Pregnenolone, dehydroepiandrosterone, and their sulfate and fatty acid esters in the rat brain

Expression of pregnenolone-synthesizing enzymes CYP11A1 and CYP1B1 in the human, rat, and mouse brain

The central nervous system (CNS) is capable of synthesizing steroids for modulating essential functions such as neurotransmission, neuroplasticity, and neuroinflammation. These locally synthesized steroids, called neurosteroids, are produced through the conversion of cholesterol into the major steroid precursor pregnenolone, followed by downstream metabolism to form various steroids such as progesterone and allopregnanolone. Given that changes in neurosteroids are implicated in many neurological and psychiatric disorders, understanding the neurosteroidogenesis pathway is crucial. Recent studies have demonstrated an alternative pathway for the biosynthesis of pregnenolone, which is classically produced by CYP11A1 but was found instead to be made by CYP1B1 in human glial cells. However, numerous studies have demonstrated Cyp11a1 expression and activity in rodent brain tissue and brain cells. To elucidate whether species differences exist for the pregnenolone synthesis enzyme in human and rodent brains, we sought to directly compare the expression levels of CYP11A1 and CYP1B1 in human, rat, and mouse CNS tissues. We found that CYP1B1 mRNA expression was significantly higher than that of CYP11A1 in almost all CNS brain regions in human, rat, and mouse. The exception is in the mouse cerebral cortex, where Cyp11a1 RNA was more abundant than Cyp1b1. However, Cyp11a1 protein was clearly detectable in rodent CNS while completely undetectable in human brain. In contrast, the presence of CYP1B1 protein can be observed in both human and rodent brains. These results suggest that CYP1B1 is likely the dominant pregnenolone synthesis enzyme in the human brain, while rodent brains may use both Cyp11a1 and Cyp1b1.

Effects of Pregnanolone Glutamate and Its Metabolites on GABAA and NMDA Receptors and Zebrafish Behavior

Multiple molecular targets have been identified to mediate membrane-delimited and nongenomic effects of natural and synthetic steroids, but the influence of steroid metabolism on neuroactive steroid signaling is not well understood. To begin to address this question, we set out to identify major metabolites of a neuroprotective synthetic steroid 20-oxo-5β-pregnan-3α-yl l-glutamyl 1-ester (pregnanolone glutamate, PAG) and characterize their effects on GABAA and NMDA receptors (GABARs, NMDARs) and their influence on zebrafish behavior. Gas chromatography-mass spectrometry was used to assess concentrations of PAG and its metabolites in the hippocampal tissue of juvenile rats following intraperitoneal PAG injection. PAG is metabolized in the peripheral organs and nervous tissue to 20-oxo-17α-hydroxy-5β-pregnan-3α-yl l-glutamyl 1-ester (17-hydroxypregnanolone glutamate, 17-OH-PAG), 3α-hydroxy-5β-pregnan-20-one (pregnanolone, PA), and 3α,17α-dihydroxy-5β-pregnan-20-one (17-hydroxypregnanolone, 17-OH-PA). Patch-clamp electrophysiology experiments in cultured hippocampal neurons demonstrate that PA and 17-OH-PA are potent positive modulators of GABARs, while PAG and 17-OH-PA have a moderate inhibitory effect at NMDARs. PAG, 17-OH-PA, and PA diminished the locomotor activity of zebrafish larvae in a dose-dependent manner. Our results show that PAG and its metabolites are potent modulators of neurotransmitter receptors with behavioral consequences and indicate that neurosteroid-based ligands may have therapeutic potential.

Modulation of Muscarinic Signalling in the Central Nervous System by Steroid Hormones and Neurosteroids

Muscarinic acetylcholine receptors expressed in the central nervous system mediate various functions, including cognition, memory, or reward. Therefore, muscarinic receptors represent potential pharmacological targets for various diseases and conditions, such as Alzheimer's disease, schizophrenia, addiction, epilepsy, or depression. Muscarinic receptors are allosterically modulated by neurosteroids and steroid hormones at physiologically relevant concentrations. In this review, we focus on the modulation of muscarinic receptors by neurosteroids and steroid hormones in the context of diseases and disorders of the central nervous system. Further, we propose the potential use of neuroactive steroids in the development of pharmacotherapeutics for these diseases and conditions.

Steroid hormones of the octopus self-destruct system

Among all invertebrates, soft-bodied cephalopods have the largest central nervous systems and the greatest brain-to-body mass ratios, yet unlike other big-brained animals, cephalopods are unusually short lived.^1-5 Primates and corvids survive for many decades, but shallow-water octopuses, such as the California two-spot octopus (Octopus bimaculoides), typically live for only 1 year.^6,7 Lifespan and reproduction are controlled by the principal neuroendocrine center of the octopus: the optic glands, which are functional analogs to the vertebrate pituitary gland.^8-10 After mating, females steadfastly brood their eggs, begin fasting, and undergo rapid physiological decline, featuring repeated self-injury and leading to death.¹¹ Removal of the optic glands completely reverses this life history trajectory,¹⁰ but the signaling factors underlying this major life transition are unknown. Here, we characterize the major secretions and steroidogenic pathways of the female optic gland using mass spectrometry techniques. We find that at least three pathways are mobilized to increase synthesis of select sterol hormones after reproduction. One pathway generates pregnane steroids, known in other animals to support reproduction.^12-16 Two other pathways produce 7-dehydrocholesterol and bile acid intermediates, neither of which were previously known to be involved in semelparity. Our results provide insight into invertebrate cholesterol pathways and confirm a remarkable unity of steroid hormone biology in life history processes across Bilateria.

