Unique and overlapping effects of triiodothyronine (T3) and thyroxine (T4) on sensory innervation of the chick cornea.

Multiple aspects of cornea development, including the innervation of the cornea by trigeminal axons, are sensitive to embryonic levels of thyroid hormone (TH). Although previous work showed that increased TH levels could enhance the rate of axonal extension within the cornea in a thyroxine (T4)-dependent manner, details underlying the stimulatory effect of TH on cornea innervation are unclear. Here, by examining the effects throughout all stages of cornea innervation of the two main THs, triiodothyronine (T3) and T4, we provide a more complete characterization of the stimulatory effects of TH on corneal nerves and begin to unravel the underlying molecular mechanisms.