3,3',5-TRIIODOTHYRONINE (T-3) UPTAKE AND EXPRESSION OF THYROID-HORMONE RECEPTORS DURING THE ADAPTATION TO HYPOTHYROIDISM OF THE BRAIN OF CHICKEN

Thyroid hormone action in the brain is strictly regulated, since these hormones play a crucial role in the development and physiological fun ctioning of the central nervous system. Hormone kinetics and molecular events at the nuclear receptor level during the adaptation of the bra in of chicken to hypothyroidism were simultaneously investigated. Data obtained by Oldendorff's 'single-pass' technique showed a significant ly higher labelled 3,3',5-triiodothyronine (I-125-T-3) uptake into the brain of surgically thyroidectomized (TX) 2-week-old broilers after 1 week of the surgery in comparison to sham-operated (SH) and T-3 suppl emented (TX + T-3) controls in the 10th second after the bolus injecti on. Telencephalons showed the highest, while cerebellum the lowest upt ake intensity in all groups. In a similar arrangement of experiments t he expression of the TR alpha- and TR beta nuclear thyroid receptors i n the telencephalon of TX and control chickens was investigated by a s emiquantitative RT-PCR study in the following way: cDNAs were standard ised using a quantitative RT-PCR-based approach for beta-actin, then a mplified for thyroid receptors. The level of both the TR alpha and TR beta coding mRNA was elevated in hypothyroidism. In conclusion, the pr esented hormone kinetics and TR expression data provide further detail s of the cellular and molecular events occurring during the adaptation to hypothyroidism of the brain of chicken.