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

The anxiogenic beta-carboline FG-7142 inhibits locomotor exploration similarly in postweanling and adult rats

The beta-carboline FG-7142 exerts many stress-like effects in the adult rat, including the inhibition of locomotor exploration. However, comparable effects in immature animals have not been reported. Stress-like effects of FG-7142 are mediated via its inverse agonist actions on gamma-aminobutyric acid (GABA) receptors. GABA systems change considerably with development and GABA agonists such as diazepam have opposite behavioral actions in immature and adult rats. Accordingly, we compared FG-7142 effects on locomotor exploration in postweanling and adult rats. Postweanling male rats (24 days) and adult rats (90 days) received a single injection of vehicle or FG-7142 (15 mg/kg i.p.) and 15 min later were placed in photocell monitors for 1 h. Although postweanling animals traveled a smaller distance overall than adults, FG-7142 inhibited locomotor exploration to a similar degree in both groups. We conclude that FG-7142 exerts stress-like effects in postweanling rats and may be considered for use as a model of childhood stress.

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.

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.

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.

Participation of the lateral septal nuclei (LSN) in the antidepressant-like actions of progesterone in the forced swimming test (FST)

The possible participation of lateral septal nuclei (LSN) in the antidepressant-like actions of progesterone was evaluated. The effect of different concentrations of progesterone (0.001, 0.01 and 0.1 M) or saline solution injected directly into the LSN of ovariectomised rats was determined using the forced swimming test (FST). In addition, the temporal course of progesterone (0.1 M) antidepressant-like actions was compared with that of the classical antidepressant imipramine (0.1 M). Finally, in order to establish the possible participation of the GABA(A) receptor in the antidepressant-like action of progesterone, the effect of pre-treatment with the GABA(A) antagonist picrotoxin (0.125 mg/kg, i.p.) was evaluated. Intraseptally administered progesterone produced a concentration-dependent decrease in immobility behaviour but did not modify locomotor activity. These antidepressant-like actions lasted 4 h, while those of imipramine lasted 72 h. Finally, progesterone-induced anti-immobility effect could be blocked by the systemic injection of picrotoxin. Present results reveal that LSN play a role in the antidepressant-like actions of progesterone that appear to be mediated by the GABA(A) receptor.

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.

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.

Withdrawal properties of a neuroactive steroid: implications for GABA(A) receptor gene regulation in the brain and anxiety behavior

Early work in the field established that the 5 alpha-reduced metabolite of progesterone 3 alpha-OH-5 alpha-pregnan-20-one (allopregnanolone or 3 alpha,5 alpha-THP) is a potent positive modulator of the GABA(A) receptor (GABAR), the receptor mediating the effects of the primary inhibitory transmitter in the brain. This steroid acts in a manner similar to sedative drugs, such as the barbiturates, both in terms of potentiating GABA-induced inhibition in vitro and in behavioral assays, by reducing anxiety and seizure susceptibility. Because sedative compounds exhibit withdrawal properties that result in behavioral hyperexcitability, our laboratory has more recently investigated the effect of prolonged application and rapid removal (i.e. 'withdrawal') of this steroid, administered in vivo to female rats. Withdrawal from 3 alpha,5 alpha-THP produces a state of increased anxiety and lowered seizure threshold, similar to withdrawal from other GABA-modulatory drugs such as the benzodiazepines and alcohol. Hormone withdrawal also produced increases in the alpha 4-containing GABAR, an effect correlated with insensitivity of the GABAR to modulation by the benzodiazepine class of tranquilizers, as would normally occur under control conditions. In addition, changes in intrinsic channel properties, including a marked acceleration in the decay rate was also observed as a result of declining levels of 3 alpha,5 alpha-THP. Such a change would result in less inhibitory total current, and the resulting increase in neuronal excitability could then underlie the observed behavioral excitability following hormone withdrawal. These results suggest that actions of this steroid on a traditional transmitter receptor in the brain lead to alterations in GABAR subunit composition that result in changes in the intrinsic channel properties of the receptor and behavioral excitability. These results may have implications for endogenous fluctuations in this hormone which may accompany premenstrual dysphoric disorder.

