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DEVELOPMENTAL THYROID HORMONE INSUFFICIENCY ALTERS THE AMPLITUDE OF THE ACOUSTIC STARTLE RESPONSE IN RATS
Citation:
Hasegawa, M., A. F. JOHNSTONE, J. M. HEDGE, M. E. GILBERT, AND K. M. CROFTON. DEVELOPMENTAL THYROID HORMONE INSUFFICIENCY ALTERS THE AMPLITUDE OF THE ACOUSTIC STARTLE RESPONSE IN RATS. Presented at International Neurotoxicology Association Annual meeting, Xian, CHINA, June 05 - 10, 2011.
Impact/Purpose:
The results also indicate that even modest TH insufficiency can cause permanent changes of the startle amplitude.
Description:
Purpose: The thyroid hormone (TH) system is one of the targets of endocrine disrupting chemicals. Since TH is essential for proper brain development, disruption by exposure to chemicals during development can result in adverse neurological outcomes. Previous studies revealed that severe transient TH insufficiency adversely affected neurobehavioral development. However, information on the influence of intermediate severities of TH insufficiency on neurobehavioral development is limited. Therefore, the present study examined the effects of transient TH insufficiency with different severities on the acoustic startle response in rats. Methods: Pregnant Long Evans rats were treated with the anti-thyroid drug, propylthiouracil (PTU) at concentrations of 0, 1, 2, 3 or 10 ppm via the drinking water on gestational day 6 to postnatal day (PND) 21. On PND 14, sera were collected from offspring in each group. Radioimmunassays were used to determine serum total T4, total T3, and TSH. Adult male and female offspring (PND 116-133) were assessed for changes in the acoustic startle response. Results: PTU exposure decreased serum T4 and increased TSH in all treated groups. The amount of T3 was significantly lower only in the 10 ppm group.The acoustic startle amplitude of the 2 and 3 ppm groups for males, and the 1, 2 and 3 ppm groups for females were significantly higher than that of the 0 ppm group. The amplitude of the 10 ppm group did not differ from that of the 0 ppm group in both males and females. Conclusions: The present study revealed that the acoustic startle amplitude was altered in the Ushaped manner as a function of the severity of the TH insufficiency in both male and female rats. The results also indicate that even modest TH insufficiency can cause permanent changes of the startle amplitude. This study was supported by Excellent Young Researcher Overseas Visit Program of Japan Society for the Promotion of Science. This abstract does not necessarily reflect the policy of the US EPA.