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1

Adaptation of motoneurons to altered physical activity

100%
Krutki P.
Acta Neurobiologiae Experimentalis
|
2015
|
tom 75
|
nr Supl.
The study shows that different models of an increased muscular activity may induce measurable effects on electrophysiological properties of motoneurons (MNs). Three types of altered motor activity were compared in rats: chronic compensatory muscle overload, whole-body vibration (WBV), and strength training. Intracellular recordings from spinal motoneurons were made to measure membrane and firing properties of MNs.Muscle overload was induced in the rat medial gastrocnemius by bilateral tenotomy of its synergists. Adaptive changes in passive and threshold properties were observed only in fast-type MNs innervating the overloaded muscle. The data suggest their higher excitability, and a shift towards electrophysiological properties of slow-type Mns. The WBV training was performed 5 days a week, for 5 weeks, and each daily session consisted of four 30-second runs of vibration at 50 Hz. No significant changes in the passive membrane properties of MNs were found after the WBV program. However, lower values of rheobase current and a leftward shift of the frequencycurrent relationship were observed for fast-type MNs. This indicates their ability to become recruited earlier (and possibly more frequent), and to achieve the same or higher firing rates at lower stimulus intensities. During strength training rats were nutritionally conditioned in order to make weightlifting put on their shoulder in a special apparatus with progressively increasing load. After 5 weeks adaptive changes in several membrane properties were revealed in fast and slow-type MNs. Increased maximum frequencies of rhythmic firing of MNs, and higher susceptibility of MNs to an increased or decreased intensity of a stimulus were observed. Adaptations of MNs to various modes of chronic activation of muscles were relatively quick, but different with respect to extent and dynamics of the effects. Supported by the National Science Center grants: 2011/01/N/ NZ4/04901, 12/04/M/NZ4/00190 and 2013/11/B/NZ7/01518.
2

Sacral projections of propriospinal neurones of the sixth cervical segment of the spinal cord in the cat

100%
Krutki P.
Acta Neurobiologiae Experimentalis
|
1995
|
tom 55
|
nr 5
3

Synaptic connections from forelimb afferents to neurones located in the cervical spinal cord that project to sacral segments and the cerebellum in the cat

100%
Krutki P.
Acta Neurobiologiae Experimentalis
|
1999
|
tom 59
|
nr 3
4

Contractions of motor units evoked by stimulation with pulses and variable interpulse intervals

100%
Krutki P.
Acta Neurobiologiae Experimentalis
|
2009
|
tom 69
|
nr 3
The rate of motoneuronal fi ring is a major factor regulating the force of motor units (MUs). During voluntary activity of a muscle, its MUs generate tetanic contractions which are characterized by variable force and fusion degree. This study aimed at analysis of force changes during tetani evoked at random stimulation patterns and their mathematical decomposition into responses to individual pulses. It was demonstrated that longer interpulse intervals and lower initial levels of force result in higher force increase during next components of tetanic contractions, and that random stimulation pattern produces higher output of MUs (and higher economy of contraction) than the constant frequency during relatively weak contractions. The decomposition revealed considerable variability in twitch responses to successive pulses. Their basic parameters can be predicted with high accuracy on the basis of the force level at which the next contraction begins. The physiological signifi cance of successive action potentials generated by active motoneurones appears to show considerable variation, so the application of constant frequency patterns during experimental analysis of functionally isolated MUs can lead to several conclusions that do not correspond to activity of MUs during natural voluntary movements. This concerns parameters of successive components of tetanic contractions: the contraction time, the instantaneous force and its variability, the effectiveness and economy of the MU’s contraction.
5

Bilateral projection of neurones of the C6 segment to S1 and S2 segments of the spinal cord in the cat

100%
Krutki P.
Acta Neurobiologiae Experimentalis
|
1997
|
tom 57
|
nr 1
6

Projection of neurones located in sacral spinal cord segments to the cerebellum and the inferior olive in the cat

63%
Mrowczynski W., Krutki P.
Acta Neurobiologiae Experimentalis
|
2001
|
tom 61
|
nr 3
7

Electrophysiological investigation of spino-olivary projections originating from sacral segments of the cat spinal cord

63%
Mrowczynski W., Krutki P.
Acta Neurobiologiae Experimentalis
|
2001
|
tom 61
|
nr 4
8

