Nanomolar allopregnanolone potentiates rat cerebellar GABAA receptors

Steroids, steroid associated substances and gestational diabetes mellitus

As gestational diabetes mellitus (GDM) is both a frequent and serious complication, steroid levels in pregnancy are extremely elevated and their role in pregnancy is crucial, this review focuses on the role of steroids and related substances in the GDM pathophysiology. Low SHBG levels are associated with insulin resistance and hyperinsulinemia, while also predicting a predisposition to GDM. Other relevant agents are placental hormones such as kisspeptin and CRH, playing also an important role beyond pregnancy, but which are synthesized here in smaller amounts in the hypothalamus. These hormones affect both the course of pregnancy as well as the synthesis of pregnancy steroids and may also be involved in the GDM pathophysiology. Steroids, whose biosynthesis is mainly provided by the fetal adrenal glands, placenta, maternal adrenal glands, and both maternal and fetal livers, are also synthesized in limited amounts directly in the pancreas and may influence the development of GDM. These substances involve the sulfated Δ5 steroids primarily acting via modulating different ion channels and influencing the development of GDM in different directions, mostly diabetogenic progesterone and predominantly anti-diabetic estradiol acting both in genomic and non-genomic way, androgens associated with IR and hyperinsulinemia, neuroactive steroids affecting the pituitary functioning, and cortisol whose production is stimulated by CRH but which suppresses its pro-inflammatory effects. Due to the complex actions of steroids, studies assessing their predominant effect and studies assessing their predictive values for estimating predisposition to GDM are needed.

Altered Steroidome in Women with Gestational Diabetes Mellitus: Focus on Neuroactive and Immunomodulatory Steroids from the 24th Week of Pregnancy to Labor

Gestational diabetes mellitus (GDM) is a complication in pregnancy, but studies focused on the steroidome in patients with GDM are not available in the public domain. This article evaluates the steroidome in GDM+ and GDM- women and its changes from 24 weeks (± of gestation) to labor. The study included GDM+ (n = 44) and GDM- women (n = 33), in weeks 24-28, 30-36 of gestation and at labor and mixed umbilical blood after delivery. Steroidomic data (101 steroids quantified by GC-MS/MS) support the concept that the increasing diabetogenic effects with the approaching term are associated with mounting progesterone levels. The GDM+ group showed lower levels of testosterone (due to reduced AKR1C3 activity), estradiol (due to a shift from the HSD17B1 towards HSD17B2 activity), 7-oxygenated androgens (competing with cortisone for HSD11B1 and shifting the balance from diabetogenic cortisol towards the inactive cortisone), reduced activities of SRD5As, and CYP17A1 in the hydroxylase but higher CYP17A1 activity in the lyase step. With the approaching term, the authors found rising activities of CYP3A7, AKR1C1, CYP17A1 in its hydroxylase step, but a decline in its lyase step, rising conjugation of neuroinhibitory and pregnancy-stabilizing steroids and weakening AKR1D1 activity.

Mating Enhances Expression of Hormonal and Trophic Factors in the Midbrain of Female Rats

Among female rats, mating enhances neurosteroid formation in the midbrain ventral tegmental area (VTA; independent of peripheral steroid-secreting glands, ovaries, and adrenals). The sources/targets for these actions are not well understood. In Experiment 1, proestrous rats engaged in a mating paradigm, or did not, and the midbrains had been assessed via the Affymetrix rat genome microarrays. In Experiment 2, the influence of gonadal and adrenal glands on the expression of these genes was assessed in rats that were proestrous, ovariectomized (OVX), or OVX and adrenalectomized (ADX). The microarrays revealed 53 target genes that were significantly up-regulated (>2.0-fold change) in response to mating. Mating significantly enhanced the midbrain mRNA expression of genes involved in hormonal and trophic actions: Gh1, S100g, and Klk1b3 in proestrous, but not OVX and/or ADX, rats; Fshb in all but OVX/ADX rats; and lutenizing hormone β and thyroid-stimulating hormone (TSH) β in all rats. Thus, mating enhances midbrain gene expression independent and dependent of peripheral glands.

