Primordial morphogenesis of the stato-acoustic ganglion of the inner ear in the mouse embryo. I. Analysis of the early morphogenesis of 9-, 9 1/2- and 10-day-old embryos

Bretos, M.

Archives de Biologie 90(2): 195-224


ISSN/ISBN: 0003-9624
PMID: 95244
Accession: 068520602

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Structural and histochemical aspects of inner ear and adjacent ganglia during morphogenesis were studied in normal embryos from the 9 to the 10 day stage. Distribution of RNA, polysaccharides, alkaline and acid phosphoatases at successive developmental stages were analyzed in serial transverse sections of the otic region. Sections submitted to the Unna-Brachet method showed the morphological evolution of embryonic primordia, and of the programmed cellular death sites. Certain aspects of nerve fiber development were elucidated in sections treated for the alkaline phosphatase reaction. Acid and alkaline phosphatase tests revealed the evolution of the primitive sensory areas. Otocyst dissections provided a better understanding of the morphological changes which the primitive otic vesicle undergoes during this period. Several transitory histochemical and morphological features suggest the successive contribution of 2 different inductors in the primary morphogenesis of the normal auditory placode: the parachordal mesoderm and the rhombencephalon. Histochemical properties of the invaginating otic pit wall testify the acquisition of a double antero-posterior and dorso-ventral polarization. The presumptive sensory area for the future anterior and lateral ampullae and for the utricular macula is easily localized owing to its selective alkaline phosphatase activity. This area is the first to arise from the macula communis. The 1st primordium of the stato-acoustic ganglion arises from cells migrating from the rostro-ventral wall of the primary auditory vesicle. In this early primordium, 2 portions are found, 1 medial and 1 lateral. The latter is characterized by its alkaline phosphatase reaction and by its location dorsal to the geniculate ganglion primoridum. These 2 primitive portions do not correspond to the future vestibular and cochlear ganglia. The central sensitive nerve fibers of the ganglionic complex appear very early, before the constitution of the different ganglionic groups. Later, the motor fibers of the facial nerve become evident. Among the peripheral nerve connections, the anterior ramus fibers become visible earlier.