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

Neurosteroid Modulation of Synaptic and Extrasynaptic GABAA Receptors of the Mouse Nucleus Accumbens

The recent approval of formulations of the endogenous neurosteroid allopregnanolone (brexanolone) and the synthetic neuroactive steroid SAGE-217 (zuranolone) to treat postpartum depression (PPD) has encouraged further research to elucidate why these potent enhancers of GABAAR function are clinically effective in this condition. Dopaminergic projections from the ventral tegmental area (VTA) to the nucleus accumbens are associated with reward/motivation and brain imaging studies report that individuals with PPD show reduced activity of this pathway in response to reward and infant engagement. However, the influence of neurosteroids on GABA-ergic transmission in the nucleus accumbens has received limited attention. Here, we investigate, in the medium spiny neurons (MSNs) of the mouse nucleus accumbens core, the effect of allopregnanolone, SAGE-217 and other endogenous and synthetic steroids of interest on fast phasic and tonic inhibition mediated by synaptic (α1/2βγ2) and extrasynaptic (α4βδ) GABAARs, respectively. We present evidence suggesting the resident tonic current results from the spontaneous opening of δ-GABAARs, where the steroid-enhanced tonic current is GABA-dependent. Furthermore, we demonstrate local neurosteroid synthesis in the accumbal slice preparation and reveal that GABA-ergic neurotransmission of MSNs is influenced by an endogenous neurosteroid tone. Given the dramatic fluctuations in allopregnanolone levels during pregnancy and postpartum, this neurosteroid-mediated local fine-tuning of GABAergic transmission in the MSNs will probably be perturbed.

Selective attention towards infants in nulliparous women across the menstrual cycle

Research in women showed that testosterone is associated with decreased selective attention towards infant stimuli, which can be compensated for by oxytocin administration. In theory, caregiving behavior is thought to be mediated by oxytocin. Oxytocin binds to dopaminergic neurons and thus supposedly motivates aspects of caregiving through its influence on dopaminergic transmission. Most previous studies on caregiving behaviors were thereby performed in women under hormonal contraception to avoid hormonal fluctuations. However, recent studies repeatedly demonstrated decisive influences of the hormonal changes across the female menstrual cycle on dopamine-mediated behaviors, suggesting that estradiol acts as dopamine agonist in the follicular phase and progesterone as dopamine antagonist in the luteal phase. In the present study, we investigated selective attention towards infants as one central aspect of caregiving behavior over the natural menstrual cycle and in relation to interindividual differences of estradiol and progesterone. As expected, we found that women with higher estradiol in the follicular phase also showed higher selective attention towards infant faces among adult distractors, whereas the correlation disappeared in the luteal phase. In contrast, progesterone did not correlate with selective attention towards infants. The present findings collectively support the assumption that estradiol may act as dopamine agonist in the follicular phase, thereby supposedly promoting an important aspect of caretaking behavior.

Behavioral characterization of co-exposure to cannabinoids and hormonal contraceptives in female rats

Hormonal contraceptives are among the most widely used drugs by young healthy women to block ovulation and avoid pregnancy. They reduce the ovarian secretion of estradiol and progesterone, hormones that also modulate neuronal plasticity, cognitive functions, emotions and mood. Cannabis is the most commonly used illicit drug worldwide and its use is increasing among young women, many of which regularly take the "pill". Despite evidence of a bidirectional interaction between the endocannabinoid system and gonadal hormones, only very few studies have examined the consequences of cannabis consumption in young females under hormonal contraceptives treatment. To fill this gap, this study evaluated the behavioral effects of co-exposure to chronic 1) hormonal contraceptives, i.e., ethinyl estradiol (EE) plus levonorgestrel (LNG), one of the synthetic estrogen-progestin combinations of hormonal contraceptives, and 2) cannabinoid receptor agonist, i.e., WIN 55,212-2 (WIN), on motor activity, emotional state and cognitive functions in young adult female rats (8-11/experimental group). Hormonal and cannabinoid treatment started at post-natal day (PND) 52 and 56, respectively, while behavioral testing occurred between PND 84-95. The results show that chronic EE-LNG treatment, at doses (0.020 and 0.060 mg/rat, respectively) known to drastically reduce plasma progesterone levels, and the contextual exposure to WIN, at a dose (12.5 μg/kg/infusion) known to be rewarding in the rat, alters the hormonal milieu but does not cause further changes in locomotor activity compared to EE-LNG or WIN alone, and does not modify anxiety-like state (as measured by the elevated plus maze and the marble burying tests) and cognitive abilities (as measured by the novel object recognition and the prepulse inhibition tests) in young adult female rats. Although exposure to EE-LNG and WIN tends to increase the duration of immobility and to reduce the time spent swimming in the forced swimming test, there was not a significant additive effect suggestive of a depressive-like state. These findings allow deepening the current knowledge on the interaction between cannabinoid agonists and hormonal contraceptives and suggest that low, rewarding doses of cannabinoids do not significantly alter the motor and cognitive skills and do not induce anxiety or depressive-like states in females that use hormonal contraceptives.

The importance of translationally evaluating steroid hormone contributions to substance use

Clinically, women appear to be more susceptible to certain aspects of substance use disorders (SUDs). The steroid hormones 17β-estradiol (E2) and progesterone (Pg) have been linked to women-specific drug behaviors. Here, we review clinical and preclinical studies investigating how cycling ovarian hormones affect nicotine-, cocaine-, and opioid-related behaviors. We also highlight gaps in the literature regarding how synthetic steroid hormone use may influence drug-related behaviors. In addition, we explore how E2 and Pg are known to interact in brain reward pathways and provide evidence of how these interactions may influence drug-related behaviors. The synthesis of this review demonstrates the critical need to study women-specific factors that may influence aspects of SUDs, which may play important roles in addiction processes in a sex-specific fashion. It is important to understand factors that impact women's health and may be key to moving the field forward toward more efficacious and individualized treatment strategies.

Allopregnanolone: The missing link to explain the effects of stress on tic exacerbation?

The neurosteroid allopregnanolone (3α-hydroxy-5α-pregnan-20-one; AP) elicits pleiotropic effects in the central nervous system, ranging from neuroprotective and anti-inflammatory functions to the regulation of mood and emotional responses. Several lines of research show that the brain rapidly produces AP in response to acute stress to reduce the allostatic load and enhance coping. These effects not only are likely mediated by GABA_A receptor activation but also result from the contributions of other mechanisms, such as the stimulation of membrane progesterone receptors. In keeping with this evidence, AP has been shown to exert rapid, potent antidepressant properties and has been recently approved for the therapy of moderate-to-severe postpartum depression. In addition to depression, emerging evidence points to the potential of AP as a therapy for other neuropsychiatric disorders, including anxiety, seizures, post-traumatic stress disorder and cognitive problems. Although this evidence has spurred interest in further therapeutic applications of AP, some investigations suggest that this neurosteroid may also be associated with adverse events in specific disorders. For example, our group has recently documented that AP increases tic-like manifestations in several animal models of tic disorders; furthermore, our results indicate that inhibiting AP synthesis and signalling reduces the exacerbation of tic severity associated with acute stress. Although the specific mechanisms of these effects remain partially elusive, our findings point to the possibility that the GABAergic activation by AP may also lead to disinhibitory effects, which could interfere with the ability of patients to suppress their tics. Future studies will be necessary to verify whether these mechanisms may apply to other externalising manifestations, such as impulse-control problems and manic symptoms.

