Time-dependent changes in rat brain neuroactive steroid concentrations and GABAA receptor function after acute stress

Studies on neurosteroids XVII. Analysis of stress-induced changes in neurosteroid levels in rat brains using liquid chromatography-electron capture atmospheric pressure chemical ionization-mass spectrometry

The analysis of stress-induced changes in the brain neurosteroid levels by liquid chromatography (LC)-electron capture atmospheric pressure chemical ionization-mass spectrometry (ECAPCI-MS) is described. In the present method, neurosteroids were derivatized with a highly electron-affinitive reagent, 2-nitro-4-trifluoromethylphenylhydrazine (NFPH), to convert them to the corresponding hydrazones. The derivatized steroids showed over a 20-fold higher sensitivity in ECAPCI-MS than intact steroids measured by positive atmospheric pressure chemical ionization (APCI)-MS. Application of this method to the analysis of rat brain samples confirmed the significant increase in the levels of pregnenolone (PREG), progesterone (PROG), 5alpha-dihydroprogesterone (DHPROG), allopregnanolone (3alpha-hydroxy-5alpha-pregn-20-one; AP), and epiallopregnanolone (3beta-hydroxy-5alpha-pregn-20-one; EpiAP) in the fixated rats. The din stress, which we examined as a new short-term mental stress model, also elevated the brain neurosteroid levels. It is known that various types of stress lower the gamma-aminobutyric acid type A (GABA(A)) receptor function and induce the neuronal overexcitation. The increase in the brain level of AP, a potent positive modulator of GABA(A) receptors, may be the defensive response against acute stress. The increase in the brain concentration of its precursors, PREG, PROG, and DHPROG, may be associated with the acceleration of the AP synthesis. Thus, the present studies suggest that changes in the brain levels of neurosteroids may play an important role in the homeostatic mechanisms that counteract the inhibitory effect of stress on the GABA(A) receptor function.

Structure−Activity Relationships and Effects on Neuroactive Steroid Synthesis in a Series of 2-Phenylimidazo[1,2-a]pyridineacetamide Peripheral Benzodiazepine Receptors Ligands

A series of 36 imidazopyridineacetamides (2-37) were designed and synthesized to evaluate the effects of structural changes on the amide nitrogen at both central (CBRs) and peripheral benzodiazepine receptors (PBRs). These changes include variations in the length and number of the alkyl groups as well as introduction of different aromatic, heteroaromatic, and conformationally constrained groups. The affinities of these compounds for CBRs and PBRs were determined, and the results indicate that bulkiness of the substituents, their branching, and length beyond an optimal value may cause hindrance to the ligand in its interaction with the receptor. The presence of aromatic or conformationally constrained substituents on the carboxamide nitrogen can be conducive to high affinity and selectivity. Furthermore, the ability of a subset of the most active ligands to stimulate synthesis of neuroactive steroids in plasma and brain was evaluated in vivo and in vitro. Compound 3 exhibited very marked effects on the peripheral and central synthesis of neuroactive steroids, while 36 (potent at subnanomolar level) showed a slight ability to affect neuroactive steroid content in the cerebral cortex.

Disadaptive disorders in women: allopregnanolone, a sensitive steroid

Allopregnanolone, a neurosteroid acting as a potent anxiolytic agonist of the gamma-aminobutyric acid A receptor, has been shown in animal models to modify its concentrations at central and peripheral levels according to the estrous cycle. Moreover, it modulates behavioral and biochemical responses to acute and chronic stress, anxiety, depression, aggressiveness, convulsions, anesthesia, sleep, memory, pain and feeding. These observations suggest that fluctuations of allopregnanolone might be involved in the development, course and prognosis of some mental disorders in humans. This has been hypothesized for depressive disorders, premenstrual dysphoria, anorexia and bulimia nervosa and Alzheimer's disease, where increased, decreased or dysregulated secretion of the main neurosteroids and their metabolites has been observed. Women show a marked gender-related sensitivity to disadaptive disorders. In addition to the well-studied role of sex steroids in modulating mood and behavior, a putative involvement of neurosteroid fluctuations, and in particular of allopregnanolone, has recently been hypothesized. In fact, several paraphysiological events and various disadaptive disorders in women are associated with modifications of circulating levels of this neurosteroid that might associated with a certain vulnerability to an altered adaptation to stressful life events.

Increased allopregnanolone levels in the fetal sheep brain following umbilical cord occlusion

Allopregnanolone (AP) is a potent modulator of the GABAA receptor. Brain AP concentrations increase in response to stress, which is thought to provide neuroprotection by reducing excitation in the adult brain. Umbilical cord occlusion (UCO) causes hypoxia and asphyxia in the fetus, which are major risk factors associated with poor neurological outcome for the neonate, and may lead to adverse sequelae such as cerebral palsy. The aims of this study were as follows: (i) to determine the effect of 10 min UCO on AP concentrations in the extracellular fluid of the fetal brain using microdialysis, and (ii) to compare the content of the steroidogenic enzymes P450scc and 5alpha-reductase type II (5alphaRII) with brain and CSF neurosteroid concentrations. UCO caused fetal asphyxia, hypertension, bradycardia and respiratory acidosis, which returned to normal levels after 1-2 h. AP concentrations in dialysate samples from probes implanted in grey and white matter of the parietal cortex were significantly increased 1 h after UCO from control levels of 10.4 +/- 0.4 and 12.4 +/- 0.3 to 26.0 +/- 5.1 and 27.6 +/- 6.4 nmol l(-1), respectively (P < 0.05), before returning to pre-occlusion levels by 3-4 h after UCO. When fetal brains were collected 1 h after a 10 min UCO, the relative increases of AP and pregnenolone content in the parietal cortex were similar to the increase observed in the extracellular (dialysate) fluid. AP, but not pregnenolone, was increased in CSF at this time. P450scc and 5alphaRII enzyme expression was significantly increased in the cerebral cortex in the UCO fetuses compared to control fetuses. These results suggest that the fetal brain is capable of transiently increasing neurosteroid production in response to asphyxia. The action of the increased neurosteroid content at GABAA receptors may serve to diminish the increased excitation due to excitotoxic amino acid release, and provide short-term protection to brain cells during such stress.

Neurosteroid consumption has anxiolytic effects in mice

The neurosteroids allopregnanolone (ALLOP) and pregnanolone (PREG), like ethanol, potentiate gamma-aminobutyric acid(A) receptor function. PREG-hemisuccinate (PREG-HS) is a negative modulator of N-methyl-D-aspartate (NMDA) receptors. Because C57BL/6J (B6) and DBA/2J (D2) mice differ in ethanol preference, voluntary consumption of ALLOP and PREG-HS (50 microg/ml solution) versus tap water was measured in B6 and D2 mice for a minimum of 8 days. Mice were acclimated to a reverse light-dark cycle prior to the initiation of experiments. In the first study, both B6 and D2 mice exhibited preference for the PREG-HS solution. In the second study, neither strain exhibited significant preference for the ALLOP solution versus water. However, the ALLOP-consuming B6 and D2 mice exhibited significant anxiolysis when they were tested on the elevated plus maze following 8 days of ALLOP consumption, compared to separate animals that consumed only water. A subsequent study determined that systemic administration of PREG-HS had significant anxiolytic effects in both B6 and D2 mice, when assessed on the elevated plus maze. Plasma ALLOP levels in the steroid-consuming mice from both studies were significantly increased versus basal levels only in the D2 strain. While the pattern of steroid intake or strain differences in steroid conversion may have influenced the differential change in plasma ALLOP levels, it is noteworthy that both strains consumed doses of ALLOP, and presumably doses of PREG-HS, that were anxiolytic.

