Pubertal hormones increase hippocampal expression of α4ßδ GABAA receptors.

CA1 hippocampal expression of α4ßδ GABAA receptors (GABARs) increases at the onset of puberty in female mice, an effect dependent upon the decline in hippocampal levels of the neurosteroid THP (3α-OH-5α-pregnan-20-one) which occurs at this time. The present study further characterized the mechanisms underlying α4ßδ expression, assessed in vivo. Blockade of pubertal levels of 17ß-estradiol (E2) (formestane, 0.5 mg/kg, i.p. 3 d) reduced α4 and δ expression by 75-80% (P < 0.05) in CA1 hippocampus of female mice, assessed using Western blot techniques. Conversely, E2 administration increased α4 and δ expression by 50-100% in adults, an effect enhanced by more than 2-fold by concomitant administration of the 5α-reductase blocker finasteride (50 mg/kg, i.p., 3d, P < 0.05), suggesting that both declining THP levels and increasing E2 levels before puberty trigger α4ßδ expression. This effect was blocked by ICI 182,780 (20 mg/kg, s.c., 3 d), a selective blocker of E2 receptor-α (ER-α). These results suggest that both the rise in circulating levels of E2 and the decline in hippocampal THP levels at the onset of puberty trigger maximal levels of α4ßδ expression in the CA1 hippocampus.

Zinc reduces antiseizure activity of neurosteroids by selective blockade of extrasynaptic GABA-A receptor-mediated tonic inhibition in the hippocampus.

Zinc is an abundant trace metal in the hippocampus nerve terminals. Previous studies demonstrate the ability of zinc to selectively block neurosteroid-sensitive, extrasynaptic GABA-A receptors in the hippocampus (Carver et al, 2016). Here we report that zinc prevents the seizure protective effects of the synthetic neurosteroid ganaxolone (GX) in an experimental model of epilepsy. GABA-gated and tonic currents were recorded from dissociated dentate gyrus granule cells (DGGCs), CA1 pyramidal cells (CA1PCs), and hippocampal slices from adult mice. Antiseizure effects of GX and the reversal of these effects by zinc were evaluated in fully-kindled mice expressing generalized (stage 5) seizures. In electrophysiological studies, zinc blocked the GABA-evoked and GX-potentiated GABA-gated chloride currents in DGGCs and CA1PCs in a concentration-dependent fashion similar to the competitive GABA-A receptor antagonists bicuculline and gabazine. Zinc completely blocked GX potentiation of extrasynaptic tonic currents, but not synaptic phasic currents. In hippocampus kindling studies, systemic administration of GX produced a dose-dependent suppression of behavioral and electrographic seizures in fully-kindled mice with complete seizure protection at the 10 mg/kg dose. However, the antiseizure effects of GX were significantly prevented by intrahippocampal administration of zinc (ED50, 150 µM). The zinc antagonistic response was reversible as animals responded normally to GX administration 24 h post-zinc blockade. These results demonstrate that zinc reduces the antiseizure effects of GX by selectively blocking extrasynaptic δGABA-A receptors in the hippocampus. These pharmacodynamic interactions have clinical implications in neurosteroid therapy for brain conditions associated with zinc fluctuations.

GR3027 reversal of neurosteroid-induced, GABA-A receptor-mediated inhibition of human brain function: an allopregnanolone challenge study.

