Progesterone metabolism in the pineal, brain stem, thalamus and corpus callosum of the female rat

Biotransformation of Δ1-Progesterone Using Selected Entomopathogenic Filamentous Fungi and Prediction of Its Products' Bioactivity

This research aimed at obtaining new derivatives of pregn-1,4-diene-3,20-dione (Δ1-progesterone) (2) through microbiological transformation. For the role of catalysts, we used six strains of entomopathogenic filamentous fungi (Beauveria bassiana KCh J1.5, Beauveria caledonica KCh J3.3, Isaria fumosorosea KCh J2, Isaria farinosa KCh KW1.1, Isaria tenuipes MU35, and Metarhizium robertsii MU4). The substrate (2) was obtained by carrying out an enzymatic 1,2-dehydrogenation on an increased scale (3.5 g/L) using a recombinant cholest-4-en-3-one Δ1-dehydrogenase (AcmB) from Sterolibacterium denitrificans. All selected strains were characterized by the high biotransformation capacity for the used substrate. As a result of the biotransformation, six steroid derivatives were obtained: 11α-hydroxypregn-1,4-diene-3,20-dione (3), 6β,11α-dihydroxypregn-1,4-diene-3,20-dione (4), 6β-hydroxypregn-1,4-diene-3,11,20-trione (5), 6β,17α-dihydroxypregn-1,4-diene-3,20-dione (6), 6β,17β-dihydroxyandrost-1,4-diene-3-one (7), and 12β,17α-dihydroxypregn-1,4-diene-3,20-dione (8). The results show evident variability of the biotransformation process between strains of the tested biocatalysts from different species described as entomopathogenic filamentous fungi. The obtained products were tested in silico using cheminformatics tools for their pharmacokinetic and pharmacodynamic properties, proving their potentially high biological activities. This study showed that the obtained compounds may have applications as effective inhibitors of testosterone 17β-dehydrogenase. Most of the obtained products should, also with a high probability, find potential uses as androgen antagonists, a prostate as well as menopausal disorders treatment. They should also demonstrate immunosuppressive, erythropoiesis-stimulating, and anti-inflammatory properties.

Polymorphism, expression and structure analysis of key genes in the ovarian steroidogenesis pathway in sheep (Ovis aries)

Background

Litter size is an important factor that significantly affects the development of the sheep industry. Our previous TMT proteomics analysis found that three key proteins in the ovarian steroidogenesis pathway, STAR, HSD3B1, and CYP11A1, may affect the litter size trait of Small Tail Han sheep.

Objective

The purpose of this study was to better understand the relationship between polymorphisms of these three genes and litter size.

Material and Method

Sequenom MassARRAY detected genetic variance of the three genes in 768 sheep. Real‐time qPCR of the three genes was used to compare their expression in monotocous and polytocous sheep in relevant tissues. Finally, bioinformatics analysis predicted the protein sequences of the different SNP variants.

Result

Association analysis showed that there was a significant difference in litter size among the genotypes at two loci of the CYP11A1 gene (p < 0.05), but no significant difference was observed in litter size among all genotypes at all loci of the STAR and HSD3B1 genes (p > 0.05). However, STAR expression was significantly different in polytocous and monotocous sheep in the pituitary (p < 0.01). Tissue‐specific expression in the ovary was observed for HSD3B1 (p < 0.05), but its expression was not different between polytocous and monotocous sheep. Bioinformatics analysis showed that the g.33217408C > T mutation of CYP11A1 resulted in major changes to the secondary and tertiary structures. In contrast, gene polymorphisms in STAR and HSD3B1 had minimal impacts on their protein structures.

Discussion

This may explain why the CYP11A1 variant impacted litter size while the others did not. The single nucleotide polymorphism of the CYP11A1 gene would serve as a good molecular marker when breeding to increase litter size in sheep. Our study provides a basis for further revealing the function of the ovarian steroidogenesis pathway in sheep reproduction and sheep breeding.

