Biomedical subjects

J Celichowski

Publications and source records attributed to J Celichowski.

At least 19 recordsLinked to original sources

PubMed2006

Interspecies differences of motor units properties in the medial gastrocnemius muscle of cat and rat.

The purpose of the study was to analyze the interspecies differences of motor unit contractile properties in two most frequently studied mammals: cats and rats. A total sample of 166 motor units (79 in cats and 85 in rats) was investigated in the medial gastrocnemius muscle. Considerable differences were found in composition of the studied muscle. In cats, fast fatigable, fast resistant and slow units formed 68, 18 and 14% of the investigated population, whereas in rats 36, 52 and 12%, respectively. The contraction and relaxation times of motor units in the cat muscle were evidently longer than in the rat and the border values for fast/slow motor units division in these species were 44 and 20 ms, respectively. The mean values of twitch and tetanic forces appeared to be 7-8 times lower in rats, for fast, while 2-5 times for slow motor units. Also variability between the strongest and the weakest units within each type revealed differences 10-60 times in cats, whereas only 3.5-14 times in rats. The summation of twitches into tetanus for fast units was comparable in both species, but for S units was evidently more effective in the cat. In fast motor units' tetanic contractions evident interspecies differences concerned sag appearance and profiles of unfused tetani of FF and FR units. Differences in contractile properties described in the study may depend on the size, number and innervation ratio of motor units in the muscle of cat and rat, as well as their biochemical variability. Differences in composition of motor unit types and uneven mechanisms of force development may reflect biological adaptation to variable behaviour of cats and rats.

Animals↗

PubMed2006

Differences between properties of male and female motor units in the rat medial gastrocnemius muscle.

Differences between motor units in hindlimb locomotor muscles of male and female Wistar rats were studied. The contractile and action potential properties of various types of motor units as well as proportions of these units in the medial gastrocnemius muscle were analyzed. Experiments were based on functional isolation and electrical stimulation of axons of single motor units. Composition of motor units was different for male and female subjects, with higher number of the fast fatigable and lower number of slow type units in male animals. The contraction and the half-relaxation times were significantly longer in male motor units, what might be due to differences in muscle size. Slower contraction of male motor units likely corresponds to lower firing rates of their motoneurons. On the other hand, no significant differences between sexes were observed with respect to force parameters of motor units (the twitch and the maximum tetanus forces), except the fast resistant units (higher force values in male muscles). The mass of the muscle was approximately 1.5 time bigger in male rats. However, the mean ratio of motor unit tetanus force to the muscle mass was almost twice smaller in this group, what indirectly suggests that muscles of male rats are composed of higher number of motor units. Finally, female muscles appeared to have higher fatigue resistance as the effect of higher proportion of resistant units (slow and fast resistant) and higher values of the fatigue index in respective motor unit types. The motor unit action potentials in female rats had slightly lower amplitudes and shorter time parameters although this difference was significant only for fast resistant units.

Action Potentials↗

PubMed2006

Monophasic and biphasic relaxation during motor unit tetanic contractions of variable fusion degree.

The phenomenon of transition of the monophasic relaxation into biphasic course in the unfused tetanic contractions was studied on functionally isolated motor units of the rat medial gastrocnemius muscle. The sample consisted of 16 FF, 16 FR and 10 S MUs which were stimulated with the same, digitally controlled patterns. The new parameter--QRT/HRT ratio, was introduced as a convenient tool for the classification of the relaxation into monophasic or biphasic. Analysis of tetani evoked at increasing stimulation frequencies revealed similar relationships between the tetanic fusion degree and the shape of relaxation for all three types of motor units investigated. In each MU, the QRT/HRT ratio fell into two distinct ranges related to either monophasic (lower values) or biphasic (higher values) relaxation. The relationship was also found between the shape of relaxation and degree of tetanic fusion--the biphasic course appeared for better fused tetani when fusion index was over the mean of 0.8. Mechanisms of development of the biphasic relaxation were discussed with respect to importance of this parameter in force development and summation of successive contractions into tetanus. Moreover, it was pointed out that adequacy of mathematical modeling of motor unit contractions should benefit from the precise analysis of the mono- or biphasic course of relaxation.