The Role of Sex and Sex Hormones in Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are a wide class of disorders of the central nervous system (CNS) with unknown etiology. Several factors were hypothesized to be involved in the pathogenesis of these diseases, including genetic and environmental factors. Many of these diseases show a sex prevalence and sex steroids were shown to have a role in the progression of specific forms of neurodegeneration. Estrogens were reported to be neuroprotective through their action on cognate nuclear and membrane receptors, while adverse effects of male hormones have been described on neuronal cells, although some data also suggest neuroprotective activities. The response of the CNS to sex steroids is a complex and integrated process that depends on (i) the type and amount of the cognate steroid receptor and (ii) the target cell type-either neurons, glia, or microglia. Moreover, the levels of sex steroids in the CNS fluctuate due to gonadal activities and to local metabolism and synthesis. Importantly, biochemical processes involved in the pathogenesis of NDs are increasingly being recognized as different between the two sexes and as influenced by sex steroids. The aim of this review is to present current state-of-the-art understanding on the potential role of sex steroids and their receptors on the onset and progression of major neurodegenerative disorders, namely, Alzheimer's disease, Parkinson's diseases, amyotrophic lateral sclerosis, and the peculiar motoneuron disease spinal and bulbar muscular atrophy, in which hormonal therapy is potentially useful as disease modifier.

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.

7α-Hydroxypregnenolone regulating locomotor behavior identified in the brain and pineal gland across vertebrates

The brain synthesizes steroids de novo from cholesterol, which are called neurosteroids. Based on extensive studies on neurosteroids over the past thirty years, it is now accepted that neurosteroidogenesis in the brain is a conserved property across vertebrates. However, the formation of bioactive neurosteroids in the brain is still incompletely elucidated in vertebrates. In fact, we recently identified 7α-hydroxypregnenolone (7α-OH PREG) as a novel bioactive neurosteroid stimulating locomotor behavior in the brain of several vertebrates. The follow-up studies have demonstrated that the stimulatory action of brain 7α-OH PREG on locomotor behavior is mediated by the dopaminergic system across vertebrates. More recently, we have further demonstrated that the pineal gland, an endocrine organ located close to the brain, is a major site of the formation of bioactive neurosteroids. In addition to the brain, the pineal gland actively produces 7α-OH PREG de novo from cholesterol as a major pineal neurosteroid that acts on the brain to control locomotor rhythms. This review summarizes the identification, biosynthesis and mode of action of brain and pineal 7α-OH PREG, a new bioactive neurosteroid regulating locomotor behavior, across vertebrates.

A comparison of sex steroid concentration levels in the vitreous and serum of patients with vitreoretinal diseases

The purpose of this study was to compare steroid hormone concentration levels in the vitreous and serum of vitreoretinal disease patients to elucidate the possibility of neurosteroid production in the retina. Serum and vitreous samples were collected from vitrectomy patients, and estradiol (E2) and testosterone (T) concentrations were measured using electro-chemiluminescence immunoassay. We measured E2 in epiretinal membrane (ERM, n = 14), macular hole (MH, n = 18), proliferative diabetic retinopathy (PDR, n = 20), and retinal detachment (RD, n = 19) cases, and T in ERM (n = 14), MH (n = 17), PDR (n = 13), and RD (n = 17) cases. No statistically significant age differences existed among the groups. Mean respective E2 concentrations (pg/ml) in the male/female vitreous were ERM: 6.67±4.04/18.82±7.10, MH: 10.3±7.02/17.00±4.8, PDR: 4.2±3.05/15.83±3.46, and RD: 10.00±4.58/16.06±4.57, while those in serum were ERM: 31.67±5.51/5.82±1.08, MH: 21.00±8.89/7.53±3.2, PDR: 29.20±7.07/12.75±10.62, and RD: 24.33±6.51/7.5±4.42. E2 concentrations were significantly higher (P<0.001) in the male serum than vitreous, yet significantly higher in the female vitreous than serum. Mean respective T concentrations (ng/ml) in the male/female vitreous were ERM: 0.15±0.03/0.15±0.01, MH: 0.15±0.01/0.15±0.01, PDR: 0.15±0.03/0.16±0.12, and RD: 0.14±0.01/0.17±0.08, while those in serum were ERM: 4.54±1.46/0.16±0.01, MH: 8.04±2.29/0.16±0.10, PDR: 5.14±1.54/0.22±0.11, and RD: 3.24±0.75/0.17±0.10. T concentrations were high in the male serum, yet extremely low in the male and female vitreous and female serum. High concentrations of E2 were found in the vitreous, and women, in particular, exhibited significantly higher concentrations in the vitreous than in the serum. This finding suggests the possibility that in vitreoretinal disease cases, the synthesis of E2 is increased locally only in female eyes.

Neurosteroid biosynthesis down-regulation and changes in GABAA receptor subunit composition: a biomarker axis in stress-induced cognitive and emotional impairment

By rapidly modulating neuronal excitability, neurosteroids regulate physiological processes, such as responses to stress and development. Excessive stress affects their biosynthesis and causes an imbalance in cognition and emotions. The progesterone derivative, allopregnanolone (Allo) enhances extrasynaptic and postsynaptic inhibition by directly binding at GABA_A receptors, and thus, positively and allosterically modulates the function of GABA. Allo levels are decreased in stress-induced psychiatric disorders, including depression and post-traumatic stress disorder (PTSD), and elevating Allo levels may be a valid therapeutic approach to counteract behavioural dysfunction. While benzodiazepines are inefficient, selective serotonin reuptake inhibitors (SSRIs) represent the first choice treatment for depression and PTSD. Their mechanisms to improve behaviour in preclinical studies include neurosteroidogenic effects at low non-serotonergic doses. Unfortunately, half of PTSD and depressed patients are resistant to current prescribed 'high' dosage of these drugs that engage serotonergic mechanisms. Unveiling novel biomarkers to develop more efficient treatment strategies is in high demand. Stress-induced down-regulation of neurosteroid biosynthesis and changes in GABA_A receptor subunit expression offer a putative biomarker axis to develop new PTSD treatments. The advantage of stimulating Allo biosynthesis relies on the variety of neurosteroidogenic receptors to be targeted, including TSPO and endocannabinoid receptors. Furthermore, stress favours a GABA_A receptor subunit composition with higher sensitivity for Allo. The use of synthetic analogues of Allo is a valuable alternative. Pregnenolone or drugs that stimulate its levels increase Allo but also sulphated steroids, including pregnanolone sulphate which, by inhibiting NMDA tonic neurotransmission, provides neuroprotection and cognitive benefits. In this review, we describe current knowledge on the effects of stress on neurosteroid biosynthesis and GABA_A receptor neurotransmission and summarize available pharmacological strategies that by enhancing neurosteroidogenesis are relevant for the treatment of SSRI-resistant patients. Linked Articles This article is part of a themed section on Pharmacology of Cognition: a Panacea for Neuropsychiatric Disease? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.19/issuetoc.