Sex Steroids, Adult Neurogenesis, and Inflammation in CNS Homeostasis, Degeneration, and Repair

Sex steroidal hormones coordinate the development and maintenance of tissue architecture in many organs, including the central nervous systems (CNS). Within the CNS, sex steroids regulate the morphology, physiology, and behavior of a wide variety of neural cells including, but not limited to, neurons, glia, endothelial cells, and immune cells. Sex steroids spatially and temporally control distinct molecular networks, that, in turn modulate neural activity, synaptic plasticity, growth factor expression and function, nutrient exchange, cellular proliferation, and apoptosis. Over the last several decades, it has become increasingly evident that sex steroids, often in conjunction with neuroinflammation, have profound impact on the occurrence and severity of neuropsychiatric and neurodegenerative disorders. Here, I review the foundational discoveries that established the regulatory role of sex steroids in the CNS and highlight recent advances toward elucidating the complex interaction between sex steroids, neuroinflammation, and CNS regeneration through adult neurogenesis. The majority of recent work has focused on neuroinflammatory responses following acute physical damage, chronic degeneration, or pharmacological insult. Few studies directly assess the role of immune cells in regulating adult neurogenesis under healthy, homeostatic conditions. As such, I also introduce tractable, non-traditional models for examining the role of neuroimmune cells in natural neuronal turnover, seasonal plasticity of neural circuits, and extreme CNS regeneration.

Central opioid inhibition of neuroendocrine stress responses in pregnancy in the rat is induced by the neurosteroid allopregnanolone

The hypothalamus-pituitary-adrenal (HPA) axis is the major neuroendocrine stress response system. Corticotropin-releasing hormone (CRH) neurons in the parvocellular paraventricular nucleus (pPVN) play a key role in coordinating responses of this system to stressors. The cytokine interleukin-1beta (IL-1beta), mimicking infection, robustly activates these CRH neurons via a noradrenergic input arising from the nucleus tractus solitarii (NTS). In late pregnancy, HPA axis responses to stressors, including IL-1beta, are attenuated by a central opioid mechanism that auto-inhibits noradrenaline release in the PVN. Here we show that the neuroactive progesterone metabolite allopregnanolone induces these changes in HPA responsiveness to IL-1beta in pregnancy. In late pregnancy, inhibition of 5alpha-reductase (an allopregnanolone-synthesizing enzyme) with finasteride restored HPA axis responses (rapidly increased pPVN CRH mRNA expression, ACTH, and corticosterone secretion) to IL-1beta. Conversely, allopregnanolone reduced HPA responses in virgin rats. In late pregnancy, activity of the allopregnanolone-synthesizing enzymes (5alpha-reductase and 3alpha-hydroxysteroid dehydrogenase) was increased in the hypothalamus as was mRNA expression in the NTS and PVN. Naloxone, an opioid antagonist, restores HPA axis responses to IL-1beta in pregnancy but had no additional effect after finasteride, indicating a causal connection between allopregnanolone and the endogenous opioid mechanism. Indeed, allopregnanolone induced opioid inhibition over HPA responses to IL-1beta in virgin rats. Furthermore, in virgin rats, allopregnanolone treatment increased, whereas in pregnant rats finasteride decreased proenkephalin-A mRNA expression in the NTS. Thus, in pregnancy, allopregnanolone induces opioid inhibition over HPA axis responses to immune challenge. This novel opioid-mediated mechanism of allopregnanolone action may alter regulation of other brain systems in pregnancy.

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.

New insights into the role of neuroactive steroids in cognitive aging

The aim of this article is to describe neuroactive steroid research that has been focused on their physiological role in cognitive aging, an attractive new field in experimental gerontology. Neuroactive steroids have been recently proposed as biomarkers of cognitive aging, however, their specific functions have not yet been fully established. For instance, data emerging from human and animal studies suggest a complex relationship between neuroactive steroids and/or metabolites and cognitive processes during aging. Thus, a better knowledge of neuroactive steroid brain distribution and function could broaden our understanding of their physiological roles and lead to novel and more effective treatments for the management of age-related brain disorders. To this end, newly developed sensitive, specific, and accurate mass spectrometry assays may allow the quantification of neuroactive steroids in discrete brain regions and greatly contribute to unravel their role in age-related cognitive deficits.

