Proconvulsant effects of neurosteroids pregnenolone sulfate and dehydroepiandrosterone sulfate in mice

Neurosteroids: A potential target for neuropsychiatric disorders

Neurosteroids are steroids produced by endocrine glands and subsequently entering the brain, and also include steroids synthesis in the brain. It has been widely known that neurosteroids influence many neurological functions, including neuronal signaling, synaptic adaptations, and neuroprotective effects. In addition, abnormality in the synthesis and function of neurosteroids has been closely linked to neuropsychiatric disorders, such as Alzheimer's disease (AD), schizophrenia (SZ), and epilepsy. Given their important role in brain pathophysiology and disorders, neurosteroids offer potential therapeutic targets for a variety of neuropsychiatric diseases, and that therapeutic strategies targeting neurosteroids probably exert beneficial effects. We therefore summarized the role of neurosteroids in brain physiology and neuropsychiatric disorders, and introduced the recent findings of synthetic neurosteroid analogues for potential treatment of neuropsychiatric disorders, thereby providing insights for further research in the future.

Neuroactive Steroids, Toll-like Receptors, and Neuroimmune Regulation: Insights into Their Impact on Neuropsychiatric Disorders

Pregnane neuroactive steroids, notably allopregnanolone and pregnenolone, exhibit efficacy in mitigating inflammatory signals triggered by toll-like receptor (TLR) activation, thus attenuating the production of inflammatory factors. Clinical studies highlight their therapeutic potential, particularly in conditions like postpartum depression (PPD), where the FDA-approved compound brexanolone, an intravenous formulation of allopregnanolone, effectively suppresses TLR-mediated inflammatory pathways, predicting symptom improvement. Additionally, pregnane neurosteroids exhibit trophic and anti-inflammatory properties, stimulating the production of vital trophic proteins and anti-inflammatory factors. Androstane neuroactive steroids, including estrogens and androgens, along with dehydroepiandrosterone (DHEA), display diverse effects on TLR expression and activation. Notably, androstenediol (ADIOL), an androstane neurosteroid, emerges as a potent anti-inflammatory agent, promising for therapeutic interventions. The dysregulation of immune responses via TLR signaling alongside reduced levels of endogenous neurosteroids significantly contributes to symptom severity across various neuropsychiatric disorders. Neuroactive steroids, such as allopregnanolone, demonstrate efficacy in alleviating symptoms of various neuropsychiatric disorders and modulating neuroimmune responses, offering potential intervention avenues. This review emphasizes the significant therapeutic potential of neuroactive steroids in modulating TLR signaling pathways, particularly in addressing inflammatory processes associated with neuropsychiatric disorders. It advances our understanding of the complex interplay between neuroactive steroids and immune responses, paving the way for personalized treatment strategies tailored to individual needs and providing insights for future research aimed at unraveling the intricacies of neuropsychiatric disorders.

Therapeutic potential of pregnenolone and pregnenolone methyl ether on depressive and CDKL5 deficiency disorders: Focus on microtubule targeting

Pregnenolone methyl-ether (PME) is a synthetic derivative of the endogenous neuroactive steroid pregnenolone (PREG), which is an important modulator of several brain functions. In addition to being the precursor of steroids, PREG acts directly on various targets including microtubules (MTs), the functioning of which is fundamental for the development and homeostasis of nervous system. The coordination of MT dynamics is supported by a plethora of MT-associated proteins (MAPs) and by a specific MT code that is defined by the post-translational modifications of tubulin. Defects associated with MAPs or tubulin post-translational modifications are linked to different neurological pathologies including mood and neurodevelopmental disorders. In this review, we describe the beneficial effect of PME in major depressive disorders (MDDs) and in CDKL5 deficiency disorder (CDD), two pathologies that are joint by defective MT dynamics. Growing evidence indeed suggests that PME, as well as PREG, is able to positively affect the MT-binding of MAP2 and the plus-end tracking protein CLIP170 that are both found to be deregulated in the above mentioned pathologies. Furthermore, PME influences the state of MT acetylation, the deregulation of which is often associated with neurological abnormalities including MDDs. By contrast to PREG, PME is not metabolised into other downstream molecules with specific biological properties, an aspect that makes this compound more suitable for therapeutic strategies. Thus, through the analysis of MDDs and CDD, this work focuses attention on the possible use of PME for neuronal pathologies associated with MT defects.

Genetic inactivation of the sigma-1 chaperone protein results in decreased expression of the R2 subunit of the GABA-B receptor and increased susceptibility to seizures

There is a growing body of evidence demonstrating the significant involvement of the sigma-1 chaperone protein in the modulation of seizures. Several sigma-1 receptor (Sig1R) ligands have been demonstrated to regulate the seizure threshold in acute and chronic seizure models. However, the mechanism by which Sig1R modulates the excitatory and inhibitory pathways in the brain has not been elucidated. The aim of this study was to compare the susceptibility to seizures of wild type (WT) and Sig1R knockout (Sig1R-/-) mice in intravenous pentylenetetrazol (PTZ) and (+)-bicuculline (BIC) infusion-induced acute seizure and Sig1R antagonist NE-100-induced seizure models. To determine possible molecular mechanisms, we used quantitative PCR, Western blotting and immunohistochemistry to assess the possible involvement of several seizure-related genes and proteins. Peripheral tissue contractile response of WT and Sig1R-/- mice was studied in an isolated vasa deferentia model. The most important finding was the significantly decreased expression of the R2 subunit of the GABA-B receptor in the hippocampus and habenula of Sig1R-/- mice. Our results demonstrated that Sig1R-/- mice have decreased thresholds for PTZ- and BIC-induced tonic seizures. In the NE-100-induced seizure model, Sig1R-/- animals demonstrated lower seizure scores, shorter durations and increased latency times of seizures compared to WT mice. Sig1R-independent activities of NE-100 included downregulation of the gene expression of iNOS and GABA-A γ2 and inhibition of KCl-induced depolarization in both WT and Sig1R-/- animals. In conclusion, the results of this study indicate that the lack of Sig1R resulted in decreased expression of the R2 subunit of the GABA-B receptor and increased susceptibility to seizures. Our results confirm that Sig1R is a significant molecular target for seizure modulation and warrants further investigation for the development of novel anti-seizure drugs.

Progesterone modulates neuronal excitability bidirectionally

Progesterone acts on neurons directly by activating its receptor and through metabolic conversion to neurosteroids. There is emerging evidence that progesterone exerts excitatory effects by activating its cognate receptors (progesterone receptors, PRs) through enhanced expression of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs). Progesterone metabolite 5α,3α-tetrahydro-progesterone (allopregnanolone, THP) mediates its anxiolytic and sedative actions through the potentiation of synaptic and extrasynaptic γ-aminobutyric acid type-A receptors (GABAARs). Here, we review progesterone's neuromodulatory actions exerted through PRs and THP and their opposing role in regulating seizures, catamenial epilepsy, and seizure exacerbation associated with progesterone withdrawal.

[New therapeutic avenues for neurosteroids in psychiatric diseases]

