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  • 1.
    Björklund, Martin
    et al.
    University of Gävle, Centre for Musculoskeletal Research.
    Radovanovic, Sasa
    Ljubisavljevic, Milos
    Windhorst, Uve
    Johansson, Håkan
    University of Gävle, Centre for Musculoskeletal Research.
    Effects of combined mechanical and nociceptive stimuli on nociceptive-responsive dorsal horn neurons of cat spinal cord2000Conference paper (Refereed)
    Abstract [en]

    The effects of large ramp and hold stretch of the gastrocnemius muscles were studied on dorsal horn nociceptive-responsive neurons (DHN) in decerebrated cats. The stretch consisted of 3 subsequent plateaus, ending with a release phase from a near maximal physiological length of the muscle. This was done in order to mimic the "therapeutical stretches" used in clinical settings to alleviate muscle tenderness and stiffness. Stretch was applied before and after i.a. injection of bradykinin (50 microg.) into the gastrocnemius muscles. Changes in DHN activity were extracellularly recorded with high impedance glass microelectrodes. Only neurons up to approximately 1 mm were recorded. Neurons were identified as nociceptive on the basis of their response to an identification procedure applied on beforehand. Responsiveness of the DHN to stretch was variable. If responsive, a typical behavior was an increased firing rate during the ramp phases, followed by a gradual decrease during the hold phases and a reduction in firing rate or a complete silence during and after the release phase, usually lasting up to 50 s. Bradykinin injections induced either excitation or inhibition of DHN.. Stretch applied directly after the bradykinin injection in most cases elicited changes in the bradykinin-induced response of the DHN, changing both response profile as well as its strength. Results indicate that nociceptive-responding DHN could be influenced by innocuous ramp and hold stretch both in conjunction with and without chemically induced activation. The behavior of the DHN to stretch in the presence of the painful stimuli may be one of the possible mechanisms that could explain the short term relieving effects of muscle stretching when applied on stiff and tender muscles.

  • 2.
    Korotkov, Alexander
    et al.
    University of Gävle, Belastningsskadecentrum.
    Radovanovic, Sasa
    University of Gävle, Belastningsskadecentrum.
    Ljubisavljevic, Milos
    University of Gävle, Belastningsskadecentrum.
    Lyskov, Eugene
    University of Gävle, Belastningsskadecentrum.
    Kataeva, Galina
    Roudas, Marina
    Pakhomov, Sergey
    Thunberg, Johan
    University of Gävle, Belastningsskadecentrum.
    Medvedev, Sviatoslav
    Johansson, Håkan
    University of Gävle, Belastningsskadecentrum.
    Comparison of brain activation after sustained non-fatiguing and fatiguing muscle contraction: a positron emission tomography study.2005In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 163, no 1, p. 65-74Article in journal (Refereed)
    Abstract [en]

    The concept of fatigue refers to a class of acute effects that can impair motor performance, and not to a single mechanism. A great deal is known about the peripheral mechanisms underlying the process of fatigue, but our knowledge of the roles of the central structures in that process is still very limited. During fatigue, it has been shown that peripheral apparatus is capable of generating adequate force while central structures become insufficient/sub-optimal in driving them. This is known as central fatigue, and it can vary between muscles and different tasks. Fatigue induced by submaximal isometric contraction may have a greater central component than fatigue induced by prolonged maximal efforts. We studied the changes in regional cerebral blood flow (rCBF) of brain structures after sustained isometric muscle contractions of different submaximal force levels and of different durations, and compared them with the conditions observed when the sustained muscle contraction becomes fatiguing. Changes in cortical activity, as indicated by changes in rCBF, were measured using positron emission tomography (PET). Twelve subjects were studied under four conditions: (1) rest condition; (2) contraction of the m. biceps brachii at 30% of MVC, sustained for 60 s; (3) contraction at 30% of MVC, sustained for 120 s, and; (4) contraction at 50% of MVC, sustained for 120 s. The level of rCBF in the activated cortical areas gradually increased with the level and duration of muscle contraction. The fatiguing condition was associated with predominantly contralateral activation of the primary motor (MI) and the primary and secondary somatosensory areas (SI and SII), the somatosensory association area (SAA), and the temporal areas AA and AI. The supplementary motor area (SMA) and the cingula were activated bilaterally. The results show increased cortical activation, confirming that increased effort aimed at maintaining force in muscle fatigue is associated with increased activation of cortical neurons. At the same time, the activation spread to several cortical areas and probably reflects changes in both excitatory and inhibitory cortical circuits. It is suggested that further studies aimed at controlling afferent input from the muscle during fatigue may allow a more precise examination of the roles of each particular region involved in the processing of muscle fatigue.

  • 3.
    Radovanovic, Sasa
    et al.
    University of Gävle, Belastningsskadecentrum.
    Dragasevic, N
    Maric, J
    Milanovic, S
    Ljubisavljevic, Milos
    University of Gävle, Belastningsskadecentrum.
    Kostic, V
    Disturbed cerebellar input affects consecutive movement performance: Comparison of healthy subjects and patients with cerebellar ataxia2005In: The 16th International Congress on Parkinson's Disease and Related Disorders, 2005, p. 245-Conference paper (Refereed)
    Abstract [en]

    Objective

    The cerebellum should be involved in providing temporal computations in motor production. The inability to compute time differences would affect time-related tasks. However, the cerebellar role in proprioception to control precise movement performance is still contradictory. The aim of the study was to investigate the characteristics of performance of the rapid terminal movements in patients with cerebellar ataxia. Ataxia of these patients had been identified as "pure" spinocerebellar ataxia.

