Development of the otic Placode and the statoacoustic ganglion in rat embryos

为了探讨耳廓发育的机制，在体内和培养的大鼠胚胎(Spraogue-Dawley品系)上观察了耳廓发育过程中细胞数量的增加和微丝分布模式的变化。用含细胞松弛素D(2×10~(-8))或5-溴-2‘-脱氧尿苷(BrdU，1.6×10~(-4)~(-4)~(gt；M))的大鼠血清培养胚胎48小时，观察到畸形的耳囊。用胶原凝胶培养法分析耳道发育情况，耳道胎盘在妊娠10.5天后24小时内发育成耳囊。耳板、耳窝和耳囊分别由700个、2800个和6000个细胞组成。本实验结果表明，细胞数目的增加可能不起作用，但微丝可能在耳囊的形成和状态听神经节细胞的迁移中起作用。在胶原凝胶培养中，状态听神经节似乎与对照胚胎在耳囊的位置相同，但神经突起是从整个状态听神经节长出的，但在对照胚胎中，状态听神经节的轴突在有限的路径上可见。

To investigate the mechanism of otic development increase of cell number and changes of the distributional pattern of microfilaments during otic development were examined in in vivo and cultured rat embryos (Sprague-Dawley strain). Embryos (9.5 days of gestation) were cultured for 48 hours in rat serum that contained cytochalasin D (2 X 10^<-8>M) or 5-bromo-2'-deoxyuridin (BrdU,1.6 X 10^<-4>M), in which malformed otocysts were observed. Otic development was also analyzed by using a collagen gel culture.The otic placode develops into the otocyst within 24 hours from day 10.5 of gestation. The otic placode, the otic pit, and the otocyst were constituted by 700,2800, and 6000 cells respectively. The results of this experiments indicated that increse of cell number may not play roles but microfilaments may play roles on formation of the otocyst and migration of statoacoustic ganglion cells. Statoacoustic ganglia were formed from the cells which were emigrated from the neural crest and the lateral part of the neural tube in the rhombencephalon, the otic crest, and the dorso-lateral portion of the otic placode.In the collagen gel culture, statoacoustic ganglia seemed to be formed in the same position at the otocyst as in control embryos, but neurites outgrew from the entire statoacoustic ganglion, although the axon of the statoacoustic ganglion was seen in the restricted route in control embryos.