Steroid modulation of the GABA/benzodiazepine receptor-linked chloride ionophore

It is all About the Chase: Neurosteroidogenesis in Male Rats is Driven by Control of Mating Pace

BACKGROUND

Masculine sexual behaviors are dependent on androstane-derived steroids; however, the modulatory effects of mating, and of mating control, on androstane neurosteroidogenesis remain largely unknown.

OBJECTIVE

Herein, we investigated the effects of mating control, prior sexual experience, and age on brain region specific neurosteroidogenic responses in male rats.

METHODS

Effects of acute sexual experience were tested in naïve male rats that either remained sexually- naïve, were exposed to a standard mating chamber, or were either given control of the mating pace in a standard mating chamber (male control) or mated wherein the female stimulus rat controlled the mating pace in a paced-mating chamber (female control). Aged (10-12 months) sexually responsive male rats were similarly euthanized from the homecage or engaged in male controlled or female controlled mating. All rats were euthanized immediately following exposure conditions for radioimmunoassay of steroids in midbrain, hypothalamus, hippocampus and cortex.

RESULTS

Consummatory sexual behavior in male vs. female-controlled mating paradigms was altered by age and prior sexual experience. Male-controlled mating increased androstane neurosteroid metabolism, such that complementary increases in the testosterone (T) metabolite 5α-androstane-3α-17β- diol (3α-diol) in the midbrain and hypothalamus of male rats corresponded to decreases in the prohormone, T. 3α-diol were increased in the hippocampus in response to the context alone, and to a lesser degree in response to mating. Mating diminished neurosteroidogenesis in the cortex. Neurosteroidogenesis was overall reduced in aged male rats compared to naïve controls, however, these effects were more prominent in sexually non-responsive aged male rats.

CONCLUSION

Extending previous findings, these results indicate differential production of androstane neurosteroids in a mating exposure, age and brain region dependent manner.

Allopregnanolone: Regenerative therapeutic to restore neurological health

Chronic stress has been proposed as a driver of altered brain structure and function, including the pathogenesis of neurodegenerative diseases and a driver of disease progression. A key outcome of stress in the brain is structural remodeling of neural architecture, which may be a sign of successful adaptation, whereas persistence of these changes when stress ends indicate failed resilience. Neuroendocrine homeostasis and stress response are mainly dependent upon the functioning of the hypothalamic-pituitary-adrenal axis. Neurosteroids will fluctuate depending on whether the stress is acute or chronic. Advancements in neurosteroid research have led to the identification of multiple targets for drug development, but the most promising innovative target may be neurogenesis, given its potential impact in neurodegenerative disorders like Alzheimer's disease. Allopregnanolone is an endogenous pregnane neurosteroid and a reduced metabolite of progesterone, which acts as a potent allosteric modulator and direct activator of the GABA-chloride channel complex. Perhaps the most intriguing finding related to the potential therapeutic effects of allopregnanolone is its potential to promote neuroregeneration.

Sex differences in the acute ethanol effects on object recognition memory: influence of estrous cycle

Effects of acute ethanol (EtOH) on memory depend on several factors, including type of behavioral task. Sex differences in EtOH effects have been reported in humans and animals, and recognition memory can be influenced by circulating sex hormones. The aim of this study was to investigate the influence of sex and estrous cycle in the acute effects of EtOH on novel object recognition memory in rats. Male and female Wistar rats were part of one of the groups: control, 0.6-g/kg EtOH and 1.8-g/kg EtOH (administered intraperitoneally before the training session). The estrous cycle was evaluated by vaginal smear. The task was conducted in an open field arena. During training, animals were exposed to two identical objects, and test sessions were performed 1 h (short-term) and 24 h (long-term) later. One of the objects was changed in each test. Increased novel object exploration was shown by male and female controls in the short- and long-term tests, respectively. In the short-term test, females did not show preference for the novel object, and EtOH 1.8 g/kg impaired performance in males. In the long-term test, both sexes showed object discrimination, and 1.8-g/kg EtOH reduced preference for the new object in male rats. The phase of the cycle, the performance on proestrus was worse compared with other phases, and EtOH failed to impair performance mainly on estrous. In conclusion, while male rats displayed ethanol-induced recognition memory deficit, female rats were unaffected by EtOH impairing effects. In addition, the performance of female rats was influenced by the estrous cycle phases.

Effects of non-contingent cocaine on 3 alpha-androstanediol. II. Disruption of lordosis of proestrous rats

Drug use influences sexual behavior, performance, and can be associated with increased sexual risk-taking. Our prior results using an animal model indicate that progestogens contribute to hormonally-mediated changes in sexual behavior of female rodents during acute cocaine exposure. Androgens, such as testosterone, and its metabolite 3ɑ-androstanediol (3α-diol), and estradiol, are known to influence male sexual behavior, but can also alter the expression of sexual behavior of female rodents. As such, we investigated the influence of endogenous androgen and estradiol fluctuations on cocaine-mediated changes in motor behavior and sexual receptivity of rats during diestrous or proestrous phases of the estrous cycle. Female rats were administered saline or cocaine (5, 10, or 20mg/kg, i.p.). Motor behavior was observed in the first 30min following drug administration, and then sexual responding was assessed for 15min. Cocaine decreased aggressive behavior in response to attempted mounts by a male among non-receptive (diestrous) rats and inhibited sexual behavior among sexually receptive (proestrous) rats. Cocaine dose-dependently altered concentrations of testosterone metabolites (estradiol and 3α-diol), but not testosterone, which correlated to motor and sexual behaviors of diestrous and proestrous rats, respectively. These data suggest that actions of 3α-diol may be involved in female sexual and motor behavior in response to cocaine, in a cycle-dependent manner.

Nongenomic glucocorticoid effects and their mechanisms of action in vertebrates

Glucocorticoids (GC) act on multiple organ systems to regulate a variety of physiological processes in vertebrates. Due to their immunosuppressive and anti-inflammatory actions, glucocorticoids are an attractive target for pharmaceutical development. Accordingly, they are one of the most widely prescribed classes of therapeutics. Through the classical mechanism of steroid action, glucocorticoids are thought to mainly affect gene transcription, both in a stimulatory and suppressive fashion, regulating de novo protein synthesis that subsequently leads to the physiological response. However, over the past three decades multiple lines of evidence demonstrate that glucocorticoids may work through rapid, nonclassical mechanisms that do not require alterations in gene transcription or translation. This review assimilates evidence across the vertebrate taxa on the diversity of nongenomic actions of glucocorticoids and the membrane-associated cellular mechanisms that may underlie rapid glucocorticoid responses to include potential binding sites characterized to date.

