Thyroid hormone determines the start of the sensitive period of imprinting and primes later learning

Abstract

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

Roots of a social brain: Developmental models of emerging animacy-detection mechanisms

“…Recent data suggest that, instead, the thyroid hormone T(3) is responsible for the opening of the sensitive period for the formation of the imprinting memory of an artificial object (e.g., Yamaguchi et al, 2012). Also pharmacological elevation of glutamate levels extends the imprinting period, indicating the role of glutamate receptors (Parsons and Rogers, 1997).…”

The current propagation systems and physiological studies of Japanese chum salmon

“…In the brain of sockeye salmon, the mRNA encoding the TRH precursor has been studied via in situ hybridization [28], and the expression of cDNA encoding TRH receptor subtypes has been examined [29]. Recently, it was reported that T 3 determines the onset of the sensitive period for imprinting, and that it plays a critical role in later learning in chicks Gallus gallus domesticus [30]. Although the onset of downstream migration, including smoltification, is under the complex regulation of several endocrine hormones, the brain-pituitary-thyroid (BPT) axis should have a critical role in imprinting during downstream migration.…”

“…NMDA is involved in the development of neural networks, learning, and memory in chicks [66]. Thyroid hormone determines the onset of the sensitive period for imprinting and plays a critical role in later learning [30]. A trial experiment has been conducted to improve the olfactory imprinting capability of juvenile masu salmon through the oral administration of these three bioactive substances, T 4 , DHA, and NMDA, and the subsequent evaluation of the gene expression levels of NMDA receptor essential subunit NR1 and TRHa/b genes.…”

Physiological Mechanisms of Imprinting and Homing Migration of Pacific Salmon

“…In the brain of sockeye salmon, the mRNA encoding the TRH precursor has been studied via in situ hybridization , and the expression of cDNA encoding TRH receptor subtypes has been examined (Saito et al 2011). It was reported that T3 determines the onset of the sensitive period for imprinting and that it plays a critical role in later learning in chicks (Gallus gallus domesticus) (Yamaguchi et al 2012). Although the onset of downstream migration, including smoltification, is under the complex regulation of several endocrine hormones, the BPT axis is considered to play critical roles in imprinting during downstream migration.…”