Underdeveloped extraocular muscles in the naked mole-rat (Heterocephalus glaber)

Colleen A. McMullen, Francisco H. Andrade, Samuel D. Crish

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


The extraocular muscles (EOM), the effector arm of the ocular motor system, have a unique embryological origin and phenotype. The naked mole-rat (NMR) is a subterranean rodent with an underdeveloped visual system. It has not been established if their ocular motor system is also less developed. The NMR is an ideal model to examine the potential codependence of oculomotor and visual system development and evolution. Our goal was to compare the structural features of NMR EOMs to those of the mouse, a similar sized rodent with a fully developed visual system. Perfusion-fixed whole orbits and EOMs were dissected from adult NMR and C57BL mice and examined by light and electron microscopy. NMR orbital anatomy showed smaller EOMs in roughly the same distribution around the eye as in mouse and surrounded by a very small Harderian gland. The NMR EOMs did not appear to have the two-layer fiber distribution seen in mouse EOMs; fibers were also significantly smaller (112.3 ± 46.2 vs. 550.7 ± 226 sq lm in mouse EOMs, *P < 0.05). Myofibrillar density was less in NMR EOMs, and triad and other membranous structures were rudimentary. Finally, mitochondrial volume density was significantly less in NMR EOMs than in mouse EOM (4.5% ± 1.9 vs. 21.2% ± 11.6, respectively, *P < 0.05). These results demonstrate that NMR EOMs are smaller and less organized than those in the mouse. The "simpler" EOM organization and structure in NMR may be explained by the poor visual ability of these rodents, initially demonstrated by their primitive visual system.

Original languageEnglish
Pages (from-to)918-923
Number of pages6
JournalAnatomical Record
Issue number5
StatePublished - May 2010


  • Extraocular muscle
  • Heterocephalus glaber
  • Mitochondria
  • Naked mole-rat

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Biotechnology
  • Anatomy
  • Histology


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