Neuronal death, not axonal degeneration, results in significant gliosis within the cochlear nucleus of adult chickens

Injury to the central nervous system initiates a series of events that lead s to neuronal cell death and glial activation. Astrocytes respond to damage and disease by becoming hyperplastic and hypertrophied. This 'reaclive gli osis' is also accompanied by the upregulation of the intermediate filament protein glial fibrillary acidic protein, the release of growth factors and the formation of the glial scar. However, the signaling cascades which regu late these events, and the molecular mechanisms that give rise to this dive rse response, have not been fully elucidated. For example, the role played by degenerating neurons vs. degenerating axons in the activation of astrocy tes remains to be determined. To investigate the influence of neuronal cell death vs. axonal degeneration on gliosis, the current study examines the a strocyte response to cochlea removal in two different breeds of adult chick ens, one of which exhibits neuronal cell death within the brainstem nucleus magnocellularis (NM) following the lesion and one which does not. Our resu lts indicate that degeneration of NM neurons leads to large increases in bo th glial proliferation and hypertrophy, while eighth nerve degeneration wit hout NM cell death results in very small increases in glial proliferation. (C) 2000 Elsevier Science B.V. All rights reserved.