Thyroid hormone (TH) is critical for many aspects of neurodevelopment and can be disrupted by a variety of environmental contaminants. Sensory systems, including audition and vision are vulnerable to TH insufficiencies, but little data are available on visual system development at less than severe levels of TH deprivation. The goal of the current experiments was to explore dose-response relations between graded levels of TH insufficiency during development and the visual function of adult offspring. Pregnant Long Evans rats received 0 or 3 ppm (Experiment 1), or 0, 1, 2, or 3 ppm (Experiment 2) of propylthiouracil (PTU), an inhibitor of thyroid hormone synthesis, in drinking water from gestation day (GD) 6 to postnatal day (PN) 21. Treatment with PTU caused dose-related reductions of serum T4, with recovery on termination of exposure, and euthyroidism by the time of visual function testing. Tests of retinal (electroretinograms; ERGs) and visual cortex (visual evoked potentials; VEPs) function were assessed in adult offspring. Dark-adapted ERG a-waves, reflecting rod photoreceptors, were increased in amplitude by PTU. Light-adapted green flicker ERGs, reflecting M-cone photoreceptors, were reduced by PTU exposure. UV-flicker ERGs, reflection S-cones, were not altered. Pattern-elicited VEPs were significantly reduced by 2 and 3 ppm PTU across a range of stimulus contrast values. The slope of VEP amplitude-log contrast functions was reduced by PTU, suggesting impaired visual contrast gain. Visual contrast gain primarily reflects function of visual cortex, and is responsible for adjusting sensitivity of perceptual mechanisms in response to changing visual scenes. The results indicate that moderate levels of pre-and post-natal TH insufficiency led to alterations in visual function of adult rats, including both retinal and visual cortex sites of dysfunction.

甲状腺激素（TH）对于神经发育的许多方面至关重要，并且会被多种环境污染物破坏。包括听觉和视觉在内的感觉系统很容易受到TH不足的影响，但是在视觉系统发展程度低于严重TH剥夺水平的情况下，几乎没有可用的数据。当前实验的目的是探讨发育过程中TH功能不全的分级水平与成年后代的视觉功能之间的剂量反应关系。怀孕的Long Evans大鼠在妊娠日（GD）的饮用水中接受了0或3 ppm（实验1）或0、1、2或3 ppm（实验2）的丙基硫氧嘧啶（PTU）（一种甲状腺激素合成抑制剂）。在出生后第6天到第21天（PN）。用PTU进行治疗可引起剂量相关的血清T4降低，并在接触终止后恢复，视功能检查时甲状腺功能正常。在成年后代中评估了视网膜（视网膜电图； ​​ERG）和视觉皮层（视觉诱发电位； VEP）的功能。通过PTU增加了暗适应的ERG a波，它反射了棒状光感受器。反射M锥感光体的，适应光的绿色闪烁ERG通过PTU暴露而减少。紫外线闪烁的ERG，反射S锥未发生变化。在各种刺激对比值范围内，模式引起的VEP分别降低了2 ppm和3 ppm PTU。PTU降低了VEP振幅-对数对比函数的斜率，表明视觉对比增益受损。视觉对比增益主要反映视觉皮层的功能，并负责响应于变化的视觉场景而调整感知机制的灵敏度。