PHOTOCHEMICAL SPECTRAL ANALYSIS OF NEURAL TUBE FORMATION

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Abstract
Chick embryos ranging in age from the primitive streak to the 8 somite stage were irradiated with monochromatic u.-v. radiation of wave lengths 2483, 2537, 2576, 2650, 2699, 2804, 2894, 2967, and 3130 A. After irradiation, which was accomplished through a small opening in the egg shell, the eggs were sealed and incubated for approx. 30 hrs. Histological studies show that radiation inhibits the folding process in neural tube formation, while cell division and vol. changes continue. The number of ergs/mm.2 of radiant energy required to prevent closure of the neural tube for a distance of at least % the body length in 50% of the cases was detd. for each of the wave lengths used. After correction for absorption by the vitelline membrane, the incident energy on the embryo necessary to produce the endpoint was plotted against wave length. The curve obtained has 2 maxima which are approx. equal, one about 2800 A, the other about 2600 A. (Incident energy at these wave lengths is of the order of 71 ergs/mm.2 and 76 ergs/mm.2, respectively.) This curve corresponds approx. to the absorption curves of vit. D precursors such as ergosterol, lumisterol, and dehydrocholesterol. Since the "inactivation spectrum" for the morphogenetic process corresponds to the absorption spectrum of compounds of this type, it is probable, on photochemical grounds, that such molecules are essential in neural tube formation.

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