    Method

    Movement performance was compared in six patients and six healthy subjects. Movements were performed from the initial to the target position, with the movement length of 40 degree in the elbow flexion. First, motor threshold of the motor cortex was determined. TMS was then applied with the double-cone coil right of the inion, in the two experimental conditions: stimulus was applied with the strength of 5% below the established motor threshold, at the moment of computer generated tone command to start the flexion movement, or stimulus was applied 20 ms before the GO signal, with the same strength. Two additional conditions were also tested: TM stimulus was applied with the strength of 30% above the motor threshold at the moment of movement start, and at 20 ms before movement start.

    Results

    Results point toward extension of the performed movement when stimulus was applied 20 ms before the movement start. Patients show tendency to lengthen their movements, and therefore accuracy of the movements deteriorate. Length of the movements was also prolonged in the conditions where stronger stimulus was applied, but accuracy was less affected with increase in the stimulus strength.

    Conclusion

    Accuracy of the movements was affected when the stimulus was applied in the phase of the movement preparation. Disturbance of the preparatory processes to establish correct movement pattern appear to be important even in the patients with pure cerebellar ataxia.

  • 4.
    Radovanovic, Sasa
    et al.
    University of Gävle, Centre for Musculoskeletal Research.
    Dragasevic, N T
    Maric, J
    Milanovic, S
    Ljubisavljevic, Milos
    University of Gävle, Centre for Musculoskeletal Research.
    Kostic, V S
    Effects of transcranial magnetic stimulation of the cerebellum on performance of consecutive rapid movements in patients with idiopathic sporadic cerebellar ataxia and healthy subjects2006In: The Movement Disorder Society’s 10th International Congress of Parkinson’s Disease and Movement: October 28 - November 2, Kyoto, Japan, 2006Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    It is known that cerebellum influences the action of the motor system. The cerebellum may exert a facilitatory influence in the motor cortex, and should be involved in temporal computations in movement performance. The inability to compute time differences would affect time-related tasks. However, the cerebellar role to control precise movement performance is contradictory. Furthermore, facilitatory effect of cerebellum might be decreased in cerebellar degeneration. The aim of the study was to investigate the performance of the rapid movements in patients with “pure” cerebellar ataxia.

    Movement performance was compared in 13 patients and 8 healthy subjects. Movements were performed from the initial to the target position, with the movement length of 40 deg in the elbow flexion. Motor threshold (MT) of the motor cortex was determined and TMS was then applied right of the inion, in two conditions: With the strength of 5% below the MT, at the moment of command to start the flexion movement, and with the same strength 20 ms before the movement start. Two additional conditions were also tested: TM stimulus was applied with the strength of 30% above the MT at the moment of movement start, and at 20 ms before movement start.

    Patients perform significantly longer movements then healthy subjects, and accuracy of the movements deteriorates. Length of the movements was also prolonged in the conditions where stronger stimulus was applied. Accuracy of the movements in patients was not different when the stimulus was applied in the phase of the movement preparation, compared in moment 0 and -20 ms. Same was true for healthy subjects in both conditions - stimulus below and above MT.

    Results that differences in disturbance timing and strength have no clear effects might speak for preprogrammed characteristics of rapid movements in both healthy subjects and ataxia patients, where sensory input is not of primary importance. Deficits in cerebellar ataxia for the movement length may be attributable to improper processing of motor command and/or sensory information.

  • 5.
    Thunberg, Johan
    et al.
    University of Gävle, Belastningsskadecentrum.
    Lyskov, Eugene
    University of Gävle, Belastningsskadecentrum.
    Korotkov, Alexander
    University of Gävle, Belastningsskadecentrum.
    Ljubisavljevic, Milos
    University of Gävle, Belastningsskadecentrum.
    Pakhomov, Sergey
    Katayeva, Galina
    Radovanovic, Sasa
    University of Gävle, Belastningsskadecentrum.
    Medvedev, Sviatoslav
    Johansson, Håkan
    University of Gävle, Belastningsskadecentrum.
    Brain processing of tonic muscle pain induced by infusion of hypertonic saline.2005In: European Journal of Pain, ISSN 1090-3801, E-ISSN 1532-2149, Vol. 9, no 2, p. 185-94Article in journal (Refereed)
    Abstract [en]

    Most of the previous studies on the effects of pain on Regional Cerebral Blood Flow (rCBF) had been done with brief cutaneous or intramuscular painful stimuli. The aim of the present study was to investigate the effect on rCBF of long lasting tonic experimental muscle pain. To this end we performed PET investigations ofrCBF following tonic experimentallow back pain induced by continuous intramuscular infusion ofhypertonic (5%) saline (HS) with computer controIled infusion pump into the right erector spinae on L3 level in 19 healthy volunteers. Changes in rCBF were measured with the use of 150 labelled water during four conditions: Baseline (before start of infusion), Early Pain (4 min after start of infusion), Late Pain (20 min after start of infusion) and Post Pain (> 15 min after stop of infusion) conditions.

    Results of S PM analysis showed relative rCBF increase in the right insula and bilateral decrease in the temporo-parieto-occipital cortex during initial phase of painful stimulation (Early Pain) followed by activation of the medial prefrontal region and bilateral inhibition ofinsula, anterior cingulat and dorso-lateral prefrontal cortex mainly in ipsilateral hemisphere during Late Pain conditions. The results show that longer lasting tonic experimental muscle pain elicited by i.m infusion ofHS results in decreases rather than increases in rCBF. Possible explanations for differences found in rCBF during tonic hypertonic saline-induced experimental muscle pain as compared with previous findings are discussed.

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