Neonatal bilabyrinthectomy leads to changes in skeletal muscle fiber form and function

Children with hypoactive semicircular canals commonly have delayed motor development. We studied ferrets whose vestibular labyrinths were removed at postnatal day 10 (P10) to evaluate 1) development of motor behavior, 2) soleus contractile characteristics, 3) muscle fiber diameter, and 4) the expression of myosin heavy chain (MHC) isoforms. At P30 labyrinthectomized (LAB) ferrets exhibited a significant delay in motor development. At P120, the LAB ferrets continued to have significantly more difficulty with dynamic balance than the SHAM ferrets. At P30, the muscle fibers were about the same diameter as those in the sham operated ferrets (SHAM) at the same age but significantly more developmental MHC isoforms were expressed in the LAB soleus muscle. At P120, both the LAB soleus and medial gastrocnemius expressed significantly more type IIX MHC. The P120 LAB soleus muscle was significantly weaker and the muscle fibers were significantly smaller. These results support the hypothesis that vestibular receptors are important to the development of upright posture and balance activities, and influence muscle fiber development and MHC expression in postural muscles.