Effects of sigma(1) receptor agonist SA4503 and neuroactive steroids on performance in a radial arm maze task in rats

Sigma-1 receptor modulation by fluvoxamine ameliorates valproic acid-induced autistic behavior in rats: Involvement of chronic ER stress modulation, enhanced autophagy and M1/M2 microglia polarization

Autism spectrum disorder (ASD) is a neurodevelopmental disorder. While, fluvoxamine (FVX) is an antidepressant and widely prescribed to ASD patients, clinical results are inconclusive and the mechanism of FVX in the management of ASD is unclear. This study determined the potential therapeutic impact of FVX, a sigma-1 receptor (S1R) agonist, against the valproic acid (VPA)-induced model of autism. On gestational day 12.5, Wistar pregnant rats were given a single intraperitoneal (i.p.) injection of either VPA (600 mg/kg) or normal saline (10 mL/kg, vehicle-control). Starting on postnatal day (PND) 21 to PND 50, FVX (30 mg/kg, P·O. daily) and NE-100, (S1R) antagonist, (1 mg/kg, i.p. daily) were given to male pups. Behavior tests and histopathological changes were identified at the end of the experiment. In addition, the cerebellum biomarkers of endoplasmic reticulum (ER) stress and autophagy were assessed. Microglial cell polarization to M1 and M2 phenotypes was also assessed. FVX effectively mitigated the histopathological alterations in the cerebellum caused by VPA. FVX enhanced sociability and stereotypic behaviors in addition to its noteworthy impact on autophagy enhancement, ER stress deterioration, and controlling microglial cell polarization. The current investigation confirmed that the S1R agonist, FVX, can lessen behavioral and neurochemical alterations in the VPA-induced rat model of autism.

A Recent Update on the Role of Estrogen and Progesterone in Alzheimer's Disease

Alzheimer's disease (AD), one of the most prevalent neurodegenerative disease responsible for 60%-80% dementia cases globally. The disease is more prevalent among elder females. Female reproductive hormones are found to be essential for cellular activities in brain. The physiological role of neurotrophins and sex hormones in hippocampal region during neurogenesis and neuron differentiation was studied as well. In addition to triggering cellular pathways, estrogen and progesterone carry out a number of biological processes that lead to neuroprotection. They might have an impact on learning and memory. One of estrogen's modest antioxidant properties is its direct scavenging of free radicals. The neurotrophic effect of estrogen and progesterone can be explained by their ability to rise the expression of the brain-derived neurotrophic factor (BDNF) mRNA. Additionally, they have the ability to degrade beta-amyloid and stop inflammation, apoptotic neuronal cell death, and tau protein phosphorylation. To enhance their neuroprotective action, various cross-talking pathways in cells that are mediated by estrogen, progesterone, and BDNF receptors. This include signaling by mitogen-activated protein kinase/extracellular regulated kinase, phosphatidylinositol 3-kinase/protein kinase B, and phospholipase/protein kinase C. Clinical research to establish the significance of these substances are fragmented, despite publications claiming a lower prevalence of AD when medication is started before menopause. This review article emphasizes an update on the role of estrogen, and progesterone in AD.

Revisiting the sigma-1 receptor as a biological target to treat affective and cognitive disorders

Depression and cognitive disorders are diseases with complex and not-fully understood etiology. Unfortunately, the COVID-19 pandemic dramatically increased the prevalence of both conditions. Since the current treatments are inadequate in many patients, there is a constant need for discovering new compounds, which will be more effective in ameliorating depressive symptoms and treating cognitive decline. Proteins attracting much attention as potential targets for drugs treating these conditions are sigma-1 receptors. Sigma-1 receptors are multi-functional proteins localized in endoplasmic reticulum membranes, which play a crucial role in cellular signal transduction by interacting with receptors, ion channels, lipids, and kinases. Changes in their functions and expression may lead to various diseases, including depression or memory impairments. Thus, sigma-1 receptor modulation might be useful in treating these central nervous system diseases. Importantly, two sigma-1 receptor ligands entered clinical trials, showing that this compound group possesses therapeutic potential. Therefore, based on preclinical studies, this review discusses whether the sigma-1 receptor could be a promising target for drugs treating affective and cognitive disorders.

Brain-derived neurotrophic factor for high-throughput evaluation of selective Sigma-1 receptor ligands

The Sigma-1 receptor (S1R) is an endoplasmic reticulum (ER) chaperone protein that has been implicated in attenuating inflammatory stress-mediated brain injuries. Selective S1R agonists represent a new class of therapeutic agent for treating neuropsychiatric and neurodegenerative disorders, however, to date, no S1R ligand has been approved for therapeutic purposes. We used three potential methods on known and potential S1R ligands to develop an unambiguous high-throughput cell screen for S1R activity. We screened known and potential S1R ligands using radioligand binding and previously reported markers of S1R activity including BDNF release, modulation of IP3 mediated calcium release, and modulation of NGF-induced neurite sprouting. Here, we present results several prototypical S1R compounds and some compounds with the potential for drug repurposing. Using an in-situ ELISA approach we demonstrated that these compounds could stimulate S1R-mediated BDNF release, which is a valuable therapeutic property since BDNF plays a critical role in neuronal support. These compounds were classified as S1R agonists because the BDNF response was comparable to the prototypical agonist 4-PPBP and because it could be reversed by a S1R selective concentration of the antagonist BD1063. When modulation of IP3 mediated calcium response and NGF-induced neurite sprouting were used as a measure of S1R activation, we were unable to reproduce the published results and determined that they are not reliable measures for evaluating functional properties of S1R ligands.

Sigma-1 Receptor: A Potential Therapeutic Target for Traumatic Brain Injury

The sigma-1 receptor (Sig-1R) is a chaperone receptor that primarily resides at the mitochondria-associated endoplasmic reticulum (ER) membrane (MAM) and acts as a dynamic pluripotent modulator regulating cellular pathophysiological processes. Multiple pharmacological studies have confirmed the beneficial effects of Sig-1R activation on cellular calcium homeostasis, excitotoxicity modulation, reactive oxygen species (ROS) clearance, and the structural and functional stability of the ER, mitochondria, and MAM. The Sig-1R is expressed broadly in cells of the central nervous system (CNS) and has been reported to be involved in various neurological disorders. Traumatic brain injury (TBI)-induced secondary injury involves complex and interrelated pathophysiological processes such as cellular apoptosis, glutamate excitotoxicity, inflammatory responses, endoplasmic reticulum stress, oxidative stress, and mitochondrial dysfunction. Thus, given the pluripotent modulation of the Sig-1R in diverse neurological disorders, we hypothesized that the Sig-1R may affect a series of pathophysiology after TBI. This review summarizes the current knowledge of the Sig-1R, its mechanistic role in various pathophysiological processes of multiple CNS diseases, and its potential therapeutic role in TBI.

