Auditory neuronal sizes after a unilateral conductive hearing loss

Abstract

The left external auditory meatus was removed in 4-day-old CBA J mice; after killing at 45 days, serial sections of the cochleae and brain stem were prepared. From these, the cross-sectional areas of spiral ganglion neurons and of 14 auditory brain stem neuronal types were measured, using a total of 210 neurons of each of the 15 types from both the right and left sides. Nine neuronal types were significantly ( P < 0.01) on the left side: spiral ganglion neurons; globular, small spherical, large spherical, octopus, multipolar, and granule cells of the ventral cochlear nucleus; Purkinje-like cells of the dorsal cochlear nucleus; and spindle cells of the lateral superior olivary nucleus. Two neuronal types were significantly smaller ( P < 0.01) on the right: principal cells of the medial nucleus of the trapezoid body (superior olivary complex), and spindle-shape principal neurons of the central nucleus of the inferior colliculus. The left ventral cochlear nucleus had significantly smaller volume ( P < 0.01) than the right but right and left dorsal cochlear nuclear volumes did not differ significantly ( P > 0.05). Right and left sides were not significantly different ( P > 0.05) for the following neuronal types: fusiform cells and coarse- and fine-Nissl deep cells of the dorsal cochlear nucleus, and rostral bipolar cells of the medial superior olivary nucleus. Neurons affected by unilateral conductive loss were not significantly different ( P > 0.05) from the same cells in mice with bilateral conductive losses; neurons not affected by unilateral conductive loss were not significantly diferent ( P > 0.05) from the same cells in normal mice.