Fredrik Hellström

Influences on the fusimotor-muscle spindle system from chemosensitive nerve endings in cervical facet joints in the cat: possible implications for whiplash induced disorders

&NA; The aim of the present study was to establish if there exists reflex connections from ligamentous structures in cervical facet joints and the fusimotor system of dorsal neck muscles. In seven cats, anaesthetized with &agr;‐chloralose, bradykinin (BK) of concentrations between 12 and 50 &mgr;g was injected into the facet joint between C1 and C2. Recordings were made from single muscle spindle afferents (MSA) originating in contralateral trapezius and splenius muscles (TrSp). Fusimotor induced changes in the sensitivity of the muscle spindle afferents were assessed by recording the responses to sinusoidal stretches of the TrSp muscles. The mean rate of discharge and the depth of modulation of a fitted sine were taken as quantitative estimates of the response. A total of 25 MSAs were recorded, and 21 of these showed clear‐cut alterations in their responses to the sinusoidal stretches following Bk. injections into contralateral facet joint. The majority of the responding afferents (13/21) showed changes in their responses indicating an increased activity of static fusimotoneurones, although responses of dynamic and mixed static and dynamic nature were also seen. Local anaesthetics applied to the intraarticular receptors abolished the effects. Injection (i.v.) of a general anaesthetic (pentobarbital) abolished the effects. The results show that there exist reflex connections between receptors in cervical facet joints and fusimotoneurones of dorsal neck muscles, and this might be of importance in the pathophysiology behind whiplash associated disorders (WAD).

Elevated Intramuscular Concentration of Bradykinin in Jaw Muscle Increases the Fusimotor Drive to Neck Muscles in the Cat

Patients suffering from temporomandibular dysfunction exhibit clinical findings such as fatigue, painful muscles, and muscles that are tender to palpation, not only in the temporomandibular area, but also in the neck/shoulder region. The mechanisms behind this are not known, although previous studies of similar spreading phenomena have revealed a possible involvement of the fusimotor system. In the present study, we evaluated the activity of this system by recording the activity of muscle spindle afferents from dorsal neck muscles after intramuscular injections of 6 μg to 25 μg bradykinin in the ipsilateral masseter muscle. A total of 23 muscle spindle afferents from the trapezius and splenius muscles was recorded at the C3-C4 level in 7 adult cats anesthetized with a-chloralose. Of these 23 afferents, 17 (74%) showed significantly different responses to bradykinin injections compared with control injections (dissolving agent, Tyrode), and the majority of the effects were compatible with an increased static fusimotor drive to the muscle spindle system. Thus, the results demonstrate potent reflex connections from groups III and IV masseter muscle afferents to fusimotor neurones on the C3-C4 level. It is concluded that the fusimotor system might play a significant role in the mechanisms behind the spread of muscle pain and tension from the temporomandibular region to the neck.

Effects of time pressure and precision demands during computer mouse work on muscle oxygenation and position sense

The present study investigated the effects of time pressure and precision demands during computer mouse work on muscle oxygenation and position sense in the upper extremity. Twenty-four healthy subjects (12 males and 12 females) performed a 45-min standardized mouse-operated computer task on two occasions. The task consisted of painting rectangles that were presented on the screen. On one occasion, time pressure and precision demands were imposed (more demanding task, MDT), whereas, on the other occasion, no such restraints were added (less demanding task, LDT). The order of the two task versions was randomized. Tissue oxygen saturation in the trapezius and extensor carpi radialis muscles was recorded throughout, and the position-matching ability of the wrist was measured before and after the tasks. In addition, measurements of autonomic nervous system reactivity and subjective ratings of tenseness and physical fatigue were obtained. Performance was measured in terms of the number of rectangles that were painted during the task. During MDT, oxygen saturation in extensor carpi radialis decreased (P<0.05) compared to LDT. These data were paralleled by increased electrodermal activity (P<0.05), skin blood flow (P<0.05), ratings of tenseness and fatigue (P<0.01), and increased performance (P<0.01) during MDT. Females exhibited lower oxygen saturation than males, during rest as well as during the computer tasks (P<0.01). Wrist repositioning error increased following LDT as compared to MDT (P<0.05). In conclusion, computer mouse work under time pressure and precision demands caused a decrease in forearm muscle oxygenation, but did not affect wrist position sense accuracy. We attribute our changes in oxygenation more to increased oxygen consumption as a result of enhanced performance, than to vasoconstriction.

