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

Expanding the therapeutic potential of neuro(active)steroids: a promising strategy for hyperdopaminergic behavioral phenotypes

Imbalances in dopamine activity significantly contribute to the pathophysiology of several neuropsychiatric disorders, including addiction, ADHD, schizophrenia, impulse control disorders, and Parkinson's Disease. Neuro(active)steroids, comprising endogenous steroids that finely modulate neuronal activity, are considered crucial regulators of brain function and behavior, with implications in various physiological processes and pathological conditions. Specifically, subclasses of Neuro(active)steroids belonging to the 5α reductase pathway are prominently involved in brain disorders characterized by dopaminergic signaling imbalances. This review highlights the neuromodulatory effects of Neuro(active)steroids on the dopamine system and related aberrant behavioral phenotypes. We critically appraise the role of pregnenolone, progesterone, and allopregnanolone on dopamine signaling. Additionally, we discuss the impact of pharmacological interventions targeting 5α reductase activity in neuropsychiatric conditions characterized by excessive activation of the dopaminergic system, ranging from psychotic (endo)phenotypes and motor complications to decision-making problems and addiction.

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.

Prefrontal allopregnanolone mediates the adverse effects of acute stress in a mouse model of tic pathophysiology

Ample evidence suggests that acute stress can worsen symptom severity in Tourette syndrome (TS); however, the neurobiological underpinnings of this phenomenon remain poorly understood. We previously showed that acute stress exacerbates tic-like and other TS-associated responses via the neurosteroid allopregnanolone (AP) in an animal model of repetitive behavioral pathology. To verify the relevance of this mechanism to tic pathophysiology, here we tested the effects of AP in a mouse model recapitulating the partial depletion of dorsolateral cholinergic interneurons (CINs) seen in post-mortem studies of TS. Mice underwent targeted depletion of striatal CINs during adolescence and were tested in young adulthood. Compared with controls, partially CIN-depleted male mice exhibited several TS-relevant abnormalities, including deficient prepulse inhibition (PPI) and increased grooming stereotypies after a 30-min session of spatial confinement - a mild acute stressor that increases AP levels in the prefrontal cortex (PFC). These effects were not seen in females. Systemic and intra-PFC AP administration dose-dependently worsened grooming stereotypies and PPI deficits in partially CIN-depleted males. Conversely, both AP synthesis inhibition and pharmacological antagonism reduced the effects of stress. These results further suggest that AP in the PFC mediates the adverse effects of stress on the severity of tics and other TS-related manifestations. Future studies will be necessary to confirm these mechanisms in patients and define the circuitry responsible for the effects of AP on tics.

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.

Positive GABAA receptor modulating steroids and their antagonists: Implications for clinical treatments

GABA is the main inhibitory neurotransmitter in the brain and GABAergic transmission has been shown to be of importance for regulation of mood, memory and food intake. The progesterone metabolite allopregnanolone (Allo) is a positive GABA_A receptor modulating steroid with potent effects. In humans, disorders such as premenstrual dysphoric disorder (PMDD), hepatic encephalopathy and polycystic ovarian syndrome are associated with elevated Allo levels and increased negative mood, disturbed memory and increased food intake in some individuals. This is surprising because Allo shares many properties with benzodiazepines and is mainly considered to be anxiolytic and anti-depressant. However, it is well established that, in certain individuals, GABA_A receptor activating compounds could have paradoxical effects and thus be anxiogenic in low physiological plasma concentrations but anxiolytic at high levels. We have demonstrated that isoallopregnanolone (Isoallo), the 3β-OH sibling of Allo, functions as a GABA_A receptor modulating steroid antagonist (GAMSA) but without any effects of its own on GABA_A receptors. The antagonistic effect is noted in most GABA_A subtypes investigated in vitro to date. In vivo, Isoallo can inhibit Allo-induced anaesthesia in rats, as well as sedation or saccadic eye velocity in humans. Isoallo treatment has been studied in women with PMDD. In a first phase II study, Isoallo (Sepranolone; Asarina Pharma) injections significantly ameliorated negative mood in women with PMDD compared with placebo. Several GAMSAs for oral administration have also been developed. The GAMSA, UC1011, can inhibit Allo induced memory disturbances in rats and an oral GAMSA, GR3027, has been shown to restore learning and motor coordination in rats with hepatic encephalopathy. In humans, vigilance, cognition and pathological electroencephalogram were improved in patients with hepatic encephalopathy on treatment with GR3027. In conclusion GAMSAs are a new possible treatment for disorders and symptoms caused by hyperactivity in the GABA_A system.

