| Abstract #710, Date 2/17/99, Session U, Podium , 2:30p |
| Tonotopic changes in 2-deoxyglucose activity in chick cochlear nucleus during hair cell loss and regeneration |
| *D.L. Park, D. Durham, D.A. Girod (University of Kansas Medical Center) |
Following cochlear ablation, electrical activity decreases in the cochlear nucleus, (n.magnocellularis, NM), resulting in 25-30% cell death. Following partial cochlear damage from gentamicin, 25-30% of rostral NM neurons die (Park, Girod, and Durham, Hearing Research, in press). In this study we examined NM neuronal activity during partial hair cell loss and regeneration by measuring glucose uptake in NM. Hatchling chicks (P11) were given a single systemic dose of gentamicin (200 mg/kg) or equal volume of saline. Chicks were sacrificed at various survival times (2, 5, 9, 16, and 28 days). On the sacrifice day, chicks were injected with 14C labeled 2-deoxyglucose (2DG). After 45 minutes of exposure to tape-recorded Beatles music, the chicks were sacrificed. The brains were frozen and the cochleae were processed for scanning electron microscopy. Brains were sectioned and apposed to x-ray film. Using NIH Image software, measurements of 2DG uptake were made from the exposed film using alternate stained sections for placement. Cochleae from the saline-treated chicks were not damaged, while damage in the gentamicin-treated chicks was confined to the high frequency, basal 25% length of the cochlea. Results of NM 2DG uptake from control chicks reveal a gradient of activity along the rostral to caudal extent of the nucleus. There is higher activity in the caudal low frequency regions, likely due to a greater proportion of neuropil. In the gentamicin-treated chicks, a gradient of activity was also observed, which changed as a function of survival time. At early survival times (2, 5 days), activity is lower in the rostral 50% of NM as compared to saline-treated chicks. At later survival times (9, 16, 21, 28 days), activity in the rostral 50% of NM appears similar to that of saline-treated chicks. The 2DG activity in the caudal 50% of NM appears unaffected by gentamicin. These results suggest that rostral NM activity, as reflected by glucose uptake, decreases soon after gentamicin administration and increases to normal levels with time. This decrease and subsequent increase in glucose uptake parallels cell counts in both NM and the cochlea. |