Pulsed Magnetic Field Treatment for Calming Neuroinflammation in Pain Conditions

Context

Neuroinflammation can be associated with inflammatory mediators, such as cytokines and chemokines, that follow damage, injury, infection, or illness in the peripheral nervous system (PNS) and/or the central nervous system (CNS). These can play strategic roles in the formation and continuation of abnormal pain behaviors. Pulsed magnetic field (PMF) treatments have attracted attention for the prevention and management of various pain conditions.

Objective

The review intended to examine the mechanisms underlying the documented anti-neuroinflammatory effects of PMF treatment and its beneficial effects for neuroinflammatory pain states.

Design

The research team performed a narrative review by searching for articles in the PubMed databases. The search used the keywords, pulsed magnetic field, neuroinflammation, cytokines, chemokines, pain, alone and in combination, without the restriction of the publication date.

Setting

This study was take place in faculty of medicine, Usak University, Usak, Turkey.

Results

Neuroinflammation is a very complex process with the contribution of many inflammatory cells and their mediators. PMF treatment may modulate the neuroinflammatory conditions in the central and peripheral neural tissues.

Conclusions

The noninvasive PMF therapy, which has parameters that can be controlled and which has no side effects, is a nonpharmacological therapeutic option with pain-relief ability through strong control of central and peripheral neuroinflammation. Further studies are needed to explore how PMF therapy controls central and peripheral neuroinflammation in various diseases and conditions.

Pulsed magnetic field treatment ameliorates the progression of peripheral neuropathy by modulating the neuronal oxidative stress, apoptosis and angiogenesis in a rat model of experimental diabetes

OBJECTIVE

The present study aimed to investigate the possible anti-neuropathic effects of daily pulsed magnetic field treatments (PMF) in streptozotocin (60 mg/kg) induced 4 weeks diabetic (type-1) wistar rats (6-8 months).

MATERIALS AND METHODS

Body mass, blood glucose and thermal and mechanical sensations were evaluated during the PMF or sham-PMF in diabetic or non-diabetic rats (n = 7/group). After the measurements of motor nerve conduction velocities (MNCV), the levels of several biomarkers for oxidative stress, apoptosis and angiogenesis in spinal cord and sciatic nerve were measured.

RESULTS

PMF for 4 weeks significantly recovered the MCNV (96.9% and 63.9%) and almost fully (100%) restored to the latency and threshold. PMF also significantly suppressed the diabetes induced enhances in biochemical markers of both neuronal tissues.

CONCLUSIONS

Findings suggested that PMF might prevent the development of functional abnormalities in diabetic rats due to its anti-oxidative, anti-apoptotic and anti-angiogenic actions in neuronal tissues.

Magnetic Field Exposure Modulates the Anti-Inflammatory Efficiency of Minocycline in Rats with Peripheral Acute Inflammation

BACKGROUND AND OBJECTIVE

Microglial activation in spinal cord is key contributor and its inhibition by Minocycline (MCN) can result in anti-inflammatory actions. Effect of pulsed magnetic field (PMF) in living system is a very complex process and many biological and cellular processes can play key roles. In this study aimed to reveal the roles of PMF exposure on anti-inflammatory potentials of MCN treatment by evaluating the inflammatory profiles of either inflamed site or spinal cord.

METHODS

In this study, we investigated the anti-inflammatory effects of PMF, MCN or their combination treatments in rats with carrageenan (CG)-induced peripheral inflammation by examining the cardinal signs, hyperalgesia, allodynia, edema and fever. The levels of various inflammation markers (tumor necrosis factor-α), interleukin (IL)-1β, IL-6, IL-17, IL-4, IL-10, C-C motif chemokine ligand3 (CCL3), C-X-C motif chemokine ligand1 and myeloperoxidase were also measured in paw and spinal cord tissues.

RESULTS

CG induced inflammation caused edema, fever, and hypersensitivities. MNC or PMF treatments ameliorated these responses by suppressing pro-inflammatory markers in both inflamed paw and spinal cord. Although anti-hypersensitive, anti-edematous and anti-pyretic actions of MCN or PMF, in combined treatments PMF exposure decreased the anti-hyperalgesic and anti-allodynic actions of MCN treatment. These may be associated with decreases in IL-4 and IL-10 levels and an increase in CCL3 level of spinal cord tissues.

