Spatio-temporal localization of the glial fibrillary acidic protein (GFAP) in the spiral ganglion from the 16th embryonic day until the 25th postnatal day in rats

The spiral ganglion (SG) is responsible for the conduction of the information between the sensory epithelium of the auditory organ (the organ of Corti) and the central nervous system. The origin and nature of the SG glial cells in mammals are barely known, although glial cells are essential to the development and the working of the nervous system. Using confocal microscopy, we studied the spatio-temporal distribution of the GFAP in the rat SG from the 16th embryonic day (E16) until the 25th postnatal day (P25). We performed a double-labelling experiment targeting GFAP- and betaIIItubulin-positive cells. BetaIII-tubulin is used for the labelling of (pro)neural cells, according to a previous preliminary study from our team. Our first results show clearly that the GFAP is expressed in the SG from P0 until P25. A homogenous labelling is found in the cytoplasm of a few dispersed unidentified cells among the (pro)neurons, whereas a granular labelling appears among a group of cells neighbouring the bundle of fibers innervating the organ of Corti. The identity of the GFAP-positive cells will be further investigated by electron microscopy. The reason why the labelling of the GFAP adopts those two different aspects is still unknown. Moreover, it seems that, surprisingly, some cells of the ganglion are not labelled by either marker. The possibility that such cells correspond to fibroblasts will be tested thanks to the labelling of vimentin.