Functional correlation between allopregnanolone and [35S]-TBPS binding in the brain of rats exposed to isoniazid, pentylenetetrazol or stress

Emerging insights into hypothalamic-pituitary-gonadal axis regulation and interaction with stress signalling

Reproduction and fertility are regulated via hormones of the hypothalamic-pituitary-gonadal (HPG) axis. Control of this reproductive axis occurs at all levels, including the brain and pituitary, and allows for the promotion or inhibition of gonadal sex steroid secretion and function. In addition to guiding proper gonadal development and function, gonadal sex steroids also act in negative- and positive-feedback loops to regulate reproductive circuitry in the brain, including kisspeptin neurones, thereby modulating overall HPG axis status. Additional regulation is also provided by sex steroids made within the brain, including neuroprogestins. Furthermore, because reproduction and survival need to be coordinated and balanced, the HPG axis is able to modulate (and be modulated by) stress hormone signalling, including cortiscosterone, from the hypothalamic-pituitary-adrenal (HPA) axis. This review covers recent data related to the neural, hormonal and stress regulation of the HPG axis and emerging interactions between the HPG and HPA axes, focusing on actions at the level of the brain and pituitary.

A single dose of allopregnanolone affects the ovarian morphology and steroidogenesis

Allopregnanolone, a progesterone metabolite, is one of the best characterized neurosteroids. In a dose that mimics serum levels during stress, allopregnanolone inhibits sexual receptivity and ovulation and induces a decrease in luteinizing hormone levels. The aim of this work was to examine the effect of an intracerebroventricular administration of allopregnanolone on ovarian morphophysiology, serum and tissue levels of progesterone and estrogen, and enzymatic activity of 3β-hydroxysteroid dehydrogenase, 20α-hydroxysteroid dehydrogenase and 3α-hydroxysteroid oxido-reductase in the ovary and in the medial basal hypothalamus on the morning of estrus. Ovarian morphology was analyzed under light microscopy. The hormone assays were performed by radioimmunoassay. The enzymatic activities were measured by spectrophotometric analysis. The morphometric analysis revealed that, in allopregnanolone-treated animals, the number of secondary and Graafian follicles was decreased while that of atretic follicles and cysts was significantly increased. Some cysts showed luteinized unruptured follicles. There were no differences in the number of tertiary follicles or corpora lutea in comparison with the corresponding control groups. In allopregnanolone-treated animals, progesterone serum levels were increased, while ovarian progesterone levels were decreased. Moreover, 3β-HSD and 3α-HSOR enzymatic activities were increased in the medial basal hypothalamus while ovarian levels were decreased. The enzyme 20α-hydroxysteroid dehydrogenase showed the opposite profile. The results of this study showed that allopregnanolone interferes on ovarian steroidogenesis and ovarian morphophysiology in rats, providing a clear evidence for the role of this neurosteroid in the control of reproductive function under stress situations.

NPY-Y1 coexpressed with NPY-Y5 receptors modulate anxiety but not mild social stress response in mice

The Y1 and Y5 receptors for neuropeptide Y have overlapping functions in regulating anxiety. We previously demonstrated that conditional removal of the Y1 receptor in the Y5 receptor expressing neurons in juvenile Npy1r(Y5R-/-) mice leads to higher anxiety but no changes in hypothalamus-pituitary-adrenocortical axis activity, under basal conditions or after acute restraint stress. In the present study, we used the same conditional system to analyze the specific contribution of limbic neurons coexpressing Y1 and Y5 receptors on the emotional and neuroendocrine responses to social chronic stress, using different housing conditions (isolation vs. group-housing) as a model. We demonstrated that control Npy1r(2lox) male mice housed in groups show increased anxiety and hypothalamus-pituitary-adrenocortical axis activity compared with Npy1r(2lox) mice isolated for six weeks immediately after weaning. Conversely, Npy1r(Y5R-/-) conditional mutants display an anxious-like behavior but no changes in hypothalamus-pituitary-adrenocortical axis activity as compared with their control littermates, independently of housing conditions. These results suggest that group housing constitutes a mild social stress for our B6129S mouse strain and they confirm that the conditional inactivation of Y1 receptors specifically in Y5 receptor containing neurons increases stress-related anxiety without affecting endocrine stress responses.

Revisiting the roles of progesterone and allopregnanolone in the nervous system: resurgence of the progesterone receptors

Progesterone is commonly considered as a female reproductive hormone and is well-known for its role in pregnancy. It is less well appreciated that progesterone and its metabolite allopregnanolone are also male hormones, as they are produced in both sexes by the adrenal glands. In addition, they are synthesized within the nervous system. Progesterone and allopregnanolone are associated with adaptation to stress, and increased production of progesterone within the brain may be part of the response of neural cells to injury. Progesterone receptors (PR) are widely distributed throughout the brain, but their study has been mainly limited to the hypothalamus and reproductive functions, and the extra-hypothalamic receptors have been neglected. This lack of information about brain functions of PR is unexpected, as the protective and trophic effects of progesterone are much investigated, and as the therapeutic potential of progesterone as a neuroprotective and promyelinating agent is currently being assessed in clinical trials. The little attention devoted to the brain functions of PR may relate to the widely accepted assumption that non-reproductive actions of progesterone may be mainly mediated by allopregnanolone, which does not bind to PR, but acts as a potent positive modulator of γ-aminobutyric acid type A (GABA(A) receptors. The aim of this review is to critically discuss effects of progesterone on the nervous system via PR, and of allopregnanolone via its modulation of GABA(A) receptors, with main focus on the brain.

Paradoxical effects of GABA-A modulators may explain sex steroid induced negative mood symptoms in some persons

Some women have negative mood symptoms, caused by progestagens in hormonal contraceptives or sequential hormone therapy or by progesterone in the luteal phase of the menstrual cycle, which may be attributed to metabolites acting on the GABA-A receptor. The GABA system is the major inhibitory system in the adult CNS and most positive modulators of the GABA-A receptor (benzodiazepines, barbiturates, alcohol, GABA steroids), induce inhibitory (e.g. anesthetic, sedative, anticonvulsant, anxiolytic) effects. However, some individuals have adverse effects (seizures, increased pain, anxiety, irritability, aggression) upon exposure. Positive GABA-A receptor modulators induce strong paradoxical effects including negative mood in 3%-8% of those exposed, while up to 25% have moderate symptoms. The effect is biphasic: low concentrations induce an adverse anxiogenic effect while higher concentrations decrease this effect and show inhibitory, calming properties. The prevalence of premenstrual dysphoric disorder (PMDD) is also 3%-8% among women in fertile ages, and up to 25% have more moderate symptoms of premenstrual syndrome (PMS). Patients with PMDD have severe luteal phase-related symptoms and show changes in GABA-A receptor sensitivity and GABA concentrations. Findings suggest that negative mood symptoms in women with PMDD are caused by the paradoxical effect of allopregnanolone mediated via the GABA-A receptor, which may be explained by one or more of three hypotheses regarding the paradoxical effect of GABA steroids on behavior: (1) under certain conditions, such as puberty, the relative fraction of certain GABA-A receptor subtypes may be altered, and at those subtypes the GABA steroids may act as negative modulators in contrast to their usual role as positive modulators; (2) in certain brain areas of vulnerable women the transmembrane Cl(-) gradient may be altered by factors such as estrogens that favor excitability; (3) inhibition of inhibitory neurons may promote disinhibition, and hence excitability. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.

