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Background: Being a scavenger of free radicals, C 60 fullerenes can influence on the physiological processes in skeletal muscles, however, the effect of such carbon nanoparticles on muscle contractility under acute muscle inflammation remains unclear. Thus, the aim of the study was to reveal the effect of the C 60 fullerene aqueous solution (C 60 FAS) on the muscle contractile properties under acute inflammatory pain., Methods: To induce inflammation a 2.5% formalin solution was injected into the rat triceps surae (TS) muscle. High-frequency electrical stimulation has been used to induce tetanic muscle contraction. A linear motor under servo-control with embedded semi-conductor strain gauge resistors was used to measure the muscle tension., Results: In response to formalin administration, the strength of TS muscle contractions in untreated animals was recorded at 23% of control values, whereas the muscle tension in the C 60 FAS-treated rats reached 48%. Thus, the treated muscle could generate 2-fold more muscle strength than the muscle in untreated rats., Conclusions: The attenuation of muscle contraction force reduction caused by preliminary injection of C 60 FAS is presumably associated with a decrease in the concentration of free radicals in the inflamed muscle tissue, which leads to a decrease in the intensity of nociceptive information transmission from the inflamed muscle to the CNS and thereby promotes the improvement of the functional state of the skeletal muscle., (© 2023. The Author(s).)

This study examines some of the non-linear effects of signal transduction in the human motor system, with particular emphasis on muscle hysteresis. The movement tests were analyzed in a group of eight subjects, which were asked to develop tangential force using visual biofeedback while performing slow, externally imposed, circular movements of right hand holding a moving handle operated by a computerized mechatronic system. The positional changes in the averaged EMGs of the elbow and shoulder muscles were compared for all combinations of direction of movement and generated force. Additionally, for one of the subjects, there was carried out MRI identification and 3D printing of the bones of the forelimb, shoulder, scapula and collarbone, which made it possible to reconstruct for him the length and force traces of all the muscles under study. The averaged EMG traces in muscles of both joints show their close correspondence to the related force traces, however, the co-activation patterns of activity in agonists and antagonists were also often encountered. The EMG waves related to the respective force waves were strongly dependent on the predominant direction of the muscle length changes within the correspondent force wave locations: the EMG intensities were higher for the shortening muscle movements ( concentric contractions) and lower during muscle lengthening ( eccentric contractions). The data obtained allows to suggest that for two-joint movements of the forelimbs, it is sufficient to consider the force and activation synergies (patterns of simultaneous activity in different muscles), ignoring at the first stage the effects associated with kinematic synergy . On the other hand, the data obtained indicate that the movement kinematics has a strong modulating effect on the activation synergy , dividing it into concentric and eccentric subtypes, in accordance with the known non-linear features of the muscle dynamics. It has been shown that the concentric and eccentric differences in the responses of the shoulder muscles are more clearly distinguishable than those in the elbow muscles. The shoulder muscles also have a more pronounced symmetry of the averaged EMG responses with respect to the ascending and descending phases of force waves, while demonstrating a lower degree of antagonist cocontraction. The data obtained suggest that the central commands in two-joint movements are determined mainly by the interdependence of force and activation synergies including both intra- and inter-joint components, while kinematic synergy can be interpreted as a potent modulator of activation synergy ., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Kostyukov, Gorkovenko, Kulyk, Lehedza, Shushuiev, Zasada and Strafun.)

This paper presents the results of study of titanium-magnesium catalysts often used in polymerization processes, by photoluminescence spectroscopy (PL) in combination with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The interaction of dibutyl phthalate (DBP) with MgCl 2 was studied at DBP added /Mg = 0-1 (mol/mol). The luminescence spectra with excitation at 278 nm and the excitation spectra for main emission bands were recorded. It was shown that DBP adsorbed on magnesium chloride, both in the form of donor-acceptor complexes (D + A - ) and in the form of molecular complexes. At DBP added /Mg <0.15, the formation of D + A - complexes occur predominantly; with an increase in DBP added /Mg, the fraction of molecular complexes increases. Molecular complexes are destroyed during the treatment of the support by TiCl 4 . In this case, the structure of magnesium chloride is disordered and new coordination-unsaturated sites are formed. This work is a first attempt to apply PL spectroscopy in combination with DRIFTS spectroscopy to study titanium-magnesium Ziegler-Natta catalysts. The application of PL spectroscopy to such systems made it possible to detect interactions within and between donor molecules, which would be particularly challenging to achieve using other spectroscopic methods. Both spectroscopic methods provided crucial information about the existence of two types of complexes on the sample surface which is important for tuning the synthesis procedure of the titanium-magnesium catalysts for olefin polymerization.

The fundamental aspects related to the mechanisms of action of C 60 fullerene nanoparticles on the level of the central nervous system in different experimental conditions are still unclear. Electrophysiological investigation and immunohistochemical techniques of c-fos expression were combined to determine which neural elements within the lumbar segments and in the central nucleus of the amygdala (CeA) are activated under skeletal muscle fatigue development with prior application of C 60 fullerenes (dissolved in dimethyl sulfoxide and in distilled water, FDS). After high-frequency electrical stimulation of the triceps surae muscle, the main fatigue-related increases in the c-Fos expression level were registered ipsilaterally within lamina 1 and 5 of the lumbar segments and within the contralateral capsular part of the CeA. C 60 fullerene pretreatment in animals with subsequent electrical stimulation induced a distinct (2-4 times) decrease in the level of Fos immunoreactivity in the observed structures in comparison with only fatigue-induced rats. It can be supposed that FDS, as antioxidant compound, can decrease the concentration of free radicals in fatigued tissue and reduce the transmission intensity of nociceptive information from muscles to the spinal cord and amygdala, thereby changing the level of c-Fos expression within the lumbar segments and CeA.

The effect of C60 fullerene aqueous colloid solution (C60FAS) on the intensity of long‑lasting (persisting for one hour) rotational movements in non‑anesthetized rats was investigated. For this purpose, an experimental hemiparkinsonic animal model was used in the study. Rotational movements in hemiparkinsonic animals were initiated by the intraperitoneal administration of the dopamine receptor agonist apomorphine. It was shown that a preliminary injection of C60FAS (a substance with powerful antioxidant properties) in hemiparkinsonic rats induced distinct changes in animal motor behavior. It was revealed that fullerene‑pretreated animals, in comparison with non‑pretreated or vehicle‑pretreated rats, rotated for 1 h at an approximately identical speed until the end of the experiment, whereas the rotation speed of control rats gradually decreased to 20-30% of the initial value. One can assume that the observed changes in the movement dynamics of the hemiparkinsonic rats after C60FAS pretreatment presumably can be induced by the influence of C60FAS on the dopaminergic system, although the isolated potentiation of the action of apomorphine C60FAS cannot be excluded. Nevertheless, earlier data on the action of C60FAS on muscle dynamics has suggested that C60FAS can activate a protective action of the antioxidant system in response to long‑lasting muscular activity and that the antioxidant system in turn may directly decrease fatigue‑relate d changes during long‑lasting muscular activity.