Glutamate and prostaglandin E2 in the trapezius muscle of female subjects with chronic muscle pain and controls determined by microdialysis

Much is still unknown concerning the mechanisms underlying the development of chronic muscle pain. The presence and magnitude of inflammatory substances and neurotransmitters in chronic painful conditions is not clear. The aims of the present study were to determine, with the use of microdialysis, the interstitial concentrations and the equilibration times for PGE2 and glutamate in the trapezius muscles of nine female subjects with chronic muscle pain, and nine pain‐free age‐matched controls. A microdialysis probe was implanted in the upper part of the trapezius muscle and perfused with Ringer‐acetate solution at a flow rate of 0.3 μL/min. Samples were obtained every 30 min, during a 4‐h rest period. At equilibration, the mean concentrations (−SE) of PGE2 were 0.71 (−0.11) ng/mL for the pain‐group and 0.97 (−0.35) ng/mL for the controls. For glutamate the mean concentrations for the pain‐group were 66.3 (−13.3) μmol/L and 60.6 (−22.9) μmol/L for the controls. For the pain group and the control group, respectively, equilibration for PGE2 was reached at 180 and 150 min, and for glutamate at 150 and 120 min. The present study showed no differences between groups in the concentrations of PGE2 and glutamate in the trapezius muscle. Further, it revealed that when using the slow‐flow method, a period of at least 2.0‐2.5 h is needed, after probe insertion, to reach steady state for glutamate and PGE2.

Increased intra-articular concentration of bradykinin in the temporomandibular joint changes the sensitivity of muscle spindles in dorsal neck muscles in the cat.

The aim of the present study was to investigate to what extent activation of bradykinin-sensitive nerve endings of the temporomandibular joint (TMJ) might induce changes in the muscle spindles output from neck muscles through reflex effects on cervical fusimotor neurones. To this end, 26 muscle spindle afferents (MSAs) emanating from the trapezius and splenius muscles of the anaesthetised cat (alpha-chloralose, initial dosage 60 mg/kg) were recorded during injection of Bradykinin (BK) (12.5-50 microg/ml) in the ipsilateral TMJ. Fifteen (58%) MSAs exhibited statistically significant fusimotor effects to injection of BK into the TMJ. Of the 15, ten MSAs showed a response related to activation of static fusimotor neurones, three MSAs showed a response related to an activation of both static and dynamic fusimotor neurones and two MSAs showed a inhibition of both static and dynamic fusimotor neurones. The control experiments suggests that the effects observed were due to activation of BK sensitive nerve endings in the TMJ. It seems possible that the reflex connections between TMJ nociceptors and the fusimotor-muscle spindle system of dorsal neck muscles might be involved in the pathophysiological mechanisms responsible for the sensory-motor disturbances in the neck region often found on patients with temporomandibular disorders.

Comparative metabolomics of muscle interstitium fluid in human trapezius myalgia: an in vivo microdialysis study