Enhanced Sensitivity to Ethanol-Induced Inhibition of LTP in CA1 Pyramidal Neurons of Socially Isolated C57BL/6J Mice: Role of Neurosteroids

Ethanol (EtOH) induced impairment of long-term potentiation (LTP) in the rat hippocampus is prevented by the 5α-reductase inhibitor finasteride, suggesting that this effect of EtOH is dependent on the increased local release of neurosteroids such as 3α,5α-THP that promote GABA-mediated transmission. Given that social isolation (SI) in rodents is associated with altered plasma and brain levels of such neurosteroids as well as with an enhanced neurosteroidogenic action of EtOH, we examined whether the inhibitory effect of EtOH on LTP at CA3-CA1 hippocampal excitatory synapses is altered in C57BL/6J mice subjected to SI for 6 weeks in comparison with group-housed (GH) animals. Extracellular recording of field excitatory postsynaptic potentials (fEPSPs) as well as patch-clamp analysis were performed in hippocampal slices prepared from both SI and GH mice. Consistent with previous observations, recording of fEPSPs revealed that the extent of LTP induced in the CA1 region of SI mice was significantly reduced compared with that in GH animals. EtOH (40 mM) inhibited LTP in slices from SI mice but not in those from GH mice, and this effect of EtOH was abolished by co-application of 1 μM finasteride. Current-clamp analysis of CA1 pyramidal neurons revealed a decrease in action potential (AP) frequency and an increase in the intensity of injected current required to evoke the first AP in SI mice compared with GH mice, indicative of a decrease in neuronal excitability associated with SI. Together, our data suggest that SI results in reduced levels of neuronal excitability and synaptic plasticity in the hippocampus. Furthermore, the increased sensitivity to the neurosteroidogenic effect of EtOH associated with SI likely accounts for the greater inhibitory effect of EtOH on LTP in SI mice. The increase in EtOH sensitivity induced by SI may be important for the changes in the effects of EtOH on anxiety and on learning and memory associated with the prolonged stress attributable to SI.

Neuroregenerative mechanisms of allopregnanolone in Alzheimer's disease

The proliferative pool and regenerative potential of neural stem cells diminishes with age, a phenomenon that may be exacerbated in prodromal and mild Alzheimer's disease (AD) brains. In parallel, the neuroactive progesterone metabolite, allopregnanolone (APα), along with a host of other factors, is decreased in the AD brain. Results of preclinical analyses demonstrate that APα is a potent inducer of neural progenitor proliferation of both rodent and human derived neural progenitor cells in vitro. In vivo, APα significantly increased neurogenesis within the subgranular zone of the dentate gyrus and subventricular zone of the 3xTgAD mouse model. Functionally, APα reversed the learning and memory deficits of 3xTgAD mice prior to and following the onset of AD pathology and was comparably efficacious in aged normal mice. In addition to inducing regenerative responses in mouse models of AD, APα significantly reduced beta-amyloid burden, beta-amyloid binding alcohol dehydrogenase load, and microglial activation. In parallel, APα increased markers of white matter generation and cholesterol homeostasis. Analyses to determine the optimal treatment regimen in the 3xTgAD mouse brain indicated that a treatment regimen of APα once per week was optimal for both inducing neurogenesis and reducing AD pathology. Pharmacokinetic analyses indicated that APα is rapidly increased in both plasma and brain following a single dose. APα is most efficacious when administered once per week which will contribute to its margin of safety. Further, analyses in both animals and humans have provided parameters for safe APα dosage exposure in humans. From a translational perspective, APα is a small molecular weight, blood brain barrier penetrant molecule with substantial preclinical efficacy data as a potential Alzheimer's therapeutic with existing safety data in animals and humans. To our knowledge, APα is the only small molecule that both promotes neural progenitor regeneration in brain and simultaneously reduces AD pathology burden.

Neurosteroids and GABA-A Receptor Function

Neurosteroids represent a class of endogenous steroids that are synthesized in the brain, the adrenals, and the gonads and have potent and selective effects on the GABAA-receptor. 3α-hydroxy A-ring reduced metabolites of progesterone, deoxycorticosterone, and testosterone are positive modulators of GABA(A)-receptor in a non-genomic manner. Allopregnanolone (3α-OH-5α-pregnan-20-one), 5α-androstane-3α, 17α-diol (Adiol), and 3α5α-tetrahydrodeoxycorticosterone (3α5α-THDOC) enhance the GABA-mediated Cl(-) currents acting on a site (or sites) distinct from the GABA, benzodiazepine, barbiturate, and picrotoxin binding sites. 3α5α-P and 3α5α-THDOC potentiate synaptic GABA(A)-receptor function and activate δ-subunit containing extrasynaptic receptors that mediate tonic currents. On the contrary, 3β-OH pregnane steroids and pregnenolone sulfate (PS) are GABA(A)-receptor antagonists and induce activation-dependent inhibition of the receptor. The activities of neurosteroid are dependent on brain regions and types of neurons. In addition to the slow genomic action of the parent steroids, the non-genomic, and rapid actions of neurosteroids play a significant role in the GABA(A)-receptor function and shift in mood and memory function. This review describes molecular mechanisms underlying neurosteroid action on the GABA(A)-receptor, mood changes, and cognitive functions.

Sex steroid induced negative mood may be explained by the paradoxical effect mediated by GABAA modulators

Certain women experience negative mood symptoms as a result of progesterone during the luteal phase of the menstrual cycle, progestagens in hormonal contraceptives, or the addition of progesterone or progestagens in sequential hormone therapy (HT). This phenomenon is believed to be mediated via the action of the progesterone metabolites on the GABA(A) system, which is the major inhibitory system in the mammalian CNS. The positive modulators of the GABA(A) receptor include allopregnanolone and pregnanolone, both neuroactive metabolites of progesterone, as well as benzodiazepines, barbiturates, and alcohol. Studies on the effect of GABA(A) receptor modulators have shown contradictory results; although human and animal studies have revealed beneficial properties such as anaesthesia, sedation, anticonvulsant effects, and anxiolytic effects, recent reports have also indicated adverse effects such as anxiety, irritability, and aggression. It has actually been suggested that several GABA(A) receptor modulators, including allopregnanolone, have biphasic effects, in that low concentrations increase an adverse, anxiogenic effect whereas higher concentrations decrease this effect and show beneficial, calming properties. The allopregnanolone increase during the luteal phase in fertile women, as well as during the addition of progesterone in HT, has been shown to induce adverse mood in women. The severity of these mood symptoms is related to the allopregnanolone serum concentrations in a manner similar to an inverted U-shaped curve. Negative mood symptoms occur when the serum concentration of allopregnanolone is similar to endogenous luteal phase levels, while low and high concentrations have less effect on mood. It has also been shown that progesterone/allopregnanolone treatment in women increases the activity in the amygdala (as measured with functional magnetic resonance imaging) in a similar way to the changes seen during anxiety reactions. However, it is evident that only certain women experience adverse mood during progesterone or GABA(A) receptor modulator treatments. Women with premenstrual dysphoric disorder (PMDD) have severe luteal phase related symptoms; in this phase, they show changes in GABA(A) receptor sensitivity and GABA concentrations that are related to the severity of the condition. These findings suggest that negative mood symptoms in women with PMDD are caused by the paradoxical effect of allopregnanolone mediated via the GABA(A) receptor.

CONCLUSION

Progesterone and progestagens induce negative mood, most probably via their GABA(A) receptor active metabolites. In postmenopausal women treated with progesterone and animals treated with allopregnanolone, there is a bimodal association between serum allopregnanolone concentration and adverse mood, resembling an inverted U-shaped curve. In humans, the maximal effective concentration of allopregnanolone for producing negative mood is within the range of physiological luteal phase serum concentrations.