Allopregnanolone: An overview on its synthesis and effects

Allopregnanolone, a 3α,5α-progesterone metabolite, acts as a potent allosteric modulator of the γ-aminobutyric acid type A receptor. In the present review, the synthesis of this neuroactive steroid occurring in the nervous system is discussed with respect to physiological and pathological conditions. In addition, its physiological and neuroprotective effects are also reported. Interestingly, the levels of this neuroactive steroid, as well as its effects, are sex-dimorphic, suggesting a possible gender medicine based on this neuroactive steroid for neurological disorders. However, allopregnanolone presents low bioavailability and extensive hepatic metabolism, limiting its use as a drug. Therefore, synthetic analogues or a different therapeutic strategy able to increase allopregnanolone levels have been proposed to overcome any pharmacokinetic issues.

Allopregnanolone in mood disorders: Mechanism and therapeutic development

The neuroactive steroid allopregnanolone (ALLO) is an endogenous positive allosteric modulator of GABA type A receptor (GABA_AR), and the down-regulation of its biosynthesis have been attributed to the development of mood disorders, such as depression, anxiety and post-traumatic stress disorder (PTSD). ALLO mediated depression/anxiety involves GABAergic mechanisms and appears to be related to brain-derived neurotrophic factor (BDNF), dopamine receptor, glutamate neurotransmission, and Ca²⁺ channel. In the clinical, brexanolone, as a newly developed intravenous ALLO preparation, has been approved for the treatment of postpartum depression (PPD). In addition, traditional antidepressants such as selective serotonin reuptake inhibitor (SSRI) could reverse ALLO decline. Recently, the translocation protein (TSPO, 18 kDa), which involves in the speed-limiting step of ALLO synthesis, and ALLO derivatization have been identified as new directions for antidepressant therapy. This review provides an overview of ALLO researches in animal model and patients, discusses its role in the development and treatment of depression/anxiety, and directs its therapeutic potential in future.

Dopamine multilocus genetic profiles predict sex differences in reactivity of the human reward system

Sex differences in the neural processing of decision-making are of high interest as they may have pronounced effects on reward- and addiction-related processes. In these, the neurotransmitter dopamine plays a central role by modulating the responsiveness of the reward circuitry. The present functional magnetic resonance imaging study aimed to explore sex and dopamine transmission interactions in decision-making. 172 subjects (111 women) performed a behavioral self-control task assessing reward-related activation during acceptance and rejection of conditioned rewards. Participants were genotyped for six key genetic polymorphisms in the dopamine system that have previously been associated with individual differences in reward sensitivity or dopaminergic transmission in the human striatum, such as rs7118900 (dopamine receptor D2 (DRD2) Taq1A), rs1554929 (DRD2 C957T), rs907094 (DARPP-32), rs12364283 (DRD2), rs6278 (DRD2), and rs107656 (DRD2). The selected polymorphisms were combined in a so-called multilocus genetic composite (MGC) score reflecting the additive effect of different alleles conferring relative increased dopamine transmission in every individual. We successfully demonstrated that reward-related activation in the ventral striatum and ventral tegmental area (VTA) was significantly modulated by biologically informed MGC profiles and sex. When comparing men and women with low MGC profiles that may indicate lower dopamine transmission, only women displayed a reduced down-regulation of activation in the mesolimbic system during reward rejection and additionally, a significant non-linear u-shape relationship between MGC score and VTA activation. Taken together, by integrating neuroimaging and genetics, the present findings contribute to a better understanding of the effects of sex differences on the human brain.

Allopregnanolone Decreases Evoked Dopamine Release Differently in Rats by Sex and Estrous Stage

Mesolimbic dopamine transmission is dysregulated in multiple psychiatric disorders, including addiction. Previous studies found that the endogenous GABAergic steroid (3α,5α)-3-hydroxy-5-pregnan-20-one (allopregnanolone) modulates dopamine levels in the nucleus accumbens and prefrontal cortex. As allopregnanolone is a potent positive allosteric modulator of GABA_A receptors, and GABA_A receptors can regulate dopamine release, we hypothesized that allopregnanolone would reduce phasic fluctuations in mesolimbic dopamine release that are important in learning and reward processing. We used fast-scan cyclic voltammetry in anesthetized female and male rats to measure dopamine release in the nucleus accumbens evoked by electrical stimulation of the ventral tegmental area, before and after administration of allopregnanolone. Allopregnanolone (7.5–25 mg/kg, IP) reduced evoked dopamine release in both male and female rats, compared to β-cyclodextrin vehicle. In males, all doses of allopregnanolone decreased dopamine transmission, with stronger effects at 15 and 25 mg/kg allopregnanolone. In females, 15 and 25 mg/kg allopregnanolone reduced dopamine release, while 7.5 mg/kg allopregnanolone was no different from vehicle. Since allopregnanolone is derived from progesterone, we hypothesized that high endogenous progesterone levels would result in lower sensitivity to allopregnanolone. Consistent with this, females in proestrus (high progesterone levels) were less responsive to allopregnanolone than females in other estrous cycle stages. Furthermore, 30 mg/kg progesterone reduced evoked dopamine release in males, similar to allopregnanolone. Our findings confirm that allopregnanolone reduces evoked dopamine release in both male and female rats. Moreover, sex and the estrous cycle modulated this effect of allopregnanolone. These results extend our knowledge about the pharmacological effects of neurosteroids on dopamine transmission, which may contribute to their therapeutic effects.

Physiopathological role of the enzymatic complex 5α-reductase and 3α/β-hydroxysteroid oxidoreductase in the generation of progesterone and testosterone neuroactive metabolites

The enzymatic complex 5α-reductase (5α-R) and 3α/3β-hydroxysteroid oxidoreductase (HSOR) is expressed in the nervous system, where it transforms progesterone (PROG) and testosterone (T) into neuroactive metabolites. These metabolites regulate myelination, brain maturation, neurotransmission, reproductive behavior and the stress response. The expression of 5α-R and 3α-HSOR and the levels of PROG and T reduced metabolites show regional and sex differences in the nervous system and are affected by changing physiological conditions as well as by neurodegenerative and psychiatric disorders. A decrease in their nervous tissue levels may negatively impact the course and outcome of some pathological events. However, in other pathological conditions their increased levels may have a negative impact. Thus, the use of synthetic analogues of these steroids or 5α-R modulation have been proposed as therapeutic approaches for several nervous system pathologies. However, further research is needed to fully understand the consequences of these manipulations, in particular with 5α-R inhibitors.

Avoidance Learning Across the Menstrual Cycle: A Conceptual Replication

Hormonal transitions across the menstrual cycle may modulate human reward processing and reinforcement learning, but previous results were contradictory. Studies assessed relatively small samples (n < 30) and exclusively used within-subject designs to compare women in hormonally distinct menstrual cycle phases. This increased the risk of sporadic findings and results may have been disproportionally affected by expectancy effects. Also, replication studies are widely missing, which currently precludes any reliable inferences. The present study was intended as a conceptual replication of a previous study [(1), Neuropsychologia 84; n = 15]. There, we had observed a reduction in avoidance learning capacity when women were in the high estradiol state of the late follicular phase as compared to the mid luteal phase with enhanced progesterone influence. These results conformed to the idea that estradiol and progesterone may antagonistically modulate dopaminergic transmission as a dopamine agonist and antagonist, respectively. Heightened progesterone in the luteal phase thereby supported the ability to learn from the negative outcomes of one's actions, while the follicular rise in estradiol interfered with this capacity. Here, we re-examined the above described within-subject difference between the follicular and the luteal phase in a between-subjects design. Seventy-five women were tested once with a probabilistic feedback learning task, while being either in the follicular (36 women) or luteal phase (39 women), and were compared for phase-related differences in behavior. Secondly, we combined the new data with data from three previous studies from our laboratory that used the same task and menstrual cycle phases. This meta-analysis included only data from the first test day, free of any biasing expectancy effects. Both analyses demonstrated the consistency of the decline in avoidance learning in the follicular relative to the luteal phase. We also showed that this decline reliably occurred in all of the included samples. Altogether, these results provide evidence for the consistency of a behavioral difference and its apparent association with a transient change in hormonal state that occurs in the natural menstrual cycle. Our findings may also open new avenues for the development of reliable between-subjects test protocols in menstrual cycle research.

