Ethanol-induced increases in neuroactive steroids in the rat brain and plasma are absent in adrenalectomized and gonadectomized rats

Advances in steroid research from the pioneering neurosteroid concept to metabolomics: New insights into pregnenolone function

Advances in neuroendocrinology have led to major discoveries since the 19th century, identifying adaptive loops for maintaining homeostasis. One of the most remarkable discoveries was the concept of neurosteroids, according to which the brain is not only a target but also a source of steroid production. The identification of new membrane steroid targets now underpins the neuromodulatory effects of neurosteroids such as pregnenolone, which is involved in functions mediated by the GPCR CB1 receptor. Structural analysis of steroids is a key feature of their interactions with the phospholipid membrane, receptors and resulting activity. Therefore, mass spectrometry-based methods have been developed to elucidate the metabolic pathways of steroids, the ultimate approach being metabolomics, which allows the identification of a large number of metabolites in a single sample. This approach should enable us to make progress in understanding the role of neurosteroids in the functioning of physiological and pathological processes.

Stress and drug abuse-related disorders: The promising therapeutic value of neurosteroids focus on pregnenolone-progesterone-allopregnanolone pathway

The pregnenolone-progesterone-allopregnanolone pathway is receiving increasing attention in research on the role of neurosteroids in pathophysiology, particularly in stress-related and drug use disorders. These disorders involve an allostatic change that may result from deficiencies in allostasis or adaptive responses, and may be downregulated by adjustments in neurotransmission by neurosteroids. The following is an overview of findings that assess how pregnenolone and/or allopregnanolone concentrations are altered in animal models of stress and after consumption of alcohol or cannabis-type drugs, as well as in patients with depression, anxiety, post-traumatic stress disorder or psychosis and/or in those diagnosed with alcohol or cannabis use disorders. Preclinical and clinical evidence shows that pregnenolone and allopregnanolone, operating according to a different or common pharmacological profile involving GABAergic and/or endocannabinoid system, may be relevant biomarkers of psychiatric disorders for therapeutic purposes. Hence, ongoing clinical trials implicate synthetic analogs of pregnenolone or allopregnanolone, and also modulators of neurosteroidogenesis.

Acute alcohol and cognition: Remembering what it causes us to forget

Addiction has been conceptualized as a specific form of memory that appropriates typically adaptive neural mechanisms of learning to produce the progressive spiral of drug-seeking and drug-taking behavior, perpetuating the path to addiction through aberrant processes of drug-related learning and memory. From that perspective, to understand the development of alcohol use disorders, it is critical to identify how a single exposure to alcohol enters into or alters the processes of learning and memory, so that involvement of and changes in neuroplasticity processes responsible for learning and memory can be identified early. This review characterizes the effects produced by acute alcohol intoxication as a function of brain region and memory neurocircuitry. In general, exposure to ethanol doses that produce intoxicating effects causes consistent impairments in learning and memory processes mediated by specific brain circuitry, whereas lower doses either have no effect or produce a facilitation of memory under certain task conditions. Therefore, acute ethanol does not produce a global impairment of learning and memory, and can actually facilitate particular types of memory, perhaps particular types of memory that facilitate the development of excessive alcohol use. In addition, the effects on cognition are dependent on brain region, task demands, dose received, pharmacokinetics, and tolerance. Additionally, we explore the underlying alterations in neurophysiology produced by acute alcohol exposure that help to explain these changes in cognition and highlight future directions for research. Through understanding the impact that acute alcohol intoxication has on cognition, the preliminary changes potentially causing a problematic addiction memory can better be identified.

Neurosteroids and potential therapeutics: Focus on pregnenolone

Considerable evidence from preclinical and clinical studies shows that steroids and in particular neurosteroids are important endogenous modulators of several brain-related functions. In this context, it remains to be elucidated whether neurosteroids may serve as biomarkers in the diagnosis of disorders and might have therapeutic potential for the treatment of these disorders. Pregnenolone (PREG) is the main steroid synthesized from cholesterol in mammals and invertebrates. PREG has three main sources of synthesis, the gonads, adrenal glands and brain and is submitted to various metabolizing pathways which are modulated depending on various factors including species, steroidogenic tissues and steroidogenic enzymes. Looking at the whole picture of steroids, PREG is often known as the precursor to other steroids and not as an active steroid per se. Actually, physiological and brain functions have been studied mainly for steroids that are very active either binding to specific intracellular receptors, or modulating with high affinity the abundant membrane receptors, GABAA or NMDA receptors. However, when high sensitive and specific methodological approaches were available to analyze low concentrations of steroids and then match endogenous levels of different steroid metabolomes, several studies have reported more significant alterations in PREG than in other steroids in extraphysiological or pathological conditions, suggesting that PREG could play a functional role as well. Additionally, several molecular targets of PREG were revealed in the mammalian brain and beneficial effects of PREG have been demonstrated in preclinical and clinical studies. On this basis, this review will be divided into three parts. The first provides a brief overview of the molecular targets of PREG and the pharmacological effects observed in animal and human studies. The second will focus on the possible functional role of PREG with an outline of the modulation of PREG levels in animal and in human research. Finally, the review will highlight the possible therapeutic uses of PREG that point towards the development of pregnenolone-like molecules.

Blunted neuroactive steroid and HPA axis responses to stress are associated with reduced sleep quality and negative affect in pregnancy: a pilot study

RATIONALE

Anxiety during pregnancy has been linked to adverse maternal health outcomes, including postpartum depression (PPD). However, there has been limited study of biological mechanisms underlying behavioral predictors of PPD during pregnancy.

OBJECTIVES

Considering the shared etiology of chronic stress amongst antenatal behavioral predictors, the primary goal of this pilot study was to examine associations among stress-related physiological factors (including GABA-ergic neurosteroids) and stress-related behavioral indices of anxiety during pregnancy.

METHODS

Fourteen nulliparous women in their second trimester of a singleton pregnancy underwent speech and mental arithmetic stress, following a 2-week subjective and objective recording of sleep-wake behavior.

RESULTS

Lower cortisol, progesterone, and a combined measure of ALLO + pregnanolone throughout the entire stressor protocol (area under the curve, AUC) were associated with greater negative emotional responses to stress, and lower cortisol AUC was associated with worse sleep quality. Lower adrenocorticotropic hormone was associated with greater anxious and depressive symptoms. Stress produced paradoxical reductions in cortisol, progesterone, and a combined measure of allopregnanolone + pregnanolone, while tetrahydrodeoxycorticosterone levels were elevated.

CONCLUSIONS

These data suggest that cortisol, progesterone, and ALLO + pregnanolone levels in the second trimester of pregnancy are inversely related to negative emotional symptoms, and the negative impact of acute stress challenge appears to exert its effects by reducing these steroids to further promote negative emotional responses.

Alcohol Effects on Stress Pathways: Impact on Craving and Relapse Risk

A significant amount of neurobiological research regarding the development of alcohol use disorders (AUDs) has focused on alcohol-related activation and long-term alterations in the mesocortical dopaminergic reward pathways. However, alcohol does not only interact with brain reward systems. Many of its acute and chronic effects may be related to allostatic adaptations in hypothalamic and extrahypothalamic stress regulation pathways. For example, acute binge intoxication is associated with hypothalamically driven increases in blood cortisol, norepinephrine, and sex steroid metabolite levels. This may contribute to the development of mesocortical sensitization to alcohol. Furthermore, chronic alcohol exposure is associated with systemic dysregulation of the hypothalamic pituitary adrenal axis, sympathetic adrenal medullary system, and sex steroid systems. This dysregulation appears to manifest as neuroendocrine tolerance. In this review, we first summarize the literature suggesting that alcohol-induced alterations in these hypothalamic systems influence craving and contribute to the development of AUDs. We note that for women, the effects of alcohol on these neuroendocrine stress regulation systems may be influenced by the rhythmic variations of hormones and steroids across the menstrual cycle. Second, we discuss how changes in these systems may indicate progression of AUDs and increased risk of relapse in both sexes. Specifically, neuroendocrine tolerance may contribute to mesocortical sensitization, which in turn may lead to decreased prefrontal inhibitory control of the dopaminergic reward and hypothalamic stress systems. Thus, pharmacological strategies that counteract alcohol-associated changes in hypothalamic and extrahypothalamic stress regulation pathways may slow the development and progression of AUDs.