Discovered in the eighties by Pr Baulieu and colleagues, neurosteroids are a class of neuroactive brain-born steroids, which comprises the steroid hormones, their biosynthesis precursors and their metabolites. They can act through genomic as well as non-genomic pathways. Genomic pathways, only triggered by the neurosteroid hormones, are, in the brain, the same as those largely described in the periphery: the binding of these steroid hormones to nuclear receptors leads to transcription regulations. On the other hand, their precursors and metabolites, such as pregnenolone (PREG), dehydroepiandrosterone (DHEA), their respective sulfate esters, pregnenolone sulfate (PREG-S) and DHEA sulfate (DHEA-S) and allopregnanolone (ALLOP), are defined as neurosteroids, but no corresponding nuclear receptors have been identified so far. In fact, they trigger non-genomic pathways which consist in (i) inhibitory ionotropic receptors, (ii) excitatory ionotropic receptors and (iii) the microtubular system. Hence, inhibitory neurosteroids, whose mostly studied representative is ALLOP, positively modulate, or directly activate, the ionotropic GABA-A receptors. In contrast, excitatory neurosteroids, represented by PREG-S, DHEA-S and DHEA, inhibit the GABA-A receptors, and activate, directly or indirectly, through the sigma-1 receptors, the NMDA glutamate receptors. Neurosteroids of the third group, the microtubular neurosteroids, are able to bind microtubule associated proteins, in particular MAP2, to promote microtubule assembly, neurite outgrowth and in fine structural neuroplasticity. So far, PREG, DHEA and progesterone are the three identified microtubular neurosteroids. The pharmacological properties of neurosteroids have led to specific investigations for assessing their therapeutic potentialities in psychiatric diseases, using validated animal models. In some cases, clinical trials were also performed. These studies showed that ALLOP, the main inhibitory neurosteroid, displayed clear-cut anxiolytic-like and antidepressant-like efficacy in animals. It has been subsequently developed as Brexanolone and tested with success in phase III of clinical trials for the treatment of post-partum depression. Although showing pro-cognitive properties in animals, the sulfated neurosteroids, PREG-S and DHEA-S, were, in contrast, never tested in clinical trials, probably due to their poor stability and proconvulsivant side effects. Their respective non-sulfated forms, PREG and DHEA, showed antidepressant and antipsychotic efficacies in clinical trials, but these drugs never reached the phase III of clinical development because their therapeutic uses would have led to an overproduction of active metabolites responsible for intolerable side effects. The alternative strategy which has been selected consists of the development of non-metabolizable synthetic derivatives of these natural steroids, which keep the same neuroactive properties as their parent molecules, but are devoid of any hormonal side effects. An example of such innovative drugs is MAP4343, a synthetic derivative of PREG, which exhibits potent antidepressant-like efficacy in validated animal models. It is currently tested in depressed patients.

Neurosteroids and Seizure Activity

Still circa 25% to 30% of patients with epilepsy cannot be efficiently controlled with available antiepileptic drugs so newer pharmacological treatment options have been continuously searched for. In this context, a group of endogenous or exogenous neurosteroids allosterically positively modulating GABA-A receptors may offer a promising approach. Among endogenous neurosteroids synthesized in the brain, allopregnanolone or allotetrahydrodeoxycorticosterone have been documented to exert anticonvulsant activity in a number of experimental models of seizures-pentylenetetrazol-, bicuculline- pilocarpine-, or 6 Hz-induced convulsions in rodents. Neurosteroids can also inhibit fully kindled seizures and some of them have been reported to counteract maximal electroshock-induced convulsions. An exogenous neurosteroid, alphaxalone, significantly elevated the threshold for maximal electroconvulsions in mice but it did not potentiate the anticonvulsive action of a number of conventional antiepileptic drugs against maximal electroshock-induced seizures. Androsterone not only elevated the threshold but significantly enhanced the protective action of carbamazepine, gabapentin and phenobarbital against maximal electroshock in mice, as well. Ganaxolone (a 3beta-methylated analog of allopregnanolone) needs special consideration for two reasons. First, it performed better than conventional antiepileptic drugs, diazepam or valproate, in suppressing convulsive and lethal effects of pentylenetetrazol in pentylenetetrazol-kindled mice. Second, ganaxolone has been evaluated in the randomized, double-blind, placebo-controlled phase 2 trial in patients with intractable partial seizures, taking maximally 3 antiepileptic drugs. The initial results indicate that add-on therapy with ganaxolone resulted in reduced seizure frequency with adverse effect being mainly mild to moderate. Possibly, ganaxolone may be also considered against catamenial seizures. Some positive effects of ganaxolone as an adjuvant were also observed in children with refractory seizures and its use may also prove efficient for the management of neonatal seizures associated with hypoxic injury. Neurosteroids positively modulating GABA-A receptor complex exert anticonvulsive activity in many experimental models of seizures. Their interactions with antiepileptic drugs seem ambiguous in mice. Initial clinical data indicate that ganaxolone may provide a better seizure control in patients with drug-resistant epilepsy.

Neurosteroid regulation of GABAA receptors: A role in catamenial epilepsy

The female reproductive hormones progesterone and estrogen regulate network excitability. Fluctuations in the circulating levels of these hormones during the menstrual cycle cause frequent seizures during certain phases of the cycle in women with epilepsy. This seizure exacerbation, called catamenial epilepsy, is a dominant form of drug-refractory epilepsy in women of reproductive age. Progesterone, through its neurosteroid derivative allopregnanolone, increases γ-aminobutyric acid type-A receptor (GABAR)-mediated inhibition in the brain and keeps seizures under control. Catamenial seizures are believed to be a neurosteroid withdrawal symptom, and it was hypothesized that exogenous administration of progesterone to maintain its levels high during luteal phase will treat catamenial seizures. However, in a multicenter, double-blind, phase III clinical trial, progesterone treatment did not suppress catamenial seizures. The expression of GABARs with reduced neurosteroid sensitivity in epileptic animals may explain the failure of the progesterone clinical trial. The expression of neurosteroid-sensitive δ subunit-containing GABARs is reduced, and the expression of α4γ2 subunit-containing GABARs is upregulated, which alters the inhibition of dentate granule cells in epilepsy. These changes reduce the endogenous neurosteroid control of seizures and contribute to catamenial seizures.

Dehydroepiandrosterone and Dehydroepiandrosterone-Sulfate and Emotional Processing

Steroid hormones are important regulators of brain development, physiological function, and behavior. Among them, dehydroepiandrosterone (DHEA) and dehydroepiandrosterone-sulfate (DHEAS) also do modulate emotional processing and may have mood enhancement effects. This chapter reviews the studies that bear relation to DHEA and DHEAS [DHEA(S)] and brain emotional processing and behavior. A brief introduction to the mechanisms of action and variations of DHEA(S) levels throughout life has also been forward in this chapter. Higher DHEA(S) levels may reduce activity in brain regions involved in the generation of negative emotions and modulate activity in regions involved in regulatory processes. At the electrophysiological level, higher DHEA-to-cortisol and DHEAS-to-DHEA ratios were related to shorter P300 latencies and shorter P300 amplitudes during the processing of negative stimuli, suggesting less interference of negative stimuli with the task and less processing of the negative information, which in turn may suggest a protective mechanism against negative information overload. Present knowledge indicates that DHEA(S) may play a role in cortical development and plasticity, protecting against negative affect and depression, and at the same time enhancing attention and overall working memory, possibly at the cost of a reduction in emotional processing, emotional memory, and social understanding.

Genetic and Molecular Regulation of Extrasynaptic GABA-A Receptors in the Brain: Therapeutic Insights for Epilepsy

GABA-A receptors play a pivotal role in many brain diseases. Epilepsy is caused by acquired conditions and genetic defects in GABA receptor channels regulating neuronal excitability in the brain. The latter is referred to as GABA channelopathies. In the last two decades, major advances have been made in the genetics of epilepsy. The presence of specific GABAergic genetic abnormalities leading to some of the classic epileptic syndromes has been identified. Advances in molecular cloning and recombinant systems have helped characterize mutations in GABA-A receptor subunit genes in clinical neurology. GABA-A receptors are the prime targets for neurosteroids (NSs). However, GABA-A receptors are not static but undergo rapid changes in their number or composition in response to the neuroendocrine milieu. This review describes the recent advances in the genetic and neuroendocrine control of extrasynaptic and synaptic GABA-A receptors in epilepsy and its impact on neurologic conditions. It highlights the current knowledge of GABA genetics in epilepsy, with an emphasis on the neuroendocrine regulation of extrasynaptic GABA-A receptors in network excitability and seizure susceptibility. Recent advances in molecular regulation of extrasynaptic GABA-A receptor-mediated tonic inhibition are providing unique new therapeutic approaches for epilepsy, status epilepticus, and certain brain disorders. The discovery of an extrasynaptic molecular mechanism represents a milestone for developing novel therapies such as NS replacement therapy for catamenial epilepsy.

