Antipsychotic-like properties of 5-alpha-reductase inhibitors

The role of neuroactive steroids in tic disorders

Tics are sudden, repetitive movements or vocalizations. Tic disorders, such as Tourette syndrome (TS), are contributed by the interplay of genetic risk factors and environmental variables, leading to abnormalities in the functioning of the cortico-striatal-thalamo-cortical (CSTC) circuitry. Various neurotransmitter systems, such as gamma-aminobutyric acid (GABA) and dopamine, are implicated in the pathophysiology of these disorders. Building on the evidence that tic disorders are predominant in males and exacerbated by stress, emerging research is focusing on the involvement of neuroactive steroids, including dehydroepiandrosterone sulfate (DHEAS) and allopregnanolone, in the ontogeny of tics and other phenotypes associated with TS. Emerging evidence indicates that DHEAS levels are significantly elevated in the plasma of TS-affected boys, and the clinical onset of this disorder coincides with the period of adrenarche, the developmental stage characterized by a surge in DHEAS synthesis. On the other hand, allopregnanolone has garnered particular attention for its potential to mediate the adverse effects of acute stress on the exacerbation of tic severity and frequency. Notably, both neurosteroids act as key modulators of GABA-A receptors, suggesting a pivotal role of these targets in the pathophysiology of various clinical manifestations of tic disorders. This review explores the potential mechanisms by which these and other neuroactive steroids may influence tic disorders and discusses the emerging therapeutic strategies that target neuroactive steroids for the management of tic disorders.

Neurosteroid influence on affective tone

Affective disorders such as depression and anxiety are among the most prevalent psychiatric illnesses and causes of disability worldwide. The recent FDA-approval of a novel antidepressant treatment, ZULRESSO® (Brexanolone), a synthetic neurosteroid has fueled interest into the role of neurosteroids in the pathophysiology of depression as well as the mechanisms mediating the antidepressant effects of these compounds. The majority of studies examining the impact of neurosteroids on affective states have relied on the administration of exogenous neurosteroids; however, neurosteroids can also be synthesized endogenously from cholesterol or steroid hormone precursors. Despite the well-established influence of exogenous neurosteroids on affective states, we still lack an understanding of the role of endogenous neurosteroids in modulating affective tone. This review aims to summarize the current literature supporting the influence of neurosteroids on affective states in clinical and preclinical studies, as well as recent evidence suggesting that endogenous neurosteroids may set a baseline affective tone.

Prefrontal allopregnanolone synergizes with D1 receptor activation to disrupt sensorimotor gating in male Sprague-Dawley rats

RATIONALE

The prepulse inhibition (PPI) of the startle reflex is the best-established index of sensorimotor gating. We documented that the neurosteroid allopregnanolone (AP) is necessary to reduce PPI in response to D₁ dopamine receptor agonists. Since Sprague-Dawley (SD) rats are poorly sensitive to the PPI-disrupting effects of these drugs, we hypothesized that AP might increase this susceptibility.

OBJECTIVES

We tested whether AP is sufficient to increase the vulnerability of SD rats to PPI deficits in response to the D₁ receptor full agonist SKF82958.

METHODS

SD rats were tested for PPI after treatment with SKF82958 (0.05-0.3 mg/kg, SC) in combination with either intraperitoneal (1-10 mg/kg) or intracerebral (0.5 μg/μl/side) AP administration into the medial prefrontal cortex (mPFC) or nucleus accumbens shell. To rule out potential confounds, we measured whether SKF82958 affected the endogenous mPFC levels of AP.

RESULTS

SD rats exhibited marked PPI deficits in response to the combination of systemic and intra-mPFC AP with SKF82958 but not with the D₂ receptor agonist quinpirole (0.3-0.6 mg/kg, SC). SKF82958 did not elevate mPFC levels of AP but enhanced the content of its precursor progesterone. The PPI deficits caused by SKF82958 in combination with AP were opposed by the AP antagonist isoallopregnanolone (10 mg/kg, IP) and the glutamate NMDA receptor positive modulator CIQ (5 mg/kg, IP).

CONCLUSION

These results suggest that AP enables the detrimental effects of D₁ receptor activation on sensorimotor gating. AP antagonism or glutamatergic modulation counters these effects and may have therapeutic potential for neuropsychiatric disorders characterized by gating deficits.

Pregnenolone for the treatment of L-DOPA-induced dyskinesia in Parkinson's disease

Growing preclinical and clinical evidence highlights neurosteroid pathway imbalances in Parkinson's Disease (PD) and L-DOPA-induced dyskinesias (LIDs). We recently reported that 5α-reductase (5AR) inhibitors dampen dyskinesias in parkinsonian rats; however, unraveling which specific neurosteroid mediates this effect is critical to optimize a targeted therapy. Among the 5AR-related neurosteroids, striatal pregnenolone has been shown to be increased in response to 5AR blockade and decreased after 6-OHDA lesions in the rat PD model. Moreover, this neurosteroid rescued psychotic-like phenotypes by exerting marked antidopaminergic activity. In light of this evidence, we investigated whether pregnenolone might dampen the appearance of LIDs in parkinsonian drug-naïve rats. We tested 3 escalating doses of pregnenolone (6, 18, 36 mg/kg) in 6-OHDA-lesioned male rats and compared the behavioral, neurochemical, and molecular outcomes with those induced by the 5AR inhibitor dutasteride, as positive control. The results showed that pregnenolone dose-dependently countered LIDs without affecting L-DOPA-induced motor improvements. Post-mortem analyses revealed that pregnenolone significantly prevented the increase of validated striatal markers of dyskinesias, such as phospho-Thr-34 DARPP-32 and phospho-ERK1/2, as well as D1-D3 receptor co-immunoprecipitation in a fashion similar to dutasteride. Moreover, the antidyskinetic effect of pregnenolone was paralleled by reduced striatal levels of BDNF, a well-established factor associated with the development of LIDs. In support of a direct pregnenolone effect, LC/MS-MS analyses revealed that striatal pregnenolone levels strikingly increased after the exogenous administration, with no significant alterations in downstream metabolites. All these data suggest pregnenolone as a key player in the antidyskinetic properties of 5AR inhibitors and highlight this neurosteroid as an interesting novel tool to target LIDs in PD.

