ONTOGENY OF TYPE-II SPIRAL GANGLION NEURONS DURING DEVELOPMENT - PERIPHERIN IMMUNOHISTOCHEMISTRY

In this study, we analysed the distribution of the intermediate filame nt peripherin in the developing cochlea of the rat. At gestational day 16, weak immunolabeling was observed in neuronal somas throughout the spiral ganglion. At gestational day 20, the peripherin labeling incre ased in intensity throughout the cochlea but became especially strong in some ganglion neurons of the basal turn. Homogeneous immunolabeling was observed throughout the spiral ganglion of the apical turn. Doubl e immunofluorescence labeling of the prenatal cochlea with peripherin and neurofilament (NF) antibodies revealed colocalization on the same structures. By postnatal day 3, the peripherin labeling intensity had decreased in the majority of spiral ganglion neurons, but remained str ong in some cells of the basal turn. Only a few neurons continued to b e immunolabeled into adulthood that correspond to Type II spiral gangl ion neurons expressing both NF protein and peripherin, two classes of intermediate filament proteins. In the organ of Corti, the first immun olabeling was observed on gestational day 20 as peripheral fibers reac hing the receptor cells. Positive fibers were observed below both inne r (IHCs) and outer (OHCs) hair cells. At birth and at postnatal day 3, peripherin immunolabeling was still observed below both IHCs and OHCs . By postnatal day 4, peripherin labeling became more dominant in fibe rs below OHCs, but some immunoreactivity was still present below IHCs. No immunoreactivity was present in the intraganglionic spiral bundle (IGSB) fibers containing the olivary complex efferent fibers before bi rth. A few days after birth some fibers of the IGSB started to be immu noreactive.