Hormonal influences on seizures: basic neurobiology

There are sex differences and effects of steroid hormones, such as androgens, estrogens, and progestogens, that influence seizures. Androgens exert early organizational and later activational effects that can amplify sex/gender differences in the expression of some seizure disorders. Female-typical sex steroids, such as estrogen (E2) and progestins, can exert acute activational effects to reduce convulsive seizures and these effects are mediated in part by the actions of steroids in the hippocampus. Some of these anticonvulsive effects of sex steroids are related to their formation of ligands which have agonist-like actions at gamma-aminobutyric acid (GABAA) receptors or antagonist actions at glutamatergic receptors. Differences in stress, developmental phase, reproductive status, endocrine status, and treatments, such as anti-epileptic drugs (AEDs), may alter levels of these ligands and/or the function of target sites, which may mitigate differences in sensitivity to, and/or tolerance of, steroids among some individuals. The evidence implicating sex steroids in differences associated with hormonal, reproductive, developmental, stress, seizure type, and/or therapeutics are discussed.

Effects of swim stress on mRNA and protein levels of steroid 5α-reductase isozymes in prefrontal cortex of adult male rats

The metabolite of progesterone, allopregnanolone, is among the most potent known ligands of the gamma-aminobutyric acid receptor complex (GABA(A)-R) in the central nervous system. This neuroactive steroid is markedly increased in an animal model of acute stress. Allopregnanolone is synthesized from progesterone by steroidogenic enzymes 5alpha-reductase (5alpha-R) and 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD), with the former being the rate-limiting enzyme in this reaction sequence. In this paper, a quantitative RT-PCR method coupled to laser-induced fluorescence capillary electrophoresis (LIF-CE) and Western blot were used to measure both mRNA and protein levels of 5alpha-R type 1 (5alpha-R1) and 5alpha-R type 2 (5alpha-R2) isozymes in prefrontal cortex of male rats after acute swim stress situations. Our results demonstrate that both 5alpha-R isozymes are significantly higher in prefrontal cortex of male rats after acute swim stress in comparison with control rats. These data may open up a new research line that could improve our understanding of the role of 5alpha-R isozymes in processes that accompany stress situations.

The relevance of neuroactive steroids in schizophrenia, depression, and anxiety disorders

1. Neuroactive steroids are steroid hormones that exert rapid, nongenomic effects at ligand-gated ion channels. There is increasing awareness of the possible role of these steroids in the pathology and manifestation of symptoms of psychiatric disorders. The aim of this paper is to review the current knowledge of neuroactive steroid functioning in the central nervous system, and to assess the role of neuroactive steroids in the pathophysiology and treatment of symptoms of schizophrenia, depression, and anxiety disorders. Particular emphasis will be placed on GABAA receptor modulation, given the extensive knowledge of the interactions between this receptor complex, neuroactive steroids, and psychiatric illness. 2. A brief description of neuroactive steroid metabolism is followed by a discussion of the interactions of neuroactive steroids with acute and chronic stress and the HPA axis. Preclinical and clinical studies related to psychiatric disorders that have been conducted on neuroactive steroids are also described. 3. Plasma concentrations of some neuroactive steroids are altered in individuals suffering from schizophrenia, depression, or anxiety disorders compared to values in healthy controls. Some drugs used to treat these disorders have been reported to alter plasma and brain concentrations in clinical and preclinical studies, respectively. 4. Further research is warranted into the role of neuroactive steroids in the pathophysiology of psychiatric illnesses and the possible role of these steroids in the successful treatment of these disorders.

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.

Effects of some neurosteroids injected into some brain areas of WAG/Rij rats, an animal model of generalized absence epilepsy

Neurosteroids are synthesized in the brain and have been demonstrated to modulate various cerebral functions. Allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one), a naturally occurring neurosteroid, and ganaxolone (3alpha-hydroxy-3beta-methyl-5alpha-pregnan-20-one), a synthetic derivative, are two neurosteroids acting as positive allosteric modulators of the GABA(A) receptor complex acting on a specific steroid recognition site. Both agents antagonize generalized tonic-clonic seizures in various animal models of epilepsy. Pregnenolone sulphate (3beta-hydroxy-5alpha-pregnen-20-one 3-sulphate; PS) is a negative allosteric modulator of GABA(A) receptors and a positive modulator of the NMDA receptors. We have evaluated the effects of such compounds in a genetic animal model of absence epilepsy, the WAG/Rij rat. Animals were chronically implanted with five frontoparietal cortical electrodes for electrocorticogram (EEG) recordings and bilateral guide cannulae into specific brain areas of the cortico-thalamic circuit in order to evaluate the effects of these compounds on the number and duration of epileptic spike-wave discharges (SWDs). The focal and bilateral microinjection of the two GABA(A) positive modulators into some thalamic nuclei (nucleus ventralis posteromedialis, nucleus reticularis thalami, nucleus ventralis posterolateralis was usually able to significantly worsen the occurrence of SWDs in WAG/Rij rats. Whereas both compounds were able to reduce the number and duration of SWDs when microinjected into the peri-oral region of the primary somatosensory cortex. The effects of PS were more complex depending on both the dose and the site of administration, generally, at low doses in thalamic nuclei and cortex, PS induced an increase of absence activity and a reduction at higher doses. These findings suggest that neurosteroids might play a role in absence epilepsies and that it might depend on the involvement of specific neuronal areas.

Decreased neuroactive steroids induced by combined oral contraceptive pills are not associated with mood changes

OBJECTIVE

To evaluate the effects of a low-dose combined oral contraceptive pill (OCP) on peripheral neuroactive steroid concentrations, precursors for neuroactive steroid synthesis, and mood in healthy women desiring contraception. These neuroactive steroids are gamma-aminobutyric acid receptor agonists and are important in the modulation of affect and adaptation to stress.

DESIGN

Prospective observational study.

SETTING

Human ambulatory patient study.

PATIENT(S)

Healthy OCP-naive women without current or history of affective disorder.

INTERVENTION(S)

A 0.020-mg ethinyl E2-0.1-mg levonorgestrel containing OCP for 3 months.

MAIN OUTCOME MEASURE(S)

Serum neuroactive steroids allopregnanolone, allotetrahydrodeoxycorticosterone, and DHEA; neuroactive steroid precursors P and pregnenolone; E2; and mood and anxiety as assessed by the Premenstrual Syndrome Daily Ratings Form, Beck Depression Inventory, Spielberger State-Trait Anxiety Inventory, and Profile of Mood States.

RESULT(S)

The combined OCP resulted in a decrease in neuroactive steroids and neuroactive steroid precursors as well as in E2. However, this decline was not associated with adverse mood changes on any of the well-validated assessment tools.

CONCLUSION(S)

Healthy women without underlying mood or anxiety disorder who were given a low-dose OCP did not experience adverse psychological symptoms despite a significant reduction in neuroactive steroids.

