Whiplash trauma did not predict jaw pain after 2 years: an explorative study.

OBJECTIVES: To explore predictive factors for the development and maintenance of jaw pain over a 2-year period. METHODS: One hundred nineteen cases (73 women) and 104 controls (59 women), mean age 34.9 years (SD 13.9), attended baseline and 2-year follow-up examinations. The whiplash cases visited the emergency department at Umeå University Hospital, Sweden, with neck pain within 72 h following a car accident, and baseline questionnaires were answered within a month after trauma. Controls were recruited via advertising. Inclusion criteria were age 18-70 years, living in Umeå municipality and Swedish speaking. The exclusion criterion was neck fracture for cases and a previous neck trauma for controls. Validated questionnaires recommended in the standardized Research Diagnostic Criteria for temporomandibular disorders were used. Jaw pain was assessed by two validated screening questions answered with "yes" or "no." A logistic regression analysis was used to predict the outcome variable jaw pain (yes/no) after 2 years. RESULTS: Whiplash trauma did not increase the odds of development of jaw pain over a 2-year period (OR 1.97, 95% CI 0.53-7.38). However, non-specific physical symptoms (OR 8.56, 95% CI 1.08-67.67) and female gender (OR 4.89, 95% CI 1.09-22.02) did increase the odds for jaw pain after 2 years. CONCLUSION: The development and maintenance of jaw pain after whiplash trauma are primarily not related to the trauma itself, but more associated with physical symptoms. CLINICAL RELEVANCE: The development of jaw pain in connection with a whiplash trauma needs to be seen in a biopsychosocial perspective, and early assessment is recommended.

Development of integrated jaw-neck motor function in children at 6, 10 and 13 years of age compared to adults: A kinematic longitudinal study.

BACKGROUND: The functional integration of the jaw and neck motor systems, of great importance to everyday oral activities, is established in early childhood. Detailed characterisation of this developmental progress is largely unknown. OBJECTIVE: To establish developmental changes in jaw-neck motor function in children over the ages 6-13 years compared to adults. METHODS: Jaw and head movement kinematics during jaw opening-closing and chewing were longitudinally recorded in 20 Swedish children (8 girls) at 6 (6.3 ± 0.4), 10 (10.3 ± 0.3) and 13 (13.5 ± 0.7) years of age and 20 adults (9 women, 28.2 ± 6.7). Movement amplitudes, jaw movement cycle time (CT), coefficient of variation (CV) and head/jaw ratio for amplitudes were analysed. Linear mixed effect analysis and Welch's t-test were used. RESULTS: Children showed pronounced movement variability and longer CT at 6 and 10 years old during opening and chewing (p < .001). Compared to adults, 6-year-olds showed higher head/jaw ratios (p < .02) and longer CT (p < .001) during opening and chewing, and higher CV-head (p < .001) during chewing. Whereas 10-year-olds showed larger jaw and head amplitudes (p < .02) and longer CT (p < .001) during opening, and longer CT (p < .001) and higher CV-head (p < .001) during chewing. For 13-year-olds, longer CT (p < .001) during chewing was found. CONCLUSION: Children showed pronounced movement variability and longer movement cycle time at 6-10 years and developmental progress in jaw-neck integration from 6 to 13 years, with 13-year-olds displaying adult-like movements. These results add new detailed understanding to the typical development of integrated jaw-neck motor function.

Clinical signs in the jaw and neck region following whiplash trauma-A 2-year follow-up.