Increased expression of the gene for the Y1 receptor of neuropeptide Y in the amygdala and paraventricular nucleus of Y1R/LacZ transgenic mice in response to restraint stress

A sustained increase in the brain concentrations of neuroactive steroids was previously shown to induce Y1 receptor gene expression in the amygdala of Y1R/LacZ transgenic mice which harbour a construct comprising the murine Y1 receptor gene promoter and the lacZ reporter gene. We now investigated the effects of restraint stress on both the cerebrocortical concentrations of neuroactive steroids and Y1 receptor gene expression in the amygdala and hypothalamic paraventricular nucleus (PVN) of Y1R/LacZ transgenic mice. The cerebrocortical concentrations of allopregnanolone and allotetrahydrodeoxycorticosterone were significantly increased immediately after a 1-h exposure to restraint stress and had returned to control values within 30 min. Expression of Y1R/LacZ was increased in the amygdala and PVN 6 h after restraint. The 5alpha-reductase inhibitor finasteride, that prevented the increase in neuroactive steroid concentrations, did not block that in transgene expression induced by 1-h restraint. Daily exposure to restraint for 10 days also increased the cerebrocortical concentrations of neuroactive steroids but failed to affect transgene expression. Acute but not repeated restraint thus increases Y1 receptor gene expression in the amygdala and PVN, suggesting that tolerance develops towards this stressor. The effect of acute restraint is not mediated by the increase in the brain concentrations of neuroactive steroids but may rather reflect a ligand-induced increase in Y1 receptor gene transcription. Data support a role of Y1 receptors in the behavioural and neuroendocrine responses to stress.

Sexually dimorphic effects of postnatal allopregnanolone on the development of anxiety behavior after early deprivation

Stress early in life exerts persistent detrimental effects on brain development. In this experiment, a rodent model of child neglect, early deprivation (ED), was used to investigate the role of the neurosteroid allopregnanolone [AlloP; 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP)] in the development of anxiety behavior. Subjects were either undisturbed controls or ED: separated individually for 6 h per day from postnatal day (PN) 2 to 6. Control and ED subjects were also either noninjected, vehicle-injected or injected with 5 mg/kg AlloP prior to the isolation. At PN 7, responses to 2.5 or 5 microg icv injections of AlloP were determined for separation-induced ultrasonic vocalizations (USVs). Tolerance to the USV-reducing effect of daily AlloP was seen in control but not ED pups, and daily AlloP reversed the expected ED suppression of USVs. As adults, controls treated with postnatal AlloP were less anxious than all other groups on the elevated plus maze. ED counteracted this effect. Male controls showed a reversal of the typical sex difference. There were no effects on open-field activity. These results suggest that the neonatal brain is responsive to alterations in AlloP levels, and that neuroactive progesterone metabolites may play a role in mediating the development of stress-related sex differences.

Protective effect of pregnanolone against lipoperoxidation and free radicals generation induced in hypothalamus of ovariectomized rats submitted to CO2 exposure

Several studies support an association between gonadal hormones and oxidative state. This study aimed to determine the consequence of the absence of ovarian hormones on the oxidative status of animals submitted to acute stress induced by CO(2) inhalation. We also evaluated the effect of pregnanolone administration upon the oxidative status in distinct brain structures of ovariectomized (OVX) rats exposed to CO(2). Female rats were divided into intact and OVX and exposed or unexposed to CO(2). Oxidative status was evaluated by 2',7'-dichlorofluorescein (DCF) assay, assessment of malondialdehyde (MDA), as an indicator of lipoperoxidation (through the thiobarbituric acid-reactive substances assay, TBARS), and the total antioxidant reactivity (TAR). Both DCF and TBARS were increased in the hypothalamus of animals submitted to OVX and stress. Nevertheless, free radical production and MDA levels were not affected in either condition alone. In the cerebral cortex, lower MDA levels were observed in OVX animals. Pregnanolone administered to rats submitted to CO(2)+OVX resulted in reduced MDA levels and free radicals production in hypothalamus. We suggest that ovarian hormones may protect the hypothalamus against oxidative stress, particularly when the animals are submitted to challenges. Pregnanolone may protect, at least in part, the hypothalamus of OVX rats from oxidative stress.

Chronic intermittent ethanol (CIE) administration in rats decreases levels of neurosteroids in hippocampus, accompanied by altered behavioral responses to neurosteroids and memory function

The administration of ethanol on a chronic intermittent regimen (CIE) involving multiple withdrawal episodes is a model for ethanol dependence. After CIE, rats exhibited reduced seizure threshold, increased anxiety, tolerance to GABAergic sedative-hypnotic drugs, and changes in GABA(A) receptor function and subunit composition in hippocampus. Previous studies have shown that acute and chronic ethanol may induce changes in the levels of the neurosteroid 3alpha-hydroxysteroid-5alpha-pregnan-20-one (3alpha, 5alpha-THP) in the brain. Therefore, the current study analyses the correlation between chronic intermittent ethanol effects on the level of 3alpha, 5alpha-THP in hippocampus of CIE rats and the behavioral changes in sensitivity to neurosteroids. After CIE, the levels for 3alpha, 5alpha-THP were significantly reduced in hippocampus of rats. The mRNA levels for the enzymes 5alpha-reductase and 3alpha-HSD in hippocampus were also reduced. In vivo, (in contrast to a tolerance to the hypnotic effect of steroids), CIE rats showed increased sensitivity to the anticonvulsant and to the anxiolytic effect of the steroid alphaxalone. Perhaps, this is a response to lowered levels of endogenous neuroactive steroids. CIE rats also showed impairment of hippocampus-dependent memory function. These results suggest that changes in neurosteroids level and in vivo sensitivity to these compounds are involved in the development of ethanol dependence in the CIE model.

Neurosteroids and neuroactive drugs in mental disorders

Clinical and preclinical studies have suggested that fluctuations in the peripheral and brain concentrations of progesterone and deoxycorticosterone and its metabolites 3alpha,5alpha-tetrahydroprogesterone and 3alpha,5alpha-tetrahydrodeoxycorticosterone, respectively, might play an important role in certain pathological conditions characterized by emotional or affective disturbances, including major depression, anxiety disorders, and schizophrenia. Moreover, it has been shown that administration of drugs having clinical relevance in the treatment of these pathologies influence the secretion of these steroids. It remains to be determined, however, whether such changes in the concentrations of neuroactive steroids are a cause of, a risk factor for, or a consequence of mental disorders. The observation that effective pharmacological treatment of some of these pathologies influences the concentrations of neuroactive steroids suggests that these endogenous compounds might themselves prove to be efficacious in the treatment of mental illness.

The role of pregnane neurosteroids in ethanol withdrawal: behavioral genetic approaches

Within the last 20 years, rapid nongenomic actions of steroid hormones have been demonstrated to occur via an interaction with ligand-gated ion channels. For example, the pregnane neurosteroid allopregnanolone (ALLOP) is a potent positive modulator of gamma-aminobutyric acid(A) (GABA(A)) receptors. The physiological significance of fluctuations in endogenous ALLOP levels has been investigated with regard to disease states and the effect of therapeutic agents on ALLOP levels. Because the pharmacological profile of ALLOP is similar to that of ethanol (EtOH), the modulatory effect of pregnane neurosteroids on EtOH dependence and withdrawal will be the focus of this review. Data on the effects of chronic EtOH exposure and withdrawal on pregnane neurosteroid levels, biosynthetic enzymes, and changes in neurosteroid sensitivity will be summarized. Results from genetic animal models indicate that seizure-prone animals have a persistent decrease in endogenous ALLOP levels during EtOH withdrawal in conjunction with tolerance to ALLOP's anticonvulsant effect. Manipulation of endogenous ALLOP levels with finasteride also markedly reduced the severity of chronic EtOH withdrawal. Gene mapping studies provide a hint for an interaction between genes for GABA(A) receptor subunits and the biosynthetic enzyme 5alpha-reductase. Overall, the results are suggestive of a relationship between endogenous pregnane neurosteroid levels and behavioral changes in excitability during EtOH withdrawal, consistent with recent findings in humans. While the findings with ALLOP emphasize the therapeutic potential of neurosteroid treatment during EtOH withdrawal, the gene mapping studies suggest that pregnane neurosteroid biosynthesis may represent a target for therapeutic intervention in the treatment of alcohol dependence.

