Biosynthesis and action of neurosteroids in the cerebellar Purkinje neuron

Progesterone Inhibitory Role on Gastrointestinal Motility

Progesterone is a steroidal hormone that is produced from the corpus luteum of the ovaries and from the placenta. The main function of progesterone is to promote the secretory differentiation in the endometrium of the uterus and to maintain pregnancy by inhibiting uterine contractions throughout pregnancy. Progesterone performs its actions by activating the classical progesterone nuclear receptors that affect gene transcription and by the non-classical activation of cell surface membrane receptors that accounts for the rapid actions of progesterone. Besides the reproductive roles of progesterone, it exerts functions in many tissues and systems such as the nervous system, the bone, the vascular system, and the gastrointestinal (GI) tract. This review will summarize the recent literature that investigated the role of progesterone in GI tract motility. Most literature indicates that progesterone exerts an inhibitory role on gut smooth muscle cells in part by elevating nitric oxide synthesis, which induces relaxation in smooth muscle. Moreover, progesterone inhibits the signaling pathways that lead to contraction such as Rho kinase inhibition. These data serve as a quick resource for the future directions of progesterone research that could lead to better understanding and more effective treatment of gender-related GI tract motility disorders.

Neuroprotective actions of cerebellar and pineal allopregnanolone on Purkinje cells

The brain produces steroids de novo from cholesterol, so‐called “neurosteroids.” The Purkinje cell, a cerebellar neuron, was discovered as a major site of the biosynthesis of neurosteroids including sex steroids, such as progesterone, from cholesterol in the brain. Allopregnanolone, a progesterone metabolite, is also synthesized in the cerebellum and acts on the Purkinje cell to prevent cell death of this neuron. Recently, the pineal gland was discovered as an important site of the biosynthesis of neurosteroids. Allopregnanolone, a major pineal neurosteroid, acts on the Purkinje cell for the survival of this neuron by suppressing the expression of caspase‐3, a crucial mediator of apoptosis. This review summarizes the discovery of cerebellar and pineal allopregnanolone and its neuroprotective action on Purkinje cells.

Unraveling the steroid hormone response in male marathon runners: Correlation of running time with aldosterone and progesterone

Marathon running is a physical and psychological stressor. We aimed to characterize the response of nine steroid hormones, which include estradiol, progesterone, testosterone, cortisol, aldosterone, 17-hydroxyprogesterone, cortisone, androstenedione, and dehydroepiandrosterone sulfate, to marathon running and their association with performance. Blood samples of sixty men (age: 49.3 ± 5.9 years) who participated in the Berlin marathon were collected within 3 days before, within 30 min and within 58 h after the end of the marathon. The nine steroid hormones in serum were quantified using liquid chromatography-tandem mass spectrometry. The responses of nine steroid hormones to marathon running were characterized. Aldosterone (fold change: 8.5), progesterone (fold change: 6.6), and cortisol (fold change: 3.7) showed significant increases within 30 min after the marathon (all p < 0.0001). Estradiol but not testosterone increased in the male runners. Marathon running time was significantly related to aldosterone increase (beta=-0.238, p = 0.008) and progesterone increase (beta=-0.192, p = 0.036) in addition to body mass index, self-reported training distance, and age. Serum progesterone correlated with aldosterone and cortisol (r = 0.81 and r = 0.92, respectively, p < 0.001). Progesterone, as a precursor hormone, is increased after the completion of marathon running in association with the increase of aldosterone and cortisol. These findings reveal a contribution of progesterone during the response to the psycho-physical stress of marathon running in males.

Kobayashi award: Discovery of cerebellar and pineal neurosteroids and their biological actions on the growth and survival of Purkinje cells during development (review)

The brain has traditionally been considered to be a target site of peripheral steroid hormones. On the other hand, extensive studies over the past thirty years have demonstrated that the brain is a site of biosynthesis of several steroids. Such steroids synthesized de novo from cholesterol in the brain are called neurosteroids. To investigate the biosynthesis and biological actions of neurosteroids in the brain, data on the regio- and temporal-specific synthesis of neurosteroids are needed. In the mid 1990s, the Purkinje cell, an important cerebellar neuron, was discovered as a major cell producing neurosteroids in the brain of vertebrates. It was the first demonstration of de novo neuronal biosynthesis of neurosteroids in the brain. Subsequently, neuronal biosynthesis of neurosteroids and biological actions of neurosteroids have become clear by the follow-up studies using the Purkinje cell as an excellent cellular model. Progesterone and estradiol, which are known as sex steroid hormones, are actively synthesized de novo from cholesterol in the Purkinje cell during development, when cerebellar neuronal circuit formation occurs. Importantly, progesterone and estradiol synthesized in the Purkinje cell promote dendritic growth, spinogenesis and synaptogenesis via their cognate nuclear receptors in the Purkinje cell. Neurotrophic factors may mediate these neurosteroid actions. Futhermore, allopregnanolone (3α,5α-tetrahydroprogesterone), a progesterone metabolite, is also synthesized in the cerebellum and acts on the survival of Purkinje cells. On the other hand, at the beginning of 2010s, the pineal gland, an endocrine organ located close to the cerebellum, was discovered as an important site of the biosynthesis of neurosteroids. Allopregnanolone, a major pineal neurosteroid, acts on the Purkinje cell for the survival of Purkinje cells by suppressing the expression of caspase-3, a crucial mediator of apoptosis. I as a recipient of Kobayashi Award from the Japan Society for Comparative Endocrinology in 2016 summarize the discovery of cerebellar and pineal neurosteroids and their biological actions on the growth and survival of Purkinje cells during development.

