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1.
Jürgen Kröller 《Biological cybernetics》1996,74(1):9-20
The response of primary muscle spindle afferent fibers to muscle stretch is nonlinear. Now spindle responses (trains of action potentials) to band-limited Gaussian white noise length perturbations of the gastrocnemius muscles (input signal) are described in cats. The input noise upper cutoff frequency was clearly above the frequency range of physiological length changes in cat hindleg muscles. The input-output relation was analyzed by means of peri-spike averages (PSAs), which could be shown to correspond to the kernels of Wiener's white noise approach to systems identification. The present approach (the reverse correlation analysis) was applied up to the third order. An experiment consisted of two recordings: one (the source recording) to determine PSAs and the other (the test recording) to provide an input signal for predicting responses. The predictions of different orders were compared with the actual neuronal response (the observation) of the test recording. Four different approximation procedures were developed to adapt prediction and observation and to determine weighting factors for the predictions of different orders. The approximations also yielded the value of the power density P of the input noise signal: at a variety of stimulus parameters, P from approximations had the same magnitude as P determined directly from the input signal amplitude spectrum. The prediction of a sequence of action potentials improved the higher the order of components. 37 of 42 action potentials of a test recording (the observation) could be confidently predicted from PSAs or kernels. Compared with the size of the linear first-order prediction curve, the relative sizes of the second and third-order prediction curves were: 1.0∶0.47∶0.26. 相似文献
2.
Djordje Boskov Mirjana Jocic Ksenija Jovanovic Milos Ljubisavljevic Radmila Anastasijevic 《Biological cybernetics》1994,71(4):341-348
Spike discharges of skeletomotor neurons innervating triceps surae muscles elicited by white noise modulated transmembrane
current stimulation and muscle stretch were studied in decerebrated cats. The white noise modulated current intensity ranged
from 4.3 to 63.2 nA peak-to-peak, while muscle stretches ranged from 100 μm to 4.26 mm peak-to-peak. The neuronal responses
were studied by averaging the muscle length records centered at the skeletomotor action potentials (peri-spike average, PSA)
and by Wiener analysis. Skeletomotor spikes appeared after a sharp peak in PSA of the injected current, preceded by a longer-lasting
smaller wavelet of either depolarizing or hyperpolarizing direction. The PSA amplitude was not related to the injected current
amplitude nor showed any differences related to the motor unit type. The PSA amplitudes were virtually independent of the
stretching amplitude σ, after an initial increase with stretching amplitudes in the range of 15–40 μm (S.D.), or 100–270 μm
peak-to-peak.Analyses of cross-spectra indicated a small or absent increase in gain with frequency in response to injected
current, but about 20 dB/decade in the range 10–100 Hz in response to muscle stretch. The peaks of both Wiener kernels in
response to current injection appear to decrease with the amplitude of injected current, but this decrease was not statistically
significant. The narrow first-order kernels suggest that the transfer function between the current input and spike discharge
is lowpass with a wide passband, i.e. there is very little change in dynamics. The values of the second-order kernels appear
to be nonzero only along the main diagonal. This is characteristic of a simple Hammerstein type cascade, i.e. a zero memory
nonlinearity followed by a linear system. Small values of second-order kernels away from the origin and narrow first-order
kernels suggest that the linear cascade contributes very little to the overall dynamic response.In contrast to Wiener kernels
found in response to current injection, the Wiener kernels in response to stretch showed a decreasing trend with stretch amplitude.
The size of the second-order kernels decreased to a somewhat larger extent with input amplitude than that of the first-order
kernels, indicating an amplitude-dependent nonlinearity. Overall, the transformation between length and spike output was described
as an LNNL cascade with second-order nonlinearities.
Received: 1 April 1993/Accepted in revised form: 24 March 1994 相似文献
3.
In this report, the input/output relations in an isolated ganglion of the leech Hirudo medicinalis were studied by simultaneously using six or eight suction pipettes and two intracellular electrodes. Sensory input was mimicked
by eliciting action potentials in mechanosensory neurons with intracellular electrodes. The integrated neural output was measured
by recording extracellular voltage signals with pipettes sucking the roots and the connectives. A single evoked action potential
activated electrical activity in at least a dozen different neurons, some of which were identified. This electrical activity
was characterized by a high degree of temporal and spatial variability. The action potentials of coactivated neurons, i.e.
activated by the same mechanosensory neuron, did not show any significant pairwise correlation. Indeed, the analysis of evoked
action potentials indicates clear statistical independence among coactivated neurons, presumably originating from the independence
of synaptic transmission at distinct synapses. This statistical independence may be used to increase reliability when neuronal
activity is averaged or pooled. It is suggested that statistical independence among coactivated neurons may be a usual property
of distributed processing of neuronal networks and a basic feature of neural computation.
