Androgen and progesterone metabolism in the central and peripheral nervous system

Estradiol and 3β-diol protect female cortical astrocytes by regulating connexin 43 Gap Junctions

While estrogens have been described to protect or preserve neuronal function in the face of insults such as oxidative stress, the prevailing mechanistic model would suggest that these steroids exert direct effects on the neurons. However, there is growing evidence that glial cells, such as astrocytes, are key cellular mediators of protection. Noting that connexin 43 (Cx43), a protein highly expressed in astrocytes, plays a key role in mediating inter-cellular communication, we hypothesized that Cx43 is a target of estradiol (E2), and the estrogenic metabolite of DHT, 3β-diol. Additionally, we sought to determine if either or both of these hormones attenuate oxidative stress-induced cytotoxicity by eliciting a reduction in Cx43 expression or inhibition of Cx43 channel permeability. Using primary cortical astrocytes, we found that E2 and 3β-diol were each protective against the mixed metabolic/oxidative insult, iodoacetic acid (IAA). Moreover, these effects were blocked by estrogen receptor antagonists. However, E2 and 3β-diol did not alter Cx43 mRNA levels in astrocytes but did inhibit IAA-induced Cx43 gap junction opening/permeability. Taken together, these data implicate astrocyte Cx43 gap junction as an understudied mediator of the cytoprotective effects of estrogens in the brain. Given the wide breadth of disease states associated with Cx43 function/dysfunction, further understanding the relationship between gonadal steroids and Cx43 channels may contribute to a better understanding of the biological basis for sex differences in various diseases.

Epigenetic Modifications by Estrogen and Androgen in Alzheimer's Disease

For the development and maintenance of neuron networks in the brain, epigenetic mechanisms are necessary, as indicated by recent findings. This includes some of the high-order brain processes, such as behavior and cognitive functions. Epigenetic mechanisms could influence the pathophysiology or etiology of some neuronal diseases, altering disease susceptibility and therapy responses. Recent studies support epigenetic dysfunctions in neurodegenerative and psychiatric conditions, such as Alzheimer's disease (AD). These dysfunctions in epigenetic mechanisms also play crucial roles in the transgenerational effects of the environment on the brain and subsequently in the inheritance of pathologies. The possible role of gonadal steroids in the etiology and progression of neurodegenerative diseases, including Alzheimer's disease, has become the subject of a growing body of research over the last 20 years. Recent scientific findings suggest that epigenetic changes, driven by estrogen and androgens, play a vital role in brain functioning. Therefore, exploring the role of estrogen and androgen-based epigenetic changes in the brain is critical for the deeper understanding of AD. This review highlights the epigenetic modifications caused by these two gonadal steroids and the possible therapeutic strategies for AD.

Non-Status Epilepticus female rats show seizure-like behaviors in the chronic phase of Pilocarpine experimental model

Abstract Only few studies have focus on animals that received Pilocarpine (Pilo) and did not develop behavioral status epilepticus (SE) and, whether they may become epileptic in the model’s chronic phase. Previews works observed mossy fiber sprouting in the hippocampus of Non-SE (NSE) rats, while others observed spontaneous and recurrent seizures (SRS) 6 - 8 months after animals received Pilo. It is known that neuronal excitability is influenced by female hormones, as well as, the occurrence of SE in castrated and non-castrated female rats. However, it is not known whether females that received Pilo and did not show SE, may have SRS. The aim of this work was to investigate whether castrated and non-castrated female rats that did not show behavioral SE after Pilo, will develop SRS in the following one-year. For that, animals received 360 mg/kg of Pilo and were video monitored for 12 months. SE females from castrated and non-castrated groups became epileptic since the first month after drug injection. Epileptic behaviors were identified watching video monitoring recordings in the fast speed. Castrated and Non-castrated NSE animals showed behaviors resembling seizures described by Racine Scale stages 1 - 3. Motor alterations showed by NSE groups could be observed only when recordings were analyzed in slow speed. In addition, behavioral manifestations as, rhythmic head movements, sudden head movements, whole body movements and immobility were also observed in both, SE and NSE groups. We concluded that NSE female rats may have become epileptic. Adding to it, slow speed analysis of motor alterations was essential for the observation of NSE findings, which suggests that possibly many motor alterations have been underestimated in epilepsy experimental research.

Molecular docking and molecular dynamics simulation study the mechanism of progesterone in the treatment of spinal cord injury

PURPOSE

Spinal cord injury can lead to incomplete or complete loss of voluntary movement and sensory function, leading to serious complications. Numerous studies have shown that progesterone exhibits strong therapeutic potential for spinal cord injury. However, the mechanism by which progesterone treats spinal cord injury remains unclear. Therefore, this article explores the mechanism of progesterone in the treatment of spinal cord injury by means of molecular docking and molecular dynamics simulation.

METHODS

We used bioinformatics to screen active pharmaceutical ingredients and potential targets, and molecular docking and molecular dynamics were used to validate and analysis by the supercomputer platform.

RESULTS

Progesterone had 3606 gene targets, spinal cord injury had 6560 gene targets, the intersection gene targets were 2355. GO and KEGG analysis showed that the abundant pathways involved multiple pathways related to cell metabolism and inflammation. Molecular docking showed that progesterone played a role in treating spinal cord injury by acting on BDNF, AR, NGF and TNF. Molecular dynamics was used to prove and analyzed the binding stability of active ingredients and protein targets, and AR/Progesterone combination has the strongest binding energy.

CONCLUSION

Progesterone promotes recovery from spinal cord injury by promoting axonal regeneration, remyelination, neuronal survival and reducing inflammation.

Neuroprotective Effect of Exogenous Galectin-1 in Status Epilepticus

Intrahippocampal pilocarpine microinjection (H-PILO) induces status epilepticus (SE) that can lead to spontaneous recurrent seizures (SRS) and neurodegeneration in rodents. Studies using animal models have indicated that lectins mediate a variety of biological activities with neuronal benefits, especially galectin-1 (GAL-1), which has been identified as an effective neuroprotective compound. GAL-1 is associated with the regulation of cell adhesion, proliferation, programmed cell death, and immune responses, as well as attenuating neuroinflammation. Here, we administrated GAL-1 to Wistar rats and evaluated the severity of the SE, neurodegenerative and inflammatory patterns in the hippocampal formation. Administration of GAL-1 caused a reduction in the number of class 2 and 4 seizures, indicating a decrease in seizure severity. Furthermore, we observed a reduction in inflammation and neurodegeneration 24 h and 15 days after SE. Overall, these results suggest that GAL-1 has a neuroprotective effect in the early stage of epileptogenesis and provides new insights into the roles of exogenous lectins in temporal lobe epilepsy (TLE).

The 5α-reductase inhibitor finasteride reduces opioid self-administration in animal models of opioid use disorder

Opioid use disorder (OUD) has become a leading cause of death in the United States, yet current therapeutic strategies remain highly inadequate. To identify potential treatments for OUD, we screened a targeted selection of over 100 drugs using a recently developed opioid self-administration assay in zebrafish. This paradigm showed that finasteride, a steroidogenesis inhibitor approved for the treatment of benign prostatic hyperplasia and androgenetic alopecia, reduced self-administration of multiple opioids without affecting locomotion or feeding behavior. These findings were confirmed in rats; furthermore, finasteride reduced the physical signs associated with opioid withdrawal. In rat models of neuropathic pain, finasteride did not alter the antinociceptive effect of opioids and reduced withdrawal-induced hyperalgesia. Steroidomic analyses of the brains of fish treated with finasteride revealed a significant increase in dehydroepiandrosterone sulfate (DHEAS). Treatment with precursors of DHEAS reduced opioid self-administration in zebrafish in a fashion akin to the effects of finasteride. These results highlight the importance of steroidogenic pathways as a rich source of therapeutic targets for OUD and point to the potential of finasteride as a new treatment option for this disorder.