Animals↗

PubMed2006

Changes in the time course of potentiated and fatigued contractions of fast motor units in rat muscle.

The contraction and relaxation times of the twitches and the last contractions within 32 unfused tetani of FF and 27 unfused tetani of FR motor units in the rat medial gastrocnemius muscle were studied during prolonged activity. The pattern of the MU stimulation included single pulses (to evoke twitches) and series of three trains of stimuli at 40, 50 and 60 Hz (to evoke unfused tetani), repeated 30 times. The analysis concerned changes of force and time parameters at the beginning of activity, during the potentiation and then during the fatigue. It was found that changes of force during the potentiation and the fatigue were mainly accompanied by changes in the course of relaxation. The significant prolongation of the half-relaxation time during the potentiation of either twitches or unfused tetani was revealed in both types of fast MU. The twitch contraction time did not change markedly, whereas significantly shortened in the last contractions of unfused tetani during the potentiation. These changes of time parameters correlated to the increase of the fusion degree. During the fatigue, the time parameters shortened, however, changes of the half-relaxation times were remarkably higher. The shortening of relaxation was responsible for the decrease of the fusion degree. Changes of the fusion index exceeding 0.75 during the potentiation or decreasing below this value during the fatigue, were accompanied by respective appearance or disappearance of the biphasic relaxation.

Action Potentials↗

PubMed2006

Interspecies differences in the force-frequency relationship of the medial gastrocnemius motor units.

Single, functionally isolated motor units were studied in the medial gastrocnemius (MG) muscle of cats and rats. Axons of their motoneurons were stimulated with trains of pulses at frequencies increasing from 1 to 150 Hz and forces developed by muscle fibers were measured and force-frequency curves were compared between species. The following observations were made: (1) the most steep parts of curves (related to unfused tetani of motor units) begun at lower frequencies of stimulations in all types of feline motor units, (2) for fast motor units, the same relative values of force of unfused tetani were achieved at significantly lower frequencies of stimulations in the cat than in the rat. Twitch time parameters of both species influenced the course of force-frequency curves. It was showed that the contraction times of feline units varied in the wide range (21-81 ms), and these units reached 60% of the maximum force at stimulation frequencies between 10 and 38 Hz. On the other hand, contraction times of rat units ranged from 10 to 34 ms, whereas stimulation frequencies necessary to reach 60% of the maximum force varied considerably, from 12 to 65 Hz. The correlations between the above parameters were found for motor units of each species. However, the regression lines drown for the collected population of cat and rat units did not form linear continuity. Thus it seems that interspecies differences in the twitch contraction times do not fully explain different force-frequency relationships in mammalian skeletal muscles.

Action Potentials↗

PubMed2005

Experimentally verified model of mechanomyograms recorded during single motor unit contractions.

The aim of the paper is to create a model which enables to observe the mechanomyographic (MMG) wave generated during single motor unit contractions in a muscle, while the muscle is immersed in paraffin oil. The muscle model is described as a rheological membrane. Both the muscle and the medium models have been built by using Stiff-Finite-Element-Method (SFEM), which allows one to simulate the muscle surface displacement and the acoustic propagation of this effect in the oil. Such a modelling enables one to determine the impact of the rheological properties of the liquid environment on the shape of the MMG wave. In order to verify the model, the MMG signals and the contraction forces have been recorded in vivo from the medial gastrocnemius muscle of a rat. In these experiments single motor units were stimulated with various stimulation frequencies. A piezotransducer, immersed in paraffin oil, has been used to record the MMG signal recording. The signals recorded during individual twitches of the motor units have been used to estimate the parameters of the model. Subsequently, the model has been experimentally verified. The signals recorded in experiments during unfused and fused tetani have been compared with the simulated model responses in the analogous stimulation program. It has been observed that the MMG signals obtained with the proposed linear model have been consistent with the results of in vivo experiments.