Received: 20 September 1999 / Accepted in revised form: 3 March 2000 相似文献
4.
We consider the response of the classical Hodgkin–Huxley (HH) spatial system in the weak to intermediate noise regime near
the bifurcation to repetitive spiking. The deterministic component of the input (signal) is restricted to a small segment
near the origin whereas noise, with parameter σ, occurs either only in the signal region or throughout the whole neuron. In both cases small noise inhibits the spiking and
there is a minimum in the spike counts at σ ≈ 0.15. At the same value of σ, the variance of the spike counts undergoes a pronounced maximum. For spatially restricted noise, the spike count continues
to increase beyond the minimum until σ = 0.5, but in the case of spatially extended noise the spike count begins to decline around σ = 0.35 to give a local maximum. For both spatial distributions of noise, the variance of the spike count is found to also
have a local minimum at about σ = 0.4. Examples are given of the probability distributions of the spike counts and the spatial distributions of spikes with
varying noise level. The differences in behaviours of the spike counts as noise increases beyond 0.3 are attributable to noise-induced
spiking outside the signal region, which has a larger probability of occurrence when the noise is over an extended region.
This aspect is investigated by ascertaining the probability of noise-induced spiking as a function of noise level and examination
of the corresponding latency distributions. These findings prompt a definition of weak noise in the standard HH model as that
for which the probability of secondary phenomena is negligible, which occurs when σ is less than about 0.3. Finally, if signal and weak (σ < 0.3) noise are applied on disjoint intervals, then the noise has no effect on the instigation or propagation of spikes,
no matter how large its region of application. These results are expected to apply to type 2 neurons in general, including
the majority of cortical pyramidal cells. 相似文献
5.
H. Schmitz M. Mürtz H. Bleckmann 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2000,186(6):543-549
The pit organs of the beetle Melanophilaacuminata were stimulated with monochromatic infrared radiation using a continuous wave CO overtone infrared laser. Best sensitivity
was in the wavelength range 2.8–3.5 μm. In this range a stimulus intensity of 14.7 mW cm−2 was sufficient to generate single action potentials. At a wavelength of 5 μm receptor performance significantly decreased.
An increase in stimulus intensity caused a decrease in response latency and an increase in the number of action potentials
elicited. At a given wavelength (3.4 μm) the dynamic amplitude range of action potential responses covered 12 dB. At high
stimulus intensities (94.2 mW cm−2) a stimulus duration of 4 ms was sufficient to generate one to two action potentials and a stimulus duration of 60 ms already
caused response saturation (with up to nine action potentials). In a repetitive stimulus regime distinct receptor potentials
were visible up to a frequency of 600 Hz.
Accepted: 18 March 2000 相似文献
6.
J. Kröller 《Biological cybernetics》1993,69(5-6):447-456
The nonlinear responses of deefferented primary muscle spindle afferent fibers to muscle stretching consisted of a train of action potentials which was analyzed when random changes in muscle length (band-limited gaussian white noise) were applied in cats. The upper cutoff frequency of the applied noise (the source stimulus) was varied between 1.6 and 570 Hz; the amplitude of the random input was varied between 0.002 and 1.2 mm. In a previous report the reverse correlation of 1st and 2nd order was studied for its ability to analyze data of a continuous input signal and pulsatile events in the output. Computations of the Wiener kernelsh
1 andh
2 or their equivalents, the perispike averages of the 1st and 2nd order, were computed from the random stretch responses of muscle-spindle afferents. Then the 1st- and the 2ndorder predictions and the summation of both to random muscle stretch was estimated. A general finding was that the 1st-order component was approximately 10 times that of the 2nd-order component, when both were combined in approximation procedures to give the closest prediction of observed responses to random test stimuli. The approximation was poor when the source stimulus was less than 0.03 mm and improved when it was greater. With the increase in the upper cutoff frequency of the random source input, the approximation worsened continuously. Predictions to ramp-and-hold stimuli were computed, as well as responses to random stimulation. Limiting the upper cutoff frequency did not diminish the value of the techniques applied. 相似文献
7.