Neurosteroid Actions in Memory and Neurologic/Neuropsychiatric Disorders

Memory dysfunction is a symptomatic feature of many neurologic and neuropsychiatric disorders; however, the basic underlying mechanisms of memory and altered states of circuitry function associated with disorders of memory remain a vast unexplored territory. The initial discovery of endogenous neurosteroids triggered a quest to elucidate their role as neuromodulators in normal and diseased brain function. In this review, based on the perspective of our own research, the advances leading to the discovery of positive and negative neurosteroid allosteric modulators of GABA type-A (GABA_A), NMDA, and non-NMDA type glutamate receptors are brought together in a historical and conceptual framework. We extend the analysis toward a state-of-the art view of how neurosteroid modulation of neural circuitry function may affect memory and memory deficits. By aggregating the results from multiple laboratories using both animal models for disease and human clinical research on neuropsychiatric and age-related neurodegenerative disorders, elements of a circuitry level view begins to emerge. Lastly, the effects of both endogenously active and exogenously administered neurosteroids on neural networks across the life span of women and men point to a possible underlying pharmacological connectome by which these neuromodulators might act to modulate memory across diverse altered states of mind.

Biosynthesis and biological action of pineal allopregnanolone

The pineal gland transduces photoperiodic changes to the neuroendocrine system by rhythmic secretion of melatonin. We recently provided new evidence that the pineal gland is a major neurosteroidogenic organ and actively produces a variety of neurosteroids de novo from cholesterol in birds. Notably, allopregnanolone is a major pineal neurosteroid that is far more actively produced in the pineal gland than the brain and secreted by the pineal gland in juvenile birds. Subsequently, we have demonstrated the biological action of pineal allopregnanolone on Purkinje cells in the cerebellum during development in juvenile birds. Pinealectomy (Px) induces apoptosis of Purkinje cells, whereas allopregnanolone administration to Px chicks prevents cell death. Furthermore, Px increases the number of Purkinje cells that express active caspase-3, a crucial mediator of apoptosis, and allopregnanolone administration to Px chicks decreases the number of Purkinje cells expressing active caspase-3. It thus appears that pineal allopregnanolone prevents cell death of Purkinje cells by suppressing the activity of caspase-3 during development. This paper highlights new aspects of the biosynthesis and biological action of pineal allopregnanolone.

Prostaglandin E2 stimulates estradiol synthesis in the cerebellum postnatally with associated effects on Purkinje neuron dendritic arbor and electrophysiological properties

Prostaglandins (PGs) are ubiquitous membrane-derived, lipid-signaling molecules with wide ranging effects throughout the body. In the brain, PGE(2) is the key regulator of fever after inflammation but is also implicated in neural development and synaptic plasticity. The steroid hormone estradiol is also a key regulator of neural development and synaptic plasticity. Recently, we showed that administering cyclooxygenase (COX) inhibitors to block PGE(2) production increased the total length of Purkinje cell dendrites, the number of dendritic spines, and the level of spinophilin protein, which is enriched in dendritic spines. Correspondingly, PGE(2) administration into the cerebellum decreased spinophilin protein content. We now report that PGE(2) stimulates estradiol synthesis in the immature rat cerebellum via enhanced activity of the aromatase enzyme. Treatment with cyclooxygenase inhibitors reduced cerebellar aromatase activity and estradiol content whereas PGE(2) administration increased both. Treatment with either PGE(2) or estradiol stunted Purkinje neuron dendritic length and complexity and produced a corresponding reduction in spinophilin content. Treatment with formestane to inhibit aromatase activity led to excessive sprouting of the dendritic tree, whereas elevated estradiol had the opposite effect. Electrophysiological measurements from Purkinje neurons revealed novel sex differences in input resistance and membrane capacitance that were abolished by estradiol exposure, whereas a sex difference in the amplitude of the afterhyperpolarization after an action potential was not. Correlated changes in action potential threshold suggest that prolonged alterations in neuronal firing activity could be a consequence of increased estradiol content during the second week of life. These findings reveal a previously unappreciated role for PG-stimulated steroidogenesis in the developing brain and a new potential route for inflammation-mediated disruption of neuronal maturation.

