A New Model for Congenital Vestibular Disorders
Many developmental disorders of the inner ear are manifested clinically as delayed motor development and challenges in maintaining posture and balance, indicating involvement of central vestibular circuits. How the vestibular circuitry is rewired in pediatric cases is poorly understood due to lack of a suitable animal model. Based on this, our lab designed and validated a chick embryo model to study vestibular development in congenital vestibular disorders. The developing inner ear or “otocyst” on the right side of 2-day-old chick embryos (E2) was surgically rotated 180° in the anterior–posterior axis, forming the “anterior–posterior axis rotated otocyst chick” or ARO chick. The ARO chick has a reproducible pathology of a sac with truncated or missing semicircular canals. A sac is the most common inner ear defect found in children with congenital vestibular disorders. In E13 ARO chicks, the sac contained all three cristae and maculae utriculi and sacculi, but the superior crista and macula utriculi were shortened in anterior–posterior extent. Also, the number of principal cells of the tangential vestibular nucleus, a major avian vestibular nucleus, was decreased 66 % on the rotated side. After hatching, no difference was detected between ARO and normal chicks in their righting reflex times. However, unlike normal chicks, ARO hatchlings had a constant, right head tilt, and after performing the righting reflex, ARO chicks stumbled and walked with a widened base. Identifying the structure and function of abnormally developed brain regions in ARO chicks may assist in improving treatments for patients with congenital vestibular disorder.
Keywordsotocyst rotation chick vestibular nuclei
We would like to acknowledge Ms. Lakshmi Kammili of GWU Pathology Core Laboratory for processing the chick specimens for paraffin embedding, tissue sectioning, and Nissl staining.
This work was supported in part by research funds from the GWU Department of Anatomy and Cell Biology and GWU Luther Rice Undergraduate Fellowships (SJL and HES).
Compliance with Ethical Standards
Animal protocols were approved by the Institutional Animal Care and Use Committee (IACUC) of the George Washington University. The experiments also conform to the International Guidelines for the Ethical Treatment of Animals.
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