Neurosteroids in rat brain: extraction, isolation, and analysis by nanoscale liquid chromatography-electrospray mass spectrometry

A method designed for the analysis of sulfated neurosteroids and unconjugated ketonic neurosteroids in rat brain using nanoscale liquid chromatography-electrospray (nano-LC-ES) mass spectrometry is described. Neurosteroids in rat brain tissue were extracted, purified, and separated into two groups, neutral unconjugated steroids and steroid sulfates, by employing solid-phase partition, cation- and anion-exchange chromatography. The steroid sulfate fraction was analyzed by nano-LC-ES mass spectrometry. Contrary to expectations, the sulfates of pregnenolone and dehydroepiandrosterone (DHEA) were not detected. Internal standards, including pregnenolone sulfate, were recovered and the detection limit of the method was 0.3 ng/g of wet brain. Cholesterol sulfate was detected at a level of 1.2 microg/g of wet brain. The neutral unconjugated steroid fraction was derivatized with hydroxylamine hydrochloride to convert oxosteroids into their oximes. The oximes were isolated using cation-exchange chromatography and were analyzed by nano-LC-ES tandem mass spectrometry. The analyses of the neutral unconjugated steroid fraction confirmed the presence in rat brain of pregnenolone, pregnanolone isomers, progesterone, testosterone, and DHEA, which were characterized by their retention times, the mass of the protonated molecules, and characteristic fragment ions. The levels were estimated by addition of [3,4-(13)C(2)]-progesterone as an internal standard and found to be in a range of 0.04-20 ng/g.

Biosynthesis and action of neurosteroids

Over the past decade, it has become clear that the brain, like the gonad, adrenal and placenta, is a steroidogenic organ. However, unlike classic steroidogenic tissues, the synthesis of steroids in the nervous system requires the coordinate expression and regulation of the genes encoding the steroidogenic enzymes in several different cell types (neurons and glia) at different locations in the nervous system, and at distances from the cell bodies. The steroids synthesized by the brain and nervous system, given the name neurosteroids, have a wide variety of diverse functions. In general, they mediate their actions, not through classic steroid hormone nuclear receptors, but through other mechanisms such as through ion gated neurotransmitter receptors, or through direct or indirect modulation of other neurotransmitter receptors. We have briefly summarized the biochemistry of the enzymes involved in the biosynthesis of neurosteroids, their localization during development and in the adult, and the regulation of their expression, highlighting both similarities and differences between expression in the brain and in classic steroidogenic tissues.

Neurosteroids: biosynthesis and function of these novel neuromodulators

Over the past decade, it has become clear that the brain is a steroidogenic organ. The steroids synthesized by the brain and nervous system, given the name neurosteroids, have a wide variety of diverse functions. In general, they mediate their actions, not through classic steroid hormone nuclear receptors, but through ion-gated neurotransmitter receptors. This paper summarizes what is known about the biosynthesis of neurosteroids, the enzymes mediating these reactions, their localization during development and in the adult, and their function and mechanisms of action in the developing and adult central and peripheral nervous systems. The expression of the steroidogenic enzymes is developmentally regulated, with some enzymes being expressed only during development, while others are expressed during development and in the adult. These enzymes are expressed in both neurons and glia, suggesting that these two cell types must work in concert to produce the appropriate active neurosteroid. The functions attributed to specific neurosteroids include modulation of GABA(A) and NMDA function, modulation of sigma receptor function, regulation of myelinization, neuroprotection, and growth of axons and dendrites. Neurosteroids have also been shown to modulate expression of particular subunits of GABA(A) and NMDA receptors, providing additional sites at which these compounds can regulate neural function. The pharmacological properties of specific neurosteroids are described, and potential uses of neurosteroids in specific neuropathologies and during normal aging in humans are also discussed.