Neurosteroidogenesis Today: Novel Targets for Neuroactive Steroid Synthesis and Action and Their Relevance for Translational Research

Neuroactive steroids are endogenous neuromodulators synthesised in the brain that rapidly alter neuronal excitability by binding to membrane receptors, in addition to the regulation of gene expression via intracellular steroid receptors. Neuroactive steroids induce potent anxiolytic, antidepressant, anticonvulsant, sedative, analgesic and amnesic effects, mainly through interaction with the GABAA receptor. They also exert neuroprotective, neurotrophic and antiapoptotic effects in several animal models of neurodegenerative diseases. Neuroactive steroids regulate many physiological functions, such as the stress response, puberty, the ovarian cycle, pregnancy and reward. Their levels are altered in several neuropsychiatric and neurological diseases and both preclinical and clinical studies emphasise a therapeutic potential of neuroactive steroids for these diseases, whereby symptomatology ameliorates upon restoration of neuroactive steroid concentrations. However, direct administration of neuroactive steroids has several challenges, including pharmacokinetics, low bioavailability, addiction potential, safety and tolerability, which limit its therapeutic use. Therefore, modulation of neurosteroidogenesis to restore the altered endogenous neuroactive steroid tone may represent a better therapeutic approach. This review summarises recent approaches that target the neuroactive steroid biosynthetic pathway at different levels aiming to promote neurosteroidogenesis. These include modulation of neurosteroidogenesis through ligands of the translocator protein 18 kDa and the pregnane xenobiotic receptor, as well as targeting of specific neurosteroidogenic enzymes such as 17β-hydroxysteroid dehydrogenase type 10 or P450 side chain cleavage. Enhanced neurosteroidogenesis through these targets may be beneficial not only for neurodegenerative diseases, such as Alzheimer's disease and age-related dementia, but also for neuropsychiatric diseases, including alcohol use disorders.

Neurosteroids and GABAergic signaling in health and disease

Endogenous neurosteroids such as allopregnanolone, allotetrahydrodeoxycorticosterone, and androstanediol are synthesized either de novo in the brain from cholesterol or are generated from the local metabolism of peripherally derived progesterone or corticosterone. Fluctuations in neurosteroid concentrations are important in the regulation of a number of physiological responses including anxiety and stress, reproductive, and sexual behaviors. These effects are mediated in part by the direct binding of neurosteroids to γ-aminobutyric acid type-A receptors (GABAARs), resulting in the potentiation of GABAAR-mediated currents. Extrasynaptic GABAARs containing the δ subunit, which contribute to the tonic conductance, are particularly sensitive to low nanomolar concentrations of neurosteroids and are likely their preferential target. Considering the large charge transfer generated by these persistently open channels, even subtle changes in neurosteroid concentrations can have a major impact on neuronal excitability. Consequently, aberrant levels of neurosteroids have been implicated in numerous disorders, including, but not limited to, anxiety, neurodegenerative diseases, alcohol abuse, epilepsy, and depression. Here we review the modulation of GABAAR by neurosteroids and the consequences for health and disease.

Structure-activity relationship studies on neuroactive steroids in memory, alcohol and stress-related functions: a crucial benefit from endogenous level analysis

RATIONALE

New research findings in the field of neuroactive steroids strongly suggest that to understand their role in physiopathology, it is essential to accurately measure their tissue levels. Through his broad chemical expertise and extensive knowledge of steroids, Dr. Robert H. Purdy pioneered structure-activity relationship studies on these compounds and developed innovative detection assays that are essential to assess their function in biological tissues.

OBJECTIVE

The goal of the present paper is to point out the specific contributions of Dr. Purdy and his collaborators to the current knowledge on the role of neuroactive steroids in the modulation of memory and alcohol- and stress-related effects with particular emphasis on the detection assays he developed to assess their endogenous levels. Reviewed here are the major results as well as the original and valuable methodological strategies issued by the long-term collaboration between Dr Purdy and many scientists worldwide on the investigation of the structure-activity relationship of neuroactive steroids.

RESULTS

Altogether, the data presented herein put forward the original notion that knowledge of the chemical structure of steroids is essential for their detection and the understanding of their role in physiological and pathological conditions, including the stress response.

CONCLUSIONS

The current challenge is to identify and quantify using appropriate methods neuroactive steroids in the context of both animal and clinical studies in order to reveal how their levels change under physiological and disease states. Dr. Purdy passed away in September 2012, but scientists all over the world will always be grateful for his pioneering work on steroid chemistry and for his great enthusiasm in research.

Divergent neuroactive steroid responses to stress and ethanol in rat and mouse strains: relevance for human studies

RATIONALE

Neuroactive steroids are endogenous or synthetic steroids that rapidly alter neuronal excitability via membrane receptors, primarily γ-aminobutyric acid type A (GABAA) receptors. Neuroactive steroids regulate many physiological processes including hypothalamic-pituitary-adrenal (HPA) axis function, ovarian cycle, pregnancy, aging, and reward. Moreover, alterations in neuroactive steroid synthesis are implicated in several neuropsychiatric disorders.

OBJECTIVES

This review will summarize the pharmacological properties and physiological regulation of neuroactive steroids, with a particular focus on divergent neuroactive steroid responses to stress and ethanol in rats, mice, and humans.

RESULTS

GABAergic neuroactive steroids exert a homeostatic regulation of the HPA axis in rats and humans, whereby the increase in neuroactive steroid levels following acute stress counteracts HPA axis hyperactivity and restores homeostasis. In contrast, in C57BL/6J mice, acute stress decreases neurosteroidogenesis and neuroactive steroids exert paradoxical excitatory effects upon the HPA axis. Rats, mice, and humans also differ in the neuroactive steroid responses to ethanol. Genetic variation in neurosteroidogenesis may explain the different neuroactive steroid responses to stress or ethanol.

CONCLUSIONS

Rats and mouse strains show divergent effects of stress and ethanol on neuroactive steroids in both plasma and brain. The study of genetic variation in the various processes that determine neuroactive steroids levels as well as their effects on cell signaling may underlie these differences and may play a relevant role for the potential therapeutic benefits of neuroactive steroids.

Ethanol alters local cellular levels of (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP) independent of the adrenals in subcortical brain regions

The neuroactive steroid (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP or allopregnanolone) is a positive modulator of GABAA receptors synthesized in the brain, adrenal glands, and gonads. In rats, ethanol activates the hypothalamic-pituitary-adrenal axis and elevates 3α,5α-THP in plasma, cerebral cortex, and hippocampus. In vivo, these effects are dependent on both the pituitary and adrenal glands. In vitro, however, ethanol locally increases 3α,5α-THP in hippocampal slices, in the absence of adrenal influence. Therefore, it is not known whether ethanol can change local brain levels of 3α,5α-THP in vivo, independent of the adrenals. To directly address this controversy, we administered ethanol (2 g/kg) or saline to rats that underwent adrenalectomy (ADX) or received sham surgery and performed immunohistochemistry for 3α,5α-THP. In the medial prefrontal cortex (mPFC), ethanol increased 3α,5α-THP after sham surgery, compared with saline controls, with no ethanol-induced change in 3α,5α-THP following ADX. In subcortical regions, 3α,5α-THP was increased independent of adrenals in the CA1 pyramidal cell layer, dentate gyrus polymorphic layer, bed nucleus of the stria terminalis, and paraventricular nucleus of the hypothalamus. Furthermore, ethanol decreased 3α,5α-THP labeling in the nucleus accumbens shore and central nucleus of the amygdala, independent of the adrenal glands. These data indicate that ethanol dynamically regulates local 3α,5α-THP levels in several subcortical regions; however, the adrenal glands contribute to 3α,5α-THP elevations in the mPFC. Using double immunofluorescent labeling we determined that adrenal dependence of 3α,5α-THP induction by ethanol is not due to a lack of colocalization of 3α,5α-THP with the cholesterol transporters steroidogenic acute regulatory protein (StAR) or translocator protein (TSPO).

Failure of acute ethanol administration to alter cerebrocortical and hippocampal allopregnanolone levels in C57BL/6J and DBA/2J mice

BACKGROUND

Ethanol (EtOH) administration increases brain allopregnanolone levels in rats, and this increase contributes to sensitivity to EtOH's behavioral effects. However, EtOH's effects on allopregnanolone may differ across species. We investigated the effects of acute EtOH administration on allopregnanolone, progesterone, and corticosterone levels in cerebral cortex and hippocampus of C57BL/6J and DBA/2J mice, 2 inbred strains with different alcohol sensitivity.

METHODS

Naïve male C57BL/6J and DBA/2J mice received EtOH (1, 2, 3, or 4 g/kg, intraperitoneally [i.p.]) or saline and were euthanized 1 hour later. For the time-course study, mice received EtOH (2 g/kg, i.p.) and were euthanized 15, 30, 60, and 120 minutes later. Steroids were measured by radioimmunoassay.

RESULTS

Acute EtOH administration did not alter cerebrocortical and hippocampal levels of allopregnanolone and progesterone in these strains at any of the doses and time points examined. Acute EtOH dose-dependently increased cerebrocortical corticosterone levels by 319, 347, and 459% in C57BL/6J mice at the doses of 2, 3, and 4 g/kg, and by 371, 507, 533, and 692% in DBA/2J mice at the doses of 1, 2, 3, and 4 g/kg, respectively. Similar changes were observed in the hippocampus. EtOH's effects on cerebrocortical corticosterone levels were also time dependent in both strains. Moreover, acute EtOH administration time-dependently increased plasma levels of progesterone and corticosterone. Finally, morphine administration increased cerebrocortical allopregnanolone levels in C57BL/6J (+77, +93, and +88% at 5, 10, and 30 mg/kg, respectively) and DBA/2J mice (+81% at 5 mg/kg), suggesting that the impairment in brain neurosteroidogenesis may be specific to EtOH.

CONCLUSIONS

These results underline important species differences on EtOH-induced brain neurosteroidogenesis. Acute EtOH increases brain and plasma corticosterone levels but does not alter cerebrocortical and hippocampal concentrations of allopregnanolone and progesterone in naïve C57BL/6J and DBA/2J mice.