Neurosteroids and potential therapeutics: Focus on pregnenolone

Considerable evidence from preclinical and clinical studies shows that steroids and in particular neurosteroids are important endogenous modulators of several brain-related functions. In this context, it remains to be elucidated whether neurosteroids may serve as biomarkers in the diagnosis of disorders and might have therapeutic potential for the treatment of these disorders. Pregnenolone (PREG) is the main steroid synthesized from cholesterol in mammals and invertebrates. PREG has three main sources of synthesis, the gonads, adrenal glands and brain and is submitted to various metabolizing pathways which are modulated depending on various factors including species, steroidogenic tissues and steroidogenic enzymes. Looking at the whole picture of steroids, PREG is often known as the precursor to other steroids and not as an active steroid per se. Actually, physiological and brain functions have been studied mainly for steroids that are very active either binding to specific intracellular receptors, or modulating with high affinity the abundant membrane receptors, GABAA or NMDA receptors. However, when high sensitive and specific methodological approaches were available to analyze low concentrations of steroids and then match endogenous levels of different steroid metabolomes, several studies have reported more significant alterations in PREG than in other steroids in extraphysiological or pathological conditions, suggesting that PREG could play a functional role as well. Additionally, several molecular targets of PREG were revealed in the mammalian brain and beneficial effects of PREG have been demonstrated in preclinical and clinical studies. On this basis, this review will be divided into three parts. The first provides a brief overview of the molecular targets of PREG and the pharmacological effects observed in animal and human studies. The second will focus on the possible functional role of PREG with an outline of the modulation of PREG levels in animal and in human research. Finally, the review will highlight the possible therapeutic uses of PREG that point towards the development of pregnenolone-like molecules.

Effects of acute and chronic administration of neurosteroid dehydroepiandrosterone sulfate on neuronal excitability in mice

Background

Neurosteroid dehydroepiandrosterone sulfate (DHEAS) has been associated with important brain functions, including neuronal survival, memory, and behavior, showing therapeutic potential in various neuropsychiatric and cognitive disorders. However, the antagonistic effects of DHEAS on γ-amino-butyric acid_A receptors and its facilitatory action on glutamatergic neurotransmission might lead to enhanced brain excitability and seizures and thus limit DHEAS therapeutic applications. The aim of this study was to investigate possible age and sex differences in the neuronal excitability of the mice following acute and chronic DHEAS administration.

Methods

DHEAS was administered intraperitoneally in male and female adult and old mice either acutely or repeatedly once daily for 4 weeks in a 10 mg/kg dose. To investigate the potential proconvulsant properties of DHEAS, we studied the effects of acute and chronic DHEAS treatment on picrotoxin-, pentylentetrazole-, and N-methyl-D-aspartate-induced seizures in mice. The effects of acute and chronic DHEAS administration on the locomotor activity, motor coordination, and body weight of the mice were also studied. We also investigated the effects of DHEAS treatment on [³H]flunitrazepam binding to the mouse brain membranes.

Results

DHEAS did not modify the locomotor activity, motor coordination, body weight, and brain [³H]flunitrazepam binding of male and female mice. The results failed to demonstrate significant effects of single- and long-term DHEAS treatment on the convulsive susceptibility in both adult and aged mice of both sexes. However, small but significant changes regarding sex differences in the susceptibility to seizures were observed following DHEAS administration to mice.

Conclusion

Although our findings suggest that DHEAS treatment might be safe for various potential therapeutic applications in adult as well as in old age, they also support subtle interaction of DHEAS with male and female hormonal status, which may underline observed sex differences in the relationship between DHEAS and various health outcomes.

Regulation of local steroidogenesis in the brain and in prostate cancer: lessons learned from interdisciplinary collaboration

Sex steroids play critical roles in the regulation of the brain and many other organs. Traditionally, researchers have focused on sex steroid signaling that involves travel from the gonads via the circulation to intracellular receptors in target tissues. This classic concept has been challenged, however, by the growing number of cases in which steroids are synthesized locally and act locally within diverse tissues. For example, the brain and prostate carcinoma were previously considered targets of gonadal sex steroids, but under certain circumstances, these tissues can upregulate their steroidogenic potential, particularly when circulating sex steroid concentrations are low. We review some of the similarities and differences between local sex steroid synthesis in the brain and prostate cancer. We also share five lessons that we have learned during the course of our interdisciplinary collaboration, which brought together neuroendocrinologists and cancer biologists. These lessons have important implications for future research in both fields.

Neurosteroid interactions with synaptic and extrasynaptic GABA(A) receptors: regulation of subunit plasticity, phasic and tonic inhibition, and neuronal network excitability

RATIONALE

Neurosteroids are steroids synthesized within the brain with rapid effects on neuronal excitability. Allopregnanolone, allotetrahydrodeoxycorticosterone, and androstanediol are three widely explored prototype endogenous neurosteroids. They have very different targets and functions compared to conventional steroid hormones. Neuronal γ-aminobutyric acid (GABA) type A (GABA(A)) receptors are one of the prime molecular targets of neurosteroids.

OBJECTIVE

This review provides a critical appraisal of recent advances in the pharmacology of endogenous neurosteroids that interact with GABA(A) receptors in the brain. Neurosteroids possess distinct, characteristic effects on the membrane potential and current conductance of the neuron, mainly via potentiation of GABA(A) receptors at low concentrations and direct activation of receptor chloride channel at higher concentrations. The GABA(A) receptor mediates two types of inhibition, now characterized as synaptic (phasic) and extrasynaptic (tonic) inhibition. Synaptic release of GABA results in the activation of low-affinity γ2-containing synaptic receptors, while high-affinity δ-containing extrasynaptic receptors are persistently activated by the ambient GABA present in the extracellular fluid. Neurosteroids are potent positive allosteric modulators of synaptic and extrasynaptic GABA(A) receptors and therefore enhance both phasic and tonic inhibition. Tonic inhibition is specifically more sensitive to neurosteroids. The resulting tonic conductance generates a form of shunting inhibition that controls neuronal network excitability, seizure susceptibility, and behavior.

CONCLUSION

The growing understanding of the mechanisms of neurosteroid regulation of the structure and function of the synaptic and extrasynaptic GABA(A) receptors provides many opportunities to create improved therapies for sleep, anxiety, stress, epilepsy, and other neuropsychiatric conditions.

Role of hormones and neurosteroids in epileptogenesis

This article describes the emerging evidence of hormonal influence on epileptogenesis, which is a process whereby a brain becomes progressively epileptic due to an initial precipitating event of diverse origin such as brain injury, stroke, infection, or prolonged seizures. The molecular mechanisms underlying the development of epilepsy are poorly understood. Neuroinflammation and neurodegeneration appear to trigger epileptogenesis. There is an intense search for drugs that truly prevent the development of epilepsy in people at risk. Hormones play an important role in children and adults with epilepsy. Corticosteroids, progesterone, estrogens, and neurosteroids have been shown to affect seizure activity in animal models and in clinical studies. However, the impact of hormones on epileptogenesis has not been investigated widely. There is emerging new evidence that progesterone, neurosteroids, and endogenous hormones may play a role in regulating the epileptogenesis. Corticosterone has excitatory effects and triggers epileptogenesis in animal models. Progesterone has disease-modifying activity in epileptogenic models. The antiepileptogenic effect of progesterone has been attributed to its conversion to neurosteroids, which binds to GABA-A receptors and enhances phasic and tonic inhibition in the brain. Neurosteroids are robust anticonvulsants. There is pilot evidence that neurosteroids may have antiepileptogenic properties. Future studies may generate new insight on the disease-modifying potential of hormonal agents and neurosteroids in epileptogenesis.

Allopregnanolone potentiates the glutamate-mediated seizures induced by 4-aminopyridine in rat hippocampus in vivo

Excitatory and inhibitory neurotransmission in the central nervous system can be modulated by neurosteroids. We previously found that in rat hippocampal slices allopregnanolone (3α-hydroxy-5α-pregnan-20-one), a positive GABA(A) receptor modulator, suppresses the epileptic discharges induced by 4-aminopyridine (4-AP), a convulsant K(+) channel blocker that stimulates glutamate release. Here, we tested the action of allopregnanolone on the epileptogenic and excitotoxic effects of the intrahippocampal administration of 4-AP in vivo. Drugs were perfused by a microdialysis cannula-electrode in the dorsal hippocampus and the EEG was recorded. Extracellular levels of aspartate, glutamate and GABA were analyzed by HPLC in the microdialysis fractions, and 24 h after the experiment the hippocampus was studied histologically. 4-AP induced intense epileptic discharges, increased the extracellular levels of aspartate, glutamate, and GABA by 383, 420, and 245%, respectively, and produced a notable neurodegeneration in CA1 and CA3 areas. Allopregnanolone administration alone did not affect the electrical activity, amino acids levels or cellular morphology, but when co-infused with 4-AP incremented 55-77% the duration of the epileptic discharges, and potentiated 32-49% the release of glutamate in comparison with 4-AP alone. The 4-AP-induced neurodegeneration was not modified by allopregnanolone. The NMDA receptor antagonist MK-801 protected against the epilepsy and neurodegeneration produced by 4-AP, and allopregnanolone did not affect this protection. We conclude that, differently from the observations in vitro, allopregnanolone potentiated the stimulatory effect of 4-AP on glutamate release and that this may explain the potentiation of the epileptogenic effect of 4-AP in vivo.