Hormonal changes and increased anxiety-like behavior in a perimenopause-animal model induced by 4-vinylcyclohexene diepoxide (VCD) in female rats

Perimenopause, a transition period that precedes menopause, is characterized by neuroendocrine, metabolic and behavioral changes, and is associated with increased vulnerability to affective disorders. The decrease in ovarian follicles during perimenopause contributes to a dynamic and complex hormonal milieu that is not yet well characterized. In rodents, 4-vinylcyclohexene diepoxide (VCD) induces a gradual depletion of ovarian follicles, modeling the transition to menopause in women. This study was aimed to investigate, in VCD-treated rats, the hormonal status and the behavior in the elevated plus-maze (EPM), a widely used test to assess anxiety-like behavior. From the postnatal day 28, rats were treated with VCD or vehicle for 15 days. At 80±5 days after the beginning of treatment the experiments were performed at proestrus and diestrus. In the first experiment rats were decapitated, ovary was collected and blood samples were taken for estradiol, progesterone, follicle stimulant hormone (FSH), testosterone, dihydrotestosterone (DHT) and corticosterone measurements. In the second experiment, rats were subjected to the EPM for 5 min, and behavioral categories recorded. Administration of VCD induced follicular depletion as well as an increase of the number of atretic follicles demonstrating the treatment efficacy. The transitional follicular depletion was accompanied by lower progesterone, testosterone and DHT with no changes in the FSH, estradiol and corticosterone plasma levels. On the EPM, rats showed decreased open arm exploration and increased risk assessment behavior, indicating increased anxiety. These findings show that administration of VCD to induce ovarian failure results in endocrine and anxiety-related changes that are similar to the symptoms exhibited by women during menopause transition. Thus, this model seems to be promising in the study of perimenopause-related changes.

Gestational or acute restraint in adulthood reduces levels of 5α-reduced testosterone metabolites in the hippocampus and produces behavioral inhibition of adult male rats

Stressors, during early life or adulthood, can alter steroid-sensitive behaviors, such as exploration, anxiety, and/or cognitive processes. We investigated if exposure to acute stressors in adulthood may alter behavioral and neuroendocrine responses of male rats that were exposed to gestational stress or not. We hypothesized that rats exposed to gestational and acute stress may show behavioral inhibition, increased corticosterone, and altered androgen levels in the hippocampus. Subjects were adult, male offspring of rat dams that were restrained daily on gestational days 14–20, or did not experience this manipulation. Immediately before testing, rats were restraint stressed for 20 min or not. During week 1, rats were tested in a battery of tasks, including the open field, elevated plus maze, social interaction, tailflick, pawlick, and defensive burying tasks. During week 2, rats were trained and tested 24 h later in the inhibitory avoidance task. Plasma corticosterone and androgen levels, and hippocampal androgen levels, were measured in all subjects. Gestational and acute restraint stress increased plasma levels of corticosterone, and reduced levels of testosterone's 5α-reduced metabolites, dihydrotestosterone (DHT) and 3α-androstanediol (3α-diol), but not the aromatized metabolite, estradiol (E₂), in plasma or the hippocampus. Gestational and acute restraint stress reduced central entries made in the open field, and latencies to enter the shock-associated side of the inhibitory avoidance chamber during testing. Gestational stress reduced time spent interacting with a conspecific. These data suggest that gestational and acute restraint stress can have actions to produce behavioral inhibition coincident with increased corticosterone and decreased 5α-reduced androgens of adult male rats. Thus, gestational stress altered neural circuits involved in the neuroendocrine response to acute stress in early adulthood.

Dissociating behavioral, autonomic, and neuroendocrine effects of androgen steroids in animal models

Developments in behavioral assessment, autonomic and/or baseline reactivity, psychopharmacology, and genetics, have contributed significantly to the assessment of performance-enhancing drugs in animal models. Particular classes of steroid hormones: androgenic steroids are of interest. Anecdotally, the performance enhancing effects of androgens are attributed to anabolic events. However, there is a discrepancy between anecdotal evidence and investigative data. While some androgen steroids may promote muscle growth (myogenesis), effects of androgens on performance enhancement are not always seen. Indeed, some effects of androgens on performance may be attributable to their psychological and cardiovascular effects. As such, we consider androgen effects in terms of their behavioral, autonomic, and neuroendocrine components. Techniques are discussed in this chapter, some of which are well established, while others have been more recently developed to study androgen action. Androgens may be considered for their positive impact, negative consequence, or psychotropic properties. Thus, this review aims to elucidate some of the effects and/or mechanisms of androgens on behavioral, autonomic, and/or neuroendocrine assessment that may underlie their controversial performance enhancing effects.

Investigation of the mechanisms of progesterone protection following oxygen-glucose deprivation in organotypic hippocampal slice cultures

This study aimed to test the hypothesis that progesterone is neuroprotective against oxygen-glucose deprivation (OGD) through its conversion to the active metabolite allopregnanolone (AlloP) and the potentiation of GABA(A) receptors. Organotypic hippocampal cultures were exposed to 2h of OGD and the resulting cell death was quantified 24h later using combined propidium iodide and Hoechst immunostaining. Initially, we confirmed, that both progesterone and AlloP were protective in terms of reducing cell death following OGD in hippocampal cultures and for both, the optimal level of protection was observed at a concentration of 0.1μM. However, the protective effect of progesterone was absent in the presence of finasteride (10μM) which inhibits the metabolism of progesterone to active metabolites, including AlloP. In addition, the concurrent application of picrotoxin (100μM), a potent GABA(A) receptor antagonist, prevented the protection previously seen by either progesterone or AlloP alone. These results indicate that progesterone protects hippocampal cultures from cell death following OGD largely due to its conversion to AlloP and that GABA(A) receptors are important mediators of the protective effects of both progesterone and AlloP.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders

Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

Antiseizure effects of 3alpha-androstanediol and/or 17beta-estradiol may involve actions at estrogen receptor beta

Testosterone (T), the principal androgen secreted by the testes, can have antiseizure effects. Some of these effects may be mediated by T's metabolites. T is metabolized to 3alpha-androstanediol (3alpha-diol). T, but not 3alpha-diol, binds androgen receptor. We investigated effects of 3alpha-diol (1 mg/kg, SC) and/or an androgen receptor blocker (flutamide 10 mg, SC), 1 hour prior to administration of pentylenetetrazol (85 mg/kg, IP). Juvenile male rats administered 3alpha-diol had less seizure activity than those administered vehicle. Flutamide had no effects. T is aromatized to 17beta-estradiol (E(2)), which, like 3alpha-diol, acts at estrogen receptors (ERs). Selective estrogen receptor modulators that favor ERalpha (propyl pyrazole triol, 17alpha-E(2)) or ERbeta (diarylpropionitrile, coumestrol, 3alpha-diol), or both (17beta-E(2)), were administered (0.1 mg/kg, SC) to juvenile male rats 1 hour before pentylenetetrazol. Estrogens with activity at ERbeta, but not those selective for ERalpha, produced antiseizure effects. Actions at ERbeta may underlie some antiseizure effects of T's metabolites.