A model of the muscle fibre extracellular action potentials (ECAPs) calculation using experimentally recorded intracellular
action potentials (ICAPs) has been applied to investigate the effect of repetitive stimulation on the electrical activity
of isolated frog muscle fibres. The ECAPs were calculated both at small (0.01 mm) and at large (5 mm) radial distances to
the fibre axis, and their relationship with the original ICAP parameters has been inferred. Fourier transformation of the
calculated ECAPs in order to obtain the spectral characteristics and to trace out their behaviour during continuous fibre
activity was performed. Stimulation frequency dependence on the ECAP time characteristics and on the shift of the maximum
spectral density towards low frequencies at small and large radial distance were observed. The spectral density peak frequency
is propagation velocity (PV)-dependent. The advantage of the presented method over the available experimental extracellular
recording techniques from isolated muscle fibers is the possibility to show the effect of continuous muscle fibre activity
on the parameters of the ECAPs and their spectral characteristics at large radial distance, which is not experimentally accessible.
Our results are in agreement with those experimentally obtained. The results from the model prove the role of changes in PV
of excitation along the muscle fibres (representing the last link in the complex organized motor system) in the development
of fatigue.
Received: 24 July 1997 / Accepted in revised form: 2 July 1998 相似文献
8.
Andreas Erkens Klaus Schneider A. Müller 《Journal of biological inorganic chemistry》1996,1(2):99-110
In this study we confirmed the previous observation that the cytoplasmic NAD-linked hydrogenase of Alcaligenes eutrophus H16 is EPR-silent in the oxidized state. We also demonstrated the presence of significant Ni-EPR signals when the enzyme
was either reduced with the natural electron carrier NADH (5–10 mM) or carefully titrated with sodium dithionite to an intermediate,
narrow redox potential range (–280 to –350 mV). Reduction with NADH under argon atmosphere led to a complex EPR spectrum at
80 K with g values at 2.28, 2.20, 2.14, 2.10, 2.05, 2.01 and 2.00. This spectrum could be differentiated by special light/dark treatments
into three distinct signals: (1) the "classical" Ni-C signal with g values at 2.20, 2.14 and 2.01, observed with many hydrogenases in the reduced, active state; (2) the light-induced signal
(Ni-L) with g values at 2.28, 2.10 and 2.05 and (3) a flavin radical (FMN semiquinone) signal at g = 2.00. The assignment of the Ni-EPR signal was clearly confirmed by EPR spectra of hydrogenase labeled with 61Ni (nuclear spin I = 3/2) yielding a broadening of the Ni spectra at all g values and a resolved 61Ni hyperfine splitting into four lines of the low field edge in the case of the light-induced Ni-EPR signal. The redox potentials
determined at pH 7.0 for the described redox components were: for FMN –170 mV (midpoint potential, Em, for appearance), –200 mV (EPR signal intensity maximum) and –230 mV (Em for disappearance); for the Ni centre (Ni-C), –290 mV (Em for appearance), –305 mV (signal intensity maximum) and –325 mV (Em for disappearance). Exposure of the NADH-reduced hydrogenase to carbon monoxide led to an apparent Ni-CO species indicated
by a novel rhombic EPR signal with g values at 2.35, 2.08 and 2.01.
Received: 19 July 1995 / Accepted: 10 September 1995 相似文献
9.
Tock Y Ljubisavljevic M Thunberg J Windhorst U Inbar GF Johansson H 《Biological cybernetics》2002,87(4):241-248
The information transmission properties of single, de-efferented primary muscle-spindle afferents from the hind limb of the
cat were investigated. The gastrocnemius medialis muscle was stretched randomly while recording spike trains from several
muscle-spindle afferents in the dorsal root. Two classes of input stimuli were used: (i) Gaussian noise with band-limited
flat spectrum, and (ii) Gaussian noise with a more “naturalistic” 1/f
n
spectrum. The “reconstruction” method was used to calculate a lower bound to the information rate (in bits per second) between
the muscle spindles and the spinal cord. Results show that in response to the flat-spectrum input, primary muscle-spindle
afferents transfer information mainly about high frequencies, carrying 2.12 bits/spike. In response to naturalistic-spectrum
inputs, primary muscle-spindle afferents transfer information about both low and high frequencies, with “spiking efficiency”
increasing to 2.67 bits/spike. A simple muscle-spindle simulation model was analyzed with the same method, emphasizing the
important part played by the intrafusal fiber mechanical properties in information transmission.