The averaged electromyograms (EMGs) were registered from the arm muscles of ten subjects in movements of the right hand performed under visual guidance on the horizontal plane along linear trajectories going parallel to the frontal plane at various distances from the trunk. The tests consisted of the steady movements (speed 4 cm/s) between two points symmetrical about the shoulder axis; the hand moved firstly from left to right, then in the opposite direction. The tests repeated ten times for each of two equal loads (10.2 N) applied to the hand along movement trajectory in the right- ( F r ) or leftward ( F l ) directions. The elbow and shoulder flexors reacted predominantly on F r loads; the extensors were mostly activated by F l loads. Positional changes of the averaged EMGs in both flexor and extensor muscles belonging to different joints demonstrated hysteresis properties; the respective hysteresis loops had counterclockwise direction in flexors and clockwise in extensors. The muscles predominantly opposing the loading forces of a given direction participate in a cocontraction mode as antagonists when the direction of load is changed; in this case, together with a decrease in the amplitude of the hysteresis loops, their direction is also reversed. The multiplication index of synergy (MIS), which is based on multiplication of the respective normalized averaged EMG records, has been proposed to evaluate quantitatively changes in the synergy effects between various muscle groups. For distal shifts of the movement traces, the synergy effects are shown to be changed in different directions, increasing in flexors and decreasing in extensors. The obtained results demonstrate that the muscle hysteresis leads to strong modification of the central commands during movements., (Copyright © 2019 Kostyukov, Lehedza, Gorkovenko, Abramovych, Pilewska, Mischenko and Zasada.)

The two-segment model of the human arm is considered; the shoulder and elbow joint torques (JTs) are simulated, providing a slow, steady rotation of the force vector at any end-point of the horizontal working space. The sinusoidal waves describe the JTs, their periods coincide with that of the rotation, and phases are defined by the slopes of the correspondent lines from the joint axes to the end-point. Analysis of the JTs includes an application of the same discrete changes in one joint angle under fixation of the other one and vice versa; the JT pairs are compared for the "shoulder" and "elbow" end-point traces that pass under fixation of the elbow and shoulder angles, respectively. Both shifts between the sinusoids and their amplitudes are unchanged along the "shoulder" traces, whereas these parameters change along the "elbow" ones. Therefore, if we consider a combined action of both JTs acting at the proximal and distal joints, we can assume that for the end-point transitions along the "shoulder," and "elbow" traces this action possesses isotropic and anisotropic properties, respectively. The model also determines the patterns of the torques of coinciding and opposing directions (TCD, TOD), which would evoke a simultaneous loading of the elbow and shoulder muscles with the coinciding or opposing function (flexors, extensors). For a complete force vector turn, the relationship between the TCD and TOD remains fixed in transitions at the "shoulder" end-point traces, whereas it is changing at the "elbow" ones.

The effects of C 60 FAS (50 and 500  μ g/kg) supplementation, in a normal physiological state and after restraint stress exposure, on prooxidant/antioxidant balance in rat tissues were explored and compared with the effects of the known exogenous antioxidant N-acetylcysteine. Oxidative stress biomarkers (ROS, O 2 · - , H 2 O 2 , and lipid peroxidation) and indices of antioxidant status (MnSOD, catalase, GPx, GST, γ -GCL, GR activities, and GSH level) were measured in the brain and the heart. In addition, protein expression of Nrf2 in the nuclear and cytosol fractions as well as the protein level of antiradical enzyme MnSOD and GSH-related enzymes γ -GCLC, GPx, and GSTP as downstream targets of Nrf2 was evaluated by western blot analysis. Under a stress condition, C 60 FAS attenuates ROS generation and O 2 · - and H 2 O 2 releases and thus decreases lipid peroxidation as well as increases rat tissue antioxidant capacity. We have shown that C 60 FAS supplementation has dose-dependent and tissue-specific effects. C 60 FAS strengthened the antiradical defense through the upregulation of MnSOD in brain cells and maintained MnSOD protein content at the control level in the myocardium. Moreover, C 60 FAS enhanced the GSH level and the activity/protein expression of GSH-related enzymes. Correlation of these changes with Nrf2 protein content suggests that under stress exposure, along with other mechanisms, the Nrf2/ARE-antioxidant pathway may be involved in regulation of glutathione homeostasis. In our study, in an in vivo model, when C 60 FAS (50 and 500  μ g/kg) was applied alone, no significant changes in Nrf2 protein expression as well as in activity/protein levels of MnSOD and GSH-related enzymes in both tissues types were observed. All these facts allow us to assume that in the in vivo model, C 60 FAS affects on the brain and heart endogenous antioxidative statuses only during the oxidative stress condition.

The aim of this study is to detect the effects of C 60 fullerenes, which possess pronounced antioxidant properties, in comparison with the actions of the known exogenous antioxidants N -acetylcysteine (NAC) and β-Alanine in terms of exercise tolerance and contractile property changes of the m. triceps surae ( TS ) during development of the muscle fatigue in rats. The electrical stimulation of the TS muscle during four 30 min series in control rats led to total reduction of the muscle contraction force. Furthermore, the effects of prior intraperitoneal (i.p.) or oral C 60 FAS application and preliminary i.p. injection of NAC or β-Alanine on muscle contraction force under fatigue development conditions is studied. In contrast to control rats, animals with C 60 FAS, NAC, or β-Alanine administration could maintain a constant level of muscle effort over five stimulation series. The accumulation of secondary products and changes in antioxidant levels in the muscle tissues were also determined after the fatigue tests. The increased levels of lactic acid, thiobarbituric acid reactive substances and H 2 O 2 after stimulation were statistically significant with respect to intact muscles. In the working muscle, there was a significant ( p < 0.05) increase in the activity of endogenous antioxidants: reduced glutathione, catalase, glutathione peroxidase, and superoxide dismutase. Treated animal groups showed a decrease in endogenous antioxidant activity relative to the fatigue-induced animals ( P < 0.05). Oral C 60 FAS administration clearly demonstrated an action on skeletal muscle fatigue development similar to the effects of i.p. injections of the exogenous antioxidants NAC or β-Alanine. This creates opportunities to oral use of C 60 FAS as a potential therapeutic agent. Due to the membranotropic activity of C 60 fullerenes, non-toxic C 60 FAS has a more pronounced effect on the prooxidant-antioxidant homeostasis of muscle tissues in rats.

We investigated neuronal activation of the rat intermediolateral (IML) nucleus of the thoracolumbar spinal cord, initiated by Achilles tendon vibration, after intramuscular (m. triceps surae) administration of 7‑nitroindazole (7‑NI) or L‑arginine (LA). The spindle afferent response to vibratory stimuli induced a distinct bilateral increase in the activation of c‑Fos immunoreactivity in the spinal neurons in three groups of rats (tendon‑vibrated, tendon‑vibrated + 7‑NI and tendon‑vibrated + LA). The T5/T13 segments in tendon‑vibrated +7‑NI animals showed the highest increase of Fos‑immunoreactive neurons. This increase was two times higher than that in tendon only‑vibrated control rats and endon‑vibrated + LA animals. The highest mean number of labelled neurons were observed in the IML nucleus and in layers 4 and 7 of the T5-L3 segments in tendon‑vibrated and tendon‑vibrated + 7‑NI animals, and in the IML nucleus and layer 4 in tendon‑vibrated + LA rats. The highest mean number of activated neurons was found ipsilaterally in the IML nucleus of the T5/T13 segment. These results indicate that decreased nitric oxide release after injection of 7‑NI was accompanied by a potentiation of the early c‑fos gene expression induced by muscle proprioceptive activity within the thoracolumbar region of the rat spinal cord. Thus, enhanced c‑Fos immunoreactivity in the IML nucleus indicated that the sympathetic nervous system can exert a direct influence on the muscle spindles.