The steroidogenic inhibitor finasteride reverses pramipexole-induced alterations in probability discounting

Pramipexole is a potent agonist of D₃ and D₂ dopamine receptors, currently approved for clinical use in Parkinson's disease (PD) and restless leg syndrome. Several studies have shown that pramipexole significantly increases the risk of pathological gambling and impulse-control disorders. While these iatrogenic complications can impose a severe social and financial burden, their treatment poses serious clinical challenges. Our group previously reported that the steroidogenic inhibitor finasteride reduced pathological gambling severity in PD patients who developed this complication following pramipexole treatment. To study the mechanisms underlying these effects, here we tested the impact of finasteride in a rat model of pramipexole-induced alterations of probability discounting. We previously showed that, in rats exposed to low doses of the monoamine-depleting agent reserpine (1mg/kg/day, SC), pramipexole (0.3mg/kg/day, SC) increased the propensity to engage in disadvantageous choices. This effect was paralleled by a marked D₃ receptor upregulation in the nucleus accumbens. First, we tested how finasteride (25-50mg/kg, IP) intrinsically affects probability discounting. While the highest dose of finasteride produced a marked lack of interest in lever pressing (manifested as a significant increase in omissions), the 25mg/kg (IP) dose did not intrinsically modify probability discounting. However, this finasteride regimen significantly reduced the adverse effects of reserpine and pramipexole in probability discounting by diminishing rats' propensity to engage in highly disadvantageous probabilistic choices. The same regimen also reversed the upregulation of D₃ receptors in the nucleus accumbens induced by reserpine and pramipexole. These findings confirm that finasteride opposes the impulsivity caused by pramipexole and suggest that this effect may be underpinned by a normalizing effect on D₃ receptor expression in the nucleus accumbens.

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

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

The connection of 5-alpha reductase inhibitors to the development of depression

Recent literature connects 5-alpha reductase inhibitors (5-ARIs) with neuropsychiatric adverse effects. Several clinical studies have indicated that former 5-ARIs users had a higher incidence of depressive symptoms and neuropsychiatric side effects than non-users. However, the underlying mechanisms involved in the depression in former 5-ARIs patients, a condition known as "post finasteride syndrome (PFS)", are not thoroughly understood. This review aims to summarize and discuss the association between 5-ARIs and depression as well as possible mechanisms. We used PubMed search terms including "depression", "depressive symptoms", "MDD", "anxiety", or "suicidal idea", and "5-alpha reductase inhibitors", "finasteride", "dutasteride", "5-ARIs". All relevant articles from in vivo and clinical studies from 2002 to 2021 were carefully reviewed. Any contradictory findings were included and debated. The potential mechanisms that link 5-ARIs and depression include alteration in neuroactive steroids, dopaminergic dysfunction, reduced hippocampal neurogenesis, increased neuroinflammation, alteration of the HPA axis, and epigenetic modifications. From this review, we hope to provide information for future studies based on animal experiments, and potential therapeutic strategies for depressive patients with PFS.

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.

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

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

Sex differences in steroid levels and steroidogenesis in the nervous system: Physiopathological role

The nervous system, in addition to be a target for steroid hormones, is the source of a variety of neuroactive steroids, which are synthesized and metabolized by neurons and glial cells. Recent evidence indicates that the expression of neurosteroidogenic proteins and enzymes and the levels of neuroactive steroids are different in the nervous system of males and females. We here summarized the state of the art of neuroactive steroids, particularly taking in consideration sex differences occurring in the synthesis and levels of these molecules. In addition, we discuss the consequences of sex differences in neurosteroidogenesis for the function of the nervous system under healthy and pathological conditions and the implications of neuroactive steroids and neurosteroidogenesis for the development of sex-specific therapeutic interventions.

Isoallopregnanolone reduces tic-like behaviours in the D1CT-7 mouse model of Tourette syndrome

Tourette syndrome (TS) is a neuropsychiatric disorder characterised by multiple, persistent tics. These semi-voluntary motor and phonic manifestations are typically aggravated by exposure to acute stress, yet the mechanisms underlying this exacerbation remain unclear. Using a well-characterised animal model of TS, the D1CT-7 mouse, we recently showed that acute stress increases tic-like responses and causes sensorimotor gating deficits, as measured by the prepulse inhibition of the startle. We showed that these effects are promoted by the brain synthesis of the neurosteroid allopregnanolone (AP). In line with this idea, inhibition of AP synthesis by finasteride was found to suppress the tic-exacerbating effects of stress; conversely, AP administration resulted in a marked enhancement of the number of tic-like motor bursts. Given that the primary mechanism of AP is based on the positive allosteric modulation of GABA_A receptors, in the present study, we hypothesised that the enhancement in tic-like behaviours induced by either stress or AP may be countered by isoallopregnanolone (isoAP), the natural 3β-epimer of AP that acts as an antagonist to the AP-binding site within GABA_A receptors. In agreement with our hypothesis, isoAP (5-10 mg kg^-1 , s.c.) dose-dependently reduced the number of tic-like behaviours induced by stress in D1CT-7 mice. These effects were comparable to those elicited by both the benchmark TS therapy haloperidol (0.3 mg kg^-1 , i.p.), as well as finasteride (25 mg kg^-1 , i.p.). IsoAP also countered the prepulse inhibition deficits secondary to stress in D1CT-7 mice. Finally, isoAP opposed the enhancement of tic-like behaviours induced by AP (15 mg kg^-1 , i.p.). Given that isoAP is well-tolerated and has an optimal safety profile, these data suggest that this steroid may have therapeutic properties in TS.

Neurobehavioural complications of sleep deprivation: Shedding light on the emerging role of neuroactive steroids

Sleep deprivation (SD) is associated with a broad spectrum of cognitive and behavioural complications, including emotional lability and enhanced stress reactivity, as well as deficits in executive functions, decision making and impulse control. These impairments, which have profound negative consequences on the health and productivity of many individuals, reflect alterations of the prefrontal cortex (PFC) and its connectivity with subcortical regions. However, the molecular underpinnings of these alterations remain elusive. Our group and others have begun examining how the neurobehavioural outcomes of SD may be influenced by neuroactive steroids, a family of molecules deeply implicated in sleep regulation and the stress response. These studies have revealed that, similar to other stressors, acute SD leads to increased synthesis of the neurosteroid allopregnanolone in the PFC. Whereas this up-regulation is likely aimed at counterbalancing the detrimental impact of oxidative stress induced by SD, the increase in prefrontal allopregnanolone levels contributes to deficits in sensorimotor gating and impulse control, signalling a functional impairment of PFC. This scenario suggests that the synthesis of neuroactive steroids during acute SD may be enacted as a neuroprotective response in the PFC; however, such compensation may in turn set off neurobehavioural complications by interfering with the corticolimbic connections responsible for executive functions and emotional regulation.