BACKGROUND: Pain in the orofacial region is often reported after whiplash trauma. However, prospective studies evaluating clinical signs related to orofacial pain and disability in whiplash populations are rare. The aim of the present study was to evaluate clinical signs related to pain and dysfunction in orofacial and neck regions after whiplash trauma, in a short- and long-term perspective. METHODS: In total, 84 cases (48 women) diagnosed with neck distortion after a car accident and 116 controls (68 women) were examined within 1 month, and 49 cases (27 women) and 71 controls (41 women) were re-examined 2 years later. Outcome measures were pain on palpation of jaw and neck muscles and maximal jaw opening. Analysis was performed using mixed-models. RESULTS: Cases and women were at higher risk for pain on palpation of jaw muscles (OR:7.7; p < 0.001 and OR:3.2; p = 0.010 respectively) and neck muscles (OR:12.7; p < 0.001 and OR:2.9; p = 0.020 respectively) but with no significant effect of time. Cases and women also had lower maximal jaw opening (-3.1; p = 0.001 and -3.3; p = 0.001 respectively). There was no significant time effect, but a significant interaction between cases and time (2.2; p = 0.004). CONCLUSION: Individuals with a whiplash trauma present a higher risk for pain on palpation in jaw and neck muscles both in a short- and long-term perspective, but show normal jaw movements. No time effect suggests that cases do not spontaneously improve nor get worse. Investigating pain on palpation in the jaw and neck muscles after whiplash trauma can identify individuals at risk for developing long-term orofacial pain and dysfunction. SIGNIFICANCE: Orofacial pain is often reported after whiplash trauma but most previous studies concerning orofacial pain in whiplash populations have been questionnaire studies. Cases with a previous whiplash trauma and women, in general, had higher risk for pain on palpation in the jaw and neck region. Investigating pain on palpation after a whiplash trauma can help to identify individuals at risk of developing long-lasting pain in the orofacial region.

Jaw-neck motor strategy during jaw-opening with resistance load.

BACKGROUND: The jaw and neck motor systems have a close functional integration but the effect of resistance load to the mandible during jaw opening on the jaw-neck integration is not known. OBJECTIVES: To evaluate the effect of resistance load compared to no load on integrated jaw and neck motor function in individuals free from pain and dysfunction in the jaw and neck regions. METHODS: Jaw and head movements during continuous jaw opening were recorded with an optoelectronic system (MacReflex® ) in 26 pain-free individuals (14 women, 12 men, mean age 22 years). Jaw opening was performed with and without resistance load (1600 g) to the mandible. The relationship between jaw movement amplitude, head movement amplitude, head/jaw ratio (quotient of head and jaw movement amplitude) and resistance load were modelled using linear mixed-model analysis. A p-value <.05 was considered statistically significant. RESULTS: The expected head/jaw ratio mean was increased by 0.05 (95% CI: 0.03, 0.08, p < .001) with resistance load as compared to no load. This corresponds to an increase in expected mean by 55.6%. With resistance load, expected mean head movement amplitude increased by 1.4 mm (95% CI: 0.2, 2.5, p = .018), and expected mean jaw movement amplitude decreased by 3.7 mm (95% CI: -7.0, -0.5, p = .025). CONCLUSION: There is a compensation and adaptation of integrated jaw-neck motor function with an altered jaw-neck motor strategy during jaw opening with resistance load compared to no load. The head/jaw ratio demonstrates increased proportional involvement of the neck during increased load on the jaw system.

Effects of a Ketogenic Diet on Muscle Fatigue in Healthy, Young, Normal-Weight Women: A Randomized Controlled Feeding Trial.

Ketogenic low-carbohydrate high-fat (LCHF) diets are increasingly popular in broad sections of the population. The main objective of this study was to evaluate the effects of a non-energy-restricted ketogenic LCHF diet on muscle fatigue in healthy, young, and normal-weight women. Twenty-four women were randomly allocated to a 4-week ketogenic LCHF diet followed by a 4-week control diet (a National Food Agency recommended diet), or the reverse sequence due to the crossover design. Treatment periods were separated by a 15 week washout period. Seventeen women completed the study and were included in the analyses. Treatment effects were evaluated using mixed models. The ketogenic LCHF diet had no effect on grip strength or time to fatigue, measured with handgrip test (day 24-26). However, cycling time to fatigue decreased with almost two minutes (-1.85 min 95% CI:[-2.30;-1.40]; p < 0.001) during incremental cycling (day 25-27), accommodated with higher ratings of perceived exertion using the Borg scale (p < 0.01). Participants' own diary notes revealed experiences of muscle fatigue during daily life activities, as well as during exercise. We conclude that in young and healthy women, a ketogenic LCHF diet has an unfavorable effect on muscle fatigue and might affect perceived exertion during daily life activities.