GABAA receptors: building the bridge between subunit mRNAs, their promoters, and cognate transcription factors

The type A gamma-aminobutyric acid (GABA(A)) receptors mediate the majority of fast inhibitory neurotransmission in the CNS, and alterations in GABA(A) receptor function is believed to be involved in the pathology of several neurological and psychiatric illnesses, such as epilepsy, anxiety, Alzheimer's disease, and schizophrenia. GABA(A) receptors can be assembled from eight distinct subunit families defined by sequence similarity: alpha(1-6), beta(1-3), gamma(1-3), delta, pi, theta, and rho(1-3). The regulation of GABA(A) receptor function in the brain is a highly compensating system, influencing both the number and the composition of receptors at the cell surface. While transcriptional and translational points of control operate in parallel, it is becoming increasingly evident that many functional changes in GABA(A) receptors reflect the differential gene regulation of its subunits. The fact that certain GABA(A) receptor subunit genes are transcribed in distinct cell types during specific periods of development strongly suggests that genetic control plays a major role in the choice of subunit variants available for receptor assembly. This review focuses on the physiological conditions that alter subunit mRNA levels, the promoters that may control such levels, and the use of a conceptual framework created by bioinformatics to study coordinate and independent GABA(A) receptor subunit gene regulation. As this exciting field moves closer to identifying the language hidden inside the chromatin of GABA(A) receptor subunit gene clusters, future experiments will be aimed at testing models generated by computational analysis with biologically relevant in vivo and in vitro assays. It is hoped that through this functional genomic approach there will be the identification of new targets for therapeutic intervention.

Changes in expression of the neuropeptide Y Y1 receptor gene in the medial amygdala of transgenic mice during pregnancy and after delivery

Long-term administration of progesterone or allopregnanolone was previously shown to increase Y1 receptor gene expression in the medial amygdala of Y1R/LacZ transgenic mice, which harbor a construct comprising the murine Y1 receptor gene promoter and a lacZ reporter. We have now investigated the effects of physiological fluctuations in the cerebrocortical concentrations of neuroactive steroids during pregnancy on Y1R/LacZ transgene expression by quantitative histochemical analysis of beta-galactosidase activity. Cerebrocortical concentrations of progesterone and its metabolites allopregnanolone and allotetrahydrodeoxycorticosterone were increased on day 18 of pregnancy and had returned to control values 2 days after delivery. Transgene expression in the medial amygdala was also increased on day 18 of pregnancy and had returned to control values 2 days after delivery. Similar results were obtained after analysis of Y1R mRNA levels in the medial amygdala of pregnant mice by in situ hybridization. Administration of the 5alpha-reductase inhibitor finasteride to pregnant mice prevented both the increase in the cerebrocortical concentrations of neuroactive steroids as well as the increase in transgene expression. These data suggest that fluctuations in the brain concentrations of endogenous neuroactive steroids during pregnancy are associated with changes in Y1 receptor gene expression in the medial amygdala, further supporting a functional interaction between the GABAergic and NPY-Y1 receptor systems.

The neurosteroid allopregnanolone increases dopamine release and dopaminergic response to morphine in the rat nucleus accumbens

Neurosteroids are a subclass of steroids that can be synthesized in the central nervous system independently from peripheral sources. Clinical studies in humans have associated these hormones with depression and postpartum mood disorders. In rodents, allopregnanolone (AlloP) has been shown to have anxiolytic and rewarding properties. These observations suggest that neurosteroids could interact with mood and motivation. However, the possible neural substrates of these effects remain unknown. In this report, we have studied the action of AlloP on the activity of the mesencephalic dopaminergic (DA) projection to the nucleus accumbens, which is considered one of the biological substrates of motivation and reward. This study was conducted by measuring extracellular concentrations of dopamine (DA) in the nucleus accumbens by means of microdialysis in freely moving rats. We studied both the direct effect of AlloP and the influence of this hormone on the DA response to an injection of morphine. AlloP dose-dependently increased the release of DA in the nucleus accumbens. Furthermore, this hormone doubled the DA response to morphine. These effects were observed for AlloP doses of 50 and 100 pmol injected intracerebroventricularly. These results suggest that the stimulatory effect of AlloP on DA could mediate some of the behavioural effects of neurosteroids and, in particular, the interaction of these hormones with mood and motivation.

A rapid method for obtaining finasteride, a 5alpha-reductase inhibitor, from commercial tablets

To study the effects of allopregnanolone (AP) depletion on stress-induced dopamine changes in cortical dopamine, the 5alpha-reductase inhibitor finasteride on a gram-scale is required. Two procedures for the extraction of finasteride from tablets are outlined (method A and B). In method A, a suspension of powdered tablets was preliminary extracted with chloroform and the extracts dried and evaporated. The resulting residue was then purified on column chromatography. Method B involves a direct chromatographic separation of the powdered tablets. In terms of isolated yields, the second procedure works well, is cheaper, and less time-consuming. The efficiency of the method was tested by measuring progesterone, AP and THDOC content in plasma and cerebral cortex of rats. The protocol enables the prompt availability of sufficient amount of finasteride in experimental grade, useful in examining the role of endogenous cerebrocortical AP in brain homeostasis.

Stress and neuroactive steroids

The discovery that the endogenous steroid derivatives 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone, or 3 alpha,5 alpha-TH PROG) and 3 alpha,21-dihydroxy-5 alpha-pregnan-20-one (allotetrahydrodeoxycorticosterone, or 3 alpha,5 alpha-TH DOC) elicit marked anxiolytic and anti-stress effects and selectively facilitate gamma-aminobutyric acid (GABA)-mediated neurotransmission in the central nervous system (see Chapter 3) has provided new perspectives for our understanding of the physiology and neurobiology of stress and anxiety. Evidence indicating that various stressful conditions that downregulate GABAergic transmission and induce anxiety-like states (Biggio et al., 1990) also induce marked increases in the plasma and brain concentrations of these neuroactive steroids (Biggio et al., 1996, 2000) has led to the view that stress, neurosteroids, and the function of GABAA receptors are intimately related. Changes in the brain concentrations of neurosteroids may play an important role in the modulation of emotional state as well as in the homeostatic mechanisms that counteract the neuronal overexcitation elicited by acute stress. Indeed, neurosteroids not only interact directly with GABAA receptors but also regulate the expression of genes that encode subunits of this receptor complex. This chapter summarizes observations from our laboratories and others, suggesting that neurosteroids and GABAergic transmission are important contributors to the changes in emotional state induced by environmental stress.

Changes in GABAA receptor gamma 2 subunit gene expression induced by long-term administration of oral contraceptives in rats

The effects of oral contraceptives (OCs) on neurosteroid concentrations were evaluated in female rats and women. In rats, ethynylestradiol and levonorgestrel (0.030 and 0.125 mg, respectively, subcutaneously) administered daily for 6 weeks reduced the concentrations of pregnenolone (-41%) progesterone (-74%) and allopregnanolone (-79%) in the cerebral cortex; the plasma concentrations of these steroids were also reduced but by smaller extents. OC administration for 3 months also reduced the serum concentrations of pregnenolone, progesterone and allopregnanolone in women. Chronic administration of OCs in rats increased the abundance of gamma-aminobutyric acid type A (GABA(A)) receptor gamma 2L and gamma 2S subunit mRNAs and the relative protein in the cerebral cortex, while the amounts of various alpha and beta subunit mRNAs were unaffected. Ovariectomy did not modify the effect of OCs administration on the concentrations of neurosteroids in the rat cerebral cortex (but not in the plasma) as well as on the GABA(A) receptor gene expression, suggesting a direct effect of OCs in brain. Finally, rats treated with OCs exhibited an anxiety-like behavior in the elevated plus-maze test. These results indicate that long-term treatment with OCs induced a persistent reduction in the concentrations of pregnenolone, progesterone and its GABA(A) receptor-active metabolite, allopregnanolone, both in rats and women. In rats this effect was associated with a plastic adaptation of GABA(A) receptor gene expression in the rat cerebral cortex.