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.

2D:4D ratios as an indicator of intrauterine androgen exposure in children who stutter

AIM

We aimed to explore whether there is a relationship between stuttering and digit ratio (2D:4D), which is thought to be a marker of prenatal testosterone exposure.

METHODS

We evaluated a total of 90 children who stutter (CWS; n = 40 mild-to-moderate and n = 50 severe stutters) and 40 healthy peers (CWNS) as controls. We used the Clinical Global Impression-Severity (CGIS) scale to measure the severity of stuttering. We measured the lengths of index finger (2D) and ring finger (4D) of both hands directly and divided to calculate 2D:4D ratio. The difference between the right and the left hand 2D:4D ratio (D_R-L) was also calculated.

RESULT

Significant difference was found in right 2D:4D and the mean D_R-L between the CWS and CWNS groups. Right 2D:4D was significantly lower in stuttering boys than in control boys, and in stuttering girls than control girls. Also, D_R-L was significantly lower in stuttering boys than control boys. In ANOVA, there were significant differences between the mild-to-moderate, severe stuttering and control groups in terms of right 2D:4D and D_R-L. Right hand 2D:4D and D_R-L decreased from controls to severe stutterers.

CONCLUSION

Our results suggest that lower right 2D:4D and D_R-L were related to the presence and severity of stuttering in children, i.e. CWS had lower 2D:4D and D_R-L than CWNS. Further large-scale prospective studies are needed to clarify the reliability of 2D:4D ratio as an indicator of fetal sex hormone exposure level and its relation with the presence and severity of stuttering in children.

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'.

The 5α-Reductase Inhibitor Finasteride Exerts Neuroprotection Against Ischemic Brain Injury in Aged Male Rats

Progesterone (P4) exerts potent neuroprotection both in young and aged animal models of stroke. The neuroprotection is likely to be mediated by allopregnanolone (ALLO) metabolized from P4 by 5α-reductase, since the neuroprotection is attenuated by the 5α-reductase inhibitor finasteride, which was done only with young animals though. Thus, we do not know the contribution of ALLO to the P4-induced neuroprotection in aged animals. We examined effects of finasteride on the P4-induced neuroprotection in aged (16-18-month-old) male rats subjected to transient focal cerebral ischemia. Transient focal cerebral ischemia was induced by left middle cerebral artery occlusion (MCAO) and occlusion of the bilateral common carotid arteries. MCAO rats were given an 8 mg/kg P4 6 h after MCAO followed by the same treatment once a day for successive 3 days. Finasteride, a 5α-reductase inhibitor, at 20 mg/kg was intraperitoneally injected 30 min prior to the P4-injections. P4 markedly reduced neuronal damage 72 h after MCAO, and the P4-induced neuroprotection was apparently suppressed by finasteride in the aged animals. However, post-ischemic administration of finasteride alone (20 mg/kg) significantly prevented neuronal damage and the impairment of Rotarod performance after MCAO in aged male rats, but not in young ones. The androgen receptor antagonist flutamide markedly suppressed the neuroprotection of finasteride in the cerebral cortex, but not in the striatum, suggesting the androgen receptor-dependent mechanism of the finasteride-induced neuroprotection in the cerebral cortex. Our findings suggested, for the first time, the potential of finasteride as a therapeutic agent in post-ischemic treatment of strokes in aged population.

Tourette syndrome: a disorder of the social decision-making network

Tourette syndrome is a common neurodevelopmental disorder defined by characteristic involuntary movements, tics, with both motor and phonic components. Tourette syndrome is usually conceptualized as a basal ganglia disorder, with an emphasis on striatal dysfunction. While considerable evidence is consistent with these concepts, imaging data suggest diffuse functional and structural abnormalities in Tourette syndrome brain. Tourette syndrome exhibits features that are difficult to explain solely based on basal ganglia circuit dysfunctions. These features include the natural history of tic expression, with typical onset of tics around ages 5 to 7 years and exacerbation during the peri-pubertal years, marked sex disparity with higher male prevalence, and the characteristic distribution of tics. The latter are usually repetitive, somewhat stereotyped involuntary eye, facial and head movements, and phonations. A major functional role of eye, face, and head movements is social signalling. Prior work in social neuroscience identified a phylogenetically conserved network of sexually dimorphic subcortical nuclei, the Social Behaviour Network, mediating many social behaviours. Social behaviour network function is modulated developmentally by gonadal steroids and social behaviour network outputs are stereotyped sex and species specific behaviours. In 2011 O'Connell and Hofmann proposed that the social behaviour network interdigitates with the basal ganglia to form a greater network, the social decision-making network. The social decision-making network may have two functionally complementary limbs: the basal ganglia component responsible for evaluation of socially relevant stimuli and actions with the social behaviour network component responsible for the performance of social acts. Social decision-making network dysfunction can explain major features of the neurobiology of Tourette syndrome. Tourette syndrome may be a disorder of social communication resulting from developmental abnormalities at several levels of the social decision-making network. The social decision-making network dysfunction hypothesis suggests new avenues for research in Tourette syndrome and new potential therapeutic targets.