Metabolism of selective 20-epi-vitamin D3 analogs in rat osteosarcoma UMR-106 cells: Isolation and identification of four novel C-1 fatty acid esters of 1α,25-dihydroxy-16-ene-20-epi-vitamin D3

Analogs of 1α,25-dihydroxyvitamin D₃ (S1) with 20-epi modification (20-epi analogs) possess unique biological properties. We previously reported that 1α,25-dihydroxy-20-epi-vitamin D₃ (S2), the basic 20-epi analog is metabolized into less polar metabolites (LPMs) in rat osteosarcoma cells (UMR-106) but not in a perfused rat kidney. Furthermore, we also noted that only selective 20-epi analogs are metabolized into LPMs. For example, 1α,25-dihydroxy-16-ene-20-epi-vitamin D₃ (S4), but not 1α,25-dihydroxy-16-ene-23-yne-20-epi-vitamin D₃ (S5) is metabolized into LPMs. In spite of these novel findings, the unequivocal identification of LPMs has not been achieved to date. We report here on a thorough investigation of the metabolism of S4 in UMR-106 cells and isolated two major LPMs produced directly from the substrate S4 itself and two minor LPMs produced from 3-epi-S4, a metabolite of S4 produced through C-3 epimerization pathway. Using GC/MS, ESI-MS and ¹H NMR analysis, we identified all the four LPMs of S4 as 25-hydroxy-16-ene-20-epi-vitamin D₃-1-stearate and 25-hydroxy-16-ene-20-epi-vitamin D₃-1-oleate and their respective C-3 epimers. We report here for the first time the elucidation of a novel pathway of metabolism in UMR-106 cells in which both 1α,25(OH)₂-16-ene-20-epi-D₃ and 1α,25(OH)₂-16-ene-20-epi-3-epi-D₃ undergo C-1 esterification into stearic and oleic acid esters.

Current status and future perspectives: TSPO in steroid neuroendocrinology

The mitochondrial translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor (PBR), has received significant attention both as a diagnostic biomarker and as a therapeutic target for different neuronal disease pathologies. Recently, its functional basis believed to be mediating mitochondrial cholesterol import for steroid hormone production has been refuted by studies examining both in vivo and in vitro genetic Tspo-deficient models. As a result, there now exists a fundamental gap in the understanding of TSPO function in the nervous system, and its putative pharmacology in neurosteroid production. In this review, we discuss several recent findings in steroidogenic cells that are in direct contradiction to previous studies, and necessitate a re-examination of the purported role for TSPO in de novo neurosteroid biosynthesis. We critically examine the pharmacological effects of different TSPO-binding drugs with particular focus on studies that measure neurosteroid levels. We highlight the basis of key misconceptions regarding TSPO that continue to pervade the literature, and the need for interpretation with caution to avoid negative impacts. We also summarize the emerging perspectives that point to new directions that need to be investigated for understanding the molecular function of TSPO, only after which the true potential of this therapeutic target in medicine may be realized.

Nongenomic actions of neurosteroid pregnenolone and its metabolites

Steroids have been widely used in the clinical setting. They bind and activate nuclear receptors to regulate gene expression. In addition to activating genomic transcription, steroids also exert nongenomic actions. The current article focuses on the nongenomic actions of neurosteroids, including pregnenolone (P5), 7α-hydroxypregnenolone, pregnenolone sulfate and allopregnanolone. Pregnenolone and its derivatives promote neuronal activity by enhancing learning and memory, relieving depression, enhancing locomotor activity, and promoting neuronal cell survival. They exert these effects by activating various target proteins located in the cytoplasm or cell membrane. Pregnenolone and its metabolites bind to receptors such as microtubule-associated proteins and neurotransmitter receptors to elicit a series of reactions including stabilization of microtubules, increase of ion flux into cells, and dopamine release. The wide actions of neurosteroids indicate that pregnenolone derivatives have great potential in future treatment of neurological diseases.

How to contribute to the progress of neuroendocrinology: New insights from discovering novel neuropeptides and neurosteroids regulating pituitary and brain functions

Obtaining new insights by discovering novel neuropeptides and neurosteroids regulating pituitary and brain functions is essential for the progress of neuroendocrinology. At the beginning of 1970s, gonadotropin-releasing hormone (GnRH) was discovered in mammals. Since then, it was generally accepted that GnRH is the only hypothalamic neuropeptide regulating gonadotropin release in vertebrates. In 2000, however, gonadotropin-inhibitory hormone (GnIH), a novel hypothalamic neuropeptide that actively inhibits gonadotropin release, was discovered in quail. The follow-up studies demonstrated that GnIH acts as a new key player for regulation of reproduction across vertebrates. It now appears that GnIH acts on the pituitary and the brain to serve a number of behavioral and physiological functions. On the other hand, a new concept has been established that the brain synthesizes steroids, called neurosteroids. The formation of neurosteroids in the brain was originally demonstrated in mammals and subsequently in other vertebrates. Recently, 7α-hydroxypregnenolone was discovered as a novel bioactive neurosteroid inducing locomotor behavior of vertebrates, indicating that neurosteroidogenesis in the brain is still incompletely elucidated in vertebrates. At the beginning of 2010s, it was further found that the pineal gland actively produces neurosteroids. Pineal neurosteroids act on the brain to regulate locomotor rhythms and neuronal survival. Furthermore, the interaction of neuropeptides and neurosteroids is becoming clear. GnIH decreases aggressive behavior by regulating neuroestrogen synthesis in the brain. This review summarizes these new insights by discovering novel neuropeptides and neurosteroids in the field of neuroendocrinology.

