Immunocytochemical localization of neurofilament subunits in the spiral ganglion of normal and neomycin-treated guinea pigs.

Neurofilaments are a major component of the neuronal cytoskeleton and present in all neurons. The expression of subunits of neurofilaments has been shown to be altered by conditions such as development, aging, degeneration and regeneration of the neuron. In the present study, we determined 1) the distribution of neurofilament subunits in spiral ganglion cells of normal guinea pigs and 2) if this distribution is altered by hair cell degeneration. Immunocytochemical analyses were done with monoclonal antibodies to the 200,000 (NF 200), 160,000 (NF 160), and 68,000 (NF 68) daltons neurofilament subunits. In the normal guinea pig, type II spiral ganglion cells were intensely labeled with NF 200, NF 160, NF 68 antibodies, whereas type I cells were significantly labeled only with NF 200 antibody. Neurofilament subunit immunoreactivity was also localized in the auditory nerve and afferent and efferent fibers to the hair cells. To determine the effects of hair cell loss on neurofilament expression in spiral ganglion cells, guinea pigs were treated with neomycin at doses known to cause extensive hair cell damage. Type I and type II spiral ganglion cells responded differently to this treatment. Type II cells remained strongly immunoreactive after treatment although the number of such cells was reduced, especially in the longer surviving animals. NF 160 and NF 68 immunoreactivities increased gradually from base to apex in type I cells after neomycin treatment, while NF 200 immunoreactivity decreased in all turns.