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      Synthetic neurosteroids on brain protection

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          Abstract

          Neurosteroids, like allopregnanolone and pregnanolone, are endogenous regulators of neuronal excitability. Inside the brain, they are highly selective and potent modulators of GABA A receptor activity. Their anticonvulsant, anesthetics and anxiolytic properties are useful for the treatments of several neurological and psychiatric disorders via reducing the risks of side effects obtained with the commercial drugs. The principal disadvantages of endogenous neurosteroids administration are their rapid metabolism and their low oral bioavailability. Synthetic steroids analogues with major stability or endogenous neurosteroids stimulation synthesis might constitute promising novel strategies for the treatment of several disorders. Numerous studies indicate that the 3α-hydroxyl configuration is the key for binding and activity, but modifications in the steroid nucleus may emphasize different pharmacophores. So far, several synthetic steroids have been developed with successful neurosteroid-like effects. In this work, we summarize the properties of various synthetic steroids probed in trials throughout the analysis of several neurosteroids-like actions.

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          The distribution of thirteen GABAA receptor subunit mRNAs in the rat brain. III. Embryonic and postnatal development.

          The embryonic and postnatal expression of 13 GABAA receptor subunit genes in the rat CNS was studied by in situ hybridization. Each transcript exhibited a unique regional and temporal developmental expression profile. For example, in both embryonic and early postnatal cortex and thalamus, expression of the alpha 2, alpha 3, alpha 5, and beta 3 mRNAs was pronounced. In particular, the alpha 5 gene expression underwent a prominent peak in early brain. Subsequently, the thalamocortical expression of these four genes substantially diminished and was superseded in the adult by the alpha 1, alpha 4, beta 2, and delta subunit mRNAs. Similarly, gamma 1 and gamma 3 gene expression also dropped markedly during development, their initial stronger expression being restricted to relatively few structures. In contrast, gamma 2 gene expression was widespread and mostly remained constant with increasing age. The medial septum and globus pallidus were regions expressing few subunits in both early postnatal and adult stages, allowing clear developmental combinatorial changes to be inferred (alpha 2/alpha 3 beta 2 gamma 2 to alpha 1 beta 2 gamma 2, alpha 2/alpha 3 beta 2 gamma 1 to alpha 1 beta 2 gamma 1/gamma 2, respectively). In contrast, cerebellar Purkinje cells exhibited no developmental switch, expressing only the alpha 1, beta 2, beta 3, and gamma 2 mRNAs from birth to adult. Certain GABAA transcripts were also detected in germinal zones (e.g., beta 1, beta 3, gamma 1) and in embryonic peripheral tissues such as dorsal root ganglia (e.g., alpha 2, alpha 3, beta 3, gamma 2) and intestine (gamma 3). Some parallels in regional and temporal CNS expression were noted (e.g., alpha 1 beta 2, alpha 2 beta 3, alpha 4/alpha 6 delta), whereas the alpha 5 and beta 1 regional mRNA expressions converted over time. The changes of GABAA receptor subunit gene expression suggest a molecular explanation for earlier observations on changing ligand binding affinities. Thus, the composition, and presumably properties, of embryonic/early postnatal rat GABAA receptors differs markedly from those expressed in the adult brain.
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            The distribution of 13 GABAA receptor subunit mRNAs in the rat brain. I. Telencephalon, diencephalon, mesencephalon.