Received: 22 January 2002 / Accepted in revised form: 17 June 2002
Correspondence to: Y. Tock (e-mail: ytock@tx.technion.ac.il, Fax: +972-4-8323041) 相似文献
10.
Minoru Shinohara Motoki Kouzaki Takeshi Yoshihisa Tetsuo Fukunaga 《European journal of applied physiology and occupational physiology》1997,76(4):314-319
The mechanical activity of the human quadriceps muscle during maximal incremental cycle ergometry was investigated by mechanomyography
(MMG). MMG and surface electromyography (EMG) recordings of vastus lateralis muscle activity were obtained from nine males.
Cycle ergometry was performed at 60 rev/min and work load was incremented step wise by 20 W (3.2 Nm) every minute until volitional
fatigue. The mean amplitudes of MMG (mMMG) and EMG (mEMG) during the contraction phase were calculated from the last six contractions
in each load. The duration, load and work rate of exercise at exhaustion were 13.3 (1.6) min, 44.1 (5.5) Nm, 276.7 (34.7) W,
respectively. A linear relationship between mMMG and load was evident in each subject (r = 0.868–0.995), while mEMG seemed to dissociate as the load became greater. In the grouped mean data, mMMG was linearly related
to load whether aligned to the absolute (r = 0.995) or maximal (r = 0.995) load. Involvement of the noise component was further investigated by studying passive cycling by four subjects.
Pedals were rotated passively for the first half of each stage (PAS) and the subject then pushed the pedals for the second
half (ACT). In the lighter load region, the mMMG of ACT was as small as that of PAS. However, the change in the mMMG of PAS
was very small compared with that of ACT. In conclusion, this study demonstrates a linear relationship between the mMMG of
the quadriceps muscle and work load during maximal incremental cycle ergometry. The effect of movement noise was thought to
be small and stable.
Accepted: 22 April 1997 相似文献
11.
The encoding of mechanical stimuli into action potentials in two types of spider mechanoreceptor neurons is modeled by use
of the principal dynamic modes (PDM) methodology. The PDM model is equivalent to the general Wiener–Bose model and consists
of a minimum set of linear dynamic filters (PDMs), followed by a multivariate static nonlinearity and a threshold function.
The PDMs are obtained by performing eigen-decomposition of a matrix constructed using the first-order and second-order Volterra
kernels of the system, which are estimated by means of the Laguerre expansion technique, utilizing measurements of pseudorandom
mechanical stimulation (input signal) and the resulting action potentials (output signal). The static nonlinearity, which
can be viewed as a measure of the probability of action potential firing as a function of the PDM output values, is computed
as the locus of points of the latter that correspond to output action potentials. The performance of the model is assessed
by computing receiver operating characteristic (ROC) curves, akin to the ones used in decision theory and quantified by computing
the area under the ROC curve. Three PDMs are revealed by the analysis. The first PDM exhibits a high-pass characteristic,
illustrating the importance of the velocity of slit displacement in the generation of action potentials at the mechanoreceptor
output, while the second and third PDMs exhibit band-pass and low-pass characteristics, respectively. The corresponding three-input
nonlinearity exhibits asymmetric behavior with respect to its arguments, suggesting directional dependence of the mechanoreceptor
response on the mechanical stimulation and the PDM outputs, in agreement to our findings from a previous study (Ann Biomed
Eng 27:391–402, 1999). Differences between the Type A and B neurons are observed in the zeroth-order Volterra kernels (related
to the average firing), as well as in the magnitudes of the second and third PDMs that perform band-pass and low-pass processing
of the input signal, respectively. 相似文献
12.