Effect of gonadectomy on activity of neuronal 3β-hydroxysteroid dehydrogenase in some brain structures

3β-Hydroxysteroid dehydrogenase is a key enzyme in the synthesis of steroid hormones in steroid-producing organs, including the brain producing neurosteroids. 3β-Hydroxysteroid dehydrogenase activity can be a marker of steroid-producing cells. We present the results of histochemical assay of this enzyme in the neocortex, hippocampus, and cerebellar cortex of gonadectomized prepubertal rats. The positive reaction was detected in hippocampal neurons, ganglionic layer cells of the cerebellar cortex (Purkinje cells), and solitary neocortical neurons of male and female rats. Gonadectomy significantly increased enzyme activity in neocortical (layer V) and hippocampal neurons and had no effect on the intensity of the reaction in Purkinje cells.

Development of Purkinje cells in the ovine brain

Purkinje cells are involved in many vital functions within the body. Twenty ovine fetuses ranging from 2 to 5 months of gestation, two lambs in the first week after birth and three adult sheep were studied. Sections of the cerebellum were stained with haematoxylin and eosin, cresyl violet and Klüver-Barrera. This study indicates that Purkinje cells began to appear after the 15(th) week of gestation. There were varying degrees of development of Purkinje cells in different zones of the cerebellum. Our findings in sheep fetuses suggest that the maturation of Purkinje cells starts in the caudal regions of the cerebellum and that the process begins in the vermis before it does in the cerebellar hemispheres. The alignment of Purkinje cells was found to be very regular in the caudal regions of the cerebellum. A partial absence of Purkinje cells in the rostral regions of the cerebellum was observed in both sheep fetuses and adult sheep. In the first post-natal week, some ectopic Purkinje cells were found in the white matter of the cerebellum.

Activation of steroid-sensitive TRPM3 channels potentiates glutamatergic transmission at cerebellar Purkinje neurons from developing rats

The functional implications of transient receptor potential melastatin 3 (TRPM3) activation, the most recently described member of the melastatin subfamily of cation permeable TRP channels, have begun to be elucidated in recent years. The discovery of TRPM3 activation by the steroid pregnenolone sulfate (PregS) has shed new light on the physiological role of this channel. For example, TRPM3 activation enhances insulin secretion from β pancreatic cells, induces contraction of vascular smooth muscle, and is also involved in the detection of noxious heat. Although TRPM3 expression has been detected in several regions of the developing and mature brain, little is known about the roles of TRPM3 in brain physiology. In this study, we demonstrate the abundant expression of TRPM3 steroid-sensitive channels in the developing cerebellar cortex. We also show that TRPM3-like channels are expressed at glutamatergic synapses in neonatal Purkinje cells. We recently showed that PregS potentiates spontaneous glutamate release onto neonatal Purkinje cells during a period of active glutamatergic synapse formation; we now show that this effect of PregS is mediated by TRPM3-like channels. Mefenamic acid, a recently discovered TRPM3 antagonist, blocked the effect of PregS on glutamate release. The PregS effect on glutamate release was mimicked by other TRPM3 agonists (nifedipine and epipregnanolone sulfate) but not by a TRMP3-inactive steroid (progesterone). Our findings identify TRPM3 channels as novel modulators of glutamatergic transmission in the developing brain.

Biosynthesis, mode of action, and functional significance of neurosteroids in the purkinje cell

The brain has traditionally been considered to be a target site of peripheral steroid hormones. In addition to this classical concept, we now know that the brain has the capacity to synthesize steroids de novo from cholesterol, the so-called "neurosteroids." In the middle 1990s, the Purkinje cell, an important cerebellar neuron, was identified as a major site for neurosteroid formation in the brain of mammals and other vertebrates. This discovery has provided the opportunity to understand neuronal neurosteroidogenesis in the brain. In addition, biological actions of neurosteroids are becoming clear by the studies using the Purkinje cell, an excellent cellular model, which is known to play an important role in memory and learning processes. Based on the studies on mammals over the past decade, it is considered that the Purkinje cell actively synthesizes progesterone and estradiol from cholesterol during neonatal life, when cerebellar neuronal circuit formation occurs. Both progesterone and estradiol promote dendritic growth, spinogenesis, and synaptogenesis via each cognate nuclear receptor in the developing Purkinje cell. Such neurosteroid actions mediated by neurotrophic factors may contribute to the formation of cerebellar neuronal circuit during neonatal life. 3α,5α-Tetrahydroprogesterone (allopregnanolone), a progesterone metabolite, is also synthesized in the cerebellum and considered to act as a survival factor of Purkinje cells in the neonate. This review summarizes the current knowledge regarding the biosynthesis, mode of action, and functional significance of neurosteroids in the Purkinje cell during development in terms of synaptic formation of cerebellar neuronal networks.