Steroidogenic acute regulatory protein: its presence and function in brain neurosteroidogenesis

Neurosteroids are synthesized de novo and involved in a variety of physiological functions in the central and peripheral nervous systems. Although the steroidogenic acute regulatory protein (StAR) plays an essential role in the steroidogenesis of peripheral endocrine glands, its presence and role in the brain had been previously questioned because of difficulties in detecting it. However, a number of recent studies have confirmed the presence of StAR in rodent and human brains. Moreover, there is evidence suggesting that StAR plays a role in steroidogenesis in the brain, as it does in peripheral endocrine organs. The present review presents data regarding the presence and role of StAR in brain steroidogenesis, demonstrating the essential characteristics of the protein.

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

Peripheral administration of alcohol has been demonstrated to cause significant increases in neurosteroid levels in the brain and periphery. These findings have led to several theories suggesting a role for neurosteroids in the actions of alcohol. However, the anatomical sources of these steroids (e.g., brain or periphery) are as yet unknown. This study utilized gas chromatography/mass spectrometry (GC/MS) to assess the levels of several neuroactive steroids in plasma and brain frontal cortex 30-360 min following acute administration of alcohol (2 g/kg, i.p.). Concentrations of pregnenolone, allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one), and allotetrahydrodeoxycorticosterone (3alpha,21-dihydroxy-5alpha-pregnan-20-one) were all measured. In order to determine the contribution of peripheral endocrine organs to neurosteroid responses, neuroactive steroid levels were measured in both intact and adrenalectomized/gonadectomized male Wistar rats 30 min after acute administration of alcohol. Intact animals exhibited a maximal increase of pregnenolone in plasma and frontal cortex 30 min after acute administration of alcohol. In addition, allopregnanolone levels increased, with a maximal effect observed at 60 min in plasma. However, in the adrenalectomized/gonadectomized groups treated with alcohol, no significant increases of pregnenolone, allopregnanolone, or allotetrahydrodeoxycorticosterone were found after 30 min. Thus, the alcohol-induced response was associated first with a relatively rapid increase in the first and rate-limiting step in the conversion of cholesterol to steroids, leading to increases in pregnenolone levels. This response was followed by the further secretion of the anxiolytic neuroactive steroids allopregnanolone and allotetrahydrodeoxycorticosterone, both of which appeared to be of adrenal and gonadal origin.

Sex differences in the effect of ethanol injection and consumption on brain allopregnanolone levels in C57BL/6 mice

The pharmacological profile of allopregnanolone, a neuroactive steroid that is a potent positive modulator of gamma-aminobutyric acidA (GABAA) receptors, is similar to that of ethanol. Recent findings indicate that acute injection of ethanol increased endogenous allopregnanolone to pharmacologically relevant concentrations in male rats. However, there are no comparable data in mice, nor has the effect of ethanol drinking on endogenous allopregnanolone levels been investigated. Therefore, the present studies measured the effect of ethanol drinking and injection on allopregnanolone levels in male and female C57BL/6 mice. One group was given 17 days of 2-h limited access to a 10% v/v ethanol solution in a preference-drinking paradigm, while another group had access to water only. The ethanol dose consumed in 2 h exceeded 2 g/kg. Then, separate groups of mice were injected with either 2 g/kg ethanol or saline. Mice were killed 30 min after the 2-h drinking session or injection. Blood ethanol concentration was significantly higher in the ethanol-injected versus ethanol-drinking groups, even though the dose was similar. Consumption of ethanol significantly increased brain allopregnanolone levels in male but not female mice, compared with animals drinking water, but did not alter plasma corticosterone levels. In contrast, injection of ethanol did not significantly alter brain allopregnanolone levels in male or female mice and only significantly increased plasma corticosterone levels in the male mice, when compared with saline-injected animals. The sex differences in the effect of ethanol administration on endogenous allopregnanolone levels suggest that the hormonal milieu may impact ethanol's effect on GABAergic neurosteroids. Importantly, these data are the first to report the effect of ethanol drinking on allopregnanolone levels and indicate that ethanol consumption and ethanol injection can produce physiologically relevant allopregnanolone levels in male mice. These results have important implications for studies investigating the potential role of endogenous allopregnanolone levels in modulating susceptibility to ethanol abuse.

Molecular mechanisms of tolerance to and withdrawal of GABA(A) receptor modulators

Here, we summarize recent data pertaining to the effects of GABA(A) receptor modulators on the receptor gene expression in order to elucidate the molecular mechanisms behind tolerance and dependence induced by these drugs. Drug selectivity and intrinsic activity seems to be important to evidence at the molecular level the GABA(A) receptor tolerance. On the contrary, we suggested that all drug tested are equally potentially prone to induce dependence. Our results demonstrate that long-lasting exposure of GABA(A) receptors to endogenous steroids, benzodiazepines and ethanol, as well as their withdrawal, induce marked effects on receptor structure and function. These results suggest the possible synergic action between endogenous steroids and these drugs in modulating the functional activity of specific neuronal populations. We report here that endogenous steroids may play a crucial role in the action of ethanol on dopaminergic neurons.

Anti-nociception following exposure to trimethylthiazoline, peripheral or intra-amygdala estrogen and/or progesterone

Estradiol (E(2)) and/or progesterone (P) to the amygdala may influence stress-induced analgesia following predator odor, trimethylthiazoline (TMT), exposure. Ovariectomized (ovx) rats were administered subcutaneous (SC) or intra-amygdala vehicle, E(2), P, or E(2)+P. The effects on performance in a test of pain sensitivity, the tailflick task, was observed in animals that experienced an acute exposure to TMT or no odor (control) in a small chamber. Rats that were exposed to TMT had increased tailflick latencies compared to rats not exposed to TMT, this was partially attenuated by the opiate antagonist naloxone. Systemic E(2), P, or E(2)+P increased tailflick latencies compared to vehicle administration to ovx rats. Ovx rats administered E(2)+P to the amygdala had increased tailflick latencies compared to control rats. These data suggest that following exposure to predator odor, pain sensitivity in the tailflick task is decreased and that E(2) and/or P may have actions in the amygdala to produce similar anti-nociceptive effects.

Neurosteroids, GABAA receptors, and escalated aggressive behavior

Aggressive behavior can serve important adaptive functions in social species. However, if it exceeds the species-typical pattern, it may become maladaptive. Very high or escalated levels of aggressive behavior can be induced in laboratory rodents by pharmacological (alcohol-heightened aggression), environmental (social instigation), or behavioral (frustration-induced aggression) means. These various forms of escalated aggressive behavior may be useful in further elucidating the neurochemical control over aggression and violence. One neurochemical system most consistently linked with escalated aggression is the GABAergic system, in conjunction with other amines and peptides. Although direct stimulation of GABA receptors generally suppresses aggression, a number of studies have found that positive allosteric modulators of GABAA receptors can cause increases in aggressive behavior. For example, alcohol, benzodiazepines, and many neurosteroids are all positive modulators of the GABAA receptor and all can cause increased levels of aggressive behavior. These effects are dose-dependent and higher doses of these compounds generally shift from heightening aggressive behavior to being sedative and anti-aggressive. In addition, these modulators interact with each other and can have additive effects on the GABAA receptor and on behavior, including aggression. The GABAA receptor is a heteropentameric protein that can be constituted from various subunits. It has been shown that subunit composition can affect sensitivity of the receptor to some modulators and that subunit composition differentially affects the sedative vs anxiolytic actions of benzodiazepines. Initial studies targeting alpha subunits of the GABAA receptor point to their significant role in the aggression-heightening effects of alcohol, benzodiazepines, and neurosteroids.

