A Comparison of Thyroid Function in DBA/2J and C57BL/6J Mice

Abstract

DBA/2J mice exhibit audiogenic seizure susceptibility (AGSS) and lower electroshock seizure thresholds compared with C57BL/6J mice. Thyroid function, including thyroxine (T4), 3,5,3'-triiodothyronine (T3), and thyrotropin (TSH) concentrations, T4/T3 ratio, and iodide uptake, of DBA and C57 mice were compared. Thyroid function was also assessed in relation to AGSS and severity in DBA mice. DBA mice have a larger thyroidal pool of iodide due to increased iodide uptake and possibly decreased release, but not to an increased organification rate. This increased iodide uptake exists until about 40 days of age. DBA mice also have a decreased radiochloride space and increased thyroid weight, indicative of enhanced TSH activity. The DBA mice show high T4 and TSH concentrations and a high T4/T3 ratio between the ages of 20 and 40 days. Beginning at 40 days of age the DBA mice have high T4, TSH, and T3 concentrations leading to a T4/T3 ratio approximating the C57 ratio. At any age, DBA mice demonstrating clonic/tonic seizures in response to auditory stimulation have hormone concentrations similar to their 21-day-old counterparts with seizures. Mice that show decreased response to auditory stimulation have hormone concentrations similar to the older age group. The increased thyroid activity of DBA mice is the result of enhanced TSH secretion. The increased TSH production is due to adaptations corresponding to the different age and AGSS. A decreased conversion of T4 to T3 by 3,3,5'-monodeiodinase, is responsible for the increase in TSH due to loss of T3 negative feedback on the anterior pituitary gland. By 40 days of age, the Type I 5'-deiodinase matures whereas the brain deiodinase activity remains subnormal.(ABSTRACT TRUNCATED AT 250 WORDS)

T3Deficiency Prolongs Convulsions Induced by Acute Pentylenetetrazole

“…However, our data do not support the suggestion that brain T3 deficiency would increase seizure susceptibility (8), perhaps because seizures were induced by different methods.…”

“…found a positive correlation between serum 14 levels and susceptibility of DBA/2J mice to audiogenic seizures (AS); however, there is evidence suggesting that a subnormal brain deiodinase activity could produce a deficiency of 13 in the brain, but not in the rest of the body (8), leading to the proposal that the increased T4/T3 ratio is more important than 14 serum levels as a determinant of brain excitability.…”

Glial Contribution to Seizure: Carbonic Anhydrase Activity in Epileptic Mammalian Brain

“…The age-related increase in CA activity in both strains may be related only to the maturation of glial cells during that period, and the difference between the strains may be linked to their different genetic background. Differences in thyroid function between the two strains have also been shown and proposed to be at least partially responsible for the audiogenic susceptibility (Engstrom et al, 1984~;Sawitzke et al, 1988). Thyroid function is of great importance in maturation of the central nervous system (Disbrow et al, 1986), particularly glial cells.…”