Increased expression of the neuropeptide Y receptor Y(1) gene in the medial amygdala of transgenic mice induced by long-term treatment with progesterone or allopregnanolone

The neurosteroid allopregnanolone, a reduced metabolite of progesterone, induces anxiolytic effects by enhancing GABA(A) receptor function. Neuropeptide Y (NPY) and GABA are thought to interact functionally in the amygdala, and this interaction may be important in the regulation of anxiety. By using Y(1)R/LacZ transgenic mice, which harbour a fusion construct comprising the promoter of the mouse gene for the Y(1) receptor for NPY linked to the lacZ gene, we previously showed that long-term treatment with benzodiazepine receptor ligands modulates Y(1) receptor gene expression in the medial amygdala. We have now investigated the effects of prolonged treatment with progesterone or allopregnanolone on Y(1)R/LacZ transgene expression, as determined by quantitative histochemical analysis of beta-galactosidase activity. Progesterone increased both the cerebrocortical concentration of allopregnanolone and beta-galactosidase expression in the medial amygdala. Finasteride, a 5alpha-reductase inhibitor, prevented both of these effects. Long-term administration of allopregnanolone also increased both the cortical concentration of this neurosteroid and transgene expression in the medial amygdala. Treatment with neither progesterone nor allopregnanolone affected beta-galactosidase activity in the medial habenula. These data suggest that allopregnanolone regulates Y(1) receptor gene expression through modulation of GABA(A) receptor function, and they provide further support for a functional interaction between GABA and neuropeptide Y in the amygdala.

The anxiolytic effect of allopregnanolone is associated with gonadal hormonal status in female rats

The behavioural display in the plus-maze, an established experimental model of anxiety, was studied in rats injected into the lateral brain ventricle (i.c.v.) with the neurosteroid 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone). Female rats under different gonadal hormonal status were chosen. Allopregnanolone enhanced exploration of the open arms in both estrous rats and ovariectomized estrogen and progesterone primed rats. No effect was observed in diestrous 1 and ovariectomized not-primed rats. In all cases, the plus-maze locomotor-exploratory behaviour was not affected by allopregnanolone. The GABA(A) receptor antagonist, bicuculline (9.8 microM i.c.v.) reversed the allopregnanolone action in the ovariectomized primed rats. When bicuculline was injected i.c.v. in conjunction with allopregnanolone, the anxiogenic effect of bicuculline was reversed by the highest dose (25 microM) of allopregnanolone only. These results suggest that allopregnanolone exerts an anxiolytic action interacting with the GABA(A) receptor in an estrogen-dependent manner.

Swim stress alters the behavioural response of mice to GABA-related and some GABA-unrelated convulsants

To elucidate the relationship between stress and seizures, the effect of a single swim stress on the convulsive signs and death produced by several GABA-related and GABA-unrelated convulsants, and the effect of repeated swim stress on picrotoxin-induced convulsions was studied. Mice were subjected to swim stress (10 min swimming at 18-19 degrees C), and the i.v. infusion of convulsants started 15 min thereafter. The latency to the onset of several convulsant signs and death was measured, and the doses of convulsants producing convulsions and death were calculated. Additional experiments included mice swimming at room temperature, and those which were stressed repeatedly (twice a day for four consecutive days, plus one stressful procedure on the fifth day). Swim stress increased the dose needed to produce convulsant signs and death after bicuculline, picrotoxin, pentylenetetrazole, strychnine and 4-aminopyridine, while kainic acid-induced convulsions were not affected. Using picrotoxin infusion, the effect of swimming in room temperature water was less than the effect of swimming in 18-19 degrees C water. In addition, the effect of repeated stress was less than the effect of acute stress on picrotoxin-induced convulsions. The results demonstrate that acute swim stress lowers the convulsive potency of GABA-related and some GABA-unrelated convulsants. Repeatedly stressed animals develop tolerance to anticonvulsive effect of swim stress.

Steroidogenesis in rat brain induced by short- and long-term administration of carbamazepine

Although carbamazepine (CBZ) is used therapeutically in the treatment of various neurological and psychiatric conditions, its mechanism of action remains largely unknown. CBZ has now been shown to inhibit the binding of [(3)H]PK 11195 to peripheral benzodiazepine receptors (PBRs) in rat brain and ovary membranes in vitro with a potency (IC(50), approximately 60 microM) much lower than that of unlabeled PK 11195 (IC(50), approximately 2.0 nM). Administration of CBZ to rats induced dose (25 to 100 mg/kg, i.p.) and time (15 to 60 min) dependent increases in the concentrations of pregnenolone, progesterone, allopregnanolone, and allotetrahydrodeoxycorticosterone in both the cerebral cortex and plasma. CBZ also induced steroidogenesis in the brain of adrenalectomized-orchiectomized rats, suggesting that this effect is mediated in a manner independent of peripheral PBRs. The increase in brain concentrations of neuroactive steroids induced by a single injection of CBZ was associated with a marked protective effect against isoniazid-induced convulsions. In contrast, long-term administration of CBZ (50 mg/kg, twice a day for 30 days) induced tolerance to the anticonvulsant action of the drug. This same treatment, however, did not prevent the ability of a challenge dose of CBZ to stimulate steroidogenesis. These results indicate that CBZ-induced steroidogenesis might not be responsible for the anticonvulsant activity of this drug.

Anticonvulsive effect of swim stress in mice

To explore the possible involvement of glucocorticoids in the previously observed anticonvulsive effect of swim stress, mice were, prior to administration of convulsants, subjected to treatments that diminish or enhance plasma corticosterone levels. Aminoglutethimide, the inhibitor of steroid synthesis, failed to modify convulsant doses of picrotoxin, but enhanced threshold doses of pentylenetetrazole producing myoclonus and death, both in unstressed and stressed animals. The same drug prevented the effect of stress on pentylenetetrazole-induced running bouncing clonus (RB clonus) and abolished the appearance of tonic hindlimb extension (THE). Doses of kainic acid producing convulsions and death were not affected by stress, but they were enhanced by aminoglutethimide. Corticosterone administration could not imitate the effect of swim stress. Finasteride, a 5 alpha-reductase inhibitor, did not interfere with the effect of stress on picrotoxin-induced convulsions. Swim stress failed to modify the binding of the convulsant t[3H]-butylbicycloorthobenzoate [3H]TBOB, to washed mouse forebrain membranes. The results confirmed an anticonvulsant effect of swim stress against convulsions produced by GABA-related convulsants, but they do not support the hypothesis suggesting the involvement of glucocorticoids or neurosteroids in this effect.

Caffeine-induced increases in the brain and plasma concentrations of neuroactive steroids in the rat

The effects of caffeine, a naturally occurring stimulant, on the brain and plasma concentrations of neuroactive steroids were examined in the rat. A single intraperitoneal injection of caffeine induced dose- and time-dependent increases in the concentrations of pregnenolone, progesterone, and 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) in the cerebral cortex. The increases were significant at a caffeine dose of 25 mg/kg and greatest (+188, +388, and +71%, respectively) at a dose of 100 mg/kg in rats killed 30 min after caffeine administration. Caffeine also increased the plasma concentrations of pregnenolone and progesterone with a dose-response relation similar to that observed in the brain, whereas the caffeine-induced increase in the plasma concentration of allopregnanolone was maximal at a dose of 50 mg/kg. Caffeine increased the plasma concentration of corticosterone, but it had no effect on the brain or plasma concentrations of 3alpha, 21-dihydroxy-5alpha-pregnan-20-one and dehydroepiandrosterone. Moreover, the brain and plasma concentrations of pregnenolone, progesterone, and allopregnanolone were not affected by caffeine in adrenalectomized-orchiectomized rats. These results suggest that neuroactive steroids may modulate the stimulant and anxiogenic effects of caffeine.

