Projecting from the superior olivary complex to the inner ear in the cat: a retrograde fluorescent labelling study

Abstract

To investigate the distribution and projective feature of cat olivocochlear neurons. Eleven adult cats were divided into two groups randomly. The experimental group of eight cats was injected of 1% cholera toxin B (CTB) to the left cochlea, while injected of 5% fluoro gold (FG) to the right cochlea. The control group of three cats was injected of saline to bilateral cochlea. After a survival time of 7 days, serial frozen sections were cut in the cat brainstem. All the sections were processed by immunofluorescent procedure for CTB and FG, and the labeled olivocochlear neurons were observed by fluorescent microscope. In the experimental group, the mean total of olivocochlear neurons labeled by CTB and FG was 3210 +/- 168, including lateral olivocochlear neurons (LOC, 2298 +/- 120) and medial olivocochlear neurons (MOC, 913 +/- 64). The labeled neurons were divided into three different types according to their feature of projection: neurons which only projected to the ipsilateral cochlea, neurons which only projected to the contralateral cochlea, and double-labeled neurons which projected both to the ipsilateral and contralateral cochlea, but the double-labeled neurons comprised 3.9% and 15.1% in the LOC and MOC system respectively. No labeled neurons were found in the control group. There are three types of neurons in the cat olivocochlear system. The neurons which projected to the bilateral cochlea may distribute both in the LOC and MOC system.