| Abstract #583, Date 2/16/99, Session R3, Poster (B83) |
| Ventral cochlear nucleus multipolar neurons that innervate the dorsal cochlear nucleus differ in their projections outside the cochlear nucleus |
| *J.R. Doucet, H.B. Cahill, M. Ohlrogge (Johns Hopkins Univ. Sch. of Med., Dept. of Otolaryngology-HNS); D.K. Ryugo (Johns Hopkins Univ. Sch. of Med., Depts. of Otolaryngology-HNS and Neuroscience) |
At least three classes of ventral cochlear nucleus (VCN) multipolar neurons in the rat can be defined based on their dendritic morphology, neurochemistry, and projections to the dorsal cochlear nucleus (DCN). Two of the classes (radiate and planar neurons) are found in the magnocellular core of the VCN whereas the third class (marginal neurons) is located in the small cell cap. Planars appear to be excitatory neurons that process sound information within narrow spectral bands. Radiates appear to be inhibitory neurons that process sound information over wide spectral bands. Less is known about marginal neurons, but the small cell cap receives auditory nerve fiber input predominantly from the low spontaneous rate, high threshold fibers. In this study, we examined the axonal targets of these three classes outside the cochlear nucleus using a fluorescent double labeling protocol. We labeled planar, radiate, and marginal neurons by making an extracellular injection of biotinylated dextran amine (BDA) into the DCN. In the same experiment, Diamidino Yellow (DiY) was injected into either the contralateral inferior colliculus (IC) or the contralateral cochlear nucleus. BDA-filled neurons were visualized using streptavidin conjugated to Cy3; thus, double labeled cells had a red cytoplasm (BDA label) and a yellow nucleus (DiY label). We found several double labeled planar and marginal neurons when DiY injections were made in the IC, whereas few radiate neurons were double labeled. In contrast, when DiY injections were placed in the contralateral CN, many radiate neurons were double labeled while few planar and marginal neurons were double labeled. These results suggest that while all three classes innervate the ipsilateral DCN, the axons of planar and marginal neurons also target the contralateral inferior colliculus whereas the axons of radiate neurons project to the contralateral cochlear nucleus. These divergent projections reinforce the idea that planar, radiate, and marginal neurons are playing fundamentally different roles in the processing of sound. |