Characterization of the vestibular and spiral ganglion cell somata of the rat by distribution of neurofilament proteins.

Neurons of the spiral and vestibular ganglia of the adult rat were labelled with a panel of monoclonal and polyclonal antibodies which were raised against different subunits of neurofilament proteins (NFPs). Thirteen antibodies labelled intensely the perikarya of a distinct group of somata in both the spiral and vestibular ganglia while the majority of somata were unreactive or showed a weaker reaction. The distinction between intensely immunostained and other cell somata was more conspicuous in the spiral than in the vestibular ganglia. Intensely stained somata formed a subpopulation comprising about 9% (range from 7.2 to 11.1%) in the spiral and about 32% (range from 21.2 to 36.4%) in the vestibular ganglia of the total ganglion cell population. Antibodies against different subunits of NFPs seemed always to stain the same somata. In morphometric analysis the mean diameters of intensely labelled spiral ganglion cells were clearly smaller (9.9 microns) than those of the slightly reactive cells (11.9 microns). In Scarpa's ganglia the intensely reactive cells were larger in size (mean diameter 21.4 microns) than the slightly reactive cells (mean diameter 14.7 microns). In the spiral ganglia, the intensely labelled group of neurons seems to correspond to the morphologically distinct type II cells which may also functionally differ from type I cells. In Scarpa's ganglia, the intensely stained subgroup of somata may correspond to the large neurons innervating central regions of cristae and maculae. Their functional significance remains to be elucidated.