CONCLUSION

Present findings support that MCN or PMF has anti-inflammatory properties duo to the down-regulating central microglial and/or peripheral inflammatory markers. Our data showed here, for the first time, PMF exposure may suppress the anti-hypersensitive actions of MCN by modulating microglia function/phenotype and microglial markers.

Pro-inflammatory or anti-inflammatory effects of pulsed magnetic field treatments in rats with experimental acute inflammation

In this study, we evaluated the possible effects of sequenced pulsed magnetic fields (PMF) of 1-mT treatments with designed different frequencies (PMF-1-1, 3, 5, 7 Hz or PMF-2-7, 9, 12, 14 Hz) on the inflammatory signs such as abnormal pain behaviors, hyperalgesia and allodynia, edema, and fever in carrageenan (CG)-induced hind paw inflammation model in rats. Paw tissues were also histologically examined. PMF exposure was applied 3 times in 24 h. CG injection gradually decreased the thermal latencies and mechanical threshold and caused significant increases in temperature and mass of paw. PMF treatments significantly reduced the temperature and mass in the paw of rats with inflammation. PMF-1 treatments caused significant increases in the latencies and thresholds. However, administration of PMF-2 treatment was significantly decreased the latency and threshold. Furthermore, the histological pieces of evidence also suggested the anti-inflammatory effects of PMF-1 treatments or inflammatory actions of PMF-2 treatments. Findings presented in this paper suggest that 1-mT PMF treatments may have anti-edematous and antipyretics activities in inflamed rats. However, the effects of PMF treatments on abnormal pain hypersensitivities may be different. PMF treatments may make inflammatory pain relief or worse in inflamed rats depending on the PMF frequencies in sequence.

Effects of immune cell-targeted treatments result from the suppression of neuronal oxidative stress and inflammation in experimental diabetic rats

In this study, we hypothesized that reduction of immune cell activation as well as their oxidant or inflammatory mediators with minocycline (MCN), liposome-encapsulated clodronate (LEC), or anti-Ly6G treatments can be neuroprotective approaches in diabetic neuropathy. MCN (40 mg/kg) for reduction of microglial activation, LEC (25 mg/kg) for of macrophage inhibition, or anti-Ly6G (150 μg/kg) for neutrophil suppression injected to streptozotocin (STZ)-induced diabetic rats twice, 3 days, and 1 week (half dose) after STZ. Animal mass and blood glucose levels were measured; thermal and mechanical sensitivities were tested for in pain sensations. The levels of chemokine C-X-C motif ligand 1 (CXCL1), CXCL8, and C-C motif ligand 2 (CCL2), CCL3, and total oxidant status (TOS) and total antioxidant status (TAS) were measured in the spinal cord and sciatic nerve tissues of rats. LEC significantly reduced the glucose level of diabetic rats compared with drug control. However, MCN or anti-LY6G did not change the glucose level. While diabetic rats showed a marked decrease in both thermal and mechanical sensations, all treatments alleviated these abnormal sensations. The levels of chemokines and oxidative stress parameters increased in diabetic rats. All drug treatments significantly decreased the CCL2, CXCL1, and CXCL8 levels of spinal cord tissues and ameliorated the neuronal oxidative stress compared with control treatments. Present findings suggest that the neuroprotective actions of MCN, LEC, or anti-Ly6G treatments may be due to the modulation of neuronal oxidative stress and/or inflammatory mediators of immune cells in diabetic rats with neuropathy.

Antiinflammatory properties of antiLy6G antibody disappear during magnetic field exposure in rats with carrageenan induced acute paw inflammation

