The origins of the cochlear efferent bundle of Rasmussen in primates

Abstract

The spatial distribution of neurons emitting fibers of the olivocochlear bundle was determined by injecting horseradish peroxidase into the round window in a series of new and old world monkeys. Animals were perfused 24–28 h later. Sections through the pons and medulla were reacted with tetramethyl benzidine and counterstained with thionin and/or neutral red. Perikarya containing reaction product numbered over 800 in one case. The greatest concentration of labeled cells was located in the dorsal periolivary area intermediate between the dorsal margins of the lateral and medial superior olivary nuclei. Approximately 400 cells were ipsilateral to the injection, opposed to 100 contralaterally. The dorsolateral periolivary area contained over 100 labeled cells ipsilaterally, and only about one-third as many contralaterally. While 95 labeled cells occupied the region of the contralateral medial preolivary nucleus, about two-thirds as many labeled cells were found in the comparable ipsilateral nucleus. Although a few labeled neurons were present bilaterally in the lateral preolive and the lateral superior olivary nucleus, no labeled cells were found in the region of the dorsomedial or ventromedial periolivary nuclei (medial to the medial superior olive). [Work supported by the Deafness Research Foundation.]