Steroid Hormones and Their Action in Women's Brains: The Importance of Hormonal Balance

Sex hormones significantly impact women's lives. Throughout the different stages of life, from menarche to menopause and all stages in between, women experience dramatic fluctuations in the levels of progesterone and estradiol, among other hormones. These fluctuations affect the body as a whole, including the central nervous system (CNS). In the CNS, sex hormones act via steroid receptors. They also have an effect on different neurotransmitters such as GABA, serotonin, dopamine, and glutamate. Additionally, studies show that sex hormones and their metabolites influence brain areas that regulate mood, behavior, and cognitive abilities. This review emphasizes the benefits a proper hormonal balance during the different stages of life has in the CNS. To achieve this goal, it is essential that hormone levels are evaluated considering a woman's age and ovulatory status, so that a correct diagnosis and treatment can be made. Knowledge of steroid hormone activity in the brain will give women and health providers an important tool for improving their health and well-being.

Repurposing steroidogenesis inhibitors for the therapy of neuropsychiatric disorders: Promises and caveats

Steroids exert a profound influence on behavioral reactivity, by modulating the functions of most neurotransmitters and shaping the impact of stress and sex-related variables on neural processes. This background - as well as the observation that most neuroactive steroids (including sex hormones, glucocorticoids and neurosteroids) are synthetized and metabolized by overlapping enzymatic machineries - points to steroidogenic pathways as a powerful source of targets for neuropsychiatric disorders. Inhibitors of steroidogenic enzymes have been developed and approved for a broad range of genitourinary and endocrine dysfunctions, opening to new opportunities to repurpose these drugs for the treatment of mental problems. In line with this idea, preliminary clinical and preclinical results from our group have shown that inhibitors of key steroidogenic enzymes, such as 5α-reductase and 17,20 desmolase-lyase, may have therapeutic efficacy in specific behavioral disorders associated with dopaminergic hyperfunction. While the lack of specificity of these effects raises potential concerns about endocrine adverse events, these initial findings suggest that steroidogenesis modulators with greater brain specificity may hold significant potential for the development of alternative therapies for psychiatric problems. This article is part of the Special Issue entitled 'Drug Repurposing: old molecules, new ways to fast track drug discovery and development for CNS disorders'.

Pregnenolone-progesterone-allopregnanolone pathway as a potential therapeutic target in first-episode antipsychotic-naïve patients with schizophrenia

Neurosteroids are both endogenous and exogenous steroids that rapidly alter neuronal excitability through interactions with ligand-gated ion channels and other cell surface receptors. They are originated from cholesterol and have important implications for schizophrenia (SZ) pathophysiology and treatment strategies. Specifically, pregnenolone (PREG), progesterone (PROG) and allopregnanolone (ALLO) exhibit similar psychotropic properties. Using enzyme immunoassay, we compared the neurosteroids in PREG downstream pathways in plasma between healthy controls (HC, n = 43) and first-episode antipsychotic-naïve patients with SZ (FEAN-SZ, n = 53) before antipsychotic drug (APD) treatment. Comparisons were also made particularly along PREG-PROG-ALLO pathway in the same FEAN-SZ patients across multiple time points following initiation of treatment for 12 months (m). Firstly, at baseline, levels of PREG were significantly higher and those of ALLO were lower in FEAN-SZ than in HC, whereas PROG, cortisol, dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulfate (DHEAS) were not different. Consequently, the molar ratios of ALLO/PREG and ALLO/PROG in FEAN-SZ were significantly reduced. Secondly, in response to APD at 1 month, ALLO levels in FEAN-SZ were markedly elevated, whereas PREG and PROG levels decreased. Thirdly, among FEAN-SZ, lower levels of PROG (reflecting higher conversion to ALLO) at baseline may predict better therapeutic outcome after 1 month of APD treatment. These findings point to the perturbations of the PREG-PROG-ALLO pathway early in psychosis, and further study of this pathway may inform alternative and innovative therapeutic targets for SZ.

Neurosteroids in Schizophrenia: Pathogenic and Therapeutic Implications

Neurosteroids are a group of important endogenous molecules affecting many neural functions in the brain. Increasing evidence suggests a possible role of these neurosteroids in the pathology and symptomatology of schizophrenia (SZ) and other mental disorders. The aim of this review is to summarize the current knowledge about the neural functions of neurosteroids in the brain, and to evaluate the role of the key neurosteroids as candidate modulators in the etiology and therapeutics of SZ. The present paper provides a brief introduction of neurosteroid metabolism and distribution, followed by a discussion of the mechanisms underlying neurosteroid actions in the brain. The content regarding the modulation of the GABAA receptor is elaborated, given the considerable knowledge of its interactions with other neurotransmitter and neuroprotective systems, as well as its ameliorating effects on stress that may play a role in the SZ pathophysiology. In addition, several preclinical and clinical studies suggested a therapeutic benefit of neurosteroids in SZ patients, even though the presence of altered neurosteroid pathways in the circulating blood and/or brain remains debatable. Following treatment of antipsychotic drugs in SZ, therapeutic benefits have also been linked to the regulation of neurosteroid signaling. Specifically, the neurosteroids such as pregnenolone and dehydroepiandrosterone affect a broad spectrum of behavioral functions through their unique molecular characteristics and may represent innovative therapeutic targets for SZ. Future investigations in larger cohorts with long-term follow-ups will be required to ascertain the neuropsychopharmacological role of this yet unexploited class of neurosteroid agents.

DAT1-Genotype and Menstrual Cycle, but Not Hormonal Contraception, Modulate Reinforcement Learning: Preliminary Evidence

Hormone by genotype interactions have been widely ignored by cognitive neuroscience. Yet, the dependence of cognitive performance on both baseline dopamine (DA) and current 17ß-estradiol (E2) level argues for their combined effect also in the context of reinforcement learning. Here, we assessed how the interaction between the natural rise of E2 in the late follicular phase (FP) and the 40 base-pair variable number tandem repeat polymorphism of the dopamine transporter (DAT1) affects reinforcement learning capacity. 30 women with a regular menstrual cycle performed a probabilistic feedback learning task twice during the early and late FP. In addition, 39 women, who took hormonal contraceptives (HC) to suppress natural ovulation, were tested during the "pill break" and the intake phase of HC. The present data show that DAT1-genotype may interact with transient hormonal state, but only in women with a natural menstrual cycle. We found that carriers of the 9-repeat allele (9RP) experienced a significant decrease in the ability to avoid punishment from early to late FP. Neither homozygote subjects of the 10RP allele, nor subjects from the HC group showed a change in behavior between phases. These data are consistent with neurobiological studies that found that rising E2 may reverse DA transporter function and could enhance DA efflux, which would in turn reduce punishment sensitivity particularly in subjects with a higher transporter density to begin with. Taken together, the present results, although based on a small sample, add to the growing understanding of the complex interplay between different physiological modulators of dopaminergic transmission. They may not only point out the necessity to control for hormonal state in behavioral genetic research, but may offer new starting points for studies in clinical settings.

Changes in stress-stimulated allopregnanolone levels induced by neonatal estradiol treatment are associated with enhanced dopamine release in adult female rats: reversal by progesterone administration

BACKGROUND

Allopregnanolone plays a role in the stress response and homeostasis. Alterations in the estrogen milieu during the perinatal period influence brain development in a manner that persists into adulthood. Accordingly, we showed that a single administration of estradiol benzoate (EB) on the day of birth decreases brain allopregnanolone concentrations in adult female rats.

OBJECTIVE

We examined whether the persistent decrease in allopregnanolone concentrations, induced by neonatal EB treatment, might affect sensitivity to stress during adulthood.