Ethanol administration produces divergent changes in GABAergic neuroactive steroid immunohistochemistry in the rat brain

BACKGROUND

The 5α-reduced pregnane neuroactive steroid (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP or allopregnanolone) is a potent positive modulator of GABAA receptors capable of modulating neuronal activity. In rats, systemic ethanol (EtOH) administration increases cerebral cortical and hippocampal levels of 3α,5α-THP, but the effects of EtOH on 3α,5α-THP levels in other brain regions are unknown. There is a large body of evidence suggesting that 3α,5α-THP enhances EtOH sensitivity, contributes to some behavioral effects of EtOH, and modulates EtOH reinforcement and motivation to drink. In this study, we used immunohistochemistry (IHC) to determine EtOH-induced changes in cellular 3α,5α-THP expression in brain regions associated with EtOH actions and responses.

METHODS

Male Wistar rats were administered EtOH (2 g/kg) or saline intraperitoneally and after 60 minutes transcardially perfused. IHC was performed on free-floating sections (3 to 4 sections/animal/brain region) using an affinity purified anti-3α,5α-THP primary antibody, and immunoreactivity was visualized with 3,3'-diaminobenzidine.

RESULTS

EtOH significantly increased 3α,5α-THP immunoreactivity by 24 ± 6% in the medial prefrontal cortex, 32 ± 12% in the hippocampal Cornu Ammonis area 1 (CA1) pyramidal cell layer, 52 ± 5% in the polymorph cell layer of the dentate gyrus (DG), 44 ± 15% in the bed nucleus of the stria terminalis, and 36 ± 6% in the paraventricular nucleus of the hypothalamus. In contrast, EtOH administration significantly reduced 3α,5α-THP immunoreactivity by 25 ± 5% in the nucleus accumbens "shore" and 21 ± 3% in the central nucleus of the amygdala. No changes were observed in the ventral tegmental area, dorsomedial striatum, granule cell layer of the DG, or the lateral and basolateral amygdala.

CONCLUSIONS

The results suggest acute EtOH (2 g/kg) produces divergent, brain region specific, effects on cellular 3α,5α-THP levels. Regional differences in the effects of EtOH suggest there may be regional brain synthesis of 3α,5α-THP independent of the adrenal glands and novel mechanisms that reduce cellular 3α,5α-THP. Regional differences in EtOH-induced changes in 3α,5α-THP levels likely contribute to EtOH effects on neuronal function in brain.

Alteration of neonatal Allopregnanolone levels affects exploration, anxiety, aversive learning and adult behavioural response to intrahippocampal neurosteroids

Neurosteroids (NS) are well known to exert modulatory effects on ionotropic receptors. Recent findings indicate that NS could also act as important factors during development. In this sense, neonatal modifications of Allopregnanolone (Allop) levels during critical periods have been demonstrate to alter the morphology of the hippocampus but also other brain structures. The aim of the present work is to screen whether the alterations of Allop levels modify adult CA1 hippocampal response to NS administration. For this purpose, pups were injected with Allop (20 mg/kg s.c.), Finasteride (5α-reductase inhibitor that impedes Allop synthesis) (50 mg/kg s.c.) or Vehicle from postnatal day 5 (P5) to postnatal day 9 (P9). NS levels were tested at P5. To test the behavioural hippocampal response to NS in adulthood, animals were implanted with a bilateral cannula into the CA1 hippocampus at 80 days old and injected with Allop (0.2 μg/0.5 μl), Pregnenolone sulphate (5 ng/0.5 μl) or Vehicle in each hippocampus. After injections animals were tested in the Boisser test to assess exploratory behaviour, the elevated plus maze to assess anxiety and the passive avoidance to test aversive learning. Results indicate that alteration of neonatal Allop or pregnenolone levels (by Allop and Finasteride administration, respectively) suppressed intrahippocampal Allop anxiolytic effect in the EPM. Moreover our results also indicate that manipulation of neonatal Allop levels (Allop and Finast administration) alters exploratory and anxiety-like behaviour and impairs aversive learning in the adulthood. These data point out the role of Allop in the maturation of hippocampal function and behaviour.

Genetic analysis of the neurosteroid deoxycorticosterone and its relation to alcohol phenotypes: identification of QTLs and downstream gene regulation

BACKGROUND

Deoxycorticosterone (DOC) is an endogenous neurosteroid found in brain and serum, precursor of the GABAergic neuroactive steroid (3α,5α)-3,21-dihydroxypregnan-20-one (tetrahydrodeoxycorticosterone, THDOC) and the glucocorticoid corticosterone. These steroids are elevated following stress or ethanol administration, contribute to ethanol sensitivity, and their elevation is blunted in ethanol dependence.

METHODOLOGY/PRINCIPAL FINDINGS

To systematically define the genetic basis, regulation, and behavioral significance of DOC levels in plasma and cerebral cortex we examined such levels across 47 young adult males from C57BL/6J (B6)×DBA/2J (D2) (BXD) mouse strains for quantitative trait loci (QTL) and bioinformatics analyses of behavior and gene regulation. Mice were injected with saline or 0.075 mg/kg dexamethasone sodium salt at 8:00 am and were sacrificed 6 hours later. DOC levels were measured by radioimmunoassay. Basal cerebral cortical DOC levels ranged between 1.4 and 12.2 ng/g (8.7-fold variation, p<0.0001) with a heritability of ∼0.37. Basal plasma DOC levels ranged between 2.8 and 12.1 ng/ml (4.3-fold variation, p<0.0001) with heritability of ∼0.32. QTLs for basal DOC levels were identified on chromosomes 4 (cerebral cortex) and 14 (plasma). Dexamethasone-induced changes in DOC levels showed a 4.4-fold variation in cerebral cortex and a 4.1-fold variation in plasma, but no QTLs were identified. DOC levels across BXD strains were further shown to be co-regulated with networks of genes linked to neuronal, immune, and endocrine function. DOC levels and its responses to dexamethasone were associated with several behavioral measures of ethanol sensitivity previously determined across the BXD strains by multiple laboratories.

CONCLUSIONS/SIGNIFICANCE

Both basal and dexamethasone-suppressed DOC levels are positively correlated with ethanol sensitivity suggesting that the neurosteroid DOC may be a putative biomarker of alcohol phenotypes. DOC levels were also strongly correlated with networks of genes associated with neuronal function, innate immune pathways, and steroid metabolism, likely linked to behavioral phenotypes.

Variation in genes encoding the neuroactive steroid synthetic enzymes 5α-reductase type 1 and 3α-reductase type 2 is associated with alcohol dependence

BACKGROUND

Studies of alcohol effects in rodents and in vitro implicate endogenous neuroactive steroids as key mediators of alcohol effects at GABA(A) receptors. We used a case-control sample to test the association with alcohol dependence (AD) of single nucleotide polymorphisms in the genes encoding two key enzymes required for the generation of endogenous neuroactive steroids: 5α-reductase, type I (5α-R), and 3α-hydroxysteroid dehydrogenase, type 2 (3α-HSD), both of which are expressed in human brain.

METHODS

We focused on markers previously associated with a biological phenotype. For 5α-R, we examined the synonymous SRD5A1 exon 1 SNP rs248793, which has been associated with the ratio of dihydrotestosterone to testosterone. For 3α-HSD, we examined the nonsynonymous AKR1C3 SNP rs12529 (H5Q), which has been associated with bladder cancer. The SNPs were genotyped in a sample of 1,083 non-Hispanic Caucasians including 552 controls and 531 subjects with AD.

RESULTS

The minor allele for both SNPs was more common among controls than subjects with AD: SRD5A1 rs248793 C-allele (χ(2)(1) = 7.6, p = 0.006) and AKR1C3 rs12529 G-allele (χ(2)(1) = 14.6, p = 0.0001). There was also an interaction of these alleles such that the "protective" effect of the minor allele at each marker for AD was conditional on the genotype of the second marker.

CONCLUSIONS

We found evidence of an association with AD of polymorphisms in two genes encoding neuroactive steroid biosynthetic enzymes, providing indirect evidence that neuroactive steroids are important mediators of alcohol effects in humans.

Chronic ethanol exposure produces tolerance to elevations in neuroactive steroids: mechanisms and reversal by exogenous ACTH

Acute ethanol administration increases potent GABAergic neuroactive steroids, specifically (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP) and (3α,5α)-3,21-dihydroxypregnan-20-one. In addition, neuroactive steroids contribute to ethanol actions. Chronic ethanol exposure results in tolerance to many effects of ethanol, including ethanol-induced increases in neuroactive steroid levels. To determine the mechanisms of tolerance to ethanol-induced increases in neuroactive steroids, we investigated critical signaling molecules that are required for acute ethanol effects. Male Sprague-Dawley rats were administered ethanol via liquid diet for 2 weeks and steroid levels, adrenocorticotrophic hormone (ACTH) and adrenal steroidogenic acute regulatory (StAR) protein expression were measured. Chronic ethanol exposure elicits tolerance to ethanol-induced elevation of serum ACTH and the steroids pregnenolone and progesterone. Surprisingly, chronic ethanol exposure does not result in tolerance to ethanol-induced increases in adrenal StAR protein. However, ethanol-induced StAR phosphorylation is decreased when compared to acute ethanol administration. A separate group of rats exposed to chronic ethanol diet were subsequently challenged with ethanol (2 g/kg) and exhibited a blunted elevation of serum ACTH and progesterone as well as cerebral cortical and hippocampal 3α,5α-THP. Administration of ACTH with the ethanol challenge restored the elevation of serum ACTH and progesterone as well as cerebral cortical 3α,5α-THP levels to those observed in ethanol-naïve rats. Thus, chronic ethanol exposure disrupts ACTH release, which results in tolerance to ethanol-induced increases in neuroactive steroid levels. Loss of the ethanol-induced increases in neuroactive steroids may contribute to behavioral tolerance to ethanol and influence the progression towards alcoholism.

