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

Opioid peptides as possible neuromodulators in the frog peripheral nerve system

Sciatic nerves of the frog Rana ridibunda were examined for the effects of applied opioid peptide, methionine-enkephalin, synthetic enkephalin analogue, leucine-enkephalin-NH(2) and opiate antagonist, naloxone. The effect of both peptides in concentrations of 1x10(-6) and 1x10(-5)M or naloxone in 1x10(-6)M was investigated on the action potential parameters using electrophysiological techniques. The isolated nerves were stimulated by single square pulses each of which lasted for 0.5ms at supramaximal strength. Effect of each single dose of peptides at 0min was compared with the remaining time segments. Both peptides produced changes in action potential of nerve when compared with untreated nerves. Methionine-enkephalin in both concentrations reduced the amplitude between 7% and 41% and conduction velocity at about 26-61%. This peptide in the same concentrations prolonged the duration around 12-53% and increased the stimulating voltage at about 9-50%. In contrast, leucine-enkephalin-NH(2) in both concentrations caused a decrease in amplitude between 13% and 48% and in conduction velocity around 20-50%. The same concentrations of this peptide prolonged the duration at about 3-33% and increased the stimulating voltage at about 10-56%, but naloxone in 1x10(-6)M antagonized the responses of both peptides over 75%. The results indicate that both opioid peptides produce changes in action potential parameters in frog peripheral nerve system and these changes are partially reversed by naloxone.

The actions of lamotrigine and levetiracetam on the conduction properties of isolated rat sciatic nerve

The purpose of this study was to investigate the actions of lamotrigine and levetiracetam on the conduction properties of isolated rat sciatic nerves in-vitro. Compound action potentials from rat sciatic nerves were recorded using a sucrose-gap technique with single and repetitive stimulation. Lamotrigine, at 0.01 to 1 mM, reduced the amplitude of compound action potentials (3.9+/-0.6% to 47.9+/-2.4%) and produced at high frequency dependent (phasic) and independent (tonic) conduction block. Lamotrigine extended the peak time of the compound action potentials significantly without changing the half falling-time (P<0.05). Lamotrigine reduced the amplitude of the delayed depolarization, which was more pronounced than that of the amplitude of the compound action potentials in the presence of 4-aminopyridine. With tonic and phasic stimulation, 0.1 to 10 mM of levetiracetam did not alter the amplitude, peak time and half falling time of the compound action potentials. In addition, levetiracetam did not change the amplitude of the delayed depolarization and the area of the compound action potentials following application of 4-aminopyridine. These results indicate that lamotrigine produces a powerful tonic block with delayed depolarization, whereas it produces a weaker phasic block in rat sciatic nerve. Levetiracetam has no effect on peripheral nerve conduction even at high concentrations. These results may have the relevance to our understanding of the peripheral effects of lamotrigine and levetiracetam.

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.

Does tramadol wound infiltration offer an advantage over bupivacaine for postoperative analgesia in children following herniotomy?

BACKGROUND

It has been demonstrated that tramadol is an effective analgesic. We aimed to compare postoperative analgesic effects of wound infiltration with tramadol (T) or bupivacaine (B) and intramuscular tramadol (I) after herniotomy in children.

METHODS

In this study, 75 children were randomly assigned to group T, group B and group I. Wound infiltration was performed to the patients in group T (2 mg.kg-1 tramadol in 0.2 ml.kg-1 saline) and group B (0.2 ml.kg-1 0.25% bupivacaine) into the surgical incision. Twenty minutes before the end of the surgery 2 mg.kg-1 tramadol was injected i.m. in group I. Faces pain scale was used for assessing pain severity. Patients with pain score>2 were treated with paracetamol. The frequency of side effects and analgesic use were recorded. Patients were discharged on the next day.

RESULTS

No side effects were recorded in any group. The pain scores of the patients at the first, fourth and eighth hours were significantly higher in group B and group I than group T (P<0.05). The pain scores of the patients at the first hour were significantly higher in group I compared with group B (P<0.05). Average time to first analgesic requirement was significantly longer in group T (6.72+/-4.09 h after herniotomy than both group I (4.49+/-3.9 h) and group B (6.04+/-3.7 h) (P<0.05).

CONCLUSIONS

Wound infiltration with tramadol may be a good choice for postoperative analgesia in children having inguinal herniotomy.

Tramadol, but not its major metabolite (mono-O-demethyl tramadol) depresses compound action potentials in frog sciatic nerves

BACKGROUND AND PURPOSE

Although tramadol is known to exhibit a local anaesthetic effect, how tramadol exerts this effect is not understood fully.

