Alpha fetoprotein is present in the blood of neonatal rats. does not readily penetrate the blood-brain barrier. deactivates circulating estradiol. all of the above none of the above
The correct answer and explanation is:
Correct Answer: All of the above
Explanation:
Alpha-fetoprotein (AFP) is a glycoprotein that plays a crucial role during fetal development, particularly in rodents and humans. It is often discussed in neuroendocrinology due to its protective role in brain development, especially with respect to sex differentiation.
- “Is present in the blood of neonatal rats”
✔️ True. AFP is synthesized in large amounts by the fetal liver and yolk sac in many vertebrates, including rats. It circulates at high concentrations in the fetal and neonatal bloodstream. After birth, AFP levels decrease significantly, but it remains detectable in neonatal rats. - “Does not readily penetrate the blood-brain barrier”
✔️ True. AFP is a relatively large molecule and does not easily cross the blood-brain barrier (BBB). This property is critical because its function involves binding and sequestering maternal estrogens, especially estradiol, in the periphery to prevent these hormones from reaching and influencing the developing brain. - “Deactivates circulating estradiol”
✔️ True, in context. AFP does not chemically “deactivate” estradiol, but it binds strongly to estradiol in the fetal bloodstream, preventing it from entering the brain and masculinizing it. This binding effectively neutralizes estradiol’s action on the brain, allowing normal female brain development in genetically female fetuses. In males, the presence of testosterone (which later gets converted into estradiol in the brain via aromatase) masculinizes the brain.
Conclusion:
Since all three statements are accurate, the correct answer is “All of the above.” AFP plays a crucial role in sex-specific brain development by acting as a barrier between circulating maternal estrogens and the fetal brain, ensuring proper hormonal regulation during critical developmental windows.