Pinna G, Uzunova V, Matsumoto K, Puia G, Mienville J M, Costa E, Guidotti A
Department of Radiology and Nuclear Medicine, Universitatsklinikum, Benjamin Franklin Free University of Berlin, Germany.
Neuropharmacology. 2000 Jan 28;39(3):440-8. doi: 10.1016/s0028-3908(99)00149-5.
Allopregnanolone (ALLO), a potent positive-allosteric modulator of the action of GABA at GABA(A) receptors, is synthesized in the brain from progesterone by the sequential action of two enzymes: 5alpha-reductase and 3alpha-hydroxysteroidoxidoreductase. The concentration of ALLO in various parts of the mouse brain varies substantially, from 15 pmol/g in the olfactory bulb, to approximately 6 pmol/g in the frontoparietal cortex, and 2.7 pmol/g in the cerebellum. The systemic administration of 48 micromol/kg of the Type I and Type II 5alpha-reductase inhibitor, (17beta)-17-[bis (1-methylethyl) amino carbonyl)] androsta-3, 5-diene-3-carboxylic acid (SKF 105,111), reduced brain ALLO content by 80-90% in 30 min; the rate constant (k) of ALLO decrease in each brain area can be utilized to establish the rate of ALLO biosynthesis, which is higher in the olfactory bulb (62 pmol/g/h) than in the frontoparietal cortex (24 pmol/g/h) or cerebellum (11 pmol/g/h). The duration of the righting reflex loss elicited by the potent GABA(A) receptor agonist muscimol was reduced in SKF 105,111-treated ALLO-depleted mice. SKF 105,111 treatment had no effect on muscimol metabolism or on brain levels of pregnenolone and progesterone; however, the brain levels of 5alpha-DHP, the precursor of ALLO, were also decreased. Administration of ALLO at a dose of 15 micromol/kg i.p. by itself did not alter the muscimol-induced loss of the righting reflex; but it completely blocked the effect of SKF 105,111. To elucidate the possible molecular mechanism by which a decrease of brain ALLO content can shorten the duration of the righting reflex loss elicited by muscimol, we patch-clamped neocortical pyramidal neurons of mice pretreated with SKF 105,111 or vehicle, and studied the efficiency of muscimol in eliciting Cl- currents. The current amplitude was significantly smaller in neurons from SKF 105,111-treated mice, especially at lower doses (0.1-1 microM) of muscimol, and the muscimol dose-response (0.1-10 microM) relationship displayed cooperativity (nH=1.4). These data suggest that ALLO synthesized in brain plays an important physiological permissive role in the modulation of GABA-gated Cl- channel function.
别孕烯醇酮（ALLO）是γ-氨基丁酸（GABA）作用于GABA(A)受体的一种强效正变构调节剂，它在大脑中由孕酮通过两种酶的顺序作用合成：5α-还原酶和3α-羟基类固醇氧化还原酶。小鼠大脑各部位的ALLO浓度差异很大，嗅球中为15 pmol/g，额顶叶皮质中约为6 pmol/g，小脑中为2.7 pmol/g。全身给予48 μmol/kg的I型和II型5α-还原酶抑制剂（17β）-17-[双（1-甲基乙基）氨基羰基]雄甾-3,5-二烯-3-羧酸（SKF 105,111），30分钟内可使大脑ALLO含量降低80-90%；每个脑区ALLO降低的速率常数（k）可用于确定ALLO的生物合成速率，嗅球中的速率（62 pmol/g/h）高于额顶叶皮质（24 pmol/g/h）或小脑（11 pmol/g/h）。在SKF 105,111处理的ALLO耗竭小鼠中，强效GABA(A)受体激动剂蝇蕈醇引起的翻正反射丧失持续时间缩短。SKF 105,111处理对蝇蕈醇代谢或大脑中孕烯醇酮和孕酮水平没有影响；然而，ALLO的前体5α-二氢孕酮的大脑水平也降低了。腹腔注射15 μmol/kg的ALLO本身不会改变蝇蕈醇引起的翻正反射丧失；但它完全阻断了SKF 105,111的作用。为了阐明大脑中ALLO含量降低可缩短蝇蕈醇引起的翻正反射丧失持续时间的可能分子机制，我们对用SKF 105,111或溶剂预处理的小鼠新皮质锥体神经元进行膜片钳记录，并研究蝇蕈醇引发Cl-电流的效率。来自SKF 105,111处理小鼠的神经元中的电流幅度明显较小，尤其是在较低剂量（0.1-1 μM）的蝇蕈醇时，并且蝇蕈醇剂量-反应（0.1-10 μM）关系显示出协同性（nH = 1.4）。这些数据表明，大脑中合成的ALLO在调节GABA门控Cl-通道功能中起重要的生理允许作用。