METHODS

Female rats were treated with 10 μg of EB or vehicle on the day of birth. During adulthood, the response to acute foot shock stress was assessed by measuring changes in brain allopregnanolone and corticosterone levels, as well as extracellular dopamine output in the medial prefrontal cortex (mPFC).

RESULTS

Neonatal EB treatment enhanced stress-stimulated allopregnanolone levels in the hypothalamus, as well as extracellular dopamine output in the mPFC; this latest effect is reverted by subchronic progesterone treatment. By contrast, neonatal EB treatment did not alter stress-induced corticosterone levels, sensitivity to hypothalamic-pituitary-adrenal (HPA) axis negative feedback, or abundance of glucocorticoid and mineralocorticoid receptors.

CONCLUSIONS

The persistent decrease in brain allopregnanolone concentrations, induced by neonatal EB treatment, enhances stress-stimulated allopregnanolone levels and extracellular dopamine output during adulthood. These effects are not associated to an impairment in HPA axis activity. Heightened sensitivity to stress is a risk factor for several neuropsychiatric disorders; these results suggest that exposure to estrogen during development may predispose individuals to such disorders.

The differential effects of alprazolam and oxazepam on methamphetamine self-administration in rats

BACKGROUND

Methamphetamine is the second most commonly used illicit drug in the world, and despite recent attempts by the Drug Enforcement Administration to combat this epidemic, methamphetamine use is still on the rise. As methamphetamine use increases so does polydrug use, particularly that involving methamphetamine and benzodiazepines. The present study was designed to examine the effects of two benzodiazepines on methamphetamine self-administration.

METHODS

Five doses of methamphetamine (0.0075, 0.015, 0.03, 0.09, and 0.12mg/kg/infusion) were tested, producing an inverted U-shaped dose-response curve. Rats were then pretreated with oxazepam, alprazolam, or vehicle prior to methamphetamine self-administration. To determine if the effects of these drugs were due to the GABAA receptor and/or translocator protein (TSPO), we also pretreated rats with an antagonist for the benzodiazepine-binding site on the GABAA receptor (i.e., flumazenil) and a TSPO antagonist (i.e., PK11195) prior to alprazolam or oxazepam administration.

RESULTS

Oxazepam significantly reduced methamphetamine self-administration as demonstrated by a downward shift of the dose-response curve. In contrast, alprazolam significantly enhanced methamphetamine self-administration as evidenced by a leftward shift of the dose-response curve. Flumazenil completely blocked the effects of alprazolam on methamphetamine self-administration. When administered individually, both flumazenil and PK11195 partially reversed the effects of oxazepam on methamphetamine self-administration. However, when these two antagonists were combined, the effects of oxazepam were completely reversed.

CONCLUSIONS

The GABAA receptor is responsible for the alprazolam-induced enhancement of methamphetamine self-administration, while the activation of both the GABAA receptor and TSPO are responsible for the oxazepam-induced reduction of methamphetamine self-administration.

Ventral tegmental area dopamine revisited: effects of acute and repeated stress

Aversive events rapidly and potently excite certain dopamine neurons in the ventral tegmental area (VTA), promoting phasic increases in the medial prefrontal cortex and nucleus accumbens. This is in apparent contradiction to a wealth of literature demonstrating that most VTA dopamine neurons are strongly activated by reward and reward-predictive cues while inhibited by aversive stimuli. How can these divergent processes both be mediated by VTA dopamine neurons? The answer may lie within the functional and anatomical heterogeneity of the VTA. We focus on VTA heterogeneity in anatomy, neurochemistry, electrophysiology, and afferent/efferent connectivity. Second, recent evidence for a critical role of VTA dopamine neurons in response to both acute and repeated stress will be discussed. Understanding which dopamine neurons are activated by stress, the neural mechanisms driving the activation, and where these neurons project will provide valuable insight into how stress can promote psychiatric disorders associated with the dopamine system, such as addiction and depression.

Be quick about it. Endogenous estradiol level, menstrual cycle phase and trait impulsiveness predict impulsive choice in the context of reward acquisition

This article is part of a Special Issue "Estradiol and Cognition". Variations in the steroid hormone 17ß-estradiol (E2) may promote intra-individual differences in reward seeking behavior and temporal decision-making (Reimers et al., 2014; Front. Neurosci. 8: 401). Yet, in humans the exact role of E2 in impulsive choice still needs to be determined. The present study assessed the effect of a cycle-dependent rise in endogenous E2 on temporal response adaptation across the follicular phase (FP). For this purpose a reward acquisition paradigm was employed that is sensitive to hormone-induced changes in central dopamine (DA) level. The present data show that women acted more impulsively in the early as opposed to the late FP. Early follicular E2 further correlated with an increased capacity to speed up for reward maximization, while simultaneously the ability to wait for higher reward was compromised. This correlation was most pronounced in women with low trait impulsiveness. In contrast, E2 and optimized response speed failed to correlate in women with high trait impulsiveness and in the late FP, despite a generally higher E2 level. Collectively, these findings support the theory that E2 may act as an endogenous DA agonist. The fact that the hormone-behavior relationship was restricted to women with low trait impulsiveness and thus supposedly lower central DA level provides indirect support for this idea. Yet, choices became relatively less impulsive in the state of heightened E2 (i.e., in the late FP), suggesting that the relationship between E2 and impulsive choice may not be linear, but might resemble an inverted U-function.

Effects of inhibitory GABA-active neurosteroids on cocaine seeking and cocaine taking in rats

RATIONALE

Several compounds that potentiate GABA-induced inhibitory currents also decrease stress, anxiety and addiction-related behaviors. Because of the well-established connection between stress and addiction, compounds that reduce stress-induced responses might be efficacious in treating addiction. Since endogenous neurosteroids such as allopregnanolone may function in a manner similar to benzodiazepines to reduce HPA axis activation and anxiety following stressful stimuli, we hypothesized that exogenously applied neurosteroids would reduce cocaine reinforcement in two animal models.

METHODS

Male Wistar rats were trained to self-administer cocaine and food under a concurrent alternating operant schedule of reinforcement. Two separate groups of rats were trained to self-administer cocaine or food pellets and were then exposed to similar cue-induced reinstatement paradigms. Both groups of rats were pretreated with various doses of neurosteroids.

RESULTS

Allopregnanolone and 3α-hydroxy-3β-methyl-17β-nitro-5α-androstane (R6305-7, a synthetic neurosteroid) were ineffective in selectively decreasing cocaine relative to food self-administration. On the other hand, both allopregnanolone and R6305-7 significantly decreased the cue-induced reinstatement of extinguished cocaine seeking, confirmed by one-way ANOVA.

CONCLUSIONS

These results suggest that neurosteroids may be effective in reducing the relapse to cocaine use without affecting ongoing cocaine self-administration.

Ethanol alters local cellular levels of (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP) independent of the adrenals in subcortical brain regions

The neuroactive steroid (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP or allopregnanolone) is a positive modulator of GABAA receptors synthesized in the brain, adrenal glands, and gonads. In rats, ethanol activates the hypothalamic-pituitary-adrenal axis and elevates 3α,5α-THP in plasma, cerebral cortex, and hippocampus. In vivo, these effects are dependent on both the pituitary and adrenal glands. In vitro, however, ethanol locally increases 3α,5α-THP in hippocampal slices, in the absence of adrenal influence. Therefore, it is not known whether ethanol can change local brain levels of 3α,5α-THP in vivo, independent of the adrenals. To directly address this controversy, we administered ethanol (2 g/kg) or saline to rats that underwent adrenalectomy (ADX) or received sham surgery and performed immunohistochemistry for 3α,5α-THP. In the medial prefrontal cortex (mPFC), ethanol increased 3α,5α-THP after sham surgery, compared with saline controls, with no ethanol-induced change in 3α,5α-THP following ADX. In subcortical regions, 3α,5α-THP was increased independent of adrenals in the CA1 pyramidal cell layer, dentate gyrus polymorphic layer, bed nucleus of the stria terminalis, and paraventricular nucleus of the hypothalamus. Furthermore, ethanol decreased 3α,5α-THP labeling in the nucleus accumbens shore and central nucleus of the amygdala, independent of the adrenal glands. These data indicate that ethanol dynamically regulates local 3α,5α-THP levels in several subcortical regions; however, the adrenal glands contribute to 3α,5α-THP elevations in the mPFC. Using double immunofluorescent labeling we determined that adrenal dependence of 3α,5α-THP induction by ethanol is not due to a lack of colocalization of 3α,5α-THP with the cholesterol transporters steroidogenic acute regulatory protein (StAR) or translocator protein (TSPO).