Luminescent spectroscopy combined with the technique of luminescent probing with rare earth ions (europium, gadolinium, terbium) and an actinide ion (uranyl) was used to differentiate enantiopure and racemic alanine, the simplest chiral proteinogenic amino acid. Using the achiral luminescent probes, small differences between pure L and DL alanine in the solid state were strongly amplified. Based on the observed electronic transitions of the probes, the position of the triplet level of the coordinated alanine was estimated. Formation of homo- and heterochiral complexes between enantiomers of alanine and the metal ions is discussed as a possible mechanism of chiral self-discrimination., (© 2017 Wiley Periodicals, Inc.)

Background: Bioactive soluble carbon nanostructures, such as the C 60 fullerene can bond with up to six electrons, thus serving by a powerful scavenger of reactive oxygen species similarly to many natural antioxidants, widely used to decrease the muscle fatigue effects. The aim of the study is to define action of the pristine C 60 fullerene aqueous colloid solution (C 60 FAS), on the post-fatigue recovering of m. triceps surae in anaesthetized rats., Results: During fatigue development, we observed decrease in the muscle effort level before C 60 FAS administration. After the application of C 60 FAS, a slower effort decrease, followed by the prolonged retention of a certain level, was recorded. An analysis of the metabolic process changes accompanying muscle fatigue showed an increase in the oxidative stress markers H 2 O 2 (hydrogen peroxide) and TBARS (thiobarbituric acid reactive substances) in relation to the intact muscles. After C 60 FAS administration, the TBARS content and H 2 O 2 level were decreased. The endogenous antioxidant system demonstrated a similar effect because the GSH (reduced glutathione) in the muscles and the CAT (catalase) enzyme activity were increased during fatigue., Conclusions: C 60 FAS leads to reduction in the recovery time of the muscle contraction force and to increase in the time of active muscle functioning before appearance of steady fatigue effects. Therefore, it is possible that C 60 FAS affects the prooxidant-antioxidant muscle tissue homeostasis, subsequently increasing muscle endurance.

Slow circular movements of the hand with a fixed wrist joint that were produced in a horizontal plane under visual guidance during conditions of action of the elastic load directed tangentially to the movement trajectory were studied. The positional dependencies of the averaged surface EMGs in the muscles of the elbow and shoulder joints were compared for four possible combinations in the directions of load and movements. The EMG intensities were largely correlated with the waves of the force moment computed for a corresponding joint in the framework of a simple geometrical model of the system: arm - experimental setup. At the same time, in some cases the averaged EMGs exit from the segments of the trajectory restricted by the force moment singular points (FMSPs), in which the moments exhibited altered signs. The EMG activities display clear differences for the eccentric and concentric zones of contraction that are separated by the joint angle singular points (JASPs), which present extreme at the joint angle traces. We assumed that the modeled patterns of FMSPs and JASPs may be applied for an analysis of the synergic interaction between the motor commands arriving at different muscles in arbitrary two-joint movements.

The main purpose was to analyze quantitatively the the average surface EMGs of the muscles that function around the elbow and shoulder joints of both arms in bimanual "rowing" movements, which were produced under identical elastic loads applied to the levers ("oars"). The muscles of PM group ("pulling" muscles: elbow flexors, shoulder extensors) generated noticeable velocity-dependent dynamic EMG components during the pulling and returning phases of movement and supported a steady-state activity during the hold phase. The muscles of RM group ("returning" muscles: elbow extensors, shoulder flexors) co-contracted with PM group during the movement phases and decreased activity during the hold phase. The dynamic components of the EMGs strongly depended on the velocity factor in both muscle groups, whereas the side and load factors and combinations of various factors acted only in PM group. Various subjects demonstrated diverse patterns of activity redistribution among muscles. We assume that central commands to the same muscles in two arms may be essentially different during execution of similar movement programs. Extent of the diversity in the EMG patterns of such muscles may reflect the subject's skilling in motor performance; on the other hand, the diversity can be connected with redistribution of activity between synergic muscles, thus providing a mechanism directed against development of the muscle fatigue.

The features of the formation of targeted tonic isometric effort created by muscles of the shoulder girdle and shoulder were compared for two opposite changes of the directions of arbitrary force vector-clockwise and counterclockwise. The magnitude of the effort vector remained constant. The intensity of the central motor commands (CMC) was evaluated according to the area of founded rectified, averaged and approximated electromyographic (EMG) recorded from the investigated muscles. The effort development was carried out in determined direction in operation space of the horizontal plane under angles of 75 degrees in the shoulder joint and 90 degrees in the elbow one. The synergic interaction of individual functional groups of muscles under certain reaction force was found. In the case of space, it was determined the main activity areas of the investigated muscles within the operating space. The differences were shown in the levels of EMG amplitude in opposite directions bypass of effort vector. Coactivation of flexor muscles was found, while the extensors showed their activity only within their functional sectors. Half of the investigated muscles showed an increase of the EMG amplitude for the counter-clockwise direction in relation to EMG amplitude for the clockwise direction. This can be attributed to more complex patterns of motor commands organization which consistently addressed to the muscles of the shoulder and forearm caused by atypical sequence of activation of antagonist muscles under making hand movements in cyclic mode during tonic isometric contraction.

The effects of dynorphin B (an agonist of κ-opioid receptors) and naloxone (an antagonist of opioid receptors) on the field potentials (FPs) evoked in the lumbar spinal cord of spinalized cats were examined following successive stimulation of pairs of identical peripheral nerves on both sides of the body. The FPs were recorded bilaterally using microelectrodes from symmetrical sites of the gray matter between the L6 and L7 segments of the spinal cord transected at level of Th11. Significant changes (up to 75%) were registered in the areas of the initial positive components of the FPs evoked by sequential stimulation of the nn. gastrocnemius-soleus, flexor digitorum longus, and tibialis at both hind limbs; a difference between the effects of various nerves was not observed. Two-Way ANOVA analysis showed that two factors, the injection type and recording side, as well as a combination of these factors, strongly influenced the amplitudes of the FPs. Statistically significant side- and injection-dependent differences were registered in the majority of the tests. Both the directions of the changes in the FPs and their relative amplitudes were not strongly connected with a definite side of the spinal cord in different animals. Therefore, it is possible to postulate that the κ-opioid receptors are distributed inhomogeneously over the neuronal populations transmitting the peripheral afferent signals from different hind limbs, thus indicating a possible presence of the lateral asymmetry effects.

The experiments presented here and performed in anaesthetized cats aimed at studying the dynamics of interactions between antagonist muscle groups. The tendons of triceps surae muscles of both hindlimbs were connected with an artificial joint (a pulley installed on a shaft). The muscles were activated by the distributed stimulation of five filaments of cut ventral roots L7-S1 on both sides of the spinal cord; movements were evoked by the rate-modulation of the stimulation trains. The study mostly compared programs of reciprocal activation and co-activation, including different changes in stimulation rates of muscle antagonists. The most common feature of the movements in both activation modes was hysteresis of the joint angle changes in dependence on stimulus rate. Reciprocal activation appeared suitable for a precise regulation of both amplitude and velocity of the movements in direction of the agonist shortening; maximal effectiveness was achieved during full switching off the antagonist stimulation at plateaus of the movement traces. The reverse movements during decrease of the agonist's stimulation rate demonstrated an explicit nonlinear form with pronounced initial phase of the joint angle fixation. The co-activation pattern distinctly reduced the hysteresis of joint movements and suppressed the stimulation after-effects, such as the lasting residual movements after fixation of the stimulation rates.