New steps forward in the neuroactive steroid field

Evidence accumulated in recent years suggests that the systemic treatment with neuroactive steroids, or the pharmacological modulation of its production by brain cells, represent therapeutic options to promote neuroprotection. However, new findings, which are reviewed in this paper, suggest that the factors to be considered for the design of possible therapies based on neuroactive steroids are more complex than previously thought. Thus, although as recently reported, the nervous system regulates neuroactive steroid synthesis and metabolism in adaptation to modifications in peripheral steroidogenesis, the neuroactive steroid levels in the brain do not fully reflect its levels in plasma. Even, in some cases, neuroactive steroid level modifications occurring in the nervous tissues, under physiological and pathological conditions, are in the opposite direction than in the periphery. This suggests that the systemic treatment with these molecules may have unexpected outcomes on neural steroid levels. In addition, the multiple metabolic pathways and signaling mechanisms of neuroactive steroids, which may change from one brain region to another, together with the existence of regional and sex differences in its neural levels are additional sources of complexity that should be clarified. This complexity in the levels and actions of these molecules may explain why in some cases these molecules have detrimental rather than beneficial actions for the nervous system. This article is part of a Special Issue entitled 'Steroid Perspectives'.

Breakthrough in neuroendocrinology by discovering novel neuropeptides and neurosteroids: 2. Discovery of neurosteroids and pineal neurosteroids

Bargmann-Scharrer's discovery of "neurosecretion" in the first half of the 20th century has since matured into the scientific discipline of neuroendocrinology. Identification of novel neurohormones, such as neuropeptides and neurosteroids, is essential for the progress of neuroendocrinology. Our studies over the past two decades have significantly broadened the horizons of this field of research by identifying novel neuropeptides and neurosteroids in vertebrates that have opened new lines of scientific investigation in neuroendocrinology. We have established de novo synthesis and functions of neurosteroids in the brain of various vertebrates. Recently, we discovered 7α-hydroxypregnenolone (7α-OH PREG), a novel bioactive neurosteroid that acts as a key regulator for inducing locomotor behavior by means of the dopaminergic system. We further discovered that the pineal gland, an endocrine organ located close to the brain, is an important site of production of neurosteroids de novo from cholesterol (CHOL). The pineal gland secretes 7α-OH PREG and 3α,5α-tetrahydroprogesterone (3α,5α-THP; allopregnanolone) that are involved in locomotor rhythms and neuronal survival, respectively. Subsequently, we have demonstrated their mode of action and functional significance. This review summarizes the discovery of these novel neurosteroids and its contribution to the progress of neuroendocrinology.

Pregnenolone sulfate as a modulator of synaptic plasticity

RATIONALE

The neurosteroid pregnenolone sulfate (PregS) acts as a cognitive enhancer and modulator of neurotransmission, yet aligning its pharmacological and physiological effects with reliable measurements of endogenous local concentrations and pharmacological and therapeutic targets has remained elusive for over 20 years.

OBJECTIVES

New basic and clinical research concerning neurosteroid modulation of the central nervous system (CNS) function has emerged over the past 5 years, including important data involving pregnenolone and various neurosteroid precursors of PregS that point to a need for a critical status update.

RESULTS

Highly specific actions of PregS affecting excitatory N-methyl-D-aspartate receptor (NMDAR)-mediated synaptic transmission and the pharmacological effects of PregS on various receptors and ion channels are discussed. The discovery of a high potency (nanomolar) signal transduction pathway for PregS-induced NMDAR trafficking to the cell surface via a Ca(2+)- and G protein-coupled receptor (GPCR)-dependent mechanism and a potent (EC50 ~ 2 pM) direct enhancement of intracellular Ca(2+) levels is discussed in terms of its agonist effects on long-term potentiation (LTP) and memory. Lastly, preclinical and clinical studies assessing the promnestic effects of PregS and pregnenolone toward cognitive dysfunction in schizophrenia, and altered serum levels in epilepsy and alcohol dependence, are reviewed.

CONCLUSIONS

PregS is present in human and rodent brain at physiologically relevant concentrations and meets most of the criteria for an endogenous neurotransmitter/neuromodulator. PregS likely plays a significant role in modulation of glutamatergic excitatory synaptic transmission underlying learning and memory, yet the molecular target(s) for its action awaits identification.

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.

Pregnenolone sulfate: from steroid metabolite to TRP channel ligand

Pregnenolone sulfate is a steroid metabolite with a plethora of actions and functions. As a neurosteroid, pregnenolone sulfate modulates a variety of ion channels, transporters, and enzymes. Interestingly, as a sulfated steroid, pregnenolone sulfate is not the final- or waste-product of pregnenolone being sulfated via a phase II metabolism reaction and renally excreted, as one would presume from the pharmacology textbook knowledge. Pregnenolone sulfate is also the source and thereby the starting point for subsequent steroid synthesis pathways. Most recently, pregnenolone sulfate has been functionally “upgraded” from modulator of ion channels to an activating ion channel ligand. This review will focus on molecular aspects of the neurosteroid, pregnenolone sulfate, its metabolism, concentrations in serum and tissues and last not least will summarize the functional data.

Brain and pineal 7α-hydroxypregnenolone stimulating locomotor activity: identification, mode of action and regulation of biosynthesis

Biologically active steroids synthesized in the central and peripheral nervous systems are termed neurosteroids. However, the biosynthetic pathways leading to the formation of neurosteroids are still incompletely elucidated. 7α-Hydroxypregnenolone, a novel bioactive neurosteroid stimulating locomotor activity, has been recently identified in the brain of newts and quail. Subsequently, the mode of action and regulation of biosynthesis of 7α-hydroxypregnenolone have been determined. Moreover, recent studies on birds have demonstrated that the pineal gland, an endocrine organ located close to the brain, is an important site of production of neurosteroids de novo from cholesterol. 7α-Hydroxypregnenolone is a major pineal neurosteroid that stimulates locomotor activity in juvenile chickens, connecting light-induced gene expression with locomotion. This review summarizes the advances in our understanding of the identification, mode of action and regulation of biosynthesis of brain and pineal 7α-hydroxypregnenolone, a potent stimulator of locomotor activity.