Differential regulation of steroid 5alpha-reductase isozymes expression by androgens in the adult rat brain

The enzyme 5alpha-reductase (5alpha-R) is present in many mammalian tissues, including the brain. The physiological importance of 5alpha-R in the brain derives from its capability to convert testosterone (T) to a more potent androgen, dihydrotestosterone (DHT), and to convert progesterone and deoxycorticosterone (DOC) to their respective 5alpha-reduced derivatives, precursors of allopregnanolone and tetrahydroDOC, potent allosteric modulators of the gamma-aminobutyric acid receptor (GABA(A)-R). 5alpha-R occurs as two isoforms, 5alpha-R type 1 (5alpha-R1) and 5alpha-R type 2 (5alpha-R2). We studied the effects of T and DHT on the mRNA levels of both 5alpha-R isozymes in the prefrontal cortex of the adult rat, using an accurate and precise method that combines the high specificity of one-step quantitative RT-PCR with the sensitivity of capillary electrophoresis. Our results demonstrate that both isozymes of 5alpha-R are expressed in the cerebral cortex of adult rats. The gene expression of 5alpha-R type 2 is under the positive control of T and DHT. The gene that codes for 5alpha-R type 1 is not constitutive, because its expression is negatively regulated by T and DHT. These results open up a new research line that may lead to a better understanding of the role of 5alpha-R isozymes in the physiology of the central nervous system.

StAR and steroidogenic enzyme transcriptional regulation in the rat brain: effects of acute alcohol administration

In this study, we showed the presence of steroidogenic acute regulatory protein (StAR) mRNA in the rat brain using Northern blot analysis and revealed its localization using in situ hybridization histochemistry. Although the expression level is less than peripheral steroidogenic organs, the brain has two kinds of StAR transcripts with the same size as peripheral endocrine organs. As expected, StAR mRNA levels were maintained in the brain after gonadectomy and adrenalectomy, which indicates its independent expression. Acute alcohol administration affected the mRNA expression of a variety of steroidogenic enzymes, as well as StAR, in several brain regions, and these changes varied from one region to another. It is suggested that StAR may take part in brain steroidogenesis along with steroidogenic enzymes and that various neurosteroids are synthesized differentially to meet local demands.

Anxiogenic effects of neurosteroid exposure: sex differences and altered GABAA receptor pharmacology in adult rats

Acute exposure to progesterone or its neurosteroid derivative allopregnanolone (3alpha,5alpha-THP) is anxiolytic, consistent with the GABA modulatory effects of 3alpha,5alpha-THP at the GABA(A) receptor. However, continuous exposure to progesterone increases anxiety in association with increased expression of the benzodiazepine-insensitive GABA(A) receptor alpha4 subunit. Furthermore, negative mood symptoms and altered GABA(A) receptor pharmacology in patients with premenstrual dysphoric disorder occur in the early luteal phase in association with peak circulating levels of progesterone and 3alpha,5alpha-THP. Because sex differences have been reported in steroid-regulated anxiety responses, the present study investigated the role of sex and development in the regulation of anxiety after short-term exposure to 3alpha,5alpha-THP. To this end, we compared the effects of hormone administration in adult male, adult female, and juvenile female rats. Increased anxiety in the elevated plus maze was evident in all groups after 48-h exposure to either 3alpha,5alpha-THP or progesterone. At this time point, alterations in the anxiolytic profile of benzodiazepine agonists and antagonists were also observed in both adult males and females in the elevated plus maze. However, sex differences in the acoustic startle response were observed after short-term hormone treatment such that only female rats displayed an increased response indicative of higher anxiety levels. These results suggest that although neurosteroid exposure may influence both the pharmacological properties of the GABA(A) receptor and the manifestation of anxiety in both sexes, the effects of neurosteroids may be modulated in a sex- and task-specific manner.

Social isolation-induced increase in the sensitivity of rats to the steroidogenic effect of ethanol

Social isolation of rats for 30 days immediately after weaning results in marked decreases in the cerebrocortical and plasma concentrations of pregnenolone, progesterone, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG), and 3alpha,5alpha-tetrahydrodeoxycorticosterone (3alpha,5alpha-TH DOC), as well as a moderate increase in the plasma concentration of corticosterone. This mildly stressful condition has now been shown to increase the sensitivity of rats to the effect of acute ethanol administration on the cerebrocortical and plasma concentrations of neuroactive steroids. The percentage increases in the brain and plasma concentrations of pregnenolone, progesterone, 3alpha,5alpha-TH PROG, and 3alpha,5alpha-TH DOC, apparent 20 min after a single intraperitoneal injection of ethanol (1 g/kg), were thus markedly greater in isolated rats than in group-housed animals. A subcutaneous injection of isoniazid (300 mg/kg) also induced greater percentage increases in the concentrations of these steroids in isolated rats than in group-housed animals. These results suggest that mild chronic stress, such as that induced by social isolation, enhances the steroidogenic effect of ethanol, a drug abused by humans under stress or affected by neuropsychiatric disorders. Social isolation also induced hyper-responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis, as was apparent after reduction of GABA-mediated inhibitory tone by isoniazid administration.

Is there a physiological role for the neurosteroid THDOC in stress-sensitive conditions?

Endogenous neurosteroids affect brain excitability during physiological states such as pregnancy and the menstrual cycle, and during conditions of acute and chronic stress. The neurosteroid allotetrahydrodeoxycorticosterone (THDOC) is an allosteric modulator of the GABA(A) receptor. Although the role of THDOC within the brain is undefined, recent studies indicate that stress induces THDOC to levels that can activate GABA(A) receptors. These results might have significant implications for human stress-sensitive conditions such as epilepsy, post-traumatic stress disorder and depression.

Nicotine-induced changes in cerebrocortical neuroactive steroids and plasma corticosterone concentrations in the rat

Nicotine, one of the most widely used psychotropic substances, is able to induce both anxiolytic and anxiogenic effects. The effect of this drug on the brain and plasma concentrations of neuroactive steroids was examined in the rat. Anxiolytic doses of nicotine (0.03-0.3 mg/kg) had no significant effect, whereas administration of anxiogenic doses (0.5 to 2 mg/kg) produced a dose- and time-dependent increase in the cerebrocortical concentrations of pregnenolone, progesterone, and allopregnanolone, with the greatest observed effects (+180%, +223%, and +124%, respectively) apparent at the dose of 2 mg/kg. In contrast, nicotine (1-2 mg/kg) decrease by 31% and 38%, respectively, the concentration of 3alpha,21-dihydroxy-5alpha-pregnan-20-one (allotetrahydrodeoxycorticosterone, or THDOC) in the cerebral cortex. Nicotine also increased the plasma concentrations of pregnenolone and progesterone, whereas failed to affect significantly those of allopregnanolone or THDOC. Nicotine induced a dose- and time-dependent increase in the plasma concentration of corticosterone, indicating that this drug activates the hypothalamic-pituitary-adrenal (HPA) axis. These results suggest that the changes in emotional behavior elicited by nicotine, similar to those induced by stressful stimuli or other anxiogenic drugs, are associated with an increase in neuroactive steroids content of the brain.

Inhibition by pregnenolone sulfate of nicotinic acetylcholine response in adrenal chromaffin cells

To evaluate whether pregnenolone sulfate, an abundant neurosteroid in the brain, modulates nicotinic receptor-mediated responses, the effect of pregnenolone sulfate on acetylcholine-induced catecholamine secretion was investigated in cultured bovine adrenal chromaffin cells. Pregnenolone sulfate inhibited acetylcholine-induced catecholamine secretion (IC(50): 27 microM). In addition, pregnenolone sulfate inhibited acetylcholine-induced Na(+) (IC(50): 12 microM) and Ca(2+) (IC(50): 20 microM) influxes. However, pregnenolone sulfate did not inhibit either catecholamine secretion or Ca(2+) influx stimulated by high K(+). Binding of [3H]nicotine to nicotinic receptors was not altered by pregnenolone sulfate. The inhibitory effect on the acetylcholine-induced secretion was insurmountable by increasing acetylcholine concentrations, but was enhanced by decreasing external Na(+) concentrations. These results suggest strongly that pregnenolone sulfate noncompetitively inhibits nicotinic receptor-operated ion channels, thereby suppressing Na(+) influx through the channels and, consequently, attenuates both Ca(2+) influx and catecholamine secretion. Our results further indicate that pregnenolone sulfate may modulate nicotinic receptor-mediated responses in the brain.