1. Nonlinear second order white-noise analysis has been applied to the isolated frog muscle spindle. Power (2) of the Gaussian white noise (GWN) and the average prestretch level L were varied and the response of both the isolated receptor potential (transducer) and the action potential (encoder) level were analysed. 2. The standard white-noise method is briefly presented. Particular emphasis, however, is put on the limitations in the range of validity of the method and, consequently, on the use and interpretation of the kernels as a Wiener model. Conclusions in the present paper are within this frame and are mainly of qualitative nature. 3. The analysis reveals that the nonlinear contributions of the model are essential for approximating physiological results, thus ruling out purely linear modelling for this receptor organ. 4. The dependence of the transducer kernels on are compatible with the behaviour of a rectifier. Rectification is represented by the lack of hyperpolarization within the isolated receptor potential and is enhanced by the substantial memory in the linear and nonlinear kernels as demonstrated by their extent in time. This is equivalent to low power in high frequencies of the response. Obviously, the hyperpolarizing potentials following each spike counteract the long transducer memory. 5. At the encoder level the memory of the system is strongly reduced. This is achieved by using predominantly high frequency components of the receptor potential for triggering the process of impulse generation, and by the precise coupling and high frequency content of the impulses. This coupling precision is possible because of the sensitivity of the spike-generating mechanism to steep rising transients of the receptor potential and also owing to the reduction in transducer memory by the hyperpolarizing afferpotentials. 6. The preference given to the high frequency components is also read from the structure of the second order transducer kernel and from both the linear and the second order encoder kernels, which allows the most effective input waveform for triggering action potentials to be determined. 6. When the operating point is changed to higher prestretch values, kernel heights increase strongly implying higher response strength of the muscle spindle. The kernel structure is changed as well in the direction of reducing the effective memory already at the level of the receptor potentials, probably a means to prevent too high depolarization values. 相似文献
13.
T. Heinbockel P. Kloppenburg J. G. Hildebrand 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,182(6):703-714
Using intra- and extracellular recording methods, we studied the activity of pheromone-responsive projection neurons in the
antennal lobe of the moth Manduca sexta. Intracellularly recorded responses of neurons to antennal stimulation with the pheromone blend characteristically included
both inhibitory and excitatory stages of various strengths. To observe the activity of larger groups of neurons, we recorded
responses extracellularly in the macroglomerular complex of the antennal lobe. The macroglomerular complex is part of a specialized
olfactory subsystem and the site of first-order central processing of sex-pheromonal information. Odors such as the pheromone
blend and host-plant (tobacco) volatiles gave rise to evoked potentials that were reproducible upon repeated antennal stimulation.
Evoked potentials showed overriding high-frequency oscillations when the antenna was stimulated with the pheromone blend or
with either one of the two key pheromone components. The frequency of the oscillations was in the range of 30–50 Hz. Amplitude
and frequency of the oscillations varied during the response to pheromonal stimulation. Recording intracellular and extracellular
activity simultaneously revealed phase-locking of action potentials to potential oscillations. The results suggest that the
activity of neurons of the macroglomerular complex was temporally synchronized, potentially to strengthen the pheromone signal
and to improve olfactory perception.
Accepted: 19 December 1997 相似文献
14.
S. J. Brown R. B. Child S. H. Day A. E. Donnelly 《European journal of applied physiology and occupational physiology》1997,75(4):369-374
Indirect indices of exercise-induced human skeletal muscle damage and connective tissue breakdown were studied following
a single bout of voluntary eccentric muscle contractions. Subjects (six female, two male), mean (SD) age 22 (2) years performed
a bout of 50 maximum voluntary eccentric contractions of the knee extensors of a single leg. The eccentric exercise protocol
induced muscle soreness (P < 0.05 Wilcoxon test), chronic force loss, and a decline in the 20:100 Hz percutaneous electrical myostimulation force ratio
[P < 0.01, repeated measures analysis of variance (ANOVA)]. Serum creatine kinase (CK) and lactate dehydrogenase (LDH) activities
were elevated (P < 0.01, repeated measures ANOVA) following the bout. The mean (SD) CK and LDH levels recorded 3 days post-exercise were 2815
(4144) IU · l–1 and 375 (198) IU · l–1, respectively. Serum alkaline phosphatase activity showed no changes throughout the study, and a non-significant increase
(P = 0.058, repeated measures ANOVA) in pyridinoline was recorded following the bout. Urinary hydroxyproline (HP) and hydroxylysine
(HL) excretion, expressed in terms of creatinine (Cr) concentration, increased after exercise (P < 0.05 and P < 0.01, respectively, repeated measures ANOVA). An increased HP:Cr was recorded 2 days post-exercise and HL:Cr was increased
above baseline on days 2, 5, and 9 post-exercise. This indirect evidence of exercise-induced muscle damage suggests that myofibre
disruption was caused by the eccentric muscle contractions. Elevated urine concentrations of indirect indices of collagen
breakdown following eccentric muscle contractions suggests an increased breakdown of connective tissue, possibly due to a
localised inflammatory response.
