BACKGROUND Age-dependent alterations of hormonal states have been considered to be involved in age related decline of cognitive abilities. Most of the studies in animal models are based on hormonal substitution in adrenal- and/or gonadectomized rodents or infusion of steroid hormones in intact rats. Moreover, the manipulations have been done timely, closely related to test procedures, thus reflecting short-term hormonal mechanisms in the regulation of learning and memory. Here we studied whether more general states of steroid and thyroid hormone profiles, independent from acute experiences, may possibly reflect long-term learning capacity. A large cohort of aged (17-18 months) intact male rats were tested in a spatial hole-board learning task and a subset of inferior and superior learners was included into the analysis. Young male adult rats (16 weeks of age) were also tested. Four to 8 weeks after testing blood plasma samples were taken and hormone concentrations of a variety of steroid hormones were measured by gas chromatography-tandem mass spectrometry or radioimmunoassay (17β-estradiol, thyroid hormones). RESULTS Aged good learners were similar to young rats in the behavioral task. Aged poor learners but not good learners showed higher levels of triiodothyronine (T3) as compared to young rats. Aged good learners had higher levels of thyroid stimulating hormone (TSH) than aged poor learning and young rats. Both aged good and poor learners showed significantly reduced levels of testosterone (T), 4-androstenedione (4A), androstanediol-3α,17β (AD), dihydrotestosterone (DHT), 17-hydroxyprogesterone (17OHP), higher levels of progesterone (Prog) and similar levels of 17β-estradiol (E2) as compared to young rats. The learning, but not the memory indices of all rats were significantly and positively correlated with levels of dihydrotestosterone, androstanediol-3α,17β and thyroxine (T4), when the impacts of age and cognitive division were eliminated by partial correlation analyses. CONCLUSION The correlation of hormone concentrations of individuals with individual behavior revealed a possible specific role of these androgen and thyroid hormones in a state of general preparedness to learn.

中文翻译：

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年龄和认知状态取决于完整雄性大鼠血液中类固醇和甲状腺激素浓度的差异。

背景技术激素状态的年龄依赖性改变已被认为与年龄相关的认知能力下降有关。动物模型中的大多数研究都基于在肾上腺和/或性腺切除的啮齿动物中的激素替代或在完整大鼠中输注类固醇激素。而且，这些操作是及时进行的，与测试程序密切相关，因此反映了短期激素机制对学习和记忆的调节。在这里，我们研究了独立于急性经验的类固醇和甲状腺激素谱的更一般状态是否可能反映了长期学习能力。在空间孔板学习任务中测试了一大批年龄较大（17-18个月）的完好无损的雄性大鼠，并将一部分劣等和优等学习者纳入了分析。还测试了年轻的成年雄性大鼠（16周龄）。测试后四到八周，采集血浆样本，并通过气相色谱-串联质谱或放射免疫测定法（17β-雌二醇，甲状腺激素）测量多种类固醇激素的激素浓度。结果年龄好的​​学习者在行为任务上与幼鼠相似。与年轻大鼠相比，年龄较差的学习者而不是良好的学习者显示出更高的三碘甲状腺素（T3）水平。老年学习者的甲状腺刺激激素（TSH）水平高于老年学习者和幼鼠。不论年龄好的学习者和学习能力差的学习者，睾丸激素（T），4-雄烯二酮（4A）和雄甾烷二醇3α，17β（AD），双氢睾酮（DHT），17-羟基孕酮（17OHP）的水平均显着降低，与年轻大鼠相比，孕酮（Prog）的水平较高，而17β-雌二醇（E2）的水平相近。当通过部分相关分析消除了年龄和认知分裂的影响时，所有大鼠的学习而非记忆指数与二氢睾丸激素，雄甾烷二醇-3α，17β和甲状腺素（T4）的水平呈显着正相关。结论个体激素浓度与个体行为的相关性揭示了这些雄激素和甲状腺激素在一般的学习准备状态下可能具有特定的作用。通过部分相关分析消除了年龄和认知分裂的影响。结论个体激素浓度与个体行为的相关性揭示了这些雄激素和甲状腺激素在一般的学习准备状态下可能具有特定的作用。通过部分相关分析消除了年龄和认知分裂的影响。结论个体激素浓度与个体行为的相关性揭示了这些雄激素和甲状腺激素在一般的学习准备状态下可能具有特定的作用。