In Vitro and In Vivo Assessment of Metabolic Drug Interaction Potential of Dutasteride with Ketoconazole

Dutasteride (DUT) is a selective, potent, competitive, and irreversible inhibitor of both type-1 and type-2 5α-reductase (5AR) commonly used in the treatment of benign prostatic hyperplasia and androgenetic alopecia. In the present study, we developed a simple and sensitive high-performance liquid chromatography with fluorescence detection (HPLC-FL) method for simultaneous determination of DUT and its major active metabolite, 6β-hydroxydutasteride (H-DUT). Next, the pharmacokinetic interactions of DUT with ketoconazole (KET), a potent CYP3A inhibitor, were comprehensively investigated. In vivo rat intravenous and oral studies revealed that the pharmacokinetics of DUT and H-DUT were significantly altered by the co-administration of KET. Furthermore, the in vitro microsomal metabolism, blood distribution, and protein-binding studies suggest that the altered pharmacokinetics of DUT could be attributed primarily to the inhibition of the DUT metabolism by KET. To the best of our knowledge, this is the first study to show the drug interaction potential of DUT with azole antifungal drugs including KET, together with a newly developed HPLC-FL method for the simultaneous quantification of DUT and H-DUT.

The Steroidogenesis Inhibitor Finasteride Reduces the Response to Both Stressful and Rewarding Stimuli

Finasteride (FIN) is the prototypical inhibitor of steroid 5α-reductase (5αR), the enzyme that catalyzes the rate-limiting step of the conversion of progesterone and testosterone into their main neuroactive metabolites. FIN is clinically approved for the treatment of benign prostatic hyperplasia and male baldness; while often well-tolerated, FIN has also been shown to cause or exacerbate psychological problems in vulnerable subjects. Evidence on the psychological effects of FIN, however, remains controversial, in view of inconsistent clinical reports. Here, we tested the effects of FIN in a battery of tests aimed at capturing complementary aspects of mood regulation and stress reactivity in rats. FIN reduced exploratory, incentive, prosocial, and risk-taking behavior; furthermore, it decreased stress coping, as revealed by increased immobility in the forced-swim test (FST). This last effect was also observed in female and orchiectomized male rats, suggesting that the mechanism of action of FIN does not primarily reflect changes in gonadal steroids. The effects of FIN on FST responses were associated with a dramatic decrease in corticotropin release hormone (CRH) mRNA and adrenocorticotropic hormone (ACTH) levels. These results suggest that FIN impairs stress reactivity and reduces behavioral activation and impulsive behavior by altering the function of the hypothalamus-pituitary-adrenal (HPA) axis.

Evidence for enhanced androgen action in the prefrontal cortex of people with bipolar disorder but not schizophrenia or major depressive disorder

Anxiety and depressive disorders are more prevalent in hypogonadal men. Low testosterone levels are associated with greater negative symptoms and impaired cognition in men with schizophrenia. Thus, androgens may contribute to brain pathophysiology in psychiatric disorders. We investigated androgen-related mRNAs in post-mortem dorsolateral prefrontal cortex of psychiatric disorders. We also assessed androgen receptor (AR) CAG trinucleotide repeat length, a functional AR gene variant associated with AR gene expression, receptor activity, and circulating testosterone. AR CAG repeat length was determined from genomic DNA and AR and 5α-reductase mRNAs measured using quantitative PCR in schizophrenia, bipolar disorder and control cases [n = 35/group; Stanley Medical Research Institute (SMRI) Array collection]. Layer-specific AR gene expression was determined using in situ hybridisation in schizophrenia, bipolar disorder, major depressive disorder and control cases (n = 15/group; SMRI Neuropathology Consortium). AR mRNA was increased in bipolar disorder, but was unchanged in schizophrenia, relative to controls. AR and 5α-reductase mRNAs were significantly positively correlated in bipolar disorder. AR CAG repeat length was significantly shorter in bipolar disorder relative to schizophrenia. AR mRNA expression was highest in cortical layers IV and V, but no layer-specific diagnostic differences were detected. Together, our results suggest enhanced cortical androgen action in people with bipolar disorder.

Allopregnanolone is required for prepulse inhibition deficits induced by D1 dopamine receptor activation

INTRODUCTION

The extraction of salient information from the environment is modulated by the activation of dopamine receptors. Using rodent models, we previously reported that gating deficits caused by dopamine receptor activation - as measured by the prepulse inhibition (PPI) of startle - are effectively opposed by inhibitors of the steroidogenic enzyme 5α-reductase (5αR). The specific 5αR isoenzyme and steroids implicated in these effects, however, remain unknown.

METHODS

The effects of the selective D₁ dopamine receptor agonist SKF-82958 (SKF, 0.3 mg/kg, IP) and D₂ receptor agonist quinpirole (QUIN, 0.5 mg/kg, IP) were tested in the startle reflex and PPI of knockout (KO) mice for either 5αR type 1 (5αR1) or type 2 (5αR2). Furthermore, we established whether these effects may be modified by the 5α-reduced steroids dihydroprogesterone (DHP), allopregnanolone (AP), dihydrotestosterone (DHT), 5α-androstane-3α,17β-diol (3α-diol), or androsterone. To test the mechanisms whereby 5αR products may alter the PPI-disrupting properties of D₁ agonists, we studied the involvement of GABA-A and PXR, two receptors targeted by neuroactive steroids. Specifically, we tested the effects of SKF in combination with the GABA-A antagonist bicuculline, as well as in KO mice for the GABA-A δ subunit and PXR.

RESULTS

5αR1, but not 5αR2, knockout (KO) mice were insensitive to the PPI-disrupting effects of SKF. This sensitivity was reinstated by AP (3 mg/kg, IP), but not other 5α-reduced steroids. The PPI deficits induced by SKF were not modified by bicuculline, δ-subunit KO mice and PXR KO mice.

CONCLUSIONS

These results collectively suggest that 5αR1 enables the negative effects of D₁ dopamine receptor activation on information processing via production of AP. The contribution of AP to the PPI-disrupting mechanisms of D₁ receptor agonists, however, do not appear to be mediated by either GABA-A or PXR receptors.

