Distribution of glycogen in the floor plate of the chick spinal cord during development.

The present study was undertaken to characterize the structural changes and the glycogen distribution in the floor plate of the developing chick spinal cord. The floor plate consisted of ventricular zone by stage 19 (staged according to Hamburger and Hamilton, 1951). The marginal zone of this plate could be distinguished as a narrow border at stage 21. It increased progressively in thickness and was the same thickness as the ventricular zone at stage 26. It increased again in thickness from stage 38 onward. Glycogen appeared and subsequently disappeared in the floor plate of the chick spinal cord during development. Little, if any, glycogen appeared in the midportion of the floor plate at stage 19. The floor plate was weakly glycogen positive from the cervical through lumbosacral segments at stage 21. In the floor plate of the lumbosacral enlargement the glycogen staining was the highest and was maximal through stages 34-37. The floor plate of the cervical and thoracic segments except for the cervical enlargement continue to have low concentrations of glycogen. The glycogen staining of the floor plate began to decrease from stage 38, and at the same time neuroglial cells began to migrate into the marginal zone of the floor plate, later than in other regions of the cord. The glycogen staining in the floor plate was barely detectable at stage 40. The accumulation of the glycogen granules in the floor plate was found only in the radial glial cells.