Estrogen action: a historic perspective on the implications of considering alternative approaches

In the 50 years since the initial reports of a cognate estrogen receptor (ER), much has been learned about the diverse effects and mechanisms of estrogens, such as 17beta-estradiol (E(2)). This expert narrative review briefly summarizes perspectives and/or recent work of the authors, who have been addressing different aspects of estrogen action, but take a common approach of using alternative considerations to gain insight into mechanisms with clinical relevance, and inform future studies, regarding estrogen action. Their "Top Ten" favorite alternatives that are discussed herein are as follows. 1 - E(2) has actions by binding to a receptor that do not require its enzymatic conversion. 2 - Using a different strategy for antibody binding could make the estrogen receptor (ER) more discernible. 3 - Blocking ERs, rather than E(2) production, may be a useful strategy for breast cancer therapy. 4 - Secretion of alpha-fetoprotein (AFP), rather than only levels of E(2) and/or progesterone, may influence breast cancer risk. 5 - A peptide derived from the active site of AFP can produce the same benefits of the entire endogenous protein in endocrine cancers. 6 - Differential distribution of ER subtypes in the body and brain may underlie specific effects of estrogens. 7 - ERbeta may be sufficient for the trophic effects of estrogen in the brain, and ERalpha may be the primary target of trophic effects in the body. 8 - ERbeta may play a role in the trophic effects of androgens, and may also be relevant in the periphery. 9 - Downstream of E(2)'s effects at ERbeta, there may be consequences for biosynthesis of progestogens and/or androgens. 10 - Changes in histones and/or other factors, which may be downstream of ERbeta, potentially underlie the divergent effects of E(2) in the brain and peripheral tissues.

Chronic administration of androgens with actions at estrogen receptor beta have anti-anxiety and cognitive-enhancing effects in male rats

Androgen levels decline with aging. Some androgens may exert anti-anxiety and cognitive-enhancing effects; however, determining which androgens have anxiolytic-like and/or mnemonic effects is of interest given the different mechanisms that may underlie some of their effects. For example, the 5 alpha-reduced metabolite of testosterone (T), dihydrotesterone, can be further converted to 5 alpha-androstane,17beta-diol-3 alpha-diol (3 alpha-diol) and 5 alpha-androstane,17beta-diol-3beta-diol (3beta-diol), both of which bind with high affinity to the beta isomer of the intracellular estrogen receptor beta (ER beta). However, androsterone, another metabolite of T, does not bind well to ER beta. To investigate the effects of T metabolites, male rats were subjected to gonadectomy then implanted with silastic capsules of 3 alpha-diol, 3beta-diol, androsterone, or oil control. After recovery, the rats were tested in elevated plus maze (EPM), light/dark transition (LD), and Morris water maze (MWM). 3 alpha-diol both decreased anxiety-like behavior in the EPM and LD, and increased cognition in MWM, while 3beta-diol improved cognition in MWM, but had no effects on anxiety behavior, compared to vehicle or androsterone. These data suggest that the actions of 3 alpha-diol and 3beta-diol at ER beta may be responsible for some of testosterone's anti-anxiety and cognitive-enhancing effects.

Chronic administration of androgens with actions at estrogen receptor beta have anti-anxiety and cognitive-enhancing effects in male rats

Androgen levels decline with aging. Some androgens may exert anti-anxiety and cognitive-enhancing effects; however, determining which androgens have anxiolytic-like and/or mnemonic effects is of interest given the different mechanisms that may underlie some of their effects. For example, the 5 alpha-reduced metabolite of testosterone (T), dihydrotesterone, can be further converted to 5 alpha-androstane,17beta-diol-3 alpha-diol (3 alpha-diol) and 5 alpha-androstane,17beta-diol-3beta-diol (3beta-diol), both of which bind with high affinity to the beta isomer of the intracellular estrogen receptor beta (ER beta). However, androsterone, another metabolite of T, does not bind well to ER beta. To investigate the effects of T metabolites, male rats were subjected to gonadectomy then implanted with silastic capsules of 3 alpha-diol, 3beta-diol, androsterone, or oil control. After recovery, the rats were tested in elevated plus maze (EPM), light/dark transition (LD), and Morris water maze (MWM). 3 alpha-diol both decreased anxiety-like behavior in the EPM and LD, and increased cognition in MWM, while 3beta-diol improved cognition in MWM, but had no effects on anxiety behavior, compared to vehicle or androsterone. These data suggest that the actions of 3 alpha-diol and 3beta-diol at ER beta may be responsible for some of testosterone's anti-anxiety and cognitive-enhancing effects.

Depression-like behavior of aged male and female mice is ameliorated with administration of testosterone or its metabolites

There may be a role of age-related decline in androgen production and/or its metabolism for late-onset depression disorders of men and women. Thus, the anti-depressant-like effects of testosterone (T) and its metabolites are of interest. Given that these androgens have disparate mechanisms of action, it is important to begin to characterize and compare their effects in an aged animal model. We hypothesized that there would be sex differences in depression behavior of aged mice and that androgens would reduce depression-like behaviors in the forced swim test. To investigate this, male and female mice (approximately 24 months old) were subcutaneously administered T, or one of its 5alpha-reduced metabolites (dihydrotesterone-DHT, 5alpha-androstane,17beta-diol-3alpha-diol), or aromatized metabolite (estradiol--E(2)), or oil vehicle. Mice were administered androgens (1 mg/kg) 1 h before being tested in the forced swim test, an animal model of depression. We found that males spent more time immobile, and less time swimming, than females. Administration of T, DHT, or 3alpha-diol similarly reduced time spent immobile, and increased time spent struggling, of male and female mice. E(2), compared to vehicle administration, decreased time spent immobile of males and females, but increased time spent swimming of females and time spent struggling of male mice. Together, these data suggest that T and its 5alpha-reduced and aromatized metabolites have anti-depressant-like effects in aged male and female mice.

Hormonal influences on seizures: basic neurobiology

There are sex differences and effects of steroid hormones, such as androgens, estrogens, and progestogens, that influence seizures. Androgens exert early organizational and later activational effects that can amplify sex/gender differences in the expression of some seizure disorders. Female-typical sex steroids, such as estrogen (E2) and progestins, can exert acute activational effects to reduce convulsive seizures and these effects are mediated in part by the actions of steroids in the hippocampus. Some of these anticonvulsive effects of sex steroids are related to their formation of ligands which have agonist-like actions at gamma-aminobutyric acid (GABAA) receptors or antagonist actions at glutamatergic receptors. Differences in stress, developmental phase, reproductive status, endocrine status, and treatments, such as anti-epileptic drugs (AEDs), may alter levels of these ligands and/or the function of target sites, which may mitigate differences in sensitivity to, and/or tolerance of, steroids among some individuals. The evidence implicating sex steroids in differences associated with hormonal, reproductive, developmental, stress, seizure type, and/or therapeutics are discussed.