Sex Differences in the Epilepsies and Associated Comorbidities: Implications for Use and Development of Pharmacotherapies

The epilepsies are common neurologic disorders characterized by spontaneous recurrent seizures. Boys, girls, men, and women of all ages are affected by epilepsy and, in many cases, by associated comorbidities as well. The primary courses of treatment are pharmacological, dietary, and/or surgical, depending on several factors, including the areas of the brain affected and the severity of the epilepsy. There is a growing appreciation that sex differences in underlying brain function and in the neurobiology of epilepsy are important factors that should be accounted for in the design and development of new therapies. In this review, we discuss the current knowledge on sex differences in epilepsy and associated comorbidities, with emphasis on those aspects most informative for the development of new pharmacotherapies. Particular focus is placed on sex differences in the prevalence and presentation of various focal and generalized epilepsies; psychiatric, cognitive, and physiologic comorbidities; catamenial epilepsy in women; sex differences in brain development; the neural actions of sex and stress hormones and their metabolites; and cellular mechanisms, including brain-derived neurotrophic factor signaling and neuronal-glial interactions. Further attention placed on potential sex differences in epilepsies, comorbidities, and drug effects will enhance therapeutic options and efficacy for all patients with epilepsy. SIGNIFICANCE STATEMENT: Epilepsy is a common neurological disorder that often presents together with various comorbidities. The features of epilepsy and seizure activity as well as comorbid afflictions can vary between men and women. In this review, we discuss sex differences in types of epilepsies, associated comorbidities, pathophysiological mechanisms, and antiepileptic drug efficacy in both clinical patient populations and preclinical animal models.

Sex steroid hormone function in the brain niche: Implications for brain metastatic colonization and progression

BACKGROUND

While sex hormones and their receptors play well-known roles in progression of primary tumors through direct action on sex steroid hormone-responsive cancer cells, emerging evidence suggest that hormones also play important roles in metastatic progression by modulating the tumor microenvironment. Estrogens and androgens synthesized in gonads and within the brain influence memory, behavior, and outcomes of brain pathologies. Yet, their impact on brain metastatic colonization and progression is just beginning to be explored.

RECENT FINDINGS

Estradiol and testosterone cross the blood-brain barrier and are synthesized de novo in astrocytes and other cells within the adult brain. Circulating and brain-synthesized estrogens have been shown to promote brain metastatic colonization of tumors lacking estrogen receptors (ERs), through mechanisms involving the upregulation of growth factors and neurotrophins in ER+ reactive astrocytes. In this review, we discuss additional mechanisms by which hormones may influence brain metastases, through modulation of brain endothelial cells, astrocytes, and microglia.

CONCLUSION

A greater understanding of hormone-brain-tumor interactions may shed further light on the mechanisms underlying the adaptation of cancer cells to the brain niche, and provide therapeutic alternatives modulating the brain metastatic niche.

Design and development of letrozole nanoemulsion: A comparative evaluation of brain targeted nanoemulsion with free letrozole against status epilepticus and neurodegeneration in mice

The target of the current study is to formulate letrozole loaded nanoemulsion (LET-NE) for the direct nose to brain delivery to reduce peripheral effects of letrozole (LET). LET-NE is compared against intraperitoneally administered free LET in kainic acid (KA) induced status epilepticus (SE) in mice. LET loaded nanoemulsion (LET-NE) was prepared by aqueous microtitration method using Triacetin, Tween 80 and PEG-400 as the oil phase, surfactant, and co-surfactant. Nanoemulsion was studied for droplet size, polydispersity index (PDI), zeta potential, percentage transmittance, drug content, surface morphology. TEM images of developed formulation demonstrated spherical droplets with a mean diameter of 95.59 ± 2.34 nm, PDI of 0.162 ± 0.012 and zeta potential of -7.12 ± 0.12 mV respectively. In in-vitro and ex-vivo drug release, LET-NE showed prolonged drug release profile as compared to suspension. SE was induced by KA (10 mg/kg, i.p.) in Swiss albino mice. Behavioral seizure monitoring, biochemical estimations, and histopathological examination were performed. The onset time of SE was significantly enhanced and % incidence of SE was reduced by intranasal administration of LET-NE as compared to KA and LET administered intraperitoneally. Biochemical estimations revealed that LET-NE effectively decreased levels of 17-β estradiol while the levels of 5α-Dihydrotestosterone (5α-DHT) and 3α-androstanediol (3α-Diol) were significantly increased in the hippocampus. In cresyl violet staining LET-NE showed better protection of the hippocampus from neurotoxicity induced by KA as compared to LET. Also, in gamma scintigraphy of mouse brain, intranasal administration of nanoemulsion exhibited the presence of high concentration of LET. The study demonstrates the anticonvulsant and neuroprotective effect of LET-NE probably by inhibition of aromatization of testosterone into 17-β estradiol, proconvulsant, and diverting the pathway into the synthesis of testosterone metabolites, 3α-Diol with known anticonvulsant and neuroprotective action. Brain targeting of LET-NE showed better anticonvulsant and neuroprotective action than LET.

Allopregnanolone mediates the exacerbation of Tourette-like responses by acute stress in mouse models

Tourette syndrome (TS) is a neuropsychiatric disorder characterized by multiple tics and sensorimotor abnormalities, the severity of which is typically increased by stress. The neurobiological underpinnings of this exacerbation, however, remain elusive. We recently reported that spatial confinement (SC), a moderate environmental stressor, increases tic-like responses and elicits TS-like sensorimotor gating deficits in the D1CT-7 mouse, one of the best-validated models of TS. Here, we hypothesized that these adverse effects may be mediated by neurosteroids, given their well-documented role in stress-response orchestration. Indeed, SC increased the levels of progesterone, as well as its derivatives 5α-dihydroprogesterone and allopregnanolone, in the prefrontal cortex (PFC) of D1CT-7 mice. Among these steroids, however, only allopregnanolone (5-15 mg/kg, IP) dose-dependently exacerbated TS-like manifestations in D1CT-7, but not wild-type littermates; these effects were countered by the benchmark anti-tic therapy haloperidol (0.3 mg/kg, IP). Furthermore, the phenotypic effects of spatial confinement in D1CT-7 mice were suppressed by finasteride (25-50 mg/kg, IP), an inhibitor of the main rate-limiting enzyme in allopregnanolone synthesis. These findings collectively suggest that stress may exacerbate TS symptoms by promoting allopregnanolone synthesis in the PFC, and corroborate previous clinical results pointing to finasteride as a novel therapeutic avenue to curb symptom fluctuations in TS.

The neurosteroidogenic enzyme 5α-reductase modulates the role of D1 dopamine receptors in rat sensorimotor gating

Neurosteroids exert diverse modulatory actions on dopamine neurotransmission and signaling. We previously documented that the enzyme 5α-reductase, which catalyzes the main rate-limiting step in neurosteroid synthesis, is required for the behavioral responses of Sprague-Dawley rats to non-selective dopaminergic agonists, such as the D1-D2 receptor agonist apomorphine. Specifically, systemic and intra-accumbal administrations of the 5α-reductase inhibitor finasteride countered apomorphine-induced deficits of sensorimotor gating, as measured by the prepulse inhibition (PPI) of the startle reflex; the classes of dopamine receptors involved in these effects, however, remain unknown. Prior rodent studies have revealed that the contributions of dopamine receptors to PPI regulation vary depending on the genetic background; thus, we analyzed the effect of finasteride on the PPI deficits induced by selective dopamine receptor agonists in Long-Evans (a strain exhibiting PPI deficits in response to both D1 and D2 receptor agonists) and Sprague-Dawley rats (which display PPI reductions following treatment with D2, and D3, but not D1 receptor agonists). In Long-Evans rats, finasteride opposed the PPI deficits induced by activation of D1, but not D2 receptors; conversely, in Sprague-Dawley rats, finasteride prevented the reductions in %PPI and accumbal dopamine extracellular levels caused by selective stimulation of D3, but not D2 receptors; however, the effects on %PPI were not confirmed by analyses on absolute PPI values. Our findings suggest that 5α-reductase modulates the effects of D1, but not D2 receptor agonists on sensorimotor gating. These data may help elucidate the role of neurosteroids in neuropsychiatric disorders featuring PPI deficits, including schizophrenia and Tourette syndrome.

Learning and memory: Steroids and epigenetics

Memory formation and utilization is a complex process involving several brain structures in conjunction as the hippocampus, the amygdala and the adjacent cortical areas, usually defined as medial temporal lobe structures (MTL). The memory processes depend on the formation and modulation of synaptic connectivity affecting synaptic strength, synaptic plasticity and synaptic consolidation. The basic neurocognitive mechanisms of learning and memory are shortly recalled in the initial section of this paper. The effect of sex hormones (estrogens, androgens and progesterone) and of adrenocortical steroids on several aspects of memory processes are then analyzed on the basis of animal and human studies. A specific attention has been devoted to the different types of steroid receptors (membrane or nuclear) involved and on local metabolic transformations when required. The review is concluded by a short excursus on the steroid activated epigenetic mechanisms involved in memory formation.