Animals↗

PubMed2005

Analysis of the unfused tetanus course in fast motor units of the rat medial gastrocnemius muscle.

The course of unfused tetani with the sag effect in fast motor units of rat medial gastrocnemius was studied. The analysis of the course of successive contractions within these tetani showed that the high peak force at the beginning of tetanus before the sag resulted from temporary, very efficient sum mation of contractions at this phase, both in FF (fast fatigable) and FR (fast resistant to fatigue) units. The process of summation developed in spite of parallel shortening of the contraction and relaxation. The peak of tetanus force was visible on the average at the 2nd contraction in FF units and at the 5th contraction in FR units. After the tetanus peak the process of the efficient summation was completed and the force decreased what was visible as a sag. In the following part of the tetanus, mainly in FF units, the potentiation occurred and the force of successive contractions increased. The rise of force was visible in spite of shortening of the contraction time and was due to prolongation of the relaxation in this part of the tetanus. These observations indicated that the processes of the summation of successive contractions before sag and during the potentiation underwent different mechanisms discussed in this paper. Considerable release of Ca2+ ions from the sarcoplasmic reticulum was proposed as a possible mechanism responsible for a very efficient summation at the beginning of the tetanus whereas phosphorylation of regulatory light chain of myosin (RLC) in muscle fibers was considered as the reason of potentiation. Moreover, the present analysis revealed that previously found differences in tetani profiles between FF and FR units resulted from faster development of described changes in the course of contractions summating into the tetanus in FF motor units.

Animals↗

PubMed2004

Tetanic depression in fast motor units of the cat gastrocnemius muscle.

Ability of muscle fibers to generate force is decreased when higher frequency of stimulation of motor units immediately follows lower frequency. This phenomenon called tetanic depression was found in rat medial gastrocnemius. However, it was not clear whether tetanic depression occurred only in rat muscle or it concerns all mammals. This study was conducted on motor units of cat medial gastrocnemius. Analyses were made at three successive trains of stimulation: 30 Hz, 20 and 30 Hz and again 30 Hz (the first pattern) or 40 Hz, 25 and 40 Hz and 40 Hz (the second pattern). In all fast units force generated within the middle tetanus was lower than force generated at the same, but constant frequency of stimulation applied earlier or later. The mean tetanic depression in 30 Hz tetani amounted to 10.9% for fast fatigable (FF) and 15.9% for fast resistant (FR) motor units, whereas in 40 Hz tetani mean values were 5.6% and 7.3% for FF and FR motor units, respectively. In slow motor units tetanic depression was not observed. These results proved the existence of tetanic depression in the feline muscle and indicated that its intensity depends on the fusion of tetanus. It has been concluded, that the tetanic depression is a general property of fast motor units in mammals.

Action Potentials↗

PubMed2001

Mechanomyographic signals generated during unfused tetani of single motor units in the rat medial gastrocnemius muscle.

The aim of this study was to investigate mechanomyograms (MMGs) accompanying unfused tetani of fast fatigable (FF), fast fatigue-resistant (FR) and slow (S) motor units. Signals in the MMG were analyzed during tetanus, which was fused to a variable degree, evoked by electrical stimulation at three frequencies: 20, 40 and 80 Hz. Unfused tetani were characterized by an oscillating tension. Each oscillation in the tension of an unfused contraction was reflected by a parallel pressure wave signal in the MMG. The mean peak-to-peak amplitude of signals in the MMG, the amplitude of oscillation in the tension, the velocity of the tension increase and the fusion index were calculated for the unfused tetanic contraction. The increase in stimulation frequency resulted in an increase in the peak tension, an increase in the fusion of the tetanus, a decrease in the amplitude of force oscillation in the unfused contraction and a decrease in the peak-to-peak amplitude of signals in the MMG. Moreover, it was found that the MMG amplitude was correlated with the amplitude of the three analyzed properties of the unfused contraction. It is concluded that the amplitude of signals in MMGs depends mainly on the dynamic properties of the tetanic contraction, whereas the static component of the contraction (i.e., the level around which the tension oscillates) is not reflected in the MMG.

