Retinoic acid treatment inhibits mitosis in the pre-existing spinal cord during tail regeneration of the axolotl larva, Ambystoma mexicanum

: During tail regeneration in the axolotl larva, Ambystoma mexicanum, retinoic acid reduced mitosis some 10-fold in the pre-existing spinal cord. This conclusion followed from comparisons of mitotic indices in the central grey matter of spinal cords, proximal to the amputation plane, of animals intracoelomically injected with (a) retinoic acid 2 days before amputation and the mitotic inhibitor, demecolcine 5 h before sacrifice; or (b) as for the latter but without retinoic acid; or (c) only the solvent for (a) and (b). Animals were sacrificed concurrently, 9 days after tail amputation. In addition, the demecolcine treatment revealed the true mitotic activity of the spinal cord of axolotl to be at least five times greater than might otherwise have been suspected.