Pain
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Chronic musculoskeletal complaints (MSCs) are among the major health problems, and cross-sectional studies suggest an association between smoking and MSCs. The causal relationship, however, is not known. The present study is designed to assess the association between smoking and chronic MSCs, and is based on data from a large longitudinal cohort study of all inhabitants ⩾20years in Nord-Trøndelag County (Helse Undersøkelsen i Nord-Trøndelag -HUNT), conducted in 1995-97 (HUNT 2) and 2006-08 (HUNT 3). ⋯ The results show that smoking at baseline represents a 20% increased risk (IRR=1.20, 95% CI 1.14-1.27, P=0.0001) for chronic MSCs at follow-up. The risk for chronic MSCs by daily smoking decreased with increasing age up to 50years; after this, there was no significant association. The results show that modifiable risk factors like smoking should be included in public health intervention programs for MSCs.
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Little is documented in the literature as to the function of muscle fascia in nociception and pain. The aim of this study was to examine the distribution of presumptive nociceptive nerve fibers, to characterize fascial thin-fiber sensory receptors, and to examine the spinal projection of nociceptive input from the rat crural fascia (CF). Nerve fibers labeled with specific antibodies to calcitonin gene-related peptide (CGRP) and peripherin were found to be densely distributed in the distal third of the CF. ⋯ Repetitive pinching stimulus to the CF induced c-Fos protein expression in the middle to medial part of superficial layers ie, laminae I-II of the spinal dorsal horn at segments L2 to L4, peaking at L3. These results clearly demonstrate the following: 1) peptidergic and non-peptidergic axons of unmyelinated C-fibers with nerve terminals are distributed in the CF; 2) peripheral afferents responding to noxious stimuli exist in the fascia, and 3) nociceptive information from the CF is mainly processed in the spinal dorsal horn at the segments L2 to L4. These results together indicate that the "muscle fascia," a tissue often overlooked in pain research, can be an important source of nociception under normal conditions.
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Estrogen status and psychological stress contribute to the expression of several chronic pain conditions including temporomandibular muscle and joint disorders (TMJD). Sensory neurons that supply the temporomandibular joint (TMJ) region terminate in laminae I and V of the spinal trigeminal nucleus (Vc/C1-2 region); however, little is known about lamina-specificity and environmental influences on the encoding properties of TMJ brainstem neurons. To test the hypothesis that Vc/C1-2 neurons integrate both interoceptive and exteroceptive signals relevant for TMJ nociception, we recorded TMJ-evoked activity in superficial and deep laminae of ovariectomized rats under high and low estradiol (E2) and stress conditions. ⋯ By contrast, FS conditioned rats displayed increased background firing and TMJ-evoked activity of neurons in deep, but not superficial, laminae independent of E2 status. FS also enhanced TMJ-evoked masseter muscle activity and suggested the importance of deep dorsal horn neurons in mediating evoked jaw muscle activity. In conclusion, E2 status and psychophysical stress play a significant role in modifying the encoding properties of TMJ-responsive medullary dorsal horn neurons with a marked lamina-specificity.
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Pain sometimes has a throbbing, pulsating quality, particularly when it is severe and disabling. We recently challenged the presumption that this throbbing quality is a sensory experience of arterial pulsations, but were unable to offer an alternative explanation for its rhythmic character. Here we report a case study of a woman with a history of daily headache consistent with the diagnosis of chronic migraine, but whose throbbing quality persisted long after the resolution of the headache. ⋯ On spectral analysis of the electroencephalogram, we found that the overall amount of activity in the alpha range (8 to 12Hz), or alpha power, increased in association with greater throbbing intensity. In addition, we also found that the rhythmic oscillations of overall alpha power, the so-called modulations of alpha power, coincided with the timing of the throbbing rhythm, and that this synchrony, or coherence, was proportional to the subjective intensity of the throbbing quality. This index case will motivate further studies whose aim is to determine whether modulations of alpha power could more generally represent a neurophysiological correlate of the throbbing quality of pain.