Expression of subtypes NF-L, NF-M and NF-H of neurofilament triplet proteins in the developing rat inner ear.

The expression of each subtype (NF-L, NF-M and NF-H) of neurofilament (NF) triplet proteins in the developing rat inner ear was analysed using the immunofluorescence method (FITC). On the 15th gestational day (GD), immunostaining of NF subtypes did not occur in the otic region. On the 18th GD, positivity for NF-L and NF-M occurred in nerve fibres in both the sensory and the subepithelial layers of the inner ear but was lacking for NF-H. At 4 days after birth immunoreactivity was present for each NF subtype but with topographic differences in their distribution. The cell bodies of (different?) subpopulations of vestibular and spiral ganglion cells were immunostained with monoclonal antibodies for NF-L and NF-M, but a subpopulation of both vestibular and spiral ganglion cells showed immunoreactivity for all three NF subtypes. The vestibular nerve fibres and ganglion cells evidenced stronger positivity than cochlear nerve fibres and spiral ganglion cells. This study confirms that the cytoskeletal maturation of inner ear nerve fibres precedes the onset of at least the auditory function by several days.