Jaw-neck movement integration in 6-year-old children differs from that of adults.

BACKGROUND: A functional integration between the jaw and neck regions during purposive jaw movements is well described in adults, but there is a lack of knowledge of such integration during jaw function in children. OBJECTIVES: To determine the movement integration between the jaw and neck during jaw motor tasks in 6-year-olds, whether there is a difference between children and adults. METHODS: Jaw and neck movements were recorded with an optoelectronic 3D system in 25 healthy 6-year-olds (12 girls, 13 boys) and 24 healthy adults (12 women, 12 men) during paced jaw opening-closing and self-paced gum chewing. Jaw and neck movement amplitudes, intra-individual variation in movement amplitude, ratio between neck-jaw movement amplitudes and movement cycle time were analysed. Differences between children and adults were evaluated with Mann-Whitney U test for independent samples. RESULTS: Compared to adults, 6-year-old children showed larger neck movement amplitudes (P = .008) during chewing, higher intra-individual variability in amplitudes of jaw (P = .008) and neck (P = .001) movements, higher ratio between neck-jaw movement amplitudes for jaw opening-closing (P = .026) and chewing (P = .003), and longer jaw movement cycle time (P ≤ .0001) during the jaw opening-closing task. CONCLUSION: Despite integrated jaw-neck movements in 6-year-old children, the movement pattern differs from that of adults and may be interpreted as an immature programming of jaw-neck motor behaviour. The well-integrated movements observed in adults most likely develop over years, perhaps into adolescence, and needs further research including well-controlled longitudinal studies to map this development in order to provide appropriate age-related clinical treatment for functional disorders.

Multimodal Sensory Stimulation of the Masseter Muscle Reduced Precision but Not Accuracy of Jaw-Opening Movements.

A functional integration between the trigeminal and craniocervical sensorimotor systems has been demonstrated, with simultaneous jaw and head-neck movements during jaw opening-closing. We previously showed that pain induction in the masseter muscle increased the relative contribution of the neck component of integrated jaw-neck movements. Induced pain or manipulation of proprioception by vibration did not affect accuracy during a jaw-opening task in men. It is not known how multimodal sensory stimulation, with a combination of pain induction and vibration, affects jaw-opening accuracy and precision. The aim was to investigate how jaw-neck movements, and specifically accuracy and precision of jaw-opening, are affected during concomitant nociceptive and proprioceptive stimulation of the masseter muscle. Twenty-one healthy men performed jaw-opening to a target position, defined as 75% of individual maximum jaw opening, during control (Ctr), vibration of masseter muscles (Vib), pain induction in the masseter (Pain), and concomitant vibration and pain induction in the masseter muscle (VibPain). Simultaneous jaw and head movements were recorded with an optoelectronic system and amplitudes calculated for each jaw opening-closing cycle. Accuracy of jaw movements was defined as the achievement of the target position. Precision of jaw movements was defined as the cycle-to-cycle variability from the mean of cycles 2-10 (coefficient of variation, CV). Differences between the trials were analyzed with Friedman's test, Dunn's test, and Benjamini-Hochberg correction. There were no significant differences between the trials for jaw movement amplitudes. For head movements, amplitudes for cycles 2-10 were larger during Pain compared to Ctr and Vib (both p = 0.034), and larger during VibPain compared to Ctr (p = 0.034) and Vib (p = 0.035). There were no differences in accuracy of jaw movements between the trials. For precision of jaw movements, the cycle-to-cycle variability was larger during VibPain compared to Ctr (p = 0.027) and Vib (p = 0.018). For integrated jaw-neck motor strategy, there was a difference between pain and non-pain trials, but no differences between unimodal and multimodal stimulation trials. For achievement of jaw-opening to a target position, the results show no effect on accuracy, but a reduced precision of jaw movements during combined proprioceptive and nociceptive multimodal stimulation.

