CNS DEVELOPMENT UNDER HYPERGRAVITY : MODULATION BY TH?

描述(由申请人提供)：为了评估与空间探索相关的潜在风险，拟议的研究将评估重力变化对发展中的中枢神经系统的影响。具体地说，这些研究将探索这样一种假设，即重力变化会影响小脑发育，并且这种影响是通过改变甲状腺状态来调节的。这一假说基于以下几点：(1)暴露在微重力和超重力下的宇航员和成年动物的中枢神经系统和甲状腺状态都受到抑制；(2)甲状腺激素(TH)对中枢神经系统的正常发育至关重要；(3)受小脑控制的运动协调性在重力变化的情况下对宇航员和动物都有影响。为验证这一假设而设计的实验将利用24英尺离心机的超重力范例，因为它为研究重力变化对发育中的哺乳动物的影响提供了最具适应性的系统。根据初步发现，从妊娠到断奶期间暴露在离心机中会导致发育中的小脑改变和新生大鼠甲状腺状态的改变，我们预测：(1)在15G时观察到的小脑大小和结构的变化在较高的重力负荷下将变得更加明显；(2)在1.5G时观察到的轻度甲状腺功能减退在较高的重力负荷下将变得更加严重。超重力对新生儿小脑的影响将主要通过人脑的大小和浦肯野细胞和颗粒细胞的数量来评估；母婴和新生儿的甲状腺状况将主要通过血浆促甲状腺激素(TSH)、游离T3和T4以及新生儿在P6到P21的小脑T3和T4来评估。这些参数将在静止对照(SC)、旋转对照(RC)和超重力暴露(HG，1.5G。1.65g。(1)胚胎发育的第二阶段(GIL-P21)；(2)仅胚胎发育的第二阶段(GIL-P1)；以及(3)仅新生儿期(P1至P21)。为了检查营养不良等其他因素的可能贡献，将包括配对喂养对照，以评估母子互动的贡献，HG新生儿将被交叉养育到SC大坝。下丘脑-垂体-甲状腺(HPT)轴的状态将通过测量新生儿血清甲状腺结合蛋白(TBG，TTR)和甲状腺大小来检查。这些研究是否应该支持Thin直接参与新生儿对超重力的反应！将向水坝或幼崽提供补充剂，以试图防止重力变化的不利影响。其他分子研究，包括免疫化学、免疫组织学和基因表达分析(Northern blots、RPA和大鼠特异性cDNA微阵列，重点关注TH调节基因)将探索重力反应所涉及的分子机制(S)。这些研究将有助于理解重力变化如何影响中枢神经系统的发育，甲状腺激素在这种反应中扮演什么角色，以及这种反应是否可以通过激素治疗进行调节。

DESCRIPTION (provided by applicant): To evaluate the potential risks associated with space exploration, the proposed studies will assess the impact of altered gravity on the developing CNS. Specifically, these studies will probe the hypothesis that changes in gravity affect cerebellar development and that this effect is mediated by altered thyroid status. This hypothesis is based on the following: (1) both the CNS and thyroid status are inhibited in astronauts and in adult animals exposed to micro- and hypergravity; (2) thyroid hormone (TH) is critical for normal CNS development; and (3) motor coordination, controlled by the cerebellum, is affected in both astronauts and animals under altered gravity. The experiments designed to test this hypothesis will utilize the hypergravity paradigm of a 24-ft centrifuge, since it provides the most adaptable system for studying the effect of altered gravity on developing mammals. Based on preliminary findings suggesting that exposure to centrifugation from gestation through weaning results in changes in the developing cerebellum and altered thyroid status in rat neonates, we predict that: (1) changes in cerebellar size and structure observed at 15G will become more pronounced at higher gravitational loading; (2) the mild hypothyroidism observed at 1.5 G will become more severe at higher gravitational loading. The effect of hypergravity on neonatal cerebellum will be evaluated primarily in terms of the celebellar size and number of Purkinje and granule cells; the thyroid status of dams and neonates will be assessed primarily in terms of plasma thyroid stimulating hormone (TSH), free T3 and T4, and neonatal cerebellar T3 and T4 at P6 to P21. These parameters will be compared between stationary controls (SC), rotational controls (RC) and hypergravity-exposed (HG, 1.5G. 1.65G. and 1.75G) dams and/or pups during one of the three developmental periods: (1) the second part of embryonic development through the neonatal period (Gil to P21); (2) the second part of embryonic development only (Gil-P 1); and (3) the neonatal period only (P1 to P21). To examine the possible contribution of other factors such as malnutrition, pair-fed controls will be included to evaluate the contribution of maternal-offspring interactions, HG neonates will be cross-fostered to SC dams. The status of the hypothalamic-pituitary-thyroid (HPT) axis will be examined by measuring neonatal serum thyroid-binding proteins (TBG, TTR) and thyroid size. Should these studies support the direct involvement of THin the neonatal response to hypergravity, a TI! supplement will be given to dams or pups to attempt to prevent the adverse effects of altered gravity. Additional molecular studies, including immuno-chemical immunohistological, and gene expression analyses (northern blots, RPA, and rat-specific cDNA arrays, focusing on TH-regulated genes) will probe the molecular mechanism(s) involved in gravity response. These studies will aid in developing an understanding of how altered gravity affects CNS development, what role the thyroid hormone plays in that response, and whether this response can be modulated by hormonal therapy.