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Acquisition of acoustic startle response in relation to growth and thyroid function in rats
1Department of Developmental Genetics and Anatomy, Case Western Reserve University, Cleveland, OH 44106.
Insights
Thiourea exposure in pregnant rats impaired pup development. High doses severely impacted thyroid function, growth, and acoustic startle reflex, while lower doses affected growth but not the reflex.
Area of Science:
- Developmental toxicology
- Endocrinology
- Neurobehavioral science
Background:
- Thyroid hormones are crucial for mammalian development.
- Disruptions in thyroid function can lead to developmental deficits.
- The specific impact of thyroid disruption on neurobehavioral development requires further elucidation.
Purpose of the Study:
- To investigate the effects of maternal thiourea administration on thyroid function, body growth, and acoustic startle reflex acquisition in rat pups.
- To determine the dose-dependent effects of thiourea on developmental parameters.
Main Methods:
- Pregnant and lactating rats were administered thiourea via gavage from gestational day 18 to postnatal day 10 at high (900 mg/kg/day) and low (350 mg/kg/day) doses.
- Neonatal body weight was monitored from birth to postnatal day 14.
- Acoustic startle reflex acquisition was assessed starting on postnatal day 10.
- Serum thyroxine (T4) and thyrotropin (TSH) levels were measured on postnatal day 14.
Main Results:
- High-dose thiourea significantly inhibited pup thyroid function, depressed body growth, and retarded acoustic startle response development.
- Low-dose thiourea significantly reduced pup body growth but did not affect acoustic startle reflex acquisition.
- Pups exposed to the low dose of thiourea were functionally euthyroid, with no significant differences in free T4 and TSH compared to controls.
Conclusions:
- Thyroid hormone is essential for the development of the acoustic startle reflex.
- Retarded body growth alone, in the absence of significant thyroid hormone deficiency, does not necessarily impair the development of the acoustic startle reflex.
- These findings highlight the critical role of thyroid hormones in neurodevelopmental processes.
Abstract:
Thiourea was administered by gavage to pregnant and lactating rats from gestational day 18 until postnatal day 10, at doses of 100 or 250 mg per day (approximately 350 or 900 mg/kg/day). From the day after birth until postnatal day 14 the neonates were weighed, and beginning on postnatal day 10 acquisition of acoustic startle reflex was assessed. Serum thyroxine and thyrotropin were measured on postnatal day 14. High dose thiourea severely inhibited thyroid function in pups, significantly depressed body growth, and retarded development of the acoustic startle response. At the low dose there was a significant reduction in growth, but no effect on acquisition of acoustic startle reflex. Low dose pups appeared to be functionally euthyroid (free T4 and thyrotropin were not significantly different from control). In conjunction with other studies, these results strongly suggest that, while development of acoustic startle is dependent upon thyroid hormone, it is not readily affected by retarded body growth.