N-methyl-D-aspartate receptor subunit expression in adult and adolescent brain following chronic ethanol exposure

Substantial evidence suggests that glutamatergic neurotransmission is a critical mediator of the experience-dependent synaptic plasticity that may underlie alcohol dependence. Substance abuse typically begins in adolescence; therefore, the impact of alcohol on glutamatergic systems during this critical time in brain development is of particular importance. The N-methyl-d-aspartate receptor (NMDAR) is involved in developmental mechanisms underlying neuronal differentiation and synaptogenesis and as such may be a target system for alcohol effects during adolescence. In the present study quantitative biochemical determinations were made of the relative abundance of different protein expressions of NMDAR subunits in adolescents and adults after 2 weeks of ethanol vapor exposure, and 24 h and 2 weeks following withdrawal. After 2 weeks of ethanol vapor exposure N-methyl-d-aspartate receptor NR1 subunit (NR1), N-methyl-d-aspartate receptor NR2A subunit (NR2A), and N-methyl-d-aspartate receptor NR2B subunit (NR2B) subunit expression was found to be increased in hippocampus of the adults. In contrast, 2 weeks of ethanol exposure resulted in no significant changes in NR1 and NR2B subunits and a reduction NR2A subunit expression in hippocampus in adolescents. Twenty-four h and 2 weeks following withdrawal from ethanol vapor NR1 and NR2A subunit expression in hippocampus was decreased in adolescents, whereas in adults it had returned to control levels. In frontal cortex, 2 weeks of chronic ethanol exposure produced decreases in NR1 subunit expression in both adults and adolescents but also produced decreases in NR2A and NR2B subunit expression in adults that returned or exceeded control levels by 2 weeks following withdrawal from ethanol vapor. These results demonstrate that NMDAR subunit composition can be modulated differentially between adolescents and adults by chronic ethanol exposure and withdrawal. These developmental differences in NMDAR subunits composition may also be associated with the enhanced vulnerability of the adolescent brain to ethanol dependence.

"Binge" drinking experience in adolescent mice shows sex differences and elevated ethanol intake in adulthood

Binge drinking, defined as achieving blood ethanol concentrations (BEC) of 80 mg%, has been increasing in adolescents and was reported to predispose later physical dependence. The present experiments utilized an animal model of binge drinking to compare the effect of ethanol "binge" experience during adolescence or adulthood on subsequent ethanol intake in male and female C57BL/6 mice. Adolescent and adult mice were initially exposed to the scheduled high alcohol consumption procedure, which produces BECs that exceed the levels for binge drinking following a 30-min ethanol session every third day. Ethanol intake and BECs were significantly higher in the adolescent ( approximately 3 g/kg, 199 mg%) versus adult ( approximately 2 g/kg, 135 mg%) mice during the first three ethanol sessions, but were more equivalent during the final two ethanol sessions (1.85-2.0 g/kg, 129-143 mg%). Then, separate groups of the ethanol-experienced mice were tested with ethanol naïve adolescent and adult mice for 2-h limited access (10% and 20% solutions) or 24-h (5%, 10% and 20% solutions) ethanol preference drinking. Limited access ethanol intake was significantly higher in female versus male mice, but was not altered by age or ethanol experience. In contrast, 24-h ethanol intake was significantly higher in the adolescent versus adult mice and in female versus male mice. Furthermore, binge drinking experience in the adolescent mice significantly increased subsequent ethanol intake, primarily due to intake in female mice. Thus, adolescent binge drinking significantly increased unlimited ethanol intake during adulthood, with female mice more susceptible to this effect.

Manipulation of GABAergic steroids: Sex differences in the effects on alcohol drinking- and withdrawal-related behaviors

Alcoholism is a complex disorder that represents an important contributor to health problems worldwide and that is difficult to encompass with a single preclinical model. Additionally, alcohol (ethanol) influences the function of many neurotransmitter systems, with the interaction at gamma-aminobutyric acid(A) (GABA(A)) receptors being integral for ethanol's reinforcing and several withdrawal-related effects. Given that some steroid derivatives exert rapid membrane actions as potent positive modulators of GABA(A) receptors and exhibit a similar pharmacological profile to that of ethanol, studies in the laboratory manipulated GABAergic steroid levels and determined the impact on ethanol's rewarding- and withdrawal-related effects. Manipulations focused on the progesterone metabolite allopregnanolone (ALLO), since it is the most potent endogenous GABAergic steroid identified. The underlying hypothesis is that fluctuations in GABAergic steroid levels (and the resultant change in GABAergic inhibitory tone) alter sensitivity to ethanol, leading to changes in the positive motivational or withdrawal-related effects of ethanol. This review describes results that emphasize sex differences in the effects of ALLO and the manipulation of its biosynthesis on alcohol reward-versus withdrawal-related behaviors, with females being less sensitive to the modulatory effects of ALLO on ethanol-drinking behaviors but more sensitive to some steroid manipulations on withdrawal-related behaviors. These findings imply the existence of sex differences in the sensitivity of GABA(A) receptors to GABAergic steroids within circuits relevant to alcohol reward versus withdrawal. Thus, sex differences in the modulation of GABAergic neurosteroids may be an important consideration in understanding and developing therapeutic interventions in alcoholics.

Differential effects of ethanol on serum GABAergic 3alpha,5alpha/3alpha,5beta neuroactive steroids in mice, rats, cynomolgus monkeys, and humans

BACKGROUND

Acute ethanol administration increases plasma and brain levels of progesterone and deoxycorticosterone-derived neuroactive steroids (3alpha,5alpha)-3-hydroxypregnan-20-one (3alpha,5alpha-THP) and (3alpha,5alpha)-3,21-dihydroxypregnan-20-one (3alpha,5alpha-THDOC) in rats. However, little is known about ethanol effects on GABAergic neuroactive steroids in mice, nonhuman primates, or humans. We investigated the effects of ethanol on plasma levels of 3alpha,5alpha- and 3alpha,5beta-reduced GABAergic neuroactive steroids derived from progesterone, deoxycorticosterone, dehydroepiandrosterone, and testosterone using gas chromatography-mass spectrometry.

METHODS

Serum levels of GABAergic neuroactive steroids and pregnenolone were measured in male rats, C57BL/6J and DBA/2J mice, cynomolgus monkeys, and humans following ethanol administration. Rats and mice were injected with ethanol (0.8 to 2.0 g/kg), cynomolgus monkeys received ethanol (1.5 g/kg) intragastrically, and healthy men consumed a beverage containing 0.8 g/kg ethanol. Steroids were measured after 60 minutes in all species and also after 120 minutes in monkeys and humans.

RESULTS

Ethanol administration to rats increased levels of 3alpha,5alpha-THP, 3alpha,5alpha-THDOC, and pregnenolone at the doses of 1.5 g/kg (+228, +134, and +860%, respectively, p < 0.001) and 2.0 g/kg (+399, +174, and +1125%, respectively, p < 0.001), but not at the dose of 0.8 g/kg. Ethanol did not alter levels of the other neuroactive steroids. In contrast, C57BL/6J mice exhibited a 27% decrease in serum 3alpha,5alpha-THP levels (p < 0.01), while DBA/2J mice showed no significant effect of ethanol, although both mouse strains exhibited substantial increases in precursor steroids. Ethanol did not alter any of the neuroactive steroids in cynomolgus monkeys at doses comparable to those studied in rats. Finally, no effect of ethanol (0.8 g/kg) was observed in men.

CONCLUSIONS

These studies show clear species differences among rats, mice, and cynomolgus monkeys in the effects of ethanol administration on circulating neuroactive steroids. Rats are unique in their pronounced elevation of GABAergic neuroactive steroids, while this effect was not observed in mice or cynomolgus monkeys at comparable ethanol doses.