Introduction: Expression of c-fos initiated by muscle proprioceptive signaling was studied in rats after inhibition of neuronal nitric oxide synthase (nNOS) with administration of 7-nitroindazole (7-NI)., Methods: Fos-immunoreactive (Fos-ir) neurons were visualized immunohistochemically in the lumbar cord after vibration of the Achilles tendon and/or 7-NI systemic injections., Results: The total number of Fos-ir interneurons and motoneurons (per slice) was significantly greater in the 7-NI-pretreated and tendon-vibrated (7-NI + Tv) group than in the isolated tendon vibration group (Tv group). The greatest increases in the number of Fos-ir neurons were found in the L4 (+100%) and L5 (+105%) segments (P < 0.05)., Conclusions: Suppression of NO release after introduction of 7-NI was associated with potentiation of Fos immunoreactivity induced by muscle proprioceptive signaling within distinctive regions of the spinal cord., (Copyright © 2012 Wiley Periodicals, Inc.)

The aim of the study was to define the spike threshold changes in motoneurons during naturally evoked activation. Spike activity was evoked in the gastrocnemius-soleus motoneurons of decerebrate cats by controlled stretches of the homonymous muscles. The spike thresholds were defined by using the first derivative of the membrane potential and statistical boundaries of its change. The evoked firing was analyzed in terms of the spike thresholds and the membrane potential trajectories between spikes, which were dependent on the intensity of the firing. The main inference of the study is the absence of a single-valued dependence between the spike rates and thresholds; the last ones can both increase and decrease with a rise in the firing rate; moreover, opposite directions in the threshold changes are often observed at various phases of the stretch-evoked firing. The dependency of the spike thresholds on firing rates was checked in 42 of the total set of 57 motoneurons. In a group of cells (n = 27) showing statistically significant correlation (P < 0.05), this parameter was negative in 18 and positive in 9 motoneurons. The obtained results indicate that the threshold-crossing models with a single-valued dependency of the spike thresholds on the firing rates are not completely suitable to analyze the spike generation processes in the motor unit records.

Responses of gastrocnemius-soleus motoneurones to stretches of the homonymous muscles were recorded intrasomatically in decerebrate cats; changes of membrane potential (MP) were evoked by smoothed trapezoid stretches of the muscles. Amplitudes of separate excitatory postsynaptic potentials (EPSPs) were defined via differences between values of MP at the end and beginning of the positive derivative waves, which were also used as basic elements in the model of the excitatory postsynaptic currents (EPSCs). EPSCs were assumed to be transformed into EPSPs by low-pass filtering properties of the somatic membrane; parameters of the filtering were firstly defined from analysis of Ia EPSP in the same cell and then were applied in model P ( m0). The model showed unsatisfactory quality in tracking slow components of MP; to overcome the disadvantage there was proposed model P ( m1) based on addition to P ( m0) the difference between two low-pass filtered signals MP and P ( m0) (the cutoff frequency 10 or 20 Hz). An overestimation of EPSPs' amplitudes was corrected in model P ( m2). The mismatch in tracking slow changes of MP was assumed to be connected with summation of a great number of low-amplitude EPSPs generated at distal dendrites; information about waveform of separate EPSPs could disappear in this process. One can speculate that slow components of membrane depolarization at least partly are linked with the persistent inward currents in dendrites; variable and, sometimes, too fast decays in EPSPs seem to reflect inhibitory synaptic influences.

The aim of this research was to study the changes of the motor reflex activity (monosynaptic reflex (MSR) of the flexor and extensor muscles) and Fos immunoreactivity in lumbo-sacral spinal cord after acute induced myositis of m. gastrocnemius-soleus (GS). The experiments were carried out on ischaemic decerebrated, spinalized in C1 cats. After infiltration of the GS muscle with carrageenan (2%) MSRs of flexors and extensors showed a significant increase in amplitude +127+/-24.5% and +155+/-28.5%, respectively, p<0.05. The exposed effect was initiated within 30 min and achieved a maximum 2.8h after the intramuscular injections of carrageenan. After analysis of dynamics of the MSRs, animals were perfused and c-fos expression in the spinal segments L6-S1 was evaluated. In comparison to sham-operated animals, the number of Fos-immunoreactive (Fos-ir) cells was noticeably increased in the lumbar cord of cats with carrageenan-induced myositis. The labeled cells were concentrated in the ipsilateral laminae I/II, neck of the dorsal horn (V/VI) and intermediate zone (VII), however, clear predominance of their concentration was found in the deep laminae. The effect of muscle inflammation was also expressed as a significant decline in the number of NADPH-d-reactive cells (p<0.05) in ipsilateral laminae I/II of L6/L7. The results show that the input from acutely inflamed muscles may induce an increase of the reflex responsiveness of flexors and extensors which is not mediated via the gamma-spindle-loop and which coincides with a significant increase in c-fos expression in the deep laminae of the lumbar spinal cord.

c-fos gene expression in the cervical spinal cord and amygdala was examined in anaesthetized rats following muscle fatigue caused by intermittent high-rate (100 s(-1)) electrical stimulation of the dorsal neck muscles (m. trapezius and m. splenius). Fatigue-related increases in c-fos expression were observed on the stimulated muscle side in the cervical C2-C4 (layers 1, 3-5, 7 and 10) spinal segments, bilaterally in the lumbar L4-L6 (layer 1) segments and in contralateral central (Ce), medial (Me), and basomedial (BM) amygdaloid nuclei. A scarce number of staining cells were found within lateral and basolateral nuclei. The rostro-caudal extent of c-fos expression in the spinal cord supports functional coupling of the cervical and lumbar regions during the neck muscle fatigue development. The distinct c-fos expression in the Ce and Me amygdaloid nuclei suggests that they may contribute to mediating the neck muscle fatigue-related nociception, autonomic and behavioural responses.

Healthy adult humans performed elbow movements in a horizontal plane under a small external extending torque (2.1-3.3 Nm). Test movements (TMs) consisted of slow ramp-and-hold flexions in the absence of visual feedback, with the target joint angle to be remembered from a preceding conditioning movement (CM). The CM was produced by matching two beams on the monitor screen: (1) command representing the target position (a straight line); and (2) a signal from the sensor of the elbow joint angle. Two kinds of CM were applied, which had the same target position (50 degrees in most experiments) but differed in initial positions: (1) fully extended joint (0 degrees, P1 CMs); (2) flexed joint (100 degrees, P2 CMs). In a group of 25 subjects, the target in TMs was usually overshot, with the position errors depending on the CMs: 2.7 +/- 0.6 degree (mean +/- SEM) for P1 CMs, and 10.9 +/- 0.7 degree (P < 0.001) for P2 CMs. Vibration of the elbow flexors substantially diminished the difference between the position errors, amounting to--0.31 +/- 0.5 degree and 2.33 +/- 0.6 degrees, respectively. It is suggested that the observed position errors resulted from after-effects in the activity of muscle spindles in agonist and antagonist muscles, but influence of differences in dynamic components of the afferent signals during oppositely directed approaches to the target cannot be excluded.

The distribution of c-fos expression and NADPH-diaphorase reactivity in the cervical and lumbar segments after stimulation of the vanilloid receptors in the dorsal neck muscles with capsaicin was studied in cats anaesthetized with alpha-chloralose. After the unilateral intramuscular injection of capsaicin, the mean number of Fos-immunoreactive neurons detected with an avidin-biotin-peroxidase technique was significantly increased in the superficial laminae (I), neck of the dorsal horn (V), and area around the central canal (VII) within both the cervical and lumbar spinal cord. Most Fos-immunoreactive neurons in the cervical spinal cord were giant and small cells. The widespread distribution of Fos-immunoreactive cells throughout the cervical cord within the intermediate zone (VII) coincided with the sites of localization of last-order premotor interneurons and cells of origin of inter-segmental crossed and uncrossed descending propriospinal pathways to the lumbar spinal cord. Fos-immunoreactive neurons were co-distributed with nitric oxide-generating cells at both levels of the spinal cord, although the double-labeled cells were not observed. In conclusion, the analysis of c-fos expression and NADPH-diaphorase reactivity shows that stimulation of vanilloid receptors in the neck muscles can initiate distinctive neuronal plasticity in the cervical (C1-C8) and lumbar (L1-L7) segments, and confirms the anatomical and functional coupling of both regions during processing of nociceptive signals from the dorsal neck muscles.