Overexpression of the steroidogenic enzyme cytochrome P450 side chain cleavage in the ventral tegmental area increases 3α,5α-THP and reduces long-term operant ethanol self-administration

Neuroactive steroids are endogenous neuromodulators capable of altering neuronal activity and behavior. In rodents, systemic administration of endogenous or synthetic neuroactive steroids reduces ethanol self-administration. We hypothesized this effect arises from actions within mesolimbic brain regions that we targeted by viral gene delivery. Cytochrome P450 side chain cleavage (P450scc) converts cholesterol to pregnenolone, the rate-limiting enzymatic reaction in neurosteroidogenesis. Therefore, we constructed a recombinant adeno-associated serotype 2 viral vector (rAAV2), which drives P450scc expression and neuroactive steroid synthesis. The P450scc-expressing vector (rAAV2-P450scc) or control GFP-expressing vector (rAAV2-GFP) were injected bilaterally into the ventral tegmental area (VTA) or nucleus accumbens (NAc) of alcohol preferring (P) rats trained to self-administer ethanol. P450scc overexpression in the VTA significantly reduced ethanol self-administration by 20% over the 3 week test period. P450scc overexpression in the NAc, however, did not alter ethanol self-administration. Locomotor activity was unaltered by vector administration to either region. P450scc overexpression produced a 36% increase in (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP, allopregnanolone)-positive cells in the VTA, but did not increase 3α,5α-THP immunoreactivity in NAc. These results suggest that P450scc overexpression and the resultant increase of 3α,5α-THP-positive cells in the VTA reduces ethanol reinforcement. 3α,5α-THP is localized to neurons in the VTA, including tyrosine hydroxylase neurons, but not astrocytes. Overall, the results demonstrate that using gene delivery to modulate neuroactive steroids shows promise for examining the neuronal mechanisms of moderate ethanol drinking, which could be extended to other behavioral paradigms and neuropsychiatric pathology.

Multifunctional aspects of allopregnanolone in stress and related disorders

Allopregnanolone (3α-hydroxy-5α-pregnan-20-one) is a major cholesterol-derived neurosteroid in the central nervous system and is synthesized from progesterone by steroidogenic enzymes, 5α-reductase (the rate-limiting enzyme) and 3α-hydroxysteroid dehydrogenase. The pathophysiological role of allopregnanolone in neuropsychiatric disorders has been highlighted in several investigations. The changes in neuroactive steroid levels are detected in stress and stress-related disorders including anxiety, panic and depression. The changes in allopregnanolone in response to acute stressor tend to restore the homeostasis by dampening the hyper-activated HPA axis. However, long standing stressors leading to development of neuropsychiatric disorders including depression and anxiety are associated with decrease in the allopregnanolone levels. GABAA receptor complex has been considered as the primary target of allopregnanolone and majority of its inhibitory actions are mediated through GABA potentiation or direct activation of GABA currents. The role of progesterone receptors in producing the late actions of allopregnanolone particularly in lordosis facilitation has also been described. Moreover, recent studies have also described the involvement of other multiple targets including brain-derived neurotrophic factor (BDNF), glutamate, dopamine, opioids, oxytocin, and calcium channels. The present review discusses the various aspects of allopregnanolone in stress and stress-related disorders including anxiety, depression and panic.

Ethanol administration produces divergent changes in GABAergic neuroactive steroid immunohistochemistry in the rat brain

BACKGROUND

The 5α-reduced pregnane neuroactive steroid (3α,5α)-3-hydroxypregnan-20-one (3α,5α-THP or allopregnanolone) is a potent positive modulator of GABAA receptors capable of modulating neuronal activity. In rats, systemic ethanol (EtOH) administration increases cerebral cortical and hippocampal levels of 3α,5α-THP, but the effects of EtOH on 3α,5α-THP levels in other brain regions are unknown. There is a large body of evidence suggesting that 3α,5α-THP enhances EtOH sensitivity, contributes to some behavioral effects of EtOH, and modulates EtOH reinforcement and motivation to drink. In this study, we used immunohistochemistry (IHC) to determine EtOH-induced changes in cellular 3α,5α-THP expression in brain regions associated with EtOH actions and responses.

METHODS

Male Wistar rats were administered EtOH (2 g/kg) or saline intraperitoneally and after 60 minutes transcardially perfused. IHC was performed on free-floating sections (3 to 4 sections/animal/brain region) using an affinity purified anti-3α,5α-THP primary antibody, and immunoreactivity was visualized with 3,3'-diaminobenzidine.

RESULTS

EtOH significantly increased 3α,5α-THP immunoreactivity by 24 ± 6% in the medial prefrontal cortex, 32 ± 12% in the hippocampal Cornu Ammonis area 1 (CA1) pyramidal cell layer, 52 ± 5% in the polymorph cell layer of the dentate gyrus (DG), 44 ± 15% in the bed nucleus of the stria terminalis, and 36 ± 6% in the paraventricular nucleus of the hypothalamus. In contrast, EtOH administration significantly reduced 3α,5α-THP immunoreactivity by 25 ± 5% in the nucleus accumbens "shore" and 21 ± 3% in the central nucleus of the amygdala. No changes were observed in the ventral tegmental area, dorsomedial striatum, granule cell layer of the DG, or the lateral and basolateral amygdala.

CONCLUSIONS

The results suggest acute EtOH (2 g/kg) produces divergent, brain region specific, effects on cellular 3α,5α-THP levels. Regional differences in the effects of EtOH suggest there may be regional brain synthesis of 3α,5α-THP independent of the adrenal glands and novel mechanisms that reduce cellular 3α,5α-THP. Regional differences in EtOH-induced changes in 3α,5α-THP levels likely contribute to EtOH effects on neuronal function in brain.

Neurosteroid and neurotransmitter alterations in Parkinson's disease

Parkinson's disease (PD) is associated with a massive loss of dopaminergic cells in the substantia nigra leading to dopamine hypofunction and alteration of the basal ganglia circuitry. These neurons, are under the control, among others, of the excitatory glutamatergic and inhibitory γ-aminobutyric acid (GABA) systems. An imbalance between these systems may contribute to excitotoxicity and dopaminergic cell death. Neurosteroids, a group of steroid hormones synthesized in the brain, modulate the function of several neurotransmitter systems. The substantia nigra of the human brain expresses high concentrations of allopregnanolone (3α, 5αtetrahydroprogesterone), a neurosteroid that positively modulates the action of GABA at GABAA receptors and of 5α-dihydroprogesterone, a neurosteroid acting at the genomic level. This article reviews the roles of NS acting as neuroprotectants and as GABAA receptor agonists in the physiology and pathophysiology of the basal ganglia, their impact on dopaminergic cell activity and survival, and potential therapeutic application in PD.