5alpha-reductase inhibitors dampen L-DOPA-induced dyskinesia via normalization of dopamine D1-receptor signaling pathway and D1-D3 receptor interaction

Although 1-3,4-dihydroxyphenylalanine (L-DOPA) is the mainstay therapy for treating Parkinson's disease (PD), its long-term administration is accompanied by the development of motor complications, particularly L-DOPA induced dyskinesia (LID), that dramatically affects patients' quality of life. LID has consistently been related to an excessive dopamine receptor transmission, particularly at the down-stream signaling of the striatal D₁ receptors (D₁R), resulting in an exaggerated stimulation of cAMP-dependent protein kinase and extracellular signal-regulated kinase (ERK) pathway. We previously reported that pharmacological blockade of 5alpha-reductase (5AR), the rate-limiting enzyme in neurosteroids synthesis, attenuates the severity of a broad set of behavioral alterations induced by D₁R and D₃R activation, without inducing extrapyramidal symptoms. In line with this evidence, in a recent study, we found that inhibition of 5AR by finasteride (FIN) produced a significant reduction of dyskinesia induced by L-DOPA and direct dopaminergic agonists in 6-OHDA-lesioned rats. In the attempt to further investigate the effect of 5AR inhibitors on dyskinesia and shed light on the mechanism of action, in the present study we compared the effect of FIN and dutasteride (DUTA), a potent dual 5AR inhibitor, on the development of LID, on the therapeutic efficacy of L-DOPA, on the molecular alterations downstream to the D₁R, as well as on D₁R-D₃R interaction. The results indicated that both FIN and DUTA administration significantly reduced development and expression of LID; however, DUTA appeared more effective than FIN at a lower dose and produced its antidyskinetic effect without impacting the ability of L-DOPA to increase motor activation, or ameliorate forelimb use in parkinsonian rats. Moreover, this study demonstrates for the first time that 5AR inhibitors are able to prevent key events in the appearance of dyskinesia, such as L-DOPA-induced upregulation of striatal D₁R-related cAMP/PKA/ERK signaling pathways and D₁R-D₃R coimmunoprecipitation, an index of heteromer formation. These findings are relevant as they confirm the 5AR enzyme as a potential therapeutic target for treatment of dyskinesia in PD, suggesting the first ever evidence that neurosteroidogenesis may affect functional interaction between dopamine D₁R and D₃R.

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

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

Steroid 5α-reductase 2 deficiency leads to reduced dominance-related and impulse-control behaviors

The enzyme steroid 5α-reductase 2 (5αR2) catalyzes the conversion of testosterone into the potent androgen 5α-dihydrotestosterone. Previous investigations showed that 5αR2 is expressed in key brain areas for emotional and socio-affective reactivity, yet the role of this enzyme in behavioral regulation remains mostly unknown. Here, we profiled the behavioral characteristics of 5αR2 heterozygous (HZ) and knockout (KO) mice, as compared with their wild-type (WT) littermates. While male 5αR2 KO mice displayed no overt alterations in motoric, sensory, information-processing and anxiety-related behaviors, they exhibited deficits in neurobehavioral correlates of dominance (including aggression against intruders, mating, and tube dominance) as well as novelty-seeking and risk-taking responses. Furthermore, male 5αR2 KO mice exhibited reduced D₂-like dopamine receptor binding in the shell of the nucleus accumbens - a well-recognized molecular signature of social dominance. Collectively, these results suggest that 5αR2 is involved in the establishment of social dominance and its behavioral manifestations. Further studies are warranted to understand how the metabolic actions of 5αR2 on steroid profile may be implicated in social ranking, impulse control, and the modulation of dopamine receptor expression in the nucleus accumbens.

Considering the role of adolescent sex steroids in schizophrenia

Schizophrenia is a disabling illness that is typically first diagnosed during late adolescence to early adulthood. It has an unremitting course and is often treatment-resistant. Many clinical aspects of the illness suggest that sex steroid-nervous system interactions may contribute to the onset, course of symptoms and the cognitive impairment displayed by men and women with schizophrenia. Here, we discuss the actions of oestrogen and testosterone on the brain during adolescent development and in schizophrenia from the perspective of experimental studies in animals, human post-mortem studies, magnetic resonance imaging studies in living humans and clinical trials of sex steroid-based treatments. We present evidence of potential beneficial, as well as detrimental, effects of both testosterone and oestrogen. We provide a rationale for the necessity to further elucidate sex steroid mechanisms of action at different ages, sexes and brain regions to more fully understand the role of testosterone and oestrogen in the pathophysiology of schizophrenia. The weight of the evidence suggests that sex steroid hormones influence mammalian brain function, including both cognition and emotion, and that pharmaceutical agents aimed at sex steroid receptors appear to provide a novel treatment avenue to reduce symptoms and improve cognition in men and women with schizophrenia.

Finasteride inhibited brain dopaminergic system and open-field behaviors in adolescent male rats

AIMS

Finasteride inhibits the conversion of testosterone to dihydrotestosterone. Because androgen regulates dopaminergic system in the brain, it could be hypothesized that finasteride may inhibit dopaminergic system. The present study therefore investigates the effects of finasteride in adolescent and early developmental rats on dopaminergic system, including contents of dopamine and its metabolites (dihydroxy phenyl acetic acid and homovanillic acid) and tyrosine hydroxylase expressions both at gene and protein levels. Meanwhile, open-field behaviors of the rats are examined because of the regulatory effect of dopaminergic system on the behaviors.

METHODS

Open-field behaviors were evaluated by exploratory and motor behaviors. Dopamine and its metabolites were assayed by liquid chromatography-mass spectrometry. Tyrosine hydroxylase mRNA and protein expressions were determined by real-time qRT-PCR and western blot, respectively.

RESULTS

It was found that in adolescent male rats, administration of finasteride at doses of 25 and 50 mg/kg for 14 days dose dependently inhibited open-field behaviors, reduced contents of dopamine and its metabolites in frontal cortex, hippocampus, caudate putamen, nucleus accumbens, and down-regulated tyrosine hydroxylase mRNA and protein expressions in substantia nigra and ventral tegmental area. However, there was no significant change of these parameters in early developmental rats after finasteride treatment.

CONCLUSION

These results suggest that finasteride inhibits dopaminergic system and open-field behaviors in adolescent male rats by inhibiting the conversion of testosterone to dihydrotestosterone, and imply finasteride as a potential therapeutic option for neuropsychiatric disorders associated with hyperactivities of dopaminergic system and androgen.

