Thyroid Hormone Acts Locally to Increase Neurogenesis, Neuronal Differentiation, and Dendritic Arbor Elaboration in the Tadpole Visual System.

Abstract

Thyroid hormone (TH) is a critical regulator of perinatal brain development in vertebrates. Abnormal TH signaling in early pregnancy is associated with significant cognitive deficits in humans; however, it is difficult to probe the function of TH in early brain development in mammals because of the inaccessibility of the fetal brain in the uterine environment and the challenge of disambiguating maternal versus fetal contributions of TH. The external development of tadpoles allows manipulation and direct observation of the molecular and cellular mechanisms underlying TH's effects on brain development in ways not possible in mammals. We find that endogenous TH locally regulates neurogenesis at developmental stages relevant to circuit assembly by affecting neural progenitor cell proliferation and differentiation and by acting on neurons to enhance dendritic arbor elaboration.