Antiinflammatory properties of pulsed magnetic field (PMF) treatments or administration of antiLy6G antibody have been previously reported. In this study, we hypothesized that, the combination of PMF treatments and antiLy6G administration may synergistically potentiate their antiinflammatory actions. The effects of the combination of PMF treatments and antiLy6G administration were investigated by examining the inflammatory signs, histopathological properties of the inflamed site, and measuring the macrophage inflammatory protein-1 alpha (MIP-1α/CCL3) and myeloperoxidase (MPO) levels of inflamed paw tissues in rats with carrageenan-induced acute paw inflammation. In this present study, PMF treatments alone or administration of antiLy6G alone ameliorated the acute inflammation. However, their combination exacerbated the inflammatory signs, hyperalgesia, allodynia, edema and fever, and aggravated the inflammatory conditions by excessive infiltration of inflammatory cells to the inflamed site. These opposing effects of the combined treatments may correlate with enhanced levels of MIP-1α and MPO in inflamed paws. Present results indicated that the combination of the PMF treatments and antiLy6G administration may not provide additional benefits and may actually cause an aggravation of the acute inflammatory process. Findings may also suggest that during neutrophil or immune cell-targeted treatments for inflammatory states, magnetic field exposure may cause unexpected negative consequences.

Pulsed magnetic field enhances therapeutic efficiency of mesenchymal stem cells in chronic neuropathic pain model

Cell-based or magnetic field therapies as alternative approaches to pain management have been tested in several experimental pain models. The aim of this study therefore was to investigate the actions of the cell-based therapy (adipose tissue derived mesenchymal stem cells; ADMSC) or pulsed magnetic field (PMF) therapy and magneto-cell therapy (combination of ADMSC and PMF) in chronic constriction nerve injury model (CCI). The actions of individual ADMSC (route dependent [systemic or local], time-dependent [a day or a week after surgery]), or PMF and their combination (magneto-cell) therapies on hyperalgesia and allodynia were investigated by using thermal plantar test and a dynamic plantar aesthesiometer, respectively. In addition, various cytokine levels (IL-1β, IL-6, and IL-10) of rat sciatic nerve after CCI were analyzed. Following the CCI, both latency and threshold significantly decreased. ADMSC or PMF significantly increased latencies and thresholds. The combination of ADMSC with PMF even more significantly increased latency and threshold when compared with ADMSC alone. However, ADMSC-induced decrease in pro-inflammatory or increase in anti-inflammatory cytokines levels were partially prevented by PMF treatments. Present findings may suggest that both cell-based and magnetic therapies can effectively attenuate chronic neuropathic pain symptoms. Combined magneto-cell therapy may also efficiently reverse neuropathic signs. Bioelectromagnetics. 38:255-264, 2017. © 2017 Wiley Periodicals, Inc.

Impact of Magnetic Field on Pressures of Programmable Cerebrospinal Fluid Shunts: An Experimental Study

AIM

To investigate whether programmable cerebrospinal fluid (CSF) shunts are influenced by exposure to the magnetic field and to compare the effects of magnetic field in 4 different brands of programmable CSF shunts.

MATERIAL AND METHODS

This experimental study was performed in the laboratory using a novel design of magnetic field. Four types of programmable CSF shunts (Miethke®, Medtronic®, Sophysa® and Codman®Hakim®) were exposed to the magnetic field generated by an apparatus consisting of Helmholtz coil for 5 minutes. In every CSF shunt, initial pressures were adjusted to 110 mm H2O and pressures after exposure to magnetic field were noted. These measurements were implemented at frequencies of 5 Hz, 20 Hz, 30 Hz, 40 Hz, 60 Hz and 80 Hz. In each type, three shunts were utilized and evaluations were made twice for every shunt.

RESULTS

At 5, 30, 40 and 60 Hz, Groups 1, 2 and 3 had significantly higher average pressures than Group 4. At 20 and 80 Hz, Groups 1 and 2 had notably different pressure values than Groups 3 and 4. Group 3 displayed the highest pressure, while Group 4 demonstrated the lowest pressure.

CONCLUSION

Exposure to magnetic fields may affect the pressures of programmable CSF shunts. However, further controlled, clinical trials are warranted to elucidate the in-vivo effects of magnetic field exposure.

Dexmedetomidine modifies uterine contractions in pregnancy terms of rats

OBJECTIVES

The present study was aimed at determining the effective doses of Dexmedetomidine (Dex) involved in amplitude of contraction-force and frequency of uterine rings in pregnancy terms of rats. All experiments involving animal subjects were carried out with the approval of animal care and use Ethical Committee of Cukurova University. Experiments were performed on female Albino-Wistar rats (200-260 g; n = 40).