Androgens with activity at estrogen receptor beta have anxiolytic and cognitive-enhancing effects in male rats and mice

Testosterone (T) and its metabolites may underlie some beneficial effects for anxiety and cognition, but the mechanisms for these effects are unclear. T is reduced to dihydrotestosterone (DHT), which can be converted to 5alpha-androstane,3alpha,17beta-diol (3alpha-diol) and/or 5alpha-androstane-3beta,17beta-diol (3beta-diol). Additionally, T can be converted to androstenedione, and then to androsterone. These metabolites bind with varying affinity to androgen receptors (ARs; T and DHT), estrogen receptors (ERbeta; 3alpha-diol, 3beta-diol), or GABA(A)/benzodiazepine receptors (GBRs; 3alpha-diol, androsterone). Three experiments were performed to investigate the hypothesis that reduced anxiety-like and enhanced cognitive performance may be due in part to actions of T metabolites at ERbeta. Experiment 1: Gonadectomized (GDX) wildtype and ERbeta knockout mice (betaERKO) were subcutaneously (SC) administered 3alpha-diol, 3beta-diol, androsterone, or oil vehicle at weekly intervals, and tested in anxiety tasks (open field, elevated plus maze, light-dark transition) or for cognitive performance in the object recognition task. Experiment 2: GDX rats were administered SC 3alpha-diol, 3beta-diol, androsterone, or oil vehicle, and tested in the same tasks. Experiment 3: GDX rats were androsterone- or vehicle-primed and administered an antagonist of ARs (flutamide), ERs (tamoxifen), or GBRs (flumazenil), or vehicle and then tested in the elevated plus maze. Both rats and wildtype mice, but not betaERKO mice, consistently had reduced anxiety and improved performance in the object recognition task. Androsterone was only effective at reducing anxiety-like behavior in the elevated plus maze and this effect was modestly reduced by flumazenil administration. Thus, actions at ERbeta may be required for T's anxiety-reducing and cognitive-enhancing effects.

Extra-nuclear signaling of estrogen receptors

Estrogen controls multiple biological functions through binding to estrogen receptors (ERs). Traditionally, ERs have been regarded as transcription factors regulating the expression of target genes. However, growing evidence of rapid estrogen's actions in a number of tissues has been accumulating and alternative mechanisms of signal transduction have been proposed. These so called "extra-nuclear actions" do not require gene expression or protein synthesis and are independent of the nuclear localization of ERs. Indeed, some of these actions are elicited by ERs residing at or near the plasma membrane. Membrane-associated molecules such as ion channels, G proteins, the tyrosine kinase c-Src as well as growth factor receptors are modulated by liganded ERs within the membrane, leading to the activation of downstream cascades such as mitogen-activated protein kinase, phosphatidylinositol 3-OH kinase, protein kinase A, and protein kinase C. These cascades mediate some important rapid actions of estrogen, such as the activation of nitric oxide synthesis or the remodeling of actin cytoskeleton. In addition, these pathways are critical for the regulation of the expression of a number of target proteins implicated in cell proliferation, apoptosis, differentiation, movement, and homeostasis. In this manner, the extra-nuclear pathways are tightly integrated with the genomic pathways to orchestrate the full spectrum of estrogen's biological functions. The recent advancements in the characterization of the molecular basis of the extra-nuclear signaling of estrogen helps to understand the role of estrogen on human cells, and may in future turn out to be of relevance for clinical purposes.

Ischemic insult to cerebellar Purkinje cells causes diminished GABAA receptor function and allopregnanolone neuroprotection is associated with GABAA receptor stabilization

Cerebellar Purkinje cells (PC) are particularly vulnerable to ischemic injury and excitotoxicity, although the molecular basis of this sensitivity remains unclear. We tested the hypothesis that ischemia causes rapid down-regulation of GABA(A) receptors in cerebellar PC, thereby increasing susceptibility to excitotoxicity. Oxygen-glucose deprivation (OGD) caused a decline in functional GABA(A) receptors, within the first hour of re-oxygenation. Decreased amplitude of miniature inhibitory post-synaptic potentials confirmed that OGD caused a significant decrease in functional synaptic GABA(A) receptors and quantitative Western blot analysis demonstrated the loss of GABA(A) receptor current was associated with a decline in total receptor protein. Interestingly, the potent neuroprotectant allopregnanolone (ALLO) prevented the decline in GABA(A) receptor current and protein. Consistent with our in vitro data, global ischemia in mice caused a significant decline in total cerebellar GABA(A) receptor protein and PC specific immunoreactivity. Moreover, ALLO provided strong protection of PC and prevented ischemia-induced decline in GABA(A) receptor protein. Our findings indicate that ischemia causes a rapid and sustained loss of GABA(A) receptors in PC, whereas ALLO prevents the decline in GABA(A) receptors and protects against ischemia-induced damage. Thus, interventions which prevent ischemia-induced decline in GABA(A) receptors may represent a novel neuroprotective strategy.

Conserved site for neurosteroid modulation of GABA A receptors

This study addresses whether the potentiation site for neurosteroids on GABA(A) receptors is conserved amongst different GABA(A) receptor isoforms. The neurosteroid potentiation site was previously identified in the alpha1beta2gamma2S receptor by mutation of Q241 to methionine or leucine, which reduced the potentiation of GABA currents by the naturally occurring neurosteroids, allopregnanolone or tetrahydrodeoxycorticosterone (THDOC). By using heterologous expression of GABA(A) receptors in HEK cells, in combination with whole-cell patch clamp recording methods, a relatively consistent potentiation by allopregnanolone of GABA-activated currents was evident for receptors composed of one alpha subunit isoform (alpha2-5) assembled with beta3 and gamma2S subunits. Using mutant alphabetagamma receptors, the neurosteroid potentiation was universally dependent on the conserved glutamine residue in M1 of the respective alpha subunit. Studying wild-type and mutant receptors composed of alpha4beta3delta subunits revealed that the delta subunit is unlikely to contribute to the neurosteroid potentiation binding site and probably affects the efficacy of potentiation. Thus, in keeping with the ability of neurosteroids to potentiate GABA currents via a broad variety of GABA(A) receptor isoforms in neurons, the potentiation site is structurally highly conserved on this important neurotransmitter receptor family.

The endocrine nervous system: source and target for neuroactive steroids

For a long time the endocrine brain was considered to the hypothalamus and to its special relationships with the hypophysis. The discovery of the wide distribution of steroid hormone receptors, as well as that of the possibility of metabolizing or synthesizing steroids by neural cells (neuroactive steroids), suggest, on the contrary, that interactions among steroids and nervous system are key points of the regulatory processes in the central and peripheral nervous system in normal conditions as well as in pathological conditions. In this brief overview we illustrate a few examples of these relationships with major emphasis on papers collected in this special issue.