RATIONALE: GR3027 is a novel small molecule GABA-A receptor-modulating steroid antagonist, which in non-clinical studies has shown promise for treatment of human disorders due to allosteric over-activation of GABA-A receptors by neurosteroids, such as allopregnanolone. We here studied its safety, pharmacokinetics, and ability to inhibit allopregnanolone effects in humans. METHODS: Safety and pharmacokinetics were studied in healthy adult males receiving ascending single or multiple oral GR3027 vs. placebo. GR3027-mediated reversal of allopregnanolone effect on maximal saccadic eye velocity (SEV), and self-rated somnolence was studied in a double-blind, placebo-controlled, three-part cross-over study in which 3 or 30 mg oral GR3027 preceded 0.05 mg/kg of i.v. allopregnanolone. RESULTS: GR3027 was well tolerated, adverse events were generally mild and transient, and no dose-limiting toxicity or grade 3 adverse events were observed up to the highest single (200 mg) or multiple (100 mg every 12 h for 5 days) doses. The maximum concentration (Cmax) and systemic exposure (area under the plasma concentration-time curve from dose extrapolated to infinity [AUC0-∞] and/or AUC during the dosing interval [AUCτ]) varied linearly with dose; with dose-dependent accumulation ratios of 1.3-1.6. Allopregnanolone decreased SEV and induced somnolence in most, but not all subjects. By predefined analyses, 30 mg GR3027 significantly inhibited allopregnanolone-induced decrease in SEV (p = 0.03); 3 and 30 mg GR3027 non-significantly inhibited allopregnanolone-induced sedation. By post hoc analyses restricted to subjects with allopregnanolone-induced changes and the time period over which they occurred, GR3027 dose dependently inhibited allopregnanolone-induced decrease in SEV (p = 0.04 at 30 mg, non-significant at 3 mg) and allopregnanolone-induced sedation (p = 0.01/0.05 at 3/30 mg doses). CONCLUSION: Oral GR3027 mitigates inhibition of brain function induced by allopregnanolone at doses which are clinically well tolerated and associated with linear pharmacokinetics.

Isoallopregnanolone antagonize allopregnanolone-induced effects on saccadic eye velocity and self-reported sedation in humans.

Allopregnanolone (AP) is an endogenous neurosteroid. It modulates the effect of γ-amino-butyric acid (GABA) on the GABA type A (GABAA) receptor, which leads to increased receptor activity. Since the GABA-system is mainly inhibitory, increased AP activity leads to modulation of neuronal activity. In vitro studies of GABAA receptor activity and in vivo animal studies of sedation have shown that AP-induced effects can be inhibited by another endogenous steroid, namely isoallopregnanolone (ISO). In this study we investigated if ISO can antagonize AP-induced effects in healthy female volunteers, via measurements of saccadic eye velocity (SEV) and self-rated sedation. With a single-blind cross-over design, 12 women were studied on three separate occasions; given AP alone or AP in combination with one of two ISO doses. Congruent with previous reports, AP administration decreased SEV and induced sedation and these effects were diminished by simultaneous ISO administration. Also, the ISO effect modulation was seemingly stronger for SEV than for sedation. These effects were observed already at an ISO dose exposure that was approximately half of that of AP. In conclusion, ISO antagonized AP-induced decrease in SEV and self-reported sedation, probably in a non-competitive manner.

Neurosteroids are endogenous neuroprotectants in an ex vivo glaucoma model.

PURPOSE: Allopregnanolone is a neurosteroid and powerful modulator of neuronal excitability. The neuroprotective effects of allopregnanolone involve potentiation of γ-aminobutyric acid (GABA) inhibitory responses. Although glutamate excitotoxicity contributes to ganglion cell death in glaucoma, the role of GABA in glaucoma remains uncertain. The aim of this study was to determine whether allopregnanolone synthesis is induced by high pressure in the retina and whether allopregnanolone modulates pressure-mediated toxicity. METHODS: Ex vivo rat retinas were exposed to hydrostatic pressure (10, 35, and 75 mm Hg) for 24 hours. Endogenous allopregnanolone production was determined by liquid chromatography and tandem mass spectrometry (LC-MS/MS) and immunochemistry. We also examined the effects of allopregnanolone, finasteride, and dutasteride (inhibitors of 5α-reductase), picrotoxin (a GABA(A) receptor antagonist), and D-2-amino-5-phosphonovalerate (APV, a broad-spectrum N-methyl-D-aspartate receptor [NMDAR] antagonist). RESULTS: Pressure loading at 75 mm Hg significantly increased allopregnanolone levels as measured by LC-MS/MS. Elevated hydrostatic pressure also increased neurosteroid immunofluorescence, especially in the ganglion cell layer and inner nuclear layers. Staining was negligible at lower pressures. Enhanced allopregnanolone levels and immunostaining were substantially blocked by finasteride, but more effectively inhibited by dutasteride and APV. Administration of exogenous allopregnanolone suppressed pressure-induced axonal swelling in a concentration-dependent manner, while picrotoxin overcame these neuroprotective effects. CONCLUSIONS: These results indicate that the synthesis of allopregnanolone is enhanced mainly via NMDARs in the pressure-loaded retina, and that allopregnanolone diminishes pressure-mediated retinal degeneration via GABAA receptors. Allopregnanolone and other related neurosteroids may serve as potential novel therapeutic targets for the prevention of pressure-induced retinal damage in glaucoma.