Role of anticonvulsant and antiepileptogenic neurosteroids in the pathophysiology and treatment of epilepsy

This review highlights the role of major endogenous neurosteroids in seizure disorders and the promise of neurosteroid replacement therapy in epilepsy. Neurosteroids are endogenous modulators of seizure susceptibility. Neurosteroids such as allopregnanolone (3α-hydroxy-5α-pregnane-20-one) and allotetrahydrodeoxycorticosterone (3α,21-dihydroxy-5α-pregnan-20-one) are positive modulators of GABA-A receptors. Aside from peripheral tissues, neurosteroids are synthesized within the brain, mostly in principal neurons. Neurosteroids potentiate synaptic GABA-A receptor function and also activate δ-subunit-containing extrasynaptic GABA-A receptors that mediate tonic currents and thus may play an important role in neuronal network excitability and seizure susceptibility. Our studies over the past decade have shown that neurosteroids are broad-spectrum anticonvulsants and confer seizure protection in various animal models. They protect against seizures induced by GABA-A receptor antagonists, 6-Hz model, pilocarpine-induced limbic seizures, and seizures in kindled animals. Unlike benzodiazepines, tolerance does not occur to their actions during chronic administration. Our recent studies provide compelling evidence that neurosteroids may have antiepileptogenic properties. There is emerging evidence that endogenous neurosteroids may play a key role in the pathophysiology of catamenial epilepsy, stress-sensitive seizure conditions, temporal lobe epilepsy, and alcohol-withdrawal seizures. It is suggested that neurosteroid replacement with natural or synthetic neurosteroids may be useful in the treatment of epilepsy. Synthetic analogs of neurosteroids that are devoid of hormonal side effects show promise in the treatment of diverse seizure disorders. Agents that stimulate endogenous production of neurosteroids may also be useful for treatment of epilepsy.

Catamenial epilepsy: hormonal aspects

The term catamenial epilepsy is used to describe the cyclical occurrence of seizure exacerbations during particular phases of menstrual cycle in women with preexisting epilepsy. Recent investigations have demonstrated the existence of at least three patterns of catamenial seizure exacerbation: perimenstrual and periovulatory in ovulatory cycle and entire luteal phase in anovulatory cycle. Cyclical changes in the circulating levels of estrogens (proconvulsant) and progesterone (anticonvulsant) play a central role in the development of catamenial epilepsy. Also, variations in concentrations of antiepileptic drugs across the menstrual cycle may contribute to increased seizure susceptibility. A variety of approaches have been proposed for the treatment of catamenial epilepsy.

Neurosteroids: endogenous role in the human brain and therapeutic potentials

This chapter provides an overview of neurosteroids, especially their impact on the brain, sex differences and their therapeutic potentials. Neurosteroids are synthesized within the brain and rapidly modulate neuronal excitability. They are classified as pregnane neurosteroids, such as allopregnanolone and allotetrahydrodeoxycorticosterone, androstane neurosteroids, such as androstanediol and etiocholanolone, and sulfated neurosteroids such as pregnenolone sulfate. Neurosteroids such as allopregnanolone are positive allosteric modulators of GABA-A receptors with powerful anti-seizure activity in diverse animal models. Neurosteroids increase both synaptic and tonic inhibition. They are endogenous regulators of seizure susceptibility, anxiety, and stress. Sulfated neurosteroids such as pregnenolone sulfate, which are negative GABA-A receptor modulators, are memory-enhancing agents. Sex differences in susceptibility to brain disorders could be due to neurosteroids and sexual dimorphism in specific structures of the human brain. Synthetic neurosteroids that exhibit better bioavailability and efficacy and drugs that enhance neurosteroid synthesis have therapeutic potential in anxiety, epilepsy, and other brain disorders. Clinical trials with the synthetic neurosteroid analog ganaxolone in the treatment of epilepsy have been encouraging. Neurosteroidogenic agents that lack benzodiazepine-like side effects show promise in the treatment of anxiety and depression.

The role of neurosteroids in the pathophysiology and treatment of catamenial epilepsy

Catamenial epilepsy is a multifaceted neuroendocrine condition in which seizures are clustered around specific points in the menstrual cycle, most often around perimenstrual or periovulatory period. Generally, a twofold or greater increase in seizure frequency during a particular phase of the menstrual cycle could be considered as catamenial epilepsy. Based on this criteria, recent clinical studies indicate that catamenial epilepsy affects 31-60% of the women with epilepsy. Three types of catamenial seizures (perimenstrual, periovulatory and inadequate luteal) have been identified. However, there is no specific drug available today for catamenial epilepsy, which has not been successfully treated with conventional antiepileptic drugs. Elucidation of the pathophysiology of catamenial epilepsy is a prerequisite to develop specific targeted approaches for treatment or prevention of the disorder. Cyclical changes in the circulating levels of estrogens and progesterone play a central role in the development of catamenial epilepsy. There is emerging evidence that endogenous neurosteroids with anticonvulsant or proconvulsant effects could play a critical role in catamenial epilepsy. It is thought that perimenstrual catamenial epilepsy is associated with the withdrawal of anticonvulsant neurosteroids. Progesterone and other hormonal agents have been shown in limited trials to be moderately effective in catamenial epilepsy, but may cause endocrine side effects. Synthetic neurosteroids, which enhance the tonic GABA-A receptor function, might provide an effective approach for the catamenial epilepsy therapy without producing hormonal side effects.

Onset of late posttraumatic seizure after dehydroepiandrosterone treatment

OBJECTIVE

To describe the first reported case of a seizure in a patient using the dietary supplement DHEA in an attempt to improve ovarian oocyte production.

DESIGN

Case report.

SETTING

University-affiliated teaching hospital, neurologic department.

PATIENT(S)

A 30-year-old woman with fragile X syndrome and no history of any convulsive disorder who was receiving IVF treatment.

INTERVENTION(S)

Daily treatment with the dietary supplement DHEA.

MAIN OUTCOME MEASURE(S)

Generalized seizure.

RESULT(S)

After 1 month of DHEA treatment, the patient was admitted with a generalized seizure.

CONCLUSION(S)

A generalized seizure, associated with concurrent intake of DHEA.

The role of sex steroids in catamenial epilepsy and premenstrual dysphoric disorder: implications for diagnosis and treatment

Despite our understanding of hormonal influences on central nervous system (CNS) function, there is still much to learn about the pathogenesis of menstrual cycle-linked disorders. A growing literature suggests that the influence of sex steroids on neurological and psychiatric disorders is in part mediated by an aberrant CNS response to neuroactive steroids. Although sex steroids such as estradiol, progesterone, and the progesterone derivative allopregnanolone (ALLO) influence numerous neurotransmitter systems, it is their potent effect on the brain's primary inhibitory and excitatory neurotransmitters gamma-aminobutyric acid (GABA) and glutamate that links the study of premenstrual dysphoric disorder (PMDD) and catamenial epilepsy (CE). After providing an overview of these menstrual cycle-linked disorders, this article focuses on the preclinical and clinical research investigating the role of estradiol and progesterone (via ALLO) in the etiology of PMDD and CE. Through exploration of the phenomenological and neurobiological overlap between CE and PMDD, we aim to highlight areas for future research and development of treatments for menstrual cycle-linked neuropsychiatric disorders.