Ethanol induction of steroidogenesis in rat adrenal and brain is dependent upon pituitary ACTH release and de novo adrenal StAR synthesis

The mechanisms of ethanol actions that produce its behavioral sequelae involve the synthesis of potent GABAergic neuroactive steroids, specifically the GABAergic metabolites of progesterone, (3alpha,5alpha)-3-hydroxypregnan-20-one (3alpha,5alpha-THP), and deoxycorticosterone, (3alpha,5alpha)-3,21-dihydroxypregnan-20-one. We investigated the mechanisms that underlie the effect of ethanol on adrenal steroidogenesis. We found that ethanol effects on plasma pregnenolone, progesterone, 3alpha,5alpha-THP and cortical 3alpha,5alpha-THP are highly correlated, exhibit a threshold of 1.5 g/kg, but show no dose dependence. Ethanol increases plasma adrenocorticotropic hormone (ACTH), adrenal steroidogenic acute regulatory protein (StAR), and adrenal StAR phosphorylation, but does not alter levels of other adrenal cholesterol transporters. The inhibition of ACTH release, de novo adrenal StAR synthesis or cytochrome P450 side chain cleavage activity prevents ethanol-induced increases in GABAergic steroids in plasma and brain. ACTH release and de novo StAR synthesis are independently regulated following ethanol administration and both are necessary, but not sufficient, for ethanol-induced elevation of plasma and brain neuroactive steroids. As GABAergic steroids contribute to ethanol actions and ethanol sensitivity, the mechanisms of this effect of ethanol may be important factors that contribute to the behavioral actions of ethanol and risk for alcohol abuse disorders.

The role of neuroactive steroids in ethanol/stress interactions: proceedings of symposium VII at the Volterra conference on alcohol and stress, May 2008

This report summarizes the proceedings of the symposium VII on the role of neuroactive steroids in stress/alcohol interactions. The production of GABAergic neuroactive steroids, including (3alpha,5alpha)-3-hydroxypregnan-20-one and (3alpha,5alpha)-3,21-dihydroxypregnan-20-one is a consequence of both acute stress and acute ethanol exposure. Acute, but not chronic ethanol administration elevates brain levels of these steroids and enhances GABA(A) receptor activity. Neuroactive steroids modulate acute anticonvulsant effects, sedation, spatial memory impairment, anxiolytic-like, antidepressant-like, and reinforcing properties of ethanol in rodents. Furthermore, these steroids participate in the homeostatic regulation of the hypothalamic-pituitary-adrenal axis. Therefore, it is not surprising that neuroactive steroids are involved in ethanol/stress interactions. Nevertheless, the interactions are complex and not well understood. This symposium addressed the role of neuroactive steroids in both stress and alcohol responses and their interactions. Professor Giovanni Biggio of the University of Cagliari, Italy presented the effects of juvenile isolation stress on neuroactive steroids, GABA(A) receptor expression, and ethanol sensitivity. Professor Howard Becker of the Medical University of South Carolina, USA presented evidence for neuroactive steroid involvement in ethanol dependence and drinking behavior. Professor Patrizia Porcu of the University of North Carolina, USA described a potential neuroactive steroid biomarker that may predict heavy drinking in monkeys and mice. These presentations provide a framework for new theories on the nature of ethanol/stress interactions that may be amenable to therapeutic interventions.

The role of GABA(A) receptors in the acute and chronic effects of ethanol: a decade of progress

The past decade has brought many advances in our understanding of GABA(A) receptor-mediated ethanol action in the central nervous system. We now know that specific GABA(A) receptor subtypes are sensitive to ethanol at doses attained during social drinking while other subtypes respond to ethanol at doses attained by severe intoxication. Furthermore, ethanol increases GABAergic neurotransmission through indirect effects, including the elevation of endogenous GABAergic neuroactive steroids, presynaptic release of GABA, and dephosphorylation of GABA(A) receptors promoting increases in GABA sensitivity. Ethanol's effects on intracellular signaling also influence GABAergic transmission in multiple ways that vary across brain regions and cell types. The effects of chronic ethanol administration are influenced by adaptations in GABA(A) receptor function, expression, trafficking, and subcellular localization that contribute to ethanol tolerance, dependence, and withdrawal hyperexcitability. Adolescents exhibit altered sensitivity to ethanol actions, the tendency for higher drinking and longer lasting GABAergic adaptations to chronic ethanol administration. The elucidation of the mechanisms that underlie adaptations to ethanol exposure are leading to a better understanding of the regulation of inhibitory transmission and new targets for therapies to support recovery from ethanol withdrawal and alcoholism.

Sex differences in acute ethanol withdrawal severity after adrenalectomy and gonadectomy in Withdrawal Seizure-Prone and Withdrawal Seizure-Resistant mice

Recent findings suggest that the ability of ethanol (EtOH) to increase the levels of neurosteroids with potent gamma-aminobutyric acid (GABA)ergic properties can influence measures of EtOH sensitivity. Earlier studies determined that removal of the adrenals and gonads diminished the steroidogenic effect of EtOH and significantly increased acute EtOH withdrawal severity in two inbred mouse strains that differed in withdrawal severity, suggesting the contribution of anticonvulsant GABAergic steroids to acute withdrawal in intact animals. Thus, the goal of the present study was to investigate the consequence of steroid removal on acute EtOH withdrawal through excision of the adrenals and gonads, in another genetic animal model of EtOH withdrawal differences, the Withdrawal Seizure-Prone (WSP) and Withdrawal Seizure-Resistant (WSR) selected lines. Male and female WSP and WSR mice underwent surgical removal of the adrenals and gonads or no organ removal (SHAM). One to 2 weeks later, baseline handling-induced convulsions (HICs) were assessed, mice were given a 4 g/kg dose of EtOH, and HICs were measured hourly for 12 h and then at 24 h. The combination surgery significantly increased EtOH withdrawal in WSP and WSR female mice, as measured by area under the curve (AUC) and peak HIC scores. The AUC was significantly positively correlated with plasma corticosterone levels and significantly negatively correlated with progesterone levels. In contrast, surgical status did not alter withdrawal severity in male WSP and WSR mice. Overall, the increase in acute EtOH withdrawal severity in female WSP and WSR mice after adrenalectomy and gonadectomy corroborate our recent evidence that withdrawal from a high dose of EtOH can be modulated by anticonvulsant steroids produced in the periphery.

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.

Discriminative stimulus effects of ethanol, pregnanolone, and dehydroepiandrosterone (DHEA) in rats administered ethanol or saline as adolescents

Adolescent alcohol use may produce long-term changes in the receptors and neurosteroids that putatively mediate alcohol's effects and consequently contribute to alcohol abuse and dependence as an adult. To test this possibility, ethanol (0.18-1.8 g/kg) and two neurosteroids, pregnanolone (1-10 mg/kg) and dehydroepiandrosterone (DHEA, 1-100 mg/kg), were administered alone and in combination to adult, male Long-Evans rats discriminating 1 g/kg ethanol (15% v/v) under a fixed ratio (FR) 20 schedule of food presentation after adolescent treatment with 15 injections of ethanol (n = 9, 2 g/kg, 20% v/v) or saline (n = 7). When compared as adults, ethanol-treated adolescents (as opposed to saline-treated adolescents) had higher percentages of ethanol-lever responding at doses smaller than the training dose, and higher response rates after both control and ethanol injections. Neither pregnanolone nor DHEA substituted for ethanol in either adolescent-treated group up to doses that substantially decreased response rates. When administered with ethanol, 1 and 3.2 mg/kg of pregnanolone enhanced the discriminative stimulus effects of small ethanol doses more in saline-treated adolescents than in ethanol-treated adolescents. Unlike pregnanolone, 32 and 100 mg/kg of DHEA attenuated the discriminative stimulus effects of ethanol modestly in both adolescent-treated groups. These results in adult rats suggest that adolescent ethanol administration can enhance the discriminative stimulus effects of small ethanol doses and affect the capacity of pregnanolone, but not DHEA, to interact with ethanol's discriminative stimulus effects.

Indomethacin improves locomotor deficit and reduces brain concentrations of neuroinhibitory steroids in rats following portacaval anastomosis

Hepatic encephalopathy (HE) is a neuropsychiatric complication of both acute and chronic liver failure characterized by progressive neuronal inhibition. Some neurosteroids are potent positive allosteric modulators of the gamma-aminobutyric acid (GABA)-A receptor complex, and 'increased GABAergic tone' has been proposed to explain the neuroinhibition characteristics of HE. Brain levels of the neurosteroids pregnenolone, allopregnanolone and tetrahydrodesoxycorticosterone (THDOC) and the functional status of the GABA-A receptor complex were assessed in rats following portacaval anastomosis (PCA). Effects of indomethacin, an inhibitor of the 3alpha-hydroxysteroid dehydrogenase enzyme involved in neurosteroid synthesis, on PCA rat locomotor activity and brain neurosteroid levels were also assessed. Significant increases of the neurosteroid pregnenolone (2.6-fold), allopregnanolone (1.7-fold) and THDOC (4.7-fold) were observed in brains of PCA rats. Brain levels of these neurosteroids were in the nanomolar range, sufficient to exert positive allosteric modulatory effects at the GABA-A receptor. Indomethacin (0.1-5 mg kg(-1)) ameliorated dose-dependently the locomotor deficit of PCA rats and concomitantly normalized brain levels of allopregnanolone and THDOC. Increased brain levels of neurosteroids with positive allosteric modulatory actions at the neuronal GABA-A receptor offer a cogent explanation for the notion of 'increased GABAergic tone' in HE. Pharmacological approaches using agents that either reduce neurosteroid synthesis or modulate the neurosteroid site on GABA-A receptor could offer new therapeutic tools for the management and treatment of HE.