Decreased allopregnanolone induced by hormonal contraceptives is associated with a reduction in social behavior and sexual motivation in female rats.

RATIONALE: Allopregnanolone is a neurosteroid involved in depression, memory, social, and sexual behavior. We have previously demonstrated that treatment with a combination of ethinylestradiol (EE) and levonorgestrel (LNG), two compounds frequently used in hormonal contraception, decreased brain allopregnanolone concentrations. These changes may contribute to some of the emotional and sexual disorders observed in hormonal contraceptive users. OBJECTIVES: We thus examined whether the reduction in allopregnanolone concentrations induced by long-term EE/LNG administration was associated with altered emotional, learning, social, and sexual behaviors. METHODS: Rats were orally treated with a combination of EE (0.030 mg) and LNG (0.125 mg) once a day for 4 weeks and were subjected to behavioral tests 24 h after the last administration. RESULTS: EE/LNG treatment reduced immobility behavior in the forced swim test, without affecting sucrose preference and spatial learning and memory. In the resident-intruder test, EE/LNG-treated rats displayed a decrease in dominant behaviors associated with a reduction in social investigation. In the paced mating test, EE/LNG treated rats showed a reduction in proceptive behaviors, while the lordosis quotient was not affected. Progesterone, but not estradiol, administration to EE/LNG-treated rats increased sexual activity and cerebrocortical allopregnanolone concentrations. Prior administration of finasteride decreased allopregnanolone concentrations and abolished the increase in proceptivity induced by progesterone administration. CONCLUSIONS: The decrease in brain allopregnanolone concentrations induced by EE/LNG treatment is associated with a reduction in social behavior and sexual motivation in female rats. These results might be relevant to the side effects sometimes exhibited by women taking hormonal contraceptives.

Neurosteroid allopregnanolone attenuates development of nicotine withdrawal behavior in mice.

Avoidance of the nicotine withdrawal syndrome as well as the positive subjective effects of nicotine is the major predisposing factor to motivate nicotine abuse. However, its underlying neurobehavioral mechanisms remain perplexing. In the present study, we investigated the influence of the neurosteroid allopregnanolone (ALLO; 0.5-2mg/kg) on the development of nicotine withdrawal in mice. Chronic nicotine injections (2mg/kg, four times daily, 10 days) followed by its withdrawal, elicited severe somatic signs, anxiety and marked reduction in locomotion. However, these withdrawal signs were not evident in animals pretreated with ALLO or progesterone (Day 8-10) daily before 1st injection of nicotine. This effect of neurosteroid on the nicotine withdrawal signs was reversed by indomethacin and finasteride the inhibitors of neurosteroid biosynthesis. On the contrary, single or repeated dose administration of ALLO or progesterone during nicotine withdrawal (Day 11) did not affect the expression of nicotine withdrawal signs. Thus, compounds that modulate endogenous neurosteroid ALLO are likely to have therapeutic potential for treating various aspects of nicotine dependence and withdrawal.

RU486 blocks effects of allopregnanolone on the response to restraint stress.

These experiments were designed to provide information about the potential involvement of progesterone receptors in the ability of allopregnanolone (3α-hydroxy-5α-pregnan-20-one) to reduce the lordosis-inhibiting effects of restraint stress. Ovariectomized Fischer rats were hormonally primed with 10 µg estradiol benzoate and 4 mg/kg allopregnanolone or vehicle. One hour before allopregnanolone, rats were injected with the progesterone receptor antagonist, RU486 (11ß-(4-dimethylamino)phenyl-17ß-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one), or vehicle. Four hours after allopregnanolone or vehicle, sexual behavior was examined before and after a 5-min restraint stress. Lordosis behavior of rats primed only with estradiol benzoate declined after the 5 min of restraint while allopregnanolone prevented this decline. RU486 attenuated the ability of allopregnanolone to prevent the restraint-induced decline in lordosis behavior. These findings are consistent with earlier suggestions that progesterone receptors are involved in allopregnanolone's ability to reduce the effects of restraint stress.

Sex-dependent effect of a low neurosteroid environment and intrauterine growth restriction on foetal guinea pig brain development.

