Axonal excitability and conduction alterations caused by levobupivacaine in rat

In this study, effects of the long-acting amide-type local anesthetic levobupivacaine on axonal conduction and excitability parameters of the rat sciatic nerve were thoroughly examined both in vitro and in vivo. In order to deduce its effects on isolated nerve conduction, compound nerve action potential (CNAP) recordings were performed using the suction method over sciatic nerves of Wistar rats before and after administration of 0.05 % (1.7 mmol L–1) levobupivacaine. Levobupivacaine caused complete CNAP area and amplitude depression by blocking conduction in a time-dependent manner. To assess the influence of levobupivacaine on in vivo excitability properties, threshold-tracking (TT) protocols were performed at sciatic nerves of rats injected with perineural 0.05 % (1.7 mmol L–1) levobupivacaine or vehicle alone. Charge-duration TT results revealed that levobupivacaine increases the rheobase and decreases the strength-duration time constant, suggesting interference of the anesthetic with the opening of Na+ channels. Twenty and 40 % threshold electrotonus curves were found for both groups to follow the same paths, suggesting no significant effect of levobupivacaine on K+ channels for either the fastest or relatively slow conducting fibers. Current-threshold relationship results revealed no significant effect on axonal rectifying channels. However, according to the results of the recovery cycle protocol yielding the pattern of excitability changes following the impulse, potential deviation was found in the recovery characteristics of Na+ channels from the absolute refractory period. Consequently, conduction blockage caused by levobupivacaine may not be due to the passive (capacitive) properties of axon or the conductance of potassium channels but to the decrease in sodium channel conductance

Comparison of Excitability Properties of Dominant and Recessive Hands’ Median Nerve Branches

Amaç: Eşik izleme “threshold tracking” yöntemi sinir uyarılabilirlik özelliklerinin detaylı olarakbelirlenmesini sağlaması nedeniyle son yıllarda sıklıkla tercih edilmektedir. Yapmış olduğumuzçalışma ile bu non-invazif yöntem kullanılarak temel ve klinik çalışmalara bir altyapı oluşturmak içinsağ eli baskın gönüllülerin her iki elinin medyan sinirinin uyardığı baş, orta ve işaret parmaklarınuyarılabilirlik özelliklerinin belirlenmesi amaçlanmıştır. Aynı zamanda, sağ ve sol el parmaklarıarasındaki olası uyarılabilirlik farklılıkları da karşılaştırmalı olarak araştırılmıştır.Gereç ve Yöntemler: Çalışmada, eşik izleme yöntemi protokolleri sağ el baskın 21 sağlıklı gönüllüdeneğe uygulanmıştır. Uyarılabilirlik ölçümlerini gerçekleştirmek amacıyla medyan sinir el bileğindenuyarılarak, halka biçimindeki kayıt elektrotları ile sağ ve sol el baş, işaret ve orta parmaklarındanbileşik sinir aksiyon potansiyelleri kaydedilmiştir. Her bir deneyde, eşik izleme protokollerine ait eşikelektrotonus, toparlanma döngüsü, eşik akım uyaran-yanıt ilişkisi ve eşik yük-uyaran süresi ilişkisiverileri toplanmıştır.Bulgular: Şiddet süre zaman sabiti, 2. ms’deki refraktörlük (%), dinlenim akım-voltaj eğimi, reobazve maksimal yanıtın %50’sini elde etmek için gerekli uyaran şiddeti ortalamaları karşılaştırılmış, sağve sol el parmakları arasında fark görülmemiştir (p0,05). Uyaran-yanıt, şiddet-süre ilişkisi, % 40 eşikelektrotonus, akım-eşik ilişkisi ve toparlanma döngüsü eğrilerinin karşılaştırılmasında da anlamlı farkbulunmamıştır (p0,05).Sonuç: Bulgularımız, parmak kaslarını innerve eden medyan sinire ait zardaki hem Na kanallarıhem de hızlı, yavaş ve doğrultucu K kanallarının aktivitelerinin benzer olduğunu göstermiştir. Sonuçolarak, hangi elin baskın olduğunun distal motor ünitelerde yani nöromüsküler düzeyde herhangibir farka neden olmadığını, aksine el baskınlığında insan motor kontrolünün daha üst seviyelerininve motor öğrenmenin (davranışsal seviyede) rolü olduğunu göstermesi açısından önem taşımaktadır.Objective: “Threshold tracking” is a commonly preferred method in recent years to provideexcitability properties in detail. With this study, we aimed to determine the excitability properties ofthe thumb and the index and medius fingers innervated by the median nerve by using non-invasivethreshold tracking methods from both the right and left hands of right-handed volunteers to providea basis for basic and clinical studies. Additionally, possible differences between the fingers of left andright hands were investigated.Material and Methods: Protocols of threshold tracking method were applied to 21 right-handedhealthy volunteers. The median nerve was stimulated at the elbow, and nerve compound actionpotential recordings were then performed from the thumb and index and medius fingers of the leftand right hand with ring-shaped electrodes to conduct excitability measurements. The thresholdelectrotonus, recovery cycle, threshold current stimulus-response relationship and the amount ofthreshold charge-stimulus duration relationship data were collected for each experiment.Results: Strength duration time constant, refractoriness (%) at 2 ms, resting current-voltage slope, rheobase and 50% stimulus intensityrequired to elicit the maximal response did not differ significantly for three fingers of the left and right hand (p0.05). There wasalso no significant difference for the stimulus-response, strength-duration relationship, 40% threshold electrotonus, current-thresholdrelationship and recovery cycle curves (p0.05).Conclusion: The findings indicated that the activities of Na and all fast, slow and rectifier K channels in the membrane of themedian nerve that innervates finger muscles were similar. In conclusion, our results may suggest that the distal end of the movementcircuit (neuro-muscular level) has no role in handedness and rather addresses the importance of higher levels of human motor control and motor learning (neural-behavioral level)

Axonal excitability and conduction alterations caused by levobupivacaine in rat

In this study, effects of the long-acting amide-type local anesthetic levobupivacaine on axonal conduction and excitability parameters of the rat sciatic nerve were thoroughly examined both in vitro and in vivo. In order to deduce its effects on isolated nerve conduction, compound nerve action potential (CNAP) recordings were performed using the suction method over sciatic nerves of Wistar rats before and after administration of 0.05 % (1.7 mmol L−1) levobupivacaine. Levobupivacaine caused complete CNAP area and amplitude depression by blocking conduction in a time-dependent manner