Increase in testosterone metabolism in the rat central nervous system by formalin-induced tonic pain

The effects of formalin-induced tonic pain (FITP) on testosterone (T) concentrations in the central nervous system (CNS) and serum were investigated in rats. T was nearly eliminated from the brain and spinal cord 1.5 and 24 h after a single subcutaneous injection (100 microl/rat, sc) of 5% formalin and its levels were similar to that seen following castration. In serum, T concentrations were decreased significantly 1.5 h following formalin injection, but after 24 h, the serum level of T was within normal range. T concentrations in the brain, spinal cord, and serum were not modified 20 min after formalin injection. Pretreatment of rats with finasteride, a 5alpha-reductase (5alpha-R) inhibitor (5 mg/kg, sc) blocked T elimination from the brain and spinal cord by FITP, but it failed to prevent decrease in serum T. However, 3 h after administration of exogenous T (5 mg/kg, sc), FITP did not cause a significant decrease in T levels in the CNS and serum. These results suggest that FITP eliminates endogenous T in the brain and spinal cord by increasing 5alpha-R activity in the CNS.

Endotoxin increases sleep and brain allopregnanolone concentrations in newborn lambs

Infection has been identified as a risk factor for sudden infant death syndrome (SIDS). Synthesis of allopregnanolone, a neuroactive steroid with potent sedative properties, is increased in response to stress. In this study, we investigated the effect of endotoxin (lipopolysaccharide, LPS) on brain and plasma allopregnanolone concentrations and behavior in newborn lambs. LPS was given intravenously (0.7 micro g/kg) at 12 and 15 d of age (n = 7), and resulted in a biphasic febrile response (p < 0.001), hypoglycemia, lactic acidemia (p < 0.05), a reduction in the incidence of wakefulness, and increased nonrapid eye movement sleep and drowsiness (p < 0.05) compared with saline-treated lambs (n = 5). Plasma allopregnanolone and cortisol were significantly (p < 0.05) increased after LPS treatment. These responses to LPS lasted 6-8 h, and were similar at 12 and 15 d of age. Each lamb was then given LPS at 20 d of age and killed 3 h posttreatment to obtain samples of the brain. Allopregnanolone concentrations were increased (p < 0.05) in all brain areas except the cerebellum and diencephalon. We suggest that LPS-induced increase of allopregnanolone in the brain may contribute to somnolence in the newborn, and may be responsible for the reduced arousal thought to contribute to the risk of SIDS in human infants.

Neurosteroids and infantile spasms: the deoxycorticosterone hypothesis

Deoxycorticosterone (DOC) is a mineralocorticoid precursor that has anticonvulsant properties in animals and possibly also in humans. Studies indicate that the anticonvulsant activity of DOC requires its enzymatic conversion to 5 alpha,3 alpha-tetrahydrodeoxycorticosterone (THDOC), a neurosteroid that lacks classical hormonal properties but acts as a powerful positive allosteric modulator of GABAA receptors. DOC can be considered a stress hormone because its synthesis is under the control of ACTH. Therefore, stress-induced fluctuations in seizure susceptibility could in part result from alterations in DOC availability. Also, the therapeutic activity of ACTH in infantile spasms could partially relate to its stimulatory effects on the synthesis of DOC, which then undergoes biotransformation to neurosteroids. The recent demonstration that the synthetic neurosteroid analog ganaxolone reduces spasm frequency in children with intractable infantile spasms suggests that neurosteroid-related anticonvulsants may offer a potential new nonhormonal approach for the treatment of infantile spasms and other developmental epilepsies. In addition, it further confirms the utility of pharmacological enhancement of GABA-mediated inhibition in the control of infantile spasms.

Progesterone withdrawal increases the alpha4 subunit of the GABA(A) receptor in male rats in association with anxiety and altered pharmacology - a comparison with female rats

Withdrawal from the neurosteroid 3alpha,5alpha-allopregnanolone after chronic administration of progesterone increases anxiety in female rats and up-regulates the alpha4 subunit of the GABA(A) receptor (GABA(A)-R) in the hippocampus. We investigated if these phenomena would also occur in male rats. Progesterone withdrawal (PWD) induced higher alpha4 subunit expression in the hippocampus of both male and female rats, in association with increased anxiety (assessed in the elevated plus maze) comparable to effects previously reported. Because alpha4-containing GABA(A)-R are insensitive to the benzodiazepine (BDZ) lorazepam (LZM), and are positively modulated by flumazenil (FLU, a BDZ antagonist), we therefore tested the effects of these compounds following PWD. Using whole-cell patch clamp techniques, LZM-potentiation of GABA ((EC20))-gated current was markedly reduced in CA1 pyramidal cells of male rats undergoing PWD compared to controls, whereas FLU had no effect on GABA-gated current in control animals but increased it in PWD animals. Behaviorally, both male and female rats were significantly less sensitive to the anxiolytic effects of LZM. In contrast, FLU demonstrated significant anxiolytic effects following PWD. These data suggest that neurosteroid regulation of the alpha4 GABA(A)-R subunit may be a relevant mechanism underlying anxiety disorders, and that this phenomenon is not sex-specific.

Reinforcing effects of the neurosteroid allopregnanolone in rats

The GABA(A) receptor positive modulator allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one) is a potent neurosteroid with behavioral and biochemical characteristics similar to ethanol, barbiturates, and benzodiazepines. This suggests that neurosteroids may provide an alternative class of sedative/hypnotic, anticonvulsant, and anxiolytic pharmacotherapies. However, there is evidence from animal models that neurosteroids may be susceptible to abuse by humans. Thus, the present study evaluated the reinforcing effects of orally administered allopregnanolone in rats. In the first experiment, male Long-Evans rats (n=9) were allowed to voluntarily consume a 50-microg/ml allopregnanolone (50A) solution or water in an unlimited-access two-bottle choice procedure for 10 days. Subsequently, the same animals were trained to lever-press to receive a 50A solution in daily 30-min operant sessions using a sucrose substitution procedure. In the two-bottle choice procedure, rats consumed significantly more allopregnanolone than water, suggesting that allopregnanolone was serving as a reinforcer. In the operant self-administration procedure, allopregnanolone did not maintain levels of responding that were different from water, suggesting that allopregnanolone did not function as a reinforcer in this procedure. These results suggest that orally administered allopregnanolone possesses reinforcing properties; however, additional studies are necessary to determine whether operant oral self-administration will be a viable index of allopregnanolone's reinforcing effects.

Prevention of the stress-induced increase in the concentration of neuroactive steroids in rat brain by long-term administration of mirtazapine but not of fluoxetine

The effects of acute and chronic administration of fluoxetine on the basal and stress-induced increases in cerebrocortical and plasma concentrations of allopregnanolone (3alpha,5alpha-tetrahydroprogesterone; 3alpha,5alpha-TH PROG) and tetrahydrodeoxycorticosterone (3alpha,5alpha-TH DOC) were compared with those of mirtazapine, an antidepressant that (unlike fluoxetine) is not a selective serotonin reuptake inhibitor. A single injection (20 mg/kg i.p.) of fluoxetine or mirtazapine resulted in significant increases in the cerebrocortical and plasma concentrations of 3alpha,5alpha-TH PROG and 3alpha,5alpha-TH DOC. In contrast, long-term administration (10 mg/kg i.p., once daily for 2 weeks) of fluoxetine, but not that of mirtazapine, induced marked decreases in the cortical and plasma concentrations of these neuroactive steroids. Chronic treatment with fluoxetine, however, did not inhibit the increases in the cortical and plasma concentrations of 3alpha,5alpha-TH PROG and 3alpha,5alpha-TH DOC induced by acute foot-shock stress. In contrast, chronic treatment with mirtazapine prevented or significantly reduced the stress-induced increases in neurosteroid concentrations in the cerebral cortex and plasma, respectively. These results show that mirtazapine, similar to fluoxetine, initially increases the cortical concentration of neuroactive steroids; however, chronic administration of this drug modulates the plasma and brain availability of these hormones in a manner distinct from that of fluoxetine.