Progesterone and its neuroactive metabolite, allopregnanolone, are present in high concentrations during pregnancy, but drop significantly following birth. Allopregnanolone influences foetal arousal and enhances cognitive and behavioural recovery following traumatic brain injury. Inhibition of allopregnanolone synthesis increases cell death in foetal animal brains with experimental hypoxia. We hypothesised that complications during pregnancy, such as early or preterm loss of placental steroids and intrauterine growth restriction (IUGR), would disrupt the foetal neurosteroid system, contributing to poor neurodevelopmental outcomes. This study aimed to investigate the effects of chronic inhibition of allopregnanolone synthesis before term and IUGR on developmental processes in the foetal brain. Guinea pig foetuses were experimentally growth restricted at mid-gestation and treated with finasteride, an inhibitor of allopregnanolone synthesis. Finasteride treatment reduced foetal brain allopregnanolone concentrations by up to 75% and was associated with a reduction in myelin basic protein (MBP) (P = 0.001) and an increase in glial fibrillary acidic protein expression in the subcortical white matter brain region (P < 0.001). IUGR resulted in decreased MBP expression (P < 0.01) and was associated with a reduction in the expression of steroidogenic enzyme 5α-reductase (5αR) type 2 in the foetal brain (P = 0.061). Brain levels of 5αR1 were higher in male foetuses (P = 0.008). Both IUGR and reduced foetal brain concentrations of allopregnanolone were associated with altered expression of myelination and glial cell markers within the developing foetal brain. The potential role of neurosteroids in protecting and regulating neurodevelopmental processes in the foetal brain may provide new directions for treatment of neurodevelopmental disorders in infants who are exposed to perinatal insults and pathologies.

Dopamine is involved in the antidepressant-like effect of allopregnanolone in the forced swimming test in female rats.

Evidence from both animal and human studies suggests a role for dopamine in the therapeutic effect of antidepressant drugs. Consistently, dopamine receptor antagonists antagonize the effect of antidepressant drugs in different experimental models of depression. Neurosteroids, and in particular allopregnanolone, seem to be involved both in the pathophysiology of depression and in the mechanism of action of antidepressant drugs, and their role seems to be particularly important in the understanding of mood disturbances related to the different phases of the reproductive life in women. The aim of this study was to investigate the possible role of dopamine on the antidepressant-like effect of allopregnanolone in a model of depression. Thus, we examined (i) the behaviour of female Sprague-Dawley rats in the forced swimming test during estrus and diestrus and their response to allopregnanolone treatment (0.5, 1 and 2 mg/kg), and (ii) the effect of the dopamine D1-like and D2-like receptor antagonists SCH 23390 (0.01 and 0.025 mg/kg) and raclopride (0.05 and 0.2 mg/kg) on the antidepressant-like effect of allopregnanolone (2 mg/kg) in the same experimental model. We failed to observe differences in depressive-like behaviour between estrous phases, and allopregnanolone administration in both estrus and diestrus resulted in an antidepressant-like effect consisting in an increase of swimming behaviour. The allopregnanolone effect was unaffected by a dose of the dopamine D1-like receptor antagonist SCH 23390 displaying a marked inhibitory effect on basal activity, while it was turned into a potentiation of the depressive-like behaviour of the forced swimming condition by treatment with the higher dose of raclopride. The present results indicate an involvement of dopamine transmission in the allopregnanolone antidepressant-like effect in the forced swimming model of depression, and suggest that this effect depends mainly on stimulation of dopamine D2-like receptors.

Increasing 3alpha,5alpha-THP following inhibition of neurosteroid biosynthesis in the ventral tegmental area reinstates anti-anxiety, social, and sexual behavior of naturally receptive rats.