Effect of the 5α-reductase enzyme inhibitor dutasteride in the brain of intact and parkinsonian mice

Dutasteride is a 5alpha-reductase inhibitor in clinical use to treat endocrine conditions. The present study investigated the neuroprotective mechanisms of action of dutasteride in intact and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned mice using a low dose of MPTP not affecting motor activity modeling early stages of Parkinson's disease (PD). We hypothesized that dutasteride neuroprotection is due to altered steroids levels. Dutasteride pre-treatment prevented loss of striatal dopamine (DA) and its metabolite DOPAC. Dutasteride decreased effects of MPTP on striatal dopamine transporter (DAT), vesicular monoamine transporter 2 (VMAT2) and D2 DA receptor specific binding while D1 receptor specific binding remained unchanged. Dutasteride enhanced DAT specific binding and the glycosylated form of DAT in intact mice. MPTP-lesioned mice had plasma and brain testosterone and dihydrotestosterone levels lower than control mice whereas progesterone and its metabolites (dihydroprogesterone, isopregnanolone and tetrahydroprogesterone) pathway showed increases. Dutasteride treatment by inhibiting transformation of progesterone and testosterone to its metabolites elevated plasma and brain concentrations of testosterone compared to MPTP mice and decreased DHT levels in intact mice. Plasma and brain estradiol levels were low and remained unchanged by MPTP and/or dutasteride treatment. Dutasteride treatment did not affect striatal phosphorylation of Akt and its downstream substrate GSK3β as well as phosphorylation of ERK1/2 in intact and MPTP lesioned MPTP mice. Striatal glial fibrillary acidic protein (GFAP) levels were markedly elevated in MPTP compared to control mice and dutasteride reduced GFAP levels in MPTP mice. Treatment with dutasteride post-lesion left unchanged striatal DA levels. These results suggest dutasteride as promising drug for PD neuroprotection.

The Neurosteroidogenic Enzyme 5α-Reductase Mediates Psychotic-Like Complications of Sleep Deprivation

Acute sleep deprivation (SD) can trigger or exacerbate psychosis- and mania-related symptoms; the neurobiological basis of these complications, however, remains elusive. Given the extensive involvement of neuroactive steroids in psychopathology, we hypothesized that the behavioral complications of SD may be contributed by 5α-reductase (5αR), the rate-limiting enzyme in the conversion of progesterone into the neurosteroid allopregnanolone. We first tested whether rats exposed to SD may exhibit brain-regional alterations in 5αR isoenzymes and neuroactive steroid levels; then, we assessed whether the behavioral and neuroendocrine alterations induced by SD may be differentially modulated by the administration of the 5αR inhibitor finasteride, as well as progesterone and allopregnanolone. SD selectively enhanced 5αR expression and activity, as well as AP levels, in the prefrontal cortex; furthermore, finasteride (10-100 mg/kg, IP) dose-dependently ameliorated PPI deficits, hyperactivity, and risk-taking behaviors, in a fashion akin to the antipsychotic haloperidol and the mood stabilizer lithium carbonate. Finally, PPI deficits were exacerbated by allopregnanolone (10 mg/kg, IP) and attenuated by progesterone (30 mg/kg, IP) in SD-subjected, but not control rats. Collectively, these results provide the first-ever evidence that 5αR mediates a number of psychosis- and mania-like complications of SD through imbalances in cortical levels of neuroactive steroids.

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.

What makes you tic? Translational approaches to study the role of stress and contextual triggers in Tourette syndrome

Tourette syndrome (TS) is a neurodevelopmental condition characterized by multiple, recurring motor and phonic tics. Rich empirical evidence shows that the severity of tics and associated manifestations is increased by several stressors and contextual triggers; however, the neurobiological mechanisms responsible for symptom exacerbation in TS remain poorly understood. This conceptual gap partially reflects the high phenotypic variability in tics, as well as the existing difficulties in operationalizing and standardizing stress and its effects in a clinical setting. Animal models of TS may be highly informative tools to overcome some of these limitations; these experimental preparations have already provided critical insights on key aspects of TS pathophysiology, and may prove useful to identify the neurochemical alterations induced by different stressful contingencies. In particular, emerging knowledge on the role of contextual triggers in animal models of TS may inform the development of novel pharmacological interventions to reduce tic fluctuations in this disorder.

Exploring the neural mechanisms of finasteride: a proteomic analysis in the nucleus accumbens

The enzyme 5α-reductase (5αR) catalyzes the conversion of progesterone and testosterone into neuroactive steroids implicated in a wide array of behavioral functions. The prototypical 5αR inhibitor, finasteride (FIN), is clinically approved for the treatment of androgenic alopecia and benign prostatic hyperplasia. Recent evidence has shown that FIN, albeit generally well tolerated, can induce untoward psychological effects in a subset of patients; furthermore, this drug may have therapeutic efficacy for a number of different neuropsychiatric conditions, ranging from Tourette syndrome to schizophrenia. In rat models of these conditions, FIN has been shown to block the effects of dopamine receptors in the nucleus accumbens (NAcc), a key terminal of the dopamine mesolimbic system. The biological underpinnings of these effects, however, remain mostly elusive. To elucidate the neurochemical networks that may be responsible for the behavioral effects of FIN, we evaluated the proteomic profile of the NAcc following acute (100mg/kg, IP) and subchronic (7 days; 100mg/kg/day, IP) treatment with this drug, in comparison with vehicle treatment (n=5/group). Two-dimensional electrophoresis (2-DE) analysis coupled to mass spectrometry revealed significant changes in the expression of nine proteins (CRMP2, PSMD1, STX18, KCNC3, CYP255, GABRP, GABT, PRPS1, CYP2B3), which were further analyzed by ontological classification (PANTHER). These results point to a number of novel potential chemical targets of FIN, and may help elucidate the underpinnings of FIN's behavioral effects and therapeutic potential for neuropsychiatric disorders.

5α-Reductase Inhibition Prevents the Luteal Phase Increase in Plasma Allopregnanolone Levels and Mitigates Symptoms in Women with Premenstrual Dysphoric Disorder

Changes in neurosteroid levels during the luteal phase of the menstrual cycle may precipitate affective symptoms. To test this hypothesis, we stabilized neurosteroid levels by administering the 5α-reductase inhibitor dutasteride to block conversion of progesterone to its neurosteroid metabolite allopregnanolone in women with premenstrual dysphoric disorder (PMDD) and in asymptomatic control women. Sixteen women with prospectively confirmed PMDD and 16 control women participated in one of two separate randomized, double-blind, placebo-controlled, cross-over trials, each lasting three menstrual cycles. After one menstrual cycle of single-blind placebo, participants were randomized to receive, for the next two menstrual cycles, either double-blind placebo or dutasteride (low-dose 0.5 mg/day in the first eight PMDD and eight control women or high-dose 2.5 mg/day in the second group of women). All women completed the daily rating form (DRF) and were evaluated in clinic during the follicular and luteal phases of each menstrual cycle. Main outcome measures were the DRF symptoms of irritability, sadness, and anxiety. Analyses were performed with SAS PROC MIXED. In the low-dose group, no significant effect of dutasteride on PMDD symptoms was observed compared with placebo (ie, symptom cyclicity maintained), and plasma allopregnanolone levels increased in women with PMDD from follicular to the luteal phases, suggesting the absence of effect of the low-dose dutasteride on 5α-reductase. In contrast, the high-dose group experienced a statistically significant reduction in several core PMDD symptoms (ie, irritability, sadness, anxiety, food cravings, and bloating) on dutasteride compared with placebo. Dutasteride had no effect on mood in controls. Stabilization of allopregnanolone levels from the follicular to the luteal phase of the menstrual cycle by blocking the conversion of progesterone to its 5α-reduced neurosteroid metabolite mitigates symptoms in PMDD. These data provide preliminary support for the pathophysiologic relevance of neurosteroids in this condition.