Inhibition of 17α-hydroxylase/C17,20 lyase reduces gating deficits consequent to dopaminergic activation

Cogent evidence points to the involvement of neurosteroids in the regulation of dopamine (DA) neurotransmission and signaling, yet the neurobiological bases of this link remain poorly understood. We previously showed that inhibition of 5α-reductase (5αR), a key neurosteroidogenic enzyme, attenuates the sensorimotor gating deficits induced by DA receptor activation, as measured by the prepulse inhibition (PPI) of the acoustic startle reflex. To extend these findings, the present study was aimed at the assessment of the role of other key neurosteroidogenic enzymes in PPI, such as 17α-hydroxylase/C17,20 lyase (CYP17A1), 3α- and 3β-hydroxysteroid dehydrogenase (HSD), in Sprague-Dawley rats. The PPI deficits induced by the DAergic non-selective agonist apomorphine (APO, 0.25mg/kg, SC) were dose-dependently attenuated by the selective CYP17A1 inhibitor abiraterone (ABI, 10-50mg/kg, IP) in a fashion akin to that of the 5αR inhibitor finasteride (FIN, 100mg/kg, IP). These systemic effects were reproduced by intracerebroventricular injection of ABI (1 μg/1 μl), suggesting the involvement of brain CYP17A1 in PPI regulation. Conversely, the PPI disruption induced by APO was not significantly affected by the 3α- and 3β-HSD inhibitors indomethacin and trilostane. Given that CYP17A1 catalyzes androgen synthesis, we also tested the impact on PPI of the androgen receptor (AR) antagonist flutamide (10mg/kg, IP). However, this agent failed to reverse APO-induced PPI deficits; furthermore, AR endogenous ligands testosterone and dihydrotestosterone failed to disrupt PPI. Collectively, these data highlight CYP17A1 as a novel target for antipsychotic-like action, and suggest that the DAergic regulation of PPI is modulated by androgenic neurosteroids, through AR-unrelated mechanisms.

Inhibition of 5α-reductase attenuates behavioral effects of D1-, but not D2-like receptor agonists in C57BL/6 mice

Converging lines of evidence point to the involvement of neurosteroids in the regulation of dopamine (DA) neurotransmission and signaling, yet the neurobiological bases of this link remain poorly understood. We previously showed that inhibition of steroid 5α-reductase (5αR), the key rate-limiting enzyme in neurosteroidogenesis, attenuates the behavioral effects of non-selective DA receptor agonists in rats, including stereotyped responses and sensorimotor gating deficits, as measured by the prepulse inhibition (PPI) of the acoustic startle reflex. Since previous findings suggested that the role of DA D(1)- and D(2)-like receptor families in behavioral regulation may exhibit broad interspecies and interstrain variations, we assessed the impact of 5αR blockade on the behavioral effects of DAergic agonists in C57BL/6 mice. The prototypical 5αR inhibitor finasteride (FIN; 25-50 mg/kg, intraperitoneally, IP) dose-dependently countered the PPI deficits and the enhancement of rearing responses induced by the full D(1)-like receptor agonist SKF-82958 (0.3 mg/kg, IP); however, FIN did not significantly affect the hyperlocomotive and startle-attenuating effects of SKF-82958. Whereas the D(2)-like receptor agonist quinpirole (QUIN; 0.5 mg/kg, IP) did not induce significant changes in PPI, the combination of this agent and FIN surprisingly produced marked gating and startle deficits. In contrast with previous data on rats, FIN did not affect the reductions of startle reflex and PPI produced by the non-selective DAergic agonist apomorphine (APO; 0.5 mg/kg, IP). These findings collectively indicate that, in C57BL/6 mice, 5αR differentially modulates the effects of D(1)- and D(2)-like receptor agonists in behavioral regulation.

Role of testosterone in memory impairment of Alzheimer disease induced by Streptozotocin in male rats

BACKGROUND AND PURPOSE OF THE STUDY

Recent studies demonstrate that androgens, beyond regulating sexual behavior, exert several neuroprotective functions in the brain. The present study was designed to explore effect of testosterone in memory impairment induced by intra- cerebroventricular (icv) injection of streptozotocin (STZ) as a model of sporadic AD.

METHODS

Study was carried out on male Wistar rats. Animals were randomly divided into 11 equal groups. Experimental model of AD was induced by bilateral icv injection of STZ at the dose of 750 μg/Rat/10 μl ACSF at days 1 and 3. STZ-induced memory impairment was assessed two weeks after the last dose of STZ by using a passive avoidance task (1 mA). The interval between the placement of animals in the illuminated chamber and the entry into the dark chamber was measured as a step-through latency (STL). Castration was performed by surgical removing of testis and behavioral study of memory impairment was done after 4 weeks.

RESULTS

Results of this study showed that icv injection of STZ could induce marked (p < 0.05) memory impairment at the dose of 750 μg/Rat/dissolve10 μl CSF/bilateral/days 1 and 3. Therefore, we used this dose of STZ for induction of experimental model of AD. Memory was worsened in castrated rats (P < 0.05) when compared with normal and sham-operated animals. Testosterone replacement therapy (1 mg/kg, sc, for 6 days) in 4 week castrated rats restored memory up to the level of control groups. Testosterone had not any significant effect on memory impairments of non-castrated rats.

MAJOR CONCLUSION

According to the obtained results it can be concluded that testosterone improves cognitive and memory impairment of AD. We suggest that testosterone replacement therapy may have beneficial effect in ameliorating memory impairments of senile patients suffering from AD. Further clinical studies should be carried out to prove possible useful effect of testosterone as an adjuvant therapy in AD.

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

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

Continuous estrone treatment impairs spatial memory and does not impact number of basal forebrain cholinergic neurons in the surgically menopausal middle-aged rat

CEE (conjugated equine estrogens) is the most widely prescribed estrogen-only menopausal hormone therapy in the United States, and is comprised of over 50% estrone (E1) sulfate. Following CEE administration, E1 is the principal circulating estrogen. However, the cognitive and neurobiological effects of E1 in a middle-aged rodent model have not yet been evaluated. We assessed cognitive effects of continuous E1 treatment in middle-aged surgically menopausal rats using a maze battery. We also quantified number of choline acetyltransferase-immunoreactive (ChAT-IR) neurons in distinct basal forebrain regions known in earlier studies in to be impacted by the most potent naturally-circulating estrogen in rodents and women, 17β-estradiol (17β-E2), as well as CEE. On the spatial working memory delayed-match-to-sample water maze, the highest E1 dose impaired memory performance during acquisition and after delay challenge. E1 did not impact ChAT-IR neuron number in the medial septum (MS) or horizontal/vertical diagonal bands. In a comparison study, 17β-E2 increased MS ChAT-IR neuron number. Findings indicate that E1 negatively impacts spatial working memory and memory retention, and does not increase ChAT-IR neuron number in basal forebrain, as does 17β-E2. Thus, data from prior studies suggest that 17β-E2 and CEE can enhance cognition and increase number of ChAT-IR basal forebrain neurons, while here we show that E1 does not induce these effects. Findings from preclinical basic science studies can inform the design of specific combinations of estrogens that could be beneficial to the brain and cognition. Accumulating data suggest that E1 is not likely to be among these key beneficial estrogens.

The Buzz about anabolic androgenic steroids: electrophysiological effects in excitable tissues

Anabolic androgenic steroids (AAS) comprise a large and growing class of synthetic androgens used clinically to promote tissue-building in individuals suffering from genetic disorders, injuries, and diseases. Despite these beneficial therapeutic applications, the predominant use of AAS is illicit: these steroids are self-administered to promote athletic performance and body image. Hand in hand with the desired anabolic actions of the AAS are untoward effects on the brain and behavior. While the signaling routes by which the AAS impose both beneficial and harmful actions may be quite diverse, key endpoints are likely to include ligand-gated and voltage-dependent ion channels that govern the activity of electrically excitable tissues. Here, we review the known effects of AAS on molecular targets that play critical roles in controlling electrical activity, with a specific focus on the effects of AAS on neurotransmission mediated by GABA(A) receptors in the central nervous system.

