Muscle injury and inflammation (myositis) in a rabbit model of an unilateral muscle overuse were examined. It is unknown if the\r\ntachykinin system has a functional role in this situation. In this study, therefore, the neurokinin-1 receptor (NK-1R) expression\r\npatterns were evaluated. White blood cells, nerve fascicles, fine nerve fibers, and blood vessel walls in myositis areas showed NK-\r\n1R immunoreaction. NK-1R mRNA reactions were observable for white blood cells and blood vessel walls of these areas. NK-1R\r\nimmunoreaction and NK-1R mRNA reactions were also seen for muscle fibers showing degenerative and regenerative features.\r\nThere were almost no NK-1R immunoreactions in normal muscle tissue. Interestingly, marked NK-1R expressions were seen for\r\nmyositis areas of both the experimental side and the contralateral nonexperimental side. EIAanalyses showed that the concentration\r\nof substance P in the muscle tissue was clearly increased bilaterally at the experimental end stage, as compared to the situation\r\nfor normal muscle tissue. These observations show that the tachykinin system is very much involved in the processes that occur\r\nin muscle injury/myositis. The effects can be related to proinflammatory effects and/or tissue repair. The fact that there are also\r\nmarked NK-1R expressions contralaterally indicate that the tachykinin system has crossover effects.
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