Physiological modulation of GABA(A) receptor plasticity by progesterone metabolites

The possible functional relation between changes in brain and plasma concentrations of neurosteroids and the plasticity of gamma-aminobutyric acid type A (GABA(A)) receptors in the brain during pregnancy and after delivery was investigated in rats. The concentrations in the cerebral cortex and plasma of pregnenolone as well as of progesterone and its neuroactive derivatives allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one) and allotetrahydrodeoxycorticosterone (5alpha-hydroxy-3alpha,21-diol-20-one) increased during pregnancy, peaking around day 19, before returning to control (estrus) values immediately before delivery (day 21). In the postpartum period, steroid concentrations in plasma and brain did not differ from control values. The densities of [3H]GABA, [3H]flunitrazepam, and t-[35S]butylbicyclophosphorotionate (TBPS) binding sites in the cerebral cortex also increased during pregnancy, again peaking on day 19 and returning to control values on day 21; receptor density was decreased further 2 days after delivery and again returned to control values within 7 days. These changes were accompanied by a decrease in the apparent affinity of the binding sites for the corresponding ligand on day 19 of pregnancy. The amount of the gamma2L subunit mRNA decreased progressively during pregnancy, in the cerebral cortex and hippocampus, returned to control value around the time of delivery and did not change in the postpartum period. On the contrary, the amount of alpha4 subunit mRNA was not modified during pregnancy both in the cerebral cortex and hippocampus whereas significantly increased 7 days after delivery only in the hippocampus. No significant changes were apparent for alpha1, alpha2, alpha3, beta1, beta2, beta3 and gamma2S subunit mRNAs. Administration of finasteride, a specific 5alpha-reductase inhibitor, to pregnant rats from days 12 to 18 markedly reduced the increases in the plasma and brain concentrations of allopregnanolone and allotetrahydrodeoxycorticosterone as well as prevented both the increase in the densities of [3H]flunitrazepam and [35S]TBPS binding sites and the decrease of gamma2L mRNA normally observed during pregnancy. The results demonstrate that the changes in the plasticity of GABA(A) receptors that occur in rat brain during pregnancy and after delivery are related to the physiological changes in plasma and brain concentrations of neurosteroids.

Antagonism by pivagabine of stress-induced changes in GABAA receptor function and corticotropin-releasing factor concentrations in rat brain

Pivagabine [4-(2.2-dimethyl-l-oxopropylamino) butanoic acid] (PVG) is a hydrophobic 4-aminobutyric acid derivative with neuromodulatory activity. The effects of subchronic treatment with PVG on stress-induced changes both on brain concentrations of corticotropin-releasing factor (CRF) and neurosteroids and on the function of the gamma-aminobutyric acid type A (GABAA) receptor complex were investigated in male rats. Subchronic treatment with PVG (100-200 mg/kg, i.p.) resulted in a dose-dependent inhibition of the foot shock-induced increase in the binding of t-[35S]butylbicyclophosphorothionate to unwashed membranes prepared from the cerebral cortex of rats killed immediately after stress; PVG treatment alone had no effect on this parameter. This antagonistic action of PVG was also shown in adrenalectomized-orchietomized rats. Foot-shock stress decreased by 74% and increased by 125% the CRF concentration in the hypothalamus and cerebral cortex, respectively. PVG prevented these effects of stress on CRF concentration in both brain regions; this drug per se reduced hypothalamic CRF concentration by 52% but had no effect in the cortex. Moreover, intracerebroventricular injection of CRF, like stress, induced a dose-dependent increase of [35S]TBPS binding to cerebral cortical membranes: an effect not prevented by subchronic treatment of PVG. Finally, PVG did not antagonize the stress-induced increases in the concentrations of neuroactive steroids in brain or plasma. These results suggest that the marked antistress action of PVG is mediated by antagonizing the effects of stress on GABA(A) receptor function and CRF concentrations in the brain, but not by altering the stress-induced increase in neurosteroid concentrations.

Sexual differentiation modifies the allopregnanolone anxiolytic actions in rats

The administration of progesterone (0.0, 1.0 and 2.0 mg/rat, s.c.) and allopregnanolone (5 alpha, 3 alpha dihydroprogesterone) (0.0, 0.5 and 1.0 mg/rat, s.c.) to both, males and females, produced a similar reduction in burying behavior. Only allopregnanolone showed a gender-dependent effect on burying behavior latency. Allopregnanolone actions were established in five groups of animals according to their neonatal hormonal manipulation: intact males and females, neonatally-testosterone propionate-treated female rats (TP, 30 and 120 micrograms/rat, s.c. at day 5) and neonatally (4-12 h after delivery) castrated males. Males and females showed a reduction in anxiety after treatment with allopregnanolone. Both neonatally-androgenized-females and -castrated males were completely insensitive to allopregnanolone anxiolytic action tested in both burying behavior and plus-maze paradigm. The virilizing action of neonatally administered TP was demonstrated by dose-dependent delayed vaginal opening, a persistent estrus in their vaginal smears and the presence of polifollicular ovaries. Results are discussed on the bases of the differences and similarities between males, females, androgenized females and neonatally castrated males to anxiolytic steroids and the underlying possible processes.

Ovarian steroids and stress produce changes in peripheral benzodiazepine receptor density

Although past research has described changes in the density of the peripheral benzodiazepine receptor in brain and in peripheral organs in response to stressors and steroid hormone exposure, their combined influence had yet to be determined. This study examined the effect of swim-stress as a function of ovarian hormone administration on the binding of an isoquinoline carboxamide derivative, [3H]PK 11195, in brain and peripheral tissues. In olfactory bulb and adrenal gland, stress increased peripheral benzodiazepine receptor density in ovariectomized rats with and without estradiol and progesterone replacement injection, even when compared with unstressed animals treated with hormones, where estradiol + progesterone decreased peripheral benzodiazepine receptor number in olfactory bulb, but estradiol and estradiol + progesterone increased it in adrenal gland. In frontal cortex, stress decreased peripheral benzodiazepine receptor number, an effect that was reversed by estradiol. In hippocampus estradiol decreased peripheral benzodiazepine receptor density in unstressed animals and estradiol + progesterone decreased peripheral benzodiazepine receptor number in unstressed and stressed animals. In cerebellum, stress, estradiol and estradiol + progesterone alone decreased peripheral benzodiazepine receptor density. In uterus of unstressed controls, estradiol + progesterone increased peripheral benzodiazepine receptor density, and stress produced a further increase in steroid-treated females. Stress did not affect peripheral benzodiazepine receptor density in kidney, except in animals that received estradiol + progesterone injections, where swim-stress produced a significant decrease in peripheral benzodiazepine receptor density. Thus, steroid hormones regulate peripheral benzodiazepine receptor density in endocrine organs and brain, and the hormonal state of the organism modifies the peripheral benzodiazepine receptor response to stress in a tissue- and brain region-specific manner, suggesting that the peripheral benzodiazepine receptor may play a pivotal role in an integrated response to stress.