The impact of gonadectomy and adrenalectomy on acute withdrawal severity in male and female C57BL/6J and DBA/2J mice following a single high dose of ethanol

BACKGROUND

Steroid hormones can influence neuronal excitability and subsequent seizure susceptibility through genomic and nongenomic mechanisms. For example, there are proconvulsant steroids such as estradiol and corticosterone and anticonvulsant steroids such as testosterone, progesterone, and their GABAergic metabolites. Recent findings indicated that a single, acute administration of ethanol increased levels of GABAergic steroids and that the source of this increase was peripheral organs such as the adrenals and gonads. Thus, the purpose of the present study was to determine the impact of removal of the adrenals and/or gonads on withdrawal severity following a single high dose of ethanol in 2 genotypes that differ in ethanol withdrawal severity.

METHOD

Male and female C57BL/6J (B6) and DBA/2J (D2) mice were either left intact (SHAM), adrenalectomized (ADX), gonadectomized (GDX), or underwent ADX/GDX surgery. Seven days following surgery, baseline handling-induced convulsions (HICs) were measured prior to administration of a 4 g/kg dose of ethanol. HICs were assessed following the ethanol injection, then hourly for 12 hours and at 24 hours. A separate group of mice were used to measure the impact of surgical status on ethanol metabolism at 30, 60, 120, and 240 minutes after a single 4 g/kg dose of ethanol.

RESULTS

ADX and ADX/GDX treatments in male B6 and D2 mice increased ethanol withdrawal severity following a single dose of ethanol, measured by area under the withdrawal curve and peak HIC scores. Acute ethanol withdrawal also was increased in female D2 mice that had undergone ADX/GDX. In contrast, surgical status did not alter ethanol withdrawal severity in female B6 mice. Surgical status had only minor effects on ethanol metabolism.

CONCLUSIONS

Removal of peripherally derived steroids with anticonvulsant properties significantly increased HIC scores during acute ethanol withdrawal following a single dose of ethanol in male and female D2 mice and in male B6 mice. These increases were not due to changes in ethanol metabolism.

Steroids in relation to epilepsy and anaesthesia

Increasing numbers of reports indicate direct effects of ovarian steroids on the central nervous system. Effects of progesterone and its metabolites on brain excitability in humans and in experimental animals have been studied. Anti-epileptic effects have been shown in cats and in women with partial epilepsy and well-defined epileptic foci. The reduced progesterone metabolite 5 alpha-pregnan-3 alpha-ol-20-one and its 5 beta analogue also decreased the epileptic activity resulting from a penicillin-induced cortical focus in cats. 5 alpha-Pregnan-3 alpha-ol-20-one protected mice against metrazol-, bicuculline- and picrotoxin-induced seizures but not against electroshock-and strychnine-induced seizures. Progesterone, 5 alpha-pregnan-3 alpha-ol-20-one and 5 beta-pregnan-3 alpha-ol-20-one also induce anaesthesia in humans and animals; in a rat model of anaesthesia 5 alpha-pregnan-3 alpha-ol-20-one was eight times more potent than methohexitone (the most potent anaesthetic barbiturate). Anaesthesia with loss of the eyelash reflex was observed in humans 75-90 seconds after the intravenous injection of 5 beta-pregnan-3 alpha-ol-20-one in lipid emulsion. The in vivo production and brain distribution of centrally active steroids has also been studied in relation to the phases of the ovarian and menstrual cycle. A subset of women with epilepsy show changes in seizure frequency in relation to hormonal variations during the menstrual cycle. In the luteal phase when progesterone levels are high the number of generalized seizures is low. It is possible that progesterone and its metabolites play a role in epileptic seizures and also in the premenstrual syndrome.

Non-genomic mechanisms of action of steroid hormones

Sex steroid hormones are known to act through intracellular receptors and their cognate hormone response elements, located in the promoters of hormone-regulated genes. However, this classical mechanism of action cannot account for a variety of rapid effects of steroids (within seconds or minutes). In this review, non-genomic modes of target cell responses to sex steroids are described. The prototypical example is the resumption of meiosis in amphibian oocytes, triggered by progesterone at the plasma membrane level. Membrane effects of progesterone may also account for sperm maturation. Other membrane-mediated effects of steroids are reviewed. Whether a steroid hormone might elicit responses from a single cell through both genomic and membrane mechanisms remains an open question.

Engaging in paced mating, but neither exploratory, anti-anxiety, nor social behavior, increases 5alpha-reduced progestin concentrations in midbrain, hippocampus, striatum, and cortex

Sequential actions of 17beta-estradiol (E(2)) and progesterone (P(4)) in the hypothalamus and the P(4) metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), in the midbrain ventral tegmental area (VTA) respectively mediate the initiation and intensity of lordosis of female rats and may also modulate anxiety and social behaviors, through actions in these, and/or other brain regions. Biosynthesis of E(2), P(4), and 3alpha,5alpha-THP can also occur in brain, independent of peripheral gland secretion, in response to environmental/behavioral stimuli. The extent to which engaging in tasks related to reproductive behaviors and/or mating increased E(2) or progestin concentrations in brain was investigated. In Experiment 1, proestrous rats were randomly assigned to be tested in individual tasks, including the open field, elevated plus maze, partner preference, social interaction, or no test control, in conjunction with paced mating or no mating. Engaging in paced mating, but not other behaviors, significantly increased dihydroprogesterone (DHP) and 3alpha,5alpha-THP levels in midbrain, hippocampus, striatum, and cortex. In Experiment 2, proestrous rats were tested in the combinations of the above tasks (open field and elevated plus maze, partner preference, and social interaction) with or without paced mating. As in Experiment 1, only engaging in paced mating increased DHP and 3alpha,5alpha-THP concentrations in midbrain, hippocampus, striatum, and cortex. Thus, paced mating enhances concentrations of 5alpha-reduced progestins in brain areas associated with reproduction (midbrain), as well as exploration/anxiety (hippocampus and striatum) and social behavior (cortex).