Stress-induced deoxycorticosterone-derived neurosteroids modulate GABA(A) receptor function and seizure susceptibility

Stress affects seizure susceptibility in animals and humans, but the underlying mechanisms are obscure. Here, we provide evidence that GABA(A) receptor-modulating neurosteroids derived from deoxycorticosterone (DOC) play a role in stress-related changes in seizure control. DOC, an adrenal steroid whose synthesis is enhanced during stress, undergoes sequential metabolic reduction by 5alpha-reductase and 3alpha-hydroxysteroid oxidoreductase to form 5alpha-dihydrodeoxycorticosterone (DHDOC) and allotetrahydrodeoxycorticosterone (THDOC), a GABA(A) receptor-modulating neurosteroid with anticonvulsant properties. Acute swim stress in rats significantly elevated plasma THDOC concentrations and raised the pentylenetetrazol (PTZ) seizure threshold. Small systemic doses of DOC produced comparable increases in THDOC and PTZ seizure threshold. Pretreatment with finasteride, a 5alpha-reductase inhibitor that blocks the conversion of DOC to DHDOC, reversed the antiseizure effects of stress. DOC also elevated plasma THDOC levels and protected mice against PTZ, methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate, picrotoxin, and amygdala-kindled seizures in mice (ED50 values, 84-97 mg/kg). Finasteride reversed the antiseizure activity of DOC (ED50, 7.2 mg/kg); partial antagonism was also obtained with indomethacin (100 mg/kg), an inhibitor of 3alpha-hydroxysteroid oxidoreductase. Finasteride had no effect on seizure protection by DHDOC and THDOC, whereas indomethacin partially reversed DHDOC but not THDOC. DHDOC, like THDOC, potentiated GABA-activated Cl- currents in cultured hippocampal neurons (< or =1 microm) and directly activated GABA(A) receptor currents (> or =1 microm), compatible with a role for DHDOC in the antiseizure activity of DOC. DOC is a mediator of the physiological effects of acute stress that could contribute to stress-induced changes in seizure susceptibility through its conversion to neurosteroids with modulatory actions on GABA(A) receptors including THDOC and possibly also DHDOC.

Allopregnanolone inhibits learning in the Morris water maze

The progesterone metabolite allopregnanolone (3alpha-OH-5alpha-pregnane-20-one) inhibits neural functions, enhancing the GABA induced GABA(A) receptor activation. This effect is benzodiazepine like and benzodiazepines are known to impair memory. Acute effects of allopregnanolone on the hippocampus dependent spatial learning in the Morris water maze have not been studied. Adult male Wistar rats where injected (i.v.) with allopregnanolone (2 mg/kg), or vehicle, daily for 11 days. At 8 or 20 min after each injection, studies of place navigation were performed in the Morris water maze. Allopregnanolone concentrations in plasma and in nine different brain areas where analyzed by radioimmunoassay. The latency to find the platform was increased 8 min after the allopregnanolone injection, while normal learning was seen after 20 min. Swim speed did not differ between groups. A higher number of rats were swimming close to the pool wall (thigmotaxis) in the 8 min allopregnanolone group compared to the other groups. Allopregnanolone concentrations in the brain tissue at 8 min were 1.5 to 2.5 times higher then at 20 min after the allopregnanolone injections. After vehicle injections the brain concentrations of allopregnanolone were at control levels. Plasma concentrations of allopregnanolone followed the same pattern as in the brain, with the exception of an increase 8 min after vehicle injections. The natural progesterone metabolite allopregnanolone can inhibit learning in the Morris water maze, an effect not caused by motor impairment. The learning impairment might be due to a combination of changed swimming behavior and difficulties in navigation.

Neuroactive steroid changes in response to challenge with the panicogenic agent pentagastrin

BACKGROUND

Female hormones and female hormone derivatives, including neuroactive steroids (NASs) have been suspected to play a role in the pathophysiology of panic disorder (PD). The panicogenic agent CO(2) has been shown to induce a delayed release of NASs in both brain and plasma of rats. In the present study, we measured NASs plasma levels in response to challenge with another panicogenic agent, pentagastrin, and assessed the effect of ethynil estradiol (EE) pretreatment.

METHODS

A double-blind cross-over placebo-controlled design with randomization of the order of a three day pretreatment of EE (50 microg/day) or placebo was used to assess the effect of a 30 microg iv bolus injection of pentagastrin on the release of allopregnanolone (ALLO) and dehydroepiandrosterone (DHEA) into plasma in 15 male PD patients and 10 male healthy volunteers (HV).

RESULTS

After pentagastrin challenge there was a significant release of DHEA and a trend for the release of ALLO. EE pretreatment did not affect the pentagastrin-induced panic response or NAS release.

CONCLUSIONS

Pentagastrin induced release of NASs into plasma, the purpose of which remains to be determined.

GABA(B) receptor-mediated increase of neurosteroids by gamma-hydroxybutyric acid

Among the pharmacological actions of gamma-hydroxybutyric acid (GHB), some may involve GABA(A) receptor-mediated mechanisms. GHB, however, fails to directly interact with sites for agonists and modulators on the GABA(A) receptor complex. We hypothesized that, in vivo, GHB may interfere with GABA(A) receptor function by altering the brain concentrations of the neurosteroids 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone, AP) and 3 alpha,21-dihydroxy-5 alpha-pregnan-20-one (allotetrahydrodeoxycorticosterone, THDOC), positive allosteric modulators of GABA-gated chloride currents. In male Wistar rats, GHB dose-dependently (75-1000 mg/kg, i.p.) increased AP, THDOC and their precursors pregnenolone and progesterone in brain cortex and hippocampus. The increases of AP (4-5 fold) and THDOC (3-4 fold) elicited by 300 mg/kg GHB peaked between 30 and 90 min and abated by 180 min. The selective GABA(B) receptor antagonist SCH 50911 (50 mg/kg, i.p.) prevented the action of GHB, while the GABA(B) receptor agonist baclofen (5-10 mg/kg) mimicked it. NCS-382 (50 mg/kg, i.p.), the purported selective antagonist of the GHB receptor, failed to antagonize GHB, but at 300 mg/kg increased brain cortical neurosteroids to the same extent as 300 mg/kg GHB; coadministration of GHB and NCS-382, however, failed to yield an additive effect. These results strongly suggest that GHB, via a GABA(B) receptor-mediated mechanism, increases the brain concentrations of neurosteroids, whose properties as amplifiers of the GABA-gated chloride conductances may play a role in the GABA(A) receptor-mediated pharmacological actions of GHB.

Depletion of cortical allopregnanolone potentiates stress-induced increase in cortical dopamine output

In freely moving rats finasteride markedly reduced the cortical content of allopregnanolone. This treatment significantly prolonged the increase in the extracellular concentration of dopamine in the prefrontal cortex induced by foot shock. Moreover, finasteride enhanced both maximal increase of dopamine and its duration elicited by a single injection of the anxiogenic drug FG 7142. These results suggest that endogenous allopregnanolone may modulate the excitatory response of cortical dopaminergic neurons to stressful and anxiogenic stimuli.

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.

Neurosteroids and behavior

Neurosteroid production may be a mechanism to counteract the negative effects of stress and return organisms toward homeostasis. Stress induces an increase in neurosteroid production. Neurosteroids affect two of the most widely distributed neurotransmitter and receptor systems in the central nervous system (CNS): gamma-aminobutyric acid (GABA) and glutamate. This ability of this class of compounds to affect both the primary excitatory and the inhibitory systems in the CNS allows the modulation of a wide array of behaviors. For example, neurosteroids modulate anxiety, cognition, sleep, ingestion, aggression, and reinforcement. In general, neurosteroids that are positive modulators of N-methyl-D-aspartate receptors enhance cognitive performance and decrease appetite. Neurosteroids that are positive modulators of GABAA receptors decrease anxiety, increase feeding and sleeping, and exhibit a bimodal effect on aggression that may be secondary to effects on anxiety and cognition. Some data suggest that neurosteroids have reinforcing effects, which could affect their clinical utility. Drug discrimination studies are helping scientists to dissect more closely the receptor systems affected by neurosteroids at the behavioral level.