The α6 subunit-containing GABAA receptor: A novel drug target for inhibition of trigeminal activation

Novel treatments against migraine are an urgent medical requirement. The α6 subunit-containing GABA_A receptors (α6GABA_ARs) are expressed in trigeminal ganglia (TG), the hub of the trigeminal vascular system (TGVS) that is involved in the pathogenesis of migraine. Here we reveal an unprecedented role of α6GABA_ARs in ameliorating TGVS activation using several pharmacological approaches in an animal model mimicking pathological changes in migraine. TGVS activation was induced by intra-cisternal (i.c.) instillation of capsaicin in Wistar rats. Centrally, i.c. capsaicin activated the trigeminal cervical complex (TCC) measured by the increased number of c-Fos-immunoreactive (c-Fos-ir) TCC neurons. Peripherally, it elevated calcitonin gene-related peptide immunoreactivity (CGRP-ir) in TG and depleted CGRP-ir in the dura mater. Pharmacological approaches included a recently identified α6GABA_AR-selective positive allosteric modulator (PAM), the pyrazoloquinolinone Compound 6, two α6GABA_AR-active PAMs (Ro15-4513 and loreclezole), an α6GABA_AR-inactive benzodiazepine (diazepam), an α6GABA_AR-selective antagonist (furosemide), and a clinically effective antimigraine agent (topiramate). We examined effects of these compounds on both central and peripheral TGVS responses induced by i.c. capsaicin. Compound 6 (3-10 mg/kg, i.p.) significantly attenuated the TCC neuronal activation and TG CGRP-ir elevation, and dural CGRP depletion induced by capsaicin. All these effects of Compound 6 were mimicked by topiramate, Ro15-4513 and loreclezole, but not by diazepam. The brain-impermeable furosemide antagonized the peripheral, but not central, effects of Compound 6. These results suggest that the α6GABA_AR in TG is a novel drug target for TGVS activation and that α6GABA_AR-selective PAMs have the potential to be developed as a novel pharmacotherapy for migraine.

Effect of ganaxolone and THIP on operant and limited-access ethanol self-administration

Recent evidence suggests that GABA(A) receptor ligands may regulate ethanol intake via effects at both synaptic and extrasynaptic receptors. For example, the endogenous neurosteroid, allopregnanolone (ALLO) has a similar pharmacological profile as ethanol, and it alters ethanol intake in rodent models. Additionally, recent evidence suggests that δ-subunit-containing extrasynaptic GABA(A) receptors may confer high sensitivity to both ethanol and neurosteroids. The purpose of the present study was to determine the effects of ganaxolone (GAN; an ALLO analog) and gaboxadol (THIP; a GABA(A) receptor agonist with selectivity for the extrasynaptic δ-subunit) on ethanol intake, drinking patterns, and bout characteristics in operant and limited-access self-administration procedures. In separate studies, the effects of GAN (0-10 mg/kg) and THIP (2-16 mg/kg) were tested in C57BL/6J male mice provided with 2-h access to a two-bottle choice of water or 10% ethanol or trained to respond for 30 min of access to 10% ethanol. GAN had no overall significant effect on operant ethanol self-administration, but tended to decrease the latency to consume the first bout. In the limited-access procedure, GAN dose-dependently decreased ethanol intake. THIP dose-dependently decreased ethanol intake in both paradigms, altering both the consummatory and appetitive processes of operant self-administration as well as shifting the drinking patterns in both procedures. These results add to literature suggesting time-dependent effects of neurosteroids to promote the onset, and to subsequently decrease, ethanol drinking behavior, and they support a role for extrasynaptic GABA(A) receptor activation in ethanol reinforcement.

Alteration of ethanol drinking in mice via modulation of the GABA(A) receptor with ganaxolone, finasteride, and gaboxadol

BACKGROUND

Neurosteroids and other γ-aminobutyric acid(A) (GABA(A) ) receptor-modulating compounds have been shown to affect ethanol intake, although their mechanism remains unclear. This study examined how patterns of 24-hour ethanol drinking in mice were altered with the synthetic GABAergic neurosteroid ganaxolone (GAN), with an inhibitor of neurosteroid synthesis (finasteride [FIN]), or a GABA(A) receptor agonist with some selectivity at extrasynaptic receptors (gaboxadol HCL [THIP]).

METHODS

Male C57BL/6J mice had continuous access to a 10% v/v ethanol solution (10E) or water. Using lickometer chambers, drinking patterns were analyzed among mice treated in succession to GAN (0, 5, and 10 mg/kg), FIN (0 or 100 mg/kg), and THIP (0, 2, 4, 8, and 16 mg/kg).

