Origin of intramuscular nerve action potential.

The origin of the intramuscular nerve action potential (INAP) was investigated using conventional surface recording electrodes. The appearance of the INAP was (1) associated with subjective paresthesias, (2) recorded only when the reference electrode (G2) was over an appropriate digital nerve, (3) increased in latency as G2 was placed more distally, (4) blocked by an orthodromic sensory nerve action potential arising from the thumb, and (5) abolished with an anaesthetic block in the digital nerve proximal to G2. The findings indicate that the INAP is recorded by the G2 electrode from the digital nerve.     

Compensation of intraoperative transcranial motor-evoked potential monitoring by compound muscle action potential after peripheral nerve stimulation.

It is often difficult to evaluate the results of transcranial motor-evoked potential (TCMEP) monitoring in patients under general anesthesia because these results are strongly affected by anesthetics and muscle relaxants. To exclude effects of muscle relaxants on TCMEP, compound muscle action potential (CMAP) by supramaximum stimulation of the median nerve immediately after transcranial stimulation (300 to 600 V) was recorded in 70 neurosurgical operations. A relative amplitude index (RAI) was defined as the amplitude of TCMEP after the operative procedure divided by the amplitude of TCMEP before the operative procedure. The RAI was calculated and was compensated by the amplitude of CMAP in 141 limbs. In 12 limbs of 7 patients with postoperatively progressed motor paresis, the compensated RAI was less than 0.2. The compensated RAI in all other 129 limbs of 63 patients without postoperative motor palsy was more than 0.2. These results suggest that compensation of TCMEP monitoring by CMAP is an easy and accurate method for removing the effects of muscle relaxants in TCMEP.     

Origin of action potential recorded by fluid electrodes

The concept that action potentials recorded by fluid electrodes may be generated at the point of the entrance to and the exit from the partition and that the action potential recorded by the fluid electrodes with a number of partitions between them may be equal to the algebraic sum of the action potentials recorded by the electrodes adjacent to each partition was directly verified in this study.     

Determinants of motor unit action potential duration.

OBJECTIVE: Motor unit action potential (MUAP) recordings are modeled by means of a single muscle fiber simulation program, to define two key subcomponents comprising the complete physiologic MUAP duration. A number of defining properties of these subcomponents are further developed. METHODS: A single muscle fiber simulation program is utilized with various muscle fiber lengths and conduction velocities to generate near-field and far-field waveforms. RESULTS: Two key subcomponents to the total physiologic single muscle fiber and hence MUAP duration are identified. One, defined as the near-field component, is directly dependent upon muscle fiber hemi-length. The other, defined as the far-field component, is independent of fiber length, but matches the internal action potential in duration. Both the near-field and far-field components are inversely dependent upon intracellular action potential conduction velocity. Additionally, temporal dispersion among the individual fibers contributing to a MUAP must be included in the overall MUAP duration calculation. CONCLUSIONS: It is hoped that this approach to MUAP duration may allow a more complete appreciation of the components contributing to the MUAP, than permitted by the empirically derived values for MUAP duration presently under clinical use.     

Motor unit action potential components and physiologic duration.

Motor unit action potentials (MUAPs) recorded from the same motor unit at two distances along the biceps brachii muscle with monopolar needle electrodes at high amplifier gains (20 microV/division) and averaged 2000-3000 times reveal total potential durations of 39.6 +/- 4.6 ms. In addition, the terminal segment for each of these two MUAPs contained a late far-field potential with a mean duration of 23.8 +/- 4.1 ms. Computer simulations of MUAPs suggest that this long-duration positive far-field mirrors the true morphology of the intracellular action potential (IAP), which is monophasic positive, possessing a terminal repolarization phase approaching 30 ms. This investigation suggests that the MUAP's physiologic duration is directly proportional to the muscle fiber length and the IAP's duration, which becomes manifest as a positive far-field potential when the IAP encounters the musculotendinous junction and slowly dissipates. The leading/trailing dipole model is used to explain qualitatively this study's quantitative clinical and computer simulation findings.     