Responses of gastrocnemius-soleus (G-S) motoneurones to stretches of the homonymous muscles were recorded intracellularly in decerebrate cats before, during and after fatiguing stimulation (FST) of G-S muscles. Ventral roots (VR) L7 and S1 were cut, and FST was applied to VR S1, a single FST session including 4 to 5 repetitions of 12-s periods of regular 40 s(-1) stimulation. Muscle stretches consisted of several phases of slow sinusoidal shortening-lengthening cycles and intermediate constant lengths. The maximal stretch of the muscles was 8.8 mm above the rest length. Effects of FST on excitatory postsynaptic potentials (EPSPs) and spikes evoked by the muscle stretches were studied in 12 motoneurones from ten experiments. Stretch-evoked EPSPs and firing were predominantly suppressed after FST, with the exception of a post-contraction increase of the first EPSP after FST, which was most likely due to after-effects in the activity of muscle spindle afferents. The post-fatigue suppression of EPSPs and spike activity was followed by restoration within 60-100 s. Additional bouts of FST augmented the intensity of post-fatigue suppression of EPSPs, with the spike activity sometimes disappearing completely. FST itself elicited EPSPs at latencies suggesting activation of muscle spindle group Ia afferents via stimulation of beta-fibres. The suppression of the stretch-evoked responses most likely resulted from fatigue-evoked activity of group III and IV muscle afferents. Presynaptic inhibition could be one of the mechanisms involved, but homosynaptic depression in the FST-activated group Ia afferents may also have contributed.

In the present study, c-fos expression in the spinal cord has been used as a marker of neuronal activation induced by capsaicin-sensitive sensory afferents from the dorsal neck muscles in cats (n = 6). The number of Fos-immunoreactive neurons, which were revealed using the avidin-biotin-peroxidase method, was significantly increased in the cervical and lumbar spinal cord. In contrast to the control group (n = 3), 2 h after intramuscular capsaicin injection, c-fos expression was more extensive ipsilaterally to the injected side in the C3-C6 segments, and bilaterally in the L4-L6 segments. Most labeled neurons in the cervical spinal cord were small and giant cells, predominantly located in the middle and lateral parts of lamina I and, additionally, at the neck of the dorsal horn (lamina V), i.e., within the zones of termination of high-threshold muscle afferents. The widespread distribution of labeled cells throughout the cervical cord within the intermediate zone (lamina VII) coincided with the sites of last-order premotor interneurons and cells of origin of long crossed and uncrossed descending propriospinal pathways to the lumbar spinal cord. These findings suggest possible mechanisms for spreading of nociceptive signals between cervical and lumbar regions., (Copyright 2004 Elsevier Ireland Ltd.)

In decerebrate cats, changes in the monosynaptic reflex (MSR) of gastrocnemius-soleus (G-S) motoneurones were studied after fatiguing stimulation (FST) of the G-S muscles. Monosynaptic reflexes were evoked by stimulation of Ia fibres in the G-S nerve and recorded from a filament of ventral root (VR) L7. FST (intermittent 40 s(-1) stimulation for 10-12 min) was applied to the distal part of the cut VR S1. FST reduced MSR amplitudes to 0.64 +/- 0.04 (mean +/-s.e.m.) of the prefatigue values. The suppression remained stable for approximately 25 min and then MSR amplitudes gradually returned towards the normal. To test for the involvement of presynaptic and recurrent inhibition, MSRs were conditioned by stimulation of the nerve to the posterior biceps and semitendinosus (PBSt) muscles or a filament of VR L7, respectively. The intensity of presynaptic inhibition (reduction of the normalized value of MSR amplitude during conditioning) increased from 0.19 +/- 0.02 in prefatigue to 0.44 +/- 0.04 within a 5.3-18.2 min interval after FST, followed by a recovery. In contrast, the intensity of recurrent inhibition first diminished from 0.23 +/- 0.02 in prefatigue to 0.15 +/- 0.01 within 15.6-30.1 min after FST and then gradually recovered. Both primary afferent depolarization and the intensity of antidromic discharges in primary afferents increased with the presynaptic inhibition intensity. These results demonstrate a fatigue-related suppression of Ia excitation of synergistic motoneurones, probably arising from the activation of group III and IV afferents. The effects could in part be due to increased presynaptic inhibition, while recurrent inhibition plays a minor role.

The aim of the study was to characterize the species-related differences in the distribution of nitric oxide synthase (NOS)-containing neurons in rodents and carnivores medullary cardiovascular centers that take part in regulation of the sympathetic or parasympathetic drives. The order of the mean number of NOS-containing neurons in the dorsomedial and ventrolateral medulla (per section) in different animals was as follows: dog>cat>rat. Although the density of the positive cells in the both regions was changed in the following sequence: rat=cat>dog. Within the dorsal motor nucleus of vagus significant exceeding of the mean number and density of positive cells (preganglionic vagal neurons) in dog were found. Differences in the distribution of NO-generating neurons in the medullary cardiovascular centers and the heterogeneity in the basal level of NO release may contribute to the distinctive alterations of the hemodynamic reactions in the studied species after administration of NOS inhibitors.

In anaesthetised rats, Fos-immunoreactive and NADPH-diaphorase-positive neurons in the medulla and, for comparison, in the spinal cord were studied after fatiguing stimulation of the hindlimb muscles. Following both direct muscle stimulation and L5 ventral root stimulation, fatigue-related c-fos gene expression was most prominent in the dorsal horn of the ipsilateral L2-L5 segments and within the ipsilateral nucleus tractus solitarius, the caudoventrolateral and rostroventrolateral reticular nuclei, and the intermediate reticular nucleus at levels of -14.3 and -13.8 mm, and contralaterally at -13.2 mm caudal to the bregma. The order of intensity of c-fos expression was as follows: nucleus tractus solitarius>caudoventrolateral and rostroventrolateral reticular nuclei>intermediate reticular nucleus>lateral paragigantocellular nucleus. NADPH-diaphorase reactivity was changed in the following sequence: NTS>intermediate reticular nucleus lateral paragigantocellular nucleus>rostroventrolateral reticular nucleus. Fos-immunoreactive neurons were codistributed with NADPH-diaphorase-reactive cells within the dorsomedial and ventrolateral medulla, and double-staining neurons were found in the nucleus tractus solitarius, intermediate reticular nucleus and lateral paragigantocellular nucleus. The patterns of distribution of c-fos expression and NADPH-diaphorase reactivity show that afferent signals arising from fatiguing muscles may activate spinal and medullary neurons which are involved in nociceptive and cardiovascular reflex pathways. The functional role of nitric oxide (NO) in the generation of cardiovascular and somatosensory responses in the medulla during fatigue of skeletal muscles is discussed.