RESULTS

GAN shifted drinking in a similar but extended manner to previous reports using low doses of the neurosteroid allopregnanolone (ALLO); drinking was increased in hour 1, decreased in hours 2 and 3, and increased in hours 4 and 5 postinjection. THIP (8 mg/kg) and FIN both decreased 10E drinking during the first 5 hours postinjection by 30 and 53%, respectively, while having no effect on or increasing water drinking, respectively. All 3 drugs altered the initiation of drinking sessions in a dose-dependent fashion. FIN increased and GAN decreased time to first lick and first bout. THIP (8 mg/kg) decreased time to first lick but increased time to first bout and attenuated first bout size.

CONCLUSIONS

The present findings support a role for the modulation of ethanol intake by neurosteroids and GABA(A) receptor-acting compounds and provide hints as to how drinking patterns are shifted. The ability of THIP to alter 10E drinking suggests that extrasynaptic GABA(A) receptors may be involved in the modulation of ethanol intake. Further, the consistent results with THIP to that seen previously with high doses of ALLO suggest that future studies should further examine the relationship between neurosteroids and extrasynaptic GABA(A) receptors, which could provide a better understanding of the mechanism by which neurosteroids influence ethanol intake.

Neurosteroids' effects and mechanisms for social, cognitive, emotional, and physical functions

Hormones are trophic factors that integrate central and peripheral nervous system functions, and can influence social, cognitive, emotional and physical (SCEP) processes. Greater understanding of behavioral and neurobiological underpinnings of mental, cognitive, and/or physical changes with maturation is becoming increasingly important as the world's population ages. There are individual differences in how people age, but the factors that influence these differences are not well understood. Social supports are one factor that may influence the trajectory of age-related processes. The loss of close relationships, especially among older persons, is one of the greatest risk factors for mental and physical decline. Progesterone, secreted by the ovaries, or produced de novo in the brain, is readily converted centrally to 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), and can influence SCEP, through rapid, non-classical steroid-mediated actions. Our hypothesis is that 3alpha,5alpha-THP is a key trophic factor in SCEP and development. Our research has demonstrated that 3alpha,5alpha-THP facilitates social and sexual behavior of rodents, which evokes further increases in 3alpha,5alpha-THP in midbrain and hippocampus, brain areas involved in SCEP. The role of 3alpha,5alpha-THP to influence social and/or sexual experience, and thereby SCEP, is discussed in this review. Further understanding of these neurobiological and/or behavioral factors may lead to findings that ultimately can promote health and prevent disease.

Structure-activity relationship of etomidate derivatives at the GABA(A) receptor: Comparison with binding to 11beta-hydroxylase

At the GABA(A) receptor, low concentrations of etomidate potentiate the inhibitory effect of GABA on specific binding of the closed channel ligand [(3)H]ethynylpropylbicycloorthobenzoate ([(3)H]EBOB). Here, we present SARs for etomidate and structurally related compounds inducing this effect. In the absence of GABA, similar SARs, but 14-20 times weaker potencies were observed. We discuss these SARs in comparison to the much higher potencies of these compounds as inhibitors of 11beta-hydroxylase.

The role of GABA(A) receptors in the development of alcoholism

Alcoholism is a common, heritable, chronic relapsing disorder. GABA(A) receptors undergo allosteric modulation by ethanol, anesthetics, benzodiazepines and neurosteroids and have been implicated in the acute as well as the chronic effects of ethanol including tolerance, dependence and withdrawal. Medications targeting GABA(A) receptors ameliorate the symptoms of acute withdrawal. Ethanol induces plasticity in GABA(A) receptors: tolerance is associated with generally decreased GABA(A) receptor activation and differentially altered subunit expression. The dopamine (DA) mesolimbic reward pathway originating in the ventral tegmental area (VTA), and interacting stress circuitry play an important role in the development of addiction. VTA GABAergic interneurons are the primary inhibitory regulators of DA neurons and a subset of VTA GABA(A) receptors may be implicated in the switch from heavy drinking to dependence. GABA(A) receptors modulate anxiety and response to stress; important elements of sustained drinking and relapse. The GABA(A) receptor subunit genes clustered on chromosome 4 are highly expressed in the reward pathway. Several recent studies have provided strong evidence that one of these genes, GABRA2, is implicated in alcoholism in humans. The influence of the interaction between ethanol and GABA(A) receptors in the reward pathway on the development of alcoholism together with genetic and epigenetic vulnerabilities will be explored in this review.

