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The Effects of 2-Acetylaminofluorene on the Embryonic Development of the Zebrafish^*

I. Morphological Studies

Kenichi Kenneth Hisaoka

( Department of Zoology, Rutgers University, New Brunswick, N.J.)

1. In general, 2-acetylaminofluorene (AAF) caused the retardation of both growth and differentiation of the zebrafish. The visceral organs were particularly retarded in development.

2. Embryos were most sensitive to AAF during the early cleavage stage. For example, embryos exposed to 0.03 per cent AAF during the early cleavage stage were immediately arrested in development. However, if exposures to 0.03 per cent AAF were made during the optic cup stage, development proceeded to the prehatching stage. Increased resistance to AAF was noted as later stages of development and shorter periods of exposure were used.

3. Abnormalities caused by AAF included: edema of the pericardial and coelomic areas; cardiac failure and circulatory stasis; protuberances of the yolk mass; disorganization of the brain, spinal cord, and sense organs; deformities of the trunk and tail associated with abnormalities of the somatic musculature and notochord; cellular degeneration of the liver, epidermal hyperplasia, and interference in melanin synthesis.

4. The extent or the degree of abnormality varied and was dependent upon the dosage, the duration of exposure, and the developmental stage. The earlier stages, the higher concentrations, and the longer periods of exposure to AAF contributed to greater teratogenic effects.

5. The following changes were specific to AAF action:

a) The liver, which was one of the major target organs of AAF, was characterized by the presence of degenerating cells and a diminished staining reaction. Disorganization and degeneration of the brain were also characteristic of AAF action.

b) AAF caused a specific inhibition of melanogenesis. In experiments in which the early cleavage stages were exposed to 0.03 per cent AAF, melanin synthesis was completely halted, and such embryos were characterized by a marked pallor. In addition, melanin (dermal, retinal, and pericoelomic) was destroyed when larval stages of the zebrafish were exposed to solutions of AAF ranging from 0.002 to 0.03 per cent. AAF did not affect the xanthophores.

c) Typical hyperplastic cells of the epidermis, which were induced by AAF, contained a single nucleus which was located near the cell membrane and just outside the margin of the large central vacuole. Cell types representing different stages of hyperplasia were obtained.

6. Supplemental and replacement experiments with thiouracil were unsuccessful in counteracting the effects of AAF. However, abnormalities such as edema, epidermal hyperplasia, disorganization of the central nervous system, and pigment defects were corrected if the embryos were transferred to water after short exposures to AAF. The degree of recovery was also dependent upon the concentration of AAF and the stage of development at which the embryo was exposed.

^* This investigation was aided by a grant from the Rutgers University Research Council.

Present address: Department of Biological Sciences, Loyola University, 6525 Sheridan Road, Chicago 26, Ill.

Received 11/ 5/57.

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