Pregnenolone sulfate increases glutamate release at neonatal climbing fiber-to-Purkinje cell synapses

Development of cerebellar Purkinje cells (PCs) is modulated by neuroactive steroids. Developing hippocampal pyramidal neurons retrogradely release a pregnenolone sulfate (PregS)-like neurosteroid that may contribute to glutamatergic synapse stabilization. We hypothesized that PregS could exert a similar effect on developing PCs. To test this hypothesis, we performed whole-cell patch-clamp recordings from PCs in acute cerebellar vermis slices from neonatal rats. PregS induced a robust (∼3000%) and reversible increase in AMPA receptor-mediated miniature excitatory postsynaptic current (AMPA-mEPSC) frequency without affecting the amplitude, time-to-rise, or half-width of these events. PregS also increased the frequency of GABA(A) receptor-mediated miniature postsynaptic currents but to a significantly lesser extent (<100%). The PregS-induced increase of AMPA-mEPSC frequency was not significantly decreased by antagonists of receptors (NMDA, glycine, α7 nicotinic acetylcholine and σ1) that have been shown to modulate glutamatergic transmission at PCs and/or mediate the actions of PregS on neurotransmitter release. Ca(2+) chelation experiments suggested that PregS acts by increasing presynaptic terminal [Ca(2+)](i), an effect that is independent of voltage-gated Ca(2+) channels, but is blocked by the antagonist of transient receptor potential (TRP) channels, La(3+). PregS also increased the amplitude of EPSCs evoked by climbing fiber (CF) stimulation and decreased the paired-pulse ratio of these events. Neither CF nor parallel fiber-evoked EPSCs were affected by PregS in slices from juvenile rats. These results suggest that glutamate release at CF-to-PC synapses is an important target of PregS in the neonatal cerebellar cortex, an effect that may play a role in the refinement of these synapses.

Neurosteroid Biosynthesis and Action in the Purkinje Cell

It is now clearly established that steroids can be synthesized de novo by the vertebrate brain. Such steroids are called neurosteroids. To understand neurosteroid action in the brain, data on the regio- and temporal-specific synthesis of neurosteroids are needed. In the middle 1990s, the Purkinje cell, an important cerebellar neuron, was identified as a major site for neurosteroid formation in vertebrates. This discovery has allowed deeper insights into neuronal neurosteroidogenesis and biological actions of neurosteroids have become clear by the studies using the Purkinje cell as an excellent cellular model, which is known to play an important role in memory and learning processes. From the past 10 years of research on mammals, we now know that the Purkinje cell actively synthesizes progesterone and estradiol de novo from cholesterol during neonatal life, when cerebellar neuronal circuit formation occurs. Both progesterone and estradiol promote dendritic growth, spinogenesis, and synaptogenesis via each cognate nuclear receptor in the developing Purkinje cell. Such neurosteroid actions that may be mediated by neurotrophic factors contribute to the formation of cerebellar neuronal circuit during neonatal life. Allopregnanolone, a progesterone metabolite, is also synthesized in the cerebellum and acts on Purkinje cell survival in the neonate. The aim of this review is to summarize the current knowledge regarding the biosynthesis and biological actions of neurosteroids in the Purkinje cell during development.

Neurosteroids in the Purkinje cell: biosynthesis, mode of action and functional significance

Neurosteroids are synthesized de novo from cholesterol in the brain. To understand neurosteroid action in the brain, data on the regio- and temporal-specific synthesis of neurosteroids are needed. Recently the Purkinje cell, an important cerebellar neuron, has been identified as a major site for neurosteroid formation in vertebrates. This is the first demonstration of de novo neuronal neurosteroidogenesis in the brain. Since this discovery, organizing actions of neurosteroids are becoming clear by the studies using the Purkinje cell as an excellent cellular model. In mammals, the Purkinje cell actively synthesizes progesterone and estradiol de novo from cholesterol during neonatal life. Both progesterone and estradiol promote dendritic growth, spinogenesis, and synaptogenesis via each cognate nuclear receptor in the developing Purkinje cell. Such organizing actions that may be mediated by neurotrophic factors, such as brain-derived neurotrophic factor (BDNF), contribute to the formation of cerebellar neuronal circuit during neonatal life. Allopregnanolone, a progesterone metabolite, is also synthesized in the cerebellum and acts on Purkinje cell survival in the neonate. This review summarizes the advances made in our understanding of the biosynthesis, mode of action and functional significance of neurosteroids in the Purkinje cell.