New biosynthesis and biological actions of avian neurosteroids

De novo neurosteroidogenesis from cholesterol occurs in the brain of various avian species. However, the biosynthetic pathways leading to the formation of neurosteroids are still not completely elucidated. We have recently found that the avian brain produces 7α-hydroxypregnenolone, a novel bioactive neurosteroid that stimulates locomotor activity. Until recently, it was believed that neurosteroids are produced in neurons and glial cells in the central and peripheral nervous systems. However, our recent studies on birds have demonstrated that the pineal gland, an endocrine organ located close to the brain, is an important site of production of neurosteroids de novo from cholesterol. 7α-Hydroxypregnenolone is a major pineal neurosteroid that stimulates locomotor activity of juvenile birds, connecting light-induced gene expression with locomotion. The other major pineal neurosteroid allopregnanolone is involved in Purkinje cell survival during development. This paper highlights new aspects of neurosteroid synthesis and actions in birds.

Biosynthesis and biological actions of pineal neurosteroids in domestic birds

The central and peripheral nervous systems have the capacity of synthesizing steroids de novo from cholesterol, the so-called 'neurosteroids'. De novo synthesis of neurosteroids from cholesterol appears to be a conserved property across the subphylum vertebrata. Until recently, it was generally believed that neurosteroids are produced in neurons and glial cells in the central and peripheral nervous systems. However, our recent studies on birds have demonstrated that the pineal gland, an endocrine organ located close to the brain, is an important site of production of neurosteroids de novo from cholesterol. 7α-Hydroxypregnenolone is a major pineal neurosteroid that stimulates locomotor activity of juvenile birds, connecting light-induced gene expression with locomotion. The other major pineal neurosteroid allopregnanolone is involved in Purkinje cell survival by suppressing the activity of caspase-3, a crucial mediator of apoptosis during cerebellar development. This review is an updated summary of the biosynthesis and biological actions of pineal neurosteroids.

Quantitative determination of dehydroepiandrosterone fatty acyl esters in human female adipose tissue and serum using mass spectrometric methods

Dehydroepiandrosterone-fatty acyl esters (DHEA-FAE) are naturally occurring water-insoluble metabolites of DHEA, which are transported in plasma exclusively by lipoproteins. To find out whether DHEA, like estradiol, might be stored in adipose tissue in FAE form, we set up a mass spectrometric method to quantify DHEA-FAE and free DHEA in human adipose tissue and serum. The method consists of chromatographic purification steps and final determination of hydrolyzed DHEA-FAE and free DHEA, which was carried out by gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS). Our results showed that no detectable amounts of DHEA-FAE could be found in adipose tissue although 32-178 pmol/g of free DHEA were determined by GC-MS and LC-MS/MS. The DHEA-FAE concentrations in serum quantified by GC-MS were 1.4±0.7 pmol/ml in premenopausal women (n=7), and 0.9±0.4 pmol/ml in postmenopausal women (n=5). Correspondingly, the free DHEA concentrations were 15.2±6.3 pmol/ml and 6.8±3.0 pmol/ml. In addition, the mean proportions of DHEA-FAE of total DHEA (DHEA-FAE+free DHEA) in serum were 8.6% and 11.2% in pre- and postmenopausal women, respectively. Serum DHEA-FAE concentration was below quantification limit for LC-MS/MS (signal-to-noise ratio, S/N=10), while free DHEA concentrations varied between 5.8 and 23.2 pmol/ml. In conclusion, the proportion of DHEA-FAE of total DHEA in serum was approximately 9%. However, in contrast to our previous findings for estradiol fatty acid esters in adipose tissue which constituted about 80% of total estradiol (esterified+free), the proportion of DHEA-FAE of total DHEA was below 5%. Four to ten times higher concentrations of free DHEA were quantified in adipose tissue compared to those in serum.

Effect of progesterone on phosphamidon-induced impairment of memory and oxidative stress in rats

Progesterone (a neurosteroid) is an important modulator of the nervous system functioning. Organophosphorus pesticides like phosphamidon have been shown to adversely affect memory and induce oxidative stress on both acute and chronic exposure. The present study was therefore designed to investigate the effects of progesterone (PROG) on phosphamidon-induced modulation of cognitive function and oxidative stress in rats. Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus and transfer latency (TL) on an elevated plus maze. Oxidative stress was assessed by examining the levels of thiobarbituric acid reactive species (TBARS) and non-protein thiols (NP-SH) in isolated homogenized whole brain samples. The results showed a significant reduction in SDL and prolongation of TL in the phosphamidon (1.74 mg/kg/d; p.o.) treated group at weeks 6 and 8 as compared to the control group. Two weeks treatment with PROG (15 mg/kg/d; i.p.) antagonized the effect of phosphamidon on SDL as well as TL. Phosphamidon alone produced a significant increase in the brain TBARS levels and decrease in the brain NP-SH levels. Treatment with PROG (15 mg/kg/d; i.p.) attenuated the effect of phosphamidon on oxidative stress. Together, the results showed that progesterone attenuated the cognitive dysfunction and increased oxidative stress induced by phosphamidon in the 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.

Neurosteroid biosynthesis and function in the brain of domestic birds

It is now established that the brain and other nervous systems have the capability of forming steroids de novo, the so-called "neurosteroids." The pioneering discovery of Baulieu and his colleagues, using rodents, has opened the door to a new research field of "neurosteroids." In contrast to mammalian vertebrates, little has been known regarding de novo neurosteroidogenesis in the brain of birds. We therefore investigated neurosteroid formation and metabolism in the brain of quail, a domestic bird. Our studies over the past two decades demonstrated that the quail brain possesses cytochrome P450 side-chain cleavage enzyme (P450scc), 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4)-isomerase (3β-HSD), 5β-reductase, cytochrome P450 17α-hydroxylase/c17,20-lyase (P450(17α,lyase)), 17β-HSD, etc., and produces pregnenolone, progesterone, 5β-dihydroprogesterone (5β-DHP), 3β, 5β-tetrahydroprogesterone (3β, 5β-THP), androstenedione, testosterone, and estradiol from cholesterol. Independently, Schlinger's laboratory demonstrated that the brain of zebra finch, a songbird, also produces various neurosteroids. Thus, the formation and metabolism of neurosteroids from cholesterol is now known to occur in the brain of birds. In addition, we recently found that the quail brain expresses cytochrome P450(7α) and produces 7α- and 7β-hydroxypregnenolone, previously undescribed avian neurosteroids, from pregnenolone. This paper summarizes the advances made in our understanding of neurosteroid formation and metabolism in the brain of domestic birds. This paper also describes what are currently known about physiological changes in neurosteroid formation and biological functions of neurosteroids in the brain of domestic and other birds.