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.

Neuroactive gonadal drugs for neuroprotection in male and female models of Parkinson's disease

The existence of sex differences in Parkinson's disease (PD) incidence is well documented with greater prevalence and earlier age at onset in men than in women. These reported sex differences could be related to estrogen exposure. In PD animal models, estrogen is well documented to be neuroprotective against dopaminergic neuron loss induced by neurotoxins. Using the 1-methyl 4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) mouse model, we showed that several compounds are neuroprotective on dopaminergic neurons including estrogen, the selective estrogen receptor modulator raloxifene, progesterone, dehydroepiandrosterone, the estrogen receptor alpha (ERα) agonist PPT as well as the G protein-coupled membrane estrogen receptor (GPER1) specific agonist G1. Accumulating evidence suggests that GPER1 could be implicated in the neuroprotective effects of estrogen, raloxifene and G1 in collaboration with ERα. We recently reported that the 5α-reductase inhibitor Dutasteride is also neuroprotective and could bring an alternative to estrogens for therapy in male. Additional studies are needed to optimize therapies with these gonadal drugs into safe personalized treatments according to sex for treatment of PD.

Targeting neurosteroid synthesis as a therapy for schizophrenia-related alterations induced by early psychosocial stress

BACKGROUND

Cogent evidence has shown that schizophrenia vulnerability is enhanced by psychosocial stress in adolescence, yet the underpinnings of this phenomenon remain elusive. One of the animal models that best capture the relationship between juvenile stress and schizophrenia is isolation rearing (IR). This manipulation, which consists in subjecting rats to social isolation from weaning through adulthood, results in neurobehavioral alterations akin to those observed in schizophrenia patients. In particular, IR-subjected rats display a marked reduction of the prepulse inhibition (PPI) of the startle reflex, which are posited to reflect imbalances in dopamine neurotransmission in the nucleus accumbens (NAcc). We recently documented that the key neurosteroidogenic enzyme 5α-reductase (5αR) plays an important role in the dopaminergic regulation of PPI; given that IR leads to a marked down-regulation of this enzyme in the NAcc, the present study was designed to further elucidate the functional role of 5αR in the regulation of PPI of IR-subjected rats.

METHODS

We studied the impact of the prototypical 5αR inhibitor finasteride (FIN) on the PPI deficits and NAcc steroid profile of IR-subjected male rats, in comparison with socially reared (SR) controls.

RESULTS

FIN (25-100 mg/kg, i.p.) dose-dependently countered IR-induced PPI reduction, without affecting gating integrity in SR rats. The NAcc and striatum of IR-subjected rats displayed several changes in neuroactive steroid profile, including a reduction in pregnenolone in both SR and IR-subjected groups, as well as a decrease in allopregnanolone content in the latter group; both effects were significantly opposed by FIN.

CONCLUSIONS

These results show that 5αR inhibition counters the PPI deficits induced by IR, possibly through limbic changes in pregnenolone and/or allopregnanolone concentrations.

Side Effects of 5-Alpha Reductase Inhibitors: A Comprehensive Review

INTRODUCTION

5α-reductase inhibitors (5ARI) include finasteride and dutasteride, and are commonly prescribed in the treatment of benign prostatic hyperplasia and androgenic alopecia. 5ARIs are associated with several known adverse effects (AEs), with varying reported prevalence rates.

AIM

The aim was to review and summarize findings from published literature detailing AEs associated with 5ARI use. A secondary aim was to review potential mechanisms of action, which may account for these observed and reported AEs.

METHODS

A PubMed search was conducted on articles published from 1992 to 2012, which reported AEs with 5ARIs. Priority was given to randomized, placebo-controlled trials. Studies investigating potential mechanisms of action for 5ARIs were included for review.

MAIN OUTCOME MEASURES

AE data reported from available trials were summarized and reviewed.

RESULTS

Reported AEs with 5ARIs include sexual dysfunction, infertility, mood disorders, gynecomastia, high-grade prostate cancer, breast cancer, and cardiovascular morbidity/risk factors, although their true association, prevalence, causality, and clinical significance remain unclear. A pooled summary of all randomized, placebo-controlled trials evaluating 5ARIs (N = 62,827) revealed slightly increased rates over placebo for decreased libido (1.5%), erectile dysfunction (ED) (1.6%), ejaculatory dysfunction (EjD) (3.4%), and gynecomastia (1.3%). The limited data available on the impact of 5ARIs on mood disorders demonstrate statistically significant (although clinically minimal) differences in rates of depression and/or anxiety. Similarly, there are limited reports of reversible, diminished fertility among susceptible individuals. Post-marketing surveillance reports have questioned the actual prevalence of AEs associated with 5ARI use and suggest the possibility of persistent symptoms after drug discontinuation. Well-designed studies evaluating these reports are needed.

CONCLUSIONS

5ARIs are associated with slightly increased rates of decreased libido, ED, EjD, gynecomastia, depression, and/or anxiety. Further studies directed at identifying prevalence rates and persistence of symptoms beyond drug discontinuation are required to assess causality. Trost L, Saitz TR, and Hellstrom WJG. Side effects of 5-alpha reductase inhibitors: A comprehensive review. Sex Med Rev 2013;1:24-41.

Adverse effects of 5α-reductase inhibitors: What do we know, don't know, and need to know?