Molecular Interplay Between the Sigma-1 Receptor, Steroids, and Ion Channels

Cell excitability is tightly regulated by the activity of ion channels that allow for the passage of ions across cell membranes. Ion channel activity is controlled by different mechanisms that change their gating properties, expression or abundance in the cell membrane. The latter can be achieved by forming complexes with a diversity of proteins like chaperones such as the Sigma-1 receptor (Sig-1R), which is one with unique features and exhibits a role as a ligand-operated chaperone. This molecule also displays high intracellular mobility according to its activation level since, depletion of internal Ca⁺² stores or the presence of specific ligands, produce Sig-1R’s mobilization from the endoplasmic reticulum toward the plasma membrane or nuclear envelope. The function of the Sig-1R as a chaperone is regulated by synthetic and endogenous ligands, with some of these compounds being a steroids and acting as key endogenous modifiers of the actions of the Sig-1R. There are cases in the literature that exemplify the close relationship between the actions of steroids on the Sig-1R and the resulting negative or positive effects on ion channel function/abundance. Such interactions have been shown to importantly influence the physiology of mammalian cells leading to changes in their excitability. The present review focuses on describing how the Sig-1R regulates the functional properties and the expression of some sodium, calcium, potassium, and TRP ion channels in the presence of steroids and the physiological consequences of these interplays at the cellular level are also discussed.

SA4503, A Potent Sigma-1 Receptor Ligand, Ameliorates Synaptic Abnormalities and Cognitive Dysfunction in a Mouse Model of ATR-X Syndrome

α-thalassemia X-linked intellectual disability (ATR-X) syndrome is caused by mutations in ATRX. An ATR-X model mouse lacking Atrx exon 2 displays phenotypes that resemble symptoms in the human intellectual disability: cognitive defects and abnormal dendritic spine formation. We herein target activation of sigma-1 receptor (Sig-1R) that can induce potent neuroprotective and neuroregenerative effects by promoting the activity of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF). We demonstrated that treatment with SA4503, a potent activator of Sig-1R, reverses axonal development and dendritic spine abnormalities in cultured cortical neurons from ATR-X model mice. Moreover, the SA4503 treatment rescued cognitive deficits exhibited by the ATR-X model mice. We further found that significant decreases in the BDNF-protein level in the medial prefrontal cortex of ATR-X model mice were recovered with treatment of SA4503. These results indicate that the rescue of dendritic spine abnormalities through the activation of Sig-1R has a potential for post-diagnostic therapy in ATR-X syndrome.

Role of σ1 Receptors in Learning and Memory and Alzheimer's Disease-Type Dementia

The present chapter will review the role of σ1 receptor in learning and memory and neuroprotection , against Alzheimer's type dementia. σ1 Receptor agonists have been tested in a variety of pharmacological and pathological models of learning impairments in rodents these last past 20 years. Their anti-amnesic effects have been explained by the wide-range modulatory role of σ1 receptors on Ca2+ mobilizations, neurotransmitter responses, and particularly glutamate and acetylcholine systems, and neurotrophic factors. Recent observations from genetic and pharmacological studies have shown that σ1 receptor can also be targeted in neurodegenerative diseases, and particularly Alzheimer's disease . Several compounds, acting partly through the σ1 receptor, have showed effective neuroprotection in transgenic mouse models of Alzheimer's disease . We will review the data and discuss the possible mechanisms of action, particularly focusing on oxidative stress and mitochondrial integrity, trophic factors and a novel hypothesis suggesting a functional interaction between the σ1 receptor and α7 nicotinic acetylcholine receptor. Finally, we will discuss the pharmacological peculiarities of non-selective σ1 receptor ligands, now developed as neuroprotectants in Alzheimer's disease , and positive modulators, recently described and that showed efficacy against learning and memory deficits.

Sigma 1 receptor activation regulates brain-derived neurotrophic factor through NR2A-CaMKIV-TORC1 pathway to rescue the impairment of learning and memory induced by brain ischaemia/reperfusion

RATIONALE

Sigma-1 receptor (Sig-1R) agonists showed anti-amnesic properties in Alzheimer's disease models and anti-inflammatory properties in cerebrum ischaemia models. The agonist of Sig-1R was reported to up-regulate brain-derived neurotrophic factor (BDNF) levels in the hippocampus of mice. Here, we investigate whether the activation of Sig-1R attenuates the learning and memory impairment induced by ischaemia/reperfusion and how it affects the expression of BDNF.

OBJECTIVES

Bilateral common carotid artery occlusion (BCCAO) was induced for 20 min in C57BL/6 mice.

MATERIALS AND METHODS

Sig-1R agonist, PRE084, sigma 1/2 non-selective agonist, DTG, Sig-1R antagonist and BD1047 were injected once daily throughout the experiment. Behavioural tests were performed from day 8. On day 22 after BCCAO, mice were sacrificed for biochemical analysis.

RESULTS

PRE084 and DTG ameliorated learning and memory impairments in the Y maze, novel object recognition, and water maze tasks and prevented the decline of synaptic proteins and BDNF expression in the hippocampus of BCCAO mice. Furthermore, PRE084 and DTG up-regulated the level of NMDA receptor 2A (NR2A), calcium/calmodulin-dependent protein kinase type IV (CaMKIV) and CREB-specific co-activator transducer of regulated CREB activity 1 (TORC1). Additionally, the effects of PRE084 and DTG were antagonised by the co-administration of BD1047.

CONCLUSIONS

Sig-1R activation showed an attenuation in the ischaemia/reperfusion model and the activation of Sig-1R increased the expression of BDNF, possibly through the NR2A-CaMKIV-TORC1 pathway, and Sig-1R agonists might function as neuroprotectant agents in vascular dementia.