MATERIALS AND METHODS

Uterine rings from pregnant rats were placed in organ bath with Krebs and calcium ion (Ca(2+))-free solutions to record and exposed to serially increasing log10 concentrations of Dex.

RESULTS

In Krebs solution, while Dex caused an increase in the spontaneous contraction-forces in all pregnancy terms of rats in a significant dose-dependent manner, it led to a decrease in contraction-frequency in late-pregnancy term of rats. In Ca(2+)-free, the spontaneous contraction-force decreased in late-pregnancy term and increased in early and middle-pregnancy terms. In addition, while Dex increased the contraction-frequency in early and middle-pregnancy terms, it decreased in late-pregnancy term in a dose-dependent manner.

STATISTICAL ANALYSIS USED

The data were subjected to one-way analysis of variance. Repeated measures were employed for comparison of several group means through the Tukey post-hoc test (SPSS 10.00 Inc., Chicago, Ill, USA). P < 0.05 was considered statistically significant.

CONCLUSIONS

This study suggested that Dex might differently alter the spontaneous contraction-forces and contraction-frequencies of uterine rings in all pregnancy terms of rats in Krebs and Ca(2+)-free solutions.

Antinociceptive activities of lidocaine and the nav1.8 blocker a803467 in diabetic rats

The streptozocin-induced diabetic rat is a model of chronic pain that shows signs of hyperalgesia and allodynia and may replicate signs in diabetic humans. Here we investigated the antinociceptive effects of A803467, a highly selective blocker of Nav1.8 channels, in diabetic rats with painful neuropathy. We systemically (intraperitoneal) or locally (intraplantar) administered A803467 (or lidocaine, a nonselective sodium channel blocker, as a control) to diabetic rats with hyperalgesia and allodynia and then measured thermal latencies and mechanical thresholds. With intraperitoneal administration, A803467 led to 6-fold greater reduction of hyperalgesia and 2-fold greater reduction of allodynia than did lidocaine. Whereas the antihyperalgesic effects of lidocaine and A803467 were similar after intraplantar administration, A803467 (1 mg) was at least 2 times more effective as an antiallodynic than was lidocaine (0.5 mg). These results suggest that compared with lidocaine, systemic or local blockade of Nav1.8 channels by A803467 may more effectively relieve hyperalgesia and allodynia in diabetic neuropathy.

Comparison of actions of systemically and locally administrated local anaesthetics in diabetic rats with painful neuropathy

Nothing is known about actions of levobupivacaine, a long-acting local anaesthetic belonging to the amino amide group, in diabetes-induced neuropathic pain conditions. In this study, we therefore investigated the possible antihyperalgesic and antiallodynic effects of levobupivacaine in diabetic animal model. Actions of systemically (intraperitoneal) or locally (intraplantar) administrated levobupivacaine on streptozotocin-induced diabetic rats with painful neuropathy were examined using a thermal plantar test and a dynamic plantar aesthesiometer. Effects of levobupivacaine were compared with those of a well-known amide local anaesthetic lidocaine. Levobupivacaine was more potent than lidocaine in all tests employed on diabetic rats. After intraperitoneal injections to diabetic rats, levobupivacaine, but not lidocaine, produced pronounced antihyperalgesic and antiallodynic effects. However, intraplantar administration of both levobupivacaine and lidocaine produced antihyperalgesic and antiallodynic action in diabetic rats. In contrast to the transient effects of lidocaine (30 min), antihyperalgesic and antiallodynic actions of levobupivacaine gradually disappeared within 120 min after intraplantar injections. Intraperitoneal or intraplantar administrations of levobupivacaine or lidocaine at the effective dose had no effect on any parameters in intact rats. Findings revealed that antiallodynic and antihyperalgesic potency of levobupivacaine was higher in comparison with that of lidocaine after their intraperitoneal or intraplantar administration to diabetic animals. Furthermore, locally administrated levobupivacaine has the greatest antihyperalgesic and antiallodynic actions in diabetic rats.