A high prevalence of TMD is related to somatic awareness and pain intensity among healthy dental students.

OBJECTIVE: Dental students have been identified as a group with high risks of developing both temporomandibular disorders (TMD) and psychosocial conditions. Our primary aim was to evaluate the cross-sectional prevalence of TMD diagnoses, as defined in the Diagnostic Criteria (DC)/TMD, among dental students. The secondary aim was to evaluate the prevalence and association of behavioural and psychosocial factors in relation to DC/TMD diagnoses. MATERIALS AND METHODS: The study was conducted among undergraduate dental students during the second semester of their third year at the Department of Odontology, Medical Faculty, Umeå University, Sweden. Three consecutive cohorts were recruited during August in 2013, 2014, 2015. In total, 54 students were included and examined according the DC/TMD procedure. RESULTS AND CONCLUSIONS: The prevalence of any DC/TMD diagnosis was 30%. The most prevalent TMD diagnosis was myalgia. Individuals with a TMD-pain diagnosis (i.e. myalgia or arthralgia) reported significantly higher pain intensity levels according to the Graded Chronic Pain Scale (GCPS) as compared to individuals without TMD-pain (Fisher's exact test p < .001, two-sided). In addition, individuals with any TMD scored significantly higher jaw functional limitations according to the Jaw Functional Limitation Scale 20 (JFLS-20, p < .001) and oral parafunctions according to the Oral Behavior Checklist (OBC, p = .005) as compared to individuals without TMD. The psychosocial factors evaluated did not differ between individual with or without a TMD diagnosis. The majority of the dental students reported symptoms that are already identified as risk factors for developing TMD and pain conditions. However, longitudinal data are needed to evaluate how this evolves over time.

Systematic review of quantitative imaging biomarkers for neck and shoulder musculoskeletal disorders.

BACKGROUND: This study systematically summarizes quantitative imaging biomarker research in non-traumatic neck and shoulder musculoskeletal disorders (MSDs). There were two research questions: 1) Are there quantitative imaging biomarkers associated with the presence of neck and shoulder MSDs?, 2) Are there quantitative imaging biomarkers associated with the severity of neck and shoulder MSDs? METHODS: PubMed and SCOPUS were used for the literature search. One hundred and twenty-five studies met primary inclusion criteria. Data were extracted from 49 sufficient quality studies. RESULTS: Most of the 125 studies were cross-sectional and utilized convenience samples of patients as both cases and controls. Only half controlled for potential confounders via exclusion or in the analysis. Approximately one-third reported response rates. In sufficient quality articles, 82% demonstrated at least one statistically significant association between the MSD(s) and biomarker(s) studied. The literature synthesis suggested that neck muscle size may be decreased in neck pain, and trapezius myalgia and neck/shoulder pain may be associated with reduced vascularity in the trapezius and reduced trapezius oxygen saturation at rest and in response to upper extremity tasks. Reduced vascularity in the supraspinatus tendon may also be a feature in rotator cuff tears. Five of eight studies showed an association between a quantitative imaging marker and MSD severity. CONCLUSIONS: Although research on quantitative imaging biomarkers is still in a nascent stage, some MSD biomarkers were identified. There are limitations in the articles examined, including possible selection bias and inattention to potentially confounding factors. Recommendations for future studies are provided.

Does induced masseter muscle pain affect integrated jaw-neck movements similarly in men and women?

Normal jaw opening-closing involves simultaneous jaw and head-neck movements. We previously showed that, in men, integrated jaw-neck movements during jaw function are altered by induced masseter muscle pain. The aim of this study was to investigate possible sex-related differences in integrated jaw-neck movements following experimental masseter muscle pain. We evaluated head-neck and jaw movements in 22 healthy women and 16 healthy men in a jaw opening-closing task. The participants performed one control trial and one trial with masseter muscle pain induced by injection of hypertonic saline. Jaw and head movements were registered using a three-dimensional optoelectronic recording system. There were no significant sex-related differences in jaw and head movement amplitudes. Head movement amplitudes were significantly greater in the pain trials for both men and women. The proportional involvement of the neck motor system during jaw movements increased in pain trials for 13 of 16 men and for 18 of 22 women. Thus, acute pain may alter integrated jaw-neck movements, although, given the similarities between men and women, this interaction between acute pain and motor behaviour does not explain sex differences in musculoskeletal pain in the jaw and neck regions.