Dehydroepiandrosterone sulphate: action and mechanism in the brain

Dehydroepiandrosterone sulphate (DHEAS) is synthesised from dehydroepiandrosterone by the enzyme sulphotransferase. DHEAS is one of the most important neurosteroids in the brain. The concentration of DHEAS in the brain is sometimes higher than peripheral system. At the cellular level, DHEAS has been shown to modulate a variety of synaptic transmission, including cholinergic, GABAergic dopaminergic and glutamatergic synaptic transmission. In addition to the effect on the release of a number of neurotransmitters, DHEAS could also modulate the activity of postsynaptic receptors. DHEAS has been found to have multiple important effects on brain functions, such as memory enhancing, antidepressant and anxiolytic effects, and may have relationships with many brain diseases.

The cholinergic system, sigma-1 receptors and cognition

This article provides an overview of present knowledge regarding the relationship between the cholinergic system and sigma-1 receptors, and discusses potential applications of sigma-1 receptor agonists in the treatment of memory deficits and cognitive disorders. Sigma-1 receptors, initially considered as a subtype of the opioid family, are unique ligand-regulated molecular chaperones in the endoplasmatic reticulum playing a modulatory role in intracellular calcium signaling and in the activity of several neurotransmitter systems, particularly the cholinergic and glutamatergic pathways. Several central nervous system (CNS) drugs show high to moderate affinities for sigma-1 receptors, including acetylcholinesterase inhibitors (donepezil), antipsychotics (haloperidol, rimcazole), selective serotonin reuptake inhibitors (fluvoxamine, sertraline) and monoamine oxidase inhibitors (clorgyline). These compounds can influence cognitive functions both via their primary targets and by activating sigma-1 receptors in the CNS. Sigma-1 agonists show powerful anti-amnesic and neuroprotective effects in a large variety of animal models of cognitive dysfunction involving, among others (i) pharmacologic target blockade (with muscarinic or NMDA receptor antagonists or p-chloroamphetamine); (ii) selective lesioning of cholinergic neurons; (iii) CNS administration of β-amyloid peptides; (iv) aging-induced memory loss, both in normal and senescent-accelerated rodents; (v) neurodegeneration induced by toxic compounds (CO, trimethyltin, cocaine), and (vi) prenatal restraint stress.

Progestogens influence cognitive processes in aging

Steroid hormones may alter mnemonic processes. The majority of investigations have focused on the effects of 17β-estradiol (E(2)) to mediate learning. However, progesterone (P(4)), which varies across endogenous hormonal milieu with E(2), may also have effects on cognitive processes. P(4) may have effects in the hippocampus, prefrontal cortex (PFC) and/or striatum to enhance cognitive performance. Cognitive performance/learning has been assessed using tasks that are mediated by the hippocampus (water maze), PFC (object recognition) and striatum (conditioning). Our findings suggest that progestogens can have pervasive effects to enhance cognitive performance and learning in tasks mediated by the hippocampus, PFC and striatum and that these effects may be in part independent of actions at intracellular progestin receptors. Progestogens may therefore influence cognitive processes.

The sigma receptor agonist SA4503 both attenuates and enhances the effects of methamphetamine

BACKGROUND

Methamphetamine's behavioral effects have been attributed to its interaction with monoamine transporters; however, methamphetamine also has affinity for sigma receptors.

METHOD

The present study investigated the effect of the sigma receptor agonist SA 4503 and the sigma receptor antagonists BD-1047 and BD-1063 on methamphetamine-evoked [(3)H]dopamine release from preloaded rat striatal slices. The effect of SA 4503 on methamphetamine-induced hyperactivity and on the discriminative stimulus properties of methamphetamine also was determined.

RESULTS

SA 4503 attenuated methamphetamine-evoked [(3)H]dopamine release in a concentration-dependent manner. BD-1047 and BD-1063 did not affect release. SA 4503 dose-dependently potentiated and attenuated methamphetamine-induced hyperactivity. SA 4503 pretreatment augmented the stimulus properties of methamphetamine.

CONCLUSIONS

Our findings indicate that SA 4503 both enhances and inhibits methamphetamine's effects and that sigma receptors are involved in the neurochemical, locomotor stimulatory and discriminative stimulus properties of methamphetamine.

Progesterone attenuates cocaine-induced responses

In this review, we summarize literature focused on how progesterone alters cocaine-induced psychomotor, reinforcement, and physiological responses. Clinical studies suggest that progesterone attenuates the subjective effects of cocaine. Similarly, preclinical studies have demonstrated that cocaine-induced reward and psychomotor responses are attenuated after progesterone administration. In rats progesterone also reduces the reinforcement effects of cocaine attenuates acquisition, escalation, reinstatement of cocaine self-administration, and cocaine-seeking behaviors. Progesterone also counteracts the facilitatory effects of estrogen on cocaine self-administration and psychomotor activation. These findings suggest that progesterone has a potential in clinical applications as a treatment for cocaine addiction. Constantly changing progesterone serum levels in female humans and rats affect the female's reinforcement responses to cocaine and may in part contribute to the known sex differences in cocaine responses.

Computer-aided structure analysis of an epimerized dehydroepiandrosterone derivative and its biological effect in a model of reactive gliosis

The naturally occurring steroid dehydroepiandrosterone (DHEA) is reported to reduce glial fibrillary acidic protein (GFAP) overexpression in a model of reactive gliosis due to its conversion to estradiol by the enzyme aromatase. In the present study we examined the biological effect of a new epimerized derivative of DHEA, 16alpha-iodomethyl-13alpha-dehydroepiandrosterone derivative (16alpha-iodomethyl-13alpha-DHEAd, 16alpha-iodomethyl-13alpha-androst-5-en-3beta,17beta-diol), using the same model system, and compared the 3D structure of this molecule with that of DHEA and two steroidal type aromatase inhibitors, formestane and exemestane. The synthetic compound, in contrast to the reported effect of DHEA, was able to reduce GFAP overexpression only if the enzyme aromatase was inhibited. Data obtained from computational calculations fortified by X-ray crystallography revealed that contrary to the nearly planar sterane framework of DHEA, the synthetic derivative 16alpha-iodomethyl-13alpha-DHEAd has a bent sterane skeleton, resulting in a 3D structure that is similar to that of formestane or exemestane. Moreover, 16alpha-iodomethyl-13alpha-DHEAd resulted to be metabolically more stable than DHEA. The results suggest that epimerization of the sterane skeleton of DHEA inclines the plane of the D ring, leading to a significantly altered biological activity. The synthetic molecule has a DHEA-like effect on GFAP overexpression when the enzyme aromatase is inhibited and the naturally occurring DHEA is ineffective in this respect. On the other hand, based on their structural similarity it can be hypothesized that 16alpha-iodomethyl-13alpha-DHEAd applied alone might have a biological effect similar to that of formestane or exemestane.