The interaction between ethanol and pregnanolone at induction of anaesthesia investigated with a threshold method in male rats

1. An anaesthesia threshold was used to investigate the pharmacodynamic and pharmacokinetic interactions between ethanol and pregnanolone in male rats. 2. The criterion to determine threshold doses of pregnanolone was the first burst suppression of 1 s in the EEG. 3. Ethanol (0.5, 1.0, 1.5 and 2.0 g kg(-1)) was injected i.p. 15 min before pregnanolone infusion. Trunk blood, serum, cortex, cerebellum, hippocampus, striatum, brain stem, fat and muscle tissues obtained at criterion were used to determine ethanol (blood) and pregnanolone. Ethanol reduced threshold doses in a dose dependent linear manner. A similar reduction of pregnanolone tissue concentrations was only found in brain stem and striatum. Deviations consisted of larger decreases in serum, cerebellum and hippocampus after 0.5 g kg(-1) ethanol and in cerebellum, cortex and hippocampus after 2.0 g kg(-1) of ethanol. Positive correlations between dose and concentration of pregnanolone was recorded in brain stem, hippocampus, cerebellum and cortex. A kinetic component influenced the concentration in cortex. There was a correlation between dose and serum concentration of pregnanolone only after ethanol. In the muscle 0.5 g kg(-1) ethanol had no influence on pregnanolone concentration. 4. The linear, additive pharmacodynamic interaction could involve the GABA ionophore. A pharmacokinetic interaction was found in cortex. The retained high uptake of pregnanolone in muscle (after 0.5 g kg(-1)) corresponded to losses in other tissues (including serum). The reduced uptake of pregnanolone in cerebellum, cortex and hippocampus (after 2.0 g kg(-1)) was not due to a corresponding change in serum concentration. It was probably due to a reduced blood flow.

The interaction between neuroactive steroids and the sigma1 receptor function: behavioral consequences and therapeutic opportunities

Steroids, synthesized in peripheral glands or centrally in the brain--the latter being named neurosteroids--exert an important role as modulators of the neuronal activity by interacting with different receptors or ion channels. In addition to the modulation of GABA(A), NMDA or cholinergic receptors, neuroactive steroids interact with an atypical intracellular receptor, the sigma(1) protein. This receptor has been cloned in several species, and highly selective synthetic ligands are available. At the cellular level, sigma1 agonists modulate intracellular calcium mobilization and extracellular calcium influx, NMDA-mediated responses, acetylcholine release, and alter monoaminergic systems. At the behavioral level, the sigma1 receptor is involved in learning and memory processes, the response to stress, depression, neuroprotection and pharmacodependence. Pregnenolone, dehydroepiandrosterone, and their sulfate esters behave as sigma1 agonists, while progesterone is a potent antagonist. This review will detail the physiopathological consequences of these interactions, focusing on recent results on memory and depression. The therapeutical interest of selective sigma1 receptor agonists in alleviating aging-related cognitive deficits will be discussed.

Role of allopregnanolone in regulation of GABA(A) receptor plasticity during long-term exposure to and withdrawal from progesterone

Here we summarize recent data from our laboratory pertaining to the effects of fluctuations in the brain concentrations of the progesterone (PROG) metabolite allopregnanolone (3alpha,5alpha-TH PROG) on the expression and function of gamma-aminobutyric acid type A (GABA(A)) receptors. The effects of long-term exposure to progesterone and of its sudden withdrawal on the activity of GABA(A) receptors and on the abundance of receptor subunit mRNAs were examined in cultured rat cerebellar granule cells and cortical neurons. The effects of a persistent reduction in the brain concentration of 3alpha,5alpha-TH PROG on GABA(A) receptor function and gene expression were examined in vivo in rats subjected to long-term administration of oral contraceptives. Our results demonstrate that long-lasting changes in the exposure of GABA(A) receptors to this PROG metabolite induce marked effects on receptor structure and function. These effects of 3alpha,5alpha-TH PROG appear to be mediated through modulation of GABA(A) receptor signaling mechanisms that control the expression of specific receptor subunit genes. Furthermore, the specific outcomes of such signaling appear to differ among neurons derived from different regions of the brain. Neuroactive steroids such as 3alpha,5alpha-TH PROG might thus exert differential actions on GABA(A) receptor plasticity in distinct neuronal cell populations, likely accounting for some of the physiological effects induced by these compounds.

Neurosteroids mediate habituation and tonic inhibition in the auditory midbrain

Habituation of the behavioral response to a repetitive stimulus is a well-established observation in perceptual studies and is considered a basic form of nonassociative learning. There is also a long history of physiological studies suggesting that central nervous system habituation is mediated by inhibition. At higher levels of the sensory pathways, such inhibition is mainly contributed by GABAa receptor mechanisms. Concepts of modification of synaptic efficacy that apply to excitatory amino acid synaptic transmission do not have direct parallels with these inhibitory synapses: quantal release of GABA rapidly saturates available receptors at a synapse, placing an upper limit on responsiveness to increased transmitter release. However, pharmacological modulation of GABAa-receptor efficacy with exogenous agents (e.g., benzodiazepines and beta-carbolines) is known to occur through allosteric mechanisms that modulate the effectiveness (positive and negative) of GABA at this receptor. The most potent endogenous modulators are 5alpha-reduced steroids. Production of these steroids was attenuated in adult rats with systemic injection of Finasteride, a competitive substrate for 5alpha-reductase. This treatment was sufficient to block habituation of the evoked midbrain response to repetitive presentation of an acoustic click. This result confirms that simple habituation is due to an increase in active inhibition, the increase being mediated by steroid modulation of the GABAa-receptor. Finasteride treatment also brought about a 23% increase in the evoked response to a click stimulus, suggesting that 5alpha-reduced steroids normally contribute to tonic inhibition in the rat inferior colliculus.

Allopregnanolone levels and reactivity to mental stress in premenstrual dysphoric disorder

BACKGROUND

This study was designed to examine basal and stress-induced levels of the neuroactive progesterone metabolite, allopregnanolone, in women with premenstrual dysphoric disorder (PMDD) and healthy control subjects. Also, because evidence suggests that allopregnanolone negatively modulates the hypothalamic-pituitary-adrenal axis, plasma cortisol levels were examined. An additional goal was to investigate the relationship between premenstrual symptom severity and luteal phase allopregnanolone levels.

METHODS

Twenty-four women meeting prospective criteria for PMDD were compared with 12 controls during both the follicular and luteal phases of confirmed ovulatory cycles, counterbalancing phase at first testing. Plasma allopregnanolone and cortisol were sampled after an extended baseline period and again 17 min following the onset of mental stress. Owing to low follicular phase allopregnanolone levels, only luteal phase allopregnanolone and cortisol were analyzed.

RESULTS

During the luteal phase, PMDD women had significantly greater allopregnanolone levels, coupled with significantly lower cortisol levels, during both baseline and mental stress. Moreover, significantly more controls (83%) showed the expected stress-induced increases in allopregnanolone compared with PMDD women (42%). Premenstrual dysphoric disorder women also exhibited a significantly greater allopregnanolone/progesterone ratio than control subjects, suggesting alterations in the metabolic pathways involved in the conversion of progesterone to allopregnanolone. Finally, PMDD women with greater levels of premenstrual anxiety and irritability had significantly reduced allopregnanolone levels in the luteal phase relative to less symptomatic PMDD women. No relationship between symptom severity and allopregnanolone was observed in controls.

CONCLUSIONS

These results suggest dysregulation of allopregnanolone mechanisms in PMDD and that continued investigations into a potential pathophysiologic role of allopregnanolone in PMDD are warranted.

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.