EXPERIMENTAL APPROACH

The effects of tramadol and its metabolite mono-O-demethyl-tramadol (M1) on compound action potentials (CAPs) were examined by applying the air-gap method to frog sciatic nerves, and the results were compared with those of other local anaesthetics, lidocaine and ropivacaine.

KEY RESULTS

Tramadol reduced the peak amplitude of the CAP in a dose-dependent manner (IC50=2.3 mM). On the other hand, M1 (1-2 mM), which exhibits a higher affinity for mu-opioid receptors than tramadol, did not affect CAPs. These effects of tramadol were resistant to the non-selective opioid receptor antagonist naloxone and the mu-opioid receptor agonist, DAMGO, did not affect CAPs. This tramadol action was not affected by a combination of the noradrenaline uptake inhibitor, desipramine, and the 5-hydroxytryptamine uptake inhibitor, fluoxetine. Lidocaine and ropivacaine also concentration-dependently reduced CAP peak amplitudes with IC50 values of 0.74 and 0.34 mM, respectively.

CONCLUSIONS AND IMPLICATIONS

These results indicate that tramadol reduces the peak amplitude of CAP in peripheral nerve fibres with a potency which is less than those of lidocaine and ropivacaine, whereas M1 has much less effect on CAPs. This action of tramadol was not produced by activation of mu-opioid receptors nor by inhibition of noradrenaline and 5-hydroxytryptamine uptake. It is suggested that the methyl group present in tramadol but not in M1 may play an important role in producing nerve conduction block.

Recovery of neurophysiological features with time after rat sciatic nerve repair: a magneto-neurographic study

Experimental assessment of peripheral nerve regeneration in rats by electrophysiology is controversial due to low reproducibility of electrophysiological indicators and diminished quantitative evaluation in conventional experimental set-ups. Magnetoneurography (MNG) counteracts these drawbacks by magnetically recording electrophysiological signals ex vivo, thereby providing accurate and quantitative data. In 50 rats, sciatic nerve transection was followed by direct repair. MNG outcome parameters, footprints [static toe spread factor (TSF); function] and muscle weight (MW) were studied for their recovery pattern from 2 to 24 weeks. By using MNG, we showed that the regeneration process still continues when functional recovery (static TSF) becomes stagnant. With regression analysis, MNG parameters amplitude, amplitude area and conduction velocity (CV) demonstrated moderate significant correlation with MW, whereas CV was not significantly associated with static TSF. No significant association exists between MW and static TSF. A Kaplan-Meier survival curve revealed that autotomy/contracture of rat hind paws was not related to decreased MNG outcome values. In conclusion, this study highlights and discusses the dissimilarities between direct (MNG) and indirect (static TSF and MW) assessment techniques of the regeneration process. We emphasise the significance of MNG as a direct derivative of axon regeneration in experimental rat studies. Additionally, we stress the must for right-left ratios, as neurophysiological indicators vary with age, and we confute possible bias in footprint analysis caused by exclusion of autotomy/contracture animals.

Conduction blocks of lidocaine on crushed rat sciatic nerve: an in-vitro study

The effects of lidocaine on the action potential of crushed sciatic nerves were investigated. The sciatic nerves of the rats were removed 5, 15, 25, and 38 days after the crushing and the compound action potentials were recorded with sucrose gap technique. The nerves were treated with 1 mM lidocaine and the conduction blocks of nonfrequency dependent block (NFDB) and frequency depended block (FDB) at 10, 40, and 100 Hz were determined. In intact nerves, the NFDB effect of lidocaine was 38.4 +/- 0.7 %. On the 15th day after the crush, the NFDB was increased to 60.1 +/- 1.3%. On the 38th day NFDB was decreased to 46.0 +/- 0.8%. The following days after the crushing, lidocaine caused a very high rate of FDB with 10, 40, and 100 Hz stimulation. The high NFDB ratios approached normal levels with the improvement of regeneration, but FDB ratios continued to stay at high levels. The results showed that the ratios of FDB and NFDB were increased on the crushed nerve. It was concluded that, in the regeneration conditions of crushed rat sciatic nerves, the sensitivity to local anesthetic increases more than in intact nerves.

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.