Accepted: 9 October 1996 相似文献
15.
Michael S. Conley Michael H. Stone Michael Nimmons G. A. Dudley 《European journal of applied physiology and occupational physiology》1997,75(5):443-448
This study examined hypertrophy after head extension resistance training to assess which muscles of the complicated cervical
neuromuscular system were used in this activity. We also determined if conventional resistance exercises, which are likely
to evoke isometric action of the neck, induce generalized hypertrophy of the cervical muscle. Twenty-two active college students
were studied. [mean (SE) age, weight and height: 21 (1) years, 71 (4) kg and 173 (3) cm, respectively]. Subjects were assigned
to one of three groups: RESX (head extension exercise and other resistance exercises), RES (resistance exercises without specific
neck exercise), or CON (no training). Groups RESX (n = 8) and RES (n = 6) trained 3 days/week for 12 weeks with large-muscle mass exercises (squat, deadlift, push press, bent row and mid-thigh
pull). Group RESX also performed three sets of ten repetitions of a head extension exercise 3 days/week with a load equal
to the 3 × 10 repetition maximum (RM). Group CON (n = 8) was a control group. The cross-sectional area (CSA) of nine individual muscles or muscle groups was determined by magnetic
resonance imaging (MRI) of the cervical region. The CSA data were averaged over four contiguous transaxial slices in which
all muscles of interest were visible. The 3 × 10 RM for the head extension exercise increased for RESX after training [from
17.9 (1.0) to 23.9 (1.4) kg, P < 0.05] but not for RES [from 17.6 (1.4) to 17.7 (1.9)␣kg] or CON [from 10.1 (2.2) to 10.3 (2.1) kg]. RESX showed an increase
in total neck muscle CSA after training [from 19.5 (3.0) to 22.0 (3.6) cm2, P < 0.05], but RES and CON did not [from 19.6 (2.9) to 19.7 (2.9)␣cm2 and 17.0 (2.5) to 17.0 (2.4) cm2, respectively]. This hypertrophy for RESX was due mainly to increases in CSA of 23.9 (3.2), 24.0 (5.8), and 24.9 (5.3)% for
the splenius capitis, and semispinalis capitis and cervicis muscles, respectively. The lack of generalized neck muscle hypertrophy
in RES was not due to insufficient training. For example, the CSA of their quadriceps femoris muscle group, as assessed by
MRI, increased by 7 (1)% after this short-term training (P < 0.05). The results suggest that: (1) the splenius capitis, and semispinalis capitis and cervicis muscles are mainly responsible
for head extension; (2) short-term resistance training does not provide a sufficient stimulus to evoke neck muscle hypertrophy
unless specific neck exercises are performed; and (3) the postural role of head extensors provides modest loading in bipeds.
Accepted: 15 October 1996 相似文献
16.