Inhibition of neurosteroid synthesis increases asphyxia-induced brain injury in the late gestation fetal sheep

Allopregnanolone (AP) is a potent GABAergic agonist that suppresses CNS activity, seizure threshold, and excitotoxicity in the adult brain. AP is present in the fetal sheep brain and increases rapidly after asphyxial insult due to increased 5alpha-reductase type-2 (5alphaR-2) expression. The aim of this study was to use finasteride to suppress fetal neurosteroid synthesis, and then determine the effect on brain injury, particularly in the hippocampus, of asphyxia induced in utero by brief occlusion of the umbilical cord. Catheters and an inflatable umbilical cord cuff were implanted in fetal sheep at approximately 125 days gestation. Five days later the fetuses received either finasteride (20 mg/kg/h) or vehicle (40% hydroxypropyl-beta-cyclodextrin) for 2 h. The umbilical cord was occluded (UCO) for 5 min at 30 min after starting the infusion. The fetal brain was obtained 24 h later for examination of activated caspase-3 expression as an index of apoptosis, and to measure AP content. Finasteride treatment alone significantly reduced AP content and increased the number of caspase-3 positive cells in the hippocampus, cerebellum, and the subcallosal bundle, indicating that AP modulates the normal rate of apoptosis in the developing brain. UCO in vehicle and finasteride-treated fetuses produced a similar, marked decrease in O2 saturation (5.8+/-0.6%), but after finasteride treatment UCO caused a significantly greater increase in the number of caspase-3 positive cells in the hippocampal cornu ammonis 3 (CA3) (57.3+/-1.6%) compared with the vehicle-treated fetuses. Thus, 5alpha-reduced steroids such as AP may be protective in reducing cell death following acute fetal asphyxia. Perturbation of normal fetal neurosteroid levels in late gestation (e.g. due to preterm birth, or maternal synthetic steroid treatment to induce fetal lung maturation) could adversely affect brain development and increase its vulnerability to injury.

Self-administration of 3α-androstanediol increases locomotion and analgesia and decreases aggressive behavior of male hamsters

Androgens, such as testosterone (T), can have reinforcing effect, which may be due in part to actions of T's metabolite, 3alpha-androstanediol (3alpha-diol). To investigate rewarding effects of 3alpha-diol, gonadally intact adult male hamsters were given a two-bottle choice test to determine the amount of 3alpha-diol that would be self-administered over 4 days of exposure. After 2 days of habituation and 4 days of monitoring of consumption, hamsters were tested in an activity monitor and the open field (locomotion/exploration), paw lick (analgesia) and resident-intruder (aggression) tasks. Hamsters consumed significantly more 3alpha-diol than vehicle in the two-bottle choice test. Hamsters that were allowed to self-administer 3alpha-diol made significantly more beam breaks and total entries in the open field had increased latencies to pawlick, and engaged in significantly fewer attacks, than did hamsters with access to vehicle alone. Hamsters that self-administered 3alpha-diol had higher levels of 3alpha-diol in serum, hippocampus, prefrontal cortex, striatum and midbrain than did hamsters with access to vehicle alone. Together, these data suggest that 3alpha-diol may have rewarding effects.

Some rewarding effects of androgens may be mediated by actions of its 5alpha-reduced metabolite 3alpha-androstanediol

The abuse of anabolic-androgenic steroids (AS) is a growing problem; however, the effects and mechanisms underlying their addictive effects are not well understood. Research findings regarding androgen abuse in people and hedonic effects of androgens in laboratory rats are reviewed. Androgens, like other steroids, can have traditional actions via cognate intracellular steroid receptors, as well as other substrates. Our recent results indicate that testosterone (T) metabolites may have actions in part via gamma-aminobutyric acid (GABA)(A)/benzodiazepine receptor complexes (GBRs) and/or dopaminergic neurons in the nucleus accumbens, to mediate T's positive hedonic states. This may provide the basis for positive reinforcing effects of androgen seeking and use behavior. Following a comprehensive review of the background literature, our findings are presented that have explored the extent to which metabolites of T mediate euphorogenic effects of androgens by acting in the nucleus accumbens. Then results regarding whether GBRs are necessary substrates for androgens' positive hedonic effects are discussed. Lastly, research that addresses if dopaminergic neurons in the nucleus accumbens are necessary for these effects of androgens are discussed. This review provides a comprehensive examination of the hedonic properties and abuse/addiction potential of androgens and the putative mechanisms underlying these effects.

Role of androgens in epilepsy

Accumulating evidence suggests that both male- and/or female-typical sex steroids contribute to seizure susceptibility in epilepsy. Although there is rich literature regarding how female-typical sex steroids, such as progestins and estrogens, influence epilepsy, the role of androgens in seizure processes are just beginning to be understood. Given that some of the effects and mechanisms of androgen action on ictal activity may converge with that of progestins and/or estrogens, this review discusses what is known concerning the role of each of these sex steroids on seizures. Additionally, evidence that seizures and/or antiepileptic drugs can themselves influence steroid-dependent behaviors, such as affective, cognitive and reproductive function, is also reviewed. Considerations for therapeutic management and future directions for research and drug discovery are summarized.

A rapid neuromodulatory role for steroid hormones in the control of reproductive behavior

The long-term transcriptional actions of steroids that shape neuronal morphology and the probability of behavioral expression are well established. More recently, attention has been focused on the role of rapid (minute-by-minute) steroid actions on neuronal mechanisms of reproductive behavior. In this review, we first consider the rapid actions of steroids on mating and copulatory behaviors in tetrapod vertebrates. Evidence for rapid effects of steroids is presented for chemoinvestigatory behavior (genital sniffing of females by male mice), lordosis (arched-back mating posture in female rats), copulatory mounting (male mice and male Japanese quail), reproductive clasping (pre-copulatory mounting in newts), and paced mating (copulation rate as determined by female rats). We then review recent studies in teleost fish that demonstrate the rapid actions of steroids on vocal patterning at two levels: (1) central pattern generators and (2) social behavior in natural environments. Thus, we propose that steroid-dependent modulation of central pattern generators can govern the overt expression of reproductive behaviors via rapid non-transcriptional mechanisms that are likely to be widespread among vertebrates.

Effects of some neurosteroids injected into some brain areas of WAG/Rij rats, an animal model of generalized absence epilepsy

Neurosteroids are synthesized in the brain and have been demonstrated to modulate various cerebral functions. Allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one), a naturally occurring neurosteroid, and ganaxolone (3alpha-hydroxy-3beta-methyl-5alpha-pregnan-20-one), a synthetic derivative, are two neurosteroids acting as positive allosteric modulators of the GABA(A) receptor complex acting on a specific steroid recognition site. Both agents antagonize generalized tonic-clonic seizures in various animal models of epilepsy. Pregnenolone sulphate (3beta-hydroxy-5alpha-pregnen-20-one 3-sulphate; PS) is a negative allosteric modulator of GABA(A) receptors and a positive modulator of the NMDA receptors. We have evaluated the effects of such compounds in a genetic animal model of absence epilepsy, the WAG/Rij rat. Animals were chronically implanted with five frontoparietal cortical electrodes for electrocorticogram (EEG) recordings and bilateral guide cannulae into specific brain areas of the cortico-thalamic circuit in order to evaluate the effects of these compounds on the number and duration of epileptic spike-wave discharges (SWDs). The focal and bilateral microinjection of the two GABA(A) positive modulators into some thalamic nuclei (nucleus ventralis posteromedialis, nucleus reticularis thalami, nucleus ventralis posterolateralis was usually able to significantly worsen the occurrence of SWDs in WAG/Rij rats. Whereas both compounds were able to reduce the number and duration of SWDs when microinjected into the peri-oral region of the primary somatosensory cortex. The effects of PS were more complex depending on both the dose and the site of administration, generally, at low doses in thalamic nuclei and cortex, PS induced an increase of absence activity and a reduction at higher doses. These findings suggest that neurosteroids might play a role in absence epilepsies and that it might depend on the involvement of specific neuronal areas.