Influence of testosterone on synaptic transmission in the rat medial vestibular nuclei: estrogenic and androgenic effects

In brainstem slices of young male rat, we investigated the influence of the neuroactive steroid testosterone (T) on the synaptic responses by analyzing the field potential evoked in the medial vestibular nucleus (MVN) by vestibular afferent stimulation. T induced three distinct and independent long-term synaptic changes: fast long-lasting potentiation (fLP), slow long-lasting potentiation (sLP) and long-lasting depression (LD). The fLP was mediated by 17β-estradiol (E(2)) since it was abolished by blocking the estrogen receptors (ERs) or the enzyme converting T to E(2). Conversely, sLP and LD were mediated by 5α-dihydrotestosterone (DHT) since they were prevented by blocking the androgen receptors (ARs) or the enzyme converting T to DHT. Therefore, the synaptic effects of T were mediated by its androgenic or estrogenic metabolites. The pathways leading to estrogenic and androgenic conversion of T might be co-localized since, the occurrence of fLP under block of androgenic pathway, and that of sLP and LD under estrogenic block, were higher than those observed without blocks. In case of co-localization, the effect on synaptic transmission should depend on the prevailing enzymatic activity. We conclude that circulating and neuronal T can remarkably influence synaptic responses of the vestibular neurons in different and opposite ways, depending on its conversion to estrogenic or androgenic metabolites.

The testosterone-derived neurosteroid androstanediol is a positive allosteric modulator of GABAA receptors

Testosterone modulates seizure susceptibility, but the underlying mechanisms are obscure. Recently, we demonstrated that testosterone affects seizure activity via its conversion to neurosteroids in the brain. Androstanediol (5alpha-androstan-3alpha,17beta-diol) is an endogenous neurosteroid synthesized from testosterone. However, the molecular mechanism underlying the seizure protection activity of androstanediol remains unclear. Here, we show that androstanediol has positive allosteric activity as a GABA(A) receptor modulator. In whole-cell recordings from acutely dissociated hippocampus CA1 pyramidal cells, androstanediol (but not its 3beta-epimer) produced a concentration-dependent enhancement of GABA-activated currents (EC(50) of 5 microM). At 1 microM, androstanediol produced a 50% potentiation of GABA responses. In the absence of GABA, androstanediol has moderate direct effects on GABA(A) receptor-mediated currents at high concentrations. Systemic doses of androstanediol (5-100 mg/kg), but not its 3beta-epimer, caused dose-dependent suppression of behavioral and electrographic seizures in mouse hippocampus kindling, which is a model of temporal lobe epilepsy. The ED(50) value for antiseizure effects of androstanediol was 50 mg/kg, which did not produce sedation/motor toxicity. At high (2x ED(50)) doses, androstanediol produced complete seizure protection that lasted for up to 3 h after injection. The estimated plasma concentrations of androstanediol producing 50% seizure protection in the kindling model (10.6 microM) are within the range of concentrations that modulate GABA(A) receptors. These studies suggest that androstanediol could be a neurosteroid mediator of testosterone actions on neuronal excitability and seizure susceptibility via its activity as a GABA(A) receptor modulator and that androstanediol may play a key role in men with epilepsy, especially during the age-related decline in androgen levels.

Testosterone metabolites differentially maintain adult morphology in a sexually dimorphic neuromuscular system

The lumbar spinal cord of rats contains the sexually dimorphic, steroid-sensitive spinal nucleus of the bulbocavernosus (SNB). Androgens are necessary for the development of the SNB neuromuscular system, and in adulthood, continue to influence the morphology and function of the motoneurons and their target musculature. However, estrogens are also involved in the development of the SNB system, and are capable of maintaining function in adulthood. In this experiment, we assessed the ability of testosterone metabolites, estrogens and nonaromatizable androgens, to maintain neuromuscular morphology in adulthood. Motoneuron and muscle morphology was assessed in adult normal males, sham-castrated males, castrated males treated with testosterone, dihydrotestosterone, estradiol, or left untreated, and gonadally intact males treated with the 5alpha-reductase inhibitor finasteride or the aromatase inhibitor fadrozole. After 6 weeks of treatment, SNB motoneurons were retrogradely labeled with cholera toxin-HRP and reconstructed in three dimensions. Castration resulted in reductions in SNB target muscle size, soma size, and dendritic morphology. Testosterone treatment after castration maintained SNB soma size, dendritic morphology, and elevated target muscle size; dihydrotestosterone treatment also maintained SNB dendritic length, but was less effective than testosterone in maintaining both SNB soma size and target muscle weight. Treatment of intact males with finasteride or fadrozole did not alter the morphology of SNB motoneurons or their target muscles. In contrast, estradiol treatment was completely ineffective in preventing castration-induced atrophy of the SNB neuromuscular system. Together, these results suggest that the maintenance of adult motoneuron or muscle morphology is strictly mediated by androgens.

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.

Studies on neurosteroids XXIV. Determination of neuroactive androgens, androsterone and 5alpha-androstane-3alpha,17beta-diol, in rat brain and serum using liquid chromatography-tandem mass spectrometry

The development and validation of liquid chromatography-electrospray ionization-tandem mass spectrometric (LC-ESI-MS/MS) methods that enable the quantification of neuroactive androgens, androsterone (5alpha-androstan-3alpha-ol-17-one, 3alpha,5alpha-A) and 5alpha-androstane-3alpha,17beta-diol (3alpha,5alpha-Adiol), in the rat brain and serum are presented. The androgens were extracted with methanol-acetic acid, purified using solid-phase extraction cartridges, derivatized with an ESI-active reagent, isonicotinoyl azide (INA), and then subjected to LC-ESI-MS/MS. The quantifications were based on selected reaction monitoring mode using the characteristic transitions of the INA derivatives. The methods allowed the reproducible and accurate quantification of the brain and serum neuroactive androgens using a 100 mg or 100 microL sample; the intra- and inter-assay relative standard deviations were below 3.6%, and the percentage accuracy values were 97.1-103.7% for both androgens. The animal study using the methods suggests that most of 3alpha,5alpha-Adiol found in the brain is derived from the periphery, while 3alpha,5alpha-A is not only transported from the periphery into the brain, but also synthesized in the brain by the oxidation of 3alpha,5alpha-Adiol. The androgens in the rats intraperitoneally administered finasteride, a 5alpha-reductatse inhibitor, were also measured; this treatment significantly reduced the brain 3alpha,5alpha-A and 3alpha,5alpha-Adiol levels and increased only the brain level of androstenedione, the precursor of 3alpha,5alpha-A.

Antipsychotic-like properties of 5-alpha-reductase inhibitors

Recent evidence indicates that neuroactive steroids may participate in the pathogenesis of schizophrenia spectrum disorders, yet the mechanisms of this involvement are elusive. As 5-alpha-reductase (5AR) is the rate-limiting enzyme of one of the two major metabolic pathways in brain steroidogenesis, we investigated the effects of its blockade in several rat models of psychotic-like behavior. The 5AR inhibitor finasteride (FIN, 60 or 100 mg/kg, intraperitoneal, i.p.) dose- and time-dependently antagonized prepulse inhibition (PPI) deficits induced by apomorphine (APO, 0.25 mg/kg, subcutaneous, s.c.) and d-amphetamine (AMPH, 5 mg/kg, s.c.), in a manner analogous to haloperidol (HAL, 0.1 mg/kg, i.p.) and clozapine (CLO, 5 mg/kg, i.p.). Similar results were observed with the other 5AR inhibitors dutasteride (DUT, 40 or 80 mg/kg, i.p.) and SKF 105111 (30 mg/kg, i.p.). FIN (60 or 100 mg/kg, i.p.) also reduced hyperlocomotion induced by AMPH (1 or 3 mg/kg, s.c.) and attenuated stereotyped behaviors induced by APO (0.25 mg/kg, s.c.). Nevertheless, FIN (100 mg/kg, i.p.) did not reverse the PPI disruption induced by the N-methyl-d-aspartate receptor antagonist dizocilpine (0.1 mg/kg, s.c.). FIN (60-300 mg/kg, i.p.) induced no catalepsy in either the bar test or the paw test. Our results suggest that 5AR inhibitors elicit antipsychotic-like effects in animals and may be proposed as a putative novel target in the management of psychotic disorders.