B. Mercier P. Granier J. Mercier L. Foucat G. Bielicki J. Pradere J. P. Renou C. Prefaut 《European journal of applied physiology and occupational physiology》1998,78(1):20-27
We investigated whether localized 1H nuclear magnetic resonance spectroscopy (NMRS) using stimulated echoes (STEAM) with a long mixing time (t
m) allowed the suppression of the fat signal and detection of lactate in skeletal muscle. The 1H NMRS sequence was first validated in three isolated and perfused rabbit biceps brachii muscles. Spectra were obtained on a wide-bore spectrometer using a dual-tuned probe (1H and 31P). Death was simulated by ceasing the muscle perfusion, which allowed post-mortem changes to be followed. During and after the simulated death, changes in levels of pH and in content of energy-rich compounds
were observed with 31P NMRS. Our results showed an inverse linear relationship between pH and lactate in each of the three rabbits (r = 0.93, P < 0.001; r = 0.92, P < 0.01; r = 0.89, P < 0.01) and a decrease in phosphocreatine and concomitant increase in lactate. We then investigated whether this sequence
allowed repeated detection of lactate in human soleus muscle during the recovery between periods of intense exercise (force-velocity
test, F-v test). Seven subjects mean age 25.1 (SEM 0.8) years participated in this study. Soleus muscle lactate was detected at rest
and for 3 min 30 s of the 5-min recovery between periods using a 2.35-T 40-cm bore magnet spectrometer. Arm venous plasma
lactate concentration was measured at rest, during the F-v test when the subject stopped pedalling (S1), and at the end of each 5-min recovery between periods (S2). Results showed that the venous plasma lactate concentration at S1 and S2 increased significantly from the beginning of the F-v test to peak anaerobic power (W
an,peak) (P < 0.001). The spectra showed that muscle lactate resonance intensity rose markedly when W
an,peak was achieved. The muscle lactate resonance intensity plotted as a percentage of the resting value increased significantly
at W
an,peak compared with submaximal braking forces (P < 0.05). We concluded from these results that localized 1H NMRS using STEAM with a long t
m allows suppression of the fat signal and repeated detection of lactate on isolated perfused skeletal muscle in animals and
between periods of intense exercise in humans.
Accepted: 19 January 1998 相似文献
17.
Noise improves transfer of near-threshold, phase-locked activity of the cochlear nerve: evidence for stochastic resonance? 总被引:2,自引:0,他引:2
K. R. Henry 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,184(6):577-584
Stochastic resonance can be described as improved detection of weak periodic stimuli by a dynamic nonlinear system, resulting
from the simultaneous presentation of a restricted dynamic range of low-intensity noise. This property has been reported in
simple physical and biological activities. The present study describes data consistent with the interpretation that stochastic
resonance can be observed in the response of cochlear neurons. These experiments utilized low levels (−5 to 25 dB SPL) of
stimuli and noise (5 to 30 dB SPL). Stimuli consisted of simultaneously presented 8 kHz (F
1) and 8.8 kHz (F
2) tone bursts, which generated an 800 Hz F
2–F
1 cochlear nerve envelope ensemble response in the gerbil. The mean response threshold was approximately −3 dB SPL. Simultaneous
presentation of a low-intensity wideband noise increased the amplitude of this response. This was observed with tonal stimuli
having intensities of 0–5 dB SPL; responses to stimulus levels >10 dB were attenuated by noise. Response amplitude was increased
by noise levels of 10–15 dB; the amplitude was unaffected by lower levels of noise, and decreased in the presence of higher
noise levels. These properties are compatible with those of stochastic resonance.
Accepted: 11 March 1999 相似文献
18.
Jaak Jürim?e Peter J. Abernethy B. M. Quigley Kirsten Blake Michael T. McEniery 《European journal of applied physiology and occupational physiology》1997,75(4):357-362
The purpose of this investigation was to compare the myosin heavy chain (MHC) isoform expression of the triceps brachii muscle
and isoinertial, isometric and isokinetic strength indices in competitive bodybuilders (CB, n = 5), recreational resistance trainers (RT, n = 5), endurance-trained rowers (ER, n = 5) and control (C, n = 5) subjects. Muscle tissue samples were analysed for MHC isoform content using 6% sodium dodecyl sulphate-polyacrylamide
gel electrophoresis. The CB possessed significantly smaller (P < 0.05) percentage of MHC type IIb proteins [12.92 (SD 7.08)%] than RT [30.08 (SD 6.58)%] ER [31.20 (SD 2.74)%] and C [38.22
(SD 2.95)%] groups (i.e. CB < RT ≈ ER < C). While the content of MHC type IIa isoforms did not differ significantly between
the two resistance-trained groups [CB = 55.76 (SD 5.38)%; RT = 45.72 (SD 7.8)%], CB presented significantly more type IIa
MHC isoforms than ER [42.84 (SD 2.98)%] and C [34.72 (SD 1.57)%] subjects (i.e. CB ≈ RT > ER ≈ C). The MHC type I protein
content did not differ significantly among RT [24.20 (SD 4.89)%] ER [25.38 (SD 1.67)%] and C [27.06 (SD 1.81)%] groups. The
CB [31.32 (SD 2.67)%] presented significantly more type I MHC isoforms only in comparison with RT. However, when changes in
the percentage of MHC type I isoforms were converted to effect sizes (ES), it appeared that low statistical power rather than
the absence of an effect accounted for the nonsignificant differences between CB and other groups (i.e. CB > RT ≈ ER ≈ C).