In the medial gastrocnemius muscle of the decerebrate cat, the spatial spread of fatigue between active and inactive muscle parts was studied. Conditioning fatiguing stimulation (CFS) was applied to a part of the muscle to test whether it had an effect on the contraction efficiency in an unstimulated part. To exclude somato-sympathetic reflexes during CFS, a full rhizotomy of the lumbo-sacral spinal cord was performed. The same ipsilateral ventral root, either L7 or S1, was divided into seven filaments, one of which was used for the test stimulation, and four or five for CFS. The CFS consisted of 12 s sessions of distributed stimulation of five (or four) filaments at a rate of 40 s(-1), the sessions were repeated, every 40 s, 15 or more times. The test consisted of 12 s of regular stimulation at a rate of 10 s(-1), preceded and followed by a single stimulus. The tests applied just after CFS showed a strong decline of both tension and electromyogram (EMG), amounting to only [mean (SD)] 0.45 (0.18) and 0.51 (0.19) (n = 15), respectively, of the corresponding values in the tests before CFS. It thus turned out that depressive fatigue-related effects could spread within the muscle. At the same time, control reactions recorded in the lateral gastrocnemius during stimulation of its cut nerve did not change. Subsequent repetitions of the tests usually revealed a tendency towards restoration. The EMG reactions recovered more quickly than tension. The depression of EMG after CFS was accompanied by a slowing of the constituent M-waves; their latencies decreased during restoration. Distinct changes in the systemic blood pressure were observed during CFS. These changes were usually correlated well with muscle tension changes. The factors possibly underlying the observed effects may include diffusion of metabolites from active to inactive muscle fibres, lowering of the efficiency of neuro-muscular transmission due to squeezing of efferent motor terminals and changes in outer metabolite content, as well as local hypoxia due to increases in intramuscular pressure.

The distribution of Fos-immunoreactive (Fos-ir) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d)-reactive neurons in the rat lumbar spinal cord was examined following muscle fatigue caused by intermittent high-rate (100 s(-1)) electrical stimulation of the triceps surae muscle or the ventral root L5 (VRL5) for 30 min. Following both types of stimulation, the fatigue-related c-fos gene expression was more extensive in the L2-L5 segments on the stimulated side, and the majority of Fos-ir neurons were concentrated in the dorsal horn. After direct muscle stimulation, the highest number of Fos-ir neurons were detected in two regions: layer 5, and superficial layers (1 and 2(o)), although many labeled cells were also found in layers 3, 4, 6, and 7. In response to VRL5 stimulation, the maximal density of Fos-ir neurons was detected in the middle and lateral parts of layers 1 and 2(o), the zone of termination of high-threshold muscle afferents(.) Statistically significant prevalence of Fos-ir cell number was also found in layers 5 and 7 on the stimulated side. A few Fos-ir neurons were detected in the ventral horn (layer 8 and area 10) on both sides. The lamellar distribution of NADPH-d-reactive neurons was similar over all experimental groups of animals. In the L3-L6 segments, such reactive cells were arranged in two distinct regions: dorsal horn (layers 2(i), 3, and 5) and area 10; in the L1 and L2 segments, an additional cluster of NADPH-d positive cells was found in the intermediolateral cell column (IML). Double-labeled cells were not detected. We suggest that c-fos expression in response to muscle fatigue reveals activity of functionally different types of spinal neurons which could operate together with NOS-containing cells in pre-motoneuronal networks to modulate the motoneuron output.

Changes in the compound muscle action potentials of cat gastrocnemius muscle were studied during low- and high-frequency fatigue. Fatiguing session consisted of 25-28 repetitions of the standard single fatigue tests (1.5min interval between the tests) that included the part of continuous frequency-modulated stimulation preceded and followed by single stimuli evoking twitch contractions in the muscle. The rate of the continuous part was changed in accordance with symmetrical double-trapezoidal signal, including three successive phases of constant rate at 10, 40 and 10s(-1); between these phases of 4s duration the rate changed linearly within a 2s interval. During fatigue relative changes in compound muscle action potential waves were usually smaller than changes in tension. Within the same fatigue procedure applied to a fresh muscle, the drop in tension was as much as 35% for high-rate stimulation and 59-71% for low-rate stimulation, whereas the decrease of the peak-to-peak compound muscle action potential waves amplitudes did not exceed 10-20%. Compound muscle action potential waves underwent the most pronounced depression during high-rate stimulation, the decrease proceeding during the following phase of low-rate stimulation. The tension changes during long-lasting activation were different for low- and high-frequency fatigue, with more pronounced depression during low-rate stimulation. As a rule, compound muscle action potential waves changes followed opposite patterns. Compound muscle action potential waves progressively split up, which was probably associated with a continuous slowing of the action potentials in the most fatigable motor units and the subsequent disappearance of the reactions at least in part of the motor units. Hysteresis effects in muscle contraction seem to be able, at least in part, to compensate for some of the depressive effects appearing during conduction of action potentials in muscle fibres. Changes in the compound muscle action potentials were studied during development of the muscle fatigue. These changes showed pronounced dependency on stimulation rate allowing differentiating effects of low- and high-frequency stimulation of the efferents supplying muscle under study. At the same time the fatigue-related changes in the action potentials were noticeably smaller than changes in tension, thus supporting existing concepts in the field arguing that fatigue effects are mainly connected with corresponding activity-dependent changes in muscle contraction machinery.

Effects of low- and high-frequency fatigue were studied on muscle dynamics in isometric conditions of the cat gastrocnemius. Fatiguing sessions consisted of 25-28 repetitions of the standard tests that included an 18-s interval of continuous frequency-modulated stimulation preceded and followed by single stimuli evoking twitch contractions. The rate of the continuous part was changed in accordance with a symmetrical double-trapezoidal signal, including three successive phases of constant rate at 10, 40 and 10s(-1); between these phases, each lasting for 4s, the rate changed linearly within a 2-s interval. The following modes of muscle activation were applied: (i) stimulation of single filaments constituting approximately one-fifth to one-seventh of the total cross-section of the L(7) and S(1) ventral roots; (ii) the distributed stimulation of five similar filaments; and (iii) direct stimulation of muscle through bipolar wire electrodes. A relative drop in tension, the fatigue index, expressed as the ratio at the end of a fatigue session over its value at the beginning of the test, was used to quantify fatigue effects. The fatigue indices during low-rate stimulation were 0.56+/-0.03 (mean+/-S.D.) at the first phase and 0. 64+/-0.02 at the third phase, while during high-rate stimulation this parameter was only 0.32+/-0.02. The high-rate stimulation noticeably increased the mean tension during low-rate stimulation; the ratio between the reactions at the third and the first phases could be as much as two to three times greater than that at the beginning of the fatigue session. It was demonstrated that the potentiation was connected with after-effects of the rate-tension hysteresis. The hysteresis decreased with fatigue, the fatigue index for the rate-tension loop areas ranging from 0.39 to 0.52 (0.45+/-0. 05, mean+/-S.D.). The fatigue processes developed more quickly and intensively in the previously fatigued muscles: the obtained fatigue indices were 0.73+/-0.05 and 0.70+/-0.10 at the first and third phases, and 0.62+/-0.06 (mean+/-S.D.) at the second phase of stimulation, respectively. In the cases of distributed and direct stimulation applied to muscles in a fresh state, fatigue dynamics did not differ significantly from those observed during single-filament stimulation. In experiments with distributed stimulation applied to previously fatigued muscles, a powerful depression of the high-rate components was registered in several cases, which seemed to be connected with depressive effects at the level of nerve-muscle synaptic transmission. The effects of low- and high-frequency fatigue were studied in isometric conditions of muscle contraction. In addition to the well-known differentiation between low- and high-frequency fatigue effects, the complex pattern of efferent stimulation used allowed us to identify additional fatigue-related changes in the rate-tension hysteresis. This hysteresis seems to be one of the possible mechanisms directed to compensate for low-frequency fatigue in the muscle contraction.