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.

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.

The role of GABAergic neuroactive steroids in ethanol action, tolerance and dependence

This article reviews data on ethanol and neurosteroid interactions in the CNS. We discuss how GABAergic neurosteroids, including 3alpha,5alpha-TH PROG and 3alpha,5alpha-TH DOC, produced in response to systemic ethanol administration contribute to several of the effects of ethanol associated with modulation of GABA(A) receptors in rodents. There is an essential correlation between the time course of ethanol-induced 3alpha,5alpha-TH PROG production in the brain and specific behavioral and neural effects of ethanol. Furthermore, the anticonvulsant and inhibitory effects of ethanol on spontaneous neural activity were completely prevented by a key inhibitor of steroid biosynthesis. 3alpha,5alpha-TH PROG influences cognitive processing, spatial learning and memory and alters drinking behaviors in rats. Furthermore, ethanol induction of 3alpha,5alpha-TH PROG is diminished in tolerant and dependent animals. These effects are associated with increases in the sensitivity of GABA(A) receptors to neurosteroids and suggest an important role in ethanol withdrawal. Together, we suggest that 3alpha,5alpha-TH PROG and 3alpha,5alpha-TH DOC contribute to ethanol action and this interaction may represent a new mechanism of ethanol action. The identification of neurosteroid intermediaries involved in ethanol action may lead to important advances in the field and the development of novel therapeutics for alcoholism.

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.

Prevention of the stress-induced increase in frontal cortical dopamine efflux of freely moving rats by long-term treatment with antidepressant drugs

Use of antidepressant drugs in the treatment of anxiety disorders has recently increased due to the anxiolytic effect of some of these agents. Because dopaminergic transmission in the prefrontal cortex is sensitive to anxiogenic or stressful stimuli, the effects of two antidepressant drugs with different mechanisms of action, imipramine and mirtazapine, on the response of rat cortical dopaminergic neurons to stress were investigated. A 2-week (but not single dose) administration of imipramine (10 mg/kg, i.p., twice daily) or mirtazapine (10 mg/kg, i.p., once daily) reduced and completely antagonized, respectively, the increase in dopamine release in the prefrontal cortex elicited by footshock stress. Long-term administration of imipramine or mirtazapine had no marked effect on the stress-induced increases in the brain or plasma concentrations of neuroactive steroids or corticosterone. An attenuation of the response of mesocortical dopaminergic neurons to stress induced by long-term treatment with antidepressants might contribute to the anxiolytic effects of such drugs.

Short-term exposure to a neuroactive steroid increases alpha4 GABA(A) receptor subunit levels in association with increased anxiety in the female rat

Previous work from this laboratory has demonstrated that withdrawal from the neuroactive steroid 3alpha,5alpha-THP (3alpha-hydroxy-5alpha-pregnan-20-one) after 3-week exposure to its parent compound, progesterone (P), increases anxiety and produces benzodiazepine (BDZ) insensitivity in female rats. These events were linked to upregulation of the alpha4 subunit of the GABA(A) receptor (GABAR) in the hippocampus [Brain Res. 507 (1998) 91; Nature 392 (1998) 926; J. Neurosci. 18 (1998) 5275]. The present study investigates the role of shorter term hormone treatment on alpha4 subunit levels as well as relevant behavioral and pharmacological end-points related to GABAR function. After 2-3 days of P exposure, two- to threefold increases in alpha4 protein levels were observed, which declined to control values after 5-6 days of hormone exposure. This effect was due to the GABA-modulatory metabolite of P, 3alpha,5alpha-THP. alpha4 upregulation was inversely correlated with BDZ potentiation of GABA-gated current, assessed using whole cell patch clamp techniques on acutely isolated hippocampal pyramidal cells. A near total BDZ insensitivity was observed by 2-3 days of hormone exposure in association with the maximal increase in alpha4 levels. Up-regulation of the alpha4 GABAR subunit was also reflected by an increase in anxiety in the elevated plus maze. A significant decrease in open arm entries was observed after 72-h exposure to P, an effect which recovered by 6 days of P treatment. As demonstrated in vitro, alpha4 upregulation also resulted in a relative insensitivity to the anxiolytic actions of BDZ. These results suggest that short-term exposure to 3alpha,5alpha-THP produces changes in GABAR subunit composition similar to those that occur after chronic exposure and withdrawal from the steroid.