Animals↗

PubMed2001

Changes in the properties of mechanomyographic signals and in the tension during the fatigue test of rat medial gastrocnemius muscle motor units.

The influence of activity-related changes in tension on properties of the mechanomyogram (MMG) was investigated in fast fatigue-able, fast resistant and slow motor units (MUs). A standard fatigue test was used in which rhythmically repeated unfused tetani were evoked. The amplitudes of the rise in tension of the first and the last contraction within the unfused tetanus and the amplitudes of accompanying signals in MMG were calculated. For fast fatigue-able MUs a parallel decrease in the amplitudes of both analysed contractions and in the amplitudes of accompanying MMG signals during the fatigue test was observed. For majority of fast resistant MUs at the beginning of the fatigue test a potentiation occurred and this phenomenon increased the tension of the first contraction and of the peak tetanic tension. However, the potentiation coincided also with a decrease of the amplitude of the last contraction in the tension recording of an unfused tetanus. The MMG reflected both, the increase of amplitude of the first contraction and the decrease of the amplitude of the further contractions within the tetanus. The single twitch contraction evoked immediately before and after the fatigue test was additionally recorded. A decrease (fatigue) or an increase (potentiation) of the twitch tension after the fatigue test was reflected by a decrease or an increase in the amplitude of MMG, respectively. However, the fatigue failed to change significantly the time parameters of MMG. To conclude, fatigue and potentiation can occur during activity of fast MUs and both these phenomena involve changes in the amplitude of oscillations in tension of unfused tetani which are reflected in MMG.

Animals↗

PubMed2001

Tetanic depression: a phenomenon influencing the production of tension in fast-twitch motor units in rat medial gastrocnemius.

The influence of an increase or a decrease in the stimulation frequency on tension development during a tetanus was studied in motor units of the rat medial gastrocnemius muscle. These effects were tested in one tetanus evoked at two frequencies of stimulation, a lower immediately followed by a higher one or the reverse. For all fast motor units it was observed that after the first part of a tetanus at a lower frequency of stimulation the tension of the following part, of the better fused contraction, was depressed. This effect was called a tetanic depression. When the lower stimulation frequency was followed by the higher one, the depression was visible in some motor units only whereas in the remaining units a potentiation of the second part of the tetanus was visible. The tetanic depression was larger in fast resistant than in fast fatigable motor units. In slow motor units tetanic depression was not observed. The tetanic depression is a phenomenon which can influence the production of contractile tension by fast motor units.

Action Potentials↗

PubMed2001

Sensitivity of the motor unit unfused tetanus to changes in the pattern of motoneuronal firing.

The effects of decreasing as well as increasing the interpulse intervals on the tension produced by motor units in the rat medial gastrocnemius muscle were investigated. The increase and decrease in tension, resulting from these changes in interpulse intervals were observed and compared for each motor unit in tetani fused to a various degree. It was found that amplitudes of both changes in tension were the same when the tetanic fusion index was approximately 0.70 and the tension corresponded to 40-50% of the maximal tetanic tension. This observation concerned the all three types of motor units. We also studied the effects of introducing a short interpulse interval ("doublet") at the beginning of the stimulation. The doublet produced an increased tetanic tension with a more fused profile, however the tension was similarly sensitive to an increase as well as a decrease in the interpulse interval when the tetanic fusion index was also about 0.70. Therefore, the extent of tetanic fusion determines the sensitivity of motor unit tetani to changes in a pattern of stimulation. The tetanus of the fusion index about 0.70 can be considered as the most sensitive to changes in the pattern of motoneuronal firing.

Action Potentials↗

PubMed2000

Mechanisms underlying the regulation of motor unit contraction in the skeletal muscle.

