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Analyses of muscle spindles in the soleus of six inbred mouse strains
Author(s) -
Lionikas Arimantas,
Smith Colin J.,
Smith Tracey L.,
Bünger Lutz,
Banks Robert W.,
Bewick Guy S.
Publication year - 2013
Publication title -
journal of anatomy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.932
H-Index - 118
eISSN - 1469-7580
pISSN - 0021-8782
DOI - 10.1111/joa.12076
Subject(s) - muscle spindle , soleus muscle , strain (injury) , anatomy , biology , significant difference , chemistry , medicine , endocrinology , skeletal muscle , afferent
Adult muscle size and fibre‐type composition are heritable traits that vary substantially between individuals. We used inbred mouse strains in which soleus muscle mass varied by an order of magnitude to explore whether properties of muscle spindles can also be influenced by genetic factors. Skip‐serial cross‐sections of soleus muscles dissected from 15 male mice of BEH , BEL , C57 BL /6J, DUH , LG /J and SM /J strains were analysed for number of muscle spindles and characteristics of intrafusal and extrafusal fibres following ATP ase staining. The BEL and DUH strains determined the range of: soleus mean size, a 10‐fold difference from 2.1 to 22.3 mg, respectively; the mean number of extrafusal fibres, a 2.5‐fold difference from 497 to 1249; and mean fibre‐cross‐sectional area, three‐fold difference, e.g. for type 1 fibres, from 678 to 1948 μm 2 . The range of mean proportion of type 1 fibres was determined by C57 BL /6J (31%) and DUH (64%) strains. The mean number of spindles per muscle ranged between nine ( LG /J) and 13 ( BEL ) (strain effect P < 0.02). Genetic correlations between spindle count and muscle weight or properties of extrafusal fibres were weak and not statistically significant. However, there was a strong correlation between the proportion of spindles with more than one bag 2 fibre and the proportion of extrafusal fibres that were of type 1, and strain‐dependent variation in the numbers of such spindles was statistically significant. The numbers of intrafusal fibres per spindle ranged from 2 to 8, with the most common complement of four found in 75.6% of spindles. There were no significant differences between the strains in the mean numbers of intrafusal fibres; however, the variance of the number was significantly less for the C57 BL /6J strain than for any of the others. We conclude that abundance of muscle spindles and their intrafusal‐fibre composition are substantially determined by genetic factors, which are different from those affecting muscle size and properties of the extrafusal fibres.