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.

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.

Neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one modulates electrophysiological and behavioral actions of ethanol

Neuroactive steroids are synthesized de novo in brain, yet their physiological significance remains elusive. We provide biochemical, electrophysiological, and behavioral evidence that several specific actions of alcohol (ethanol) are mediated by the neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP; allopregnanolone). Systemic alcohol administration elevates 3alpha, 5alpha-THP levels in the cerebral cortex to pharmacologically relevant concentrations. The elevation of 3alpha,5alpha-THP is dose- and time-dependent. Furthermore, there is a significant correlation between 3alpha,5alpha-THP levels in cerebral cortex and the hypnotic effect of ethanol. Blockade of de novo biosynthesis of 5alpha-reduced steroids using the 5alpha-reductase inhibitor finasteride prevents several effects of ethanol. Pretreatment with finasteride causes no changes in baseline bicuculline-induced seizure threshold but reverses the anticonvulsant effect of ethanol. Finasteride pretreatment also reverses ethanol inhibition of spontaneous neural activity in medial septal/diagonal band of Broca neurons while having no direct effect on spontaneous firing rates. Thus, elevation of 3alpha,5alpha-THP levels by acute ethanol administration represents a novel mechanism of ethanol action as well as an important modulatory role for neurosteroids in the CNS.

Neuroactive steroid 3alpha-hydroxy-5alpha-pregnan-20-one modulates electrophysiological and behavioral actions of ethanol

Neuroactive steroids are synthesized de novo in brain, yet their physiological significance remains elusive. We provide biochemical, electrophysiological, and behavioral evidence that several specific actions of alcohol (ethanol) are mediated by the neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP; allopregnanolone). Systemic alcohol administration elevates 3alpha, 5alpha-THP levels in the cerebral cortex to pharmacologically relevant concentrations. The elevation of 3alpha,5alpha-THP is dose- and time-dependent. Furthermore, there is a significant correlation between 3alpha,5alpha-THP levels in cerebral cortex and the hypnotic effect of ethanol. Blockade of de novo biosynthesis of 5alpha-reduced steroids using the 5alpha-reductase inhibitor finasteride prevents several effects of ethanol. Pretreatment with finasteride causes no changes in baseline bicuculline-induced seizure threshold but reverses the anticonvulsant effect of ethanol. Finasteride pretreatment also reverses ethanol inhibition of spontaneous neural activity in medial septal/diagonal band of Broca neurons while having no direct effect on spontaneous firing rates. Thus, elevation of 3alpha,5alpha-THP levels by acute ethanol administration represents a novel mechanism of ethanol action as well as an important modulatory role for neurosteroids in the CNS.

Anxiolytic effects of the neuroactive steroid pregnanolone (3 alpha-OH-5 beta-pregnan-20-one) after microinjection in the dorsal hippocampus and lateral septum