            The expression patterns of 13 GABAA receptor subunit encoding genes (alpha 1-alpha 6, beta 1-beta 3, gamma 1-gamma 3, delta) were determined in adult rat brain by in situ hybridization. Each mRNA displayed a unique distribution, ranging from ubiquitous (alpha 1 mRNA) to narrowly confined (alpha 6 mRNA was present only in cerebellar granule cells). Some neuronal populations coexpressed large numbers of subunit mRNAs, whereas in others only a few GABAA receptor-specific mRNAs were found. Neocortex, hippocampus, and caudate-putamen displayed complex expression patterns, and these areas probably contain a large diversity of GABAA receptors. In many areas, a consistent coexpression was observed for alpha 1 and beta 2 mRNAs, which often colocalized with gamma 2 mRNA. The alpha 1 beta 2 combination was abundant in olfactory bulb, globus pallidus, inferior colliculus, substantia nigra pars reticulata, globus pallidus, zona incerta, subthalamic nucleus, medial septum, and cerebellum. Colocalization was also apparent for the alpha 2 and beta 3 mRNAs, and these predominated in areas such as amygdala and hypothalamus. The alpha 3 mRNA occurred in layers V and VI of neocortex and in the reticular thalamic nucleus. In much of the forebrain, with the exception of hippocampal pyramidal cells, the alpha 4 and delta transcripts appeared to codistribute. In thalamic nuclei, the only abundant GABAA receptor mRNAs were those of alpha 1, alpha 4, beta 2, and delta. In the medial geniculate thalamic nucleus, alpha 1, alpha 4, beta 2, delta, and gamma 3 mRNAs were the principal GABAA receptor transcripts. The alpha 5 and beta 1 mRNAs generally colocalized and may encode predominantly hippocampal forms of the GABAA receptor. These anatomical observations support the hypothesis that alpha 1 beta 2 gamma 2 receptors are responsible for benzodiazepine I (BZ I) binding, whereas receptors containing alpha 2, alpha 3, and alpha 5 contribute to subtypes of the BZ II site. Based on significant mismatches between alpha 4/delta and gamma mRNAs, we suggest that in vivo, the alpha 4 subunit contributes to GABAA receptors that lack BZ modulation.
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              Neurosteroids: endogenous role in the human brain and therapeutic potentials.

              This chapter provides an overview of neurosteroids, especially their impact on the brain, sex differences and their therapeutic potentials. Neurosteroids are synthesized within the brain and rapidly modulate neuronal excitability. They are classified as pregnane neurosteroids, such as allopregnanolone and allotetrahydrodeoxycorticosterone, androstane neurosteroids, such as androstanediol and etiocholanolone, and sulfated neurosteroids such as pregnenolone sulfate. Neurosteroids such as allopregnanolone are positive allosteric modulators of GABA-A receptors with powerful anti-seizure activity in diverse animal models. Neurosteroids increase both synaptic and tonic inhibition. They are endogenous regulators of seizure susceptibility, anxiety, and stress. Sulfated neurosteroids such as pregnenolone sulfate, which are negative GABA-A receptor modulators, are memory-enhancing agents. Sex differences in susceptibility to brain disorders could be due to neurosteroids and sexual dimorphism in specific structures of the human brain. Synthetic neurosteroids that exhibit better bioavailability and efficacy and drugs that enhance neurosteroid synthesis have therapeutic potential in anxiety, epilepsy, and other brain disorders. Clinical trials with the synthetic neurosteroid analog ganaxolone in the treatment of epilepsy have been encouraging. Neurosteroidogenic agents that lack benzodiazepine-like side effects show promise in the treatment of anxiety and depression. Copyright © 2010 Elsevier B.V. All rights reserved.
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                Author and article information

                Journal
                Neural Regen Res
                Neural Regen Res
                NRR
                Neural Regeneration Research
                Medknow Publications & Media Pvt Ltd (India )
                1673-5374
                1876-7958
                January 2015
                : 10
                : 1
                : 17-21
                Affiliations
                [1 ]Laboratorio de Neurobiología, Instituto de Biología y Medicina Experimental (IBYME-CONICET), Vuelta de Obligado 2490, (C1428ADN) Ciudad Autónoma de Buenos Aires, Argentina
                [2 ]Departamento de Bioquímica Humana, Facultad de Medicina, Universidad de Buenos Aires, Paraguay 2155, Ciudad Autónoma de Buenos Aires, Argentina
                Author notes
                [* ] Correspondence to: Héctor Coirini, hcoirini@ 123456ibyme.conicet.gov.ar .

                Author contributions: MR was responsible for writing the first draft of the manuscript and contributed to its editing and revision. HC was responsible for the review conception, and contributed to the design of the manuscript, writing and editing. Both authors approved the final version of this review .

                Article
                NRR-10-17
                10.4103/1673-5374.150640
                4357103
                6abf4a1d-70d6-4e78-8b92-215f80600137
                Copyright: © Neural Regeneration Research

                This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 17 December 2014
                Categories
                Invited Review

                allopregnanolone,synthetic steroids,gabaa receptor,neuroprotection,cerebral cortex,hippocampus

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