Chick starvation

It is now known that there are many ways, other than direct toxicity, in which the use of a pesticide can adversely affect the population of a non-target organism. Suppose an insecticide is sprayed on a held to control a particular insect pest. The chances of any adult bird being directly sprayed are very low. More vulnerable are chicks, especially if they are fed insects that are dying from the insecticide exposure, ffowever, maybe the biggest problem will be the starvation of the insect-eating chicks, if the insecticide works well. Likewise, a herbicide that is not directly toxic to birds can remove the food source (weed seeds) from a bird population. 

The chick embryo can be cultuered in vitro at a relatively early stage of development and is nutritionally responsive. For studies of protein starvation with these embryos, a medium was sought which would... 

A preliminary series of experiments with chick embryo explants cul-tered on dextran medium suggested that all regions of the embryos were not affected to the same extent by protein starvation. In order to quantitate this response, procedures were developed which would allow the dissection of embryos into brain, neural tube, somite, heart, and extraembryonic membrane (area opaca plus area pellucida) in a reproducible manner so that the quantities of DNA, RNA, and protein in these regions could be determined. Relative to embryo explants cultured on whole egg homogenate medium, in those cultured on protein starvation medium the accumulation of macromolecules in the brain region was most restricted and the heart least. 

As an initial approach to an analysis of the basis for the differences between embryo regions in their apparent sensitivity to protein starvation the breakdown of protein was studied (Klein et al., 1971). Chick embryos of 11-13 somites were exposed to C-labeled amino acids for 3 hours in buffered chick Ringer s salt solution. Explants were next cultured for 6 hours on semi-solid medium to reduce the level of free [ C]amino acids and to allow protein labeling to increase. They were then transferred to either whole egg homogenate growth medium or protein starvation medium. Explants were cultured for various periods up to 48 hours and dissected regions were analyzed for protein radioactivity and the radioactivity soluble in 5% trichloroacetic acid. Protein and DNA contents were also determined. 

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