Emergence of NMDAR-independent long-term potentiation at hippocampal CA1 synapses following early adolescent exposure to chronic intermittent ethanol: role for sigma-receptors

Adolescent humans who abuse alcohol are more vulnerable than adults to the development of memory impairments. Memory impairments often involve modifications in the ability of hippocampal neurons to establish long-term potentiation (LTP) of excitatory neurotransmission; however, few studies have examined how chronic ethanol exposure during adolescence affects LTP mechanisms in hippocampus. We investigated changes in LTP mechanisms in hippocamal slices from rats exposed to intoxicating concentrations of chronic intermittent ethanol (CIE) vapors in their period of early-adolescent (i.e., prepubescent) or late-adolescent (i.e., postpubescent) development. LTP was evaluated at excitatory CA1 synapses in hippocampal slices at 24 h after the cessation of air (control) or CIE vapor treatments. CA1 synapses in control slices showed steady LTP following induction by high-frequency stimulation, which was fully dependent on NMDAR function. By contrast, slices from early-adolescent CIE exposed animals showed a compound form of LTP consisting of an NMDAR-dependent component and a slow-developing component independent of NMDARs. These components summated to yield LTP of robust magnitude above LTP levels in age-matched control slices. Bath-application of the sigma-receptor antagonist BD1047 and the neuroactive steroid pregnenolone sulfate, but not acute ethanol application, blocked NMDAR-independent LTP, while leaving NMDAR-dependent LTP intact. Analysis of presynaptic function during NMDAR-independent LTP induction demonstrated increased presynaptic function via a sigma-receptor-dependent mechanism in slices from early-adolescent CIE-exposed animals. By contrast, CIE exposure after puberty onset in late-adolescent animals produced decrements in LTP levels. The identification of a role for sigma-receptors and neuroactive steroids in the development of NMDAR-independent LTP suggests an important pathway by which hippocampal synaptic plasticity, and perhaps memory, may be uniquely altered by chronic ethanol exposure during the prepubescent phase of adolescent development.

Alcohol related changes in regulation of NMDA receptor functions

Long-term alcohol exposure may lead to development of alcohol dependence in consequence of altered neurotransmitter functions. Accumulating evidence suggests that the N-methyl-D-aspartate (NMDA) type of glutamate receptors is a particularly important site of ethanol's action. Several studies showed that ethanol potently inhibits NMDA receptors (NMDARs) and prolonged ethanol exposition leads to a compensatory "up-regulation" of NMDAR mediated functions. Therefore, alterations in NMDAR function are supposed to contribute to the development of ethanol tolerance, dependence as well as to the acute and late signs of ethanol withdrawal.A number of publications report alterations in the expression and phosphorylation states of NMDAR subunits, in their interaction with scaffolding proteins or other receptors in consequence of chronic ethanol treatment. Our knowledge on the regulatory processes, which modulate NMDAR functions including factors altering transcription, protein expression and post-translational modifications of NMDAR subunits, as well as those influencing their interactions with different regulatory proteins or other downstream signaling elements are incessantly increasing. The aim of this review is to summarize the complex chain of events supposedly playing a role in the up-regulation of NMDAR functions in consequence of chronic ethanol exposure.

The impact of gonadectomy and adrenalectomy on acute withdrawal severity in male and female C57BL/6J and DBA/2J mice following a single high dose of ethanol

BACKGROUND

Steroid hormones can influence neuronal excitability and subsequent seizure susceptibility through genomic and nongenomic mechanisms. For example, there are proconvulsant steroids such as estradiol and corticosterone and anticonvulsant steroids such as testosterone, progesterone, and their GABAergic metabolites. Recent findings indicated that a single, acute administration of ethanol increased levels of GABAergic steroids and that the source of this increase was peripheral organs such as the adrenals and gonads. Thus, the purpose of the present study was to determine the impact of removal of the adrenals and/or gonads on withdrawal severity following a single high dose of ethanol in 2 genotypes that differ in ethanol withdrawal severity.

METHOD

Male and female C57BL/6J (B6) and DBA/2J (D2) mice were either left intact (SHAM), adrenalectomized (ADX), gonadectomized (GDX), or underwent ADX/GDX surgery. Seven days following surgery, baseline handling-induced convulsions (HICs) were measured prior to administration of a 4 g/kg dose of ethanol. HICs were assessed following the ethanol injection, then hourly for 12 hours and at 24 hours. A separate group of mice were used to measure the impact of surgical status on ethanol metabolism at 30, 60, 120, and 240 minutes after a single 4 g/kg dose of ethanol.

RESULTS

ADX and ADX/GDX treatments in male B6 and D2 mice increased ethanol withdrawal severity following a single dose of ethanol, measured by area under the withdrawal curve and peak HIC scores. Acute ethanol withdrawal also was increased in female D2 mice that had undergone ADX/GDX. In contrast, surgical status did not alter ethanol withdrawal severity in female B6 mice. Surgical status had only minor effects on ethanol metabolism.

CONCLUSIONS

Removal of peripherally derived steroids with anticonvulsant properties significantly increased HIC scores during acute ethanol withdrawal following a single dose of ethanol in male and female D2 mice and in male B6 mice. These increases were not due to changes in ethanol metabolism.

Stress, ethanol, and neuroactive steroids

Neurosteroids play a crucial role in stress, alcohol dependence and withdrawal, and other physiological and pharmacological actions by potentiating or inhibiting neurotransmitter action. This review article focuses on data showing that the interaction among stress, ethanol, and neuroactive steroids may result in plastic molecular and functional changes of GABAergic inhibitory neurotransmission. The molecular mechanisms by which stress-ethanol-neuroactive steroids interactions can produce plastic changes in GABA(A) receptors have been studied using different experimental models in vivo and in vitro in order to provide useful evidence and new insights into the mechanisms through which acute and chronic ethanol and stress exposure modulate the activity of GABAergic synapses. We show detailed data on a) the effect of acute and chronic stress on peripheral and brain neurosteroid levels and GABA(A) receptor gene expression and function; b) ethanol-stimulated brain steroidogenesis; c) plasticity of GABA(A) receptor after acute and chronic ethanol exposure. The implications of these new mechanistic insights to our understanding of the effects of ethanol during stress are also discussed. The understanding of these neurochemical and molecular mechanisms may shed new light on the physiopathology of diseases, such as anxiety, in which GABAergic transmission plays a pivotal role. These data may also lead to the need for new anxiolytic, hypnotic and anticonvulsant selective drugs devoid of side effects.

Changes in neuroactive steroid content during social isolation stress modulate GABAA receptor plasticity and function

Rats deprived of social contact with other rats at a young age experience a form of prolonged stress that leads to long-lasting alteration in their behavior profile. This chronic stress paradigm is thus thought to be anxiogenic for these normally gregarious animals and their abnormal reactivity to environmental stimuli, when reared under this condition, is thought to be a product of prolonged stress. Neurochemical, molecular, and electrophysiological evidences demonstrate that social isolation is associated with alteration in the structure and function of GABA(A) receptors and suggest that endogenous content of the progesterone metabolite 3alpha,5alpha-TH PROG may be an important determinant in regulating brain excitability and sensitivity to stimuli and point out its possible role in psychiatric and neurological disorder.

Chronic progesterone treatment augments while dehydroepiandrosterone sulphate prevents tolerance to ethanol anxiolysis and withdrawal anxiety in rats

We have recently shown that the neurosteroid allopregnanolone modulates anxiolytic effect of ethanol. In the present report, we attempted to examine whether neurosteroids progesterone and dehydroepiandrosterone sulphate (DHEAS), which modulate gamma-aminobutyric acid (GABA(A)) receptor function, affects development of tolerance to ethanol anxiolysis and withdrawal anxiety. Rats on ethanol (6% v/v in nutritionally balanced liquid diet) for prolong period (10 days) were injected twice daily either with vehicle, progesterone (a precursor of allopregnanolone, positive GABA(A) receptor modulator), finasteride (5alpha-reductase inhibitor) or DHEAS (negative GABA(A) receptor modulator). During this period, rats were acutely challenged periodically with ethanol (2 g/kg, i.p., 8% w/v) and subjected to the elevated plus maze test. For withdrawal studies, similar treatment protocols (except ethanol challenge) were employed and on day 11, rats were subjected to the elevated plus maze test at different time intervals post-ethanol withdrawal. While progesterone significantly advanced the development of tolerance to ethanol anxiolysis and enhanced withdrawal anxiety, DHEAS and finasteride prevented such behavioral alterations. These data highlight the important role played by GABAergic neurosteroids progesterone and DHEAS in the development of tolerance to ethanol anxiolysis and withdrawal anxiety in rats. Moreover, it points to the potential usefulness of specific neurosteroids as targets in the treatment of alcoholism.

