PHOTOCHEMICAL SPECTRAL ANALYSIS OF NEURAL TUBE FORMATION

¹ From the Department of Zoology, University of Missouri, Columbia, Missouri

1. Chick embryos ranging in age from the primitive streak to the 8-somite stage were irradiated with monochromatic ultraviolet radiation of wave lengths 2483 to 3130 Å and subsequently incubated for 30 hours.

2. Histological studies show that radiation inhibits the folding process in neural tube formation, while cell division and volume changes continue. This effect on the neural plate is uniform for all wave lengths except 2967 Å; nevertheless, wave length 2967 Å inhibits folding.

3. After correction for absorption by the vitelline membrane, the incident energy on the embryos required to inhibit the folding process was calculated. Folding is affected by all wave lengths except 3130 Å and photochemical efficiency curves for the folding process are presented.

4. In order to obtain information concerning the chemical nature of the material involved in folding, the photochemical efficiency curves which are an indirect measure of absorption were compared to time absorption spectra of biological compounds. The validity of this technique is based upon three fundamental assumptions which are satisfied within the limitations of the available data.

5. The photochemical efficiency curves are very similar to the absorption spectra of sterols, particularly vitamin D precursors. The small doses used in the inhibition of folding and the high sensitivity of sterols to ultraviolet light add support to the finding made with absorption measurements that sterols are involved in the folding process.