Progesterone is neuroprotective after transient middle cerebral artery occlusion in male rats

Progesterone (PROG) is a neurosteroid, possessing a variety of functions in the central nervous system. Exogenous PROG has been shown to reduce secondary neuronal loss in conjunction with attenuated brain edema after cerebral contusion and to reduce brain edema after focal cerebral ischemia. In the present study, we assessed the neuroprotective potential of PROG in a model of focal cerebral ischemia in the rat. Forty-eight male Wistar rats were randomly assigned to 4 groups, i.e. pretreatment with water soluble PROG, or dimethyl sulfoxide (DMSO) dissolved PROG, or DMSO as control or delayed treatment with DMSO dissolved PROG. Middle cerebral artery occlusion (MCAO) was induced by insertion of an intraluminal suture and reperfusion was performed by withdrawing the suture. Pretreatments were initiated 30 min before MCAO via intraperitoneal injection. Delayed treatment was initiated upon reperfusion following 2 h of MCAO. Infarct volume, body weight loss, and neurological deficit were measured 48 h after MCAO. Pre- and delayed treatment with DMSO dissolved PROG resulted in a 39% (P < 0.05) and 34% (P < 0.05) reduction in cerebral infarction, respectively, along with decreased body weight loss and improved neurological function as compared to control animals, whereas no statistically significant reduction in infarct volume by water soluble PROG was found. We demonstrated that administration of PROG to the male rat before or 2 hours after onset of MCAO reduces ischemic cell damage and improves physiological and neurological function 2 days after stroke. These results suggests potential therapeutic properties of PROG in the management of stroke.

Metabolism of progesterone in mouse brain

Incubation of whole mouse brain homogenate with [3H]progesterone resulted in two metabolites: the 5 alpha-reduced product, 5 alpha-pregnane-3,20-dione and another metabolite at a 3-fold greater yield. This differed from rat brain, which produced predominantly the 5 alpha-reduced metabolite under the same conditions. Subcellular fractionation of mouse brain demonstrated a particulate location for the 5 alpha-reduction of progesterone and a cytosolic location for the production of the unknown major metabolite. Treatment of this unknown metabolite with chromium trioxide resulted in a reconversion to progesterone, indicating the presence of a hydroxyl at position 3 or 20. Comparison of the chromatographic behaviour of the unknown metabolite with that of authentic progesterone derivatives suggested that this metabolite corresponds to 20-hydroxy-4-pregnene-3-one.

Steroidogenic enzymes: structure, function, and role in regulation of steroid hormone biosynthesis

In the pathways of steroid hormone biosynthesis there are two major types of enzymes: cytochromes P450 and other steroid oxidoreductases. This review presents an overview of the function and expression of both types of enzymes with emphasis on steroidogenic P450s. The final part of the review on regulation of steroidogenesis includes a description of the normal physiological fluctuations in the steroid output of adrenal cortex and gonads, and provides an analysis of the relative role of enzyme levels in the determination of these fluctuations. The repertoire of enzymes expressed in a steroidogenic cell matches the cell's capacity for the biosynthesis of specific steroids. Thus, steroidogenic capacity is regulated mainly by tissue and cell specific expression of enzymes, and not by selective activation or inhibition of enzymes from a larger repertoire. The quantitative capacity of steroidogenic cells for the biosynthesis of specific steroids is determined by the levels of steroidogenic enzymes. The major physiological variations in enzyme levels, are generally associated with parallel changes in gene expression. The level of expression of each steroidogenic enzyme varies in three characteristics: (a) tissue- and cell-specific expression, determined during tissue and cell differentiation; (b) basal expression, in the absence of trophic hormonal stimulation; and (c) hormonal signal regulated expression. Each of these three types of expression probably represent the functioning of distinct gene regulatory elements. In adult steroidogenic tissues, the levels of most of the cell- and tissue-specific steroidogenic enzymes depend mainly on trophic hormonal stimulation mediated by a complex network of signal transduction systems.