Recent developments in the significance and therapeutic relevance of neuroactive steroids--Introduction to the special issue

This special issue heralds an exciting time in the field when the significance of neuroactive steroids in the regulation of inhibitory transmission is being realized and translated to new treatments for intractable neurologic and psychiatric conditions. In the past year, the binding sites for neuroactive steroids on gamma-aminobutyric acid type A (GABA(A)) receptors have been discovered and clinical trials for epilepsy and traumatic brain injury have been successful. New data in animal models points to the potential value of neuroactive steroids in other central nervous system (CNS) disorders including depression, schizophrenia, alcoholism, multiple sclerosis and other neurodegenerative conditions. How can one class of compounds have so many potential applications? The answer may lie in the ability of neuroactive steroids to regulate synaptic and extrasynaptic inhibitory transmission across brain, hypothalamic-pituitary-adrenal (HPA) axis function, inflammatory processes and myelin formation. The manuscripts in this issue of Pharmacology and Therapeutics will bring you up to date on the sites of neurosteroid actions, the systemic and molecular consequences of these actions and the potential therapeutic relevance of neuroactive steroid effects for CNS disease. These studies point to the opportunity for more translational research into potential therapeutic applications and the need for evaluation of potential untoward side effects following long-term treatment.

Mechanisms of neurosteroid interactions with GABA(A) receptors

Neuroactive steroids have some of their most potent actions by augmenting the function of GABA(A) receptors. Endogenous steroid actions on GABA(A) receptors may underlie important effects on mood and behavior. Exogenous neuroactive steroids have potential as anesthetics, anticonvulsants, and neuroprotectants. We have taken multiple approaches to understand more completely the interaction of neuroactive steroids with GABA(A) receptors. We have developed many novel steroid analogues in this effort. Recent work has resulted in synthesis of new enantiomer analogue pairs, novel ligands that probe various properties of the steroid pharmacophore, fluorescent neuroactive steroid analogues, and photoaffinity labels. Using these tools, combined with receptor binding and electrophysiological assays, we have begun to untangle the complexity of steroid actions at this important class of ligand-gated ion channel.

Hypothalamic-pituitary-adrenal axis modulation of GABAergic neuroactive steroids influences ethanol sensitivity and drinking behavior

Activation of the hypothalamic-pituitary-adrenal (HPA) axis leads to elevations in gamma-aminobutyric acid (GABA)-ergic neuroactive steroids that enhance GABA neurotransmission and restore homeostasis following stress. This regulation of the HPA axis maintains healthy brain function and protects against neuropsychiatric disease. Ethanol sensitivity is influenced by elevations in neuroactive steroids that enhance the GABAergic effects of ethanol, and may prevent excessive drinking in rodents and humans. Low ethanol sensitivity is associated with greater alcohol consumption and increased risk of alcoholism. Indeed, ethanol-dependent rats show blunted neurosteroid responses to ethanol administration that may contribute to ethanol tolerance and the propensity to drink greater amounts of ethanol. The review presents evidence to support the hypothesis that neurosteroids contribute to ethanol actions and prevent excessive drinking, while the lack of neurosteroid responses to ethanol may underlie innate or chronic tolerance and increased risk of excessive drinking. Neurosteroids may have therapeutic use in alcohol withdrawal or for relapse prevention.

Social isolation stress and neuroactive steroids

Social isolation of rats immediately after weaning is associated to a reduction in the cerebrocortical and plasma concentrations of progesterone and its metabolites 3alpha,5alpha-TH PROG and 3alpha,5alpha-THDOC. Although we found that the basal plasma concentration of adrenocorticotropic hormone in isolated rats was slightly decreased compared with that in group-housed animals no other significant changes were found in the steroidogenic machinery (peripheral benzodiazepine receptors, steroidogenic regulatory protein (StAR)). However, the functional response of the hypothalamic-pituitary-adrenal axis HPA axis to an acute stressful stimulus (foot shock), or to an acute injection of ethanol or isoniazid is markedly increased in isolated rats. Behavioral studies have also indicated that the ability of ethanol to inhibit isoniazid-induced convulsions is greater in isolated rats than in group-housed animals and this effect of isolation is prevented by treatment with the 5alpha-reductase inhibitor finasteride. Social isolation modified the effects of ethanol on the amounts of StAR mRNA and protein in the brain suggesting an alteration in the mechanism of cholesterol transport in mitochondria. Moreover, the amounts of the alpha4 and delta subunits of the GABA(A) receptor in the hippocampus were increased in isolated rats, and these effects were accompanied by an increase in GABA(A) receptor-mediated tonic inhibitory currents in granule cells of the dentate gyrus. Ethanol also increased the amplitude of GABA(A) receptor-mediated miniature inhibitory postsynaptic currents (mIPSC) recorded from CA1 pyramidal neurons with a greater potency in hippocampal slices prepared from socially isolated rats than in those from group-housed, an effect inhibited by finasteride.

Studies on neurosteroids XIX. Development and validation of liquid chromatography-tandem mass spectrometric method for determination of 5alpha-reduced pregnane-type neurosteroids in rat brain and serum

A sensitive liquid chromatography-electrospray ionization-tandem mass spectrometric (LC-ESI-MS-MS) method for the simultaneous determination of 5alpha-reduced pregnan-type neurosteroids, allopregnanolone (AP), epiallopregnanolone and 5alpha-dihydroprogesterone, in rat brain and serum has been developed and validated. The brain and serum steroids were extracted with methanol-acetic acid, purified using a Strata-X cartridge, derivatized with the permanently charged reagent, 2-hydrazino-1-methylpyridine (HMP), and subjected to LC-positive ESI-MS-MS. The limits of quantitation (LOQ) for brain (0.25 ng/g tissue) and serum (0.25 ng/ml) assays using the derivatization-ESI-MS-MS method are 60-150-fold lower than the LOQs for their atmospheric pressure chemical ionization-MS method without derivatization. [17Alpha,21,21,21-2H4]-AP was used as an internal standard. This method allowed the reproducible and accurate quantification of the brain or serum neurosteroids using a 20 mg or 20 microl sample, respectively. That is, the intra- and inter-assay coefficients of variation were below 8.2 and 6.0%, respectively, and the % accuracy values were 98.5-103.0% for all the steroids in both the brain and serum. The application of the developed method to the analysis of changes in the brain and serum neurosteroid levels by immobilization stress and ethanol administration is also presented.

Social isolation-induced increase in alpha and delta subunit gene expression is associated with a greater efficacy of ethanol on steroidogenesis and GABA receptor function

Previously we have demonstrated that social isolation of rats reduces both the cerebrocortical and plasma concentrations of 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG), and potentiates the positive effects of acute ethanol administration on the concentrations of this neurosteroid. We now show that the ethanol-induced increase in 3alpha,5alpha-TH PROG is more pronounced in the brain than in the plasma of isolated rats. The ability of ethanol to inhibit isoniazid-induced convulsions is greater in isolated rats than in group-housed animals and this effect is prevented by treatment with finasteride. Social isolation modified the effects of ethanol on the amounts of steroidogenic regulatory protein mRNA and protein in the brain. Moreover, ethanol increased the amplitude of GABA(A) receptor-mediated miniature inhibitory postsynaptic currents recorded from CA1 pyramidal neurones with greater potency in hippocampal slices prepared from socially isolated rats than in those from group-housed rats, an effect inhibited by finasteride. The amounts of the alpha(4) and delta subunits of the GABA(A) receptor in the hippocampus were increased in isolated rats as were GABA(A) receptor-mediated tonic inhibitory currents in granule cells of the dentate gyrus. These results suggest that social isolation results in changes in GABA(A) receptor expression in the brain, and in an enhancement of the stimulatory effect of ethanol on brain steroidogenesis, GABA(A) receptor function and associated behaviour.

Plasma pregnenolone levels in cynomolgus monkeys following pharmacological challenges of the hypothalamic–pituitary–adrenal axis

Pregnenolone (PREG) is an endogenous neuroactive steroid that is increased in rodent brain and plasma after hypothalamic-pituitary-adrenal (HPA) activation by acute stress or ethanol administration. Plasma levels of PREG metabolites are altered by pharmacological challenges of the HPA axis, however little is known about HPA regulation of PREG levels in monkeys. PREG concentrations were determined by radioimmunoassay in plasma samples from cynomolgus monkeys, following challenge with naloxone (125 and 375 microg/kg), corticotropin-releasing factor (CRF; 1 microg/kg), dexamethasone (130 microg/kg), adrenocorticotropic hormone (ACTH; 10 ng/kg; 4-6 h after 0.5 mg/kg dexamethasone) and ethanol (1.0 and 1.5 g/kg). Naloxone increased PREG levels, while CRF appeared to increase metabolism of PREG to deoxycorticosterone (DOC). ACTH, administered after dexamethasone, reduced PREG levels, despite an increase in plasma cortisol. Ethanol did not alter PREG levels. Changes in PREG levels were correlated with changes in DOC levels after naloxone 125 microg/kg, CRF, ethanol 1.5 g/kg, and dexamethasone challenges. Furthermore, dexamethasone-induced changes in PREG levels were correlated with subsequent alcohol intake. These data suggest that PREG responses to dexamethasone challenge may represent a trait marker of alcohol drinking. The lack of effect of ethanol on PREG levels suggests differential regulation in non-human primates vs. rodents.