The Postoperative Analgesic Effect of Tramadol When Used as Subcutaneous Local Anesthetic

Recently, it has been shown that tramadol was an effective local anesthetic in minor surgery. In this study, its efficacy for relieving postoperative pain was evaluated. Forty patients undergoing minor surgery (lipoma excision and scar revision) under local anesthesia were included. The patients were randomly allocated into two groups: In group T (n = 20), 2 mg/kg tramadol, and in group L (n = 20), 1 mg/kg lidocaine were given subcutaneously. In both groups, the injection volume was 5 mL containing 1/200,000 adrenalin. The degree of the erythema, burning sensation, and pain at the injection site were recorded. Incision response, which is a degree of the pain sensation during incision, was recorded and graded with the visual analog scale (VAS) 0-10. After incision, VAS values were recorded at 15-min intervals. When the VAS score of the pain during surgery exceeded 4, an additional 0.5 mg/kg of the study drug was injected and this dosage was added to the total amount. Patients were discharged on the same day. Subjects with VAS > or =4 were advised to take paracetamol as needed. No side effects were recorded in either group except for 1 patient complaining of nausea in group T at the 30th min of operation. After 24 h, patients were called and the time of first analgesic use and total analgesic dose taken during the postoperative period were recorded. During the 24 postoperative hours, 18 of 20 (90%) subjects did not need any type of analgesia in group T, whereas this number was 10 (50%) in group L (P < 0.05). The time span before taking first analgesic medication was longer (4.9 +/- 0.3 h) in group T than that of group L (4.4 +/- 0.7 h) (P < 0.05). We propose that tramadol can be used as an alternative drug to lidocaine for minor surgeries because of its ability to decrease the demand for postoperative analgesia.

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.

Tramadol Added to 1.5% Mepivacaine for Axillary Brachial Plexus Block Improves Postoperative Analgesia Dose-Dependently

Adjuncts to local anesthetics for peripheral plexus blockade may enhance the quality and duration of anesthesia and postoperative analgesia. The analgesic, tramadol, has a unique mechanism of action that suggests efficacy as such an adjunct. It displays a central analgesic and peripheral local anesthetic effect. We designed a prospective, randomized, controlled and double-blind clinical trial to assess the effect of tramadol added to brachial plexus anesthesia. One-hundred patients scheduled for carpal tunnel release surgery under brachial plexus anesthesia were randomized into four groups. All patients received 1.5% mepivacaine 40 mL plus a study solution containing either isotonic sodium chloride (Group P, n = 17), tramadol 40 mg (Group T(40), n = 22), tramadol 100 mg (Group T(100), n = 20) or tramadol 200 mg (Group T(200), n = 20). We evaluated the time of onset of anesthesia, duration of sensory and motor blockade, duration and quality of postoperative analgesia, and occurrence of adverse effects. Onset and duration of sensory and motor blocks were not different among groups. The number of patients requesting analgesia in the postoperative period was significantly less in the 3 tramadol groups compared with the placebo group (P = 0.02); this was also noted with the placebo and T(40) groups compared with the T(200) group. No statistical significance was demonstrated between the placebo and the T(40) group or the T(100) group and the T(200) group. Furthermore, there was a significant trend effect among groups applying the Cochran-Armitage tendency test (P = 0.003), suggesting a dose-dependent decrease for additional postoperative analgesia requirements when tramadol was added. Side effects did not differ among groups, although they were more frequently recorded in the T groups. Our study suggests that tramadol added to 1.5% mepivacaine for brachial plexus block enhances in a dose-dependent manner the duration of analgesia with acceptable side effects. However, the safety of tramadol has to be investigated before allowing its use in clinical practice.

IMPLICATIONS

Tramadol's unique mechanism of action suggests efficacy as a local anesthetic adjunct for peripheral plexus blockade. Our study demonstrates that tramadol, added to mepivacaine for brachial plexus anesthesia, extends the duration and improves the quality of postoperative analgesia in a dose dependent fashion with acceptable side effects.

Evidence for the involvement of an opioid system in sciatic nerve of Rana ridibunda

The effect of opioid peptide, D-alanine2-leucine-enkephalin and opioid homolog peptide, des-tyrosine-methionine-enkephalin in concentrations of 1 x 10(-6) and 1 x 10(-5) M was investigated on the action potential parameters of frog sciatic nerve. Des-tyrosine-methionine-enkephalin was used as the control to prove the opioid action of the peptide. The effects of both peptides were examined by means of the extracellular electrophysiological technique. The isolated sciatic nerves were stimulated by single square pulses each of which lasted for 0.5 ms at supramaximal strength. Effect of each single dose of peptides at 0 min was compared with the remaining time segments. Both peptides produced changes on action potential of Rana ridibunda sciatic nerve when compared with untreated nerves. D-alanine2-leucine-enkephalin decreased significantly the amplitude at about 34-83%, the area at about 34-92%. The same concentrations of this peptide decreased significantly the conduction velocity around 35-78%. In contrast, des-tyrosine-methionine-enkephalin reduced the action potential amplitude between 8% and 80%. The same concentrations of this peptide decreased significantly the area at about 12-76% and the conduction velocity around 42-70%. The depression of both peptides in action potential parameters was partially blocked by 1 x 10(-6) M naloxone.