Non-genomic actions of androgens

Previous work in the endocrine and neuroendocrine fields has viewed the androgen receptor (AR) as a transcription factor activated by testosterone or one of its many metabolites. The bound AR acts as transcription regulatory element by binding to specific DNA response elements in target gene promoters, causing activation or repression of transcription and subsequently protein synthesis. Over the past two decades evidence at the cellular and organismal level has accumulated to implicate rapid responses to androgens, dependent or independent of the AR. Androgen's rapid time course of action; its effects in the absence or inhibition of the cellular machinery necessary for transcription/translation; and in the absence of translocation to the nucleus suggest a method of androgen action not initially dependent on genomic mechanisms (i.e. non-genomic in nature). In the present paper, the non-genomic effects of androgens are reviewed, along with a discussion of the possible role non-genomic androgen actions have on animal physiology and behavior.

Ontogeny of estrogen receptor alpha, estrogen receptor beta and androgen receptor, and their co-localization with Islet-1 in the dorsal root ganglia of sheep fetuses during gestation

The aims of the present study were to detect the ontogeny of estrogen receptor (ERalpha and ERbeta) and androgen receptor (AR) expressions and their co-localization with Islet-1 in the developing dorsal root ganglia (DRG) of sheep fetuses by immunohistochemistry. From the single staining results, the ERalpha immunoreactivity (ERalpha-ir), ERbeta immunoreactivity (ERbeta-ir) and AR immunoreactivity (AR-ir) was first detected at days 90, 120 and 90 of gestation, respectively. From days 90 to 120, ERalpha and AR were consistently detected in the nuclei of DRG neurons and the relative percentage (approximately 60%) of ERalpha-ir or AR-ir cells did not change significantly. Moreover, there was no change in ERalpha expression, while a dramatic loss of AR expression was observed at birth. From day 120 of gestation to birth, very few neurons (approximately 8%) showed nuclear ERbeta immunoreactivity. The dual staining results showed that Islet-1 was co-localized with ERalpha, ERbeta or AR in the nuclei of DRG neurons with various frequencies, and over 70% ERalpha-ir, ERbeta-ir or AR-ir cells contained Islet-1. These results imply that ERs, AR and Islet-1 may be important in regulating the differentiation and functional maintenance of some phenotypes of DRG neurons after mid-gestation in the sheep fetus.

The identification and simultaneous quantification of neuroactive androstane steroids and their polar conjugates in the serum of adult men, using gas chromatography-mass spectrometry

Certain androstane steroids (AS) modulate ionotropic receptors, as do the pregnane steroids. Whereas women produce significant amounts of neuroactive progesterone metabolites, the steroid neuromodulators in men originate mainly from the 3-oxo-4-ene C(19)-steroids, which are converted to their 3alpha- and 3beta-hydroxy-5alpha/5beta-reduced metabolites. The neuromodulating effects of AS prompted us to monitor circulating levels of the steroids to estimate metabolic pathways in the periphery that may influence brain concentrations of AS. Hence, the serum levels of 20 steroids and 16 steroid polar conjugates including 17-oxo- and 17beta-hydroxy-derivatives of 5alpha/beta-androstane-3alpha/beta-hydroxy-androstane steroids were quantified in 15 men (16-62 years of age) using GC-MS. The conjugated AS for the most part reached micromolar concentrations, these being two or three orders of magnitude higher than those of the free steroids. The ratios of conjugates to free steroids were one to two orders of magnitude higher than the values for the corresponding pregnane steroids. This data suggested that conjugation may considerably restrain the transport of free AS from the periphery into the central nervous system.

Mass spectrometric assay and physiological-pharmacological activity of androgenic neurosteroids

Steroid hormones play a key role in the pathophysiology of several brain disorders. Testosterone modulates neuronal excitability, but the underlying mechanisms are obscure. There is emerging evidence that testosterone-derived "androgenic neurosteroids", 3alpha-androstanediol and 17beta-estradiol, mediate the testosterone effects on neural excitability and seizure susceptibility. Testosterone undergoes metabolism to neurosteroids via two distinct pathways. Aromatization of the A-ring converts testosterone into 17beta-estradiol. Reduction of testosterone by 5alpha-reductase generates 5alpha-dihydrotestosterone, which is then converted to 3alpha-androstanediol, a powerful GABA(A) receptor-modulating neurosteroid with anticonvulsant properties. Although the 3alpha-androstanediol is an emerging neurosteroid in the brain, there is no specific and sensitive assay for determination of 3alpha-androstanediol in biological samples. This article describes the development and validation of mass spectrometric assay of 3alpha-androstanediol, and the molecular mechanisms underlying the testosterone modulation of seizure susceptibility. A liquid chromatography-tandem mass spectrometry assay to measure 3alpha-androstanediol is validated with excellent linearity, specificity, sensitivity, and reproducibility. Testosterone modulation of seizure susceptibility is demonstrated to occur through its conversion to neurosteroids with "anticonvulsant" and "proconvulsant" actions and hence the net effect of testosterone on neural excitability and seizure activity depends on the levels of distinct testosterone metabolites. The proconvulsant effect of testosterone is associated with increases in plasma 17beta-estradiol concentrations. The 5alpha-reduced metabolites of testosterone, 5alpha-dihydrotestosterone and 3alpha-androstanediol, had powerful anticonvulsant activity. Overall, the testosterone-derived neurosteroids 3alpha-androstanediol and 17beta-estradiol could contribute to the net cellular actions of testosterone in the brain. Because 3alpha-androstanediol is a potent positive allosteric modulator of GABA(A) receptors, it could serve as an endogenous neuromodulator of neuronal excitability in men. The 3alpha-androstanediol assay is an important tool in this area because of the growing interest in the potential to use adjuvant aromatase inhibitor therapy to improve treatment of epilepsy.

Androgens and the brain

Steroids arriving from the gonads via the circulation modulate brain function, affecting gender differentiation and sexually differentiated behavioral responses, but also the ability of the brain to process, store and retrieve sensory information. Androgens play a pivotal neuroactive role during the "organizational/developmental" phase, mainly in the fetal-neonatal period, when participated to the formation of neuronal circuits, as well as during the aging process when it has been demonstrated to directly affect hippocampal spine synapse density, suggesting a physiopathological role for androgen in the modulation cognitive function and development of neurodegenerative disease. The present short review will focus on the neuroactive effect of androgen with particular regard to the Delta4 and Delta5 androgen replacement therapy.

Steroid profiling in brain and plasma of male and pseudopregnant female rats after traumatic brain injury: analysis by gas chromatography/mass spectrometry

Steroids in brain arise from the peripheral endocrine glands and local synthesis. In traumatic brain injury (TBI), the endogenous circulating hormones at the time of injury are important for neuroprotection. In particular, pseudopregnant females recover better than males from TBI. We investigated the effect of pseudopregnancy and TBI on steroid levels in plasma and in three brain regions (within, adjacent, and distal to the lesion site), 6 and 24 h after prefrontal cortex injury. The following steroids were analyzed by gas chromatography/mass spectrometry: pregnenolone, progesterone, 5alpha-dihydroprogesterone, 3alpha,5alpha-tetrahydroprogesterone, 3beta,5alpha-tetrahydroprogesterone, dehydroepiandrosterone, Delta(4)-androstenedione, testosterone, 5alpha-dihydrotestosterone, 3alpha,5alpha-tetrahydrotestosterone, 3beta,5alpha-tetrahydrotestosterone, and 17beta-estradiol. Corticosterone was assayed in plasma to account for stress in the rats. We found different steroid profiles in brain and plasma of male and pseudopregnant female rats and specific profile changes after TBI. In sham-operated pseudopregnant females, much higher levels of progesterone, 5alpha-dihydroprogesterone, 3alpha,5alpha-tetrahydroprogesterone, and 3beta,5alpha-tetrahydroprogesterone were measured in both brain and plasma, compared with sham-operated males. Plasma levels of corticosterone were high in all groups, indicating that the surgeries induced acute stress. Six hours after TBI, the levels of pregnenolone, progesterone, and 5alpha-dihydroprogesterone increased, and those of testosterone decreased in male brain, whereas levels of 5alpha-dihydroprogesterone and 3beta,5alpha-tetrahydroprogesterone increased in brain of pseudopregnant female rats. Plasma levels of 5alpha-dihydroprogesterone did not change after TBI, suggesting a local activation of the 5alpha-reduction pathway of progesterone in both male and pseudopregnant female brain. The significant increase in neurosteroid levels in the male brain after TBI is consistent with their role in neuroprotection. In pseudopregnant females, high levels of circulating progestagens may provide protection against TBI.