Steroids are important physiological orchestrators of endocrine as well as peripheral and central nervous system functions. One of the key processes for regulation of these molecules lies in their enzymatic processing by a family of 5α-reductase (5α-Rs) isozymes. By catalyzing a key rate-limiting step in steroidogenesis, this family of enzymes exerts a crucial role not only in the physiological control but also in pathological events. Indeed, both 5α-R inhibition and supplementation of 5α-reduced metabolites are currently used or have been proposed as therapeutic strategies for a wide array of pathological conditions. In particular, the potent 5α-R inhibitors finasteride and dutasteride are used in the treatments of benign prostatic hyperplasia (BPH), as well as in male pattern hair loss (MPHL) known as androgenetic alopecia (AGA). Recent preclinical and clinical findings indicate that 5α-R inhibitors evoke not only beneficial, but also adverse effects. Future studies should investigate the biochemical and physiological mechanisms that underlie the persistence of the adverse sexual side effects to determine why a subset of patients is afflicted with such persistence or irreversible adverse effects. Also a better focus of clinical research is urgently needed to better define those subjects who are likely to be adversely affected by such agents. Furthermore, research on the non-sexual adverse effects such as diabetes, psychosis, depression, and cognitive function are needed to better understand the broad spectrum of the effects these drugs may elicit during their use in treatment of AGA or BPH. In this review, we will summarize the state of art on this topic, overview the key unresolved questions that have emerged on the pharmacological targeting of these enzymes and their products, and highlight the need for further studies to ascertain the severity and duration of the adverse effects of 5α-R inhibitors, as well as their biological underpinnings.

The 5α-reductase inhibitor Dutasteride but not Finasteride protects dopamine neurons in the MPTP mouse model of Parkinson's disease

Finasteride and Dutasteride are 5α-reductase inhibitors used in the clinic to treat endocrine conditions and were recently found to modulate brain dopamine (DA) neurotransmission and motor behavior. We investigated if Finasteride and Dutasteride have a neuroprotective effect in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) male mice as a model of Parkinson's disease (PD). Experimental groups included saline treated controls and mice treated with saline, Finasteride (5 and 12.5 mg/kg) or Dutasteride (5 and 12.5 mg/kg) for 5 days before and 5 days after MPTP administration (4 MPTP injections, 6.5 mg/kg on day 5 inducing a moderate DA depletion) and then they were euthanized. MPTP administration decreased striatal DA contents measured by HPLC while serotonin contents remained unchanged. MPTP mice treated with Dutasteride 5 and 12.5 mg/kg had higher striatal DA and metabolites (DOPAC and HVA) contents with a decrease of metabolites/DA ratios compared to saline-treated MPTP mice. Finasteride had no protective effect on striatal DA contents. Tyrosine hydroxylase (TH) mRNA levels measured by in situ hybridization in the substantia nigra pars compacta were unchanged. Dutasteride at 12.5 mg/kg reduced the effect of MPTP on specific binding to striatal DA transporter (DAT) and vesicular monoamine transporter 2 (VMAT2) measured by autoradiography. MPTP reduced compared to controls plasma testosterone (T) and dihydrotestosterone (DHT) concentrations measured by liquid chromatography-tandem mass spectrometry; Dutasteride and Finasteride increased plasma T levels while DHT levels remained low. In summary, our results showed that a 5α-reductase inhibitor, Dutasteride has neuroprotective activity preventing in male mice the MPTP-induced loss of several dopaminergic markers.

Finasteride improves motor, EEG, and cellular changes in rat brain in thioacetamide-induced hepatic encephalopathy

Neurosteroids are involved in the pathogenesis of hepatic encephalopathy (HE). This study evaluated the effects of finasteride, inhibitor of neurosteroid synthesis, on motor, EEG, and cellular changes in rat brain in thioacetamide-induced HE. Male Wistar rats were divided into the following groups: 1) control; 2) thioacetamide-treated group, TAA (300 mg·kg(-1)·day(-1)); 3) finasteride-treated group, FIN (50 mg·kg(-1)·day(-1)); and 4) group treated with FIN and TAA (FIN + TAA). Daily doses of TAA and FIN were administered in three subsequent days intraperitoneally, and in the FIN + TAA group FIN was administered 2 h before every dose of TAA. Motor and reflex activity was determined at 0, 2, 4, 6, and 24 h, whereas EEG activity was registered about 24 h after treatment. The expressions of neuronal (NeuN), astrocytic [glial fibrilary acidic protein (GFAP)], microglial (Iba1), and oligodendrocyte (myelin oligodendrocyte glycoprotein) marker were determined 24 h after treatment. While TAA decreased all tests, FIN pretreatment (FIN + TAA) significantly improved equilibrium, placement test, auditory startle, head shake reflex, motor activity, and exploratory behavior vs. the TAA group. Vital reflexes (withdrawal, grasping, righting and corneal reflex) together with mean EEG voltage were significantly higher (P < 0.01) in the FIN + TAA vs. the TAA group. Hippocampal NeuN expression was significantly lower in TAA vs. control (P < 0.05). Cortical Iba1 expression was significantly higher in experimental groups vs. control (P < 0.05), whereas hippocampal GFAP expression was increased in TAA and decreased in the FIN + TAA group vs. control (P < 0.05). Finasteride improves motor and EEG changes in TAA-induced HE and completely prevents the development of hepatic coma.

Animal models of tic disorders: a translational perspective

Tics are repetitive, sudden movements and/or vocalizations, typically enacted as maladaptive responses to intrusive premonitory urges. The most severe tic disorder, Tourette syndrome (TS), is a childhood-onset condition featuring multiple motor and at least one phonic tic for a duration longer than 1 year. The pharmacological treatment of TS is mainly based on antipsychotic agents; while these drugs are often effective in reducing tic severity and frequency, their therapeutic compliance is limited by serious motor and cognitive side effects. The identification of novel therapeutic targets and development of better treatments for tic disorders is conditional on the development of animal models with high translational validity. In addition, these experimental tools can prove extremely useful to test hypotheses on the etiology and neurobiological bases of TS and related conditions. In recent years, the translational value of these animal models has been enhanced, thanks to a significant re-organization of our conceptual framework of neuropsychiatric disorders, with a greater focus on endophenotypes and quantitative indices, rather than qualitative descriptors. Given the complex and multifactorial nature of TS and other tic disorders, the selection of animal models that can appropriately capture specific symptomatic aspects of these conditions can pose significant theoretical and methodological challenges. In this article, we will review the state of the art on the available animal models of tic disorders, based on genetic mutations, environmental interventions as well as pharmacological manipulations. Furthermore, we will outline emerging lines of translational research showing how some of these experimental preparations have led to significant progress in the identification of novel therapeutic targets for tic disorders.