Significant differences existed in isoinertial strength among the trained athletes (i.e. CB > RT > ER ≈ C), while isometric
and isokinetic strength were not significantly different among any of the trained groups. However, the ES transformation of
data demonstrated that large differences existed between resistance-trained groups and ER for isometric and isokinetic strength
(i.e. CB ≈ RT > ER ≈ C). A statistically significant negative correlation (P < 0.001) was found between MHC type IIb isoforms and isoinertial strength index (r = − 0.68). The MHC type IIa proteins were positively related to all the strength measures considered (r = 0.51 – 0.61; P < 0.001). These data demonstrated different patterns of MHC isoform expression among the different groups of athletes and
it is suggested that these differences on occasion may affect the expression of strength.
Accepted: 24 September 1996 相似文献
19.
S. E. Mathiassen T. Aminoff 《European journal of applied physiology and occupational physiology》1997,76(5):434-444
Ten females (25–50 years of age) performed isometric shoulder flexions, holding the right arm straight and in a horizontal
position. The subjects were able to see the rectified surface electromyogram (EMG) from either one of two electrode pairs
above the upper trapezius muscle and were instructed to keep its amplitude constant for 15 min while gradually unloading the
arm against a support. The EMG electrodes were placed at positions representing a “cranial” and a “caudal” region of the muscle
suggested previously to possess different functional properties. During the two contractions, recordings were made of: (1)
EMG root mean square-amplitude and zero crossing (ZC) frequency from both electrode pairs on the trapezius as well as from
the anterior part of the deltoideus, (2) supportive force, (3) heart rate (HR) and mean arterial blood pressure (MAP), and
(4) perceived fatigue. The median responses during the cranial isoelectric contraction were small as compared to those reported
previously in the literature: changes in exerted glenohumeral torque and ZC rate of the isoelectric EMG signal of −2.81% · min−1 (P = 0.003) and 0.03% · min−1 (P= 0.54), respectively, and increases in HR and MAP of 0.14 beats · min−2 (P= 0.10) and 0.06 mmHg · min−1 (P= 0.33), respectively. During the contraction with constant caudal EMG amplitude, the corresponding median responses were
−2.51% · min−1 (torque), 0.01% · min−1 (ZC rate), 0.31 beats · min−2 (HR), and 0.93 mmHg · min−1 (MAP); P=0.001, 0.69, 0.005, and 0.003, respectively. Considerable deviations from the “isoelectric” target amplitude were common
for both contractions. Individuals differed markedly in response, and three distinct subgroups of subjects were identified
using cluster analysis. These groups are suggested to represent different motor control scenarios, including differential
engagement of subdivisions of the upper trapezius, alternating motor unit recruitment and, in one group, a gradual transition
towards a greater involvement of type II motor units. The results indicate that prolonged low-level contractions of the shoulder
muscles may in general be accomplished with a moderate metabolic stress, but also that neuromuscular adaptation strategies
differ significantly between individuals. These results may help to explain why occupational shoulder-neck loads of long duration
cause musculoskeletal disorders in some subjects but not in others.
Accepted: 1 March 1997 相似文献
20.
We examined the role of cytokinins (CKs) in release of apical dominance in lateral buds of chickpea (Cicer arietinum L.). Shoot decapitation or application of CKs (benzyladenine, zeatin or dihydrozeatin) stimulated rapid bud growth. Time-lapse
video recording revealed growth initiation within 2 h of application of 200 pmol benzyladenine or within 3 h of decapitation.
Endogenous CK content in buds changed little in the first 2 h after shoot decapitation, but significantly increased by 6 h,
somewhat later than the initiation of bud growth. The main elevated CK was zeatin riboside, whose content per bud increased
7-fold by 6 h and 25-fold by 24 h. Lesser changes were found in amounts of zeatin and isopentenyl adenine CKs. We have yet
to distinguish whether these CKs are imported from the roots via the xylem stream or are synthesised in situ in the buds,
but CKs may be part of an endogenous signal involved in lateral bud growth stimulation following shoot decapitation. To our
knowledge, this is the first detailed report of CK levels in buds themselves during release of apical dominance.
Received: 12 December 1996 / Accepted: 7 January 1997 相似文献