OBJECTIVETo explore whether there could be proliferative cells in the cochlea of the newborn rat or not and what kinds of cells should be differentiated from the proliferative cells while to study the effect of the growth factors on the proliferative cells and the ultrastructure of the proliferative cells.

METHODSThe Corti's organ were dissected from the cochlea of newborn SD rats and cultured. The proliferative condition of cells was tested by infusing the 5-bromo-2-deoxyuridine (BrdU) into the culture medium. And the variety of the spheres and differentiated cells were identified by immunohistochemistry. Corti's organ from forty-eight surface preparations was randomly divided into 4 groups: control group; epidermal growth factor (EGF) group; basic fibroblast growth factor (bFGF) group and EGF + bFGF group, with each group including 12 Corti's organ, and then the number of cell spheres of each Corti's organ was counted. The data was statistically analysed with ANOVE. Finally, the proliferative cells were observed under scanning electron microscope and transmission electron microscope.

RESULTS(1) The cell spheres can be observed in the cell culture of the Corti's organ. In present experiment, 90.1% of cells in spheres were labeled by BrdU, while nestin of spheres, the marker of hair cells--myosin 7A, espin, and phalloidin of the differentiated cells were positive. The marker of neuron-microfilament-M was also positive, and some differentiated cells were labeled by myosin 7A and BrdU, espin and BrdU, NF-M and BrdU at the same time. (2) The average number (x +/- s) of spheres from single Corti's organ was: 45.3 +/- 23.00 in control group, 86.2 +/- 34.1 in EGF group, 96.5 +/- 33.6 in bFGF group and 131.2 +/- 47.00 in EGF + bFGF group. There were significant differences between other groups respectively (P < 0.05) but there was no significant differences between EGF group and bFGF group (P > 0.05). (3) Scanning electron microscopy and transmission electron microscopy showed that cells of the spheres were round and had the same size and many short and thin microvilli on the surface of these cells. The cytoplasm were rich of organellae such as endoplasmic reticulum, mitochondrion, and cytoskeleton such as microfilament, microtube, et al. Tight junction, desmosomes and gap junctions between two adjacent cells were seen.

CONCLUSIONSThe proliferative cells are observed in the cochlea of the newborn rats and proliferative cells could differentiated into hair cells with bundles-like structure and neuron. Both EGF and bFGF possess the promoting effects for proliferation on the proliferative cells while the proliferative cells have characters of earlier immature cells.