Sakamoto H, Ukena K, Tsutsui K
Laboratory of Brain Science, Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521, Japan.
J Neurosci. 2001 Aug 15;21(16):6221-32. doi: 10.1523/JNEUROSCI.21-16-06221.2001.
De novo steroidogenesis from cholesterol is a conserved property of vertebrate brains, and such steroids synthesized de novo in the brain are called neurosteroids. The identification of neurosteroidogenic cells is essential to the understanding of the physiological role of neurosteroids in the brain. We have demonstrated recently that neuronal neurosteroidogenesis occurs in the brain and indicated that the Purkinje cell actively synthesizes several neurosteroids de novo from cholesterol in vertebrates. Interestingly, in the rat, this neuron actively synthesizes progesterone de novo from cholesterol only during neonatal life, when cerebellar cortical formation occurs most markedly. Therefore, in this study, the possible organizing actions of progesterone during cerebellar development have been examined. In vitro studies using cerebellar slice cultures from newborn rats showed that progesterone promotes dose-dependent dendritic outgrowth of Purkinje cells but dose not affect their somata. This effect was blocked by the anti-progestin RU 486 [mifepristone; 17beta-hydroxy-11beta-(4-methylaminophenyl)-17alpha-(1-propynyl) estra-4,9-dien-3 one-6-7]. In vivo administration of progesterone to pups further revealed an increase in the density of Purkinje spine synapses electron microscopically. In contrast to progesterone, there was no significant effect of 3alpha,5alpha-tetrahydroprogesterone, a progesterone metabolite, on Purkinje cell development. Reverse transcription-PCR-Southern and immunocytochemical analyses showed that intranuclear progesterone receptors were expressed in Purkinje cells. These results suggest that progesterone promotes both dendritic outgrowth and synaptogenesis in Purkinje cells through intranuclear receptor-mediated mechanisms during cerebellar development. Such organizing actions may contribute to the formation of the cerebellar neuronal circuit.
胆固醇从头合成类固醇是脊椎动物大脑的一个保守特性，大脑中从头合成的此类类固醇被称为神经类固醇。鉴定神经类固醇生成细胞对于理解神经类固醇在大脑中的生理作用至关重要。我们最近证明大脑中存在神经元神经类固醇生成，并指出浦肯野细胞能在脊椎动物体内从胆固醇主动从头合成多种神经类固醇。有趣的是，在大鼠中，仅在新生期（此时小脑皮质形成最为明显），这种神经元能从胆固醇主动从头合成孕酮。因此，在本研究中，我们检测了孕酮在小脑发育过程中可能的组织作用。使用新生大鼠小脑切片培养物进行的体外研究表明，孕酮能促进浦肯野细胞树突的剂量依赖性生长，但不影响其胞体。抗孕激素RU 486 [米非司酮；17β-羟基-11β-（4-甲基氨基苯基）-17α-（1-丙炔基）雌甾-4,9-二烯-3-酮-6,7]可阻断这种作用。对幼崽进行孕酮体内给药，通过电子显微镜进一步显示浦肯野棘突触密度增加。与孕酮相反，孕酮代谢产物3α,5α-四氢孕酮对浦肯野细胞发育没有显著影响。逆转录-聚合酶链反应- Southern分析和免疫细胞化学分析表明，浦肯野细胞中表达核内孕酮受体。这些结果表明，在小脑发育过程中，孕酮通过核内受体介导的机制促进浦肯野细胞的树突生长和突触形成。这种组织作用可能有助于小脑神经元回路的形成。