Afferent input from distal forelimb nerves to branching spinoreticular-spinocerebellar neurones in the cat

63%
Krutki P., Mrowczynski W.
Acta Neurobiologiae Experimentalis
|
2002
|
tom 62
|
nr 4
9

Changes in electrophysiological properties of motoneurones innervating rat medial gastrocnemius in response to the muscle overload

51%
Haluszka A., Baczyk M., Celichowski J., Krutki P.
Acta Neurobiologiae Experimentalis
|
2011
|
tom 71
|
nr S
Various models of chronic muscular activity, as workload training, tendon transfer, or paresis and peripheral nerve damage are examples leading to muscle overload, which may induce measurable effects in motor units. The aim of this study was to investigate whether 5-week overloading of muscles connected with their voluntary activation in a running wheel and by a treadmill training change electrophysiological properties of their motoneurons. Rats were subjected to chronic overload of the medial gastrocnemius (MG) muscle by cutting the lateral gastrocnemius, soleus and plantaris muscles from the Achilles tendon and sewing them directed proximally to the skin. As the result of this operation, only the MG muscle was able to evoke a foot plantar flexion during the daily locomotor activity. After one week of convalescence, rats were subjected to extensive voluntary activity on a running wheel and additionally to a training program on a treadmill (1 hour daily with a speed of 27 cm/s) for 5 weeks, 5 days a week. The acute experiments were carried out on the MG motoneurones in deeply anaesthetized animals. Intracellular recordings were performed from MG motoneurones located in L4-L5 spinal segments using glass micropipettes filled with 2 M potassium citrate solution. The results were compared to the control group of normally active, intact animals. Parameters of antidromic action potentials were measured and effects of intracellular injection of rectangular pulses of depolarization current were analyzed. The basic electrophysiological properties were considerably modified by the overloading either in fast and slow motoneurones. Moreover, we observed changes in their rhythmic properties, as the increased maximum steady-state frequencies of motoneuronal firing resulting in changes in the course of the steady-state frequency-current curves in the overloaded animals. The results of this study may help understand neuromuscular mechanisms of plasticity of overloaded muscles.
10

Effects of ageing on the regulation of force in the rat medial gastrocnemius motor units

51%
Lochynski D., Krutki P., Celichowski J.
Acta Neurobiologiae Experimentalis
|
2005
|
tom 65
|
nr 3
11

Double stimulation modulates afterhyperpolarization phase following action potentials evoked in rat motoneurones

51%
Mrowczynski W., Krutki P., Celichowski J.
Acta Neurobiologiae Experimentalis
|
2007
|
tom 67
|
nr 4
The influence of a pair of stimuli running in time sequence between 5–10 ms (a doublet) on the basic parameters of antidromic action potentials was studied in rat motoneurones. Electrophysiological experiments were based on stimulation of axons in the sciatic nerve and intracellular recording of antidromic action potentials from individual motoneurones located in L4–L5 segments of the spinal cord. The following parameters were analyzed after application of a single stimulus and a doublet: amplitude and duration of the antidromic spike, amplitude, total duration, time to minimum, half-decay time of the afterhyperpolarization (AHP). It was demonstrated that application of a pair of stimuli resulted in: (1) a prolongation of action potentials, (2) a prolongation of the total duration and half-decay time of the AHP, (3) a decline of the time to minimum of the AHP, (4) an increase of the AHP amplitude of the spike evoked by the second stimulus. Significant differences in AHP parameters were found either in fast or slow motoneurones. We suppose that doublet-evoked changes in the AHP amplitude and duration are linked to intrinsic properties of individual motoneurones and may lead to the prolongation of the time interval to subsequent motoneuronal discharges during voluntary activity.
12

The tetanic depression in fast motor units of mammalian skeletal muscle can be evoked even by lengthening of one initial interpulse interval