Effect of short-and long-term gonadectomy on neuroactive steroid levels in the central and peripheral nervous system of male and female rats

Significant levels of neuroactive steroids are still detected in the nervous system of rodents after the removal of peripheral steroidogenic glands. However, the influence of the plasma levels of gonadal steroids on the levels of neuroactive steroids in the nervous system has not so far been clarified in detail. Accordingly, by liquid chromatography tandem mass spectrometry, we have analysed the levels of neuroactive steroids in the sciatic nerve, in three central nervous system (CNS) regions (i.e. cerebellum, cerebral cortex and spinal cord) and in the plasma of male and female animals. The levels present in gonadally intact animals were compared with those present in short- and long-term gonadectomised animals. We observed that: (i) changes in neuroactive steroid levels in the nervous system after gonadectomy do not necessarily reflect the changes in plasma levels; (ii) long-term gonadectomy induces changes in the levels of neuroactive steroids in the peripheral nervous system (PNS) and the CNS that, in some cases, are different to those induced by short-term gonadectomy; (iii) the effect of gonadectomy on neuroactive steroid levels is different between the PNS and the CNS and within different CNS regions; and (iv) the effects of gonadectomy on neuroactive steroid levels in the nervous system show sex differences. Altogether, these observations indicate that the nervous system adapts its local levels of neuroactive steroids in response to changes in gonadal hormones with sex and regional specificity and depending on the duration of the peripheral modifications.

7α-hydroxypregnenolone, a new key regulator of locomotor activity of vertebrates: identification, mode of action, and functional significance

Steroids synthesized de novo by the central and peripheral nervous systems are called neurosteroids. The formation of neurosteroids from cholesterol in the brain was originally demonstrated in mammals by Baulieu and colleagues. Our studies over the past two decades have also shown that, in birds and amphibians as in mammals, the brain expresses several kinds of steroidogenic enzymes and produces a variety of neurosteroids. Thus, de novo neurosteroidogenesis from cholesterol is a conserved property that occurs throughout vertebrates. However, the biosynthetic pathways of neurosteroids in the brain of vertebrates was considered to be still incompletely elucidated. Recently, 7α-hydroxypregnenolone was identified as a novel bioactive neurosteroid stimulating locomotor activity in the brain of newts and quail through activation of the dopaminergic system. Subsequently, diurnal and seasonal changes in synthesis of 7α-hydroxypregnenolone in the brain were demonstrated. Interestingly, melatonin derived from the pineal gland and eyes regulates 7α-hydroxypregnenolone synthesis in the brain, thus inducing diurnal locomotor changes. Prolactin, an adenohypophyseal hormone, regulates 7α-hydroxypregnenolone synthesis in the brain, and may also induce seasonal locomotor changes. This review highlights the identification, mode of action, and functional significance of 7α-hydroxypregnenolone, a new key regulator of locomotor activity of vertebrates, in terms of diurnal and seasonal changes in 7α-hydroxypregnenolone synthesis, and describes some of their regulatory mechanisms.

Reversal of propoxur-induced impairment of memory and oxidative stress by 4'-chlorodiazepam in rats

Carbamate pesticides like propoxur have been shown to adversely affect memory and induce oxidative stress on both acute and chronic exposure. The present study was designed to explore the modulation of the effects of propoxur over cognitive function by progesterone (PROG) and 4'-chlorodiazepam (4CD). Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus, transfer latency (TL) on a plus maze and spatial navigation test on Morris water maze. Oxidative stress was assessed by examining brain malondialdehyde (MDA) and reduced glutathione (GSH) levels and catalase (CAT) activity. A significant reduction in SDL and prolongation of TL and spatial navigation test was found for the propoxur (10 mg/kg/d; p.o.) treated group at weeks 6 and 7 as compared with control. One-week treatment with 4CD (0.5 mg/kg/d; i.p.) antagonized the effect of propoxur on SDL, spatial navigation test as well as TL; whereas, PROG failed to modulate this effect at a dose of 15 mg/kg/d, i.p. Propoxur produced a statistically significant increase in the brain MDA levels and decrease in the brain GSH levels and CAT activity. Treatment with 4CD at the above dose attenuated the effect of propoxur on oxidative stress whereas PROG (15 mg/kg/d; i.p.) failed to influence the same. The results of the present study thus show that 4-CD has the potential to attenuate cognitive dysfunction and oxidative stress induced by toxicants like propoxur in the brain.

Discovery of a novel avian neurosteroid, 7alpha-hydroxypregnenolone, and its role in the regulation of the diurnal rhythm of locomotor activity in Japanese quail

The discovery of two novel avian neurosteroids in the quail brain, 7alpha- and 7beta-hydroxypregnenolone is described. Intracerebroventricular administration of 7alpha-hydroxypregnenolone, but not 7beta-hydroxypregnenolone was found to stimulate locomotor activity of male quail when spontaneous nocturnal activity is low. Diurnal changes in locomotor activity in male quail were found to be correlated with a diurnal change in the concentration of diencephalic 7alpha-hydroxypregnenolone. This correlation was a not seen in female quail which have a lower amplitude diurnal rhythm of locomotor activity and lower daytime concentrations of diencephalic 7alpha-hydroxypregnenolone. Treatment of male quail with melatonin was found to depress the synthesis of 7alpha-hydroxypregnenolone in the diencephalon. This is a previously undescribed role for melatonin in the regulation of neurosteroid synthesis in the brain of any vertebrate. We therefore deduced in male quail, that the nocturnal depression in locomotory activity is a consequence of a depression in diencephalic 7alpha-hydroxypregnenolone resulting from the inhibitory action of the nocturnal increase in melatonin. This observation may be of widespread significance for the molecular control of rhythmic locomotor activity in all vertebrates.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Immunohistochemical localization of hydroxysteroid sulfotransferase and sulfatase in the brain of Rana esculenta tadpoles

