Over the past decade or two, scientists have been trying to study the effects of PTU on fish. Studies on amphibians and mammalians have been much more popular during the course of this time period. Mentioned in one of the excerpts, researchers have been able to figure out that low thyroid hormone levels prior to the development of the hypothalamus-pituitary-thyroid (HPT) axis leads to brain damage and impairments in humans and rodents. Due to the fact that the HPT axis does not form right away in zebrafish offspring, the levels of thyroid hormone comes directly from the maternal egg yolk. After about 60-72 hours post fertilization, the HPT axis is formed and the zebrafish can now produce their own thyroid hormones. Altering thyroid hormone levels is one of the major factors involved in neuronal and oligodendrocyte balance in the development of the zebrafish brain.
Comments
Remove
Removing the second sentence would keep the flow of ideas on the same path instead of branching off to 'popularized' studies.
a bit vague
I think that in scientific writing as you are trying to do here, starting with over a decade or two is a bit vague as a lot of technological advances can happen during that time. I would be a bit more specific about the time. Also, the first sentence does not seem to add anything to the paragraph it might be best to be removed entirely. Otherwise, it's really well written.
tautology
"Studies on amphibians and mammalians have been much more popular during the course of this time period." "The courses of" is repetitive and creates a tautology. The same information is being repeated twice, removing it would make the sentence more precise.