BIOSYNTHESIS AND ACTION OF NEUROSTEROIDS IN THE BRAIN

类固醇激素由外周类固醇生成腺提供，在发育和成年期调节神经元的功能。外周类固醇因其脂溶性而穿过血脑屏障，并通过细胞内受体介导的调节特定基因转录的机制作用于脑组织。因此，大脑被认为是外周类固醇的靶点。最近，我们通过生化和免疫化学方法获得了新的发现，即禽脑还具有类固醇生成酶细胞色素P450scc，并产生孕烯醇酮及其硫酸酯。此外，我们对禽脑的免疫组织化学研究表明，针对纯化的牛肾上腺P450scc的多克隆抗体在典型的小脑神经元浦肯野细胞的胞体和树突中存在强烈的免疫反应。我们进一步证明类固醇生成酶P450scc存在于大鼠浦肯野细胞即刻…中。为了了解孕烯醇酮及其硫酸酯的作用方式，我们研究了这些神经类固醇对小脑浦肯野神经元突触电流的影响。用膜片钳方法在小脑切片上记录浦肯野神经元的抑制性突触后电流。孕烯醇酮硫酸盐在灌流后1分钟内以剂量相关的方式增加IPSCs的频率，表明这种影响不太可能是通过基因转录来诱导的。相比之下，孕烯醇酮对ipscs的频率没有影响。记录在浦肯野神经元的IPSCs可被GABAA受体拮抗剂荷包牡丹碱完全阻断，提示IPSCs是由GABAA受体介导的。因此，浦肯野神经元产生的孕烯醇酮硫酸盐可能通过旁分泌激动子而不是基因组机制来调节GABA能神经元上的GABA能传递。行为学研究目前正在阐明神经类固醇的功能。最近，我们证明Purkinje神经元不仅具有P450scc，还具有3β-HSD，并通过分子和生化方法产生孕酮。有趣的是，P450scc mRNA的表达在新生儿和成年期相对稳定，而3β-HSD的mRNA表达在新生儿早期明显。3β-HSD活性产物孕酮可能在这一时期小脑神经系统结构的发育中发挥作用。较少

Steroid hormones supplied by peripheral steroidogenic glands regulate neuronal functions during development and in adulthood. Peripheral steroids cross the blood-brain barrier as a result of their lipid solubility and act on brain tissues through intracellular receptor-mediated mechanisms that regulate the transcription of specific genes. Therefore, the brain is considered to be a target site of peripheral steroids. Recently, we obtained new findings that the avian brain also possesses a steroidogenic enzyme, cytochrome P450scc, and produces pregnenolone and its sulfate ester, by biochemical and immunochemical approaches. In addition, our immunohistochemical studies with avian brain indicated that an intense immunoreaction with the polyclonal antibody directed against the purified bovine adrenal P450scc is present in soma and dendrites of the Purkinje cell, a typical cerebellar neuron. We further demonstrated that steroidogenic enzyme P450scc appears in the rat Purkinje cell immediatel … More y after its differentiation.To understand the mode of action of pregnenolone and its sulfate ester, we examined the effects of these neurosteroids on synaptic currents in cerebellar Purkinje neurons. Inhibitory postsynaptic currents (IPSCs) in Purkinje neurons were recorded in a cerebellar slice by the patch-clamp method. Pregnenolone sulfate increased, in a dose-related way, the frequency of IPSCs within 1 min of perfusion, indicating that this effect is unlikely to be induced via gene transcription. In contrast, pregnenolone had no effect on the frequency of IPSCs. The IPSCs recorded in the Purkinje neurons were completely blocked by bicuculine, a gamma-aminobutyric acid A (GABAA) receptor antagonist, suggesting that they are mediated by GABAA receptors. It is therefore possible that pregnenolone sufate, produced in Purkinje neurons, may modulate GABAergic transmission by paracrine acitons on GAGAergic neurons rather than by genomic mechanisms. Behavioral studies are now in progress to clarify the neurosteroidal function.More recently, we demonstrated that Purkinje neurons possess not only P450scc but also 3beta-HSD and produces progesterone by molecular and biochemical approaches. Interestingly, expression of the P450scc mRNA was relatively constant during neonatal life and in adulthood, whereas the 3beta-HSD mRNA expression was evident in early in early neonatal life. It is considered that progesterone, a product of 3beta-HSD activity, may play a role in the development of cerebellar nervous system structures in this period. Less