Effects of colchicine on the shape of chick neuroepithelial cells during neurulation

We have analyzed the effects of colchicine on the cell shapes in chick neuroepithelium. Cell shapes were ascertained by the position of the nucleus in plastic serial sections. We tested three colchicine doses (5 X 10(-5) M, 5 X 10(-6) M, and 5 X 10(-7) M) by two experimental treatments (in ovo and in vitro). Colchicine treatment in vitro is always effective in depolymerizing microtubules of neuroepithelial cells and reduces the percentages of wedge-shaped cells in the median area of neuroepithelium. The same effect can be observed when the embryos are treated with 5 X 10(-5) M or 5 X 10(-6) M colchicine in ovo. A concentration of colchicine of 5 X 10(-7) M in ovo cannot disrupt microtubules in stage 8 and stage 10 embryos, and the percentage of wedge-shaped cells is the same as that of the untreated cells. In stage 6 embryos this colchicine dose effects the microtubules and the percentages of wedge-shaped cells. These facts are interpreted in respect to variations in microtubular resistance to microtubular-disrupting agents that are shown by the neuroepithelial cells from different developmental stages.