Muhlenberg college

Neurulation is the primary embryological event that defines all vertebrates; the process begins with a flat sheet of epidermis-like cells, called the neural plate, that folds into a tube.  This tube becomes the future brain and spinal cord. The tube is also called the neural tube and it runs from the anterior to posterior end of the embryo. Initially, the tube has two edges, called neural folds, which gradually move towards one another at the midline. There are numerous ways in which the neural folds fuse, depending on which animal you consider, but in the axolotl the fusion occurs first in the middle of the future back, then at the ends of the tube.  The two temporary open ends are called the anterior neuropore and posterior neuropore. 

In this video you will see all of these basic structures of neurulation, from the earliest evidence of neural plate formation to the final closure of the neuropores.  You can even see the early blocks of mesoderm, called somites, coalescing next to the complete neural tube!  It took 15 hours, one image recorded per minute, to create this video.

How the video was made
Axolotls (Ambystoma mexicanum) are amphibians, similar to salamanders, and native to Mexico. Their embryos are easy to maintain in the lab and very clearly illustrate all the steps of neurulation.  We received our embryos (in stage 8 or 9) from the Axolotl Colony at the University of Kentucky and when they reached stage 14, we prepared one healthy embryo for video recording by first removing the jelly coats.  The bottom of a glass dish was covered with a half inch-thick layer of 2% agarose and then filled with 10% Holtfreter’s solution.  The embryo was placed in an agarose “well,” the same diameter of the embryo, which was made with the tip of a 3ml dropping pipette; the well held the embryo in place during the filming.  Parafilm covered the entire dish, except for a small hole that was aligned above the embryo.   The camera was attached to the Nikon dissecting microscope and a laptop computer.  The dish was placed on the stage and lit with two fiber optic flexible lights, which were adjusted so there was little or no glare on the embryo.  Motic software captured an image every minute for 15 hours at room temperature.  JPG Video from snapfiles.com was used to compile the images and create the video.