Stress and neurosteroids in adult and aged rats

The progesterone derivative 3 alpha-hydroxy-5 alpha-pregnan-20 one (allopregnanolone/AP) and the deoxycorticosterone derivative 3 alpha-21-dihydroxy-5 alpha- pregnan-20 one (allotetra-hydrodeoxycorticosterone/THDOC) are endogenous neuroactive steroids endowed with neuromodulatory actions in the central nervous system. Their best-characterized membrane-receptor-dependent action consists in the amplification of GABA-gated chloride currents mediated by specific interactions with the GABAA receptor complex, which appears responsible for the pharmacological effects (anxiolytic, anticonvulsant, hypnotic/anaesthetic) of exogenously administered AP and THDOC. Several acute stress paradigms and different negative allosteric modulators (isoniazid and FG 7142) of GABAA receptors time dependently increase brain and plasma concentrations of AP and THDOC only in intact or sham-operated but not in adrenalectomized-orchiectomized rats. These results suggest that acute stress and inhibitors of GABAA receptors increase the brain and plasma neurosteroid concentrations via a reduction of the inhibitory action exerted by GABA on the hypothalamic-pituitary-adrenal axis. The comparison between the time course of the changes in GABAA receptor function and of their behavioral correlates (proconflict behavior) and that of the changes of endogenous neuroactive steroids are consistent with the view that AP and THDOC may play a role in restoring the GABAergic tone to prestress conditions, by limiting the duration and the extent of its stress-induced reduction. The acute stress-elicited increase of AP and THDOC is observed in adult as well as in aged rats, which show a reduced basal GABAergic transmission and a greater response to the effect of stress in terms of their brain cortical neuroactive steroid concentrations than adult rats.

Modulation of gamma-aminobutyric acid (GABA) receptors and the feeding response by neurosteroids in Hydra vulgaris

Gamma-Aminobutyric acid (GABA) receptors are present in membrane preparations from Hydra vulgaris, one of the most primitive organisms with a nervous system. These receptors are sensitive to muscimol and benzodiazepines and appear to be important in the regulation of the feeding response. The effects of neurosteroids, general anaesthetics, and GABA antagonists on GABA(A) receptors in membranes prepared from Hydra and on the feeding response have now been investigated. The neurosteroids tetrahydroprogesterone and tetrahydrodeoxycorticosterone increased [3H]GABA binding to hydra membranes with nanomolar potency (EC50, 141+/-11 and 623+/-36 nM, respectively) and high efficacy (maximal increase 79+/-6.5 and 62+/-4%, respectively), whereas the 3beta-hydroxy epimer of tetrahydroprogesterone was ineffective. The benzodiazepine receptor ligands diazepam (100 microM), clonazepam (100 microM) and abecarnil (30 microM) enhanced [3H]GABA binding to Hydra membranes by 22, 20 and 24%, respectively; effects abolished by the specific benzodiazepine antagonist flumazenil (100 microM). On the contrary, the peripheral benzodiazepine receptor ligand 4'chlorodiazepam failed to affect [3H]GABA binding to Hydra membranes. The general anaesthetics propofol and alphaxalone similarly increased (+38% and +30% respectively) [3H]GABA binding. Moreover, [3H]GABA binding to Hydra membranes was completely inhibited by the GABA(A) receptor antagonist SR 95531, whereas bicuculline was without effect. The modulation of GABA(A) receptors in vitro by these various drugs correlated with their effects on the glutathione-induced feeding response in the living animals. Tetrahydroprogesterone and tetrahydrodeoxy-corticosterone (1 to 10 microM) prolonged, in a dose-dependent manner, the duration of mouth opening induced by 10 microM glutathione, with maximal effects of +33 and +29%, respectively, apparent at 10 microM neurosteroid. Alphaxalone (10 microM) similarly increased (+33%) the effect of glutathione. The effects of steroids on the feeding response were inhibited by SR 95531 in a dose-dependent manner; t-butylbyclophosphorothyonate (1 microM), a specific Cl- channel blocker, which per se, like picrotoxin but not bicuculline, shortened the duration of the response, also counteracted the steroids effects at 1 microM. These results suggest that the modulation of GABA(A) receptors by steroids is an ancient characteristic of the animal kingdom and that the pharmacological properties of these receptors have been highly conserved through evolution.

Subsensitivity to mitochondrial diazepam binding inhibitor receptor agonist FGIN-1-27-induced antiseizure effect in diazepam-withdrawn mice

We investigated the role of the mitochondrial diazepam binding inhibitor receptor (MDR) in diazepam-withdrawal seizure. In chronically vehicle-treated mice, the potent and selective MDR agonist FGIN-1-27 (N,N-di-n-hexyl 2-(4-fluorophenyl)indole-3-acetamide: 30 microg/mouse, i.c.v.) markedly increased the threshold for pentylenetetrazole (PTZ)-induced seizure. The antiseizure effect of FGIN-1-27 was blocked by pretreatment with the selective MDR antagonist PK11195 (1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxa mide). In chronically diazepam-treated mice, the seizure threshold of PTZ was decreased during diazepam withdrawal, indicating withdrawal hyperexcitability. Interestingly, FGIN-1-27 (30 microg/mouse, i.c.v.) failed to increase the seizure threshold of PTZ in diazepam-withdrawn mice, in contrast to its effect in chronically vehicle-treated mice. These findings suggest that the sensitivity of MDR-mediated pathways in the brain may be decreased during diazepam withdrawal.

Evaluation of the anticonvulsant profile of progesterone in male amygdala-kindled rats

While there is clinical evidence that progesterone has anticonvulsant activity in women with complex partial seizures, previous studies on the anticonvulsant effect of progesterone in experimental animal models are inconclusive. Moreover, the effect of progesterone on seizure parameters in fully amygdala-kindled rats which best resemble complex partial seizures has not been evaluated. Therefore, in the present work the anticonvulsant effect of progesterone at doses of 10, 30, 60 and 75 mg/kg in fully amygdala-kindled male rats was studied. Only at the high and sedative dose of 75 mg/kg, progesterone suppressed behavioral seizures and afterdischarges elicited 10 min after intraperitoneal (i.p.) administration. Pretreatment with the progesterone antagonist, 17beta-hydroxy-11beta-(4-dimethylaminophenyl)-17alpha-(prop- 1-ynyl)-estra-4,9-dien-3-one (RU 38486) at the dose of 3 mg/kg did not inhibit the anticonvulsant activity of progesterone, while pretreatment with the GABA(A) receptor antagonist, bicuculline (2 mg/kg) blocked the anticonvulsant effect of progesterone. Neither RU 38486 nor bicuculline had any effect on the seizure parameters. These findings suggest that only at large and sedative doses, progesterone has some anticonvulsant activity in male amygdala-kindled rats which may be partly mediated via the GABA(A) receptor complex interaction.

The anxiolytic-like effects of the neurosteroid allopregnanolone: interactions with GABA(A) receptors

The neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) was administered systemically to rats which were tested in the Geller-Seifter conflict paradigm, an established animal model of anxiety. Allopregnanolone was found to produce significant anxiolytic-like effects at a dose of 8 mg/kg. When three ligands that function at different sites on the gamma-aminobutyric acid/benzodiazepine receptor-chloride ionophore complex (GABA(A) receptors) were examined in conjunction with allopregnanolone, the anti-conflict effects of allopregnanolone were effectively reversed only by the benzodiazepine receptor inverse agonist RO15-4513 (ethyl-8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo [1,5-alpha]-[1,4]benzodiazepine-3-carboxylate). Since this inverse agonist has been reported to inhibit the GABA(A)-activated chloride flux in neuronal membranes, it is likely that the stimulation of the chloride channel in GABA(A) receptors is an important component of the effects of allopregnanolone. In contrast, the benzodiazepine receptor antagonist flumazenil (ethyl-8-fluoro-5,6-dihydro-5-methyl-6-oxo-4H-imidazo [1,5-alpha]-[1,4]benzodiazepine-3-carboxylate) did not block the anxiolytic-like actions of allopregnanolone, indicating that allopregnanolone does not bind at the benzodiazepine site directly. Isopropylbicyclophosphate, which binds at the picrotoxinin site on the GABA(A) receptors and blocks the behavioral actions of ethanol, also dose-dependently reversed the anti-conflict effect of this neurosteroid. The results suggest that allopregnanolone may be working either at a site specific for the benzodiazepine receptor inverse agonist RO15-4513 or at the picrotoxinin site to produce its potent anxiolytic-like behavioral effects.