Gene-sex interactions in schizophrenia: focus on dopamine neurotransmission

Schizophrenia is a severe mental disorder, with a highly complex and heterogenous clinical presentation. Our current perspectives posit that the pathogenic mechanisms of this illness lie in complex arrays of gene × environment interactions. Furthermore, several findings indicate that males have a higher susceptibility for schizophrenia, with earlier age of onset and overall poorer clinical prognosis. Based on these premises, several authors have recently begun exploring the possibility that the greater schizophrenia vulnerability in males may reflect specific gene × sex (G×S) interactions. Our knowledge on such G×S interactions in schizophrenia is still rudimentary; nevertheless, the bulk of preclinical evidence suggests that the molecular mechanisms for such interactions are likely contributed by the neurobiological effects of sex steroids on dopamine (DA) neurotransmission. Accordingly, several recent studies suggest a gender-specific association of certain DAergic genes with schizophrenia. These G×S interactions have been particularly documented for catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO), the main enzymes catalyzing DA metabolism. In the present review, we will outline the current evidence on the interactions of DA-related genes and sex-related factors, and discuss the potential molecular substrates that may mediate their cooperative actions in schizophrenia pathogenesis.

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.

The implication of neuroactive steroids in Tourette's syndrome pathogenesis: A role for 5α-reductase?

Tourette's syndrome (TS) is a neurodevelopmental disorder characterised by recurring motor and phonic tics. The pathogenesis of TS is considered to reflect dysregulations in the signalling of dopamine (DA) and other neurotransmitters, which lead to excitation/inhibition imbalances in cortico-striato-thalamocortical circuits. The causes of these deficits may reflect complex gene × environment × sex (G × E × S) interactions; indeed, the disorder is markedly predominant in males, with a male-to-female prevalence ratio of approximately 4 : 1. Converging lines of evidence point to neuroactive steroids as being likely molecular candidates to account for G × E × S interactions in TS. Building on these premises, our group has begun examining the possibility that alterations in the steroid biosynthetic process may be directly implicated in TS pathophysiology; in particular, our research has focused on 5α-reductase (5αR), the enzyme catalysing the key rate-limiting step in the synthesis of pregnane and androstane neurosteroids. In clinical and preclinical studies, we found that 5αR inhibitors exerted marked anti-DAergic and tic-suppressing properties, suggesting a central role for this enzyme in TS pathogenesis. Based on these data, we hypothesise that enhancements in 5αR activity in early developmental stages may lead to an inappropriate activation of the 'backdoor' pathway for androgen synthesis from adrenarche until the end of puberty. We predict that the ensuing imbalances in steroid homeostasis may impair the signalling of DA and other neurotransmitters, ultimately resulting in the facilitation of tics and other behavioural abnormalities in TS.

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.

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.

Testosterone regulation of sex steroid-related mRNAs and dopamine-related mRNAs in adolescent male rat substantia nigra

BACKGROUND

Increased risk of schizophrenia in adolescent males indicates that a link between the development of dopamine-related psychopathology and testosterone-driven brain changes may exist. However, contradictions as to whether testosterone increases or decreases dopamine neurotransmission are found and most studies address this in adult animals. Testosterone-dependent actions in neurons are direct via activation of androgen receptors (AR) or indirect by conversion to 17β-estradiol and activation of estrogen receptors (ER). How midbrain dopamine neurons respond to sex steroids depends on the presence of sex steroid receptor(s) and the level of steroid conversion enzymes (aromatase and 5α-reductase). We investigated whether gonadectomy and sex steroid replacement could influence dopamine levels by changing tyrosine hydroxylase (TH) protein and mRNA and/or dopamine breakdown enzyme mRNA levels [catechol-O-methyl transferase (COMT) and monoamine oxygenase (MAO) A and B] in the adolescent male rat substantia nigra. We hypothesized that adolescent testosterone would regulate sex steroid signaling through regulation of ER and AR mRNAs and through modulation of aromatase and 5α-reductase mRNA levels.

RESULTS

We find ERα and AR in midbrain dopamine neurons in adolescent male rats, indicating that dopamine neurons are poised to respond to circulating sex steroids. We report that androgens (T and DHT) increase TH protein and increase COMT, MAOA and MAOB mRNAs in the adolescent male rat substantia nigra. We report that all three sex steroids increase AR mRNA. Differential action on ER pathways, with ERα mRNA down-regulation and ERβ mRNA up-regulation by testosterone was found. 5α reductase-1 mRNA was increased by AR activation, and aromatase mRNA was decreased by gonadectomy.

CONCLUSIONS

We conclude that increased testosterone at adolescence can shift the balance of sex steroid signaling to favor androgenic responses through promoting conversion of T to DHT and increasing AR mRNA. Further, testosterone may increase local dopamine synthesis and metabolism, thereby changing dopamine regulation within the substantia nigra. We show that testosterone action through both AR and ERs modulates synthesis of sex steroid receptor by altering AR and ER mRNA levels in normal adolescent male substantia nigra. Increased sex steroids in the brain at adolescence may alter substantia nigra dopamine pathways, increasing vulnerability for the development of psychopathology.

The role of estrogen and testosterone in female rats in behavioral models of relevance to schizophrenia

RATIONALE

The sex steroid hormone, estrogen, may play a protective role in schizophrenia. We previously found that estrogen treatment inhibited serotonin-1A (5-HT(1A)) and dopamine D(2) receptor-mediated disruptions of prepulse inhibition (PPI), a measure of sensorimotor gating which is deficient in schizophrenia.

OBJECTIVES

The present study aimed to further explore the role of sex steroid hormones in schizophrenia. Part 1 of this study examined whether estrogen could inhibit PPI disruption induced by the N-methyl-D: -aspartate (NMDA) receptor antagonist, MK-801. Part 2 investigated whether the functionally protective effect of estrogen occurs in another animal model of schizophrenia, amphetamine-induced locomotor hyperactivity. Part 3 compared our previous PPI findings in estrogen-treated rats, to treatment with testosterone.

METHODS

Female Sprague-Dawley rats were ovariectomized (OVX) or sham-operated. Some OVX rats received silastic implants filled with either a low (E20) or high dose (E100) of estradiol, or a low (T5) or high dose (T20) of testosterone, for at least 2 weeks before behavioral testing.

RESULTS

The disruption of PPI caused by MK-801 (0.1 mg/kg) was significantly reduced by treatment with estradiol (E20 and E100). However, estradiol treatment did not alter amphetamine-induced (0.25 and 0.5 mg/kg) locomotor hyperactivity, in terms of distance traveled, ambulation, or vertical counts. In contrast to estrogen, testosterone treatment did not affect disruption of PPI after administration of 8-OH-DPAT (0.5 mg/kg) or apomorphine (0.3 mg/kg). Testosterone treatment significantly enhanced the MK-801-induced (0.1 mg/kg) PPI disruption.

CONCLUSIONS

Estrogen is functionally protective against 5-HT(1A)-, dopamine D(2)-, and NMDA receptor-induced PPI disruptions, while testosterone treatment enhances NMDA receptor-mediated PPI disruptions.