Modulation of neurotransmitter systems by dehydroepiandrosterone and dehydroepiandrosterone sulfate: mechanism of action and relevance to psychiatric disorders

Dehydroepiandrosterone (DHEA) is synthesized in the brain and several studies have shown that this steroid is a modulator of synaptic transmission. The effect of DHEA, and its sulfate ester DHEAS, on glutamate and GABA neurotransmission has been extensively studied but some effects on other neurotransmitter systems, such as dopamine, serotonin and nitric oxide, have also been reported. This review summarizes studies showing the effect of DHEA and DHEAS on neurotransmitter systems at different levels (metabolism, release, reuptake, receptor activation), as well as the activation of voltage-gated ion channels and calcium homeostasis, showing the variety of effects that these steroids exert on those systems, allowing the discussion of its mechanisms of action and its relevance to psychiatric disorders.

Effects of neurosteroids on hydrogen peroxide- and staurosporine-induced damage of human neuroblastoma SH-SY5Y cells

Neurosteroids are important regulators of central nervous system function and may be involved in processes of neuronal cell survival. This study was undertaken to test the effect of dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), pregnenolone (PGL), pregnenolone sulfate (PGLS), and allopregnanolone (Allo) on hydrogen peroxide- and staurosporine-induced toxicity in SH-SY5Y cells. It has been found that DHEAS inhibited the hydrogen peroxide toxicity in a concentration-dependent manner, whereas DHEA was active only at higher doses. PGL and PGLS showed neuroprotective effects only at the lowest concentration. Allo had no significant effect on hydrogen peroxide-evoked lactate dehydrogenase release and at the highest concentration aggravated its toxic effects. Next part of this study evaluated neurosteroid effects on staurosporine-induced apoptosis. DHEAS, DHEA, and PGL significantly antagonized effects of staurosporine on both caspase-3 activity and mitochondrial membrane potential. PGLS and Allo inhibited the staurosporine-induced changes in both apoptotic parameters only at the lowest concentration. Antiapoptotic properties of neurosteroids were positively verified by Hoechst staining. Furthermore, as shown by calcein assay, DHEA, DHEAS, and PGL increased viability of staurosporine-treated cells, and these effects were attenuated by specific inhibitors of phosphatidylinositol 3-kinase (PI3-K) and extracellular signal-regulated protein kinase (ERK)-mitogen activated protein kinase (MAPK). These data indicate that neurosteroids prevent SH-SY5Y cell damage related to oxidative processes and activation of mitochondrial apoptotic pathway. Moreover, neuroprotective effects of DHEA, DHEAS seem to depend on PI3-K and ERK/MAPK signaling pathways. It can be suggested that, at physiological concentrations, all studied neurosteroids participate in the inhibition of neuronal apoptosis, but with various potencies.

Neonatal finasteride induces anxiogenic-like profile and deteriorates passive avoidance in adulthood after intrahippocampal neurosteroid administration

Recent findings indicate that neurosteroids could act as important keys during the brain development. Fluctuations in neonatal allopregnanolone (AlloP) could result in altered pharmacological properties of the GABA(A) receptor system in adulthood. Recent studies demonstrated that neurosteroids play a critical role in regulating normal neurodevelopment in the hippocampus. The aim of the present work is to screen whether developmentally altered neurosteroid levels influence the behavioral response to adult intrahippocampal administration of AlloP, a GABA(A) positive modulating neurosteroid, and pregnenolone sulfate (PregS), a GABA(A) negative modulator in rats. For this purpose, pups received AlloP (10 mg/kg, s.c.), a 5alpha-reductase inhibitor (finasteride, 50 mg/kg, s.c.) or vehicle from the fifth to the ninth postnatal day. At maturity (i.e. 90 days old) a bilateral cannula was implanted into the hippocampus. After recovery from surgery, animals received an administration of AlloP (0.2 microg/0.5 microl), PregS (5 ng/0.5 microl) or vehicle in each hippocampus 5 min before they were tested in the elevated plus maze (EPM) and immediately after the passive avoidance training session, and retention was tested 24 h later. Results indicated that neonatal finasteride treatment deteriorated passive avoidance retention and elicited an anxiogenic-like effect in the EPM test in adulthood, as seen by the reduction of open arm entries and in the time spent in the open arms. Intrahippocampal PregS administration also disrupted passive avoidance, possibly related to its anxiogenic profile. Fluctuations in neonatal AlloP affect the aversive learning and the anxiety-related behavior in adulthood, and this effect could be in part mediated by alterations of the mature functions of the hippocampus, possibly via the GABA(A) receptor. These data point to the role of GABAergic neurosteroids in critical periods of vulnerability that influence normal development of GABAergic pathways in the CNS.

Pregnenolone sulfate in the brain: a controversial neurosteroid

Pregnenolone sulfate (PREGS) has been shown, either at high nanomolar or at micromolar concentrations, to increase neuronal activity by inhibiting GABAergic and by stimulating glutamatergic neurotransmission. PREGS is also a potent modulator of sigma type 1 (sigma1) receptors. It has been proposed that these actions of PREGS underlie its neuropharmacological effects, and in particular its influence on memory processes. On the other hand, the PREGS-mediated increase in neuronal excitability may become dangerous under particular conditions, for example in the case of excitotoxic stress or convulsions. However, the physiopathological significance of these observations has recently been put into question by the failure to detect significant levels of PREGS within the brain and plasma of rats and mice, either by direct analytical methods based on liquid chromatography/mass spectrometry (LC/MS) or enzyme linked immunosorbent assay (ELISA) with specific antibodies against PREGS, or by indirect gas chromatography/mass spectrometry (GC/MS) analysis with improved sample workup. These recent results have not come to the attention of a large number of neurobiologists interested in steroid sulfates. However, although available direct analytical methods have failed to detect levels of PREGS above 0.1-0.3 ng/g in brain tissue, it may be premature to completely exclude the local formation of biologically active PREGS within specific and limited compartments of the nervous system. In contrast to the situation in rodents, significant levels of sulfated 3beta-hydroxysteroids have been measured in human plasma and brain. Previous indirect measures of steroid sulfates by radioimmunoassays (RIA) or GC/MS had detected elevated levels of PREGS in rodent brain. The discrepancies between the results of different assay procedures have revealed the danger of indirect analysis of steroid sulfates. Indeed, PREGS must be solvolyzed/hydrolyzed prior to RIA or GC/MS analysis, and it is the released, unconjugated PREG which is then quantified. Extreme caution needs to be exercised during the preparation of samples for RIA or GC/MS analysis, because the fraction presumed to contain only steroid sulfates can be contaminated by nonpolar components from which PREG is generated by the solvolysis/hydrolysis/derivatization reactions.

Impact of the Hormonal Milieu on the Neurobiology of Alcohol Dependence and Withdrawal

Alcoholism, or alcohol dependence, is a complex disorder with withdrawal symptoms that are often problematic for those trying to recover from their dependence. As researchers attempt to elucidate the neurobiological underpinnings of alcohol dependence and withdrawal, it is becoming clear that numerous factors, including the hormonal environment, impact the manifestations of this disorder. Of particular interest is the observation that women have fewer and less severe withdrawal symptoms than do men even though they tend to suffer greater physiological harm from excessive alcohol consumption. In this article, the authors present an overview of their understanding of how gonadal and stress hormones interact with alcohol, which results in differential neurobiological responses between males and females. Thus far, data generated from representative animal models have shown significant differences between the sexes in behavioral responses and neuroadaptations to chronic alcohol consumption and withdrawal. Accumulating evidence suggests that treatment of alcoholism, including withdrawal, should be tailored to the patient's gender and hormonal status.

Effects of Intrahippocampal Nicotine and Neurosteroid Administration on Withdrawal in Voluntary and Chronic Alcohol-Drinking Rats

BACKGROUND

Previous studies have shown that 4.6 mug of nicotine administered to the hippocampus can deteriorate learning acquisition in alcohol-drinking rats. The aim of the present study was to research whether this nicotine dose can alter the alcohol withdrawal syndrome and whether the two neurosteroids, allopregnanolone (AlloP) and pregnenolone sulfate (PregS), at doses previously reported as anxiolytic and promnesic, respectively, can modulate these effects.