The effects of inhibitors of GABAergic transmission and stress on brain and plasma allopregnanolone concentrations

1. This study was undertaken to investigate the relationship between a reduction in brain GABAA receptor function and the cerebro-cortical content of 3 alpha-hydroxy-5 alpha-pregnan-20 one (allopregnanolone, AP), a potent endogenous positive modulator of 7-aminobutyric acid (GABA) action at GABAA receptors, with anticonflict and anticonvulsant effects in rodents. 2. An acute depletion of the cerebral content of GABA or an attenuation of GABAA receptor-mediated transmission by systemic injections of isoniazid (375 mg kg-1, s.c.) or FG 7142 (15 mg kg-1, i.p.) induced a transient increase in the cerebro-cortical and plasma concentrations of AP in handling-habituated (not stressed) rats. 3. Two stress paradigms, handling in naive rats and mild foot shock in handling-habituated rats, that reduce central GABAergic tone mimicked the effects of isoniazid and FG 7142 on cortical AP content; foot shock in handling-habituated rats, but not handling in naive animals, also increased plasma AP. Isoniazid, FG 7142, and foot shock also each increased the concentrations of the AP precursors, pregnenolone and progesterone, in both brain and plasma of handling-habituated rats, whereas handling in naive rats increased the concentrations of these steroids only in brain. 4. Pretreatment of handling-habituated rats with the anxiolytic beta-carboline derivative abecarnil, a positive allosteric modulator of GABAA receptors, which per se failed to affect the AP concentration in brain or plasma, prevented the increase in brain and plasma AP induced by foot shock or isoniazid. 5. In adrenalectomized and castrated rats foot shock or isoniazid failed to increase AP both in brain cortex and plasma. 6. These observations indicate that inhibition of GABAergic transmission, induced by foot shock or pharmacological manipulations, results in an increase in the concentrations of AP in brain and plasma, possibly via a modulation of hypothalamic-pituitary-adrenal (HPA) axis. 7. Given that AP enhances GABAA receptor function with high efficacy and potency, an increase in brain AP concentration may be important in the fine tuning of the GABA-mediated inhibitory transmission in the central nervous system.

Majonoside-R2 reverses social isolation stress-induced decrease in pentobarbital sleep in mice: possible involvement of neuroactive steroids

Majonoside-R2 (MR2) is a major ocotillol-type saponin constituent of Vietnamese ginseng. We investigated the effect of MR2 on the social isolation stress-induced decrease in pentobarbital sleep in mice, and elucidated the possible involvement of neurosteroidal sites of the GABA(A) receptor complex in the pharmacological activity of MR2. MR2 (3.1-6.2 mg/kg, i.p. or 5-10 microg, i.c.v.) dose-dependently reversed the decrease in pentobarbital sleep caused by social isolation stress to the level of sleep in the group-housed mice, but it had no effect on pentobarbital sleep in group-housed mice. Allotetrahydrodeoxycorticosterone (5alpha-pregnane-3alpha,21-diol-20-one, allo-THDOC; 12.5 microg, i.c.v.), the positive allosteric modulator of the GABA(A) receptor, and alpha-helical CRF(9-41) (alpha hCRF; 25 microg, i.c.v.), the corticotropin-releasing factor (CRF) antagonist, also reversed the decrease in pentobarbital sleep caused by social isolation stress. The reversing effects of i.c.v. MR2 and i.c.v. allo-THDOC on the decrease in pentobarbital sleep in isolated mice were significantly attenuated by pregnenolone sulfate (10 microg, i.c.v.), the steroidal negative allosteric modulator of the GABA(A) receptor. In contrast, when injected i.c.v., MR2, as well as allo-THDOC and alpha hCRF, significantly reversed the decrease in pentobarbital sleep induced by pregnenolone sulfate (10 microg, i.c.v.) and CRF (10 microg, i.c.v.) in group-housed mice. These results suggest that the reversing effect of MR2 on the social isolation stress-induced decrease in pentobarbital sleep is mediated by the neurosteroid site on the GABA(A) receptor complex in mice.

Inhibition of basal and stress-induced dopamine release in the cerebral cortex and nucleus accumbens of freely moving rats by the neurosteroid allopregnanolone

The neurosteroid allopregnanolone is a potent and efficacious modulator of γ-aminobutyric acid (GABA) type A receptors. The effects of intracerebroventricular injection of allopregnanolone (5 to 15 μg in 5 μl) on basal and stress-induced changes in the extracellular concentrations of dopamine were investigated by microdialysis in various brain areas of freely moving rats and compared with those of the benzodiazepine midazolam (1 to 10 μg in 5 μl). Allopregnanolone reduced (by a maximum of 65 to 75%) basal dopamine content in the prefrontal cortex and nucleus accumbens in a dose-dependent manner, but had no effect on dopamine output in the striatum. Allopregnanolone (10 to 15 μg) also completely prevented the increase in extracellular dopamine concentrations in the nucleus accumbens and cerebral cortex induced by foot-shock stress. Midazolam reduced basal dopamine content in all three brain regions studied as well as the stress- induced increase in dopamine content in the nucleus accumbens and cerebral cortex with a greater potency than allopregnanolone. These results suggest that endogenous neurosteroids may participate in the GABAergic modulation of dopaminergic transmission in the rat cerebral cortex and nucleus accumbens, two brain areas which are important in the regulation of emotional processes. These agents do not appear to affect striatal dopaminergic transmission which modulates motor function.

Isoniazid-induced inhibition of GABAergic transmission enhances neurosteroid content in the rat brain

Isoniazid (375 mg/kg, s.c.), a drug that decreases GABAA receptor-mediated transmission, elicited a time-dependent increase of neuroactive steroid (pregnenolone, progesterone and allotetrahydrodeoxycorticosterone) concentrations in rat brain and plasma. This treatment also time-dependently increased the plasma concentration of corticosterone. Brain and plasma neuroactive steroid levels peaked between 40 and 120 min after isoniazid administration, respectively, and returned to control values by 5 hr. Acute foot shock stress mimicked the effect of isoniazid by increasing in a time-dependent manner the same neuroactive steroids both in brain and plasma. Abecarnil (0.3 mg/kg, i.p.), a beta-carboline derivative with anxiolytic properties, antagonized the effect of both isoniazid and foot shock on brain and plasma neuroactive steroids and on plasma corticosterone level. These data indicate that an inhibition of central GABAergic transmission enhances the concentrations of THDOC and its precursors pregnenolone and progesterone in the rat brain and plasma as well as the plasma levels of corticosterone. This finding suggests that GABA exerts a tonic inhibitory action on the mechanisms involved in the regulation of the synthesis and release of these neuroactive steroids in the central nervous system and plasma.