Pregnanolone (3 alpha-hydroxy-5 alpha-pregnane-20-one), a progesterone metabolite, facilitates inhibition of synaptic transmission in the Schäffer collateral pathway of the guinea pig hippocampus in vitro

Pregnanolone (3 alpha-hydroxy-5 alpha-pregnane-20-one, a metabolite of progesterone) caused a significant depression of the amplitude of the population spike evoked in stratum pyramidale in CA1 of the guinea pig hippocampus in vitro. Local application of pregnanolone on the surface of the slice in stratum oriens depressed the population spike without effects on the presynaptic spike and the population excitatory postsynaptic potential simultaneously recorded in stratum radiatum. The depression was dose-dependent and was observed with a minimum latency of 10 s after application of a 0.5-nl droplet of 3.1 microM pregnanolone. The concentration at the recording site was computed to be 0.2 microM. The duration of the depression was 20-30 min. The depression was significantly reduced during perfusion of the slice bath with 100 microM picrotoxin in artificial cerebrospinal fluid. When pregnanolone was applied locally in stratum radiatum, the amplitudes of the presynaptic spike, the population excitatory postsynaptic potential and the population spike were depressed. The effects on the presynaptic spike and the population excitatory postsynaptic potential vanished with different time courses. It is concluded that the depression of the population spike was caused by GABAA-mediated inhibition of the pyramidal neurones. The role of pregnanolone as a positive modulator of the GABAA receptor and the effect of this modulation on the complex mechanisms underlying catamenial epilepsy are discussed.

Androgen metabolism in the brain

The paper summarizes the most recent views on androgen metabolism in the brain. In particular it will be shown that: (1) the enzyme 5 alpha-reductase is particularly concentrated in the white matter; (2) 5 alpha-reductase is also present in the myelin; 5 alpha-reductase is present in higher concentrations in neurons (isolated or cultured) that in glial cells (astrocytes and oligodendrocytes); (4) only neurons possess the capability of aromatizing androgens to estrogens; and (5) a possible role of steroid metabolism in the control of the process of myelinogenesis is suggested.

Sex- and age-dependent nature of the cytoplasmic 5 alpha-dihydrotestosterone (DHT) binding site/receptor in bovine pineal gland

Recent research has justified the presumption that the pineal gland plays a role in the regulation of the gonadal system in mammals. Evidence also exists for androgen receptors in pinealocytes. In the current study, our approach has been to assess the age- and sex-dependent nature of 5 alpha-DHT receptors in bovine pineal. Although no significant difference was noted between various groups of bulls, cows, peripuberal cows, and calves (male) for pineal weight, the cytoplasmic 5 alpha-DHT binding site/receptor content in the pineal gland differed significantly. While the males had a low androgen receptor concentration in the pineal (46 fmol/pineal), the females showed the highest (442 fmol/pineal). The peripuberal females without calves and calves (male) presented a 5 alpha-DHT receptor content in between (225 fmol/pineal; 138 fmol/pineal). When the data were related to unit weight of pineal tissue, the difference still existed. It is suggested that the concentration of cytoplasmic 5 alpha-DHT receptors reflects the cellular activity and they are inversely related. Further, low cytoplasmic receptors also indicate that most of it is confined to the nuclear sites, as generally suggested for other androgen-dependent tissues. In the light of these suggestions, it is possible that lowest cytosolic 5 alpha-DHT receptor concentration in the males, in reality, reflects a higher degree of cellular function and a high concentration of the receptors in the nuclear site. Similarly, the peripuberal cows and calves perhaps have more cellular activity in the pineal than the mature cows. The current investigation, for the first time, by directly estimating the androgen receptors/binding site in the bovine pineal gland, demonstrates the sex- and age-dependent nature.

Biosynthesis of androgens by pheochromocytomas

Homogenates from four adrenal pheochromocytomas converted 4-14C-labeled pregnenolone, 17-hydroxyprogesterone, and dehydroepiandrosterone into androstenedione and testosterone. In addition to these androgens, labeled pregnane substrates were also transformed into corticosteroids, as previously reported, and this conversion occurred in even higher yield. The formation of labeled metabolites of either pathway was greater in homogenates from intraadrenal pheochromocytomas than in those derived from an extraadrenal tumor, but less than in preparations of hyperplastic adrenal cortex. Incubations of subcellular fractions isolated from an adrenal pheochromocytoma showed that the enzyme activities involved in androgen formation from the radioactive substrates studied were associated with the microsomes and required exogenous cofactors. In contrast to adrenocortical tissue, chromaffin cell preparations uniformly failed to convert substrate [4-14C] cholesterol into either androgens or corticosteroids. The data available demonstrate the presence in chromaffin tissue of all of the enzyme activities required for the biosynthesis of androgens and corticosteroids except for those involved in the side-chain scission of cholesterol.