Benzodiazepine modulation of partial agonist efficacy and spontaneously active GABA(A) receptors supports an allosteric model of modulation

Benzodiazepines (BZDs) have been used extensively for more than 40 years because of their high therapeutic index and low toxicity. Although BZDs are understood to act primarily as allosteric modulators of GABA(A) receptors, the mechanism of modulation is not well understood. The applicability of an allosteric model with two binding sites for gamma-aminobutyric acid (GABA) and one for a BZD-like modulator was investigated. This model predicts that BZDs should enhance the efficacy of partial agonists. Consistent with this prediction, diazepam increased the efficacy of the GABA(A) receptor partial agonist kojic amine in chick spinal cord neurons. To further test the validity of the model, the effects of diazepam, flurazepam, and zolpidem were examined using wild-type and spontaneously active mutant alpha1(L263S)beta3gamma2 GABA(A) receptors expressed in HEK-293 cells. In agreement with the predictions of the allosteric model, all three modulators acted as direct agonists for the spontaneously active receptors. The results indicate that BZD-like modulators enhance the amplitude of the GABA response by stabilizing the open channel active state relative to the inactive state by less than 1 kcal, which is similar to the energy of stabilization conferred by a single hydrogen bond.

Intrahippocampal muscimol shifts learning strategy in gonadally intact young adult female rats

Learning strategy preferences depend upon circulating estrogen levels, with enhanced hippocampus-sensitive place learning coinciding with elevated estrogen levels. The effects of estrogen on strategy may be mediated by fluctuations in GABAergic function, given that inhibitory tone in the hippocampus is low when estrogen is high. We investigated the effects on learning strategy of intrahippocampal injections of a GABA(A) agonist in gonadally intact female rats. On the day of training, rats received 0.3 microL intrahippocampal infusions of muscimol (0.26 nmol or 2.6 nmol) or saline 20 min prior to training on a T-maze in which place (hippocampus-sensitive) or response (striatum-sensitive) strategies offer effective solutions. Muscimol treatment increased the use of the response strategy in a dose-dependent manner without influencing learning speed, indicating that muscimol modulated strategy and not learning ability. Furthermore, the muscimol-related shift to response strategies varied across the estrous cycle. The results indicate that increasing inhibition in the hippocampus biases rats away from hippocampus-sensitive place learning strategies and toward hippocampus-insensitive response learning strategies without a learning deficit. Furthermore, rats at proestrus demonstrated the most dramatic shift in learning strategy following muscimol treatment compared with control conditions, while rats at estrus demonstrated the most complete bias toward response strategies. The enhanced use of hippocampus-sensitive strategies at proestrus likely results from reduced hippocampal inhibition.

Actions at GABA(A) receptors in the hippocampus may mediate some antiseizure effects of progestins

Progestins can have antiseizure effects; however, the mechanisms and sites of action of these effects are not well-understood. Whether progesterone's actions at GABA(A) receptors in the hippocampus are important for its antiseizure effects was investigated. In Experiment 1, ovariectomized rats were administered sesame oil vehicle or a regimen of progesterone (500 microg sc, which produces physiological concentrations in plasma and the hippocampus), followed 2.5 hours later by administration of saline vehicle or a regimen of bicuculline (1 mg/kg, sc), a GABA(A) receptor antagonist, which does not produce any intrinsic effects on seizures. Progesterone, compared with vehicle, significantly increased the latency to, and decreased the number of, pentylenetetrazole-induced tonic seizures and increased GABA-stimulated chloride flux. Co-administration of bicuculline attenuated progesterone's antiseizure effects and decreased GABA-stimulated chloride flux in the hippocampus. Bicuculline did not alter ictal behavior compared with vehicle. In Experiment 2, ovariectomized rats were subcutaneously administered sesame oil or progesterone (500 microg), followed 2.5 hours later by bilateral infusions of bicuculline (100 ng) or vehicle (saline) into the hippocampus. Infusion of bicuculline into the hippocampus of progesterone-primed rats significantly increased ictal activity, compared with that induced by progesterone administration alone, but alone did not alter seizures compared with that produced by saline infusions into the hippocampus. These data suggest that actions of progesterone at GABA(A) receptors in the hippocampus are important for progesterone's antiseizure effects.

Attenuating 5alpha-pregnane-3alpha-ol-20-one formation in the hippocampus of female rats increases pentylenetetrazole-induced seizures

Progesterone has antiseizure effects, which may be due to the actions of its 5alpha-reduced metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). Whether metabolism of progesterone to 3alpha,5alpha-THP in the hippocampus is essential for its antiseizure effects was investigated. In Experiment 1, ovariectomized rats were administered subcutaneous progesterone (500 microg) or vehicle (sesame oil), followed 1 hour later by subcutaneous administration of an inhibitor of the 5alpha-reductase enzyme, finasteride (50 mg/kg), or vehicle (90% sesame oil, 10% ethanol). Administration of progesterone increased the latency to, and decreased the number of, tonic seizures and increased hippocampal 3alpha,5alpha-THP levels, compared with vehicle. Administration of finasteride with progesterone attenuated progesterone's antiseizure effects and decreased levels of 3alpha,5alpha-THP in the hippocampus. Finasteride administration alone did not alter ictal behavior or 3alpha,5alpha-THP levels compared with vehicle. In Experiment 2, ovariectomized rats were administered subcutaneous progesterone (500 microg) or vehicle (sesame oil), followed 1 hour later by bilateral infusions of finasteride (10 microg) or vehicle (beta-cyclodextran) into the hippocampus. Administration of finasteride to the hippocampus of progesterone-primed rats significantly increased ictal activity and decreased hippocampal 3alpha,5alpha-THP levels, compared with progesterone administration alone. These data suggest that formation of 3alpha,5alpha-THP in the hippocampus is important for progesterone's antiseizure effects.

Androgens in the hippocampus can alter, and be altered by, ictal activity

Steroid hormones, such as androgens, can modulate seizure processes. This review summarizes prior research and presents new data that support the role of androgens in modulating seizure processes. Testosterone, the primary endogenous androgen, has antiseizure effects in people and in animal models of epilepsy. Furthermore, testosterone's antiseizure effects may involve actions of its 5alpha-reduced metabolite and neuroactive steroid, 5alpha-androstane-3alpha,17beta-diol (3alpha-diol). The hippocampus is a target for androgen action and is involved in many types of seizure disorder. Data suggest that actions of androgens in the hippocampus may be important for androgens' antiseizure effects. Interestingly, there may also be a reciprocal relationship between androgens and seizures. Ictal activity can alter the gonadal responsiveness of people with epilepsy and in animal models of seizure disorder. Thus, this paper will review data in support of androgens' antiseizure effects. Further understanding of androgens' role in seizure processes is important for potential therapeutic effects.