Association between plasma concentrations of linoleic acid-derived oxylipins and the perceived pain scores in an exploratory study in women with chronic neck pain.

BACKGROUND: Chronic musculoskeletal pain may be associated with changes in the balance of algogenic and anti-nociceptive compounds, and such changes may be visible in plasma samples. We have undertaken an exploratory study to measure the levels of endocannabinoids, related N-acylethanolamines and oxylipins (primarily those derived from linoleic acid) in plasma samples from women with chronic neck pain (NP) and chronic widespread pain (CWP), and to investigate whether the observed levels are associated with the pain experienced by these women. METHODS: Blood samples from 35 women with NP, 15 with CWP and 27 age-matched controls were analysed for the lipids using ultra performance liquid chromatography coupled to tandem mass spectrometry. Current pain ("NRSday") and the average pain during the last week ("NRSweek") were rated by the participants using a numerical rating scale. RESULTS: There were no significant differences in the plasma concentrations of the fifteen lipids investigated between the women with pain and the controls. However, significant correlations were seen for the NP group between the NRSday scores and the plasma concentrations of the linoleic acid derivatives 9- and 13-hydroxy-octadecadienoic acid (Spearman's rho values 0.51 [P = 0.0016]) and 0.53 [P = 0.0011], respectively). CONCLUSIONS: The data obtained in this exploratory study indicate that although no group differences are seen in plasma lipid concentrations, there is an association between the NRSday scores and the 9- and 13-hydroxy-octadecadienoic acid levels. Whether or not the association reflects a causality (i.e. that the circulating lipids contribute to the perceived pain of the pain participants), requires further investigation.

Systematic review of biochemical biomarkers for neck and upper-extremity musculoskeletal disorders.

OBJECTIVE: This study systematically summarizes biochemical biomarker research in non-traumatic musculoskeletal disorders (MSD). Two research questions guided the review: (i) Are there biochemical markers associated with neck and upper-extremity MSD? and (ii) Are there biochemical markers associated with the severity of neck and upper-extremity MSD? METHODS: A literature search was conducted in PubMed and SCOPUS, and 87 studies met primary inclusion criteria. Following a quality screen, data were extracted from 44 articles of sufficient quality. RESULTS: Most of the 87 studies were cross-sectional and utilized convenience samples of patients as both cases and controls. A response rate was explicitly stated in only 11 (13%) studies. Less than half of the studies controlled for potential confounding through restriction or in the analysis. Most sufficient-quality studies were conducted in older populations (mean age in one or more analysis group >50 years). In sufficient-quality articles, 82% demonstrated at least one statistically significant association between the MSD and biomarker(s) studied. Evidence suggested that: (i) the collagen-repair marker TIMP-1 is decreased in fibro proliferative disorders, (ii) 5-HT (serotonin) is increased in trapezius myalgia, and (iii) triglycerides are increased in a variety of MSD. Only 5 studies showed an association between a biochemical marker and MSD severity. CONCLUSION: While some MSD biomarkers were identified, limitations in the articles examined included possible selection bias, confounding, spectrum effect (potentially heterogeneous biomarker associations in populations according to symptom severity or duration), and insufficient attention to comorbid conditions. A list of recommendations for future studies is provided.

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.

Reliability of near-infrared spectroscopy for measuring forearm and shoulder oxygenation in healthy males and females.

