DETAILS OF THE CENTRAL PROJECTIONS OF THE COCHLEAR NERVE IN THE HAMSTER REVEALED BY THE FLUORESCENT TRACER DII

A new fluorescent tracer, DiI, may be used postmortem in perfused animals making placement in small structures such as the cochlea much less difficult. We have mapped cochlear nerve terminations in the cochlear nucleus with DiI and, using three-dimensional reconstructions, have demonstrated the topography and geometry of the cochlear input. By placing DiI in two regions of the cochlea, we have demonstrated that terminations from the cochlea form stacked sheets of inputs. If enough closely situated ganglion cells were labeled in the cochlea, a well-delineated stripe of label could be found in each section of the cochlear nucleus up to the superficial granule cell region. Here a small extension of label, separate from the stripe may represent the medial olivocochlear axons. When fewer axons were labelled in the cochlear nerve, the sheets were absent and discontinuous patches of label were found. These patches apposed rostrocaudally to form bands of label that run orthogonal to the tonotopic organization.