Data processing for multi-channel optical recording: action potential detection by neural network.

Using a neural network, we have developed a program for fast and precise detection of action potentials (AP) in raw multi-channel optical recording data. The AP detection was performed in two steps: first, peaks were detected in raw optical data, and, second, the peaks were classified by the neural network into APs, noise and undecided peaks. The network was optimized and trained by the backpropagation learning algorithm, employing some thousands of manually classified peaks. The performance of the optimized network was found to be not completely satisfactory, although it was better than the classification by template matching and nearest-neighbor rules. The addition of a signal-to-noise ratio (SNR) of a peak to the network classification improved the classification performance: in comparison with the manual classification results, 96% of manually classified APs were detected. The causes of classification errors were discussed. In spite of the fact that the program required a slight amount of human intervention for undecided peaks, the program could allow mostly automatic AP detection.     

Motor unit action potential duration and muscle length.

Motor unit action potential (MUAP) components are investigated by means of single fiber computer simulations and clinical measurements. The single fiber simulations have essentially full bandwidth without noise, whereas the clinical measurements were made with a 3-10,000-Hz bandwidth utilizing approximately 1000 averages to reduce noise optimally. These parameters allow the recording of a MUAP's complete "physiologic" duration including its very slow onset and termination. The simulation results demonstrate a constant waveform onset regardless of the electrode's recording location along the fiber. A far-field potential is initiated when the action potential encounters the muscle fiber's termination. The simulated waveform's and clinically recorded MUAP's near-field component extends between the potential's onset and its corresponding far-field potential's onset. This near-field component's duration should vary with fiber length, and this prediction is clinically confirmed by measuring three different muscle lengths. The far-field potential reveals a constant duration, independent of fiber length, and appears to be associated with the muscle fiber's intracellular action potential duration. A more complete understanding of the components contributing to MUAP duration should provide a more fundamental basis for quantitative clinical MUAP duration measurements.     

Digit distribution of proper digital nerve action potential.

Antidromic sensory nerve action potential testing is well characterized and commonly used to assess the sensory component of the upper limb median and ulnar nerves. The final terminal segments of these nerves are the proper digital nerves. Ring recording electrodes are commonly used to detect the proper digital nerves' antidromic responses. Attempts to record the separate contributions of individual digital nerves along the lateral aspects of each finger, using small surface electrodes, is shown to be unreliable for determining the integrity of a single terminal digital branch. We found between 50% to 77% of the stimulated terminal branch's response amplitude when recorded at electrodes positioned over the nonstimulated branch located 180 degrees from the activated terminal branch. Detecting a single terminal nerve response was achieved by using the fourth digit and the second digit with one of the second digit's branches neurophysiologically blocked by local anesthetic. The volume-conducted response from the opposite side of the finger resulted in this relatively large recorded response, which remains within the range of reference values precluding the simple use of antidromic techniques to assess injury to a single proper digital nerve. Techniques are proposed to avoid such pitfalls and to assess most accurately the desired response.     

Ectopic action potential generation in peripheral trigeminal axons.

Spontaneous and evoked (orthodromic and antidromic) activities of 115 trigeminal ganglion neurons were studied. Three percent of cells stimulated at low frequency (less than 10 Hz) and 96% of cells stimulated at high frequencies (10 to 100 Hz) demonstrated ectopic action potentials (regardless of whether stimuli were anti- or orthodromic). However, this phenomenon was maximal in response to moderate-frequency stimuli (20 to 30 Hz) following periods of high-frequency stimulation. Collision experiments demonstrated that these extra spikes arose from the neurons' peripheral axons, and persisted after transection of the retrogasserian root. Both conditioning antidromic action potentials and subthreshold orthodromic stimuli were found to increase greatly the incidence of extra spikes produced by low-frequency orthodromic and antidromic stimuli, respectively. Repetitive firing was abolished by cooling of the neurons' receptive fields. This repetitive firing appears to be generated from the peripheral axon, possibly its terminal myelinated segment. The theoretical basis of this phenomenon has implications for the mechanism of trigeminal neuralgia.     