Progesterone biosynthesis and action in the developing neuron

The brain has traditionally been considered to be a target site of peripheral steroid hormones. By contrast, new findings over the past decade have shown that the brain itself also has the capability of forming steroids de novo, the so-called neurosteroids. De novo neurosteroidogenesis in the brain from cholesterol is a conserved property of vertebrates. When understanding the action of neurosteroids in the brain, data on the regio- and temporal-specific synthesis of neurosteroids are needed. Recently the Purkinje cell, an important brain neuron, has been identified as a major site for neurosteroid formation in vertebrates. This is the first demonstration of de novo neuronal neurosteroidogenesis in the brain. This discovery has allowed deeper insights into neuronal progesterone formation and organizing actions of progesterone have become clear by the studies using the Purkinje cell as an excellent cellular model, which is known to play an important role in memory and learning processes. In mammals, the Purkinje cell actively synthesizes progesterone de novo from cholesterol during neonatal life when cerebellar neuronal circuit formation occurs. Progesterone promotes dendritic growth, spinogenesis, and synaptogenesis via its nuclear receptor in the developing Purkinje cell. Such organizing actions may contribute to the formation of cerebellar neuronal circuit during neonatal life. Allopregnanolone, a progesterone metabolite, is also synthesized in the cerebellum and acts on Purkinje cell survival in the neonate. This paper summarizes the advances made in our understanding of progesterone formation and metabolism and actions of progesterone and its metabolite in the developing neuron.

Transcriptional activity of estrogen receptors ERalpha and ERbeta in the EtC.1 cerebellar granule cell line

Estrogen receptors alpha and beta (ERalpha and ERbeta) are expressed in the cerebellum throughout development and in the adult suggesting an important role of 17-beta-estradiol (E2) in this brain structure. In the present study, we have characterized the functionality of estrogen receptors (ERs) expressed in the immature cerebellar granule cell line E(t)C.1 by transfecting such cells with a luciferase reporter gene (ERE-Luc) coupled to an estrogen response element promoter. The induction of luciferase activity in E(t)C.1 cells by E2 and ER-subtype selective agonists was compared in normal cells and in cells overexpressing human ERalpha or ERbeta (hERalpha or hERbeta). E2-mediated transcription of the reporter gene was blocked by the ER antagonist ICI 182,780 (ICI), demonstrating the presence of functional native ERs. The selective agonist for ERalpha (PPT) showed a reduced response in luciferase induction compared to E2. Moreover, the ERbeta agonist (DPN) was unable to induce luciferase activity. E2-induced ERE-Luc transcription was not increased by overexpression of hERalpha. In contrast, hERbeta overexpression reduced the efficacy of E2 and abolished ERalpha-selective agonist activity. The ERbeta-specific agonist did not induce gene reporter activity unless hERbeta was overexpressed in the cells, suggesting that the endogenous ERbeta in E(t)C.1 cells is transcriptionally inactive. ICI inhibition of E2 responses was not affected by overexpression of the human ERs. The data suggest that ERalpha plays a predominant role in E2-mediated transcription in E(t)C.1 cells. Our data are discussed in view of other reports alluding to the complexity and cell-type specificity of E2-mediated transcription.

Fos expression at the cerebellum following non-contact arousal and mating behavior in male rats

The cerebellum is considered a center underlying fine movements, cognition, memory and sexual responses. The latter feature led us to correlate sexual arousal and copulation in male rats with neural activity at the cerebellar cortex. Two behavioral paradigms were used in this investigation: the stimulation of males by distant receptive females (non-contact sexual stimulation), and the execution of up to three consecutive ejaculations. The vermis area of the cerebellum was removed following behavioral experiments, cut into sagittal sections, and analyzed with Fos immunohistochemistry to determine neuronal activation. At the mid-vermis region (sections from the midline to 0.1 mm laterally), non-contact stimulation significantly increased the activity of granule neurons. The number of activated cells increased in every lobule, but lobules 1 and 6 to 9 showed the greatest increment. In sexual behavior tests, males reaching one ejaculation had a high number of activated neurons similar to those counted after non-contact stimulation. However, two or three consecutive ejaculations showed a smaller number of Fos-ir cells. In contrast to the mid-vermis region, sections farthest from the midline (0.1 to 0.9 mm laterally) revealed that only lobule 7 expressed activated neurons. These data suggest that a well-delineated group of granule neurons have a sexual biphasic response at the cerebellar vermis, and that Fos in them is under an active degradation mechanism. Thus, they participate as a neural substrate for male rat sexual responses with an activation-deactivation process corresponding with the sensory stimulation and motor performance occurring during copulation.