Macrophage depletion delays progression of neuropathic pain in diabetic animals

Despite the fact that it is a frequent diabetic complication, the mechanisms underlying the manifestation of diabetic neuropathic pain remain poorly understood. In this study, we hypothesized that the depletion of peripheral macrophages with liposome-encapsulated clodronate (LEC) can prevent, at least delay, the progression of diabetes-induced neuropathic pain. Therefore, the aim of this study was to evaluate the effects of macrophage depletion on mechanical allodynia and thermal hyperalgesia in the streptozotocin (STZ)-induced rat model of diabetic neuropathy. LEC was intravenously administrated to rats three times with 5-day intervals. A single intravenous injection of STZ caused an increase in the average blood glucose levels and a decrease in body weight. Although LEC treatment did not affect the body weight gain, the blood glucose level was lower and serum insulin level higher in LEC-treated diabetic rats than in that of diabetic rats. In addition, LEC treatment alleviated the excessive damage in beta cells in diabetic rats. Diabetic animals displayed marked mechanical allodynia and thermal hyperalgesia. While the treatment of diabetic rats with LEC did not significantly change the thermal withdrawal latency, diabetes-induced decrease in mechanical paw withdrawal threshold was significantly corrected by the LEC treatment. The results of this study show that thermal hyperalgesia and mechanical allodynia induced by diabetes may be associated with alterations in blood glucose level. Depletion of macrophages with LEC in diabetic rats may reduce mechanical allodynia without affecting thermal hyperalgesia. Taken together, these results suggested that depletion of macrophages in diabetes may partially postpone the development of diabetic neuropathic pain.

Roles of axonal voltage-dependent ion channels in damaged peripheral nerves

Ion channels are fundamental to the correct functioning of nerves. A high density of Na(v) channels at nodes of Ranvier is crucial for generating sufficient local current to initiate a self-regenerating action potential. K(v)7 (KCNQ) channels are also functional components of nodes of Ranvier and contribute to the repolarization of the action potential. Paranodes underlying the paranodal loops have no channels whereas K(v)1.1 and K(v)1.2 channels cluster at juxtaparanodes. The disruption of the normal balance of different channels causes the inappropriate nerve activity that underlies a variety of nervous system diseases. Axonal voltage-dependent channels, nodal Na(v) and juxtaparanodal K(v) channels disperse after the nerve injury and reorganize with regeneration.

Role of 4-aminopyridine-sensitive potassium channels in peripheral antinociception

Previous studies has report the modulation of K+ channels play key roles in the induction of peripheral antinociception induced by many types of drugs. However, the possible participation of 4-aminopyridine-sensitive K+ channels to local antinociception induced by tramadol, a mu opioid receptor agonist, and lidocaine, a local anaesthetic, has been less studied. In this study, we therefore investigated this by using thermal plantar test. Tramadol or lidocaine administered intraplantarly into the hind paw elicited an antinociceptive effect. 4-aminopyridine caused an increase in the antinociception produced by lidocaine. However, tramadol induced antinociception remained unaffected by intraplantar administration of 4-aminopyridine. These results suggest that 4-aminopyridine-sensitive K+ channels may play an important role in the thermal peripheral antinociception produced by lidocaine, but not tramadol.

Local analgesic efficacy of tramadol following intraplantar injection

Several studies have suggested that systemic tramadol, an opioid, can represent a valuable treatment in severe pain conditions because of their effects on central pain pathways. However, there are not enough studies supporting that tramadol is efficacious when administered locally. Therefore, we studied the potential local analgesic effects of tramadol in peripheral nociception. In addition, we tested the antinociceptive effects of tramadol-CaCl(2) or naloxone combinations after subcutaneous intraplantar injection in a validated rat model of acute thermal nociception. Local analgesic effects of tramadol were compared with those of lidocaine. The effects of tramadol on thermal paw withdrawal latencies were monitored using the plantar test. The antinociceptive potency of tramadol is higher and long-lasting than that of lidocaine. Naloxone was unable to inhibit the increased antinociceptive response produced by tramadol. Ca(2+) modified the effect of tramadol. When Ca(2+) dose was increased in the solution, thermal antinociceptive potency of tramadol, but not lidocaine was prolonged. Thermal nociceptive responses were not affected in the non-injected paws, indicating a lack of systemic effects with doses of tramadol and lidocaine that elicited local analgesia. These results suggest that intraplantar tramadol administration can produce local analgesic effect with a different action mechanism than that of lidocaine. In addition, extracellular Ca(2+) may play an important role in the local analgesic action of tramadol.