Pivagabine-induced increases in the abundance of CRF mRNA in the cerebral cortex and hypothalamus of rats

The effect of treatment of rats with pivagabine (4-[(2,2-dimethyl-1-oxopropyl) amino] butanoic acid) for 4 days on the abundance of corticotropin-releasing factor (CRF) mRNA in the brain was investigated. Such treatment resulted in dose-dependent (100-300 mg/kg, i.p.) increases in the amount of CRF mRNA in both the hypothalamus and cerebral cortex. The maximal increases were thus apparent with the dose of 300 mg/kg in the hypothalamus (+108%) and cerebral cortex (+49%) 30 or 60 min, respectively, after the last drug injection. Foot-shock stress administered 30 min after the final drug injection had no effect on the pivagabine-induced increases in the abundance of CRF mRNA in the hypothalamus or cerebral cortex. Such stress also had no effect on the amounts of CRF mRNA in these brain regions of vehicle-treated rats. These results demonstrate that pivagabine increases the amount of CRF mRNA in both the hypothalamus and cerebral cortex of rats, effects that might be relevant to the action of this drug in preventing the stress-induced changes in CRF hypothalamic concentration.

Quantification of neurosteroids in rat plasma and brain following swim stress and allopregnanolone administration using negative chemical ionization gas chromatography/mass spectrometry

A simplified method for the quantitative analysis of neurosteroids in rat plasma and brain is described. The method uses negative chemical ionization gas chromatography/mass spectrometry and involves the synthesis of pentafluorobenzyloxime/trimethylsilyl ether derivatives with excellent chromatographic and electron-capturing properties. Deuterium-labeled analogs of the steroids of interest were synthesized and used as internal standards. The steroids (allopregnanolone, epiallopregnanolone, pregnenolone, testosterone, and dehydroepiandrosterone) were isolated from the plasma or brain matrix by a rapid and straightforward solid-phase extraction procedure. The mass spectrometer was operated in a selective ion monitoring mode, allowing for picograms of neurosteroids to be quantified from biological extracts. The method was linear (typical R(2) = 0.999) over the concentration range (100 to 8000 pg from 0.3 ml plasma and 250 to 8000 pg from 100 mg brain tissue) with good precision and accuracy. In experimental protocols, the procedure was suitable for measuring concentrations of endogenous neurosteroids in rat plasma and brain. Significant elevations (P < 0.001) were observed in the frontal cortex for allopregnanolone and pregnenolone following a swim stress and for allopregnanolone and epiallopregnanolone following allopregnanolone injection (8 mg/kg, sc). The present method allows accurate determination of neurosteroids and will be helpful in elucidating the role of neurosteroids in health and disease.

Acute neuroactive steroid withdrawal in withdrawal seizure-prone and withdrawal seizure-resistant mice

Allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one) is an endogenously derived metabolite of progesterone, and a potent positive modulator of gamma-aminobutyric acid(A) (GABA(A)) receptors. A withdrawal syndrome, characterized by central nervous system (CNS) hyperexcitability, has been demonstrated following abrupt discontinuation of high progesterone levels in rats, which was due in part to altered levels of allopregnanolone. The purpose of the present study was to determine if a single administration of pregnanolone or allopregnanolone could produce an acute withdrawal response in mice selected for susceptibility (Withdrawal Seizure-Prone, WSP) or resistance (Withdrawal Seizure-Resistant, WSR) to ethanol withdrawal convulsions. WSP mice administered 75 mg/kg pregnanolone showed a significant increase in handling-induced convulsion (HIC) scores over a 25-h testing period. In contrast, HIC scores in WSR mice were negligible after acute administration of 25, 50, 75, or 100 mg/kg pregnanolone. WSP mice also showed a similar increase in HIC after withdrawal from 75 mg/kg allopregnanolone. This effect was evident at both the 10-h and 25-h overall withdrawal severity assessment. These results demonstrate that neuroactive steroids can elicit an acute withdrawal response similar to that of other positive modulators of GABA(A) receptors in WSP mice, supporting the notion that a common set of genes underlie acute and chronic withdrawal severity from multiple agents with depressant effects on the central nervous system.

Central allopregnanolone is increased in rat pups in response to repeated, short episodes of neonatal isolation

This experiment investigated whether neonatal isolation stress alters central concentrations of progestins. Whole brain progesterone (P), dihydroprogesterone (DHP), and allopregnanolone (3alpha, 5alpha-THP) were measured in pups that were isolated from the nest, dam, and siblings for 1 h on postnatal days (PND) 2-9 and were compared to control litters of pups that were not isolated. Isolated 2-day-old pups had significantly lower central P and higher P to DHP and 3alpha, 5alpha-THP metabolism ratios. On PND 9, pups that had been repeatedly isolated (PND 2-8), had significantly lower whole brain DHP and significantly greater whole brain 3alpha, 5alpha-THP compared to controls. Thus, the biosocial stress of isolation in neonatal rats alters central pregnane steroids.

Plasma 5alpha-androstane-3alpha,17betadiol, an endogenous steroid that positively modulates GABA(A) receptor function, and anxiety: a study in menopausal women

We tested the hypothesis that changes in endogenous neuroactive steroids acting as positive allosteric modulators of gamma-aminobutyric acid (GABA)(A) receptors may be related to the menopause-associated mood alterations. The study sample consisted of twenty five drug-free menopausal women, 1-3 years since the onset of menopause, homogeneous for age and body mass index (BMI) and without personal history of psychiatric, metabolic or endocrine disorders. Depression and anxiety-related symptoms were assessed with the Zung Self-administered Depression Scale (ZSDS) and the Cornell's Dysthymia Rating Scale (CDRS). The cut-off value predicted by the ZSDS index defined two groups of women (asymptomatic [35.5+/-4.6, n=12] and symptomatic [60.8+/-7.9, n=13]), that were also significantly different according to the CDRS scores (10.6+/-3.4 and 31.5+/-12, respectively, P<0.05). Upon evaluation of the scores relative to the anxiety factor of the CDRS (items 11-15) the symptomatic, but not the asymptomatic, group showed a moderate level of anxiety. The plasma concentrations of several neuroactive steroids were measured, after extraction and HPLC purification, by radioimmunoassay with specific antisera. Only dehydroepiandrosterone and its metabolite 5alpha-androstane-3alpha,17betadiol (3alpha-ADIOL), a positive allosteric modulator of GABA(A) receptors, were significantly (P<0.05 and P<0.005) higher (+110% and +64%, respectively) in the asymptomatic group. A highly significant and negative correlation (r=-0.672, P=0.003) was found between the plasma 3alpha-ADIOL concentrations and the scores of the anxiety factor of the CDRS. These data suggest that endogenous 3alpha-ADIOL modulates the central GABAergic tone and that higher 3alpha-ADIOL concentrations could have a role in preventing the expression of anxiety in the asymptomatic women.

Social isolation-induced decreases in both the abundance of neuroactive steroids and GABA(A) receptor function in rat brain

The effects of social isolation on behavior, neuroactive steroid concentrations, and GABA(A) receptor function were investigated in rats. Animals isolated for 30 days immediately after weaning exhibited an anxiety-like behavioral profile in the elevated plus-maze and Vogel conflict tests. This behavior was associated with marked decreases in the cerebrocortical, hippocampal, and plasma concentrations of pregnenolone, progesterone, allopregnanolone, and allotetrahydrodeoxycorticosterone compared with those apparent for group-housed rats; in contrast, the plasma concentration of corticosterone was increased in the isolated animals. Acute footshock stress induced greater percentage increases in the cortical concentrations of neuroactive steroids in isolated rats than in group-housed rats. Social isolation also reduced brain GABA(A) receptor function, as evaluated by measuring both GABA-evoked Cl(-) currents in Xenopus oocytes expressing the rat receptors and tert-[(35)S]butylbicyclophosphorothionate ([(35)S]TBPS) binding to rat brain membranes. Whereas the amplitude of GABA-induced Cl(-) currents did not differ significantly between group-housed and isolated animals, the potentiation of these currents by diazepam was reduced at cortical or hippocampal GABA(A) receptors from isolated rats compared with that apparent at receptors from group-housed animals. Moreover, the inhibitory effect of ethyl-beta-carboline-3-carboxylate, a negative allosteric modulator of GABA(A) receptors, on these currents was greater at cortical GABA(A) receptors from socially isolated animals than at those from group-housed rats. Finally, social isolation increased the extent of [(35)S]TBPS binding to both cortical and hippocampal membranes. The results further suggest a psychological role for neurosteroids and GABA(A) receptors in the modulation of emotional behavior and mood.