A 17beta-derivative of allopregnanolone is a neurosteroid antagonist at a cerebellar subpopulation of GABA A receptors with nanomolar affinity

BACKGROUND AND PURPOSE

High-affinity, subtype-selective antagonists of the neurosteroid binding sites of GABA(A) receptors are not available. We have characterized an allopregnanolone derivative as an antagonist of cerebellar GABA(A) receptors with nanomolar affinity.

EXPERIMENTAL APPROACH

Receptor binding and electrophysiological methods were used for the allosteric modulation of cerebellar GABA(A) receptors by an allopregnanolone derivative, (20R)-17beta-(1-hydroxy-2,3-butadienyl)-5alpha-androstane-3alpha-ol (HBAO). GABA(A) receptors of rat cerebellar membranes were labelled with the chloride channel blocker [(3)H]ethynylbicycloorthobenzoate (EBOB). The ionophore function of GABA(A) receptors was studied by whole-cell patch clamp electrophysiology in cultured rat cerebellar granule and cortical cells.

KEY RESULTS

Partial displacement of cerebellar [(3)H]EBOB binding by nanomolar HBAO was attenuated by 0.1 mM furosemide, an antagonist of alpha(6) and beta(2-3) subunit-containing GABA(A) receptors. Displacement curves of HBAO were reshaped by 30 nM GABA and shifted to the right. However, the micromolar potency of full displacement by allopregnanolone was not affected by 0.1 mM furosemide or 30 nM GABA. The nanomolar, but not the micromolar phase of displacement of [(3)H]EBOB binding by GABA was attenuated by 100 nM HBAO. Submicromolar HBAO did not affect [(3)H]EBOB binding to cortical and hippocampal GABA(A) receptors. HBAO up to 1 microM did not affect chloride currents elicited by 0.3-10 microM GABA, while it abolished potentiation by 1 microM allopregnanolone with nanomolar potency in cerebellar but not in cortical cells. Furosemide attenuated cerebellar inhibition by 100 nM HBAO.

CONCLUSIONS AND IMPLICATIONS

HBAO is a selective antagonist of allopregnanolone, a major endogenous positive modulator via neurosteroid sites of cerebellar (probably alpha(6)beta(2-3)delta) GABA(A) receptors.

Molecular and synaptic organization of GABAA receptors in the cerebellum: Effects of targeted subunit gene deletions

GABAA receptors form heteromeric GABA-gated chloride channels assembled from a large family of subunit genes. In cerebellum, distinct GABAA receptor subtypes, differing in subunit composition, are segregated between cell types and synaptic circuits. The cerebellum therefore represents a useful system to investigate the significance of GABAA receptor heterogeneity. For instance, studies of mice carrying targeted deletion of major GABAA receptor subunit genes revealed the role of alpha subunit variants for receptor assembly, synaptic targeting, and functional properties. In addition, these studies unraveled mandatory association between certain subunits and demonstrated distinct pharmacology of receptors mediating phasic and tonic inhibition. Although some of these mutants have a profound loss of GABAA receptors, they exhibit only minor impairment of motor function, suggesting activation of compensatory mechanisms to preserve inhibitory networks in the cerebellum. These adaptations include an altered balance between phasic and tonic inhibition, activation of voltage-independent K+ conductances, and upregulation of GABAA receptors in interneurons that are not affected directly by the mutation. Deletion of the alpha1 subunit gene leads to complete loss of GABAA receptors in Purkinje cells. A striking alteration occurs in these mice, whereby presynaptic GABAergic terminals are preserved in the molecular layer but make heterologous synapses with spines, characterized by a glutamatergic-like postsynaptic density. During development of alpha1(0/0) mice, GABAergic synapses are initially formed but are replaced upon spine maturation. These findings suggest that functional GABAA receptors are required for long-term maintenance of GABAergic synapses in Purkinje cells.

