Fibroblast growth factors (FGFs) in the cochlear nucleus of the adult mouse following acoustic overstimulation.

To see if fibroblast growth factors (FGFs) might function in the central changes following auditory overstimulation we tracked immunostaining in the cochlear nucleus of adult mice with monoclonal antibodies to FGFs (FGF-1, FGF-2) and FGF receptor. After exposure nearly all outer hair cells died, while inner hair cell and fiber loss were restricted to a region midway along the cochlear spiral. FGFs staining in the cochlear nucleus appeared in hypertrophied astrocytes in the regions of nerve fiber degeneration only. For normal-sized astrocytes there was an increase in the number stained and the intensity of staining across all frequency domains, but not in neurons. The increases were modest at 3-7 days, pronounced at 14 days, modest again by 30 days, and back to control levels by 60 days. FGF receptor staining of neurons occurred equally in all mice, exposed or not. The findings suggest that astrocytes play a role in the central responses to acoustic overstimulation and cochlear damage, involving FGFs, possibly regulating the activity of intrinsic neurons or signaling axonal growth. Not limited to regions of cochlear nerve fiber and inner hair cell loss, the changes in FGFs may represent a reaction to outer hair cell damage which spreads broadly across the central pathways.