Proefschrift--Groningen.

This investigation considered the differentiation tendencies of specific anterior-posterior regions of the neural plate in an attempt to establish the regional differentiation capacity for Ambystoma gracile neuroepithelium. Presumptive neural tissues (hindbrain and trunk spinal-cord) were isolated from the embryo at the time of primary induction (stage 11) to post-neurulation (stage 19) and cultured in vitro alone or with combinations of axial mesoderm (notochord and somite). Prior to primary induction (stage 11), the isolated presumptive neuroepithelium formed only atypical epidermis. Immediately subsequent to this induction (stage 11) both regions (hindbrain and trunk cord) demonstrated unorganized neural histogenesis, while the formation of organized neural tissue appeared later (stage 12-14 isolates). By stage 15-16, the histogenesis of the isolated hindbrain resembled that of the control, whereas the isolated trunk cord only formed a neural tube. The presence of somite tissue enhanced hindbrain differentiation considerably; notochord was effective to a limited extent. The combined effect of both tissues on neurogenesis was greater than with somite alone. The addition of notochord to trunk spinal-cord enhanced histogenesis to a greater extent than either somite alone or the combination of notochord and somite. The trunk neural tissue, whether alone or in combination with mesoderm, never demonstrated normal spinal-cord morphology and seemed to develop independently of the tissue environment during the late neurula stages (16-19). The presence of inherent differentiation tendencies within the hindbrain and the trunk spinal-cord, as well as the possible role of the mesodermal tissue in conditioning the neural tissue microenvironment with metabolic precursors, is discussed. / Science, Faculty of / Zoology, Department of / Graduate