Regenerative effects of pulsed magnetic field on injured peripheral nerves

Previous studies confirm that pulsed magnetic field (PMF) accelerates functional recovery after a nerve crush lesion. The contention that PMF enhances the regeneration is still controversial, however. The influence of a new PMF application protocol (trained PMF) on nerve regeneration was studied in a model of crush injury of the sciatic nerve of rats. To determine if exposure to PMF influences regeneration, we used electrophysiological recordings and ultrastructural examinations. After the measurements of conduction velocity, the sucrose-gap method was used to record compound action potentials (CAPs) from sciatic nerves. PMF treatment during the 38 days following the crush injury enhanced the regeneration. Although the axonal ultrastructures were generally normal, slight to moderate myelin sheath degeneration was noted at the lesion site. PMF application for 38 days accelerated nerve conduction velocity, increased CAP amplitude and decreased the time to peak of the CAP. Furthermore, corrective effects of PMF on. the abnormal characteristics of sensory nerve fibers were determined. Consequently, long-periodic trained-PMF may promote both morphological and electrophysiological properties of the injured nerves. In addition, corrective effects of PMF on sensory fibers may be considered an important finding for neuropathic pain therapy.

Comparative effects of lidocaine and tramadol on injured peripheral nerves

The aim of the present study was to investigate the action of lidocaine and tramadol on the abnormal impulse characteristics of injured peripheral nerves. The ultrastructure of nerves was studied with electron microscopy and the action of lidocaine and tramadol on intact and injured rat sciatic nerves was examined by using the sucrose gap recording technique. Tramadol and lidocaine caused concentration- and frequency-dependent decreases in the amplitude of the compound action potential. Injured nerves were more sensitive to lidocaine than to tramadol. Lidocaine suppressed the delayed depolarization and decreased the hyperpolarizing afterpotentials to a greater extent than did tramadol. A low concentration of lidocaine may restore the abnormal impulse characteristics of injured nerves without changing the normal impulse pattern. The efficacy of lidocaine and inefficacy of tramadol on abnormal impulse characteristics may contribute, at least in part, to our understanding of the mechanisms of action of these drugs in neuropathic pain therapy.

Kv1 Channels in Signal Conduction of Myelinated Nerve Fibers

The myelinated axon can be divided into three domains: the internodal axon, the paranodal axon and the nodal axon. The internodal axolemma contains high concentrations of K+ channels that are enriched in the juxtaparanodal region, whereas Na+ channels cluster in the node. This molecular organization of the myelinated axon membrane is critically important for the rapid and successful transmission of electrical impulses. The juxtaparanodal K+ channels are believed to be electrically inactive in adult peripheral nerves, but experiments with blocking drugs and genetic deletion have shown that they may serve important functions at earlier developmental stages, and during remyelination and regeneration.

Effects of tramadol on nerve action potentials in rat: comparisons with benzocaine and lidocaine

The effects of tramadol on repetitively elicited action potentials were studied in rat sciatic nerve, using the sucrose gap method. Tramadol's local anesthetic-like effects were compared with lidocaine and benzocaine at single or 10, 40, and 100 Hz stimulations. Tramadol and lidocaine both produced approximately the same level of conduction block. The depolarization time of the compound action potentials (CAP) measured from the beginning to the peak of the CAPs, was extended by lidocaine and tramadol, but benzocaine had no effect in this respect. Tramadol extended half width of CAP more than lidocaine. Lidocaine and tramadol produced similar conduction-block patterns, which were different from benzocaine. The results suggested that tramadol enhanced the nerve conduction like lidocaine. However, their frequency-dependent block patterns were similar. It was concluded that tramadol may block the Na+ channels following the hydrophilic pathway like lidocaine and block K+ channels more than lidocaine. These may accounted for the local anesthetic-like effects of tramadol.