METHODS

We used a free-choice drinking procedure that involved providing the rats with an alcoholic solution (10% ethanol) at an early age. Alcohol and control rats were assigned randomly to six groups that received two consecutive intrahippocampal (dorsal CA1) injections once per week during three consecutive weeks after one hour of ethanol drinking. The first injection was nicotine (4.6 microg, 20 mM) or saline and the second injection was PregS (5 ng, 24 microM), AlloP (0.2 microg, 1.26 microM) or saline. Blood alcohol concentrations were assessed one week before the withdrawal testing. Locomotor activity and audiogenic seizures were tested during withdrawal after 110 days of voluntary ethanol consumption. Rats were injected immediately before the withdrawal testing.

RESULTS

AlloP induced a decrease in horizontal and vertical activities, suggesting that the dose tested has sedative effects. AlloP reversed the seizures induced by ethanol withdrawal and also the spontaneous audiogenic seizures induced by the acoustic stimulation in control rats. Moreover, AlloP decreased other alcohol withdrawal signs, such as tail stiffening and body rigidity. Intrahippocampal administration of nicotine or PregS, at the doses tested, did not effectively modify the expression of audiogenic seizures induced by alcohol withdrawal.

CONCLUSIONS

These results show that hippocampal GABAergic activity and AlloP have an important role in preventing convulsive behavior. The results also highlight the therapeutic potential of AlloP for reducing the alcohol withdrawal syndrome.

Physiological role of adrenal deoxycorticosterone-derived neuroactive steroids in stress-sensitive conditions

Stress increases plasma and brain concentrations of corticosteroids and neuroactive steroids. Cortisol is the most important stress hormone in the hypothalamic pituitary adrenocortical system. However, significant amounts of the mineralocorticoid deoxycorticosterone are also released during stress. Deoxycorticosterone undergoes biotransformation to allotetrahydrodeoxycorticosterone, a neuroactive steroid with anxiolytic and anticonvulsant properties. Our studies indicate that the anticonvulsant activity of deoxycorticosterone is mediated by its conversion to allotetrahydrodeoxycorticosterone, which is a potent positive allosteric modulator of GABA(A) receptors. Although the role of allotetrahydrodeoxycorticosterone within the brain is undefined, recent studies indicate that stress induces increases in allotetrahydrodeoxycorticosterone to levels that can activate GABA(A) receptors. These results might have significant implications for human stress-sensitive conditions such as epilepsy, panic disorder, post-traumatic stress disorder, and major depression. In epilepsy, a role for adrenal allotetrahydrodeoxycorticosterone in seizure susceptibility has been suggested. Recent preclinical studies indicate a role of neuroactive steroids in ethanol actions. Although these studies provide a better understanding of the role of allotetrahydrodeoxycorticosterone and related neuroactive steroids in acute stress, further studies are clearly warranted to ascertain the specific role of neuroactive steroids in the pathophysiology of chronic stress and related brain conditions.

The intrahippocampal administration of the neurosteroid allopregnanolone blocks the audiogenic seizures induced by nicotine

Allopregnanolone (AlloP), GABA(A) positive modulator, has efficacy as anticonvulsant. In contrast, nicotine and pregnenolone sulfate (PregS) act as potent convulsants. The present study aims to evaluate whether a promnesic dose of PregS and/or an anxiolytic dose of AlloP administered in the hippocampus can affect the audiogenic seizures induced by nicotine administration. Rats were assigned at random to six groups that received two consecutive intrahippocampal (dorsal CA1) injections once a week during three consecutive weeks. First injection: nicotine (4.6 microg, 20 mM) or saline, second injection: PregS (5 ng, 24 microM), AlloP (0.2 microg, 1.26 microM) or saline. After the last injections, locomotor activity and audiogenic seizures were tested. AlloP decreased the horizontal and vertical activity, suggesting sedative effects. Nicotine induced behavioral convulsions and AlloP acted as an anticonvulsant. AlloP reversed the seizures induced by nicotine and decreased the audiogenic convulsions in comparison with the controls. PregS also reversed the nicotine-induced audiogenic seizures in the nicotine group but not in the control group. These results suggest that anticonvulsive effects of AlloP and PregS are mediated by different action mechanisms such as GABA(A) positive modulation, or negative modulatory action on neural nicotinic acetylcholine receptors. Even though several brain structures could be involved, these results highlight the important role played by hippocampal cholinergic and GABAergic activities, as well as neurosteroids, especially AlloP, in preventing convulsive behavior.

Effect of ACTH-induced hypercortisolemia on the EEG in patients with stress-related epilepsy

PURPOSE

We assess the effect of acute hypercortisolemia induced by ACTH stimulation on seizures and EEG interictal spike activity in patients with localization-related epilepsy (LRE) and stress-related seizures.

METHODS

Seven patients (3 males, 4 females) with LRE and stress-related seizures were studied. All patients underwent ACTH stimulation with 0.25-0.75 mg Cosyntropin intravenously at 8 am. Serum cortisol and ACTH levels were monitored half- to one-hourly for 4 to 6 hours. Video/EEG monitoring was also performed.

RESULTS

ACTH injection induced hypercortisolemia in all patients. Hypercortisolemia was not associated with seizures or interictal spike facilitation in any patient. Two patients experienced seizures on the day of ACTH injection, one 8 hours after and another 15 and 12 hours after the injection, during a period when their cortisol levels had returned to normal.

CONCLUSION

No reproducible interictal EEG changes occurred in any of the patients following ACTH injection.

Dehydroepiandrosterone regulates astroglia reaction to denervation of olfactory glomeruli

Effects of dehydroepiandrosterone (DHEA) on glial reactions of the peripherally denervated olfactory bulb were studied in adult male rats. Denervation was achieved by destroying the olfactory mucosa with ZnSO(4) (0.17 M) irrigation of the nasal cavities. In one series of experiments, chronic DHEA treatment was applied (daily injections for 7 days, i.p., 10 mg/kg b.w. and 25 mg/kg b.w.); in the other series of experiments, animals received a single injection of DHEA (i.p., 10 mg/kg b.w., 25 mg/kg b.w. and 50 mg/kg b.w.) 2 h following ZnSO(4) treatment. To determine whether DHEA conversion to estradiol was involved in the mechanism of DHEA action on glia, a third series of experiments was carried out in which the aromatase inhibitor fadrozole (4.16 mg/ml) was administered using subcutaneously implanted osmotic minipumps. Rats were killed on day 7 after chemical denervation, and the reaction of glial cells was monitored within the olfactory bulb, using GFAP and vimentin immunohistochemistry. Qualitative changes in GFAP expression were analyzed by Western blot. Chronic DHEA treatment with both doses (10 mg/kg b.w. and 25 mg/kg b.w.) and acute DHEA treatment with the highest dose applied (50 mg/kg b.w.), inhibited the increase in GFAP expression induced by the denervation of the olfactory bulb. Furthermore, GFAP and vimentin immunostaining in the glomerular layer of the olfactory bulb were diminished in the denervated and DHEA treated groups. However, when DHEA treatment was combined with fadrozole administration, such a decrease in GFAP expression could not be detected in the chemically denervated olfactory bulb. These findings indicate that DHEA, depending on the dose applied and the mode of administration, attenuates glial reaction to denervation and may regulate glial plasticity in the olfactory glomeruli. These effects are likely to be mediated at least in part by the conversion of DHEA to estradiol.

Role of neurosteroids in catamenial epilepsy

Catamenial epilepsy is a menstrual cycle-related seizure disorder that affects up to 70% of women with epilepsy. Catamenial epilepsy is characterized by an increase in seizures during particular phases of the menstrual cycle. Three distinct patterns of catamenial epilepsy - perimenstrual, periovulatory, and inadequate luteal phase - have been described. Currently, there is no specific treatment for catamenial epilepsy. The molecular mechanisms involved in the pathophysiology of catamenial epilepsy are not well understood. Recent studies suggest that cyclical changes of ovarian hormones estrogens (proconvulsant) and progesterone (anticonvulsant) appear to play a key role in the genesis of catamenial seizures. Progesterone reduces seizure susceptibility partly through conversion to neurosteroids such as allopregnanolone, which enhances GABA(A) receptor function and thereby inhibits neuronal excitability. In animal models, withdrawal from chronic progesterone and, consequently, of allopregnanolone levels in brain, has been shown to increase seizure susceptibility. Natural progesterone therapy has proven effective in women with epilepsy. Moreover, neurosteroids have been shown to be very effective inhibitors of catamenial seizures in animal models. Thus, synthetic neuroactive steroids, such as ganaxolone, which are orally active and devoid of hormonal side effects, represent a novel treatment strategy for catamenial epilepsy. However, their clinical efficacy in catamenial epilepsy has yet to be explored. A greater understanding of the molecular mechanisms is clearly needed for designing effective treatment and prevention strategies of catamenial epilepsy in women at risk.