Neurosteroids' effects and mechanisms for social, cognitive, emotional, and physical functions

Hormones are trophic factors that integrate central and peripheral nervous system functions, and can influence social, cognitive, emotional and physical (SCEP) processes. Greater understanding of behavioral and neurobiological underpinnings of mental, cognitive, and/or physical changes with maturation is becoming increasingly important as the world's population ages. There are individual differences in how people age, but the factors that influence these differences are not well understood. Social supports are one factor that may influence the trajectory of age-related processes. The loss of close relationships, especially among older persons, is one of the greatest risk factors for mental and physical decline. Progesterone, secreted by the ovaries, or produced de novo in the brain, is readily converted centrally to 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), and can influence SCEP, through rapid, non-classical steroid-mediated actions. Our hypothesis is that 3alpha,5alpha-THP is a key trophic factor in SCEP and development. Our research has demonstrated that 3alpha,5alpha-THP facilitates social and sexual behavior of rodents, which evokes further increases in 3alpha,5alpha-THP in midbrain and hippocampus, brain areas involved in SCEP. The role of 3alpha,5alpha-THP to influence social and/or sexual experience, and thereby SCEP, is discussed in this review. Further understanding of these neurobiological and/or behavioral factors may lead to findings that ultimately can promote health and prevent disease.

The pharmacology of sigma-1 receptors

Originally considered an enigmatic protein, the sigma-1 receptor has recently been identified as a unique ligand-regulated molecular chaperone in the endoplasmic reticulum of cells. This discovery causes us to look back at the many proposed roles of this receptor, even before its molecular function was identified, in many diseases such as methamphetamine or cocaine addiction, amnesia, pain, depression, Alzheimer's disease, stroke, retinal neuroprotection, HIV infection, and cancer. In this review, we examine the reports that have clearly shown an agonist-antagonist relationship regarding sigma-1 receptors in models of those diseases and also review the relatively known mechanisms of action of sigma-1 receptors in an attempt to spur the speculation of readers on how the sigma-1 receptor at the endoplasmic reticulum might relate to so many diseases. We found that the most prominent action of sigma-1 receptors in biological systems including cell lines, primary cultures, and animals is the regulation and modulation of voltage-regulated and ligand-gated ion channels, including Ca(2+)-, K(+)-, Na(+), Cl(-), and SK channels, and NMDA and IP3 receptors. We found that the final output of the action of sigma-1 receptor agonists is to inhibit all above-mentioned voltage-gated ion channels, while they potentiate ligand-gated channels. The inhibition or potentiation induced by agonists is blocked by sigma-1 receptor antagonists. Other mechanisms of action of sigma-1 receptors, and to some extent those of sigma-2 receptors, were also considered. We conclude that the sigma-1 and sigma-2 receptors represent potential fruitful targets for therapeutic developments in combating many human diseases.

Nanomolar concentrations of pregnenolone sulfate enhance striatal dopamine overflow in vivo

The balance between GABA-mediated inhibitory and glutamate-mediated excitatory synaptic transmission represents a fundamental mechanism for controlling nervous system function, and modulators that can alter this balance may participate in the pathophysiology of neuropsychiatric disorders. Pregnenolone sulfate (PS) is a neuroactive steroid that can modulate the activity of ionotropic glutamate and GABA(A) receptors either positively or negatively, depending upon the particular receptor subtype, and modulates synaptic transmission in a variety of experimental systems. To evaluate the modulatory effect of PS in vivo, we infused PS into rat striatum for 20 min via a microdialysis probe while monitoring local extracellular dopamine (DA) levels. The results demonstrate that PS at low nanomolar concentrations significantly increases extracellular DA levels. The PS-induced increase in extracellular DA is antagonized by the N-methyl-d-aspartate (NMDA) receptor antagonist, d-AP5 [d-(-)-2-amino-5-phosphonopentanoic acid], but not by the sigma receptor antagonist, BD 1063 [1(-)[2-(3,4-dichlorophenyl)-ethyl]-4-methylpiperazine]. The results demonstrate that exogenous PS, at nanomolar concentrations, is able to increase DA overflow in the striatum through an NMDA receptor-mediated pathway.

Further evidence for an antidepressant potential of the selective sigma1 agonist SA 4503: electrophysiological, morphological and behavioural studies

In this study, we evaluated the ability of the selective sigma1 agonist SA 4503 to produce changes in brain function, similar to those elicited by classical antidepressants. We focused more specifically on the influence of SA 4503 on central serotonergic (5-HT) transmission, and on hippocampal cell proliferation. A 2-d continuous treatment with SA 4503 (1-40 mg/kg.d) increased 5-HT neuron firing rate in a dose-dependent, bell-shaped manner, with a culminating effect of +90% at 10 mg/kg.d. The same dose induced the appearance of a 5-HT1A receptor-mediated inhibitory tonus on hippocampal pyramidal neurons, as revealed by intravenous injections of the selective 5-HT1A antagonist WAY 100635. Moreover, continuous administration of SA 4503 (3 and 10 mg/kg.d, 3 d) dose-dependently enhanced the number of bromodeoxyuridine-positive cells in the subgranular zone of the hippocampus (+48% and +94%, respectively), thus indicating an increased cell proliferation. Finally, a single administration of SA 4503 (3 and 10 mg/kg i.p.) increased the time spent swimming in the forced swimming test. Together, these results provide both functional and behavioural evidence that this compound has an important antidepressant potential. Further, the fact that the functional changes occurred within a short time-frame (2-3 d) suggest that this antidepressant potential might have a rapid onset of action.