51%
Sowinska Z., Celichowski J., Krutki P., Lochynski D.
Acta Neurobiologiae Experimentalis
|
2009
|
tom 69
|
nr 3
The tetanic depression is phenomenon observed when higher frequency of stimulation of fast motor units immediately follows the lower one. However, it is not known does only one prolonged fi rst interpulse interval can evoke this effect. This study was conducted on 27 fast motor units of cat and 47 units of rat medial gastrocnemius muscles. In experiments performed on the two species the following stimulation protocol was applied in the main part of experiment: (1) the 6-pulses train of stimuli at 20 Hz (cat) or 40 Hz (rat), i.e. at 50 and 25 ms interpulse intervals, (2) the 6-pulses train of stimuli with the fi rst interpulse interval prolonged from 50 ms to 100 ms (cat) or from 25 to 50 ms (rat) followed by 5 stimuli at 20 Hz (cat) or 40 Hz (rat), (3) the 6-pulses train of stimuli at 20 Hz (cat) or 40 Hz (rat). Effects of two-time prolongation of the fi rst interpulse interval were observed as a decrease of the force following the sixth stimulus in a train. The tetanic depression in rat motor unit tetani for fast fatigable (FF) units amounted to 5.39 ± 4.94% and 9.24 ± 4.13% for fast resistant (FR) units whereas in cats the mean values were 15.00 ± 10.15% and 27.00 ± 13.95% for FF and FR motor units, respectively. This results prove that the studied phenomenon infl uence the force development when the motoneuron begins the activity even with only one, fi rst prolonged interpulse interval.
13

Prolonged activity evokes potentiation and the “sag” phenomenon in slow motor units of rat soleus

51%
Drzymala-Celichowska H., Raikova R., Krutki P.
Acta Neurobiologiae Experimentalis
|
2016
|
tom 76
|
nr 2
Slow motor units (MUs) have no sag in their unfused tetani. This study in anesthetized rats shows that the sag can be observed in slow soleus MUs after prolonged activity. Twitches and unfused tetanic contractions were recorded from male (n=35) and female (n=39) MUs before and after the four minutes of the fatigue test (trains of 13 pulses at 40 Hz repeated every second). After this activity twitch contractions potentiated and a shift in the steep part of the force-frequency curve towards lower frequencies was observed in both sexes. Initially no sag was visible in unfused tetani, but after the fatigue test the phenomenon was observed in 77% of male and in 13% of female MUs, with the sex difference possibly related to a higher content of IIa myosin and faster MU contraction in male soleus. Decomposition of tetani with sag into trains of separate twitches elicited by successive stimuli revealed higher forces for the initial than subsequent twitches. The newly revealed enhancement of the sag in force development following long-lasting activation is more pronounced in males than in females.
14

Long-lasting effects of trans-spinal direct current stimulation on motoneuron firing properties in rats

51%
Krutki P., Drzymala-Celichowska H., Mrowczynski W., Baczyk M.
Acta Neurobiologiae Experimentalis
|
2019
|
tom 79
|
nr Suppl.1
INTRODUCTION: Trans-spinal direct current stimulation (tsDCS) is a neuromodulative technique used to improve motor functions in neurological disorders and to facilitate sport performance. However, despite the broad application of spinal cord polarization, the physiological mechanisms behind the observed effects remain unclear. We have recently demonstrated that anodal or cathodal tsDCS can alter motoneuron membrane properties and firing characteristics during its application and beyond. AIM(S): The aim of this study was to determine whether these alterations persist over a longer period of time. METHOD(S): The study was performed on adult male Wistar rats under general anesthesia. Anodal or cathodal tsDCS (0.1 mA, 15 min) was applied through an electrode located on the lumbar vertebra above the recording site. The intracellular recordings from L4‑L5 spinal motoneurons were performed at various periods after the offset of polarization (up to 3 hours). The animals not subjected to tsDCS formed the control group. RESULTS: Anodal tsDCS evoked a significant decrease in the voltage threshold, the rheobase, the threshold for rhythmic steady-state firing, as well as, an increase in the steady‑state firing frequencies and the slope of the frequency‑current relationship. Some of these modulatory effects were observed up to 60 minutes after the offset of polarization. Cathodal tsDCS induced only modest changes in motoneuron threshold properties, which could be observed no longer than 30 minutes after the end of polarization. CONCLUSIONS: This study for the first time provides the direct evidence that tsDCS evokes long-term alterations in the threshold and rhythmic firing properties of spinal motoneurons. Modulatory effects of anodal polarization are stronger and last longer than those of cathodal tsDCS. We suppose that both autonomous cell mechanisms and synaptic effects contribute to the occurrence and long-term persistence of the indicated changes in motoneuron properties. FINANCIAL SUPPORT: Supported by the National Science Center grant No 2017/25/B/NZ7/00373.
15