PurposeThe mechanisms behind trapezius myalgia are unclear. Many hypotheses have been presented suggesting an altered metabolism in the muscle. Here, muscle microdialysate from healthy and myalgic muscle is analysed using metabolomics. Metabolomics analyse a vast number of metabolites, enabling a comprehensive explorative screening of the cellular processes in the muscle.MethodsMicrodialysate samples were obtained from the shoulder muscle of healthy and myalgic subjects that performed a work and stress test. Samples from the baseline period and from the recovery period were analysed using gas chromatography—mass spectrometry (GC–MS) together with multivariate analysis to detect differences in extracellular content of metabolites between groups. Systematic differences in metabolites between groups were identified using multivariate analysis and orthogonal partial least square discriminate analysis (OPLS-DA). A complementary Mann–Whitney U test of group difference in individual metabolites was also performed.ResultsA large number of metabolites were detected and identified in this screening study. At baseline, no systematic differences between groups were observed according to the OPLS-DA. However, two metabolites, l-leucine and pyroglutamic acid, were significantly more abundant in the myalgic muscle compared to the healthy muscle. In the recovery period, systematic difference in metabolites between the groups was observed according to the OPLS-DA. The groups differed in amino acids, fatty acids and carbohydrates. Myristic acid and putrescine were significantly more abundant and beta-d-glucopyranose was significantly less abundant in the myalgic muscle.ConclusionThis study provides important information regarding the metabolite content, thereby presenting new clues regarding the pathophysiology of the myalgic muscle.

Combining microdialysis and near-infrared spectroscopy for studying effects of low-load repetitive work on the intramuscular chemistry in trapezius myalgia.

Epidemiological research provides strong evidence for a link between repetitive work (RW) and the development of chronic trapezius myalgia (TM). The aims were to further elucidate if an accumulation of sensitising substances or impaired oxygenation is evident in painful muscles during RW. Females with TM (n = 14) were studied during rest, 30 minutes RW and 60 minutes recovery. Microdialysate samples were obtained to determine changes in intramuscular microdialysate (IMMD) [glutamate], [PGE2], [lactate], and [pyruvate] (i.e., [concentration]) relative to work. Muscle oxygenation (%StO2) was assessed using near-infrared spectroscopy. During work, all investigated substances, except PGE2, increased significantly: [glutamate] (54%, P < .0001), [lactate] (26%, P < .005), [pyruvate] (19%, P < .0001), while the %StO2 decreased (P < .05). During recovery [PGE2] decreased (P < .005), [lactate] remained increased (P < .001), [pyruvate] increased progressively (P < .0001), and %StO2 had returned to baseline. Changes in substance concentrations and oxygenation in response to work indicate normal increase in metabolism but no ongoing inflammation in subjects with TM.

Experimental masseter muscle pain alters jaw-neck motor strategy.

A functional integration between the jaw and neck regions has been demonstrated during normal jaw function. The effect of masseter muscle pain on this integrated motor behaviour in man is unknown. The aim of this study was to investigate the effect of induced masseter muscle pain on jaw–neck movements during a continuous jaw opening‐closing task.

Acute muscle inflammation enhances the monosynaptic reflexes and c-fos expression in the feline spinal cord

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 30min 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.

Multivariate Modeling of Proteins Related to Trapezius Myalgia, a Comparative Study of Female Cleaners with or without Pain

The prevalence of chronic trapezius myalgia is high in women with high exposure to awkward working positions, repetitive movements and movements with high precision demands. The mechanisms behind chronic trapezius myalgia are not fully understood. The purpose of this study was to explore the differences in protein content between healthy and myalgic trapezius muscle using proteomics. Muscle biopsies from 12 female cleaners with work-related trapezius myalgia and 12 pain free female cleaners were obtained from the descending part of the trapezius. Proteins were separated with two-dimensional differential gel electrophoresis (2D-DIGE) and selected proteins were identified with mass spectrometry. In order to discriminate the two groups, quantified proteins were fitted to a multivariate analysis: partial least square discriminate analysis. The model separated 28 unique proteins which were related to glycolysis, the tricaboxylic acid cycle, to the contractile apparatus, the cytoskeleton and to acute response proteins. The results suggest altered metabolism, a higher abundance of proteins related to inflammation in myalgic cleaners compared to healthy, and a possible alteration of the contractile apparatus. This explorative proteomic screening of proteins related to chronic pain in the trapezius muscle provides new important aspects of the pathophysiology behind chronic trapezius myalgia.