The anxiolytic effects of the neuroactive steroid, 3 alpha-OH-5 beta-pregnan-20-one (pregnanolone), were determined after injection into the dorsal hippocampus or lateral septum in adult male rats. An increase in the proportion of time spent on the open arms of the elevated plus-maze was found after 2.5 and 5 micrograms of pregnanolone in the hippocampus, but not in the lateral septum. Intrahippocampal injection of 2.5 micrograms of the 3 beta-epimer of pregnanolone did not affect behavior in the plus-maze; a higher dose of 5 micrograms produced an anxiogenic effect. In the shock-probe burying test latency to burying behavior was increased by intrahippocampal or intraseptal injection of 2.5 and 5 micrograms of pregnanolone; the duration of burying behavior was decreased by 0.5, 2.5 and 5 micrograms of pregnanolone injection in the dorsal hippocampus or lateral septum. The number of contacts with the shock probe was not affected by any dose of pregnanolone in either intracranial site of injection. The anxiolytic effects of intrahippocampal or intraseptal injection of pregnanolone were blocked by intracranial pretreatment with 20 ng of picrotoxin, but not by microinjection of 5 micrograms of flumazenil or 200 ng of PK 11195. Thus, inhibition of the hippocampus, mediated by the pregnanolone's action at the GABAA receptor, produces a general anxiolytic effect. However, similar inhibition in the lateral septum attenuates active avoidance of anxiogenic stimuli (i.e., decreased burying behavior), but not passive avoidance of aversive stimuli (i.e., exploration of open arms of the plus-maze and number of shocks in the probe burying test).

Ethanol markedly increases "GABAergic" neurosteroids in alcohol-preferring rats

Alcohol administration (1 g/kg, i.p.) increased the levels of the neurosteroids 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) and 3alpha,21-dihydroxy-5alpha-pregnan-20-one (allotetrahydrodeoxycorticosterone, THDOC) in the cerebral cortex and hippocampus both in alcohol-naive Sardinian alcohol-preferring (sP) and -non-preferring (sNP) rats (two rat lines selectively bred for alcohol preference and non-preference, respectively). However, the increase reached several fold higher levels in sP than in sNP rats (6-24 vs. 2-11 fold the basal levels, respectively). Since the two neurosteroids are the most potent endogenous positive modulators of GABA(A) receptors and elicit anxiolytic and rewarding effects, while voluntary alcohol consumption produces anxiolytic and rewarding effects in sP but not in sNP rats, the results suggest that the neurosteroids may play a role in the anxiolytic and rewarding effects of alcohol in sP rats.

Neuroactive neurosteroids as endogenous effectors for the sigma1 (sigma1) receptor: pharmacological evidence and therapeutic opportunities

Neuroactive neurosteroids, including progesterone, allopregnanolone, pregnenolone and dehydroepiandrosterone, represent steroid hormones synthesized de novo in the brain and acting locally on nervous cells. Neurosteroids modulate several neurotransmitter systems such as gamma-aminobutyric acid type A (GABA(A)), N-methyl-D-aspartate (NMDA) and acetylcholine receptors. As physiologic consequences, they are involved in neuronal plasticity, learning and memory processes, aggression and epilepsy, and they modulate the responses to stress, anxiety and depression. The sigma1-receptor protein was recently purified and its cDNA was cloned in several species. The amino-acid sequences are structurally unrelated to known mammalian proteins, but shared homology with a fungal sterol C8-C7 isomerase. The sigma1-receptor ligands exert a potent neuromodulation on excitatory neurotransmitter systems, including the glutamate and cholinergic systems. Consequently, selective sigma1 agonists show neuroprotective properties and beneficial effects in memory processes, stress and depression. The evidence of a direct interaction between neurosteroids and sigma1 receptors was first suggested by the ability of several steroids to inhibit the binding of sigma1-receptor radioligands in vitro and in vivo. A crossed pharmacology between neurosteroids and sigma1-receptor ligands was described in several physiological tests and behavioral responses. This review will detail the recent evidence for a common mechanism of action between neurosteroids and sigma1-receptor ligands and focus on the potential therapeutic interests of such interaction in the physiopathology of learning and memory impairments, stress, depression and neuroprotection.