This study determined the day-to-day reliability of NIRS-derived oxygenation responses (∆StO(2)%) for isometric contractions and for cuff occlusion. Twenty-four subjects (12 males and 12 females) were tested for 2 days (4-6 days interval). Variables generated were: (1) ∆StO(2)% for isometric contractions (10, 30, 50 and 70% MVC) for descending trapezius (TD) and extensor carpi radialis (ECR) muscles; (2) slope changes in total haemoglobin (HbTslope) and deoxyhaemoglobin (HHbslope) for the ECR using upper arm venous (VO, 50 mmHg) and arterial occlusion (AO, 250 mmHg); (3) recovery slopes (Rslope) for oxygen saturation (StO(2)) following isometric contractions and AO. For each variable, an intraclass correlation (ICC) was calculated to assess the ability to differentiate between subjects, and limits of agreement (LOA) were computed to assess day-to-day consistency of the measurement. ICCs for ΔStO(2)% were lowest at 10% MVC for both ECR (0.58) and TD (0.55), and highest at 30% MVC for ECR (0.95) and at 70% MVC for TD (0.79). For both muscles, LOA for ΔStO(2)% was lowest at 10% and highest at 50 and 70% MVC. ICC for HbTslope was 0.17. For HHbslope ICC was higher for AO (0.83) than for VO (0.73), and LOA was lower for AO. For the ECR Rslope ICCs ranged from 0.88 to 0.90 for contraction, but was lower for AO (0.33); LOA was lowest at 70% MVC. For trapezius Rslope ICCs ranged from 0.63 to 0.73 and LOA was lowest at 30% MVC. For this study, establishing reliability data for the ECR and TD and including variables commonly reported are expected to have meaning for future NIRS studies of work-related upper-extremity pain as well as for other NIRS research and clinical applications.

Protein differences between human trapezius and vastus lateralis muscles determined with a proteomic approach.

BACKGROUND: The trapezius muscle is a neck muscle that is susceptible to chronic pain conditions associated with repetitive tasks, commonly referred to as chronic work-related myalgia, hence making the trapezius a muscle of clinical interest. To provide a basis for further investigations of the proteomic traits of the trapezius muscle in disease, two-dimensional difference gel electrophoresis (2D-DIGE) was performed on the healthy trapezius using vastus lateralis as a reference. To obtain as much information as possible from the vast proteomic data set, both one-way ANOVA, with and without false discovery rate (FDR) correlation, and partial least square projection to latent structures with discriminant analysis (PLS-DA) were combined to compare the outcome of the analysis. RESULTS: The trapezius and vastus lateralis showed significant differences in metabolic, contractile and regulatory proteins, with different results depending on choice of statistical approach and pre-processing technique. Using the standard method, FDR correlated one-way ANOVA, 42 protein spots differed significantly in abundance between the two muscles. Complementary analysis using immunohistochemistry and western blot confirmed the results from the 2D-DIGE analysis. CONCLUSIONS: The proteomic approach used in the present study combining 2D-DIGE and multivariate modelling provided a more comprehensive comparison of the protein profiles of the human trapezius and vastus lateralis muscle, than previously possible to obtain with immunohistochemistry or SDS-PAGE alone. Although 2D-DIGE has inherent limitations it is particularly useful to comprehensively screen for important structural and metabolic proteins, and appears to be a promising tool for future studies of patients suffering from chronic work related myalgia or other muscle diseases.

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], [PGE(2)], [lactate], and [pyruvate] (i.e., [concentration]) relative to work. Muscle oxygenation (%StO(2)) was assessed using near-infrared spectroscopy. During work, all investigated substances, except PGE(2), increased significantly: [glutamate] (54%, P < .0001), [lactate] (26%, P < .005), [pyruvate] (19%, P < .0001), while the %StO(2) decreased (P < .05). During recovery [PGE(2)] decreased (P < .005), [lactate] remained increased (P < .001), [pyruvate] increased progressively (P < .0001), and %StO(2) 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.

Movement-dependent positioning errors in human elbow joint movements.

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.

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 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.

Capsaicin-induced effects on c-fos expression and NADPH-diaphorase activity in the feline spinal cord.

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.

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 microL/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) micromol/L and 60.6 (+/-22.9) micromol/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.