Inhibition of 5α-reductase in the nucleus accumbens counters sensorimotor gating deficits induced by dopaminergic activation

Cogent evidence highlights a key role of neurosteroids and androgens in schizophrenia. We recently reported that inhibition of steroid 5α-reductase (5αR), the rate-limiting enzyme in neurosteroid synthesis and androgen metabolism, elicits antipsychotic-like effects in humans and animal models, without inducing extrapyramidal side effects. To elucidate the anatomical substrates mediating these effects, we investigated the contribution of peripheral and neural structures to the behavioral effects of the 5αR inhibitor finasteride (FIN) on the prepulse inhibition (PPI) of the acoustic startle reflex (ASR), a rat paradigm that dependably simulates the sensorimotor gating impairments observed in schizophrenia and other neuropsychiatric disorders. The potential effect of drug-induced ASR modifications on PPI was excluded by measuring this index both as percent (%PPI) and absolute values (ΔPPI). In both orchidectomized and sham-operated rats, FIN prevented the %PPI deficits induced by the dopamine (DA) receptor agonists apomorphine (APO, 0.25mg/kg, SC) and d-amphetamine (AMPH, 2.5mg/kg, SC), although the latter effect was not corroborated by ΔPPI analysis. Conversely, APO-induced PPI deficits were countered by FIN infusions in the brain ventricles (10μg/1μl) and in the nucleus accumbens (NAc) shell and core (0.5μg/0.5μl/side). No significant PPI-ameliorating effect was observed following FIN injections in other brain regions, including dorsal caudate, basolateral amygdala, ventral hippocampus and medial prefrontal cortex, although a statistical trend was observed for the latter region. The efflux of DA in NAc was increased by systemic, but not intracerebral FIN administration. Taken together, these findings suggest that the role of 5αR in gating regulation is based on post-synaptic mechanisms in the NAc, and is not directly related to alterations in DA efflux in this region.

Neurosteroids and GABA(A) Receptor Interactions: A Focus on Stress

Since the pioneering discovery of the rapid CNS depressant actions of steroids by the "father of stress," Hans Seyle 70 years ago, brain-derived "neurosteroids" have emerged as powerful endogenous modulators of neuronal excitability. The majority of the intervening research has focused on a class of naturally occurring steroids that are metabolites of progesterone and deoxycorticosterone, which act in a non-genomic manner to selectively augment signals mediated by the main inhibitory receptor in the CNS, the GABA(A) receptor. Abnormal levels of such neurosteroids associate with a variety of neurological and psychiatric disorders, suggesting that they serve important physiological and pathophysiological roles. A compelling case can be made to implicate neurosteroids in stress-related disturbances. Here we will critically appraise how brain-derived neurosteroids may impact on the stress response to acute and chronic challenges, both pre- and postnatally through to adulthood. The pathological implications of such actions in the development of psychiatric disturbances will be discussed, with an emphasis on the therapeutic potential of neurosteroids for the treatment of stress-associated disorders.

Isolation rearing-induced reduction of brain 5α-reductase expression: relevance to dopaminergic impairments

Isolation rearing (IR), a well-established rat model of early chronic psychosocial stress, engenders marked behavioral alterations related to changes of dopamine (DA) neurotransmission in cortical and subcortical brain regions. Stress-induced shifts in γ-aminobutyric acid (GABA)-ergic signaling have been implicated in the dysregulation of DA release. The neurosteroid 3α-hydroxy-5α-pregnan-20-one (allopregnanolone/AP), synthesized from progesterone by the action of the rate-limiting enzyme 5α-reductase (5AR), is a potent positive allosteric modulator of GABA(A) receptor function. Thus, alterations of 5AR activity/expression may impact upon DA neurotransmission. We studied the effects of IR on the 5AR expression/function and extracellular concentrations of DA and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) in the rat nucleus accumbens (NAcc) and medial prefrontal cortex (mPFC). Immediately after weaning, male rats were subjected to either IR or social rearing (SR) conditions for 5-8 weeks. Compared to SR, IR rats exhibited significantly lower protein expression of 5AR isoforms (1 and 2) in both brain regions and reduced brain, but not plasma, content of AP and allotetrahydrodeoxycorticosterone, the 5α-reduced metabolite of deoxycorticosterone. IR-exposed rats also exhibited higher levels of DA and DOPAC in the NAcc shell, but not in mPFC, when compared to SR rats. The 5AR inhibitor finasteride (FIN, 100 mg/kg, i.p.) enhanced DA and DOPAC content in the NAcc shell of SR, but not IR rats. FIN, however, elicited equivalent increases in DA and DOPAC levels in the mPFC of both groups. These results show that IR induces changes in expression/activity of brain 5AR which, in a brain-region specific manner, may partially underlie the alterations in DA signaling induced by this manipulation. This article is part of a Special Issue entitled 'Trends in neuropharmacology: in memory of Erminio Costa'.

Evidence for a role of progesterone in menstrual cycle-related variability in prepulse inhibition in healthy young women

Prepulse inhibition (PPI) of the startle response is sensitive to sex, with healthy young women showing less PPI compared with age-matched men, and varies according to the menstrual cycle phase in women. Relatively less is known regarding sex and hormonal influences in prepulse facilitation (PPF). Menstrual phase-related variability in PPI is suggested to be mediated by fluctuating estrogen level, based on the observations of more PPI in women during the follicular, relative to the luteal, phase. No study has directly assessed the relationship between fluctuating hormones and PPI or PPF levels over the human ovarian cycle. To examine the roles of circulating ovarian hormones in PPI and PPF, 16 non-smoking regularly menstruating healthy women were tested during both the follicular and luteal phases on PPI and PPF and provided saliva samples for measurement of 17beta-estradiol (estrogen), progesterone and testosterone. The results showed higher levels of 17beta-estradiol and progesterone during the luteal, relative to the follicular, phase; and more PPI during the follicular phase and more PPF during the luteal phase with comparable startle amplitude and habituation during the two phases. A larger increase in progesterone was associated with a smaller decrease in PPI from the follicular to the luteal phase. No significant associations were found between changes in PPI/PPF and estrogen levels. The findings confirm lower PPI during the luteal, compared with the follicular, phase and suggest a role for progesterone, more specifically an antipsychotic-like PPI-restoration action of progesterone, during the luteal phase in PPI of young women.

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

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

Estrous cycle-dependent changes in basal and ethanol-induced activity of cortical dopaminergic neurons in the rat

The influence of the estrous cycle on dopamine levels in the rat medial prefrontal cortex under basal and ethanol-stimulated conditions was evaluated by microdialysis. The basal dopamine concentration in the dialysate varied markedly during the estrous cycle, being highest in estrus and lowest in proestrus. Furthermore, a challenge intraperitoneal administration of ethanol (0.5 g/kg) induced a significant increase in dopaminergic output (+50%) during estrus but had no effect in diestrus or proestrus. Ovariectomy or pretreatment with either finasteride (a 5alpha-reductase inhibitor) or clomiphene (an estrogen receptor antagonist) prevented this ethanol-induced increase in dopamine concentration. The effect of ethanol was restored in ovariectomized rats by pretreatment with estrogen but not by that with progesterone. Our results thus show that the basal levels of dopamine in the prefrontal cortex are dependent on the phase of the estrous cycle. Furthermore, this dependence appears to be attributable to the effects of ovarian steroid hormones and results in a differential sensitivity of the dopaminergic neurons to ethanol. The hormone-induced changes in the activity of these neurons might contribute to the differences in drug sensitivity and mood state apparent among phases of the estrous cycle and between the sexes.

