Trophic support of the developing cochleovestibular ganglion by its peripheral target in vitro does not depend on neuronal cell division.
A trophic effect on the development of the cochleovestibular ganglion in the presence of its synaptic target tissue, the embryonic otocyst, has been shown in organ cultures. The basis for this trophic effect could be increased neuronal proliferation or enhanced postmitotic survival and differentiation. In order to determine if the trophic effect influenced neuronal proliferation, organ cultures of combined otocyst and cochleovestibular ganglion (embryonic stages 23-24) were grown 14 days in vitro in the continuous presence of [3H]thymidine. Serial sections of the explants made at each stage were assayed for autoradiographic labeling of cell nuclei and for numbers of cochleovestibular ganglion neurons. Explants were well developed morphologically and contained numbers of ganglionic neurons within the same range as previously reported. Many other well differentiated cell types were also present, including hair cells, supporting cells, other epithelial cells, cartilage, connective tissue, and perineuronal satellite cells. All of these non-neuronal cell types had undergone DNA synthesis in vitro, as evidenced by their heavily labeled nuclei. The cochleovestibular ganglion neurons were the only cell type with unlabeled nuclei, indicating that they had not divided or synthesized DNA during the two-week incubation. Thus all of the identifiable cochleovestibular ganglion neurons must have become postmitotic in the explants. Since ganglion cell division is still occurring in situ when the neurons are explanted, neuroblasts either failed to divide or failed to produce neuronal progeny in the culture conditions used. Therefore, the dependence of the cochleovestibular ganglion neurons on their normal target tissues most likely reflects a trophic effect on their postmitotic survival and differentiation.
Hauger
S H
SH
Department of Anatomy, University of Connecticut Health Center, Farmington 06032.
Book
K J
KJ
Morest
D K
DK
D000818:Animals; D002454:Cell Differentiation; D002455:Cell Division; D002642:Chick Embryo; D003051:Cochlea / Q000166:cytology*; D009924:Organ Culture Techniques; D013136:Spiral Ganglion / Q000166:cytology* / Q000502:physiology; D013936:Thymidine; D014725:Vestibular Nerve / Q000166:cytology* / Q000502:physiology
D013936:Thymidine