Permissive role of brain allopregnanolone content in the regulation of pentobarbital-induced righting reflex loss

Allopregnanolone [3alpha-hydroxy-5alpha-pregnan-20-one] (ALLO), a potent neurosteroid that positively modulates gamma-aminobutyric acid (GABA) action at various GABA(A) receptor subtypes is synthesized in nanomolar concentrations and stored non uniformly in various brain structures of mammals. We have measured brain ALLO content and its precursors by negative ion chemical ionization-mass-spectrometry after purification and separation of the different steroids with HPLC and gas chromatography. Our procedure measures steroids in the femtomolar range with structural information and unsurpassed selectivity. We were able to establish an association between the decrease in content of ALLO in mouse brain cortex elicited by either long-lasting social isolation or by the administration of 17beta-17 [bis (1-methylethyl) amino carbonyl] androstane-3,5-dilene-3-carboxylic acid (SKF 105111). an inhibitor of Types I and II 5alpha reductases, and the shortening of the righting reflex loss elicited by pentobarbital (PBT). SKF 105111 added to cortical brain slices in concentrations up to 10(-5) M failed per se to alter GABAergic currents or their potentiation by PTB recorded from pyramidal neurons. Fluoxetine (1.45 or 2.9 micromol/kg i.p.) doses that fail to change the PTB-induced loss of righting reflex and the level of brain ALLO in group-housed mice normalized both parameters in socially-isolated mice. In addition, we could detect both fluoxetine actions in socially isolated mice pretreated with doses of p-chlorophenylalanine (1.2 mmol/kg i.p. at 72, 48, and 24 h) that substantially inhibit brain serotonin 5HT synthesis as shown by an 80% drop of brain 5HT content. These studies for the first time have provided evidence suggesting that the endogenous cortical stores of ALLO physiologically upregulate GABAergic tone and by such a mechanism play a permissive or facilitatory role on the PTB-induced loss of the righting reflex. In the absence of such a permissive physiological influence by endogenous ALLO, the righting reflex inhibition by PTB is down regulated.

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.

2-Phenyl-imidazo[1,2-a]pyridine derivatives as ligands for peripheral benzodiazepine receptors: stimulation of neurosteroid synthesis and anticonflict action in rats

Selective activation of peripheral benzodiazepine receptors (PBRs) in adrenal cells and brain oligodendrocytes promotes steroidogenesis. Three 2-phenyl-imidazo[1,2-a]pyridine derivatives (CB 34, CB 50 and CB 54) have now been investigated with regard to their selectivity for PBRs and their ability to stimulate central and peripheral steroidogenesis in rats. The three CB compounds (10(-10)-10(-4) M) potently inhibited the binding of the PBR ligand [3H]-PK 11195 to brain and ovary membranes in vitro, without substantially affecting [3H]-flunitrazepam binding to central benzodiazepine receptors. These compounds (10(-7)-10(-4) M) also had little or no marked effects on GABA-evoked Cl- currents in voltage-clamped Xenopus oocytes expressing human alpha1beta2gamma2S GABA(A) receptors. In addition, they failed to affect ligands binding to GABA(B), D1/D2 dopamine, muscarinic acetylcholine, N-methyl-D-aspartic acid and opiate receptors. Intraperitoneal administration of CB compounds (3-50 mg kg(-1)) induced a dose-dependent increase in the concentrations of neuroactive steroids in plasma and brain. The brain concentrations of pregnenolone, progesterone, allopregnanolone and allotetrahydrodeoxycorticosterone (THDOC) showed maximal increases in 96+/-3, 126+/-14, 110+/-12 and 70+/-13% above control, respectively, 30 to 60 min after injection of CB 34 (25 mg kg(-1)). CB 34 also increased the brain concentrations of neuroactive steroids in adrenalectomized-orchiectomized rats, although to a lesser extent than in sham-operated animals, suggesting that CB compounds stimulate brain steroidogenesis independently of their effects on peripheral tissues. The increase in brain and plasma neurosteroid content induced by CB 34 was associated with a marked anticonflict effect in the Vogel test. Our results indicate that the three CB compounds tested are specific and potent agonists at peripheral benzodiazepine receptors, and that they stimulate steroidogenesis in both the brain and periphery.

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.