Progesterone to ovariectomized mice enhances cognitive performance in the spontaneous alternation, object recognition, but not placement, water maze, and contextual and cued conditioned fear tasks

Research on how steroid hormones mediate mnemonic processes have focused on effects of 17beta-estradiol (E(2)); yet, progesterone (P(4)) co-varies with E(2) across endogenous hormonal milieu, and itself may influence cognitive processes. We investigated the hypothesis that acute P(4) treatment enhances cognitive performance compared to vehicle. Ovariectomized (OVX) c57/BL6J mice were randomly assigned to be subcutaneously injected with oil vehicle or P(4) (10mg/kg). Mice were trained in the spontaneous alternation, object recognition, object placement, water maze, or fear conditioning tasks, and injected with vehicle or P(4) before training or immediately post-training, and then were tested 1, 4, or 24h later. The data obtained from these experiments supported our hypothesis. P(4) increased the percentage of spontaneous alterations made in a T-maze more so than did vehicle. P(4), compared to vehicle, increased the percentage of time spent exploring the novel object in the object recognition task, but did not alter performance in the object placement task. P(4), compared to vehicle, decreased latencies to reach the location in the water maze where the platform had been during training in a probe trial, but did not alter performance in the control, cued trial. Compared to vehicle, P(4) treatment increased freezing in contextual and cued fear testing. Thus, acute P(4) treatment to OVX mice can improve cognitive performance across a variety of tasks.

Influence of epipregnanolone on the modulation of rapid tolerance to ethanol by neurosteroids

OBJECTIVE: The objective of the present study was to investigate the effect of epipregnanolone on the influence of neurosteroids on the development of rapid tolerance to the motor impairing and hypothermic effects of ethanol. METHOD: Experiment 1: on Day 1 groups of mice were pretreated with saline or with epipregnanolone. After 30 min each group was further divided in subgroups that received ethanol or saline. Thirty, 60 and 90 min after the injections the animals were tested on the rota-rod or the body temperature was measured. On Day 2 all groups received ethanol and a similar procedure was followed to evaluate rapid tolerance. Experiment 2 and 3: On Day 1 groups of mice were treated with epipregnanolone and after 15 min each group was divided into three groups in order to receive pregnenolone sulfate, dehydroepiandrosterone sulfate or saline. Thirty minutes later, each group was further divided into two subgroups in order to receive ethanol or saline, respectively, and 30, 60 and 90 min later the animals were tested as in the experiment 1. On Day 2 all groups received ethanol and a similar procedure was followed to evaluate rapid tolerance. RESULTS: Pretreatment with epipregnanolone (0.10-0.30 mg/kg) significantly blocked the development of tolerance to the motor impairing and hypothermic effects induced by ethanol in mice. Considering tolerance to ethanol-induced motor impairment, epipregnanolone (0.15 mg/kg) reversed the stimulatory action of dehydroepiandrosterone sulfate (0.15 mg/kg), but did not affect the actions of pregnenolone sulfate (0.08 mg/kg). Moreover, epipregnanolone prevented the inhibitory action of allotetrahydrodeoxycorticosterone (0.10 mg/kg). In relation to ethanol-induced hypothermia, the results showed that pretreatment with epipregnanolone (0.30 mg/kg) significantly prevented the stimulatory action of dehydroepiandrosterone sulfate and pregnenolone sulfate, as well as the inhibitory action of allotetrahydrodeoxicorticosterone (0.20 mg/kg), on tolerance to this effect. CONCLUSIONS: The results suggest a differential interaction between neurosteroids that might modulate the development of rapid tolerance to ethanol.

Temporal effects of dehydroepiandrosterone sulfate on memory formation in day-old chicks

Dehydroepiandrosterone sulfate (DHEAS) has been shown to enhance memory retention in different animal models and in various learning paradigms. In the present study, we investigated the effect of peripherally administered DHEAS on the acquisition, consolidation and retention of memory using a weak version of the one-trial passive avoidance task in day-old chicks. Intraperitoneally administered DHEAS (20 mg/kg) either 30 min before or 30 min and 4.5 h after training on the weakly aversive stimulus, enhanced recall at 24 h following training, suggesting a potentiation of not only the acquisition but also the early and late phases of memory consolidation. In contrast, when DHEAS was administered at 30 min prior to the 24 h retention test there was no memory enhancement, indicating a lack of effect on memory retrieval. Memory recall was unaltered when DHEAS was administered at 30 min before training in a control group trained on a strongly aversive stimulus, confirming memory-specific effects. Interestingly, the memory enhancement appeared to be sex-specific as male chicks showed higher recall than females. These findings provide further evidence that DHEAS enhances memory and may be involved in the temporal cascade of long-term memory formation.

Estrogens and progestins enhance spatial learning of intact and ovariectomized rats in the object placement task

Steroid modulation of cognitive function has focused on estrogen (E(2)), but progestins naturally co-vary with E(2) and may also influence cognitive performance. Spatial performance in the object placement task over endogenous hormonal states in which E(2) and progestins vary, and when E(2) and/or progestins were administered, was examined. Experiment 1: Rats in proestrus or estrus had significantly better performance in the object placement task than did diestrus rats. Experiment 2: Rats in the third trimester, post-partum, or lactation exhibited significantly better performance in the object placement task than did rats in the first trimester. Experiment 3: Ovariectomized (ovx) rats administered 17beta-estradiol (0.9 mg/kg), subcutaneously (sc), progesterone (P; 4 mg/kg, sc), or E(2) and P, immediately after training in the object placement task, performed significantly better when tested 4h later, than did control rats administered vehicle (sesame oil 0.2 cc). Experiment 4: ovx rats administered E(2) or P with a 1.5h delay after training in the object placement task, did not perform differently than vehicle-administered controls. Experiment 5: ovx rats administered post-training E(2), which has a high affinity for both E(2) receptor (ER)alpha and beta isoforms, or propyl pyrazole triol (PPT; 0.9 mg/kg, sc), which is more selective for ERalpha than ERbeta, had significantly better performance in the object placement task than did rats administered vehicle or diarylpropionitrile (DPN; 0.9 mg/kg, sc), an ERbeta selective ligand. Experiment 6: ovx rats administered P, or its metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP; 4 mg/kg, sc), immediately post-training performed significantly better in the object placement task than did vehicle control rats. Thus, performance in the object placement task is better when E(2) and/or P are naturally elevated or when E(2), the ERalpha selective ER modulator PPT, P, or its metabolite, 3alpha,5alpha-THP, are administered post-training.