Electromyograms were recorded by surface electrodes from the mm. biceps brachii (caput longum et breve), brachioradialis and triceps brachii (caput longum) in 10 healthy human subjects during slow linear movements in the elbow joint against a weak extending torque. The test movements were carried out under visual control through combining on a monitor screen a signal from a joint angle sensor with an appropriate command generated by a computer. The movements were fulfilled against a weak constant extending torque (0.5-2.5 Nm) and the extensor muscles were inactive. Surface electromyograms were full-wave rectified, filtered and averaged within sets of 10 identical tests. For the test movements in the range from 20 degrees to 100 degrees (0 degrees corresponds to a completely extended joint in these designations) the dynamic components of the efferent commands to actively contracted muscles frequently had a well-expressed monotonous increase. The electromyography intensity during movement quite often increased exponentially in all three investigated flexors. At the same time, the averaged electromyograms in one or two muscles could contain non-monotonous oscillations, thus showing a well-expressed decrease in the intensity of the efferent inflow within a middle range of a movement phase. The non-monotonous oscillations could occur in some subjects under minimal loads (0.5-0.75 Nm); they usually appeared initially only in one muscle, whereas the frequency of their occurrence was not high. The probability of finding the non-monotonous oscillations in the electromyograms from the muscles under study increased with heightening the extending load. Under the loads of 2.0-2.5 Nm this type of reaction could be found in almost half of all records (for the three muscles in each of the 10 subjects under testing). The presence of noticeable non-monotonous components in the electromyograms of the elbow flexors during their contraction is probably connected to their biomechanical arrangement within the joint. It is known that the arms of the forces generated by elbow flexors are maximal in the middle range of joint angles and decrease with a change in angle in both directions. Thus, we can suppose that non-monotonous decrement components in the electromyograms of the elbow flexors are presumably connected with an obvious necessity for a subject to decrease the excitatory efferent inflow to the muscles in the middle range of the joint angles. The pattern of electromyograms in the flexors acting around the joint was also dependent on a redistribution of activity between agonists. In the subjects showing stable non-monotonous components on the averaged electromyogram records in two agonists, a redistribution of the activity between these muscles has been demonstrated when phases of the electromyogram diminishing in one of them coincided with the appropriate increments in the other.

In this study we have tried to elaborate necessary theoretical approaches for the adequate analysis of the central motor commands to a mammalian muscle in the equilibrium states and during transition movements between these states. At present, the equilibrium point hypothesis has obtained a wide distribution in this field. The muscle is considered in the framework of the theory as an executive element of the reflex circuits originating in the muscle proprioceptors and being closed at the level of spinal cord and the supraspinal motor centres. The main parameter defining the muscle state is supposed to be the threshold of the stretch reflex--the minimal length value at which muscle begins to resist to the externally applied force. We have attempted to show that the theory has an essential shortcoming because it does not take into account such important non-linearity in the muscle behaviour as hysteresis. In the framework of the equilibrium point hypothesis, the muscle behaviour within the stretch reflex system does not depend on movement direction. The stretch and unloading reflexes are supposed to have the same length tension dependencies when the muscle is stretching or contracting with a rather slow velocity. However, powerful hysteresis of the stretch reflex system requires taking into account the direction of the current movement, the after-effects of previous movement led to a principal uncertainty in the muscle steady-state. We would like to stress that any process of active muscle shortening should be controlled by dynamic components in efferent inflow. At the same time, the resulting steady-state develops by using effective hysteresis mechanism for its maintenance. The following hypothesis was proposed to explain the length clamping mechanisms in shortening transition movements. A significant decrement of the arrived efferent activity at the phase of the length fixation can evoke an internal elongation of the contractile elements within the muscle and corresponding hysteresis-like enhancement of the contractile effectiveness. Hence, instead of considering the quasi-static and dynamic components of movement commands as in the equilibrium point hypothesis, it is preferable to adopt a model of the shared coding of both the final position and movement velocity. The dynamic component of the efferent discharge seems to be required for a complete definition of the final steady-state, but maintenance of the state is closely associated with energetically advantageous hysteresis mechanisms. It was concluded that the dynamic phase of efferent activity should play an extremely important role in the central coding of the real movements produced, in particular, by contraction of agonists in the absence of antagonist activation.

The length changes of the cat soleus muscle have been examined in isotony within closed cycles of the stimulation rate change. Successive stimuli were applied in a cycle to five filaments of the preliminary dissected L7-S1 ventral roots (method of distributed stimulation), maximal rate did not exceed 80-90/s (16-18/s per single filament). At the beginning of a slow linear increase in the rate a muscle began shortening rather quickly, the rate changes without muscle reaction consisted of 5.91 +/- 0.28/s (mean +/- S.E.M.). A substantially linear movement was observed during increase of the input rate up to 40-50/s (i.e. 8-10/s per filament), a further rate increment could evoke a somewhat slowing of the shortening velocity with a distinctive infection of the rate-length curve. During a significant part of the rate decrease phase no movement was seen, the rate range with the absence of muscle lengthening was 29.93 +/- 1.57/s. After such a pronounced period of length fixation, a muscle began to elongate, the steady-state velocity at this part of the movement trajectory was invariably higher as compared with shortening velocity at the leading edge of the cycle. The striking feature of a powerful length clamping seen in active muscle at the phase of rate decrease preceded by previous rate increment allows us to suppose that this strongly non-linear behaviour of muscle might be a main reason for the existence of powerful dynamic components in efferent activity every time when muscle should shorten against external load in a ramp-and-hold fashion. We used the following experimental paradigm to check the assumption. Stimulation began with regular rate of 15/s; then, after transition from isometry to isotony and cessation of movement transients, the rate was raised linearly; after reaching a peak value of 50-90/s, it decreased linearly or exponentially, being afterwards fixed at several different levels between the maximal and initial values of the rate. It was demonstrated that such pattern of stimulation could be effective for a linear transition between two equilibrium lengths, provided that corresponding parameters in modulation signal were chosen in an optimal way. Duration and amplitude of the leading edge of the dynamic component seemed to completely define amplitude and velocity of the ramp phase of movement, parameters of decay to the final steady rate were, on the other hand, important for efficacy of the length clamping at hold phase. It was concluded that hysteresis effects of muscle contraction seemed to be an extremely important nonlinear property of muscle dynamics in producing any transition movements between two steady-states. Thus, oversimplified muscle models, like the spring model based on the isometric length-tension dependencies, seem to be incorrect. Possible mechanisms for the muscle hysteresis and its role in motor control are discussed.

