Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Randomized Controlled Trial Comparative Study
Spatial and temporal aspects of muscle hyperalgesia induced by nerve growth factor in humans.
Intramuscular injection of nerve growth factor (NGF) has been shown to induce long-term sensitisation and time-dependent hyperalgesia indicating potential involvement of both central and peripheral pain mechanisms. This double-blind placebo-controlled study was designed to describe the spatial distribution of muscle hyperalgesia over time (immediately after, 3 h, 1, 4, 7 and 21 days) after injecting NGF (5 mug) into the tibialis anterior (TA) muscle, to explore possibly involved central pain mechanisms and to investigate the effect of gender on development of hyperalgesia. Totally 20 healthy volunteers (10 men and 10 women) participated in the study. ⋯ Injection of NGF increased muscle soreness during muscle activity for 7 days. In this material there was no gender effect of NGF-induced muscle hyperalgesia. The expansion of muscle hyperalgesia to distant areas indicates that central mechanisms are involved.
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Randomized Controlled Trial Controlled Clinical Trial
Effects of NGF-induced muscle sensitization on proprioception and nociception.
Temporomandibular disorders (TMDs) are associated with perturbation of proprioceptive and nociceptive function. Recent studies have shown that injection of the neurotrophic protein nerve growth factor (NGF) into the masseter muscle causes sensitization to mechanical pressure stimuli; however, it is not clear if vibration sense and jaw stretch reflexes as measures of proprioceptive function as well as glutamate-evoked pain are also altered. We tested the hypothesis that NGF-induced mechanical sensitization would be associated with changes in vibration sense and stretch reflex sensitivity as well as facilitation of glutamate-evoked pain responses. ⋯ In conclusion, this study confirms that masseter muscle injection of NGF is associated with a distinct and prolonged sensitization to mechanical stimuli, but without an effect on large-diameter mechanoreceptive and the muscle spindle afferents. Additional challenge of the NGF pretreated muscle with glutamate did not indicate a conspicuous sensitization to noxious chemical stimuli. These findings are discussed in terms of the concept of "proprioceptive allodynia".
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Randomized Controlled Trial Controlled Clinical Trial
Induction of muscle cramps by nociceptive stimulation of latent myofascial trigger points.
The aim of this present study is to test the hypothesis that nociceptive stimulation of latent myofascial trigger points (MTrPs) increases the occurrence of local muscle cramps. Nociceptive muscle stimulation was obtained by a bolus injection of glutamate (0.1 ml, 0.5 M) into a latent MTrP and a control point (a non-MTrP) located in the right or left gastrocnemius medialis muscles in 14 healthy subjects. A bolus of isotonic saline (0.9%, 0.1 ml) injection served as a control. ⋯ No muscle cramps were recorded following isotonic saline injection into either the latent MTrPs or the non-MTrPs. These results suggest that latent MTrPs could be involved in the genesis of muscle cramps. Focal increase in nociceptive sensitivity at MTrPs constitutes one of the mechanisms underlying muscle cramps.
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Randomized Controlled Trial
Dissociation of nociceptive modulation of a human jaw reflex from the influence of stress.
In human beings, inhibitory jaw reflexes can be depressed by painful stimulation of remote parts of the body. Since similar effects can be produced by the stress of anticipating pain, we wished to investigate whether the effects of remote painful stimuli are dependent on stress. EMG recordings were made from a masseter muscle while subjects maintained activity in the muscle at approximately 12.5% of maximum using visual feedback. ⋯ A second series of experiments suggested that these lesser effects during the random sequences were not substantially due to any loss of temporal summation of the conditioning mechanisms. The evidence for this was that application of pairs of conditioning stimuli did not produce a significantly greater effect than single conditioning stimuli within a random sequence (39.9 +/- 9.6% as opposed to 32.7 +/- 9.1% reductions in the reflex, P = 0.117, paired t-test). Therefore since any stress in the random sequences would not have been "tied" to the conditioned responses alone, the effects of remote painful stimuli on this inhibitory jaw reflex cannot be entirely secondary to stress.
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Randomized Controlled Trial
Immediate changes in feedforward postural adjustments following voluntary motor training.
There is limited evidence that preprogrammed feedforward adjustments, which are modified in people with neurological and musculoskeletal conditions, can be trained and whether this depends on the type of training. As previous findings demonstrate consistent delays in feedforward activation of the deep abdominal muscle, transversus abdominis (TrA), in people with recurrent low back pain (LBP), we investigated whether training involving voluntary muscle activation can change feedforward mechanisms, and whether this depends on the manner in which the muscle is trained. Twenty-two volunteers with recurrent LBP were randomly assigned to undertake either training of isolated voluntary activation of TrA or sit-up training to activate TrA in a non-isolated manner to identical amplitude. ⋯ The magnitude of change in TrA EMG onset was correlated with the quality of isolated training. In contrast, all of the abdominal muscles were recruited earlier during arm flexion after sit-up training, while onset of TrA EMG was further delayed during arm extension. The results provide evidence that training of isolated muscle activation leads to changes in feedforward postural strategies, and the magnitude of the effect is dependent on the type and quality of motor training.