Intracellular labeling of afferents to the lateral superior olive in the bat, Eptesicus fuscus.

An in vitro tissue slice preparation of the bat brain stem was used to label intracellularly individual axons projecting to the lateral superior olive from two different sources: the medial nucleus of the trapezoid body (MNTB) and the anteroventral cochlear nucleus (AVCN). The tracing of individually labeled MNTB axons into the lateral superior olive reaffirms the long accepted indirect route by which information from the contralateral ear reaches the lateral superior olive. While the MNTB appears to relay input from the contralateral AVCN, information from the ipsilateral ear reaches the lateral superior olive via a direct projection from the ipsilateral AVCN. Axons from the contralateral and ipsilateral pathways have different distribution patterns upon the fusiform cells of the lateral superior olive. Axon terminals of MNTB principal cells have a perisomatic and proximal dendritic distribution pattern. Axon terminal varicosities from the ipsilateral anteroventral cochlear nucleus are distributed primarily to more distal dendrites.