Sulfation plays a major role in regulating the activity of various neurosteroids, including pregnenolone and dehydroepiandrosterone. The present report describes the immunohistochemical distribution of two enzymes involved in the control of neurosteroid sulfation, hydroxysteroid sulfotransferase (HST) and unconjugated steroid enzyme sulfatase (STS), in the brain of the European green frog Rana esculenta during development. HST and STS immunoreactivity were detected from stage VIII-XII. At this early stage, HST-positive fibers were seen in the glomerular layer and the basal rhombencephalon. Subsequently, at stage XIII-XV, HST- and STS-immunoreactive fibers were vizualized in the accessory olfactory bulb. At stage XVI-XVIII, STS-positive cell bodies were observed in the periventricular region of the diencephalon. These observations indicate that the enzymes controlling sulfation of hydroxysteroids are expressed in the frog brain during development.

Analysis of pregnenolone and dehydroepiandrosterone in rodent brain: cholesterol autoxidation is the key

Pregnenolone (PREG) and dehydroepiandrosterone (DHEA), and their respective sulfated forms PREGS and DHEAS, were among the first steroids to be identified in rodent brain. However, unreliable steroid isolation and solvolysis procedures resulted in errors, particularly in the case of brain steroid sulfates analyzed by radioimmunology or GC-MS of liberated free steroids. By using a solid-phase extraction recycling/elution procedure, allowing the strict separation of sulfated, free, and fatty acid esters of PREG and DHEA, PREGS and DHEAS, unlike free PREG, were not detected in rat and mouse brain and plasma. Conversely, considerable amounts of PREG and DHEA were released from unknown precursor(s) present in the lipoidal fraction, distinct from fatty acid ester conjugates. Chromatographic and mass spectrometric studies of the nature of the precursor(s) showed that autoxidation of brain cholesterol (CHOL) was responsible for the release of PREG and DHEA from the lipoidal fraction. When inappropriate protocols were used, CHOL was also the precursor of PREG and DHEA obtained from the fraction assumed to contain sulfated steroids. In contrast, free PREG was definitely confirmed as an endogenous steroid in rat brain. Our study shows that an early removal of CHOL from brain extracts coupled to well-validated extraction and fractionation procedures are prerequisites for reliable measurements of free and conjugated PREG and DHEA by GC-MS or other indirect methods.

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.

Steroid sulfatase and sulfuryl transferase activities in human brain tumors

Neuroactive steroids (dehydroepiandrosterone, pregnenolone) and their sulfates act as modulators of glutamate and gamma-aminobutyrate type A receptors in the brain The physiological ratio of these neuromodulators is maintained by two enzymes present in the brain, namely, steroid sulfatase (STS) and steroid sulfuryl transferase (SULT). Following previous determination of their activities in monkey brains, their activities were evaluated in human brain tumors. Radioimmunoassay and GC-MS were used for determination of products. Both enzyme activities were measured in the 55 most frequent human brain tumors (glioblastomas, pituitary adenomas, meningiomas, astrocytomas). Significant differences were found in STS activity among investigated types of tumors except the pair of pituitary adenomas-glioblastomas, while significant differences were found in SULT activity among investigated types of tumors. Spontaneous tendency to form clusters was revealed when both enzyme activities were taken as coordinates. Clustering indicated an individual metabolic behavior of glioblastomas and 72.7% of pituitary adenomas. Astrocytomas, meningiomas and remaining 27.3% pituitary adenomas showed similarities in both enzymes' activities. Differences in STS and SULT activity did not depend on the sex or age of subjects.

Pregnenolone sulfate in the brain: a controversial neurosteroid

Pregnenolone sulfate (PREGS) has been shown, either at high nanomolar or at micromolar concentrations, to increase neuronal activity by inhibiting GABAergic and by stimulating glutamatergic neurotransmission. PREGS is also a potent modulator of sigma type 1 (sigma1) receptors. It has been proposed that these actions of PREGS underlie its neuropharmacological effects, and in particular its influence on memory processes. On the other hand, the PREGS-mediated increase in neuronal excitability may become dangerous under particular conditions, for example in the case of excitotoxic stress or convulsions. However, the physiopathological significance of these observations has recently been put into question by the failure to detect significant levels of PREGS within the brain and plasma of rats and mice, either by direct analytical methods based on liquid chromatography/mass spectrometry (LC/MS) or enzyme linked immunosorbent assay (ELISA) with specific antibodies against PREGS, or by indirect gas chromatography/mass spectrometry (GC/MS) analysis with improved sample workup. These recent results have not come to the attention of a large number of neurobiologists interested in steroid sulfates. However, although available direct analytical methods have failed to detect levels of PREGS above 0.1-0.3 ng/g in brain tissue, it may be premature to completely exclude the local formation of biologically active PREGS within specific and limited compartments of the nervous system. In contrast to the situation in rodents, significant levels of sulfated 3beta-hydroxysteroids have been measured in human plasma and brain. Previous indirect measures of steroid sulfates by radioimmunoassays (RIA) or GC/MS had detected elevated levels of PREGS in rodent brain. The discrepancies between the results of different assay procedures have revealed the danger of indirect analysis of steroid sulfates. Indeed, PREGS must be solvolyzed/hydrolyzed prior to RIA or GC/MS analysis, and it is the released, unconjugated PREG which is then quantified. Extreme caution needs to be exercised during the preparation of samples for RIA or GC/MS analysis, because the fraction presumed to contain only steroid sulfates can be contaminated by nonpolar components from which PREG is generated by the solvolysis/hydrolysis/derivatization reactions.