Characterization of the convulsant action of pregnenolone sulfate

Pregnenolone sulfate (PS) is an endogenous neurosteroid synthesized by glial cells, which acts as a potent convulsant when injected intracerebroventricularly and intraperitoneally. PS is found in relatively high concentrations in the hippocampus. But its convulsant action in the hippocampus has not been characterized. A range of PS doses were infused directly into the right hippocampus of 42 rats, which were subsequently monitored for behavioral and electrographic seizures. At the highest dose (4 micromol), PS produced status epilepticus (SE) and severe behavioral convulsions. As the dose of PS was reduced, the fraction of rats having SE diminished (ED50 for SE = 2.7 micromol). At doses lower than 300 nmol, PS infusion produced discrete electrographic seizures (ED50 = 68 nmol) associated with mild behavioral seizures. Both the behavioral seizure score (BSS) and the total number of seizures during the observation period changed in a dose-dependent manner. In separate experiments in cultured hippocampal neurons, PS enhanced NMDA-evoked whole-cell currents (EC50 = 16 microM). The results demonstrate that the hippocampus is highly sensitive to the convulsant effects of PS and that the enhancement of NMDA currents could contribute to the convulsant action of PS.

Chronic pregnenolone effects in normal humans: attenuation of benzodiazepine-induced sedation

Pregnenolone is the major steroid precursor in humans. It is also a "neurosteroid" and possesses intrinsic behavioral and brain effects in animals, affecting the GABA(A) and other receptors. In two preliminary studies, we sought to characterize its tolerability and psychotropic effects in humans. In Study 1, 17 normal volunteers received pregnenolone and placebo for 4 weeks each (15 mg PO per day x2 weeks followed by 30 mg PO per day x2 weeks, vs. placebo x4 weeks) in a within-subject, double-blind, cross-over design, with a 4 week drug-free washout period separating the two arms. Subjects' behavioral responses were assessed at the beginning and end of the 4-week pregnenolone arm and the 4-week placebo arm. Pregnenolone was generally well-tolerated but, by itself, had no significant effects on mood, memory, self-rated sleep quality or subjective well-being. In Study 2, 11 subjects from Study 1 received a single dose of diazepam (0.2 mg/kg PO) immediately following completion of Study 1 in order to assess, in a between groups design, the impact of 4-weeks' pre-treatment with pregnenolone (N=5) vs. placebo (N=6) on the acute sedative, amnestic and anxiolytic effects of this benzodiazepine. Pregnenolone-pretreated subjects showed significantly less sedation following diazepam (p<0.03); this effect was clinically apparent. Diazepam's amnestic effects were non-significantly attenuated, and ratings of anxiety were unaffected. These pilot data, based on small samples, raise the possibility that chronically administered pregnenolone antagonizes certain acute effects of benzodiazepines and may enhance arousal via antagonist or inverse agonist actions at the benzodiazepine/GABA(A) receptor complex. Further larger-scale studies, utilizing a broader range of doses and experimental conditions, are warranted.

Hydrocortisone-induced convulsions

Glucocorticoids may indirectly cause convulsions by the induction of electrolytes abnormalities, severe hypertension, or severe hyperglycemia. These agents may rarely cause convulsions by a direct toxicity to the central nervous system (CNS). We describe a 23-yr-old patient with Crohn's disease in whom generalized convulsions developed on two occasions while receiving intravenous hydrocortisone.

Long-term social isolation enhances picrotoxin seizure susceptibility in mice: up-regulatory role of endogenous brain allopregnanolone in GABAergic systems

Allopregnanolone (ALLO, 3alpha,5alpha-tetrahydroprogesterone), a positive allosteric modulator of actions of gamma-aminobutyric acid GABA) at GABA(A) receptors, is synthesized in the brain from progesterone by the sequential action of two enzymes: a type I 5alpha-reductase and a 3alpha-hydroxysteroid oxidoreductase. We previously demonstrated that long-term social isolation of mice caused a significant decrease in brain ALLO content via suppression of type I 5alpha-reductase and its mRNA expression. In this study, to clarify a physiological role of endogenous brain ALLO, we investigated changes in seizure susceptibility of mice following protracted social isolation and compared with those of mice treated with SKF105111 (SKF), an inhibitor of types I and II 5alpha-reductase. Social isolation of mice for 7 weeks prior to the experiments caused a significant increase of seizure susceptibility to the GABA(A) receptor antagonist picrotoxin but not to the glycine receptor antagonist strychnine or the glutamate receptor agonist kainic acid. The change in the seizure susceptibility was completely reversed by 2.5 mg/kg ip ALLO, a dose that per se had no effect on picrotoxin-induced seizure. Treatment of mice with SKF (20 mg/kg ip) also reduced a threshold dose of picrotoxin, but not that of strychnine or kainic acid, which was required to elicit seizure in group-housed mice. The effect of SKF was attenuated by ALLO (2.5 mg/kg ip). In contrast, SKF treatment had no effect on picrotoxin-induced seizure in socially isolated mice. These findings suggest that endogenous brain ALLO plays a suppressive role in seizure susceptibility via a positive modulation of GABA(A) receptor function and that social isolation enhances seizure susceptibility in mice via reduction of GABA(A) receptor function caused by a decrease of endogenous ALLO.

Effects of neurosteroids on epileptiform activity induced by picrotoxin and 4-aminopyridine in the rat hippocampal slice

The neurosteroids allopregnanolone (5alpha-pregnan-3alpha-ol-20-one; 5alpha,3alpha-P) and its 5beta-epimer pregnanolone (5beta,3alpha-P), and pregnenolone sulfate (PS) were examined for effects on spontaneous epileptiform discharges induced by 100 microM picrotoxin (PTX) and 55 microM 4-aminopyridine (4-AP) in the CA3 region of the rat hippocampal slice. At a concentration of 10 microM, 5alpha,3alpha-P partially reduced PTX-induced bursting and at 30 and 90 microM completely suppressed bursting. In contrast, 100 microM 5beta,3alpha-P failed to alter the discharge frequency. 5alpha,3alpha-P depressed 4-AP-induced bursting with similar potency as in the PTX model; 100 microM 5beta,3alpha-P was also partially effective. In the 4-AP model, 5alpha,3alpha-P inhibited both the more frequent predominantly positive-going potentials as well as the less frequent negative-going potentials that may be generated by synchronous GABAergic interneuron firing. PS enhanced the PTX bursting frequency and, in the 4-AP model, increased the frequency of negative potentials but did not alter the frequency of positive potentials. By itself, PS did not induce bursting. The effects of the steroids in the in vitro seizure models largely correspond with their activities on GABA(A) receptors; suppression of discharges may occur as a result of direct activation of these receptors rather than modulation of GABA-mediated synaptic responses. PTX and 4-AP-induced bursting in the hippocampal slice are useful models for directly assessing neurosteroid effects on seizure susceptibility under conditions that eliminate the factor of brain bioavailability.

