FIGURE 1.

Dissection of intact spinal cords (SCs) from HH22 chicken embryos. (a) HH22 embryos were pinned down with the dorsal side down in a silicon‐coated Petri dish in sterile, cold PBS. Internal organs were removed by first cutting the ventral skin along the dashed lines and pinching out the organs with forceps. (b) Then, a laminectomy was performed, that is, the ventral vertebrae were cut along the caudal–rostral axis at the level of the outer SC boundaries and the stripe of bone structure was removed with forceps. (c) The ventral roots exiting the ventral part of the SC and the peripheral processes of the dorsal root ganglia (DRG) were cut in parallel to the SC without cutting off any DRG. (d) The SC was then cut at the level of the wings and legs. (e) The SC with attached DRG was carefully separated from the rest of the embryo with forceps. Here, special care should be given not to bend the SC by stabilizing the tissue with a second forceps. (f) At this point, the dorsal skin and dermomyotome (black arrows) were removed by first inducing an opening with forceps (white asterisk) taking care not to damage the dorsal SC. Then, using forceps, the dorsal skin and dermomyotome were carefully removed all along the caudal–rostral axis. After this step, the dorsal SC should look as clean as the ventral SC with clearly visible midline and no remaining tissues attached (compare dorsal and ventral view). (g) Finally, the intact SC with attached DRG could be embedded as straight as possible in a drop of low‐melting agarose‐medium mix with the ventral side down. White dashed lines indicate where cuts with small spring scissors should be made