Sex steroid hormones and sex hormone binding globulin levels, CYP17 MSP AI (-34T:C) and CYP19 codon 39 (Trp:Arg) variants in children with developmental stuttering

Developmental stuttering is known to be a sexually dimorphic and male-biased speech motor control disorder. In the present case-control study, we investigated the relationship between developmental stuttering and steroid hormones. Serum levels of testosterone, dihydrotestosterone (DHT), dehydroepiandrosterone (DHEA), oestradiol, progesterone, cortisol, and sex hormone binding globulin (SHBG), as well as the 2nd/4th digit ratio (2D:4D), an indicator of prenatal testosterone level, were compared between children who stutter (CWS) and children who do not stutter (CWNS). Moreover, two SNPs (CYP17 -34 T:C (MSP AI) and CYP19 T:C (Trp:Arg)) of cytochrome P450, which is involved in steroid metabolism pathways, were analysed between the groups. Our results showed significantly higher levels of testosterone, DHT, and oestradiol in CWS in comparison with CWNS. The severity of stuttering was positively correlated with the serum levels of testosterone, DHEA, and cortisol, whereas no association was seen between the stuttering and digit ratio, progesterone, or SHBG. The CYP17CC genotype was significantly associated with the disorder.

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.

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.

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.

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.

Sex differences in Parkinson's disease and other movement disorders

Movement disorders including Parkinson's disease (PD), Huntington's disease (HD), chorea, tics, and Tourette's syndrome (TS) display sex differences in disease susceptibility, disease pathogenesis, and clinical presentation. PD is more common in males than in females. Epidemiologic studies suggest that exposure to endogenous and exogenous estrogen contributes to these sex differences. There is extensive evidence that estrogen prevents dopaminergic neuron depletion induced by neurotoxins in PD animal models and therefore is neuroprotective. Estrogen may also decrease the efficacy of other neuroprotective substances such as caffeine in females but not males. Sex chromosomes can exert effects independent of sex steroid hormones on the development and maintenance of the dopamine system. As a result of hormone, chromosome and other unknown effects, there are sexual dimorphisms in the basal ganglia, and at the molecular levels in dopaminergic neurons that may lead to distinct mechanisms of pathogenesis in males and females. In this review, we summarize the evidence that estrogen and selective estrogen receptor modulators are neuroprotective in PD and discuss potential mechanisms of action. We also briefly review how sex differences in basal ganglia function and dopaminergic pathways may impact HD, chorea, and tics/Tourette's syndrome. Further understanding of these sex differences may lead to novel therapeutic strategies for prevention and treatment of these diseases.

Bisphenol A modifies the regulation exerted by testosterone on 5 α -reductase isozymes in ventral prostate of adult rats

The development, growth, and function of the prostate gland depend on androgen stimulation. The primary androgen in prostate is 5α-dihydrotestosterone (DHT) which is synthesized from circulating testosterone (T) through the action of 5α-reductase (5α-R). Although 5α-R occurs as five isozymes, only 5α-R1 and 5α-R2 are physiologically involved in steroidogenesis. The endocrine disruptor bisphenol A (BPA) alters sexual organs, including the prostate. Our previous findings indicated that BPA decreased the expression of 5α-R1 and 5α-R2 in rat prostate but also circulating T. Thus, it is unclear whether BPA exerts this effect on 5α-R isozymes by reducing circulating T or by any other mechanism. In this study, we examine the effects of short-term exposure to BPA at doses below 25 μg/Kg/d and above 300 μg/Kg/d of the TDI on mRNA levels of 5α-R1 and 5α-R2 in prostate of adult castrated rats supplemented with T to achieve constant circulating T levels. mRNA levels were measured by absolute quantitative RT-PCR, T levels by RIA, and DHT levels by ELISA. Our results indicated that in castrated rats treated with T BPA at the two doses studied significantly decreased the mRNA levels of both 5α-R isozymes in a dose-dependent manner without modifications in circulating T.