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Distinctive pattern of c-fos expression in the feline cervico-lumbar spinal cord after stimulation of vanilloid receptors in dorsal neck muscles
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Sports Medicine.
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2004 (English)In: Neuroscience Letters, ISSN 0304-3940, E-ISSN 1872-7972, Vol. 364, no 2, 94-97 p.Article in journal (Refereed) Published
Abstract [en]

In the present study, c-fos expression in the spinal cord has been used as a marker of neuronal activation induced by capsaicin-sensitive sensory afferents from the dorsal neck muscles in cats (n = 6). The number of Fos-immunoreactive neurons, which were revealed using the avidin-biotin-peroxidase method, was significantly increased in the cervical and lumbar spinal cord. In contrast to the control group (n = 3), 2 h after intramuscular capsaicin injection, c-fos expression was more extensive ipsilaterally to the injected side in the C3-C6 segments, and bilaterally in the L4-L6 segments. Most labeled neurons in the cervical spinal cord were small and giant cells, predominantly located in the middle and lateral parts of lamina I and, additionally, at the neck of the dorsal horn (lamina V), i.e., within the zones of termination of high-threshold muscle afferents. The widespread distribution of labeled cells throughout the cervical cord within the intermediate zone (lamina VII) coincided with the sites of last-order premotor interneurons and cells of origin of long crossed and uncrossed descending propriospinal pathways to the lumbar spinal cord. These findings suggest possible mechanisms for spreading of nociceptive signals between cervical and lumbar regions.

Place, publisher, year, edition, pages
Amsterdam: Elsevier Science , 2004. Vol. 364, no 2, 94-97 p.
Keyword [en]
Animals, Capsaicin/administration & dosage/pharmacology, Cats, Cell Size, Cervical Vertebrae, Female, Genes; fos/*genetics, Histocytochemistry, Injections, Lumbar Vertebrae, Male, Neck Muscles/innervation/metabolism/*physiology, Neural Pathways/physiology, Pain/physiopathology, Receptors; Drug/*agonists, Spinal Cord/*metabolism, Stimulation; Chemical
National Category
Medical and Health Sciences
URN: urn:nbn:se:umu:diva-4154DOI: 10.1016/j.neulet.2004.04.019PubMedID: 15196685OAI: diva2:143136
Available from: 2004-10-08 Created: 2004-10-08 Last updated: 2011-04-04Bibliographically approved
In thesis
1. Experimental studies of spinal mechanisms associated with muscle fatigue
Open this publication in new window or tab >>Experimental studies of spinal mechanisms associated with muscle fatigue
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Muscle fatigue is ubiquitous in every day life.Muscle fatigue might be considered as an altered state of motor behaviour, which impairs motor performance. By contrast, muscle fatigue could also be considered a positive phenomenon, which protects muscle tissue from damage that might be incurred to it by overuse.

The principal aim of the thesis was to explore some of the mechanisms of muscle fatigue at the spinal level in animal models.The activation of multiple motor units of a single calf muscle may influence contractile properties of its neighbouring, otherwise inactive units, providing evidence for spatial spreading of fatigue between different muscle parts. The release of metabolites, their action on inactive muscle units and the effects of local hypoxia are the most likely causes. Fatigue-induced metabolite shift in the interstitium provokes excitation and/or sensitisation of high-threshold afferent fibers, with complex effects on the spinal premotoneuronal network involved in the modulation of motoneuronal output. This was examined by studing the intrasegmental lamellar distribution of the lumbar spinal interneurons following fatiguing contractions of the triceps surae muscle. Furthermore, fatigue of calf muscles enhanced the activity of fusimotor neurons to these muscles irrespective of the regime of muscle activity (isometric vs. lengthening) in conditions that simulate locomotion. Altered fusimotor activity, through increased or maintained muscle spindle afferent responsiveness may be advantageous, providing support to the skeletomotor activity and enhanced information about muscle periphery to higher nervous centres. The particular effects of interneuronal network at motor input (presynaptic inhibition system) and output (recurrent inhibition system) stages were then addressed. Fatigue of triceps surae muscle induced a suppression of the monosynaptic reflex. The intensity of presynaptic inhibition increased, while the intensity of recurrent inhibition decreased. Post fatigue-evoked changes in monosynaptic reflexes and presynaptic inhibition indicate the possibility that high-threshold afferents inhibit group Ia terminals pre-synaptically, which would allow fatigue-induced signals from the muscle to reduce the relevance of proprioceptive feedback. Besides intrasegmental, intersegmental spreading of nociceptive signals was explored. Activation of sensory afferents from dorsal neck muscles by capsaicin induces powerful activation of interneurons located in the cervical spinal cord, as well as a widespread activation of cells in lumbar spinal cord segments.

The results confirm the pivotal role of small diameter muscle afferents in the orchestration of segmental responses to fatigue and show complex interactions that may lead to limited accuracy of motor output. They also depict processes that may be related to, and even become precursors of chronic muscle pain.

Umeå University medical dissertations, ISSN 0346-6612 ; 910
muscle fatigue, monosynaptic reflex, presynaptic inhibition, recurrent inhibition, fusimotor system, Fos-immunoreactivity, referral pain
Research subject
urn:nbn:se:umu:diva-332 (URN)91-7305-703-7 (ISBN)
Public defence
2004-11-12, Stora salen, Arbetslivsinstitutet, 13:00
Available from: 2004-10-08 Created: 2004-10-08 Last updated: 2010-06-28Bibliographically approved

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