Biosynthesis of catalytically active rat testosterone 5 alpha-reductase in microinjected Xenopus oocytes: evidence for tissue-specific differences in translatable mRNA

The enzyme 4-ene-3-ketosteroid-5 alpha-oxidoreductase [5 alpha-reductase; 3-oxo-5 alpha-steroid delta 4-dehydrogenase, 3-oxo-5 alpha-steroid: (acceptor) delta 4-oxidoreductase, EC 1.3.99.5] plays a key role in androgen-dependent target tissues, where it catalyzes the conversion of testosterone to the biologically active dihydrotestosterone. The regulation of 5 alpha-reductase expression has not been studied at the molecular level as the enzyme is a membrane protein that is labile in cell-free homogenates. We developed a sensitive bioassay of the enzyme activity expressed in Xenopus oocytes microinjected with rat liver and prostate mRNA. After microinjection, incubation of intact oocytes in the presence of [3H]testosterone revealed the in ovo appearance of active 5 alpha-reductase. Polyadenylated RNA was fractionated by sucrose gradient centrifugation, and the enzymatic activity was shown to be encoded by a 1600- to 2000-base-pair fraction of hepatic poly(A)+ RNA. 5 alpha-Reductase mRNA was most efficiently translated when up to 80 ng of RNA was injected per oocyte. In the injected oocytes, 5 alpha-reductase mRNA was found to be a short-lived molecule (t1/2 = 2 hr), whereas its in ovo translatable 5 alpha-reductase protein exhibited stable enzymatic activity for over 40 hr. Moreover, the levels of translatable tissue-specific 5 alpha-reductase mRNAs as monitored in the Xenopus oocytes correlated with the variable 5 alpha-reductase activities in female rat liver, male rat liver, and prostate homogenates; the ratio of their specific activities was of 2500:630:1, respectively. Altogether, these results provide supporting evidence in favor of the transcriptional control of 5 alpha-reductase expression in rat tissues.

Conversion of 17 alpha-hydroxyprogesterone to 5 alpha, 3 alpha, and 20 alpha-reduced metabolites by female rat anterior pituitary and hypothalamus

The metabolism of 17 alpha-[3H]hydroxyprogesterone was examined in female rat anterior pituitary and hypothalamic tissues. After reverse isotopic dilution analysis and purification to constant specific activity, the following 5 alpha-, 3 alpha- and 20 alpha-reduced products were detected in both tissues: 17 alpha-hydroxy-5 alpha-pregnane-3,20-dione; 3 alpha,17 alpha-dihydroxy-5 alpha-pregnan-20-one; 17 alpha,20 alpha-dihydroxy-4-pregnen-3-one and 5 alpha-pregnane-3 alpha,17 alpha,20 alpha-triol. While the metabolites formed were qualitatively the same, there were quantitative differences between the two tissues. The 3 alpha,5 alpha-reduced metabolite, 3 alpha,17 alpha-dihydroxy-5 alpha-pregnan-20-one, was the principal product in the anterior pituitary while the 5 alpha-reduced metabolite, 17 alpha-hydroxy-5 alpha-pregnane-3,20-dione, was produced in largest amount by the hypothalamus. With both tissues, the aforementioned four products plus starting substrate accounted for nearly all of the starting radioactivity. There was no evidence for the formation of C19 steroids (androgens) despite the presence of the 17 alpha-hydroxy group.

