Asymmetry in semicircular canal diameters may account for circling behavior in EphB-deficient mice.

OBJECTIVES/HYPOTHESIS Determine if differences in right and left semicircular size account for phenotypic behavior, indicating vestibulopathy in EphB deficient mice. STUDY DESIGN The diameters of the superior semicircular canals (SCC) were measured. The differences in the right and left superior SCC diameters were analyzed in homozygous EphB2 and EphB3 double knockout mice known to have head bobbing and circling behavior. Results were compared to similar analysis in wild type controls that displayed no signs of vestibulopathy. METHODS Axial frozen sections through the superior (SCC) were analyzed by light microscopy; and the diameters of the left and right canals were measured in μm for both EphB2 and EphB3 double knockout mice, as well as in wild type control mice. The differences in diameter between the left and right superior SCC was determined for each animal. RESULTS Overall, the EphB2 and EphB3 double knockout mice had smaller superior SCC diameters compared to wild type (109.0±21.4 μm vs. 185.0±5.2 μm (P<0.0001). The mean difference in left and right diameter of the superior SCC of EphB2/EphB3 double knockout mice was 29.0±8.7 μm; in wild-type controls this difference was 6.0±5.1 μm (P=0.002). In addition, the direction of circling appeared to be independent of the laterality of the smaller (or larger) superior SCC. CONCLUSION Mice deficient in EphB2/EphB3 signaling have smaller superior SCC and asymmetry in lumen sizes between the left and right sides. The laterality of the larger versus smaller is not correlated with the direction of circling behavior. LEVEL OF EVIDENCE N/A.