Phencyclidine-induced cognitive deficits in mice are improved by subsequent subchronic administration of fluvoxamine: role of sigma-1 receptors

This study was undertaken to examine the effects of the selective serotonin reuptake inhibitors fluvoxamine and paroxetine on cognitive deficits in mice after repeated administration of the N-methyl-D-aspartate receptor antagonist phencyclidine (PCP). In the novel object recognition test, repeated administration of PCP (10 mg/kg/day, 10 days) significantly decreased the exploratory preference in the retention test session, but not in the training test session. PCP-induced cognitive deficits were significantly improved by subsequent subchronic (2-week) administration of fluvoxamine (20 mg/kg/day), but not paroxetine (10 mg/kg/day). Furthermore, the effect of fluvoxamine on PCP-induced cognitive deficits was antagonized by co-administration of the selective sigma-1 receptor antagonist NE-100 (1 mg/kg/day). Moreover, PCP-induced cognitive deficits were also significantly improved by subsequent subchronic (2-week) administration of the selective sigma-1 receptor agonist SA4503 (1 mg/kg/day) or neurosteroid dehydroepiandrosterone 3-sulfate (DHEA-S; 25 mg/kg/day). The effects of SA4503 or DHEA-S were also antagonized by co-administration of NE-100 (1 mg/kg/day), suggesting the role of sigma-1 receptors in the active mechanisms of these drugs. In contrast, acute single administration of these drugs (fluvoxamine, paroxetine, SA4503) alone or combination with NE-100 did not alter PCP-induced cognitive deficits. The present study suggests that agonistic activity of fluvoxamine at sigma-1 receptors plays a role in the active mechanisms of fluvoxamine on PCP-induced cognitive deficits in mice. Therefore, sigma-1 receptor agonists such as fluvoxamine would be potential therapeutic drugs for the treatment of the cognitive deficits of schizophrenia.

Neurosteroids, neuroactive steroids, and symptoms of affective disorders

Neurosteroids (NS) are steroids synthesized by the brain. Neuroactive steroids (NAS) refers to steroids that, independent of their origin, are capable of modifying neural activities. NAS bind and modulate different types of membrane receptors. The gamma amino butyric acid (GABA) and sigma receptor complexes have been the most extensively studied. Oxidized ring A reduced pregnanes, tetrahydroprogesterone (THP), and tetrahydrodeoxycorticosterone (THDOC) bind to the progesterone intracellular receptor (PR), and in this way can also regulate gene expression. Animal experimentation showed that salient symptoms of depression, viz., anxiety, sleep disturbances, and memory and sexual dysfunctions, are modulated by NAS. In turn, psychotropic drugs modulate NS and NAS levels. NS levels as well as NAS plasma concentrations change in patients with depression syndromes, the levels return to normal baseline with recovery, but normalization is not necessary for successful therapy. Results from current studies on the evolution of nervous systems, including evolutionary developmental biology as well as anatomical and physiological findings, almost preclude a categorical classification of the psychiatric ailments the human brain succumbs to. The persistence in maintaining such essentialist classifications may help to explain why up to now the search for biological markers in psychiatry has been an unrewarding effort. It is proposed that it would be more fruitful to focus on relationships between NAS and symptoms of psychiatric disorders, rather than with typologically defined disorders.

Neurosteroids and cholinergic systems: implications for sleep and cognitive processes and potential role of age-related changes

RATIONALE

The neurosteroids pregnenolone sulfate (PREGS), dehydroepiandrosterone sulfate (DHEAS) and allopregnanolone (3alpha,5alpha THPROG) have been implicated as powerful modulators of memory processes and sleep states in young and aged subjects with memory impairment. As these processes depend on the integrity of cholinergic systems, a specific effect of neurosteroids on these systems may account for their effects on sleep and memory.

OBJECTIVE

To review the evidence for a specific and differential effect of neurosteroids on cholinergic systems.

METHODS

We carried out keyword searches in "Medline" to identify articles concerning (1) the effects of neurosteroids on cholinergic systems, sleep and memory processes, and (2) changes in neurosteroid concentrations during aging. Few results are available for humans. Most data concerned rodents.

RESULTS

Peripheral and central administrations of PREGS, DHEAS, and 3alpha,5alpha THPROG modulate the basal forebrain and brainstem projection cholinergic neurons but not striatal cholinergic interneurons. Local administration of neurosteroids to the basal forebrain and brainstem cholinergic neurons alters sleep and memory in rodents. There are a few conflicting reports concerning the effects of aging on neurosteroid concentrations in normal and pathological conditions.

CONCLUSIONS

The specific modulation of basal forebrain and brainstem cholinergic systems by neurosteroids may account for the effects of these compounds on sleep and memory processes. To improve our understanding of the role of neurosteroids in cholinergic systems during normal and pathological aging, we need to determine whether there is specific regionalization of neurosteroids, and we need to investigate the relationship between neurosteroid concentrations in cholinergic nuclei and age-related sleep and memory impairments.

The Sigma1 Protein as a Target for the Non-genomic Effects of Neuro(active)steroids: Molecular, Physiological, and Behavioral Aspects

Steroids synthesized in the periphery or de novo in the brain, so called 'neurosteroids', exert both genomic and nongenomic actions on neurotransmission systems. Through rapid modulatory effects on neurotransmitter receptors, they influence inhibitory and excitatory neurotransmission. In particular, progesterone derivatives like 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) are positive allosteric modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor and therefore act as inhibitory steroids, while pregnenolone sulphate (PREGS) and dehydroepiandrosterone sulphate (DHEAS) are negative modulators of the GABA(A) receptor and positive modulators of the N-methyl-D-aspartate (NMDA) receptor, therefore acting as excitatory neurosteroids. Some steroids also interact with atypical proteins, the sigma (sigma) receptors. Recent studies particularly demonstrated that the sigma1 receptor contributes effectively to their pharmacological actions. The present article will review the data demonstrating that the sigma1 receptor binds neurosteroids in physiological conditions. The physiological relevance of this interaction will be analyzed and the impact on physiopathological outcomes in memory and drug addiction will be illustrated. We will particularly highlight, first, the importance of the sigma1-receptor activation by PREGS and DHEAS which may contribute to their modulatory effect on calcium homeostasis and, second, the importance of the steroid tonus in the pharmacological development of selective sigma1 drugs.

