Projection from the cochlear nucleus to the peripheral vestibule in Wistar rats

To find morphological evidence of a direct projection from the cochlear nucleus (CN; at the brainstem level) in the auditory system to the peripheral end organs in the vestibular system.

Experiments were conducted on male Wistar rats (n = 24). Two neuronal tracers were used: (1) 5% molecular probe F-8793 was injected into the unilateral peripheral vestibule and used as a retrograde tracer; (2) PHA-L (Invitrogen L-11270) was injected into the unilateral CN and used as an anterograde tracer. All animals were allowed to recover for 7 days after surgery to facilitate sufficient transportation of the tracers. Subsequently, brainstems in the retrograde group and inner ears in the anterograde group were sliced coronally on a freezing microtome and observed under a fluorescence microscope.

After PHA-L injection into the CN, terminal labeling was observed in the peripheral vestibule, especially in the inferior vestibular nerve. The retrograde tracing study showed that the positive cells could be found in the ventral part of the CN.

These results suggest that there is a novel pathway with a consanguineous functional connection between the CN and peripheral vestibule.