Rapid inhibition of Ca2+ influx by neurosteroids in murine embryonic sensory neurones

The non-genomic role of neuroactive steroids on [Ca2+]i transients induced by GABA receptor activation was investigated in cultured dorsal root ganglia (DRG) neurones at embryonic stage E13. [Ca2+]i measurements were performed with Fura-2 fast fluorescence microfluorimetry. Application of the GABAA receptor agonist muscimol (Musci) evoked an increase in [Ca2+]i, confirming the excitatory effect of GABA at this embryonic stage. The muscimol-induced [Ca2+]i response was inhibited by progesterone (Proges) and its primary metabolite allopregnanolone (Allo) in a rapid, reversible and dose-dependent manner. These calcium transients were suppressed in the absence of external Ca2+ or in the presence of Ni2+ + Cd2+ suggesting an involvement of voltage-activated Ca2+ channels. In contrast, none of these steroids affected the resting [Ca2+]i nor exhibited any inhibitory effect on 50 mM KCl-induced [Ca2+]i increases. In view of the well-established potentiation of GABAA receptor by direct binding of neurosteroids, the inhibitory effects described in this study seem to involve distinct mechanisms. This new inhibitory effect of progesterone is observed at low and physiological concentrations, is rapid and independent of RU38486, an antagonist of the classic progesterone receptor, probably involving a membrane receptor. Using RT-PCR, we demonstrated the expression of progesterone receptor membrane component 1 (Pgrmc1), encoding 25-Dx, a membrane-associated progesterone binding protein in DRG neurones at different stages of development. In conclusion, we describe for the first time a rapid effect of progestins on embryonic DRG neurones involving an antagonistic effect of progesterone and allopregnanolone on GABAA receptors.

A neuroactive steroid 5alpha-androstane-3alpha,17beta-diol regulates androgen receptor level in astrocytes

Optic nerve head (ONH) astrocytes from patients with glaucomatous optic neuropathy exhibit increased production of 5alpha-androstane-3alpha,17beta-diol (3alpha-diol), a neuroactive metabolite of 5alpha-dihydrotestosterone (5alpha-DHT). To determine whether ONH astrocytes are androgen target cells, and whether 3alpha-diol is capable of regulating astrocyte functions, we studied the response of human ONH astrocytes to 3alpha-diol compared with 17beta-hydroxy-17alpha-methyl-estra-4,9,11-trien-3-one (R1881), a synthetic 5alpha-DHT agonist. In ONH astrocytes, both 3alpha-diol and R1881 increased protein levels of androgen receptor (AR) and glial fibrillary acidic protein (GFAP), however, only R1881 also increased the AR mRNA level and astrocyte proliferation. Both R1881 and 3alpha-diol rapidly activate the mitogen-activated protein kinase (MAPK) signaling pathway in ONH astrocytes, as confirmed by phosphorylation of extracellular signal-regulated kinase (ERK). 3Alpha-diol also activates the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway. 3Alpha-diol regulates the increase of AR protein level and the phosphorylation through the PI3K/Akt pathway, whereas R1881 regulates them through the MAPK/ERK pathway. Our findings demonstrate that human ONH astrocytes are androgen target cells and respond to androgens by the rapid activation of cell signaling. The activation of the PI3K/Akt pathway by 3alpha-diol may regulate various properties of astrocytes, including cell motility and survival, and may play a role in the formation and maintenance of the reactive phenotype of ONH astrocytes in glaucoma.

Androgen modulation of hippocampal synaptic plasticity

This review briefly summarizes recent developments in our understanding of the role of androgens in maintaining normal hippocampal structure. Studies in rats and vervet monkeys have demonstrated that removal of the testes reduces the density of synaptic contacts on dendritic spines of cornu ammonis 1 (CA1) pyramidal neurons. This effect is rapidly reversed by treatment with either testosterone or the non-aromatizable androgen dihydrotestosterone, suggesting that maintenance of normal synaptic density is androgen-dependent, via a mechanism that does not require intermediate estrogen biosynthesis. Similar effects of these androgens are observed in ovariectomized female rats, except that in the female the actions of testosterone include a substantial contribution from estrogen formation. The ability to stimulate hippocampal spine synapse density is not directly related to systemic androgenic potency: thus, weak androgens such as dehydroepiandrosterone exert effects that are comparable to those of dihydrotestosterone; while partial agonist responses are observed after injection of the synthetic antiandrogen, flutamide. These data provide a morphological counterpart to observations that androgens enhance cognitive function and mood state, suggesting that these effects may result at least in part from hippocampal neurotrophic responses. The unusual specificity of these responses raises the possibility that effects of androgens on the brain may be mediated via different mechanisms than the masculinizing actions of these steroids in non-neural androgen target organs.

Inhibiting biosynthesis and/or metabolism of progestins in the ventral tegmental area attenuates lordosis of rats in behavioural oestrus

In the ventral tegmental area (VTA), lordosis of rats is facilitated by 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). Central 3alpha,5alpha-THP results from metabolism of peripheral progesterone, from the ovaries and/or adrenals, by sequential enzymatic activity of 5alpha-reductase and 3alpha-hydroxysteroid oxidoreductase (3alpha-HSOR). In addition, in glial cells, cholesterol is converted into pregnenolone by the P450 side-chain cleavage enzyme (P450scc), which is then metabolized to progesterone by 3beta-hydroxysteroid dehydrogenase, and subsequently reduced to 3alpha,5alpha-THP. We hypothesize that, in the VTA, formation of 3alpha,5alpha-THP by both metabolism and biosynthesis is necessary for facilitation of lordosis of female rats. In Experiment 1, naturally-receptive rats received bilateral VTA infusions of a P450scc inhibitor, digitoxin (1 microg/side); a 5alpha-reductase inhibitor, finasteride (10 microg/side); digitoxin (1 microg/side)+finasteride (10 microg/side); or vehicle and were tested 3 h later for lordosis. In Experiment 2, the effects of VTA infusions of digitoxin, finasteride, digitoxin+finasteride, or vehicle on lordosis and midbrain and plasma 3alpha,5alpha-THP levels were examined. In Experiment 3, we investigated whether infusions of 3alpha,5alpha-THP to the VTA reinstated lordosis and midbrain 3alpha,5alpha-THP levels following administration of inhibitors. VTA infusions of digitoxin, finasteride, or digitoxin+finasteride, significantly and similarly reduced lordosis and midbrain, but not plasma 3alpha,5alpha-THP levels, compared to vehicle. Following receipt of inhibitor infusions, 3alpha,5alpha-THP to the VTA restored lordosis and midbrain 3alpha,5alpha-THP levels. These data suggest that, in the VTA, both central biosynthesis of progesterone and metabolism of progesterone (from central and/or peripheral sources) to 3alpha,5alpha-THP are important for mediating lordosis of rats.

Anticonvulsant activity of the testosterone-derived neurosteroid 3α-androstanediol

3alpha-Androstanediol is synthesized from testosterone in peripheral tissues and in the brain, but the clinical importance of this neurosteroid remains unclear. This study evaluated the effects of 3alpha-androstanediol on seizure susceptibility in mouse models of epilepsy. 3alpha-Androstanediol protected mice against seizures induced by GABAA receptor antagonists pentylenetetrazol, picrotoxin, and beta-carboline ester in a dose-dependent fashion. However, 3alpha-androstanediol was inactive against seizures induced by glutamate receptor agonists kainic acid, NMDA and 4-aminopyridine. Pretreatment with the androgen receptor antagonist flutamide had no effect on seizure protection by 3alpha-androstanediol. These results suggest that 3alpha-androstanediol has powerful anticonvulsant activity that occurs largely through non-genomic mechanisms. Testosterone-derived 3alpha-androstanediol might be an endogenous protective neurosteroid in the brain.