The progesterone metabolite allopregnanolone potentiates GABA(A) receptor-mediated inhibition of 5-HT neuronal activity

The dorsal raphe nucleus (DRN) is the origin of much of the 5-HT innervation of the forebrain. The activity of DRN 5-HT neurons is regulated by a number of receptors including GABA(A) and 5-HT(1A) inhibitory receptors and by excitatory alpha(1)-adrenoceptors. Using in vitro electrophysiological recording we investigated the action of progesterone and its metabolite, allopregnanolone on receptor-mediated responses of DRN 5-HT neurons. Neither allopregnanolone nor progesterone affected the alpha(1)-adrenoceptor agonist-induced firing. Allopregnanolone also had no effect on the inhibitory response to 5-HT. However, allopregnanolone significantly potentiated the inhibitory responses to GABA(A) receptor agonists. Progesterone did not enhance GABA(A) receptor-meditated inhibitory responses. Thus, the neuroactive metabolite of progesterone, allopregnanolone, has the ability to cause potentiation of GABA(A)-mediated inhibition of DRN 5-HT neurons. This effect on 5-HT neurotransmission may have relevance for mood disorders commonly associated with reproductive hormone events, such as premenstrual dysphoric disorder and postpartum depression.

Increased levels of pregnenolone and its neuroactive metabolite allopregnanolone in autopsied brain tissue from cirrhotic patients who died in hepatic coma

It has been suggested that neurosteroids with agonist properties at the central GABA-A receptor are implicated in the pathogenesis of hepatic encephalopathy (HE) in chronic liver disease. In order to address this issue, gas chromatography/mass spectrometry was used to measure the neurosteroids pregnenolone, allopregnanolone, and tetrahydrodeoxycorticosterone (THDOC) in postmortem brain tissue from controls, cirrhotic patients who died without HE, a patient who died in uremic coma, and cirrhotic patients who died in hepatic coma. Exposure of rat cerebral cortical membranes to brain extracts from hepatic coma patients resulted in a 53% (p < 0.001) increase in binding of [3H]muscimol, a GABA-A receptor ligand. Subsequent GC/MS analysis showed that concentrations of the GABA-A receptor agonist neurosteroid allopregnanolone were significantly increased in brain tissue from hepatic coma patients compared to patients without HE or controls (p < 0.001). Brain allopregnanolone concentrations were significantly correlated with the magnitude of induction of [3H]muscimol binding (r2 = 0.82, p < 0.0001). Concentrations of allopregnanolone comparable to those observed in hepatic coma brains are pathophysiologically relevant. Concentrations of the neurosteroid precursor pregnenolone were also increased in brain tissue from hepatic coma patients, while those of a second neurosteroid THDOC were below the levels of detection in all groups. Brain concentrations of benzodiazepine receptor ligands estimated by radioreceptor assay were not significantly increased in cirrhotic patients with or without hepatic coma. These findings suggest that increased levels of allopregnanolone rather than "endogenous benzodiazepines" offer a cogent explanation for the phenomenon of "increased GABAergic tone" previously proposed in HE.

The pheromone androstenol (5 alpha-androst-16-en-3 alpha-ol) is a neurosteroid positive modulator of GABAA receptors

Androstenol is a steroidal compound belonging to the group of odorous 16-androstenes, first isolated from boar testes and also found in humans. Androstenol has pheromone-like properties in both animals and humans, but the molecular targets of its pheromonal activity are unknown. Androstenol is structurally similar to endogenous A-ring reduced neurosteroids that act as positive modulators of GABA(A) receptors. Here we show that androstenol has neurosteroid-like activity as a GABA(A) receptor modulator. In whole-cell recordings from cerebellar granule cells, androstenol (but not its 3beta-epimer) caused a concentration-dependent enhancement of GABA-activated currents (EC(50), 0.4 microM in cultures; 1.4 microM in slices) and prolonged the duration of spontaneous and miniature inhibitory postsynaptic currents. Androstenol (0.1-1 microM) also potentiated the amplitude of GABA-activated currents in human embryonic kidney 293 cells transfected with recombinant alpha1beta2gamma2 and alpha2beta2gamma2 GABA(A) receptors and, at high concentrations (10-300 microM), directly activated currents in these cells. Systemic administration of androstenol (30-50 mg/kg) caused anxiolytic-like effects in mice in the open-field test and elevated zero-maze and antidepressant-like effects in the forced swim test (5-10 mg/kg). Androstenol, but not its 3beta-epimer, conferred seizure protection in the 6-Hz electroshock and pentylenetetrazol models (ED(50) values, 21.9 and 48.9 mg/kg, respectively). The various actions of androstenol in the whole-animal models are consistent with its activity as a GABA(A) receptor modulator. GABA(A) receptors could represent a target for androstenol as a pheromone, for which it is well suited because of high volatility and lipophilicity, or as a conventional hormonal neurosteroid.