title: Bilateral increase in expression and concentration of tachykinin in a unilateral rabbit muscle overuse model that leads to myositis.
abstract: BACKGROUND
  Tachykinins can have pro-inflammatory as well as healing effects during tissue reorganization and inflammation. Recent studies report an up-regulation in the expression of the substance P (SP)-preferred receptor, the neurokinin-1 receptor, in marked muscle inflammation (myositis). There is, however, only very little information on the expression patterns and levels of tachykinins in this situation.
  
  
  METHODS
  The tachykinin system was analyzed using a rabbit experimental model of muscle overuse, whereby unilateral muscle exercise in combination with electrical stimulation led to muscle derangement and myositis in the triceps surae muscle (experimental length 1-6 weeks). Evaluations were made for both parts of the muscle (soleus and gastrocnemius muscles) in experimental and non-experimental (contralateral) sides. Morphologic evaluation, immunohistochemistry, in situ hybridization and enzyme immunoassay (EIA) analyses were applied.
  
  
  RESULTS
  Myositis and muscle derangement occurred focally not only in the experimental side but also in the non-experimental side. In the inflammatory areas (focal myositis areas), there were frequent nerve fibers showing tachykinin-like immunoreactivity and which were parts of nerve fascicles and which were freely dispersed in the tissue. Cells in the inflammatory infiltrates showed tachykinin-like immunoreactivity and tachykinin mRNA expression. Specific immunoreactivity and mRNA expression were noted in blood vessel walls of both sides, especially in focally affected areas. With increasing experimental length, we observed an increase in the degree of immunoreactivity in the vessel walls. The EIA analyses showed that the concentration of tachykinin in the tissue on both sides increased in a time-dependent manner. There was a statistical correlation in the concentration of tachykinin and the level of tachykinin immunoreactivity in the blood vessel walls between experimental and non-experimental sides.
  
  
  CONCLUSIONS
  The observations show an up-regulation of the tachykinin system bilaterally during muscle derangement/myositis in response to pronounced unilateral muscle overuse. This up-regulation occurred in inflammatory areas and was related not only to increased tachykinin innervation but also to tachykinin expression in blood vessel walls and inflammatory cells. Importantly, the tachykinin system appears to be an important factor not only ipsilaterally but also contralaterally in these processes.
authors.affiliation: Department of Integrative Medical Biology, Section for Anatomy, Umeå University, Umeå, Sweden.
authors.forename: Yafeng
authors.initials: Y
authors.lastname: Song
authors.forename: Per S
authors.initials: PS
authors.lastname: Stål
authors.forename: Ji-Guo
authors.initials: JG
authors.lastname: Yu
authors.forename: Sture
authors.initials: S
authors.lastname: Forsgren
mesh_terms: D000818:Animals; D012090:Cumulative Trauma Disorders / Q000175:diagnosis / Q000378:metabolism*; D004195:Disease Models, Animal; D005260:Female; D005786:Gene Expression Regulation; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D009220:Myositis / Q000175:diagnosis / Q000378:metabolism*; D010805:Physical Conditioning, Animal / Q000009:adverse effects; D011817:Rabbits; D015320:Tachykinins / Q000096:biosynthesis*
chemical_list: D015320:Tachykinins