Allopregnanolone influences the consummatory processes that govern ethanol drinking in C57BL/6J mice

Although systemic allopregnanolone (ALLO; a positive modulator of GABA(A) receptors) has been shown to enhance ethanol-reinforced responding and to modulate drinking patterns in rodents, the effects of centrally administered ALLO on ethanol intake are not known. The current work examined the effects of intracranial ALLO on operant ethanol self-administration in food- and water-satiated mice, with a procedure designed to estimate ALLO's influence on appetitive versus consummatory processes. Male C57BL/6J (B6) mice were trained to press an ethanol-appropriate lever by being reinforced with 30-min of continuous access to a 10% ethanol solution. Following surgical implantation of a guide cannula aimed at the lateral ventricle and subsequent habituation to vehicle infusions, ALLO (50-400 ng; ICV) was delivered immediately prior to session start. ALLO doses of 100 and 400 ng were further evaluated for their effects on locomotor behavior within activity chambers. ALLO selectively modulated ethanol intake patterns associated with the onset and maintenance of self-administration, while leaving appetitive (i.e., ethanol seeking) measures unaltered. The effects of ALLO on drinking patterns were dissociable from changes in locomotor behavior, as evidenced by the absence of ALLO's influence on response frequency and horizontal distance traveled. These findings support the premise that manipulations in brain ALLO levels may influence the regulatory processes governing ethanol consumption.

Lack of evidence of a role for the neurosteroid allopregnanolone in ethanol-induced reward and c-fos expression in DBA/2 mice

Previous studies using the 5alpha-reductase inhibitor finasteride suggest that progesterone metabolites, particularly the endogenous neurosteroid allopregnanolone, mediate some of the effects of ethanol. Consequently, we studied the effect of finasteride (2 x 25 mg/kg s.c., 12 h apart) pretreatment on the acquisition and expression of ethanol (2 g/kg i.p.) induced conditioned place preference and c-fos expression in DBA/2 mice; a strain known to be particularly sensitive to ethanol. Ethanol administration induced a clear conditioned place preference and widespread c-fos expression, with elements of the extended amygdala, Edinger-Westphal nucleus and paraventricular nucleus being especially sensitive. However, despite an approximately 99% decrease in whole brain allopregnanolone content, finasteride pretreatment had remarkably little effect on either ethanol-induced conditioned place preference or ethanol-induced c-fos expression. Thus, aside from a general stimulatory effect on c-fos expression in the ventral tegmental area, and generally mild depression of locomotor activity, no other effects of finasteride or interaction with ethanol effects were identifiable. Together, these studies suggest that endogenous allopregnanolone plays little part in mediating acute ethanol-induced reward or neural activation in DBA/2 mice.

Perinatal allopregnanolone influences prefrontal cortex structure, connectivity and behavior in adult rats

Cortical neurosteroid levels vary dramatically across development; during the second week of life elevated levels of allopregnanolone are associated with decreased GABA(A) receptor function. Since GABA(A) receptor modulation plays a role in proliferative regulation in developing neocortex, it is possible that endogenous neurosteroids such as allopregnanolone, acting through GABA(A) receptors, modulate cortical development. We augmented normally low levels with exogenous administration of allopregnanolone (10 mg/kg) during the first week of rodent life. The localization of parvalbumin-labeled cells was markedly altered; the ratio of cell number in the deep (layers V-VI) vs. superficial (layers I-III) layers of adult prefrontal cortex increased two-fold in rats administered allopregnanolone on postnatal day 1 or 5. The mechanism underlying these anatomical changes likely involves GABA(A) receptors because similar changes in interneuron placement were observed after neonatal benzodiazepine administration. Measures of mature cortical function were also altered after neonatal neurosteroid administration, including [(3)H]MK-801 binding, prepulse inhibition and amphetamine-induced locomotor activity. Moreover, neonatal allopregnanolone administration increases the number of parvalbumin-expressing neurons in medial dorsal nucleus of the thalamus while the total neuron number is decreased. These findings suggest that connectivity between the medial dorsal nucleus of the thalamus and prefrontal cortex is likely altered by neonatal neurosteroid administration and may result in a disinhibited frontal cortex. Disinhibition in the prefrontal cortex is associated with behavioral changes relevant to human psychosis and developmental disorders. If neurosteroids play a role in normal development of prefrontal/medial dorsal patency as suggested by these studies, then alterations in neurosteroid levels may contribute to abnormal neurodevelopment.

Neuroactive steroids in schizophrenia

Schizophrenia is a psychiatric disorder with a complicated pathophysiology, involving many biochemical abnormalities in the brain. Because neuroactive steroids (NASs) modulate neurotransmitter systems that are implicated in the pathology of schizophrenia, recent research has focused on examining the role that NASs play in the illness. Although research in this area is relatively new, it appears that NASs may potentially be implicated in the pathophysiology of the illness. This paper reviews the current understanding of NASs, the research literature on NASs in schizophrenia and in animal models of the illness (including the effects of antipsychotic medication on NASs) and on the potential antipsychotic role of NASs themselves and, finally, discusses future directions for this area of schizophrenia research.

Antidepressant-like actions of intra-accumbens infusions of allopregnanolone in ovariectomized Wistar rats

This study was aimed to verify the role of the nucleus accumbens (NAcc) in the antidepressant-like effects of allopregnanolone in ovariectomized rats forced to swim. The interaction between infusions of allopregnanolone (intra-NAcc) with systemic administrations of allopregnanolone, muscimol, fluoxetine and GABA-A antagonists was assessed. Results showed that allopregnanolone (intra-NAcc; 1.5 microg, p < 0.05; 2.0 microg, p < 0.05) or systemic injections of allopregnanolone (1.5 mg/kg, p < 0.05; 2.0 mg/kg, p < 0.05; s.c.) or muscimol (0.3 mg/kg, p < 0.05; 0.6 mg/kg, p < 0.05; i.p.) reduced immobility by increasing climbing in the forced swimming task (FST), whereas fluoxetine (1.0 mg/kg, p < 0.05; 2.0 mg/kg, p < 0.05; i.p.) reduced immobility by increasing swimming. Allopregnanolone (intra-NAcc; 0.5 microg/side) synergized with systemic doses of allopregnanolone (0.5 mg/kg; p < 0.05), muscimol (0.1 mg/kg; p < 0.05) or fluoxetine (0.5 mg/kg; p < 0.05) and reduced immobility by increasing climbing. Picrotoxin (0.125 mg/kg; i.p.) attenuated the synergism of the combination allopregnanolone (intra-NAcc; 0.5 microg/side) plus fluoxetine (i.p.) or allopregnanolone (s.c.) and the effects of allopregnanolone (intra-NAcc; 1.5 microg/side). Bicuculline (2.0 mg/kg; i.p.) attenuated the synergism between the combination allopregnanolone (intra-NAcc; 0.5 microg/side) plus muscimol (i.p.), but not the synergism of the combination allopregnanolone (intra-NAcc; 0.5 microg/side) plus allopregnanolone (s.c.). In conclusion, allopregnanolone (systemic injections or intra-NAcc), fluoxetine or muscimol produced antidepressant-like effects in the FST. Subthreshold doses of allopregnanolone (intra-NAcc) synergized with systemic subthreshold doses of fluoxetine, muscimol or allopregnanolone. Antagonists of the GABA-A receptor canceled the synergism.

