Oscillating repolarization in action potentials of frog sensory myelinated nerve fibres

Current and voltage clamp experiments were performed in single myelinated sensory nerve fibres of Rana esculenta. The K current was blocked by external tetraethylammonium-chloride and internal CsCl. Negative prepotentials led to the formation of a plateau in the repolarization phase of the action potential, and further regenerative depolarizations emerged from this plateau. A three-state model for Na inactivation based on voltage clamp data was sufficient to simulate these observations.     

Comparison of the antidromic sensory nerve action potentials obtained from all fingers on the same hand

Supramaximal compound sensory nerve action potentials (CSNAPs) were recorded antidromically from five fingers of the same hand to electrical stimulation of the median, ulnar, and radial nerves in 17 normal subjects. The mean amplitudes of the median CSNAPs from the thumb, index, and middle fingers were similar in values. There was minimal radial sensory contribution to the thumb, with the mean radial CSNAP amplitude about one-fourth the size of the median CSNAPs. The mean median and ulnar CSNAP amplitudes from the ring finger were approximately half, and the mean ulnar CSNAP amplitude from the little finger was approximately 85%, of the median CSNAP amplitudes from the other fingers. The median, ulnar, and radial sensory nerve conduction velocities were close in values. There appears to be less variability in the population normative data when the size of the CSNAPs is expressed in terms of amplitude ratio rather than in absolute amplitude value.     

带血供正中神经腕部感觉束转位桥接尺神经的解剖学基础

目的：探讨带血供正中神经腕部感觉束转位桥接尺神经缺损的解剖学基础。方法：14例成人上肢标本，观测腕部正中神经和尺神经的长度、神经束、血供等。摹拟带血供腕部正中神经感觉束转位桥接尺神经缺损术。结果：①正中神经腕部长度为7．8cm(7．5～8．1cm)。神经束数为19～27束，以感觉束为主，感觉束位于尺侧，运动束和混合束位于桡侧。感觉束无损伤分离长度为10．0～14．0cm。正中神经营养动脉距桡骨茎突上方6.2cm(6．1～6．6cm)处发自桡动脉，长度为5．7cm(5．1～6．1cm)，起始外径为1．2mm(1．1～1．4mm)。②尺神经腕部长度为9．4cm(8．9—9．7cm)，神经束数为14～19束，感觉束和运动束大致相等。感觉束位于掌挠侧，运动束位于背尺侧。结论：带血供正中神经腕部感觉束转位桥接尺神经缺损具有可行性。     

Effect of interelectrode recording distance on morphology of the antidromic sensory nerve action potentials at the finger

In 15 normal subjects, antidromic median sensory compound nerve action potentials (SCNAPs) were recorded supramaximally from the middle finger with ring electrodes, using different interelectrode recording distances. The onset latencies were identical in all recording instances. The peak latency and amplitude of the major negative deflection continued to increase with increasing interelectrode distance. At and beyond a 4 cm interelectrode recording separation, they both achieved maximum values and did not increase further. On the other hand, the duration and area did continue to increase with increasing interelectrode separation. These findings suggest that in normal individuals, the true onset latency, peak latency, and amplitude are well reflected in the median SCNAP when it is recorded with an interelectrode distance of 4 cm or more at the finger; thus, they can easily be standardized. The SCNAP duration and area, however, are more variable since they both continue to change with increasing interelectrode recording separation without approaching a saturation value.     

Mixed and sensory nerve action potentials of the median nerve in patients with peripheral neuropathy or motor neurone disease

Sensory nerve action potentials (SNAP) and mixed nerve action potentials (MNAP) of the median nerve were examined in 16 patients with motor neurone disease (MND), 29 patients with peripheral neuropathy and 18 age-matched normal controls. Patients with MND showed almost normal amplitudes of SNAP and MNAP, though they had muscle weakness in the hands. The motor nerve fibres may have a negligible effect on MNAP. The amplitude of MNAP correlated well with that of SNAP. The sensory fibres may play a major role in MNAP. Patients with peripheral neuropathy showed a significant reduction in amplitude in SNAP and MNAP. In particular, patients with sensory disturbance in the hands elicited low amplitudes in SNAP and MNAP. Patients without sensory disturbance also showed a decrease in amplitude in SNAP and MNAP. Peripheral neuropathy patients without sensory disturbance might show subclinical disturbance of peripheral sensory nerve fibres.     

Influence of a self-etching primer on compound nerve action potentials

The aim of this study was to evaluate the effect of self-etching primers on nerve conductance. A self-etching primer (One Up Bond F) which combines etching and bonding in one step, and a fifth-generation bonding agent (Prime&Bond NT ) were tested. Isolated rat sciatic nerves were placed between two platinum electrodes in a bath containing Tyrode solution. The bonding agents were brought into contact with the nerves and the evoked compound action potentials (CAP) were recorded before and after contact with the materials. One Up Bond F caused total inhibition of the CAP within an average time of 7 min. All CAPs in this group were blocked irreversibly. As with Prime&Bond NT, the reduction in CAP was 45.9% after an application time of 15 min, after which readings were terminated. Recovery of the CAP in this group were maintained after rinsing with fresh tyrode solution. One Up Bond F elicited faster blocking of nerve conductance under the conditions of this model. In the context of dentin desensitization with bonding agents, the self-etching primer may be more effective, clinically.     

Models and analysis of compound nerve action potentials

Upon electrical stimulation of a peripheral nerve, a compound action potential (CAP) can be recorded, a procedure that is widely used to study the functional condition of a nerve. The CAP provides relevant information about such parameters as the number of active myelinated fibers and their propagation velocities. This paper reviews methods of model-based CAP analysis that have emerged during the last decade. First, the basic model formulation for the CAP as resulting from a linear summation of the underlying single fiber action potentials (SFAPs) is discussed. Subsequently, a survey is given of volume conductor model approaches for the prediction of the SFAPs. Attention is then concentrated on the "inverse" problem of extracting relevant nerve parameters from experimentally recorded CAPs. Finally, the applicability of such methods is discussed and a direction for future developments is outlined.     

TTX-sensitive action potentials and excitability of adult rat sensory neurons cultured in serum- and exogenous nerve growth factor-free medium

The excitability of adult rat dorsal root ganglion (DRG) neurons cultured in the absence of serum and exogenously added nerve growth factor (NGF) was studied. Current-clamp recordings revealed the presence of tetrodotoxin (TTX)-sensitive action potentials. Voltage-clamp recordings demonstrated the presence of both inward and outward currents. The inward Na+ current had a maximal amplitude near -10 mV and was completely blocked by TTX. A sustained Ca2+ inward current and a slowly activating outward K+ current were also observed. TTX-sensitive and TTX-resistant action potentials have been observed in previous studies in DRG neurons cultured in the presence of serum. By contrast, in the study reported here, only TTX-sensitive action potentials and Na+ currents were found in the neurons cultured in the absence of serum and nerve growth factor.