Thyroid hormone determines the startof the sensitive period of imprintingand primes later learning

摘要

Filial imprinting in precocial birds is the process of forming a social attachment during a sensitiveor critical period, restricted to the first few days after hatching. Imprinting is considered to bepart of early learning to aid the survival of juveniles by securing maternal care. Here we showthat the thyroid hormone 3,5,3′-triiodothyronine (T3) determines the start of the sensitiveperiod. Imprinting training in chicks causes rapid inflow of T3, converted from circulatingplasma thyroxine by Dio2, type 2 iodothyronine deiodinase, in brain vascular endothelial cells.The T3thus initiates and extends the sensitive period to last more than 1 week via non-genomicmechanisms and primes subsequent learning. Even in non-imprinted chicks whose sensitiveperiod has ended, exogenous T3enables imprinting. our findings indicate that T3determinesthe start of the sensitive period for imprinting and has a critical role in later learning.