Steroids, neuroactive steroids and neurosteroids in psychopathology

The term "neurosteroid" (NS) was introduced by Baulieu in 1981 to name a steroid hormone, dehydroepiandrosterone sulfate (DHEAS), that was found at high levels in the brain long after gonadectomy and adrenalectomy, and shown later to be synthetized by the brain. Later, androstenedione, pregnenolone and their sulfates and lipid derivatives as well as tetrahydrometabolites of progesterone (P) and deoxycorticosterone (DOC) were identified as neurosteroids. The term "neuroactive steroid" (NAS) refers to steroids which, independent of their origin, are capable of modifying neural activities. NASs bind and modulate different types of membrane receptors. The GABA and sigma receptor complexes have been the most extensively studied, while glycine-activated chloride channels, nicotinic acetylcholine receptors, voltage-activated calcium channels, although less explored, are also modulated by NASs. Within the glutamate receptor family, N-methyl-d-aspartate (NMDA) receptors, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and kainate receptors have also been demonstrated to be a target for steroid modulation. Besides their membrane effects, once inside the neuron oxidation of Ring A reduced pregnanes, THP and THDOC, bind to the progesterone intracellular receptor and regulate gene expression through this path. The involvement of NASs on depression syndromes, anxiety disorders, stress responses to different stress stimuli, memory processes and related phenomena such as long-term potentiation are reviewed and critically evaluated. The importance of context for the interpretation of behavioral effects of hormones as well as for hormonal levels in body fluids is emphasized. Some suggestions for further research are given.

Treatments for schizophrenia: a critical review of pharmacology and mechanisms of action of antipsychotic drugs

The treatment of schizophrenia has evolved over the past half century primarily in the context of antipsychotic drug development. Although there has been significant progress resulting in the availability and use of numerous medications, these reflect three basic classes of medications (conventional (typical), atypical and dopamine partial agonist antipsychotics) all of which, despite working by varying mechanisms of actions, act principally on dopamine systems. Many of the second-generation (atypical and dopamine partial agonist) antipsychotics are believed to offer advantages over first-generation agents in the treatment for schizophrenia. However, the pharmacological properties that confer the different therapeutic effects of the new generation of antipsychotic drugs have remained elusive, and certain side effects can still impact patient health and quality of life. Moreover, the efficacy of antipsychotic drugs is limited prompting the clinical use of adjunctive pharmacy to augment the effects of treatment. In addition, the search for novel and nondopaminergic antipsychotic drugs has not been successful to date, though numerous development strategies continue to be pursued, guided by various pathophysiologic hypotheses. This article provides a brief review and critique of the current therapeutic armamentarium for treating schizophrenia and drug development strategies and theories of mechanisms of action of antipsychotics, and focuses on novel targets for therapeutic agents for future drug development.

Sigma 1 receptor-related neuroactive steroids modulate cocaine-induced reward

The sigma1 receptor is critically involved in the rewarding effect of cocaine, as measured using the conditioned place preference (CPP) procedure in mice. Neuroactive steroids exert rapid neuromodulatory effects in the brain by interacting with GABA(A), NMDA, and sigma1 receptors. At the sigma1 receptor level, 3beta-hydroxy-5-androsten-17-one [dehydroepiandrosterone (DHEA)] and 3beta-hydroxy-5-pregnen-20-one (pregnenolone) act as agonists, whereas 4-pregnene-3,20-dione (progesterone) is an efficient antagonist. The present study sought to investigate the action of neuroactive steroids in acquisition of cocaine-induced CPP in C57BL/6 mice. None of these steroids induced CPP alone. However, pretreatment with DHEA or pregnenolone (5-20 mg/kg, s.c.) during conditioning with cocaine (10 mg/kg, i.p.) increased the conditioned score. On the contrary, pretreatment with either progesterone (10 or 20 mg/kg, s.c.) or finasteride (25 mg/kg, twice a day), a 5alpha-reductase inhibitor, blocked acquisition of cocaine (20 mg/kg)-induced CPP. A crossed pharmacology was observed between steroids and sigma1 ligands. The sigma1 antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine blocked cocaine-induced CPP and its potentiation by DHEA or pregnenolone. Progesterone blocked cocaine-induced CPP and its potentiation by the sigma1 agonist igmesine. These results showed that neuroactive steroids play a role in cocaine-induced appetence, through their interaction with the sigma1 receptor. Therefore, neuroendocrine control of cocaine addiction may not involve solely glucocorticoids. The importance of neuroactive steroids as factors of individual vulnerability to drug addiction should, thus, be considered.

Effects of ethanol or rimcazole on dizocilpine maleate-induced behaviors in male and female rats

The current investigation was undertaken to explore further the interactions between ethanol and the phencyclidine analog dizocilpine maleate (MK-801) on behaviors in male and female rats. It was previously found that ethanol dependence conferred cross-tolerance to the behaviorally activating effects of dizocilpine. The current set of studies was designed to assay the interactions between dizocilpine and ethanol in ethanol-naive animals by measuring open field behaviors. I also tested interactions between dizocilpine and rimcazole, a sigma receptor antagonist. In agreement with previous reports, I found significant effects of dizocilpine on several open field behaviors. In general, female rats displayed a lower level of hyperlocomotion and higher level of stereotypies than did male rats. Co-administration of ethanol delayed time to peak hyperlocomotion in male rats. It reduced locomotion in female rats compared with findings for administration of dizocilpine alone. Co-administration of ethanol with dizocilpine increased stereotypies in both sexes. Administration of ethanol increased locomotion to a greater degree in female than in male rats. In contrast, co-administration of rimcazole with dizocilpine had little effect on hyperlocomotion in male rats while increasing levels in female rats. Rimcazole increased dizocilpine-induced stereotypies to a greater extent in male than in female rats. Results of receptor-binding studies revealed small differences for cerebral cortical sigma receptors between male and female rats. Dizocilpine was unable to compete for sigma receptor-binding sites. This is in contrast to phencyclidine, which acts at both N-methyl-D-aspartate (NMDA) and sigma receptors. These findings extend previous evidence of interactions between ethanol and dizocilpine, but highlight that responses vary by measure, sex, and length of ethanol exposure. In addition, findings from the current study uncovered sex-selective interactions between dizocilpine and a sigma receptor ligand, providing further evidence for complex actions and interactions of this noncompetitive NMDA receptor antagonist with multiple sites in brain.