Sex steroid effects on extrahypothalamic CNS. II. Progesterone, alone and in combination with estrogen, modulates cerebellar responses to amino acid neurotransmitters

In a preliminary report we have shown that both intravenous and local application of progesterone (P) are capable of increasing cerebellar Purkinje cell responsiveness to microiontophoretically applied gamma-aminobutyric acid (GABA) and decreasing responsiveness to glutamate (GLUT) in the urethane-anesthetized, ovariectomized adult rat. In the present study we have examined the time course of effects of several doses of P and different combinations of both E2 and P on responses of individual Purkinje cells to GABA and GLUT. Extracellular activity of single Purkinje neurons was recorded using multibarrel glass micropipets. Spontaneous firing rate and responses of neurons to microiontophoretic pulses (10 s pulses every 40 s) of GABA (10-50 nA) and GLUT (3-40 nA) were examined before and after jugular i.v. administration of P or E2/P combinations to ovariectomized rats. In some cases animals received s.c. injections of E2 (2 micrograms) at 24 and 48 h before the day of recording. This injection schedule results in maximal reproductive effects of P. Within 5-15 min after P administration (5,50 or 500 micrograms) to ovariectomized rats, Purkinje cell responses to GLUT were decreased by 87%, and inhibitory responses to GABA were increased by 50%, with no associated change in spontaneous firing rate. In addition, the magnitude of the change in amino acid response was directly proportional to the dose of P. In most cases, complete recovery was observed 20-45 min after P administration. E2 pretreatment did not alter these P-induced effects. Combinations of E2 (300 ng/kg) and P (50 or 500 micrograms) injected simultaneously resulted in effects on GLUT responsiveness which were similar to those seen with P alone, while effects similar to E2 alone were observed with administration of E2 plus P at 5 micrograms. The administration of a protein synthesis inhibitor, anisomycin (30 mg/kg, i.v.), 20 min before the recording session did not prevent any of the above steroid effects. These results indicate that sex steroids can act to alter neuronal responsiveness to putative neurotransmitters in a CNS region not known to contain steroid receptors and that the particular combination of steroids will determine the neuronal response. These findings further suggest that the observed steroid-induced alterations in Purkinje cell responsiveness do not appear to require genomic mechanisms.

The effect of progesterone and its metabolites on the interictal epileptiform discharge in the cat's cerebral cortex

The antiepileptic effect of progesterone, 5-alpha-pregnane-3,20-dione, 3-alpha-hydroxy-5-alpha-pregnane-20-one, and 3-alpha-hydroxy-5-beta-pregnane-20-one were tested in an experimental animal model, and compared with the effect of clonazepam. The steroids were dissolved in serum from ovariectomized cats. Ovariectomized adult cats were used and spontaneous epileptic discharges were generated by placing small pieces of penicillin-soaked filter papers on the ipsi and contralateral cerebral cortex. The frequency and amplitude of the interictal epileptiform spikes were recorded, and analysed in a computer. The changes in frequency and amplitudes were calculated. The drugs were infused during 20-s periods into one cerebral hemisphere via the ipsilateral lingual artery with speeds of 1.1, 3.4 and 6.3 ml min-1. A penicillin focus on the contralateral hemisphere served as a simultaneous control. Progesterone and clonazepam showed similar inhibitory effects on epileptiform interictal spiking (median reduction of spike frequency 21%, cf. Table I). The 5-alpha-pregnane-3, 20-dione was generally less potent than progesterone (median reduction 9%) and the 5-alpha- and 5-beta-pregnanolones were two to three times more potent than progesterone (54-66% reduction). The latency of the inhibitory effect was 4-10 s measured from the entrance of the infusion into the lingual artery. The depression lasted 10-20 min. It is concluded that the pregnanolones have strong antiepileptic properties. The rapid onset of effect indicates that the steroids may interact with the neuronal function at the membrane or synaptic levels.

Locally applied progesterone metabolites alter neuronal responsiveness in the cerebellum