Developmental expression of key steroidogenic enzymes in the brain of protandrous black porgy fish, Acanthopagrus schlegeli

In the present study, we tested the hypothesis that the brain of the black porgy fish, Acanthopagrus schlegeli, has the capacity for de novo steroidogenesis and that these neurosteroids may impact sex differentiation. Gonadal histology and Dmrt1 gene expression revealed that the fish were not sex differentiated until 155 dah (days after hatching). We further demonstrated the developmental expressions of the mRNAs encoding for four key neurosteroidogenic enzymes, namely, the cytochrome P450 side chain cleavage (CYP11A1), 3beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4) isomerase (3betaHSD), cytochrome P450c17 (CYP17) and aromatase (CYP19b) in the brain at different post-hatching developmental ages. The results indicated that steroidogenic genes are expressed in brain from the earliest sampling time, 60 dah. Quantitative real-time polymerase chain reaction analysis demonstrated significantly higher expression levels of these enzymes at 120 dah compared to 60 dah in all the brain regions. However, the increase for 3betaHSD was significant only in hypothalamus and midbrain, whereas it was significant only in forebrain and hypothalamus for CYP19b. A decline in mRNA levels were observed for all the genes at 155 dah except in midbrain for CYP11A1 and in hindbrain for CYP19b. Analysis of aromatase enzyme activity showed a significant increase in aromatase activity in the forebrain at 120 dah. Thus, the present study demonstrated for the first time an age- and/or region dependent expression of the mRNAs encoding the steroidogenic enzyme genes in the brain of black porgy. The presence of key steroidogenic enzymes as early as 60 dah, before gonadal sex differentiation, demonstrates that steroid biosynthetic capacity in brain precedes histological gonad differentiation. The mRNA transcripts of these genes showed a synchronous peak at 120 dah, suggesting that oestradiol may be locally formed in most parts of the brain. The study suggests an important role for brain aromatase in male black porgy brain sex differentiation, and considers the possibility of a role for this enzyme in neurogenesis.

Mode of action and functional significance of estrogen-inducing dendritic growth, spinogenesis, and synaptogenesis in the developing Purkinje cell

Neurosteroids are synthesized de novo from cholesterol in the brain. To understand neurosteroid action in the brain, data on the regio- and temporal-specific synthesis of neurosteroids are needed. Recently, we identified the Purkinje cell as an active neurosteroidogenic cell. In rodents, this neuron actively produces several neurosteroids including estradiol during neonatal life, when cerebellar neuronal circuit formation occurs. Estradiol may be involved in cerebellar neuronal circuit formation through promoting neuronal growth and neuronal synaptic contact, because the Purkinje cell expresses estrogen receptor-beta (ERbeta). To test this hypothesis, in this study we examined the effects of estradiol on dendritic growth, spinogenesis, and synaptogenesis in the Purkinje cell using neonatal wild-type (WT) mice or cytochrome P450 aromatase knock-out (ArKO) mice. Administration of estradiol to neonatal WT or ArKO mice increased dendritic growth, spinogenesis, and synaptogenesis in the Purkinje cell. In contrast, WT mice treated with tamoxifen, an ER antagonist, or ArKO mice exhibited decreased Purkinje dendritic growth, spinogenesis, and synaptogenesis at the same neonatal period. To elucidate the mode of action of estradiol, we further examined the expression of brain-derived neurotrophic factor (BDNF) in response to estrogen actions in the neonate. Estrogen administration to neonatal WT or ArKO mice increased the BDNF level in the cerebellum, whereas tamoxifen decreased the BDNF level in WT mice similar to ArKO mice. BDNF administration to tamoxifen-treated WT mice increased Purkinje dendritic growth. These results indicate that estradiol induces dendritic growth, spinogenesis, and synaptogenesis in the developing Purkinje cell via BDNF action during neonatal life.

Cellular distribution of the GABAA receptor-modulating 3alpha-hydroxy, 5alpha-reduced pregnane steroids in the adult rat brain

The 3alpha-hydroxy,5alpha-reduced pregnane steroids, allopregnanolone and allotetrahydrodeoxycorticosterone, are the most potent endogenous positive modulators of GABA(A) receptor-mediated inhibition. This study presents the first immunohistochemical examination of the cellular distribution of 3alpha-hydroxy,5alpha-reduced pregnane steroids across the brain. We found a widespread distribution in the adult rat, with dense immunolabelling in the olfactory bulb, striatum and cerebral cortex, and lower density labelling in the brainstem reticular formation. In general terms, this distribution accords with the regional concentrations of 3alpha-hydroxy,5alpha-reduced steroids determined, in other laboratories, by brain region sampling and either gas chromatography-mass fragmentography or radioimmunoassay. However, immunohistochemistry allowed for a more detailed examination of regional distribution and cellular specificity. All immunoreactivity was confined to the cell bodies and thick dendrites of neurones; no identifiable glia were labelled. In most brain areas, the location and morphology of labelled cells identified them as excitatory neurones. In addition, cell populations known to be projecting GABAergic neurones (e.g. cerebellar Purkinje cells) were immunoreactive, whereas local inhibitory neurones generally were not. The cellular distribution of 3alpha-hydroxy,5alpha-reduced steroids suggests that sensory, motor, limbic and homeostatic systems can be influenced by neurosteroids at multiple stages of processing.