Neuroactive steroid mechanisms and GABA type A receptor subunit assembly in hypothalamic and extrahypothalamic regions

Gonadal- and neuronal-derived steroids are capable of altering brain functions through two basic mechanisms: slow (genomic) and rapid (novel nongenomic membrane) types of activities. The genomic activities that are circumscribed to the numerous neuronal and glial expressed receptor actions involve transcriptional processes regulated largely by classical steroids. On the other hand, rapid nongenomic activities are linked to the stereoselective interactions of potent neuroactive steroids. It appears that both of these steroid mechanisms can be successfully evoked at the ligand-gated heteroligomeric GABA type A receptor. However, the precise structural prerequisites and type of molecular steroid interactions implicated in this neuronal target have not been fully investigated. This article reviews the most common subunits (alpha, beta, and gamma) of the native GABA type A receptor involved in signaling pathways of slow and rapid steroidal mechanisms. Different beta-containing compositions (alpha1beta1-3gamma2) are necessary for the slow type of mechanism, whereas different alpha-containing constructs (alpha2-6beta 1/2 gamma2/2L) are linked to the rapid type. Because of the major role played by neuroactive steroids in GABA-dependent neuroendocrine and sociosexual events, distinction of the specific subunit combination is essential not only for elucidating neuronal communicative expressions during such events but also for elucidating their potential neuroprotective role in neurodegenerative disorders.

Learning and memory in two different reward tasks in a radial arm maze in rats

In an eight-arm radial maze, working and reference memory can be assessed simultaneously in the fixed position of reward task (FPRT) in which half of the arms are baited and their positions are fixed throughout the training trails. We characterized performance of rats in the variable position of reward task (VPRT), in which four out of eight arms were baited, but the positions were varied in every training trial. In the VPRT, the rats learned to choose all arms without any discrimination between baited and non-baited arms and the memory retention was time-dependent. The performance of rats in the FPRT was impaired by altering the spatial organization of the extramaze cues while it was not affected in the VPRT. The number of Fos-positive cells transiently increased in the cerebral cortex and hippocampus of both groups of animals during the training. Finally, bilateral lesions of the dorsal hippocampus resulted in an impairment of working memory in the FPRT and the performance of the rats in the VPRT. These results suggest that different strategies are used between the FPRT and VPRT but the hippocampus plays an important role in performance of rats trained for the VPRT as well as FPRT.

Pregnenolone sulfate, dehydroepiandrosterone sulfate and allotetrahydrodeoxycorticosterone affect rapid tolerance to the hypothermic effect of ethanol

Our previous study showed that the neurosteroids pregnenolone sulfate (PS) and epipregnanolone stimulated and blocked, respectively, the demonstration of chronic tolerance to the incoordinating effect of ethanol. The aim of the present study was to investigate the influence of three neurosteroids on the demonstration of tolerance to ethanol-induced hypothermia in mice using the rapid tolerance paradigm. The first experiment defined the doses of ethanol that did or did not induce rapid tolerance to ethanol-induced hypothermia. In the second, the influence of pretreatment of mice with PS (0.08 or 0.15 mg/kg, i.p.) or dehydroepiandrosterone sulfate (DHEAS; 0.15 or 0.20 mg/kg, i.p.) before ethanol (4.0 g/kg, i.p.) on rapid tolerance was studied. The third experiment examined the effect of allotetrahydrodeoxicorticosterone (ALLOT; 0.10 or 0.20 mg/kg, i.p.) before ethanol (4.0 g/kg, i.p.) on rapid tolerance. Results showed that pretreatment with PS or with DHEAS significantly facilitated the demonstration of rapid tolerance, whereas pretreatment with ALLOT interfered with the demonstration of tolerance to the hypothermic effect.

Neurosteroids in learning and memory processes

The discovery that neurosteroids could be synthesized de novo in the brain independent from the periphery and display neuronal actions led to great enthusiasm for the study of their physiological role. Pharmacological studies suggest that neurosteroids may be involved in several physiological processes, such as learning and memory. This chapter summarizes the effects of the administration of neurosteroids on learning and memory capabilities in rodents and in models of amnesia. We address the central mechanisms involved in mediating the modulation of learning and memory processes by neurosteroids. In this regard, the neurosteroid-modulated neurotransmitter systems, such as gamma-aminobutyric acid type A, N-methyl-D-aspartate, and cholinergic and sigma opioid systems, appear to be potential targets for the rapid memory alteration actions of neurosteroids. Moreover, given that some neurosteroids affect neuronal plasticity, this neuronal change could be involved in the long-term modulation of learning and memory processes. To understand the role of endogeneous neurosteroids in learning and memory processes, we present some physiological studies in rodents and humans. However, the latter do not successfully prove a role of endogenous neurosteroids in age-related memory impairments. Finally, we discuss the relative implication of a given neurosteroid vs its metabolites. For this question, a new approach using the quantitative determination of traces of neurosteroids by mass spectrometry seems to have potential for examining the role of each neurosteroid in discrete brain areas in learning and memory alterations, as observed during aging.

Influence of neurosteroids on the development of rapid tolerance to ethanol in mice

Our recent study demonstrated that neurosteroids might either facilitate or block chronic tolerance to the incoordinating effects of ethanol. The present study investigated the effects of neurosteroids on the development of rapid tolerance to ethanol-induced motor impairment using the N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine [(+)-MK-801] or the gamma-aminobutyric acid (GABA) type A (GABA(A)) receptor agonist muscimol. Male Swiss mice were pretreated with pregnenolone sulfate (0.03 to 0.15 mg/kg) or dehydroepiandrosterone sulfate (0.05 to 0.20 mg/kg) before administration of ethanol (1.9 or 2.25 g/kg) and tested with the rota-rod apparatus. Twenty-four hours later, all animals were re-tested with the rota-rod after receiving the same dose of ethanol. Pretreatment with pregnenolone sulfate or with dehydroepiandrosterone sulfate significantly facilitated the acquisition of tolerance. However, the administration of (+)-MK-801 reversed the stimulatory action of pregnenolone sulfate but did not affect the actions of dehydroepiandrosterone sulfate on ethanol tolerance. Pretreatment with pregnenolone sulfate or dehydroepiandrosterone sulfate prevented the inhibitory action of muscimol on tolerance development. Taken together, our results suggest that neurosteroids may stimulate the development of rapid tolerance to ethanol and that GABA(A) and NMDA receptor systems may be involved in these actions.

Dueling enigmas: neurosteroids and sigma receptors in the limelight

Neurosteroids can be positive or negative regulators of neurotransmitter receptor action, depending on the receptor and the chemical structure of the neurosteroid. This Perspective by Gibbs and Farb is one of two on the subject of neurosteroids. The authors address the possible role of sigma receptors in mediating neurosteroid action and describe how the regulation of inhibitory and excitatory ion channels by neurosteroids has implications for the role of these molecules in learning and memory, nociception, and excitotoxicity.