NEURULATION IN MECHANICALLY AND CHEMICALLY INHIBITED AMBLYSTOMA

Abstract

1. Mechanical pressure exerted at right angles to the plane of explanted medullary plates has been found to suppress neurulation in Amblystoma maculatum, but not the preliminary cellular elongation which is normally involved in that process. This elongation takes place irrespective of whether the medullary plate is in contact with ectoderm or with mesoderm on the normally free surface. 2. In Amblystoma tigrinum and A. maculatum neurulation is accompanied by mitosis, the mitotic rate rising after the neural tube has closed. Treatment with mammalian Ringer's solution at room temperature decreases the mitotic rate to about the same degree as it inhibits normal development; treatment with M/10 LiCl decreases the mitotic rate both relatively and absolutely. 3. No statistically significant difference was found in average nuclear area between normal and treated medullary plates. In normal germs, the nuclei elongate during neurulation, whereas in the treated germs they did not. 4. Glycogen and yolk begin to disappear from the normal neural tube about Stage 18. Neurulation-inhibiting chemicals retard the utilization of these substances. 5. Pigment granules appear to be passive factors in neurulation indicative of contraction at free cell surfaces. 6. No evidence of formed secretion from the neural plate was found. 7. Although inhibiting chemicals decrease the rate of elongation of the medullary plate, stretching continues even when neural folds fail to form. 8. The inhibiting action of LiCl is less effective at low temperatures, that of Ringer's is augmented. 9. It is concluded that neurulation in Amblystoma is autonomous to the medullary plate and may be aided by mitotic activity; changes in nuclear area (which may be indicative of cell hydration), intracellular inclusions, and longitudinal cell movements are not instrumental in the process.