| Abstract #884, Date 2/17/99, Session Y6, Poster (B149) |
| Projections from the inferior colliculus to the cochlear nuclei and the contralateral inferior colliculus in guinea pigs |
| *B.R. Schofield, S.A. Perkins (University of South Dakota, Vermillion, SD) |
We used multiple fluorescent tracers to identify cells in the inferior colliculus (IC) that send collateral projections to multiple targets. First we tested the possibility of collateral projections to the left and right cochlear nuclei. Following injections of different tracers into each cochlear nucleus, retrogradely labeled cells were present throughout the inferior colliculus (i.e., in the central nucleus as well as in the dorsal and external cortices) on both sides. In a given IC, single-labeled cells were numerous, and cells that contained different tracers were intermingled. However, there were almost no double-labeled cells, indicating that the collicular projections to the left and right cochlear nuclei originate largely from different populations of cells. In a second series of experiments, we injected different tracers into each cochlear nucleus and a third tracer into one IC to test whether single IC cells send collateral projections to some combination of these structures. Commissural cells (i.e., those that project to the contralateral IC) were labeled in all parts of the IC, and were intermingled with cells that were labeled by the injections into the left or right cochlear nuclei. We did not observe any triple-labeled cells, suggesting that no cells send collateral projections to all three targets. We did observe some double-labeled cells, providing evidence for two different patterns of projections. Some cells were labeled from the contralateral IC and ipsilateral cochlear nucleus; other cells were labeled from the contralateral IC and contralateral cochlear nucleus. The number of double-labeled cells was very small. These results demonstrate that the commissural and cochlear nuclear projections arise largely from three different populations of cells in the IC. The separate origins of these pathways suggests that they may exert different effects on each of their targets. |