Neuroactive steroids: potential therapeutic use in neurological and psychiatric disorders

Neuroactive steroids are a novel class of positive allosteric modulators of the GABAA receptor. Although neuroactive steroids are endogenous neuronal modulators, synthetic entities with improved oral bioavailability have recently been developed. These compounds demonstrate efficacy as anticonvulsants against a range of convulsant stimuli and demonstrate anti-epileptogenic activity in a kindling model of epilepsy. Efficacy has also been reported in preclinical models of anxiety, insomnia, migraine and drug dependence. Clinical evidence to date is generally supportive of these findings and indicates that neuroactive steroids are generally well tolerated. Taken as a whole, current data suggest that neuroactive steroids could have a future role in clinical practice. In this article, Maciej Gasior, Richard Carter and Jeffrey Witkin review preclinical and clinical evidence that forms the basis for predicting the potential therapeutic application of neuroactive steroids.

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.

High levels of serum allopregnanolone in women with premature ovarian failure

The endocrine characteristics of patients with premature ovarian failure (POF) have not been fully elucidated. The aim of the present study was to evaluate whether steroidogenic activity in women with POF is different with respect to fertile and postmenopausal subjects. In particular, circulating levels of allopregnanolone, a neuroactive steroid involved in modulation of reproductive function in rats, have been evaluated and correlated with serum levels of delta 4 precursor (dehydroepiandrosterone sulfate (DHEAS)), delta 5 intermediates (androstenedione, 17-hydroxyprogesterone (17-OHP), progesterone) and final products (estradiol and testosterone) of androgens. Levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) and sex hormone binding globulin (SHBG) were also determined. In all cases specific radioimmunological assays were used. Women with POF showed statistically significantly lower concentrations of 17-OHP, androstenedione and testosterone when compared to fertile controls, while no differences were found between women with POF and postmenopausal women. Serum DHEAS levels were similar in POF patients and in fertile controls and higher with respect to postmenopausal women. Serum allopregnanolone levels were significantly higher in women with POF than in postmenopausal and in fertile women. A significant inverse correlation between allopregnanolone levels and menopausal age in patients with POF was observed while no significant correlation was found between allopregnanolone and progesterone, androstenedione, 17-OHP and testosterone levels. In conclusion, allopregnanolone is scarcely influenced by the reduction of ovarian and adrenal activity observed in POF.

Molecular and functional adaptation of the GABA(A) receptor complex during pregnancy and after delivery in the rat brain

The abundance of gamma-aminobutyric acid receptor type A (GABAA receptor) subunit mRNAs and polypeptides as well as muscimol-stimulated 36Cl- uptake were measured in rat cerebral cortex or hippocampus at various times during pregnancy and after delivery. RNase protection assays revealed that the amount of the gamma2L subunit mRNA decreased progressively during pregnancy, in the cerebral cortex and hippocampus, and then returned to control values around the time of delivery. A similar pattern was observed for the alpha5 subunit mRNA in the cerebral cortex, whereas no significant changes were apparent for alpha1, alpha2, alpha3, alpha4, beta1, beta2, beta3 and gamma2S subunit mRNAs. The amounts of gamma2 and alpha1 proteins in the cerebral cortex were measured by immunoblot analysis; whereas the abundance of gamma2 protein decreased during pregnancy, no change was detected in the amount of alpha1 protein. Evaluation for functional significance of the down-regulated gamma2 and alpha5 subunit was made by determining the GABAA receptor function assessed by measurement of muscimol-stimulated 36Cl- uptake in cerebral cortical membrane vesicles. Muscimol-induced 36Cl- uptake was markedly reduced during of pregnancy compared with rats in oestrus. At this same time, the potentiating effects of diazepam and allopregnanolone on muscimol stimulation of 36Cl- uptake also were reduced. In contrast, the effects of muscimol, allopregnanolone and diazepam were significantly increased, relative to animals in oestrus, after delivery.