Influence of ginsenoside Rb1 on brain neurosteroid during acute immobilization stress

This study examined whether or not acute stress is linked to increases in the neurosteroid levels, which is a well-known neurotransmitters associated with stress stimuli. The ginsenoside, Rb1, was tested in order to better understand its potential effects on altering the neurosteroid levels and ultimately attenuating stress. The optimal stressed condition was checked by measuring the 5a-dihydroprogesterone (DHP) and allopregnanolone (THP) levels in the brain after immobilization stress at various times. Based on this result, an acute stress model was set up to give 30 min of immobilization stress. The DHP and THP brain levels of the stressed mice were then investigated after administering Rb1 orally (10 mg/kg). These results were compared with the neurosteroid level in the stressed mice not given Rbl. Saline was administered orally to the nonstressed mice to check the placebo effect. Acute immobilization stress induced an increase in the THP and DHP concentration in the frontal cortex and cerebellum. When Rb1 was administered orally prior to immobilization stress, the THP level in the frontal cortex and cerebellum was significantly lower than that in the stressed animals not given Rbl. On the other hand, the DHP level was lower in the cerebellum only. This suggests that the metabolism of the brain neurosteroids is linked to psychological stress, and Rb1 attenuates the stress-induced increase in neurosteroids.

Lack of evidence of a role for the neurosteroid allopregnanolone in ethanol-induced reward and c-fos expression in DBA/2 mice

Previous studies using the 5alpha-reductase inhibitor finasteride suggest that progesterone metabolites, particularly the endogenous neurosteroid allopregnanolone, mediate some of the effects of ethanol. Consequently, we studied the effect of finasteride (2 x 25 mg/kg s.c., 12 h apart) pretreatment on the acquisition and expression of ethanol (2 g/kg i.p.) induced conditioned place preference and c-fos expression in DBA/2 mice; a strain known to be particularly sensitive to ethanol. Ethanol administration induced a clear conditioned place preference and widespread c-fos expression, with elements of the extended amygdala, Edinger-Westphal nucleus and paraventricular nucleus being especially sensitive. However, despite an approximately 99% decrease in whole brain allopregnanolone content, finasteride pretreatment had remarkably little effect on either ethanol-induced conditioned place preference or ethanol-induced c-fos expression. Thus, aside from a general stimulatory effect on c-fos expression in the ventral tegmental area, and generally mild depression of locomotor activity, no other effects of finasteride or interaction with ethanol effects were identifiable. Together, these studies suggest that endogenous allopregnanolone plays little part in mediating acute ethanol-induced reward or neural activation in DBA/2 mice.

Subjective effects and changes in steroid hormone concentrations in humans following acute consumption of alcohol

BACKGROUND

GABAA receptors are an important site of action of endogenous neurosteroids and an important mediator of several behavioral effects of alcohol. This study examined the effects of alcohol on plasma steroid hormone concentrations on the hypothesis that the endocrine effects mediate some of the subjective effects of alcohol.

METHODS

Thirty-two healthy subjects (17 men) with no history of a substance use disorder participated in this human laboratory study. All subjects consumed three standard drinks of grain alcohol. Subjective measures and blood samples for steroid concentrations were collected at baseline and 40 min after alcohol consumption.

RESULTS

Alcohol increased self-reported stimulation, alcohol liking, and desire for more alcohol. Alcohol also increased pregnenolone (PREG) and dehydroepiandrosterone (DHEA) concentrations, while it decreased progesterone (PROG) and allopregnanolone (ALLO) concentrations, as well as ALLO/PREG and PROG/PREG ratios. In men, the change in PREG concentration was significantly correlated with alcohol liking, while the alcohol-induced change in ALLO concentration correlated significantly with both alcohol liking and desire for more alcohol.

DISCUSSION

These findings provide preliminary support for the hypothesis that endogenous neurosteroids mediate some of the subjective effects of alcohol. Efforts to replicate these findings should aim to specify more clearly the nature and time course of the effects.

Moderate doses of ethanol fail to increase plasma levels of neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one-like immunoreactivity in healthy men and women

RATIONALE

The endogenous GABAergic neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP, allopregnanolone) has been proposed to contribute to ethanol actions. Humans synthesize 3alpha,5alpha-THP, but its role in response to systemic administration of ethanol is unclear.

OBJECTIVE

The present study aims to determine the effect of a moderate dose of ethanol on progesterone and 3alpha,5alpha-THP concentrations in plasma samples of healthy male and female subjects and to determine if these levels are related to the subjective effects of ethanol. Females were tested in both the follicular and luteal phases of the menstrual cycle.

METHODS

Healthy men (N=9) and women (N=12) aged 21-35 participated in the study. Men participated in two sessions on which they received ethanol (0.8 g/kg) or placebo. Women participated in four sessions on which they received ethanol (0.7 g/kg) or placebo during the follicular and luteal phases of their cycle. Subjective states and mood were measured by standardized self-report questionnaires and a measure of psychomotor performance. Steroid levels (progesterone, 3alpha,5alpha-THP, estradiol, and cortisol) were measured in plasma samples by radioimmunoassay.

RESULTS

Ethanol significantly increased plasma levels of progesterone, but not 3alpha,5alpha-THP-like immunoreactivity, in women in the luteal phase. Ethanol had no effect on progesterone or 3alpha,5alpha-THP-like immunoreactivity levels in women in the follicular phase or in men, and it did not increase cortisol in men or women. Ethanol also did not affect estradiol in men or women.

CONCLUSIONS

3alpha,5alpha-THP-like immunoreactivity levels in human plasma are not increased following moderate ethanol consumption, suggesting that circulating levels of progesterone or its tetrahydro-reduced metabolites do not play a major role in ethanol action. However, the possibility remains that ethanol increases endogenous brain production of GABAergic neurosteroids without affecting plasma levels. Moreover, humans synthesize 5beta-reduced GABAergic steroids, and levels of these steroids may be altered in plasma or brain.

Basis of the gabamimetic profile of ethanol

This article summarizes the proceedings of a symposium held at the 2005 Research Society on Alcoholism meeting. The initial presentation by Dr. Wallner provided evidence that selected GABA(A) receptors containing the delta subunit display sensitivity to low intoxicating ethanol concentrations and this sensitivity is further increased by a mutation in the cerebellar alpha6 subunit, found in alcohol-hypersensitive rats. Dr. Mameli reported that ethanol affects gamma-aminobutyric acid (GABA) function by affecting neural circuits that influence GABA release. Dr. Parsons presented data from electrophysiological and microdialysis investigations that ethanol is capable of releasing GABA from presynaptic terminals. Dr. Morrow demonstrated that systemic ethanol increases neuroactive steroids in brain, the absence of which alters various functional responses to ethanol. Dr. Criswell presented evidence that the ability of ethanol to increase GABA was apparent in some, but not all, brain regions indicative of regional specificity. Further, Dr. Criswell demonstrated that neurosteroids alone and when synthesized locally by ethanol act postsynaptically to enhance the effect of GABA released by ethanol in a region specific manner. Collectively, this series of reports support the GABAmimetic profile of acutely administered ethanol being dependent on several specific mechanisms distinct from a direct effect on the major synaptic isoforms of GABA(A) receptors.

The relevance of neurosteroids to clinical psychiatry: from the laboratory to the bedside

Neurosteroids are important neuroactive molecules with suggested central involvement in several neurophysiological and psychiatric disease processes. The discovery of neurosteroids followed the revelation that the brain exhibited the capacity to synthesize its own steroids in situ and thus be a potential site of steroidogenesis. In contrast to some steroids that exhibit traditional genomic steroid actions, most neurosteroids appear to regulate neuronal function by means of "non-genomic" mechanisms influencing neuronal excitability. Neurosteroids are synthesized either from CNS cholesterol or from peripheral steroid precursors and exhibit a wide range of modulatory effects on neurotransmitter receptor activity, most notably at the gamma-aminobutyric acid A (GABA(A)) receptor. Neurosteroids play an important role in neurodevelopment and neuroprotective effects, many aspects of which may have particular applicability to psychiatric disorders including various gender differences. Neurosteroids appear to be relevant to the pathophysiology and pharmacological treatment of many psychiatric disorders including the most notable mood and anxiety disorders, but also psychotic, childhood, eating, dementia, stress and postpartum disorders. It has been suggested that neurosteroids may become potential targets for pharmacological intervention in the future with further neurosteroid investigation contributing to a more comprehensive understanding of human behavior and psychopathology.

Effect of isopregnanolone on rapid tolerance to the anxiolytic effect of ethanol

OBJETIVE: It has been shown that neurosteroids can either block or stimulate the development of chronic and rapid tolerance to the incoordination and hypothermia caused by ethanol consumption. The aim of the present study was to investigate the influence of isopregnanolone on the development of rapid tolerance to the anxiolytic effect of ethanol in mice. METHOD: Male Swiss mice were pretreated with isopregnanolone (0.05, 0.10 or 0.20 mg/kg) 30 min before administration of ethanol (1.5 g/kg). Twenty-four hours later, all animals we tested using the plus-maze apparatus. The first experiment defined the doses of ethanol that did or did not induce rapid tolerance to the anxiolytic effect of ethanol. In the second, the influence of pretreatment of mice with isopregnanolone (0.05, 0.10 or 0.20 mg/kg) on rapid tolerance to ethanol (1.5 g/kg) was studied. CONCLUSIONS: The results show that pretreatment with isopregnanolone interfered with the development of rapid tolerance to the anxiolytic effect of ethanol.