Variability of the twitch responses to indyvidual stimuli at random stimulation patterns of fast and slow motor units in rat medial gastrocnemius

51%
Celichowski J., Raikova R., Krutki P.
Acta Neurobiologiae Experimentalis
|
2011
|
tom 71
|
nr S
The unfused tetani evoked by train of stimuli at variable interpulse intervals (IPIs) of fast fatigable (FF), fast resistant (FR) and slow (S) motor units (MUs) were recorded and then decomposed into trains of twitch-shape responses to successive stimuli. The mean stimulation frequency was matched for each MU to evoke tetani of a similar fusion degree (lower for slow MUs, higher for fast MUs), whereas the variability range of IPIs was 50 – 150% of the mean IPI value for a given MU. The decomposition was done using an experimentally verified mathematical algorithm, described previously. Ten MUs of each type were analyzed. For each MU the twitch force, the contraction time and the force-time area for the single twitch recording were calculated and compared to both, the strongest and the weakest of the responses to successive stimuli. For each of studied MUs considerable variability of twitch parameters for responses to successive stimuli was observed, although the largest range of variability characterized slow MUs. In general, the decomposed twitch responses were stronger and had longer duration than the single twitches, although especially for 9 FF and to a smaller degree for 6 FR MUs the smallest decomposed responses were weaker but not faster than the single twitches of these MUs. The mean value of a ratio of the strongest decomposed twitch force to the single twitch force amounted to 2.4, 1.8 and 5.5 for FF, FR and S MUs, respectively. The ratio of the strongest decomposed twitch force-time area to the single twitch force-time area amounted to 1.8, 2.2 and 9.5 for FF, FR and S MUs, respectively. Analogically calculated ratio for the contraction time amounted to 1.5, 1.5 and 2.2 for FF, FR and S MUs, respectively. In conclusion, the results evidence that during voluntary activity of muscles successive action potentials generated especially by motoneurons of slow MUs have considerable variability in relation to evoked contractile responses of muscle fibers.
16

Nonlinear summation of motor unit forces in rat medial gastrocnemius muscle

51%
Drzymala H., Celichowski J., Krutki P.
Acta Neurobiologiae Experimentalis
|
2007
|
tom 67
|
nr 3
17

Changes in afterhyperpolarization after double stimuli in rat motoneurones

51%
Mrowczynski W., Krutki P., Celichowski J.
Acta Neurobiologiae Experimentalis
|
2007
|
tom 67
|
nr 3
18

The spinoreticular neurones in the second sacral segment of the cat's spinal cord

51%
Huber J., Grottel K., Krutki P., Mrowczynski W.
Acta Neurobiologiae Experimentalis
|
1995
|
tom 55
|
nr 5
19

Neurones in the cervical enlargement of the cat spinal cord with collaterals ascending to the inferior cerebellar peduncule and descending to sacral segments

51%
Mrowczynski W., Grottel K., Krutki P.
Acta Neurobiologiae Experimentalis
|
1999
|
tom 59
|
nr 3
20

Sex differences in motor unit contractile properties of the rat soleus muscle

51%
Drzymala-Celichowska H., Krutki P., Celichowski J.
Acta Neurobiologiae Experimentalis
|
2013
|
tom 73
|
nr Suppl.1
The soleus muscle has unique physiological characteristics, as a typical slow-twitch muscle, composed predominantly of slow motor units (MUs). In this study we examined electrophysiologically functionally isolated MUs of male and female adult Wistar rats. It was revealed that the mean mass of the soleus muscle in males was approximately by 80% bigger than in females, however, a relation of the muscle-to-body mass was higher for females. No differences were observed with respect to the MU twitch forces, but the maximum tetanus forces were substantially lower for female rats, what significantly influenced higher twitch-to tetanus ratios in females. The contraction and the half-relaxation times were significantly longer in female MUs, what might be due to differences in muscle architecture. The force-frequency curve of slow MUs in males was shifted rightwards with respect to females, indicating that the same relative level of a tetanic force could be achieved at a considerably higher stimulation frequency in males. The maximum force-time area per pulse was significantly higher for males, and the analysis of MU action potentials revealed about four times higher amplitudes in male rats. In conclusion, numerous sex differences in MUs of the rat soleus muscle are not directly influenced by differences in body and muscle size.
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