Effect of muscle-fiber velocity recovery function on motor unit action potential properties in voluntary contractions

Measurements of muscle-fiber conduction velocity during voluntary contractions have been used in the diagnosis of neuromuscular diseases. However, the velocity of propagation of action potentials depends on the interspike interval of activation due to the velocity recovery function (VRF) of muscle fibers. The comparison of muscle-fiber conduction velocity estimates between individuals may thus be influenced by differences in motor unit discharge rate. This study investigates action potential properties of motor units of the sternocleidomastoid muscle during voluntary modulation of discharge rate with the purpose of assessing the effect of the VRF on motor unit properties in voluntary contractions. Nineteen healthy men trained to control a target motor unit with feedback of surface multichannel electromyographic (EMG) signals. The subjects performed three 30-s contractions of cervical flexion/rotation modulating the discharge rate of the target motor unit from 6.6 +/- 1.6 pps to 28.0 +/- 6.4 pps. Action potential conduction velocity was correlated to instantaneous discharge rate (R = 0.38 +/- 0.21). Action potential conduction velocity, peak-to-peak amplitude, and duration varied between minimum and maximum discharge rate (P < 0.01; percent change 12.3 +/- 5.0, -11.8 +/- 9.9, and -12.9 +/- 7.3). Thus, the properties of surface motor unit action potentials vary with modulation of discharge rate. This has implications for the use of conduction velocity values measured during voluntary contractions to differentiate patient populations from healthy individuals and for the development of normative data.     

Pharmacological properties and mechanism of action of the cyclopyrrolones.

We present the pharmacological properties of two cyclopyrrolones, zopiclone as a hypnotic and suriclone as an anxiolytic, and examine their mechanism of action. The effects of zopiclone on the amount of time spent at each vigilance level have been studied in freely moving rats. Zopiclone from 2.5 mg/kg i.p. extends the duration of slow wave sleep (SWS), concomitantly shortening the periods awake. This SWS inducing effect of zopiclone was more potent after 10 mg/kg i.p.; moreover, zopiclone did not depress REM sleep and no rebound of activity in wakefulness or REM sleep were observed the day after zopiclone treatment. In rats, at the cortical level, zopiclone increases the spectral energy in the delta band (0.5 to 4 hertz). This rise in energy appears at doses starting from 1.25 mg/kg p.o. and can also reach the fast frequencies (beta band: 12 to 16 hertz). This power spectrum is characteristic of a compound having tranquilizing-hypnotic potential. Taken together these EEG results corroborate the clinical studies. In man, zopiclone increased SWS, decreased SWS latency and respected sleep architecture in both healthy volunteers and insomniacs. This respect of sleep structure and the relative short duration of action of zopiclone minimized the residual effects seen upon waking (drowsiness, impairment of psychomotor performance). In the Geller-Seifter test, an operant conflict procedure, the minimal effective dose (MED) of suriclone in reversing the conflict-induced inhibition of drinking behavior was 2.5 mg.kg-1 p.o. in rats. Depression of unpunished responding is only seen at higher doses (20 mg.kg-1 p.o.).(ABSTRACT TRUNCATED AT 250 WORDS)     

Abnormalities in the sensory action potential in patients with amyotrophic lateral sclerosis.

Sensory function in patients with amyotrophic lateral sclerosis (ALS) is thought to be normal; however, there is convincing morphologic evidence that sensory systems are affected in addition to motor systems. In this study, compound sensory action potentials were recorded with near nerve electrodes from 18 patients with ALS. Up to 1024 responses were averaged at high gain to determine minimum conduction velocity; that is, the conduction velocity of the slowest conducting component of the sensory action potential. Nine of 18 patients had abnormally reduced minimum conduction velocity, even when peak-to-peak amplitude and maximum conduction velocity (calculated from the latency to the initial positive peak) were normal. Only 3 of 18 patients showed abnormalities in peak-to-peak amplitude. Thus, subtle abnormalities in the sensory action potential can be detected in many patients with ALS.