Motoneurons of M. semitendinosus in domestic and wild pigs. A horseradish peroxidase and cord-survey study.

In domestic and wild pigs motor nuclei of the M. semitendinosus were labelled by retrograde transport of horseradish peroxidase (HRP) from muscle to spinal cord. Further motoneurons in the lumbosacral cord were stained with Luxol-fast-blue and cresyl violet. Motoneurons innervating M. semitendinosus were present in the ventral horns of the last (6th) lumbal and the first sacral cord segments. They were localized within two motor columns lying parallel to each other in the medial and lateroventral position. Both parts of the semitendinosus motor nuclei showed a spindle-like shape with both cranial and caudal enlargements. Localization, extent, and shape of the semitendinosus motor nuclei were similar in domestic and wild pigs. The average motoneuron diameter was larger in domestic than in wild pigs. The lumbosacral cord of the wild pig was thicker than that of the domestic pig. It is suggested that the size of alpha-motoneurons has increased as a result of selective breeding after domestication. This process might correlate with a higher incidence of myopathies in domestic pigs.