Biosynthesis, mode of action and functional significance of neurosteroids in the developing Purkinje cell

New findings over the past decade have shown that the brain has the capability of forming steroids de novo from cholesterol, the so-called "neurosteroids". To understand neurosteroid action in the brain, data on the regio- and temporal-specific synthesis of neurosteroids are needed. Recently, we have demonstrated that the Purkinje cell, a cerebellar neuron, is a major site for neurosteroid formation in a variety of vertebrates. This is the first demonstration of de novo neuronal neurosteroidogenesis in the brain. Since this discovery, organizing actions of neurosteroids are becoming clear by the studies on mammals using the Purkinje cell as an excellent cellular model. In mammals, the Purkinje cell actively synthesizes progesterone de novo from cholesterol during neonatal life, when cerebellar neuronal circuit formation occurs. The Purkinje cell may also produces estradiol in the neonate. Interestingly, both progesterone and estradiol promote dendritic growth, spinogenesis and synaptogenesis via each cognate nuclear receptor in the developing Purkinje cell. Such organizing actions may contribute to the formation of cerebellar neuronal circuit during neonatal life. This paper summarizes the advances made in our understanding of the biosynthesis, mode of action and functional significance of neurosteroids in the developing Purkinje cell.

Biosynthesis and organizing action of neurosteroids in the developing Purkinje cell

Probing undiscovered neurosubstances that play important roles in the regulation of cerebellar function is essential for the progress of our understanding of the cerebellum. New findings over the past decade have established that the cerebellum as well as other brain regions synthesizes steroids de novo from cholesterol through mechanisms at least partly independent of peripheral steroidogenic glands. Such steroids synthesized de novo in the brain are called neurosteroids. Recently the Purkinje cell, a cerebellar neuron, has been identified as a major site for neurosteroid formation in the brain. This is the first demonstration of de novo neuronal neurosteroidogenesis in the brain. In mammals, the Purkinje cell actively synthesizes progesterone de novo from cholesterol during neonatal life, when cerebellar cortical formation occurs. 3alpha,5alpha-Tetrahydroprogesterone (allopregnanolone) is metabolized from progesterone in the neonatal cerebellum. Estrogen formation in the Purkinje cell may also occur in the neonate. Subsequently, recent studies on mammals using the Purkinje cell have demonstrated organizing actions of neurosteroids. Both progesterone and estradiol promote dendritic growth, spinogenesis and synaptogenesis via each cognate nuclear receptor in Purkinje neurons. Allopregnanolone is also involved in Purkinje and granule cell survival. Thus the Purkinje cell serves as an excellent cellular model for understanding the formation of cerebellar neuronal circuit in relation to organizing actions of neurosteroids.

Systematic screening and identification of antigens recognized by monoclonal antibodies raised against the developing lateral olfactory tract

During development, olfactory bulb axons navigate a complex microenvironment composed of myriad molecules to construct a bundle called the lateral olfactory tract. The axons themselves also express thousands of different molecules. In the present study, we produced and characterized six monoclonal antibodies that label the lateral olfactory tract and its surroundings in a unique pattern. The labeling profiles suggested that the antigen molecules recognized by each antibody are heterogeneously distributed around the developing lateral olfactory tract. We developed an efficient screening method to identify the antigen molecules by combining expression of a cDNA library in COS-7 cells and the subsequent immunohistochemical staining of the cells. The systematic screening successfully identified specific cDNA clones for all of the monoclonal antibodies, which highly probably coded for the antigen molecules, and therefore unveiled the molecular nature of local components that embrace the developing lateral olfactory tract in mice.

Early postnatal Purkinje cells from staggerer mice undergo aberrant development in vitro with characteristic morphologic and gene expression abnormalities

The staggerer (sg) mutant mouse shows an early block in Purkinje cell (PC) development due to a truncation of the transcription factor retinoic acid-related orphan receptor alpha (ROR alpha). Cerebellar cultures from neonatal sg mice recapitulate many in vivo postnatal changes in PCs and allow for detailed observation of sequential dendritic outgrowth and gene expression changes. In addition, this in vitro system provides a tractable basis for ROR alpha replacement studies.

Progesterone: the forgotten hormone in men?

