion, and was adapted to the mouse model. The sciatic static index (SSI), is more simple and practical to perform, and is not so influenced by gait's velocity, but this method has not yet been adapted to the mouse model of sciatic lesion. We used 63 male Swiss mice (Mus musculus) to develop a formula to the sciatic static index in mice (SSIm). The animals were divided on three groups (control, transection and crush). They were evaluated at the preoperative and 7th, 14th, 21st, 28th, 35th and 42nd days postoperative by the ink track method (SFI), and by the acquisition of photographs of the plantar aspects of the injured and uninjured hind paws. The parameters evaluated were the 1-5 toe spread (TS), the 2-4 toe spread (ITS) and the distance between the tip of the third toe and the most posterior aspect of the paw (PL), on both methods. After verifying the temporal pattern of function, correlation and reproducibility of the measurements, we performed a multiple regression analysis using SFI values as dependent variable, and the TS, ITS and PL measured with the photo method as independent variables, and found the formula of the SSI for mice (SSIm). The three groups (control, transection and crush) had a characteristic pattern of dysfunction. The parameters measured in the ink and photo method had variable but significant correlations between them (P<0.000), but photo method of measurement showed a better reproducibility. The correlation between SFI and SSIm showed a high correlation coefficient (r=0.892, P<0.000), and demonstrates that SSIm can be used as an alternative method to assess the functional status relative of sciatic nerve activity in mice.

Assessment of effects of pinealectomy and exogenous melatonin administration on rat sciatic nerve suture repair: an electrophysiological, electron microscopic, and immunohistochemical study.

BACKGROUND: Collagen scar formation at the cut end of a nerve, an important problem in clinical practice for neurosurgeons in peripheral nerve surgery, obstructs sprouting of axons into appropriate distal fascicles, and thereby limits nerve regeneration. Researchers attempt to control collagen accumulation in the formation of neuroma by various physical and chemical methods, but these have yielded only limited functional success. This is the first experimental study investigating the effects of melatonin (MLT) on nerve repair and neuronal regeneration in rat sciatic nerve suture repair. METHODS: The hypothesis that exogenous MLT administration may inhibit the formation of neuroma in peripheral nerve surgery was investigated in rat sciatic nerve model. In this study, a total of 80 rats were used for control groups (Groups Ia, Ib, IIa, and IId), MLT group (Group Ic), surgical pinealectomy (Px) groups (Groups IIb and IIc), and group of MLT treatment following Px procedure (Group IIe). All animals underwent a surgical intervention consisting of bilateral sciatic nerve section and primary suture repair. At 8 weeks after repair, the animals were killed following completion of recording of nerve action potentials (NAPs). Then, unilateral sciatic nerve specimens including the suture repair region were carefully removed and the excised segments were processed for electron microscopy examination. Afterwards, contralateral sciatic nerve specimens from two animals from each group were removed and stained for immunohistochemical analysis. RESULTS: Results of morphometric analysis revealed that Px procedure caused an elevation of collagen content of the sciatic nerve and macroscopic neuroma formation, and that there was a statistically significant reduction in collagen content of the same region in pinealectomized animals treated with MLT (p<0.001). Accordingly, electrophysiological findings demonstrated that the stimulus intensities required to excite a NAP response were increased in surgical Px group, but the presence of a reduced threshold response was found in the group treated with MLT following Px procedure (p<0.01). Immunohistochemical staining for Type I collagen and Type III collagen was markedly more intense in the epineurium of animals after Px. Virtually no or only weak staining was observed in animals in control groups and the MLT treatment group. Results of immunohistochemical analysis revealed that surgical Px procedure caused a strong immunoreactivity for Type I collagen and Type III collagen in all connective tissue planes of the nerve, especially in the epineurium, and there was a statistically significant reduction in immunoreactivity of the repair region in animals receiving MLT treatment after Px procedure (p<0.001). CONCLUSION: This study demonstrates that exogenous MLT administration significantly inhibits collagen accumulation in the formation of neuroma in the suture repair site and thereby improves nerve regeneration. From a clinical standpoint, the positive effect of MLT administration on neuroma formation and nerve regeneration seems a particularly attractive treatment option. Therefore, we believe that nerve repair with addition of MLT may be a worthwhile option in addition to other treatment modalities in case of MLT deficiency, such as aging. However, further experimental and clinical studies using functional analysis warranted to confirm this result in future.

Collagen nerve conduits--assessment of biocompatibility and axonal regeneration.

Bridging of nerve gaps is still a major problem in peripheral nerve surgery. Alternatively to autologous nerve grafts tissue engineering of peripheral nerves focuses on biocompatible conduits to reconstruct nerves. Such non-neural conduits fail to support regeneration over larger gaps due to lacking viable Schwann cells that promote regeneration by producing growth factors and cell guiding molecules. This problem may be overcome by implantation of cultivated Schwann cells into suitable scaffolds. In the present experiments we tested a collagen type I/III tube as a potential nerve guiding matrix. Revascularization, tolerance and Schwann cell settlement were evaluated by light, fluorescence and scanning electron microscopy after different implantation times. The conduits were completely revascularized between day 5 and 7 post-operatively and well integrated into the host tissue. Implanted Schwann cells adhered, survived and proliferated on the inner surface of the conduits. Nevertheless, bridging a 2 cm gap of the sciatic nerve of adult Wistar rats with these collagen/Schwann cell conduits led to a disappointing regeneration compared to controls with autologous grafts. From these results, we conclude that a sufficient biocompatibility of bioartificial nerve conduits is a necessary prerequisite, however, it remains only one of several parameters important for peripheral nerve regeneration.