The progesterone metabolite and neurosteroid, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), has actions in the midbrain ventral tegmental area (VTA) to modulate lordosis, but its effects on other reproductively relevant behaviors are not well understood. Effects on exploration, anxiety, and social behavior resulting from inhibition of 3alpha,5alpha-THP formation, as well as 3alpha,5alpha-THP enhancement, were investigated in the midbrain VTA. Naturally sexually receptive, female rats (n=8-10/group) received infusions aimed at the midbrain VTA of vehicle, PK11195 (an inhibitor of neurosteroidogenesis), and/or indomethacin (an inhibitor of 3alpha,5alpha-THP formation from prohormones), and were subsequently infused with vehicle or FGIN 1-27 (a neurosteroidogenesis enhancer). The rats were then assessed in a behavioral battery that examined exploration (open field), anxiety (elevated plus maze), social (social interaction), and sexual (paced mating) behavior. Inhibition of 3alpha,5alpha-THP formation decreased exploratory, anti-anxiety, social, and sexual behavior, as well as midbrain 3alpha,5alpha-THP levels. Infusions of FGIN 1-27 following 3alpha,5alpha-THP inhibition restored these behaviors and midbrain 3alpha,5alpha-THP levels to those commensurate with control rats that had not been administered inhibitors. These findings suggest that 3alpha,5alpha-THP formation in the midbrain VTA may influence appetitive, as well as consummatory, aspects of mating behavior.

Ethanol intake patterns in female mice: influence of allopregnanolone and the inhibition of its synthesis.

The neurosteroid allopregnanolone (ALLO) is a positive modulator of GABA(A) receptors that exhibits a psychopharmacological profile similar to ethanol (i.e., anxiolytic, sedative-hypnotic). Based on research suggesting that manipulation of ALLO levels altered ethanol self-administration in male rodents, the current studies determined whether exogenous ALLO administration or the inhibition of its synthesis in vivo modulated ethanol intake patterns in female C57BL/6J mice. Lickometer circuits collected temporal lick records of ethanol (10%, v/v) and water consumption during daily 2h limited access sessions. Following the establishment of stable ethanol intake, studies examined the effect of an acute ALLO challenge (3.2-24.0 mg/kg) or a 7-day blockade of ALLO production with finasteride (FIN; 50 or 100 mg/kg) on ethanol intake in a within-subjects design. In contrast to results in male mice, ethanol dose (g/kg), ethanol preference and most of the bout parameters were unaltered by ALLO pretreatment in female mice. Ethanol intake in females also was recalcitrant to 7-day treatment with 50 mg/kg FIN, whereas 100 mg/kg FIN significantly reduced the ethanol dose consumed by 35%. The FIN-attenuated ethanol intake was attributable to a significant decrease in bout frequency (up to 45%), with lick patterns indicating reduced maintenance of consumption throughout the 2-h session. FIN also produced a dose-dependent decrease in brain ALLO levels. In conjunction with data in male mice, the present findings indicate that there are sex differences in the physiological regulation of ethanol intake patterns by GABAergic neurosteroids.

Isoallopregnanolone; an antagonist to the anaesthetic effect of allopregnanolone in male rats.

The interaction of isoallopregnanolone (3 beta-OH-5 alpha-pregnan-20-one) on allopregnanolone (3 alpha-OH-5 alpha-pregnan-20-one) induced anaesthesia was studied in male rats using burst suppression of 1 s ("silent second") with an electroencephalographic-threshold method. The i.v. administration of isoallopregnanolone was varied in relation to induction of "silent second". Pre-treatment with isoallopregnanolone (12.5-50 mg/kg iv) 2 min prior to the threshold test gave an increase in the threshold dose of allopregnanolone (ANOVA df(3;36), F=13.61, P<0.001), which was dose dependent (r=0.73, b [slope]=0.08, df=38, P<0.001). After isoallopregnanolone pre-treatment, but not in the controls, anaesthesia time was positively related to the dose of allopregnanolone (r=0.52, b=1.72, df=28, P<0.01). Anaesthesia times were not influenced by a corresponding administration of isoallopregnanolone immediately after induction of "silent second". When allopregnanolone and isoallopregnanolone were infused together at molar ratios of 1:1, 1:1.23, 1:1.43, a linear increase of the threshold doses of allopregnanolone was seen in relation to the dose of isoallopregnanolone (r=0.86, b=0.40, df=8, P<0.01). Thus isoallopregnanolone can antagonise the anaesthetic action of allopregnanolone.

Treatment with and withdrawal from finasteride alter ethanol intake patterns in male C57BL/6J mice: potential role of endogenous neurosteroids?