Ongoing studies in this laboratory have demonstrated that both systemically and locally administered sex steroids 17 beta estradiol (E2) and progesterone (P) alter cerebellar Purkinje cell responses to microiontophoretically applied amino acid neurotransmitters GABA and glutamate (GLUT) in the urethane-anesthetized, ovariectomized adult rat. In the present study, we have examined the effects of several locally pressure ejected P metabolites on Purkinje cell responsiveness to GABA and GLUT: 5 alpha-pregnane-20-one (5 alpha DHP), 5 alpha-pregnane-3 alpha-ol-20-one (3 alpha OH-DHP) and 5 alpha-pregnane-3 beta-ol-20-one (3 beta OH-DHP). GABA-induced inhibition was markedly enhanced immediately after onset of local application of 3 alpha OH-DHP or 5 alpha DHP, unaccompanied by alterations in background discharge. Both metabolites also attenuated excitatory responses to GLUT by 0-3 min after initiation of steroid application. In both cases, recovery to control levels of response was observed 6-9 min after termination of pressure application. These results are similar to those seen after local or systemic injection of P. In contrast, 3 beta OH-DHP did not produce any alteration in Purkinje cell responses to either amino acid. As 5 alpha DHP and 3 alpha OH-DHP can be localized in cerebellar tissue after P administration, the results presented here suggest that the neuronal effects of systemic P may be mediated by local membrane actions of P or its metabolites.

Progesterone alters GABA and glutamate responsiveness: a possible mechanism for its anxiolytic action

In this study, the neuromodulatory effects of progesterone were tested in an intact neuronal circuit of a model extrahypothalamic CNS area. Spontaneous discharge and responses of single cerebellar Purkinje neurons to microiontophoretically applied gamma-aminobutyric acid (GABA) and glutamate were monitored before, during and after either systemic injection, at physiologic doses, or local application of the steroid. By both means of administration, progesterone significantly enhanced inhibitory responses of Purkinje cells to GABA and suppressed glutamate excitation within 3-10 min post-steroid. These results are consistent with the anxiolytic actions of the steroid.

Progesterone 5 alpha-reductase in mouse brain

We have examined the distribution of progesterone 5 alpha-reductase activity in minces of discrete brain areas from two strains of adult ovariectomized mice known to be differentially responsive to the behavioral effects of exogenously administered 5 alpha-pregnane-3,20-dione (5 alpha-DHP). Minces of freshly dissected midbrain tegmentum (TEG), hypothalamus-preoptic area (HPOA), hippocampus (HIP), and parietal cortex (CTX) were incubated with [4-14C]progesterone in a Krebs-Henseleit bicarbonate buffer solution containing 10 mM glucose for 2 h at 37 degrees C. The [14C]5 alpha-DHP produced was identified by comparison with known standards in paper and thin-layer chromatography systems, derivative formation, and recrystallization to a constant 14C/3H ratio. We found a 6-fold difference in the extent to which various brain areas formed 5 alpha-DHP. The amount of conversion was similar for both strains of mice. When expressed as picomoles of 5 alpha-DHP formed per 2 h per 20 mg of tissue, the following order of activity was observed: TEG greater than HPOA greater than HIP greater than CTX.

Progesterone-induced decrease of pineal protein synthesis in rats. Possible participation in estrous-related changes of pineal function

Pineal protein synthesis in female rats, estimated from the incorporation of labeled amino acids into proteins in vitro, exhibited significant changes as a function of the stage of the estrous cycle. These changes were restricted to the proestrous and estrous days; pineal protein synthesis attained its maximum on the morning of proestrus declining abruptly by 53% during the evening, at the time of the expected gonadotrophin and prolactin release. Pineal serotonin-N-acetyltransferase activity increased by 10 to 15 times during night-time on every day of cycle; no appreciable modification of its daily rhythm was detected along the estrous cycle. Spayed rats treated for 2 days with progesterone showed a dose-dependent decrease of amino acid incorporation into pineal proteins, regardless of whether estradiol was simultaneously administered or not. Pineal protein synthesis in spayed rats administered with estradiol for 2 days and killed at 11 a.m. and 5 p.m. on the third day, did not show differences as a function of time of sacrifice. When progesterone was injected on the morning of the third day a significant decline in protein synthesis was observed at 5 p.m. Only in the latter group serum LH levels showed significantly greater values at 5 p.m. Pineal serotonin content of estradiol-treated rats increased significantly at evening, an effect which was obliterated by the administration of progesterone; progesterone alone did not affect pineal serotonin content. Radioactivity uptake by pineal glands incubated with labeled progesterone did not show changes along the estrous cycle. These data argue in favour of the involvement of progesterone in the changes of pineal protein synthesis observed during the "critical period" for gonadotrophin and prolactin release.