SPINAL CORD-NOTOCHORD RELATIONSHIP IN NORMAL HUMAN EMBRYOS AND IN A HUMAN EMBRYO WITH DOUBLE SPINAL-CORD

Spinal cord-notochord relationship was analyzed histologically and imm unohistochemically in normal human conceptuses between the 4-8 develop mental weeks and in an 8-week embryo with double spinal cord. In the e arly 4-week embryo, the gradual closure of the neural tube along the c ranio-caudal body axis was paralleled by the differentiation of the me dian hindge point cells at the ventral midline of the tube and by its temporary close association with the notochord. During the 5th-8th dev elopmental weeks, the neuroepithelium differentiating into three disti nct layers was accompanied by a solid, ventromedially positioned notoc hord. In the abnormal 8-week embryo, the additional spinal cord was lo cated ventrolaterally from the vertebral column. Both spinal cords app eared bilaterally asymmetric, with their floor and roof plates irregul arly formed. An abnormally enhanced pattern of neuroepithelial differe ntiation characterized their dorsal parts. Furthermore, additional spi nal nerves and ganglia and an abnormal bony structure were associated with the spinal cord positioned outside the vertebral column. The unde rlying vertebral bodies were misshaped and contained scattered supernu merary groups of notochord cells. Our investigation underlines the imp ortance of the notochord - neural tube relationship in the morphogenes is of the spinal cord. We suggest that the double spinal cord was indu ced by the split notochord.