The control of movements is made posible thanks to the activity of motor units in skeletal muscles. In the present paper the influence of frequency and pattern of motoneuronal firing on the tension of contraction and the tension-time area is presented and discussed. The most resistant to fatigue slow-twitch motor units are low susceptible to changes in a pattern of impulses and therefore they are well prepared to participate in long-lasting movements at low but rather stable levels of tension. Moreover, their contraction is very effective and it is performed at a low metabolic charge. Fast-twitch units have lower resistance to fatigue and they have higher tension but they have high susceptibility to a pattern of pulses and their tension can be effectively regulated by an increase or a decrease in the interpulse interval. Therefore, fast motor units are specialized to participate in the regulation of the movement force. The existence of different functional groups of motor units in skeletal muscles enables the performance of different motor tasks very effectively and at possibly low metabolic costs.

Animals↗

PubMed2000

Relationship between the tension-time area and the frequency of stimulation in motor units of the rat medial gastrocnemius muscle.

The tension-time area is an estimation of the work performed by contracting motor units. The relationship between tension and frequency of stimulation and between tension-time area and frequency have been studied on 148 single motor units of the rat medial gastrocnemius muscle, under isometric conditions. Motor units were classified as fast fatigable (FF), fast resistant to fatigue (FR) or slow (S). Trains of stimuli of increasing frequency and constant duration were used. For all motor units a half of the maximum tetanic tension corresponded to lower frequencies compared to frequencies at a half of the maximum tension-time area. Moreover, the slopes of tension-frequency and area-frequency curves (change of tension or area per 1 Hz rise in frequency) were higher for slow than for fast motor units. The tension-time area per one pulse was calculated for different frequencies of stimulation. For slow units the maximum area per pulse corresponded to significantly lower frequencies than for fast ones, especially of FF type. However, for all three types of motor units this optimal frequency corresponded to sub-fused tetani with a tension of about 75% of the maximum tension, and with the fusion index slightly over 0.90. The absolute values of the maximum tension-time area per pulse revealed that in one contraction within the tetanus, slow units are generating greater work than FR units. The work performed by FF units is nearly two times larger than for S units, although the tension of slow units is over eight times lower. The presented results reveal that the contraction of slow motor units is much more effective than was suggested based on their low tension.

Animals↗

PubMed2000

The influence of increasing and decreasing frequency of stimulation on the contraction of motor units in rat medial gastrocnemius muscle.

Motoneurons during their activity can generate firings at changing rate. Therefore, the present paper aimed at studying the evoked contractions of different types of motor units to stimulation at progressively decreasing or increasing interpulse intervals. The influence of both patterns of stimulation on the tension, the duration and the tension-time area of motor units in rat medial gastrocnemius muscle was studied. The decreasing stimulation frequency resulted in generation of a bigger tension-time area although a slightly lower tension and a shorter duration of a contraction were observed in majority of studied units. For fast units a bigger tension-time area observed during the stimulation at decreasing frequency is probably due to the potentiation resulting from the initial high-frequency stimulation. On the other hand, at increasing frequency of stimulation the influence of the initial low-frequency stimulation can depress the tension-time area. The decreasing rate of stimulation during relaxation appeared to support the tension more effectively in slow-twitch motor units than in fast ones. Therefore, slow motor units are well suited to support the tension of tonic contractions.

Animals↗

PubMed1999

The influence of changes in the stimulation pattern on force and fusion in motor units of the rat medial gastrocnemius muscle.

