Kerr J E, Allore R J, Beck S G, Handa R J
Department of Pharmacology and Experimental Therapeutics, Loyola University Chicago, Stritch School of Medicine, Maywood, Illinois 60153, USA.
Endocrinology. 1995 Aug;136(8):3213-21. doi: 10.1210/endo.136.8.7628354.
The actions of androgens in both peripheral and central tissues are linked in part to their ability to specifically bind and activate androgen receptors (ARs). ARs have been well studied in the rat hypothalamus and peripheral reproductive tissues, where they are directly involved in endocrine feedback mechanisms and reproduction. Previous studies revealed relatively high levels of AR and AR messenger RNA (mRNA) in the rat hippocampus; however, the action of androgen in this brain region remains unclear. To begin to address this issue, we used a multidisciplinary approach to quantitate hippocampal AR and AR mRNA levels and investigate their regulation after various hormonal manipulations. In vitro binding assays revealed a single, saturable, high affinity binding site for androgen in hippocampal cytosols. The expression of AR mRNA in the intact adult male rat hypothalamus and hippocampus was demonstrated using reverse transcription-polymerase chain reaction and quantified using a ribonuclease protection assay. Comparable levels of AR mRNA were found in the hippocampus and hypothalamus. In addition, in situ hybridization analysis revealed a unique distribution of AR mRNA in the hippocampus. AR mRNA was found predominately in the CA1 pyramidal cells, which form the major signal output of the hippocampal trisynaptic circuit. Reverse transcription-polymerase chain reaction of total RNA from microdissected hippocampal regions confirmed this distribution. Ribonuclease protection assay demonstrated a significant decrease in the AR mRNA content of the hippocampus in animals killed 4 days after castration or in intact rats after four daily injections of the AR antagonist, flutamide (15 mg/animal), compared to that in intact controls (P < 0.01). In contrast, a 35% increase (P < 0.05) in the hippocampal AR mRNA content was found in old (22-month-old) compared to young (5-month-old) male rats. In both cases, [3H]dihydrotestosterone binding to the cytosolic preparation did not parallel the changes observed in the AR mRNA content. Taken together, these data demonstrate that hippocampal cells containing AR can respond to circulating androgen to alter AR gene expression. Furthermore, AR mRNA autoregulation appears to be both age and tissue specific and does not directly follow the regulatory patterns described for other steroid hormone receptors found in the hippocampus.
雄激素在外周组织和中枢组织中的作用，部分与其特异性结合并激活雄激素受体（ARs）的能力相关。ARs在大鼠下丘脑和外周生殖组织中已得到充分研究，它们直接参与内分泌反馈机制和生殖过程。先前的研究表明，大鼠海马体中AR和AR信使核糖核酸（mRNA）水平相对较高；然而，雄激素在该脑区的作用仍不清楚。为了开始解决这个问题，我们采用多学科方法来定量海马体中AR和AR mRNA水平，并研究各种激素处理后它们的调节情况。体外结合试验揭示了海马体胞质溶胶中存在一个单一的、可饱和的、高亲和力的雄激素结合位点。使用逆转录-聚合酶链反应在完整成年雄性大鼠下丘脑和海马体中证实了AR mRNA的表达，并使用核糖核酸酶保护试验进行定量。在海马体和下丘脑中发现了相当水平的AR mRNA。此外，原位杂交分析揭示了AR mRNA在海马体中的独特分布。AR mRNA主要存在于CA1锥体细胞中，这些细胞构成海马体三突触回路的主要信号输出。对显微切割的海马体区域的总RNA进行逆转录-聚合酶链反应证实了这种分布。核糖核酸酶保护试验表明，与完整对照组相比，去势4天后处死的动物或完整大鼠每日注射4次AR拮抗剂氟他胺（15毫克/只动物）后，海马体中AR mRNA含量显著降低（P < 0.01）。相比之下，与年轻（5个月大）雄性大鼠相比，老年（22个月大）雄性大鼠海马体中AR mRNA含量增加了35%（P < 0.05）。在这两种情况下，[3H]二氢睾酮与胞质制剂的结合情况与AR mRNA含量的变化并不平行。综上所述，这些数据表明，含有AR的海马体细胞可以对循环中的雄激素作出反应，从而改变AR基因表达。此外，AR mRNA的自身调节似乎具有年龄和组织特异性，并不直接遵循海马体中发现的其他类固醇激素受体的调节模式。