Neuroendocrine metabolism of progesterone and related progestins

In mammalian neuroendocrine structures the metabolic processing of progesterone and related natural progestins is primarily a reductive process involving the C-4,5 double bond and the C-3 and C-20 ketones. The principal products of the neuroendocrine metabolism of progesterone in female rats are the two 5 alpha- and 3 alpha-reduced metabolites, 5 alpha-dihydroprogesterone and 3 alpha,5 alpha-tetrahydroprogesterone, with lesser amounts of the corresponding 20 alpha-reduced products. Certain of these metabolites produce some, but not all, of progesterone's biological effects. 5 alpha-Dihydroprogesterone and 3 alpha,5 alpha-tetrahydroprogesterone, in particular, have potent progesterone-like effects on neuroendocrine functions, such as gonadotropin regulation. The two other principal ovarian progestins, 20 alpha-dihydroprogesterone and 17 alpha-hydroxyprogesterone, are metabolized in an analogous manner. The major neuroendocrine progestin conversions therefore appear to be 5 alpha-reduction and 3 alpha-hydroxysteroid oxidoreduction. In the hypothalamus and anterior pituitary, the enzymic activities that catalyse these conversions appear to be under ovarian control and appear to vary with changing reproductive states. These quantitative changes in processing, together with the potent progesterone-like effects of certain metabolites, suggest that these neuroendocrine conversions may provide an important mechanism for mediating some of the effects of progesterone. Alternatively, some metabolites, by duplicating selected effects of progesterone, may provide a means of prolonging certain of its effects while others are terminated.

Reversal of lindane-induced impairment of step-down passive avoidance and oxidative stress by neurosteroids in rats

Neurosteroids (NS) are recognized as important modulators of functioning of the nervous system. Lindane, an organochlorine pesticide has been shown to adversely affect memory and induce oxidative stress on both acute and chronic exposure. The present study was designed to explore the modulation of effects of lindane over cognitive function by progesterone (PROG), pregnenolone sulfate (PREG-S) and 4'-chlorodiazepam (4CD). Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus and transfer latency (TL) on a plus maze. Oxidative stress was assessed by examining brain malondialdehyde (MDA) and non-protein thiol (NP-SH) levels. A significant reduction in SDL was found for the lindane treated group at weeks 6 and 7 as compared to control (p<0.001). One-week treatment by PREG-S or 4CD antagonized the effect of lindane on SDL. PROG failed to modulate the effect of lindane on SDL. Lindane caused a significant prolongation of TL as compared to control (p<0.001) from second week onwards. One-week administration of PROG, PREG-S or 4CD was unable to reverse this prolongation of TL. Lindane produced a statistically significant increase in the brain MDA levels (p<0.001) and significant decrease in the brain NP-SH levels (p<0.001). Treatment with PREG-S and 4CD attenuated the effect of lindane on MDA (p<0.001) and NP-SH levels. PROG failed to influence oxidative stress induced by lindane. Results of the present study thus show that some NS have potential in reversing cognitive dysfunction and oxidative stress induced by toxicants like lindane in the brain.

Immunohistochemical localization and biological activity of the steroidogenic enzyme cytochrome P450 17α-hydroxylase/C17, 20-lyase (P450C17) in the frog brain and pituitary

It is now clearly established that the brain has the capability of synthesizing various biologically active steroids including 17-hydroxypregnenolone (17OH-Delta(5)P), 17-hydroxyprogesterone (17OH-P), dehydroepiandrosterone (DHEA) and androstenedione (Delta(4)). However, the presence, distribution and activity of cytochrome P450 17alpha-hydroxylase/C17, 20-lyase (P450(C17)), a key enzyme required for the conversion of pregnenolone (Delta(5)P) and progesterone (P) into these steroids, are poorly documented. Here, we show that P450(C17)-like immunoreactivity is widely distributed in the frog brain and pituitary. Prominent populations of P450(C17)-containing cells were observed in a number nuclei of the telencephalon, diencephalon, mesencephalon and metencephalon, as well as in the pars distalis and pars intermedia of the pituitary. In the brain, P450(C17)-like immunoreactivity was almost exclusively located in neurons. In several hypothalamic nuclei, P450(C17)-positive cell bodies also contained 3beta-hydroxysteroid dehydrogenase-like immunoreactivity. Incubation of telencephalon, diencephalon, mesencephalon, metencephalon or pituitary explants with [(3)H]Delta(5)P resulted in the formation of several tritiated steroids including 17OH-Delta(5)P, 17OH-P, DHEA and Delta(4). De novo synthesis of C(21) 17-hydroxysteroids and C(19) ketosteroids was reduced in a concentration-dependent manner by ketoconazole, a P450(C17) inhibitor. This is the first detailed immunohistochemical mapping of P450(C17) in the brain and pituitary of any vertebrate. Altogether, the present data provide evidence that CNS neurons and pituitary cells can synthesize androgens.

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.

Strain differences of neurosteroid levels in mouse brain

Neurosteroids, pregnenolone (Preg), dehydroepiandrosterone (DHEA) and their sulfates (PregS and DHEAS) are reported to exert their modulatory effects of neuronal excitability and synaptic plasticity via amino acid receptors, which affect and regulate the learning and memory process, mood, and depression. Although the brain levels of these steroids have been reported in rodents, the strain differences of the levels of these steroids have not been demonstrated. We examined the concentrations of Preg, 17-OH-Preg, DHEA, androstenediol (ADIOL) and their sulfates in whole brains from DBA/2, C57BL/6, BALB/c, ddY and ICR mice, the genetic backgrounds of which are different. No differences in the brain levels of Preg and DHEA were found among the strains. In contrast, PregS levels in DBA/2 were significantly lower than in the others, while DHEAS concentrations in DBA/2 were significantly higher than those in other strains. Strain differences were found in 17-OH-Preg, ADIOL and 17-OH-PregS but not in ADIOLS levels. The ranges of Preg and PregS levels were the highest among the steroids studied. Further, we measured serum these steroid levels. Although strain differences were also found in serum steroids, correlation study between brain and serum levels revealed that brain neurosteroids studied may not come from peripheral circulation. In conclusion, this is the first report of demonstrating mammalian brain levels of 17-OH-Preg, ADIOL, 17-OH-PregS and ADIOLS and the strain differences in neurosteroid levels in mice brains. The differences in levels may involve the strain differences in their behavior, e.g. aggression, adaptation to stress or learning, in mice.