Progestins in the hippocampus of female rats have antiseizure effects in a pentylenetetrazole seizure model

PURPOSE

Progestins can have profound effects on seizure processes. However, the effects and mechanisms of progestins to modulate seizures have not been systematically investigated. The present studies were designed to characterize the effects of progestins to modulate pentylenetetrazole (PTZ)-induced seizures in female rats.

METHODS

In Experiment 1, ictal activity and plasma and hippocampal progesterone (P) and 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) levels of proestrous rats were compared with those of diestrous and ovariectomized (ovx) rats. Experiments 2 and 3 examined effects of ovx and replacement with vehicle, P, or 3alpha,5alpha-THP, systemically (Experiment 2) or to the hippocampus (Experiment 3) on seizures and plasma and hippocampal P and 3alpha,5alpha-THP concentrations.

RESULTS

Proestrous rats had reduced ictal activity and increased levels of P and 3alpha,5alpha-THP in plasma and hippocampus compared with diestrous or ovx rats (Experiment 1). Rats administered systemic P or 3alpha,5alpha-THP had significantly reduced ictal activity and increased plasma and hippocampal P and 3alpha,5alpha-THP levels compared with vehicle-administered rats (Experiment 2). Administration of P or 3alpha,5alpha-THP to the hippocampus of ovx rats significantly reduced seizure activity and increased hippocampal, but not plasma, levels of P and 3alpha,5alpha-THP compared with vehicle administration (Experiment 3).

CONCLUSIONS

Together, these data suggest that P can have antiseizure effects, and these effects may be due in part to actions of its metabolite, 3alpha,5alpha-THP, in the hippocampus.

Gonadal, adrenal, and neuroactive steroids' role in ictal activity

Of the many people that have epilepsy, only about 70% achieve seizure control with traditional pharmacotherapies. Steroids have long been known to influence ictal activity and may have a therapeutic role. This review summarizes recent investigations that have enhanced knowledge of the effects and mechanisms of gonadal, adrenal, and neuroactive steroids on seizure processes. Progesterone, which varies across reproductive cycles, pregnancy, and as a function of aging, has been shown to have anti-seizure effects among women with epilepsy and in animal models of epilepsy. Further, data suggest that progesterone's anti-seizure effects may involve its metabolism to the neuroactive steroid, 5 alpha-pregnan-3 alpha-ol-20-one (3 alpha,5 alpha-THP), and its subsequent actions at GABA(A) receptors. Androgens also have anti-seizure effects. Androgens' anti-seizure effects may be mediated, in part, through actions of the testosterone metabolite, and neuroactive steroid, 5 alpha-androstane-3 alpha,17 alpha-diol (3 alpha-diol) at GABA(A) receptors. Stress can alter seizure susceptibility, suggesting a role of adrenal steroids on seizure processes. In animal models of epilepsy, acute or chronic stress can increase ictal activity. Notably, stress and seizures can alter levels of gonadal, adrenal, and neuroactive steroids, which may then influence subsequent seizure activity. Thus, this review summarizes recent progress in the role of gonadal, adrenal, and/or neuroactive steroids in seizure processes which suggest that greater understanding of these steroids' effects and mechanisms may ultimately lead to improved seizure control for people with epilepsy.

Bicuculline seizure susceptibility and nigral GABAA alpha1 receptor mRNA is altered in adult prenatally morphine-exposed females

Prenatal morphine exposure (5-10 mg/kg twice daily on gestation days 11-18) can adversely affect neurological development, including seizure susceptibility. The present study examines the effects of prenatal morphine exposure on seizure susceptibility to the GABA antagonist and convulsant bicuculline and GABA(A) alpha(1) receptor mRNA in the substantia nigra (SN) of female rats. The results demonstrate that prenatally morphine-exposed ovariectomized (OVX) females and OVX females with estradiol benzoate (EB) replacement have an increased latency to seizure onset compared to controls. In addition, prenatal morphine exposure decreases the area covered by grains of GABA(A) alpha(1) receptor mRNA in the anterior SN in both OVX and EB+progesterone (P)-treated groups, and decreases the number of GABA(A) alpha(1) receptor mRNA-labeled cells/field in EB females. Furthermore, prenatally morphine- and saline-exposed EB and EB+P females had decreased GABA(A) alpha(1) receptor mRNA-labeled cells/field in the anterior SN compared to OVX animals of the same prenatal exposure. These results demonstrate that the long term effects of prenatal morphine exposure in female rats is dependent on their hormonal status, and suggest that seizure susceptibility may be altered via neuropharmacological changes in the GABA system in the SN.

The role of ovarian hormones in preserving cognition in aging

Hormone replacement therapy is now the standard of care for amelioration of the symptoms of menopause and prevention of osteoporosis. More recently, it has been appreciated that hormone replacement may also have beneficial effects on the brain. This review will contrast the biologic data showing that estrogen has significant neuroprotectant effects on the brain, with data from cross-sectional and epidemiologic studies of women showing that hormone replacement may have beneficial effects for cognition in aging. Together, studies suggest that the temporal pattern of hormone replacement may be critical for maintaining cognitive health in aging.

The nucleus accumbens as a site of action for rewarding properties of testosterone and its 5alpha-reduced metabolites

Testosterone (T)'s positive hedonic effects may be mediated by actions of its metabolites, dihydrotestosterone (DHT) or 3alpha-androstanediol (3alpha-diol), in the nucleus accumbens (NA). In Experiment 1, adult, intact, male rats were systemically administered 1 mg of T, DHT, 3alpha-diol or vehicle, at different time points to examine concentrations of androgens in the NA. Rats administered 3alpha-diol had significantly increased concentrations of 3alpha-diol in the region of the brain encompassing the NA. These data are consistent with previous data from our laboratory demonstrating that 3alpha-diol elicits a conditioned place preference (CPP) more effectively than either T or DHT, when administered systemically. In Experiment 2, rats received implants of T, DHT or 3alpha-diol to the NA immediately prior to placement in the CPP apparatus on conditioning days. Implants of T, DHT or 3alpha-diol, but not vehicle, significantly increased time spent on the non-preferred side of the chamber on the test day. This effect was only produced by androgenic stimulation of the shell of the NA and not the core of the NA. Thus, androgen regimens we have previously found to enhance CPP produced the greatest increases in 3alpha-diol concentrations in the NA region and direct implants of T, DHT or 3alpha-diol to the shell, but not the core, of the NA enhanced CPP. These data are consistent with the hypothesis that the hedonic effects of T may be due to actions of its metabolites in the NA.