The effects of irregularity in the pattern of stimulation on the tension produced by motor units in the rat medial gastrocnemius muscle were investigated. The effects of decreasing as well as increasing the interpulse intervals were observed for each motor unit in tetani fused to different degrees. For each motor-unit type, it was found that the effects of these changes depended on the extent of tetanic fusion. Decreasing the interpulse interval produced an increase in tension during the tetanus: the more fused the profile of tetanus, the smaller the tension increase. Increasing the interpulse interval resulted in a decrease in tetanic tension. This effect was most prominent when the tetanic fusion index was approximately 0.75. This phenomenon resulted from the prolongation in relaxation when tetanic fusion increased, thereby preventing a decrease in tension when the interpulse interval increased. We also investigated the effects of introducing a short interpulse interval ("doublet") at the beginning of the stimulation. The doublets produced increased tetanic tension with a more fused profile. However, the doublet enhanced the sensitivity of the tetanus to increases in interpulse interval and decreased its sensitivity to decreases in interpulse intervals. Slow-twitch motor units appeared to be significantly less sensitive to both increases and decreases in interpulse interval than fast-twitch units. This suggests that slow-twitch units are better suited for producing long-lasting contractions with a constant tension level. Conversely, the high sensibility of fast-twitch units to changes in stimulation frequency enhances their participation in regulation of tension of the muscular contraction.

Animals↗

PubMed1999

Distribution of the sacral neurones of origin of the ascending spinal tracts with axons passing through the lateral funiculi of the lowermost thoracic segments: an experimental HRP study in the cat.

The locations of 249 cell bodies of the ascending tract neurones in the grey matter of S1-S3 segments of the spinal cord were reconstructed by histochemical staining, after their axons (or axonal collaterals) at the level of the Thl3 segment were injected with horseradish peroxidase (HRP). In three cats in which the injections of HRP were restricted to the lateral part of the lateral funiculi (llf), about 84% of 159 retrogradely labelled cells were found on the contralateral side, while about 16% were located ipsilaterally. They were the most numerous in S2, S3 and S1 segments, respectively, and the neurones were distributed mainly in the lateral laminae I-VII, medial laminae V, VI and lamina VIII. In three other animals in which the injections of the marker were limited to the dorsal part of the lateral funiculi (dlf), 84 of the 90 ascending tract neurones were found to be distributed in the S2 and S3 segments both ipsi- (lateral laminae III-V) and contralaterally, (lateral laminae IV and V as well as the medial laminae VII and VIII) in similar numbers. The remaining six of the 90 cells with only contralateral projections at the dorsolateral funiculus at Thl3 were scattered within the S1 segment. These data are consistent with the results of studies on sacral spinocerebellar, spinothalamic and spinoreticular projections, as well as the localization of sacral spinocervical and priopriospinal neurones. They may also imply the importance of the bilateral fiber course of the neurones of origin of ascending tracts in the S2 and S3 segments within the dorsolateral funiculus.

Afferent Pathways↗

PubMed1999

Differences in the profile of unfused tetani of fast motor units with respect to their resistance to fatigue in the rat medial gastrocnemius muscle.

In most studies performed on motor units in mammalian muscles the division of these units into fast and slow types has been based on the 'sag' visible in the profile of unfused tetanus. The time course of the sag in unfused tetani of fast motor units was analysed in the present study. Fast units of rat medial gastrocnemius muscle were classified as fast fatigable (FF) or fast resistant to fatigue (FR) on the basis of a fatigue index calculated during the standard fatigue test. In middle-fused tetani (fusion index 0.25-0.75), it was observed that for FF motor units the sag was shorter and occurred earlier than for FR units. Moreover, in FF units, the sag was followed by potentiating tension, whereas for FR units this potentiation was weaker or even absent. A tetanus shape index, which expressed the ratio of the area of the first part of the tetanus record (between the tension record and the baseline, from the beginning of tetanus up to the lowest point during the sag in the tension record) to the area under the second part of tetanus (from this lowest point up to the end of the record) was introduced. For FF units, this index ranged from 0.13 to 0.47, whereas for FR units it ranged from 0.54 to 17.8 (with one exception). These results showed that the difference in unfused tetanus expressed in this tetanus shape index could be used as an accurate alternative method of dividing fast units into FF and FR groups. Moreover, the difference in sag time course in FF and FR groups. Moreover, the difference in sag time course in FF and FR units suggests that the metabolism responsible for this contractile phenomenon is significantly different time courses in IIa and IIb muscle fibres, constituting FF and FR units, respectively.

Animals↗