Morphology of the Lumbar Transversospinal Muscles Examined in a Mouse Bearing a Muscle Fiber‐Specific Nuclear Marker

Abstract

Although the morphology of human lumbar transversospinal (TSP) muscles has been studied, little is known about the structure of these muscles in the mouse (Mus musculus). Such information is relevant given mice are often used as a ''normal'' phenotype for studies modeling human development. This study describes the gross morphology, muscle fiber arrangement, and innervation pattern of the mouse lumbar TSP muscles. A unique feature of the study is the use of a transgenic mouse line bearing a muscle-specific nuclear marker that allows clear delineation of muscle fiber and connective tissue boundaries. The lumbar TSP muscles of five mice were examined bilaterally; at each spinal level muscles attached to the caudal edge of the spinous process and passed caudally as a single complex unit. Fibers progressively terminated over the four vertebral segments caudad, with multiple points of muscle fiber attachment on each vertebra. Motor endplates, defined with acetylcholinesterase histochemistry, were consistently located half way along each muscle fiber, regardless of length, with all muscle fibers arranged in-parallel rather than in-series. These results provide information relevant to interpretation of developmental and functional studies involving this muscle group in the mouse and show mouse lumbar TSP muscles are different in form to descriptions of equivalent muscles in humans and horses. Anat Rec, 293:2107Rec, 293: -2113Rec, 293: , 2010. V V C 2010 Wiley-Liss, Inc.Key words: paravertebral muscles; lumbar; morphology; mouse; fiber arrangement This work examines the normal morphology of the transversospinal (TSP) muscles of the laboratory mouse (Mus musculus). The TSP muscles are a subgroup of the paravertebral muscles, located in the space between the spinous and transverse processes of the vertebral column, and existing throughout the spine between upper cervical spine and sacrum (Slijper, 1946). This group is described as consisting of individual muscles, including the semispinalis, multifidus, and rotatores. The paravertebral muscles and vertebral column receive significant scientific attention in clinical medicine, because of the prominence of back pain and spinal pathologies in humans (Boal and Gillette, 2004;Cassidy et al., 2005;Balague et al., 2007); however, our morphological understanding of these muscles is poor.Slijper (1946) studied the structure of paravertebral muscles in a wide range of large mammalian species, including the dugong (Dugong dugon) and armadillo (Dasypus). This muscle group has also been described in

Fetal development of deep back muscles in the human thoracic region with a focus on transversospinalis muscles and the medial branch of the spinal nerve posterior ramus

“…The present S100 immunohistochemistry demonstrated a band‐like arrangement of motor endplates similar to that in the mouse lumbar transversospinalis muscle shown by Cornwall et al. (2010).…”

“…The present S100 immunohistochemistry demonstrated a band-like arrangement of motor endplates similar to that in the mouse lumbar transversospinalis muscle shown by Cornwall et al (2010). S100-positive intramuscular nerve twigs exhibited downward courses, not only in the semispinalis muscle but also (because they are independent of nerve twigs to the semispinalis) through the multifidus and rotatores muscles.…”

“…although their major interest was the nerve configuration. However, Cornwall et al (2010Cornwall et al ( , 2011 recently demonstrated that in the mouse and human, the transversospinalis muscle does not have 'in-series' architecture even for muscle bundles that extend over two or three segments. Their observations indicate that, in contrast to Fig.…”

Morphological Changes of Deep Extensor Neck Muscles in Relation to the Maximum Level of Cord Compression and Canal Compromise in Patients With Degenerative Cervical Myelopathy

“…Indeed, the structure of the MF+ Scer may be affected by spinal cord compression and specific nerve root, 27 which could be a plausible explanation for the observed increase in fatty infiltration and atrophy of the paraspinal muscles at the level of spinal cord compression. Cornwall et al 28 reported that muscular bundles of paraspinal muscle extending across 2 or 3 segments do not have consecutive/in-series architecture, and that multisegmental nerves are unlikely to supply a single muscle bundle of the paraspinal muscle. Polysegmental innervation for lumbar MF muscle has been argued in several studies, however there is no such evidence of cervical MF muscle innervation.…”