[Effect of tramadol on regeneration after experimental sciatic nerve injury]

Abnormal impulses in peripheral nerves play a critical role in neuropathic pain syndromes. The voltage-gated Na+ channels that underlie the action potential are main targets for clinically useful drugs in the pain therapy. Systemic tramadol has been shown to have clinical efficacy against some forms of neuropathic pain. Therefore, we investigated the mechanisms of action of tramadol by an in vitro model by sucrose-gap technique. Tramadol produced concentration-dependent and frequency-dependent decrements in CAP amplitude. Also, injured nerves were more sensitive to tramadol. Tramadol decreased the amplitude of the delayed depolarization and the hyperpolarizing afterpotentials. In conclusion, blocking potencies of small concentration tramadol on the delayed depolarization and hyperpolarizing afterpotential in regeneration period may be contributed for understanding of the action mechanisms of tramadol on neuropathic pain therapy.

Alterations in conduction characteristics of crushed peripheral nerves

PURPOSE

Nerve crush injury results in the incapability to maintain conduction of an impulse. Disruption in the myelin sheath causes very important changes in the activities of ion channels. Therefore, crushed and intact sciatic nerves were researched with both histological and electrophysiological methods in this study.

METHODS

Electron and light microscopy for histological examinations, a sucrose-gap recording techniques for electrophysiological examinations were used. 4-aminopyridine (4-AP) and Tetraethylammonium (TEA) were used to functional separation of the fast and slow K;+ channels.

RESULTS

The number of damaged myelinated nerve fiber was counted as 750 +/- 3.5. Lamellar separation and disruption in myelin sheath was frequently observed in these fibers. Conduction velocity of crushed nerves (19 +/- 2 m/s) was half of the intact nerves. The relationship between equally spaced interstimulus interval and their responses demonstrated that 4-AP and 4-AP plus TEA have more pronounced effects on crushed nerves than on intact nerves. After 4-AP, TEA application caused an efficiently depolarization in the membrane potential.

CONCLUSIONS

The effects of 4-AP and 4-AP plus TEA suggest the involvement of slow and fast K;+ channels and slow Na;+ currents in membrane potential and action potential repolarization. Minimal myelin damage may significantly influence the subsequent impulse generation and the patterning of action potential activity.

Role of Potassium Channels in the Frequency-Dependent Activity of Regenerating Nerves

After a peripheral nerve injury, ion channel organization and the electrical properties of nerve fibers drastically change during the regeneration process. The present study was designed to compare the frequency-dependent characteristics of regenerating nerves in the presence of 4-aminopyridine (4-AP) and tetraethylammonium (TEA). The results showed that increasing the stimulus frequency produced a greater impulse blockade (frequency-dependent block--FDB) and distinct hyperpolarizing afterpotentials (HAPs) in regenerating nerves. In particular, regenerating sciatic nerves 15 days post-crush (dpc) were more sensitive to the frequency-dependent stimulations than 38-dpc and intact nerves in the presence or absence of drugs. The frequency-dependent effects of TEA on the compound action potentials (CAPs) appeared when TEA was applied to 4-AP-treated nerves. This shows that TEA-sensitive channels may not be masked by the myelin. 4-AP was here found to have more pronounced frequency-dependent effects on regenerating nerves than on intact nerves. Delayed depolarization (in 38-dpc: 22.6 +/- 1.3 mV and 47.52 +/- 3.63 ms, in intact: 12.0 +/- 1.9 mV and 88.51 +/- 4.72 ms) elicited by 4-AP resulted in an increase in FDBs and HAP amplitudes. These results suggest that 4-AP-sensitive channels may play important roles in frequency-dependent nerve conduction. Consequently, regenerating or myelin damaged nerves are more sensitive to repetitive firing with or without drug. An understanding of the frequency-dependent properties of regenerating nerves may be of value in the treatment of the nerve diseases.

Changes in electrophysiological properties of regenerating rat peripheral nerves after crush injury

The conduction of action potential in peripheral nerves requires the coordinated opening and closing of Na(+) and K(+) channels. In the present study, we used the sucrose-gap recording technique to determine the electrophysiological changes of the regenerating nerves after sciatic nerve injury by using 4-aminopyridine (4-AP) and tetraethylammonium (TEA), and lidocaine. 4-AP enhanced the amplitude and duration of the compound action potentials (CAPs) of regenerating sciatic nerve 15 days post crush (15 dpc), and elicited delayed depolarizations (Del-dep) in 38 dpc and intact groups. Hyperpolarizing afterpotentials elicited by 4-AP were completely removed by TEA in both 15 and 38 dpc. Lidocaine effectively blocked the CAP amplitude. This blockage was more pronounced in 15 dpc than 38 dpc. This agent also exhibited a partial blockage on the Del-dep amplitude. These results may indicate that the changes in the activities of 4-AP- and TEA-sensitive K(+) channels and slow Na(+) channels may play critical roles in nerve excitability and conduction.