Tolerance to the anticonvulsant activity of midazolam and allopregnanolone in a model of picrotoxin seizures

The effects of an intracerebroventricular (i.c.v.) administration of a non-selective full benzodiazepine receptor agonist, midazolam, and a neuroactive steroid, allopregnanolone, on picrotoxin-induced seizures and striatal dopamine metabolism, were studied in mice. It was found that acute i.c.v. injections of midazolam (ED50=38.25 nmol) and allopregnanolone (ED50=26.34 nmol) blocked picrotoxin-induced seizures to a similar extent. After repeated administration at the ED(85) doses (midazolam-56.6 nmol, allopregnanolone-94.2 nmol; once or twice daily for 5 days) tolerance developed to the anticonvulsant activity of midazolam (ED50=94.14 nmol) and allopregnanolone (ED50=186.70 nmol). Acute i.c.v. injections of midazolam and allopregnanolone (at the ED50 doses established in the model of picrotoxin seizures: 38.25 and 26.34 nmol, respectively), significantly decreased the concentration of dopamine metabolites: 3-methoxytyramine and 3,4-dihydroxyphenylacetic acid, as well as the dopamine turnover rate (homovanilic acid/dopamine ratio; by about 20%), in the mouse striatum. These findings together with the recently published data on the potentiation by midazolam and allopregnanolone of ethanol-induced sleep [Pharmacol. Biochem. Behav. 67 (2000) 345] indicate a very similar central effect profile of benzodiazepines and neurosteroids. Moreover, similar efficacy of allopregnanolone and midazolam at the GABA(A) receptors has been found. Overall, the results of the present study, along with the possibility of neurosteroid conversion in the brain into other steroid hormones (testosterone, estradiol, aldosterone), add to the accumulating evidence suggesting a less favorable pharmacological profile for this class of drugs than was previously thought.

The effects of neurosteroids on picrotoxin-, bicuculline- and NMDA-induced seizures, and a hypnotic effect of ethanol

The effects of intraperitoneally (IP) or intracerebroventricularly (ICV) administered neurosteroids [allopregnanolone (AP); 5beta-tetrahydrodeoxycorticosterone (5beta-THDOC); dehydroepiandrosterone sulfate (DHEAS); pregnenolone sulfate (PS)] and their precursors [progesterone (PROG), pregnanedione (PREG)] on N-methyl-D-aspartic acid (NMDA)-, picrotoxin (PTX)- and bicuculline (BIC)-induced seizures and ethanol-induced sleep were studied in mice. It was found that IP injections of (+)MK-801 most potently antagonized NMDA-, PTX- and BIC-induced seizures, as compared to diazepam (DZP), PROG and PREG. Both precursors of neurosteroids appeared only marginally active in the applied models of convulsions. ICV injections of AP selectively blocked PTX- and BIC-induced seizures, whereas 5beta-THDOC and (+)MK-801 also antagonized NMDA-induced convulsions. ICV administered DHEAS induced seizures in a dose-dependent way. ICV injections of AP and midazolam shortened the latency and prolonged the duration of sleep induced by IP injections of ethanol (5.0 g/kg). On the contrary, DHEAS and PS significantly reduced the hypnotic-like effect of ethanol. The obtained results suggest that neurosteroids may modulate in an agonistic (AP, 5beta-THDOC), or antagonistic way (PS, DHEAS), the GABA(A) receptor complex functions. Some of them (5beta-THDOC) also interact with NMDA receptors. AP appeared to be the most selectively acting compound, with its profile of action fully comparable to that of midazolam. AP also enhanced the hypnotic effect of ethanol, pointing out to the propensity to interact with centrally depressant agents. These findings, together with the possibility of conversion of some neurosteroids in the brain to other steroid hormones (testosterone, estradiol and aldosterone), indicate the limitations of their use for the treatment of neurological and psychiatric disorders.

The effects of neurosteroids on rat behavior and 3H-muscimol binding in the brain

The effects of ICV administration of metabolites of progesterone and deoxycorticosterone [i.e., neurosteroids: AP (3alpha-hydroxy-5alpha-pregnan-20-one, allopregnanolone), 5alpha(-THDOC (3alphat-21-dihydroxy-5alpha-pregnan-20-one, 5alpha-tetrahydrodeoxycorticosterone), 5beta-THDOC (3alpha-21-dihydroxy-5beta-pregnan-20-one, 5beta-tetrahydrodeoxycorticosterone), and PS (3beta-hydroxy-5-pregnen-20-one sulfate, pregnenolone sulfate] were studied in the open-field test of neophobia and Vogel's test of conflict behavior in rats. The influence of in vivo administered 5beta-THDOC, a positive allosteric modulator of the GABA(A) receptor complex, on 3H-muscimol binding in different brain structures, was also studied with the help of quantitative autoradiography. The presented data did not reveal any anxioselective effects for a range of centrally active neurosteroids, in the ethologically orientated and conflict models of anxiety, after intracerebral drug administration. Their central effects appeared secondary to changes in rat gross behavior. It is possible that high local concentration of neurosteroids after ICV injection and production of a narrower range of behavioral effects than that of benzodiazepines, precluded manifestation of the antianxiety effects of AP, 5alpha-THDOC and 5beta-THDOC. Autoradiography did not reveal any significant changes in the specific binding of 3H-muscimol in brain structures after in vivo ICV administration of 5beta-THDOC at the behaviorally active dose. Thus, the possibility that neuroactive neurosteroids may provide a novel potential site for therapeutic interventions in anxiety disorders is not supported. The part of the experiment with 5beta-THDOC is interpreted as contributing to other results, suggesting the existence of a new category of neurosteroids acting as partial agonists of the GABA(A) receptor.

Convulsant actions of the neurosteroid pregnenolone sulfate in mice

Pregnenolone sulfate (PS) is an endogenous neurosteroid known to antagonize GABA(A) receptor-mediated inhibitory responses and potentiate NMDA receptor-mediated excitatory responses in vitro. To assess the actions of the steroid as a modulator of seizure susceptibility in vivo, PS (30-300 nmol) was administered intracerebroventricularly in mice. At doses of 50 to 150 nmol, PS elicited seizures characterized by head jerks, rearing and falling, severe forelimb and hindlimb clonus, opisthotonos and explosive running. The seizures increased in severity and frequency with time and eventually progressed to status epilepticus, tonic hindlimb extension and death. The doses producing convulsions in 50% (CD(50)) and 97% (CD(97)) of animals were 92 and 205 nmol, respectively. A subconvulsant dose of PS (50 nmol) significantly increased the convulsant potencies of systemically administered pentylenetetrazol (30-50 mg/kg) and NMDA (50-100 mg/kg). Systemically administered PS at doses as high as 100 mg/kg failed to induce seizures or alter the convulsant potencies of pentylenetetrazol and NMDA. Protection against PS (205 nmol)-induced seizures and lethality was conferred by the GABA(A) receptor positive allosteric modulators clonazepam and allopregnanolone, and by the NMDA receptor antagonists dizocilpine and (R)-CPP. The overall pharmacological profile suggests that the convulsant actions of PS are mediated predominantly via its effects on GABA(A) receptors, and also possibly by effects on NMDA receptors.

Possible role of nitric oxide in the nootropic and antiamnesic effects of neurosteroids on aging- and dizocilpine-induced learning impairment

The ability of the nitric oxide (NO) synthase inhibitor, NG-nitro-l-arginine methyl ester (L-NAME), to modulate the attenuating effects of neurosteroids on the aging- and NMDA receptor antagonist dizocilpine-induced learning impairment, was tested in mice using two different behavioral models of long-term memory. The performance of aged mice (16 months old) in step-down type of passive-avoidance and elevated plus-maze paradigms was significantly impaired compared to that of young mice (3 months old). Neurosteroids pregnenolone sulfate (PS) and dehydroepiandrosterone sulfate (DHEAS), at 1-20 mg/kg, s.c., significantly improved the passive-avoidance and plus-maze performances in aged mice. Neurosteroids PS and DHEAS, at doses 1-20 mg/kg, s.c., significantly attenuated dizocilpine (0.1 mg/kg, i.p.)-induced amnesia, without producing any promnestic effects alone in adult mice. In both cognitive tasks, the effects exhibited by the neurosteroids tested had a bell-shaped curve. Preadministration of L-NAME (10 and 20 mg/kg, i.p.), at doses that did not disrupt cognition alone in either young or aged mice, significantly blocked the beneficial and antiamnesic effects of neurosteroids PS (5 mg/kg) and DHEAS (10 mg/kg). A selective action of L-NAME on the effects of neurosteroids was indicated, since the effects of L-NAME were completely reversed by L-arginine (300 mg/kg, i.p.), a competitive substrate for NO synthase. Neither L-NAME nor L-arginine alone affected the antinociception, locomotor activity or rota-rod performance of young or aged mice. These observations suggest that a NO-dependent mechanism may be involved in the beneficial and antiamnesic effects of neurosteroids PS and DHEAS on the aging- and dizocilpine-induced impairment of learning and memory processes.