Exogenous administration of the gamma-aminobutyric acid (GABA)-ergic neurosteroid allopregnanolone (ALLO) can increase ethanol intake in rats and mice. To determine the contribution of endogenous neurosteroids (i.e., ALLO and related pregnane steroids) in the regulation of established ethanol consumption patterns in male C57BL/6J (B6) mice, the 5alpha-reductase (5alpha-R) enzyme inhibitor, finasteride (FIN), was chronically administered and then subsequently withdrawn. Mice were provided daily 2-h limited access to a 10% vol/vol ethanol solution (10E) and water in lickometer chambers during the dark phase. Following the establishment of stable 10E intake patterns, mice were injected intraperitoneally with either vehicle (20% wt/vol 2-hydroxypropyl-beta-cyclodextrin; n=8) or FIN (50 mg/kg; n=16) for 7 days. Effects of withdrawal from FIN treatment were subsequently assessed for an additional 7 days. Ethanol intakes were significantly decreased with acute FIN treatment (days 1-3) and during early withdrawal (days 1-3). Acute FIN treatment was also associated with an extended latency to first bout, reduced first bout size, and greatly attenuated sipper contact count during the initial 20-min interval of 10E access. These findings collectively indicated that acute FIN treatment markedly attenuated the initiation of 10E consumption during the limited access sessions. The influence of FIN on 10E intake patterns was largely dissipated with chronic treatment, suggesting that compensatory changes in neurosteroid modulation of inhibitory tone may have occurred. Thus, acute FIN treatment modulated ethanol intake patterns in a manner opposite to that previously demonstrated for a physiologically relevant, exogenous ALLO dose, consistent with the ability of a alpha-R inhibitor to block ALLO biosynthesis. Manipulation of endogenous neurosteroid activity via biosynthetic enzyme inhibition or antagonism of steroid binding to the GABA type A receptor may prove to be a beneficial pharmacotherapeutic strategy in the intervention of alcohol abuse and alcoholism.

Neurosteroids alter gamma-aminobutyric acid postsynaptic currents in gonadotropin-releasing hormone neurons: a possible mechanism for direct steroidal control.

Pulsatile GnRH release is required for fertility and is regulated by steroid feedback. Whether or not steroids or their metabolites act directly on GnRH neurons is not well established. In some neurons, steroid metabolites known as neurosteroids modulate the function of the GABAA receptor. Specifically, the progesterone derivative allopregnanolone is an allosteric agonist at this receptor, whereas the androgen dehydroepiandrosterone sulfate (DHEAS) is an allosteric antagonist. We hypothesized these metabolites act similarly on GnRH neurons to modify the response to GABA. Whole-cell voltage-clamp recordings of GABAergic miniature postsynaptic currents (mPSCs) were made from green fluorescent protein-identified GnRH neurons in brain slices from diestrous mice. Glutamatergic currents were blocked with antagonists and action potentials blocked with tetrodotoxin, minimizing presynaptic effects of treatments. Allopregnanolone (5 microm) increased mPSC rate of rise, amplitude and decay time by 15.9 +/- 6.1%, 16.5 +/- 6.3%, and 58.3 +/- 18.6%, respectively (n = 7 cells). DHEAS (5 microm) reduced mPSC rate of rise (32.1 +/- 5.7%) and amplitude (27.6 +/- 4.3%) but did not alter decay time (n = 8). Effects of both neurosteroids were dose dependent between 0.1 and 10 microm. In addition to independent actions, DHEAS also reversed effects of allopregnanolone on rate of rise and amplitude so that these parameters were returned to pretreatment baseline values (n = 6). These data indicate allopregnanolone increases and DHEAS decreases responsiveness of GnRH neurons to activation of GABAA receptors by differentially modulating current flow through GABAA receptor chloride channels. This provides one mechanism for direct steroid feedback to GnRH neurons.

Neuroactive steroid 3 alpha-hydroxy-5 alpha-pregnan-20-one modulates ethanol-induced loss of righting reflex in rats.