Testosterone modulation of seizure susceptibility is mediated by neurosteroids 3α-androstanediol and 17β-estradiol

Testosterone modulates seizure susceptibility in animals and humans, but the underlying mechanisms are obscure. Here, testosterone modulation of seizure susceptibility is hypothesized to occur through its conversion to neurosteroids with "anticonvulsant" and "proconvulsant" actions, and hence the net effect of testosterone on neural excitability and seizure activity depends on the levels of distinct testosterone metabolites. Testosterone undergoes metabolism to neurosteroids via two distinct pathways. Aromatization of the A-ring converts testosterone into 17beta-estradiol. Reduction of testosterone by 5alpha-reductase generates 5alpha-dihydrotestosterone (DHT), which is then converted to 3alpha-androstanediol (3alpha-Diol), a powerful GABA(A) receptor-modulating neurosteroid with anticonvulsant properties. Systemic doses of testosterone decreased seizure threshold in rats and increased the incidence and severity of pentylenetetrazol (PTZ)-induced seizures in mice. These proconvulsant effects of testosterone were associated with increases in plasma 17beta-estradiol and 3alpha-Diol concentrations. Pretreatment with letrozole, an aromatase inhibitor that blocks the conversion of testosterone to 17beta-estradiol, significantly inhibited testosterone-induced exacerbation of seizures. The 5alpha-reductase inhibitor finasteride significantly reduced 3alpha-Diol levels and also blocked letrozole's ability to inhibit the proconvulsant effects of testosterone. The 5alpha-reduced metabolites of testosterone, DHT and 3alpha-Diol, had powerful anticonvulsant activity in the PTZ test. Letrozole or finasteride had no effect on seizure protection by DHT and 3alpha-Diol, but indomethacin partially reversed DHT actions. 3alpha-Diol but not 3beta-androstanediol, a GABA(A) receptor-inactive stereoisomer, suppressed 4-aminopyridine-induced spontaneous epileptiform bursting in rat hippocampal slices. Thus, testosterone-derived neurosteroids 3alpha-Diol and 17beta-estradiol could contribute to the net cellular actions of testosterone on neural excitability and seizure susceptibility.

Gonadal steroid hormone modulation of nociception, morphine antinociception and reproductive indices in male and female rats

The purpose of this study was to examine how gonadal steroid hormones modulate basal nociception and morphine antinociception relative to regulating reproduction in the adult rat. Male and female Sprague-Dawley rats were either gonadectomized (GDX) or sham-gonadectomized (sham); GDX males were implanted subcutaneously with capsules containing testosterone (T), estradiol (E2), dihydrotestosterone (DHT), E2 and DHT, or nothing (0). GDX females received E2, T, or empty (0) capsules immediately after surgery, and vehicle or progesterone (P4) injections at 4-day intervals. Basal nociception and morphine antinociception were tested 28 days after surgery on 50 degrees C and 54 degrees C hotplate tests, and reproductive behavior and physiology were assessed shortly thereafter. There were no significant differences in baseline hotplate latencies among the male treatment groups, but morphine was significantly more potent in sham and GDX+T males than in GDX+0 males. The ability of T to increase morphine's potency was approximated by its major metabolites E2 and DHT, given together but not alone. Baseline hotplate latencies were higher in sham females tested during diestrus than in those tested during estrus. Morphine was significantly more potent in sham females tested during proestrus and diestrus than in those tested during estrus. Baseline hotplate latencies were significantly higher, and morphine was significantly less potent in GDX+E2, GDX+E2/P4 and GDX+T females than in GDX+0 females. All group differences in basal nociception and morphine antinociception observed on the 50 degrees C hotplate test were smaller and generally non-significant on the 54 degrees C hotplate test. Steroid manipulations produced the expected changes in reproductive behaviors and steroid-sensitive organs. These results demonstrate that in adult rats, gonadal steroid manipulations, that are physiologically relevant, modulate (1) basal nociception in females but not males, and (2) morphine's antinociceptive potency in both males and females.

Hypothalamic 5 alpha-reductase and 3 alpha-oxidoreductase activity in the male rat

The aim of the present study was to assess the progesterone (Pr) transforming 5 alpha-reductase (5 alpha-R) and 3 alpha-oxidoreductase (3 alpha-OR) activities in the hypothalamus of the male rat as a function of age and following castration and/or adrenalectomy performed at the sixth day of life. The hypothalamic activity of these enzymes was estimated from the sum of the 5 alpha- or 3 alpha-reduced metabolites produced from 14C-labeled Pr incubated "in vitro" with hypothalamic tissue. Plasma levels of testosterone (T), progesterone (Pr), estrone (E1), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured simultaneously. Special attention was paid to the GC/MS analysis of the endogenous content of the hypothalamic Pr-metabolites 3 alpha-hydroxy-pregn-4-en-20-one (3 alpha-Pr), 5 alpha-pregnane-3,20-dione (5 alpha-Pr) and 3 alpha-hydroxy-5 alpha-pregnan-20-one (5 alpha,3 alpha-Pr). The high 5 alpha-R and 3 alpha-OR activities estimated in the hypothalamus of prepubertal rats are not related to the action of gonadal or adrenal steroids. Substantial and comparable endogenous 3 alpha- and/or 5 alpha-Pr-metabolites were found in hypothalami from both prepubertal and mature rats. The results of the present study do not provide evidence for a contributory role of the 3 alpha-hydroxylated Pr derivative to the regulation of gonadotropin secretion in the male rat.

Anatomical and biochemical evidence for the synthesis of unconjugated and sulfated neurosteroids in amphibians

Various studies have shown that, in mammals, neurons and glial cells are capable of synthesizing bioactive steroids, or neurosteroids, which regulate the activity of the central nervous system (CNS). However, although steroid hormones are involved in the regulation of behavioral and neuroendocrine processes in amphibians, neurosteroid biosynthesis has never been studied in the CNS of non-mammalian vertebrates. Reviewed here are several data sets concerning the production of unconjugated and sulfated neurosteroids in amphibians. These data were obtained by investigating the immunohistochemical localization and activity of 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17beta-hydroxysteroid dehydrogenase (17beta-HSD) and hydroxysteroid sulfotransferase (HST), in the frog brain. Numerous 3beta-HSD-immunoreactive neurons were detected in the anterior preoptic area, nucleus of the periventricular organ, posterior tuberculum, ventral and dorsal hypothalamic nuclei. 17beta-HSD-like immunoreactivity was found in ependymal gliocytes bordering the lateral ventricles of the telencephalon. Two populations of HST-immunoreactive neurons were localized in the anterior preoptic area and the dorsal magnocellular nucleus of the hypothalamus. High amounts of progesterone (PROG), 17-hydroxyprogesterone (17OH-PROG), testosterone (T) and dehydroepiandrosterone sulfate (DHEAS) were measured in the frog brain by combining HPLC analysis of tissue extracts with radioimmunoassay detection. Incubation of telencephalic or hypothalamic explants with tritiated pregnenolone ([3H]PREG) yielded the synthesis of various metabolites including PROG, 17OH-PROG, DHEA and T. Incorporation of [35S]3'-phosphoadenosine 5'-phosphosulfate ([35S]PAPS) and [3H]PREG or [3H]DHEA into frog brain homogenates led to the formation of [3H,35S]pregnenolone sulfate ([3H,35S]PREGS) or [3H,35S]DHEAS, respectively. Altogether, these results demonstrate that the process of neurosteroid biosynthesis occurs in amphibians as previously seen in mammals.

The role of neurosteroids and non-genomic effects of progestins and androgens in mediating sexual receptivity of rodents

Progestins and androgens modulate sexual receptivity in rodents, in part through mechanisms independent of traditional intracellular steroid receptors. Progesterone (PROG) in the ventromedial hypothalamus (VMH) and ventral tegmental (VTA) facilitates lordosis but has different actions in these brain areas. Primarily using lordosis in rodents as an in vivo experimental model, we have examined the effects that progestins exert in the midbrain and hypothalamus. Localization and blocker studies indicate that PROG's actions in the VMH require intracellular progestin receptors (PRs) but in the VTA they do not. Progestins that have rapid, membrane effects, and/or are devoid of affinity for PRs, facilitate lordosis when applied to the VTA. Manipulation of GABA and/or GABA(A)/benzodiazepine receptor complexes (GBRs) in the VTA alters lordosis, which suggests that progestins may interact with GBRs to facilitate receptivity by enhancing the function of GABAergic neurons. Interfering with PROG's metabolism to, or the biosynthesis of, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-TH PROG or allopregnanolone), the most effective endogenous GBR agonist, in the VTA attenuates female sexual behavior in rodents. Stimulation of mitochondrial benzodiazepine receptors (MBRs), which enhances neurosteroid production, by infusions of an MBR agonist to the VTA enhances lordosis. 3alpha,5alpha-TH PROG is increased in the midbrain of mated>proestrous>diestrous rodents. These data suggest that in the VTA, PROG may facilitate lordosis following metabolism to and/or biosynthesis of 3alpha,5alpha-TH PROG, which may have subsequent actions at GBRs and/or MBRs to acutely modulate female sexual behavior in rodents. The 3alpha-hydroxysteroid oxidoreduced metabolite of dihydrotestosterone (DHT), 5alpha-androstane-3alpha,17beta-diol (3alpha-androstanediol), is important for termination of sexual receptivity in rodents and has these effects in the absence of functional intracellular androgens receptors. As well, altering GBR function in the hypothalamus can influence 3alpha-androstanediol's inhibition of sexual receptivity. Through actions in the hypothalamus that are independent of intracellular androgen receptors but involving GBRs, 3alpha-androstanediol inhibits lordosis. These findings suggest that the PROG metabolite and pregnane neurosteroid, 3alpha,5alpha-TH PROG, and the testosterone metabolite and androstane neurosteroid, 3alpha-androstanediol, can have proximate influences on lordosis that is via nonclassical actions at intracellular steroid receptors.

