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  • 1.
    Bergenheim, Mikael
    et al.
    University of Gävle, Belastningsskadecentrum.
    Ribot-Ciscar, E
    Roll, J-P
    Thunberg, Johan
    University of Gävle, Belastningsskadecentrum.
    Spontaneous bursting neuronal discharges recorded from peripheral nerve in human: injury discharges or not?2004In: Neuroscience Letters, ISSN 0304-3940, E-ISSN 1872-7972, Vol. 359, no 1-2, p. 1-4Article in journal (Refereed)
    Abstract [en]

    This paper deals with a spontaneous, bursting neuronal activity which can not be altered by any stimulation in the periphery or voluntary actions or by cognitive tasks. An initial description of such units led to the conclusion that this activity was generated ectopically at the site of a previous or present impalement of a nerve fibre. The aim of the current study was to record a larger number of these units by using microneurography, in order to characterise their firing properties and particularly, see if any subtypes of units could be identified. In conclusion, this paper suggests that some of these discharges could be related to an injury of the nerve fibre, however most of them could not. Some hypothesis regarding the nature of these bursting activities are suggested.

  • 2.
    Hellström, Fredrik
    et al.
    University of Gävle, Belastningsskadecentrum.
    Roatta, S
    Thunberg, Johan
    University of Gävle, Belastningsskadecentrum.
    Passatore, Magda
    Djupsjöbacka, Mats
    University of Gävle, Belastningsskadecentrum.
    Responses of muscle spindles in feline dorsal neck muscles to electrical stimulation of the cervical sympathetic nerve.2005In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 165, no 3, p. 328-42Article in journal (Refereed)
    Abstract [en]

    Previous studies performed in jaw muscles of rabbits and rats have demonstrated that sympathetic outflow may affect the activity of muscle spindle afferents (MSAs). The resulting impairment of MSA information has been suggested to be involved in the genesis and spread of chronic muscle pain. The present study was designed to investigate sympathetic influences on muscle spindles in feline trapezius and splenius muscles (TrSp), as these muscles are commonly affected by chronic pain in humans. Experiments were carried out in cats anesthetized with alpha-chloralose. The effect of electrical stimulation (10 Hz for 90 s or 3 Hz for 5 min) of the peripheral stump of the cervical sympathetic nerve (CSN) was investigated on the discharge of TrSp MSAs (units classified as Ia-like and II-like) and on their responses to sinusoidal stretching of these muscles. In some of the experiments, the local microcirculation of the muscles was monitored by laser Doppler flowmetry. In total, 46 MSAs were recorded. Stimulation of the CSN at 10 Hz powerfully depressed the mean discharge rate of the majority of the tested MSAs (73%) and also affected the sensitivity of MSAs to sinusoidal changes of muscle length, which were evaluated in terms of amplitude and phase of the sinusoidal fitting of unitary activity. The amplitude was significantly reduced in Ia-like units and variably affected in II-like units, while in general the phase was affected little and not changed significantly in either group. The discharge of a smaller percentage of tested units was also modulated by 3-Hz CSN stimulation. Blockade of the neuromuscular junctions by pancuronium did not induce any changes in MSA responses to CSN stimulation, showing that these responses were not secondary to changes in extrafusal or fusimotor activity. Further data showed that the sympathetically induced modulation of MSA discharge was not secondary to the concomitant reduction of muscle blood flow induced by the stimulation. Hence, changes in sympathetic outflow can modulate the afferent signals from muscle spindles through an action exerted directly on the spindles, independent of changes in blood flow. It is suggested that such an action may be one of the mechanisms mediating the onset of chronic muscle pain in these muscles in humans.

  • 3.
    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.

  • 4.
    Lyskov, Eugene
    et al.
    University of Gävle, Belastningsskadecentrum.
    Kalezic, Nebojsa
    University of Gävle, Belastningsskadecentrum.
    Markov, Marko
    Mild, Kjell Hansson
    Thunberg, Johan
    University of Gävle, Belastningsskadecentrum.
    Johansson, Håkan
    University of Gävle, Belastningsskadecentrum.
    Low frequency therapeutic EMF differently influences experimental muscle pain in female and male subjects.2005In: Bioelectromagnetics, ISSN 0197-8462, E-ISSN 1521-186X, Vol. 26, no 4, p. 299-304Article in journal (Refereed)
    Abstract [en]

    Effects of a pulsating, half sine wave magnetic field (MF) with a frequency of 100 pps and 15 mT rms flux density, generated by the MD TEMF device (EMF Therapeutics, Inc., Chattanooga), on subjective pain rating, heart rate, and arterial blood pressure were tested in a double blind, crossover design study employing experimental muscle pain. Each of 24 healthy volunteers (12 females and 12 males, 24.7 +/- 3.2 years of age) received painful stimulation induced by the infusion of 5% hypertonic saline (HS) into the erector spinae muscle during real and sham MF exposure, in counterbalanced order. Exposure to MF differently affects subjective pain estimates in females and males. MF exposure increased averaged pain level and time integral of pain ratings in females, whereas no statistically significant difference for these characteristics was found in males. Pain related elevation of systolic and diastolic blood pressure was observed during both real and sham EMF exposure in female and male subjects.

  • 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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