Differential effects of lidocaine and tramadol on modified nerve impulse by 4-aminopyridine in rats

We have used the sucrose gap method to measure the effects of drugs on the electrophysiological properties of rat sciatic nerves. The results showed that 4-aminopyridine produced a slight conduction block, prolonged the duration of action potential, enhanced the hyperpolarizing afterpotential, and elicited a hump that followed the action potential. In the presence of 4-aminopyridine, the impulse-blocking activity of lidocaine and tramadol was enhanced. Both lidocaine and tramadol effectively depressed the delayed depolarization generated by 4-aminopyridine. While tramadol decreased the activity-evoked hyperpolarizing afterpotentials, lidocaine completely removed them. These findings indicate that lidocaine may be more effective in blocking the Na(+) channels than tramadol. Tramadol may be more effective on the delayed rectifier K(+) channels than lidocaine.

Antioxidant activity of Arbutus unedo leaves

The ethanol and methanol extracts of Arbutus unedo leaves were screened for antioxidant activity. The antioxidant activity was determined by an improved assay based on the decolorization of the radical monocation of [2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)] (ABTS). The ethanol and methanol extract of A. unedo leaves displayed potent antioxidant activity.

Effects of calcium and magnesium on peripheral nerve conduction

Divalent cations, such as calcium and magnesium, are constantly present in extracellular compartment of most organisms. Modification of extracellular concentrations of divalent ions causes changes in physiologic functions, such as excitability and conduction of the nerves. The present study was designed to investigate and compare the effects of calcium and magnesium on nerve conduction and lidocaine-induced nerve conduction block. The aim of our study was to contribute to better understanding of physiological and pharmacological roles of divalent cations. Experiments were conducted on the sciatic nerves by using the sucrose-gap recording technique. We evaluated the effects of test solutions containing different calcium or magnesium concentrations, prepared with or without lidocaine, on compound action potentials to determine physiological and pharmacological roles of these cations. After the control recordings, the nerve was exposed to Ringer's solution containing 0, 1.9, 3.8 mM Ca2+ and 1.9 and 3.8 mM Mg2+ with or without 1 mM lidocaine. Decreasing the Ca2+ concentrations in Ringer's solution with or without lidocaine enhanced both tonic and phasic blocks. However, increased Mg2+ concentration did not change the tonic blocks but increased the phasic blocks. In conclusion, the results suggested but not prove that Ca2+ and Mg2+ may have different mechanisms of action on peripheral nerves. While Ca2+ directly affects the gating of Na+ channels, action of Mg2+ can be explained by surface charge theory.

Comparison of nerve conduction blocks by an opioid and a local anesthetic

The experiments were done on frog sciatic nerves, using a sucrose-gap recording technique. The aim of our study was to investigate and to compare the tonic and phasic conduction blocking potency of tramadol and lidocaine on whole nerve and their interactions with Ca(2+). The concentration of a tramadol solution producing the same amount of tonic and phasic conduction blocks was three and six times higher than that needed for lidocaine, respectively. Increasing the Ca(2+) concentration in the test solution enhanced the conduction blocking potency of tramadol, but decreased that of lidocaine. It is concluded that tramadol blocks nerve conduction like a local anesthetic but with a weaker effect than that of lidocaine. Interactions of Ca(2+) and these drugs suggested that these drugs might have either different binding sites or different action mechanisms.

Quantitative determination of alpha-tocopherol in Arbutus unedo by TLC-densitometry and colorimetry

A quantitative determination of alpha-tocopherol in Arbutus unedo leaves was established by TLC-densitometry and colorimetry. Data obtained by TLC-densitometry were compared with those obtained by colorimetry. Also, the alpha-tocopherol content in leaves collected at different times of the year was studied comparatively. The highest amount of alpha-tocopherol was found in the March collection.