1 2 3 4 5 6 7 8 9 10

The effects of ethanol at different treatment times

Only 2 of the 6 51-hour and 7 of the 15 27-hour treated eggs survived, suggesting that ethanol at 15% can cause sufficient disruptions in the Shh signaling pathway or elsewhere in the embryo such that development is terminated. Other mechanisms such as alcohol competition with retinol to bind with Class IV alcohol dehydrogenase (ADH), which leads to retinoic acid deficiency and and craniofacial defects, may also be a factor in the termination of embryos (Chen and Sulik, 1996; Deltour et al., 1996).

However, only 3 of the 5 51-hour and 1 of 8 27-hour control eggs also survived, suggesting that ethanol may not have been the cause of death. The malformations were consistent with the previous findings in this survey, and we conclude that effects on beak length and head diameter are in fact due to ethanol. When injecting the eggs, there was no consideration as to where the blastodisc may be located, leading to the hypothesis that perhaps needles were inserted directly into the blastodisc, disrupting and terminating development.

Within the set of harvested embryos there were notable differences in mass between the control and treated embryos in mass, head diameter, and beak length, consistent with Lawrence and Yoder's data (Figure 1, Figure 2, Figure 3, Table 3, Table 4). The presence of embryos with severe malformations including missing beaks suggests that ethanol does have a teratogenic effect, especially in the craniofacial region (Figure 8).

Neutral Red vital dye staining revealed that NCC death occured to varying degrees when ethanol was injected at different times during development. Since chick development occurs in an anterior to posterior fashion, the most posterior cells are less mature than those in the anterior region. Early exposure to alcohol results in cell death in the head region, whereas later exposure would affect more caudal regions (Smith, 1997). Thus, the older embryo showed little to no apoptosis in the craniofacial region but some apoptosis in the more posterior regions in the spine (Figure 9). The embryo injected with 15% ethanol at 27 hours exhibited much staining in the craniofacial region, most prominently in the midbrain and down the spine (Figure 8). The control embryo displayed no staining (Figure 10).

Trunk NCC are precursors for the peripheral nervous system, ganglia, and glial cells. They are determined relatively late in migration and thus are multipotent and can compensate for some cell death. Alcohol did not seem to affect these cells and their future structures to the same degree as the cranial structures. In contrast, the cranial NCC are determined at emigration and there seems to be a critical window of 18-36 hours of incubation where these cells are most sensitive to alcohol (Smith, 1997). Our embryos treated at 27 hours fit into this critical window and we see much neural crest apoptosis (Figure 8).

Distinctive facial features characterize FAS in humans and individuals exhibit neurodevelopmental deficits (Smith, 1997). Understanding mechanisms involved in FAS may help to control or limit alcohol-induced damage to the fetus, as well as propose methods to prevent or repair damage done to the prain and central nervous system later in life, an issue of great public health importance.

Embryonic viability.

Eggs which were discarded were not counted due to a lack of viability or a lethal fungal infection (data not shown). Due to the fact that we could not control for these situations, ten data points are not present for each treatment group. Furthermore, future studies should investigate whether higher doses of ethanol cause embryonic death in which the effects are not acute.

©Cebra-Thomas, 2000

Last Modified: 10 May 2004

[Lab Protocols | Students | Cebra-Thomas | Course | Links ]