ABSTRACT
The effects of cocaine and its primary metabolites, benzoylecgonine and ecgonine, on early embryogenesis were investigated in in vitro cultured chick embryos, and levels of cocaine and benzoylecgonine were measured in the embryo and in the culture medium. Neurulation was the only developmental process shown to be sensitive to cocaine. Closure of neural folds was inhibited within 4 hr of treatment of stage 6-8(-) embryos with 170-340 mug cocaine hydrochloride in 1 ml culture medium. Cocaine levels within embryos treated with 340 mug cocaine hydrochloride decreased from approximately 11 to 5 mug/embryo between 20 min and 4 hr of culture. Cocaine effects were more pronounced in continuously treated embryos.
ABSTRACT
Axons grow out along predictable routes of specific destinations. An EM study of the early development of one of the main chick wing nerves - the interosseous nerve - helps to show how they do it. The growing tip of the nerve appears frayed, consisting of nerve fibres occurring singly or in small bundles, taking slightly divergent paths. Most of these pioneer nerve fibres have the characteristic appearance of growth cones. They are not seen to advance along fibrils of the intercellular matrix (as one might expect from some tissue culture experiments), but instead are generally in close contact over their whole surface either with mesenchyme cells or with other nerve fibres. The same is true of the axons at more proximal levels of the developing nerve: they too are never naked, but always in contact either with other axons or with mesenchyme cells. Later nerve fibres follow the pioneers: their growth cones travel out in contact with the pre-existing axons, within the primitive perineurium formed by the enveloping mesenchyme cells, and most often close to the periphery of the fascicle.