The electromyograms were recorded in healthy human subjects by surface electrodes from the mm. biceps brachii (caput longum et. brevis), brachioradialis, and triceps brachii (caput longum) during slow transition movements in elbow joint against a weak extending torque. The test movements (flexion transitions between two steady-states) were fulfilled under visual control through combining on a monitor screen a signal from a joint angle sensor with a corresponding command generated by a computer. Movement velocities ranged between 5 and 80 degrees/s, subjects were asked to move forearm without activation of elbow extensors. Surface electromyograms were full-wave rectified, filtered and averaged within sets of 10 identical tests. Amplitudes of dynamic and steady-state components of the electromyograms were determined in dependence on a final value of joint angle, slow and fast movements were compared. An exponential-like increase of dynamic component was observed in electromyograms recorded from m. biceps brachii, the component had been increased with movement velocity and with load increment. In many experiments a statistically significant decrease of static component could be noticed within middle range of joint angles (40-60 degrees) followed by a well expressed increment for larger movements. This pattern of the static component in electromyograms could vary in different experiments even in the same subjects. A steady discharge in m. brachioradialis at ramp phase has usually been recorded only under a notable load. Variable and quite often unpredictable character of the static components of the electromyograms recorded from elbow flexors in the transition movements makes it difficult to use the equilibrium point hypothesis to describe the central processes of movement. It has been assumed that during active muscle shortening the dynamic components in arriving efferent activity should play a predominant role. A simple scheme could be proposed for transition to a steady-state after shortening. Decrease of the efferent inflow can evoke internal lengthening of the contractile elements in muscle and, as a result, hysteresis increase in the muscle contraction efficiency. Effectiveness in maintenance of the steady position seems to also be enhanced due to muscle thixotropy and friction processes in the joint. Hysteresis after-effects in elbow flexors were demonstrated as a difference in steady-state levels of electromyograms with oppositely directed approaches to the same joint position.

The after-effects of the firing of the primary spindle endings were studied in ankle extensor muscles of cats under Nembutal anesthesia. The activities of 27 primary endings of the muscle spindles from mm. soleus, plantaris, and gastrocnemius have been analysed in various combinations of fusimotor and extrafusal stimulation and application of the mechanostimulation to the spindle bearing muscle. Short-term simulation of static gamma-axons evoked a post-stimulation increase in the spindle ending firing, which can be recorded under both isometric and isotonic conditions on applying a weak extrafusal stimulation or without it. The movement-dependent after-effects were tested with a double-trapezoid pattern of muscle length (or load) changes. The after-effects consisted of the difference of firing rates at the same values of muscle length (or load) with opposite direction of movement to the steady states; these uncertainties were also present during constant stimulation of static gamma-axons. The rate difference showed a tendency to a certain decrease with stimulation rate increment. For diapason of the stimulation rates up to 125 impulses/s a small negative correlation (r = -0.61) between the firing rate differences and the gamma-stimulation rate has been registered in the population of primary endings tested under length servo-control conditions. Using a frequency-modulated intrafusal stimulation, a clockwise hysteresis dependence of the spindle firing rate upon stimulation rate was demonstrated. The pronounced after-effects were shown to exist for steady rates of stimulation: the discharge rates were always higher after stimulation rate increase and lower after its decrease. Fusimotor after-effects were effectively destroyed by both the extrafusal stimulation and the cyclic length (load) changes evoked lengthening-shortening movements of the muscle. The results obtained can be considered as evidence for a hypothesis that history-dependent behavior of muscle spindles is mainly connected with hysteresis of the intrafusal muscle fibers and the whole spindle bearing muscle.

The muscle spindle reactions evoked by the servo-controlled changes in the muscle length or external load were studied on the de-efferented muscles in experiments on cats under Nembutal anaesthesia. The activity of 39 primary and 10 secondary endings of the muscle spindles from four hindlimb extensor muscles: soleus, plantaris, lateral and medial heads of gastrocnemius has been recorded during servo-controlled changes in muscle length (L-control) or external load (P-control). Slow linear reciprocating (triangular) signals and their modification with fixation of the controlled parameter at the same level at forward and reverse phases were used as commands for the muscle stretcher. The steady firing rates in primary and secondary endings during fixation of muscle length or external load were shown to be strongly dependent on the direction of previous changes in these parameters. The firing rates were always higher after preceding lengthening (loading) and lower after shortening (unloading). These rate uncertainties in the steady firing of spindle endings at the same level of controlled parameter could be as much as 15-20 p.p.s. The revealed dependence of the spindle ending firing on the past history of the muscle movement was denoted as movement-dependent after-effects. Two kinds of movement-dependent after-effects in the firing of the spindle endings can be observed: (1) the movement-dependent ones being studied in the present work, and (2) those connected with the conditioning fusimotor stimulation and described elsewhere. Their common origin is supposed to be connected with the hysterical (thixotropic) properties of the intrafusal muscle fibres. Similarity of the movement-dependent after-effects in L- and P-control conditions was shown to be connected with a resemblance of the length-firing rate [F(L)] and load-firing rate [F(P)] hysterical loops registered during reciprocating movements. Both kinds of loops were in a clock-wise direction, their comparison in normalized form showed that F(L) loops were always broader than F(P) ones. Isotonic and isometric uncertainty vectors were introduced to analyse quantitatively the hysterical effects in the spindle firing and their relation to the muscle hysteresis proper. Uncertainty vectors connect the points of equal load (isotonic uncertainty vectors) and equal length (isometric uncertainty vectors) on F(L) and F(P) loops correspondingly. The projections of both uncertainty vectors onto the Y-axis give the rate uncertainty coinciding in sign for both cases, whereas their projections onto the X-axis differ in sign, being positive for isometric uncertainty vectors (the tension uncertainty) and negative for isotonic uncertainty vectors (the length uncertainty).(ABSTRACT TRUNCATED AT 400 WORDS)

Flexion and extension movements were evoked in the elbow joint of unanesthetized cats by intracortical microstimulation (ICMS) applied to deep layers of the motor cortex (areas 4 and 6). Pulse trains with duration up to 3-4 s, current intensities of 15-50 microA and rates of approximately 100/s were used. Cortically evoked movements (CEMs) were tested mechanically by applying servo-controlled torque disturbances to the joint. The disturbances consisted of two reciprocating sinusoidal pulses of torque with fixed frequencies (1.2 or 3.2 Hz). A pronounced torque-angle hysteresis with long-lasting after-effects was revealed in the presence of the torque disturbances that opposed the CEMs and/or assisted them. Two parameters were introduced to describe the mechanical testing of the CEMs quantitatively: (1) the resulting stiffness (RS) defined during the forward and reverse phases of the disturbed movement as a ratio between the amplitudes of torque wave and the overall change of angle at these phases; (2) uncertainty index (UI) defined as the subtraction of forward and reverse angle changes, which was normalized by the first of these two values. RS was shown to be dependent on the immediate past movement history of the joint, it increased with changes in the direction of movement, and its magnitude during such changes could be several times higher than when the disturbance was in the same direction as the movement.(ABSTRACT TRUNCATED AT 250 WORDS)

A phenomenological theory of muscle dynamics has been elaborated on the basis of data obtained in experiments on hind limb extensor muscles of narcotized cat. Functional dependence of muscle length on external load was explored in conditions of a constant frequency of the efferent stimulation. It was shown that the system under study could be presented for a rather wide class of input signals as a system with nonlinear statics and linear dynamics. The nonlinear statics was shown to be determined mainly by the hysteretical effects of muscle contraction, whereas dynamic element was described by the first order linear differential equation corresponding to the traditional three-component mechanical model of the muscle. A hypothesis was proposed to explain the hysteresis in active muscle on the basis of functioning of the troponin-tropomyosin regulatory complex. Elaborated mathematical model of muscle dynamics can be used to predict and evaluate changes in the muscle length evoked by arbitrary changes in the external load.

Probability of neuronal spike initiation was considered within the framework of a simple stochastic model. The time of spike occurrence was defined as the first time of crossing of a stochastic process and a determined time function. This problem has been investigated in the case of a stationary Gaussian stochastic process and a linear time function. An integral equation obtained for the probability density function of the first time crossing was numerically solved by means of computer calculations. The model was applied to the analysis of temporal pattern of spike activity evoked in the cat spinal motoneurones by depolarizing current injected through the recording microelectrode.