Systemic ethanol administration elevates plasma and brain levels of GABAergic neuroactive steroids, including 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) that contribute to specific behavioral actions of ethanol. The present study determined the effect of adrenalectomy and 5alpha-reductase type-1/type-2 enzyme inhibition, known to reduce neuroactive steroids, on ethanol-induced increases in cerebral cortical levels of 3alpha,5alpha-THP and hypnotic effects in male rats. Systemic ethanol administration to male rats increases plasma levels of progesterone and corticosterone similar to acute stress, indicating release of these steroids from adrenal glands. Adrenalectomy markedly reduced the elevation of cerebral cortical 3alpha,5alpha-THP and plasma progesterone levels and reduced the duration of ethanol-induced loss of righting reflex. Prior systemic administration of 5alpha-dihydroprogesterone (10 or 15 mg/kg, i.p.), an immediate precursor of 3alpha,5alpha-THP, to adrenalectomized rats not only restored the ethanol-induced increases in cerebral cortical 3alpha,5alpha-THP levels but also reversed the effect of adrenalectomy on ethanol-induced loss of righting reflex. Prior administration of the 5alpha-reductase inhibitor finasteride (2 x 25, 2 x 75 or 2 x 150 mg/kg, s.c.) and the 5alpha-reductase type-1 inhibitor SKF-105,111 (50 mg/kg, i.p.) did not reduce ethanol-induced increases in the cerebral cortical levels of 3alpha,5alpha-THP at hypnotic doses of ethanol. Furthermore, these drugs did not alter the duration of loss of righting reflex. However, significant correlations between cerebral cortical 3alpha,5alpha-THP levels and the duration of loss of righting reflex were obtained regardless of finasteride administration. These results demonstrate the contributory role of neuroactive steroids in the ethanol-induced loss of righting reflex and the source of ethanol-induced elevation of GABAergic neuroactive steroids. Ethanol-induced increases in neurosteroids could be pertinent to the etiology of sleep-related disorders associated with alcoholism.

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

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

Ventral tegmental area infusions of inhibitors of the biosynthesis and metabolism of 3alpha,5alpha-THP attenuate lordosis of hormone-primed and behavioural oestrous rats and hamsters.

The importance of progesterone biosynthesis and metabolism to 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), which exerts its effects via GABAA/benzodiazepine receptor complexes (GBRs) rather than intracellular progestin receptors (PRs), was investigated for its effects on sexual receptivity. Epostane, a 3beta-hydroxysteroid dehydrogenase inhibitor, blocks progesterone and 3alpha,5alpha-THP biosynthesis. Finasteride, a 5alpha-reductase inhibitor, blocks the metabolism of progesterone to dihydroprogesterone (DHP), which is subsequently metabolized to 3alpha,5alpha-THP. Indomethacin, a 3alpha-hydroxysteroid oxidoreductase inhibitor, blocks DHP's metabolism to 3alpha,5alpha-THP, and its oxidation to DHP. Epostane, finasteride, indomethacin or vehicle were infused intracranially in the ventral tegmental area (VTA) of hormone-primed or naturally receptive rats and hamsters and sexual behaviour was recorded. Epostane, finasteride and indomethacin to the VTA significantly reduced lordosis, compared to vehicle infusions, in hormone-primed and behavioural oestrous rats and hamsters. Radioimmunoassay revealed that concentrations of midbrain 3alpha,5alpha-THP were reduced following epostane, finasteride or indomethacin infusions that significantly decreased lordosis. Immunocytochemistry for 3alpha,5alpha-THP revealed the number of immunoreactive cells were significantly reduced in the VTA following epostane, finasteride or indomethacin infusion to the VTA, but not other midbrain sites. These data suggest that biosynthesis of progestins, and the metabolism of progesterone to 3alpha,5alpha-THP in the VTA, are important for progestin-facilitated sexual receptivity of rats and hamsters.

Anaesthetic effects of pregnanolone in combination with allopregnanolone, thiopental, hexobarbital and flurazepam: an EEG study in the rat.

The anaesthetic interactions of the steroid, 3 alpha-hydroxy-5 beta-pregnan-20-one, in male rats were investigated in different fixed binary combinations with the steroid allopregnanolone (3 alpha-hydroxy-5 alpha-pregnan-20-one), two barbiturates (thiopental and hexobarbital) and the benzodiazepine, flurazepam. Anaesthetic effects were determined using an EEG threshold method. Interactions were assessed using an isobolographic method. The interaction between the two steroids, pregnanolone and allopregnanolone, showed an anaesthetic effect significantly less than additive (antagonistic). The interactions between pregnanolone and the two barbiturates and the benzodiazepine showed an anaesthetic effect significantly greater than additive (potentiation) in all tests performed. These results could be explained by a pharmacodynamic interaction at the hypothetical GABA-benzodiazepine-barbiturate-steroid complex in the CNS.