Progesterone synthesis and myelin formation in peripheral nerves

Progesterone is synthesized in the nervous system by neurons and glial cells. Because of their simple structure, plasticity and capacity of regeneration, peripheral nerves are particularly well suited for studying the biosynthesis, mechanisms of action and effects of the hormone. Schwann cells, the myelinating glial cells in the peripheral nervous system, synthesize progesterone in response to a diffusible neuronal signal. In peripheral nerves, the local synthesis of progesterone plays an important role in the formation of myelin sheaths. This has been shown in vivo, after cryolesion of the mouse sciatic nerve, and in vitro, in cocultures of Schwann cells and sensory neurons. Schwann cells also express an intracellular receptor for progesterone, which thus functions as an autocrine signalling molecule. Progesterone may promote myelination by activating the expression of genes coding for transcription factors (Krox-20) and/or for myelin proteins (P0, PMP22). Recently, it has been proposed that progesterone may indirectly regulate myelin formation by influencing gene expression in neurons. Steroid hormones also influence the proliferation of Schwann cells: estradiol becomes a potent mitogen for Schwann cells when levels of cAMP are elevated and glucocorticosteroids have been shown to increase the mitogenic effects of peptide growth factors.

Brain androgen and progesterone metabolizing enzymes: biosynthesis, distribution and function

This review summarizes the biosynthesis, cell type-distribution and function of brain aromatase cytochrome P450 (P450aro) and 5alpha-reductase enzymes. This overview covers the impact of the steroid products of the P450aro and 5alpha-reductase enzymes in establishing sexually dimorphic brain structures, specifically the sexually dimorphic nucleus of the preoptic area (SDN) and the anteroventral periventricular nucleus (AVPV). Additionally, since metabolites of the P450aro and 5alpha-reductase enzymes are known to regulate the calcium-binding protein, calbindin (CALB), CALB is reviewed in relationship to its potential role in determining sexually dimorphic brain structures. Finally, recent reports indicate that phytoestrogens inhibit P450aro and 5alpha-reductase activities in peripheral tissue sites, therefore, the effects of phytoestrogens on brain P450aro and 5alpha-reductase are briefly considered and the impact of consuming a high vs. a low phytoestrogen diet on visual spatial memory in male and female rats is presented.

The ovarian hormones and absence epilepsy: a long-term EEG study and pharmacological effects in a genetic absence epilepsy model

In the first experiment, the relationship between the phase of the estrous cycle and the number of spontaneously occurring spike-wave discharges was investigated in WAG/Rij rats, a model for generalized absence epilepsy. The electroencephalogram (EEG) was continuously recorded for 96 h in eight rats chronically equipped with cortical EEG electrodes. A circadian pattern emerged for the number of spike-wave discharges: a nadir during the first hours of the light period, and an acrophase during the first hours of the dark period. This daily maximum was increased at proestrus day compared with the other days of the cycle, when the plasma level of progesterone is enhanced specifically at these hours of this day. This suggests that progesterone enhances spike-wave discharges. There was no difference in the first few hours of the light period in the number of spike-wave discharges between proestrus and the three other days, suggesting that estradiol has no effect on spike-wave discharges. In the second study, the effects of the systemic administration of progesterone and 17 beta-estradiol on spike-wave discharges and spontaneous behavior were investigated. It was shown that progesterone (20 and 30 mg/kg) but not estradiol (0.17-1.5 mg/kg) increased the number and total duration of spike-wave discharges. On the other hand, injection of RU 38486 (10 and 30 mg/kg), an antagonist of intracellular progesterone receptors, had no effect on spike-wave discharges and did not block the stimulatory effect of progesterone. The antagonist of 17 beta-estradiol tamoxifen (1 and 3 mg/kg) did not evoke alterations in the number or duration of spike-wave discharges. Our results indicate that progesterone aggravates spike-wave discharges, but is not mediated through intracellular receptors. Since progesterone is rapidly metabolized in the brain to the positive modulator of GABA(A) receptor allopregnanolone, which increases spike-wave discharges in WAG/Rij rats, it is possible that the epileptiformic effects of progesterone are mediated through this metabolite.

Ontogeny of steroid metabolizing enzymes in rat oligodendrocytes

Rat oligodendroglial cells were isolated from newborn and developing brains and used immediately after, for quantification of steroid metabolizing activities. Oligodendrocytes (Ol) and their progenitor cells were incubated with [(14)C] testosterone, [(14)C] progesterone, [(14)C] pregnenolone or [(14)C] dehydroepiandrosterone (DHEA). Oligodendrocytes and their progenitor cells expressed different steroid metabolizing enzymes. The main activities were 5 alpha reduction of testosterone and progesterone and 3 beta hydroxy steroid dehydrogenase-isomerase which transformed pregnenolone into progesterone and DHEA into Delta 4 androstenedione. 5 alpha reductase activity increased in male and female rats in parallel with testosterone or progesterone. Contrary to this, 3 beta hydroxysteroid dehydrogenase-isomerase activity was found to be high in the young rat and to decrease when testosterone and progesterone plasma concentration increased.

Androgens are neuroprotective in the dentate gyrus of adrenalectomized female rats

Neuroprotective effects of androgens have not been well-characterized, but there is evidence that 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) has anti-seizure effects. To further examine androgens' neuroprotective effects, testosterone (T), dihydrotestosterone (DHT), 3 alpha-diol (1.0 mg/kg SC daily), or sesame oil vehicle was administered to adrenalectomized or sham-operated, young, female Long Evans rats (N = 52). After seven days, animals were perfused and trunk blood was collected for radioimmunoassay of plasma corticosterone and androgens. No pyknotic cells were seen in the dentate of the sham-operated animals or those animals that had incomplete adrenalectomies (n = 20); however, cresyl violet and TUNEL stains revealed pyknotic cells in the granule layer of the dentate gyrus of adrenalectomized rats (n = 28). Testosterone, DHT, or 3 alpha-diol significantly reduced the number of pyknotic cells in the dentate gyrus compared to vehicle administered, adrenalectomized rats. Steroid-administered animals had levels of T, DHT, or 3 alpha-diol within physiological concentrations. These findings suggest that T, DHT, or 3 alpha-diol may have neuroprotective effects via a common mechanism of action.

Steroid-induced developmental plasticity in hypothalamic astrocytes: implications for synaptic patterning

We have previously demonstrated that astrocytes in the developing arcuate nucleus of the rat hypothalamus exhibit a sexually dimorphic morphology as a result of differential exposure to gonadal steroids. Testosterone via its aromatized byproduct, estrogen, induces arcuate astrocytes to undergo differentiation during the first few days of life. These differentiated astrocytes exhibit a stellate morphology. Coincident with the steroid-induced increase in astrocyte differentiation is a reduction of dendritic spines on arcuate neurons. As a result, the arcuate nucleus of males has fewer axodendritic spine synapses than females and this dimorphism is retained throughout life. In the immediately adjacent ventromedial nucleus, neonatal astrocytes are immature and unresponsive to steroids. Neurons in this region show no change in dendritic spines in the first few days of life but do exhibit increased dendritic branching as a result of testosterone exposure. These findings illustrate the importance of distinct populations of astrocytes in restricted brain regions and their potential importance to the establishment of regionally specific synaptic patterning. Conflicting reports leave the site of steroid-mediated astrocyte responsiveness in the arcuate nucleus unresolved: Are gonadal steroids acting directly on astrocytes or are steroid-concentrating neurons mediating astrocytic responsiveness? In this review, we discuss the current understanding of astrocyte-neuron interactions and the possible mechanisms for steroid-mediated, astrocyte-directed synaptic patterning in the developing hypothalamus.