'Classical' genomic progesterone receptors appear relatively late in phylogenesis, i.e. it is only in birds and mammals that they are detectable. In the different species, they mediate manifold effects regarding the differentiation of target organ functions, mainly in the reproductive system. Surprisingly, we know little about the physiology, endocrinology, and pharmacology of progesterone and progestins in male gender or men respectively, despite the fact that, as to progesterone secretion and serum progesterone levels, there are no great quantitative differences between men and women (at least outside the luteal phase). In a prospective cohort study of 1026 men with and without cardiovascular disease, we were not able to demonstrate any age-dependent change in serum progesterone concentrations. Progesterone influences spermiogenesis, sperm capacitation/acrosome reaction and testosterone biosynthesis in the Leydig cells. Other progesterone effects in men include those on the central nervous system (CNS) (mainly mediated by 5alpha-reduced progesterone metabolites as so-called neurosteroids), including blocking of gonadotropin secretion, sleep improvement, and effects on tumors in the CNS (meningioma, fibroma), as well as effects on the immune system, cardiovascular system, kidney function, adipose tissue, behavior, and respiratory system. A progestin may stimulate weight gain and appetite in men as well as in women. The detection of progesterone receptor isoforms would have a highly diagnostic value in prostate pathology (benign prostatic hypertrophy and prostate cancer). The modulation of progesterone effects on typical male targets is connected with a great pharmacodynamic variability. The reason for this is that, in men, some important effects of progesterone are mediated non-genomically through different molecular biological modes of action. Therefore, the precise therapeutic manipulation of progesterone actions in the male requires completely new endocrine-pharmacological approaches.

Dendritic growth in response to environmental estrogens in the developing Purkinje cell in rats

The cerebellar Purkinje cell is a major site for neurosteroid formation. We have demonstrated recently that the Purkinje cell actively produces sex steroids, such as estradiol and progesterone, de novo from cholesterol only during rat neonatal life, when cerebellar cortical formation occurs. We have further demonstrated that both estradiol and progesterone promote the growth of Purkinje cells through intranuclear receptor-mediated mechanisms during cerebellar development. On the other hand, environmental estrogens, such as octylphenol (OP), bisphenol A (BPA), and nonylphenol (NP) are thought to mimic the action of estrogen in the developing central nervous system. Therefore, in this study, the effect of these environmental estrogens on the growth of Purkinje cells was examined in vivo using newborn rats. OP and BPA promoted a dose-dependent dendritic outgrowth of the Purkinje cell but did not affect its soma and cell number. The stimulatory effect of OP and BPA on Purkinje dendritic growth was induced by an injection of 500 microg/day into the cerebrospinal fluid for 4 days and blocked by the estrogen receptor antagonist tamoxifen. However, there was no significant effect of NP on any Purkinje cell morphology. These results suggest that the environmental estrogens, OP and BPA, promote Purkinje dendritic growth during neonatal life. This effect may be mediated by estrogen receptor in the Purkinje cell.

Organizing actions of neurosteroids in the Purkinje neuron

It is becoming clear that steroids can be synthesized de novo by the brain of vertebrates. Such steroids synthesized de novo in the brain, as well as other areas of the nervous system, are called neurosteroids. To understand neurosteroid actions in the brain, we need data on the specific biosynthesis in particular sites of the brain at particular times. Therefore our studies for this exciting area of neuroscience research have focused on the biosynthesis and action of neurosteroids in the identified neurosteroidogenic cells underlying important brain functions. We have demonstrated that the Purkinje cell, a typical cerebellar neuron, is a major site for neurosteroid formation in the brain. This neuron actively synthesizes progesterone and estradiol de novo from cholesterol only during neonatal life, when cerebellar cortical formation occurs dramatically. This is the first observation of neuronal neurosteroidogenesis in the brain. Subsequently the actions of progesterone and estradiol during cerebellar development have become clear by a series of our studies using an excellent Purkinje cellular model. These neurosteroids promote dendritic growth, spinogenesis and synaptogenesis via each receptor in the Purkinje cell. Here we summarize the advances made in our understanding of organizing actions of neurosteroids in the Purkinje cell, an important brain neuron.

Crystal structure of the human RORalpha Ligand binding domain in complex with cholesterol sulfate at 2.2 A

The retinoic acid-related orphan receptor alpha (RORalpha) is an orphan member of the subfamily 1 of nuclear hormone receptors. Our recent structural and functional studies have led to the hypothesis that cholesterol or a cholesterol derivative is the natural ligand of RORalpha. We have now solved the x-ray crystal structure of the ligand binding domain of RORalpha in complex with cholesterol-3-O-sulfate following a ligand exchange experiment. In contrast to the 3-hydroxyl of cholesterol, the 3-O-sulfate group makes additional direct hydrogen bonds with three residues of the RORalpha ligand binding domain, namely NH-Gln(289), NH-Tyr(290), and NH1-Arg(370). When compared with the complex with cholesterol, seven well ordered water molecules have been displaced, and the ligand is slightly shifted toward the hydrophilic part of the ligand binding pocket, which is ideally suited for interactions with a sulfate group. These additional ligand-protein interactions result in an increased affinity of cholesterol sulfate when compared with cholesterol, as shown by mass spectrometry analysis done under native conditions and differential scanning calorimetry. Moreover, mutational studies show that the higher binding affinity of cholesterol sulfate translates into an increased transcriptional activity of RORalpha. Our findings suggest that cholesterol sulfate could play a crucial role in the regulation of RORalpha in vivo.