A comparison of thyroid function in DBA/2J and C57BL/6J mice.

Area of Science:

• Neuroendocrinology
• Comparative Physiology

Background:

• DBA/2J mice exhibit audiogenic seizure susceptibility (AGSS) and lower electroshock seizure thresholds than C57BL/6J mice.
• Thyroid hormones play a crucial role in neurological function and development.

Purpose of the Study:

• To compare thyroid function between DBA/2J and C57BL/6J mice.
• To investigate the relationship between thyroid function and AGSS in DBA/2J mice.

Main Methods:

• Assessed thyroid function parameters including thyroxine (T4), 3,5,3'-triiodothyronine (T3), thyrotropin (TSH) concentrations, T4/T3 ratio, and iodide uptake.
• Compared these parameters between DBA/2J and C57BL/6J mice across different ages.
• Correlated thyroid hormone levels with seizure severity in DBA/2J mice.

Main Results:

• DBA/2J mice demonstrated increased iodide uptake and thyroid weight, indicative of enhanced TSH activity.
• Elevated T4 and TSH concentrations with a high T4/T3 ratio were observed in DBA/2J mice, particularly between 20-40 days of age.
• Seizure-prone DBA/2J mice exhibited thyroid hormone profiles similar to younger DBA/2J mice, while less susceptible mice resembled older DBA/2J mice.

Conclusions:

• Enhanced TSH secretion, driven by adaptations to age and AGSS, underlies the increased thyroid activity in DBA/2J mice.
• Decreased conversion of T4 to T3 by 3,3,5'-monodeiodinase in the brain leads to elevated TSH due to reduced negative feedback.
• Maturation of Type I 5'-deiodinase by 40 days contrasts with persistently subnormal brain deiodinase activity in DBA/2J mice.