Influence of gender on chronic ethanol-induced alterations in GABAA receptors in rats

Ethanol dependence, arising from chronic ethanol exposure, is associated with neuroadaptations of GABAA receptors, evidenced by alterations in various behaviors, receptor responsiveness and subunit gene expression. The present studies explored the effects of ethanol dependence in female rats for comparison with previous studies in our laboratory using male rats. We found that ethanol dependence resulted in differential effects on GABAA receptor gene expression in female rat cerebral cortex compared to ethanol dependent male rats. Notably, chronic ethanol consumption did not change GABAA receptor alpha 1 subunit peptide levels in ethanol dependent female rat cortex, in contrast to previously observed decreases in alpha 1 subunit expression in ethanol dependent male rat cortex. The effects of ethanol dependence on additional GABAA receptor subunit peptide levels (alpha 4, beta 2/3 and gamma 2) were similar, but not identical, between female and male rat cortex. When directly compared within the experiment, male and female rats had similar baseline bicuculline seizure thresholds and displayed a similar increase in seizure susceptibility during ethanol withdrawal. Ethanol withdrawn female rats were cross tolerant to the anticonvulsant effects of diazepam, similar to the findings in ethanol withdrawn male rats. Ethanol withdrawn female rats showed a dose-dependent enhancement of the anticonvulsant effect of the neuroactive steroid, THDOC (3 alpha,21-dihydroxy-5 alpha-pregnan-20-one) compared to control animals. This finding is similar to previous observations of increased sensitivity to the anticonvulsant effect of 3 alpha,5 alpha-THP (3 alpha-hydroxy-5 alpha-pregnan-20-one) in ethanol withdrawn male and female rats. In addition, low dose administration of THDOC elevated seizure thresholds in ethanol withdrawn female but not male rats, suggesting that ethanol withdrawn female rats were more responsive to the anticonvulsant effects of this neurosteroid than were ethanol withdrawn male rats. These findings show that gender impacts on adaptations in GABAA receptors elicited by ethanol dependence. However, the physiological outcomes of the differential alterations are not clear. Taken together, these studies suggest that additional mechanisms, beyond effects on GABAA receptor gene expression are involved in the mediation of ethanol dependence and withdrawal.

Circulating levels of allopregnanolone in humans: gender, age, and endocrine influences

Allopregnanolone is a neuroactive steroid involved in modulating behavioral functions, stress, and neuroendocrine axes in rats. Changes in plasma allopregnanolone levels throughout the menstrual cycle have been reported in healthy women, but there exists no information on the possible gender or age-related changes or on the source(s) of circulating allopregnanolone. The aim of the present study was to assess serum allopregnanolone concentrations according to gender, menstrual cycle, age, and menopause in normal men and women; serum progesterone (P) and dehydroepiandrosterone (DHEA) levels were evaluated in the same specimens. In addition, the possible source of circulating allopregnanolone in fertile women was investigated by using stimulatory and inhibitory endocrine tests acting on the ovary and/or adrenal cortex. The present study included 189 fertile women, 112 postmenopausal women, and 46 men. Serum steroid levels were determined after extraction, using specific RIAs. Allopregnanolone levels in fertile women in the follicular phase were similar to those in age-matched men; no significant difference was found between fertile women in the follicular phase and postmenopausal women. The highest levels were found in fertile women during the luteal phase (P < 0.01). An age-related decrease was observed in men (P < 0.01), but not in women. P and DHEA levels were significantly higher in women than in men and were higher in fertile women than in postmenopausal women (P < 0.01). Both P and DHEA showed an age-related decrease in men and women (P < 0.01). Serum allopregnanolone and P, but not DHEA, significantly increased in response to a GnRH test, whereas corticotropin-releasing factor and ACTH tests elicited a significant increase in allopregnanolone, P, and DHEA levels (P < 0.01). The suppression of adrenal steroidogenesis by dexamethasone markedly reduced both allopregnanolone and DHEA serum levels (P < 0.01). In conclusion, the present study demonstrated that although men show an age-related decrease, serum allopregnanolone levels in women do not change with age and correlate with P levels during the menstrual cycle and in response to endocrine tests. Ovary and adrenal cortex may be major sources of circulating allopregnanolone in fertile women.