Role of neuroactive steroid allopregnanolone in antipsychotic-like action of olanzapine in rodents

Olanzapine increases brain allopregnanolone (ALLO) levels sufficiently to modulate neuronal activity by allosterically regulating GABAA receptors. Recently, we reported the antipsychotic-like profile of ALLO in rodents. The present study examined the hypothesis that olanzapine-induced elevation of endogenous neurosteroid ALLO is vital for its neuroleptic-like action. The conditioned avoidance response (CAR) and apomorphine-induced climbing behavioral paradigms were used in rodents. Administration of ALLO (1 microg, intracerebroventricular (i.c.v.)) or neurosteroidogenic agents such as the mitochondrial diazepam binding inhibitor receptor agonist, FGIN 1-27 (0.5 microg, i.c.v.) or the ALLO precursor, progesterone (10 mg/kg, i.p.) significantly potentiated olanzapine-induced blockade of CAR and apomorphine-induced climbing. In contrast, these agents failed to alter the antipsychotic-like effect of risperidone and haloperidol. On the other hand, inhibition of the endogenous biosynthesis of neurosteroids by the 3beta-hydroxysteroid dehydrogenase inhibitor, trilostane (30 mg/kg, i.p.), the 3alpha-hydroxysteroid oxidoreductase inhibitor, indomethacin (5 mg/kg, i.p.), or the GABAA receptor antagonist bicuculline (1 mg/kg, i.p.) and dehydroepiandrosterone sulfate (DHEAS) (1 mg/kg, i.p.) blocked the effect of olanzapine, but not of risperidone and haloperidol. Socially isolated animals, known to exhibit decreased brain ALLO and GABAA receptor functions, displayed a shortening in the muscimol-induced loss of righting reflex and an increased susceptibility to apomorphine-induced climbing. Administration of olanzapine, but not of haloperidol and risperidone, normalized the duration of muscimol-elicited loss of righting reflex. Although all three antipsychotics proved capable of antagonizing the apomorphine-induced climbing, a dose almost five times higher of olanzapine was required in socially isolated animals. The data obtained suggest that enhancement of the GABAergic tone plays a key role in the antipsychotic-like effect exerted by olanzapine in rodents, likely as a consequence of augmented levels of neuroactive steroids, in particular ALLO, in the brain. The present findings provide the first specific behavioral evidence in support of the hypothesis that neuroactive steroid ALLO- mediated GABAergic modulation is essential for the antipsychotic-like action of olanzapine.

Inhibition of stress-induced dopamine output in the rat prefrontal cortex by chronic treatment with olanzapine

BACKGROUND

Chronic exposure to stressful events precipitates or exacerbates many neuropsychiatric disorders, including depression and schizophrenia. Evidence suggests that treatment with the atypical antipsychotic drugs olanzapine or clozapine results in a superior amelioration of the anxious and depressive symptoms that accompany schizophrenia relative to therapy with classical antipsychotics such as haloperidol. Moreover, olanzapine and clozapine, but not haloperidol, increase the brain content of neuroactive steroids. The effects of olanzapine and clozapine on the stress-induced increase in dopamine output in the rat cerebral cortex have now been compared with that of haloperidol.

METHODS

Rats chronically treated (3 weeks, once a day) with each drug were exposed to foot-shock stress or injected with a single dose of the anxiogenic benzodiazepine receptor ligand FG7142, and dopamine release was then measured in the prefrontal cortex by vertical microdialysis.

RESULTS

Long-term administration of olanzapine or clozapine prevented or markedly inhibited, respectively, the increase in the extracellular dopamine concentration induced by foot shock; haloperidol had no such effect. Chronic olanzapine treatment also blocked the effect of FG7142 on dopamine output.

CONCLUSIONS

The reduction in the sensitivity of cortical dopaminergic neurons to stress shown to be elicited by treatment with olanzapine or clozapine may contribute to the anxiolytic actions of these drugs.

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

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

Perinatal neurosteroid levels influence GABAergic interneuron localization in adult rat prefrontal cortex

Neurosteroids are a class of steroids synthesized de novo in the brain, several of which are potent modulators of GABA(A) receptor function. In developing brain GABA(A) receptor, stimulation plays a trophic role. Cortical levels of the GABAergic neurosteroid 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP) vary dramatically across development; during the second week of life, elevated levels of 3alpha,5alpha-THP are associated with decreased GABA(A) receptor function. To determine whether alteration of endogenous 3alpha,5alpha-THP levels during development alters GABAergic interneurons in prefrontal cortex (PFC) at maturity, rat pups were exposed to 3alpha,5alpha-THP (10 mg/kg) on postnatal day 1 (P1), P2, and P5. On P80, frontal cortex tissue was assayed for GABAergic cell localization (parvalbumin and calbindin immunoreactivity), agonist-dependent [(3)H] dizocilpine (MK-801) binding to NMDA receptors in cortical homogenates, muscimol-mediated (36)Cl(-) influx into synaptoneurosomes, and 3alpha,5alpha-THP levels. The localization of parvalbumin-labeled cells was markedly altered; the ratio of cell number in the deep layers (V-VI) versus superficial layers (I-III) of adult PFC increased twofold in animals exposed to 3alpha,5alpha-THP on P1 or P5. Relative microtubule-associated protein-2 and calbindin immunoreactivity were not altered by perinatal 3alpha,5alpha-THP administration. Agonist-dependent [(3)H]MK-801 binding was decreased in PFC but not parietal cortex homogenates, whereas muscimol-mediated (36)Cl(-) influx and 3alpha,5alpha-THP levels were unchanged in frontal cortex of adult males exposed to 3alpha,5alpha-THP on P5. These data are consistent with a change in the distribution of a subset of interneurons in response to neurosteroid exposure and suggest that GABAergic neurosteroids are critical for normal development of GABAergic systems in the PFC.

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.

Olanzapine and clozapine increase the GABAergic neuroactive steroid allopregnanolone in rodents

The neuroactive steroid allopregnanolone is a potent gamma-aminobutyric acid type A (GABA(A)) receptor modulator with anxiolytic and anticonvulsant effects. Olanzapine and clozapine also have anxiolytic-like effects in behavioral models. We therefore postulated that olanzapine and clozapine would elevate allopregnanolone levels, but risperidone and haloperidol would have minimal effects. Male rats received intraperitoneal olanzapine (2.5-10.0 mg/kg), clozapine (5.0-20.0 mg/kg), risperidone (0.1-1.0 mg/kg), haloperidol (0.1-1.0 mg/kg), or vehicle. Cerebral cortical allopregnanolone and peripheral progesterone and corticosterone levels were determined. Adrenalectomized animals were also examined. Both olanzapine and clozapine increased cerebral cortical allopregnanolone levels, but neither risperidone nor haloperidol had significant effects. Olanzapine and clozapine also increased serum progesterone and corticosterone levels. Adrenalectomy prevented olanzapine- and clozapine-induced elevations in allopregnanolone. Allopregnanolone induction may contribute to olanzapine and clozapine anxiolytic, antidepressant, and mood-stabilizing actions. Alterations in this neuroactive steroid may result in the modulation of GABAergic and dopaminergic neurotransmission, potentially contributing to antipsychotic efficacy.

Progesterone enhances ethanol-induced modulation of mesocortical dopamine neurons: antagonism by finasteride

The effect of endogenous 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG) on the modulation of mesocortical dopamine extracellular concentration by ethanol was investigated by microdialysis in rats. Intraperitoneal injection of progesterone (5 mg/kg, once a day for 5 days) increased the cortical content of 3alpha,5alpha-TH PROG and potentiated the biphasic effect of acute intraperitoneal administration of ethanol on dopamine content. A dose of ethanol (0.25 g/kg) that was ineffective in naïve rats induced a 55% increase in dopamine extracellular concentration in rats pretreated with progesterone. This increase was similar to that induced by a higher dose (0.5 g/kg) of ethanol in naïve rats. Administration of ethanol at 0.5 g/kg to progesterone-pretreated rats inhibited dopamine content by an extent similar to that observed with an even higher dose (1 g/kg) in naïve rats. The administration of the 5alpha-reductase inhibitor finasteride (25 mg/kg, subcutaneous), together with progesterone, prevented the effects of the latter, both on the cortical concentration of 3alpha,5alpha-TH PROG and on the modulation by ethanol of dopamine content. These data suggest that 3alpha,5alpha-TH PROG contributes to the action of ethanol on the mesocortical dopaminergic system. They also suggest that physiological fluctuations in the brain concentrations of neuroactive steroids associated with the oestrous cycle, menopause, pregnancy and stress may alter the response of mesocortical dopaminergic neurons to ethanol.