Dose-response effects of estrogen and tamoxifen upon methamphetamine-induced behavioral responses and neurotoxicity of the nigrostriatal dopaminergic system in female mice

Delayed short-term tamoxifen treatment does not promote remyelination or neuron sparing after spinal cord injury

The tamoxifen-dependent Cre/lox system in transgenic mice has become an important research tool across all scientific disciplines for manipulating gene expression in specific cell types. In these mouse models, Cre-recombination is not induced until tamoxifen is administered, which allows researchers to have temporal control of genetic modifications. Interestingly, tamoxifen has been identified as a potential therapy for spinal cord injury (SCI) and traumatic brain injury patients due to its neuroprotective properties. It is also reparative in that it stimulates oligodendrocyte differentiation and remyelination after toxin-induced demyelination. However, it is unknown whether tamoxifen is neuroprotective and neuroreparative when administration is delayed after SCI. To properly interpret data from transgenic mice in which tamoxifen treatment is delayed after SCI, it is necessary to identify the effects of tamoxifen alone on anatomical and functional recovery. In this study, female and male mice received a moderate mid-thoracic spinal cord contusion. Mice were then gavaged with corn oil or a high dose of tamoxifen from 19-22 days post-injury, and sacrificed 42 days post-injury. All mice underwent behavioral testing for the duration of the study, which revealed that tamoxifen treatment did not impact hindlimb motor recovery. Similarly, histological analyses revealed that tamoxifen had no effect on white matter sparing, total axon number, axon sprouting, glial reactivity, cell proliferation, oligodendrocyte number, or myelination, but tamoxifen did decrease the number of neurons in the dorsal and ventral horn. Semi-thin sections confirmed that axon demyelination and remyelination were unaffected by tamoxifen. Sex-specific responses to tamoxifen were also assessed, and there were no significant differences between female and male mice. These data suggest that delayed tamoxifen administration after SCI does not change functional recovery or improve tissue sparing in female or male mice.

Astrocytes Mediate Protective Actions of Estrogenic Compounds after Traumatic Brain Injury

Traumatic brain injury (TBI) is a serious public health problem. It may result in severe neurological disabilities and in a variety of cellular metabolic alterations for which available therapeutic strategies are limited. In the last decade, the use of estrogenic compounds, which activate protective mechanisms in astrocytes, has been explored as a potential experimental therapeutic approach. Previous works have suggested estradiol (E2) as a neuroprotective hormone that acts in the brain by binding to estrogen receptors (ERs). Several steroidal and nonsteroidal estrogenic compounds can imitate the effects of estradiol on ERs. These include hormonal estrogens, phytoestrogens and synthetic estrogens, such as selective ER modulators or tibolone. Current evidence of the role of astrocytes in mediating protective actions of estrogenic compounds after TBI is reviewed in this paper. We conclude that the use of estrogenic compounds to modulate astrocytic properties is a promising therapeutic approach for the treatment of TBI.

Tamoxifen and the Risk of Parkinson's Disease in Female Patients with Breast Cancer in Asian People: A Nationwide Population-Based Study

Purpose

Whether tamoxifen affects the risk of neurodegenerative disease is controversial. This nationwide population-based study investigated the risk of Parkinson's disease (PD) associated with tamoxifen treatment in female patients with breast cancer using Taiwan's National Health Insurance Research Database.

Methods

A total of 5,185 and 5,592 female patients with breast cancer who did and did not, respectively, receive tamoxifen treatment between 2000 and 2009 were included in the study. Patients who subsequently developed PD were identified. A Cox proportional hazards model was used to compare the risk of PD between the aforementioned groups.

Results

Tamoxifen did not significantly increase the crude rate of developing PD in female patients with breast cancer (tamoxifen group, 16/5,169; non-tamoxifen group, 11/5,581; p=0.246). Tamoxifen did not significantly increase the adjusted hazard ratio (aHR) for subsequently developing PD (aHR, 1.310; 95% confidence interval [CI], 0.605-2.837; p=0.494). However, tamoxifen significantly increased the risk of PD among patients followed up for more than 6 years (aHR, 2.435; 95% CI, 1.008-5.882; p=0.048).

Conclusion

Tamoxifen treatment may increase the risk of PD in Taiwanese female patients with breast cancer more than 6 years after the initiation of treatment.

A rapid enhancement of locomotor sensitization to amphetamine by estradiol in female rats

Estradiol moderates the effects of drugs of abuse in both humans and rodents. Estradiol's enhancement of behavioral effects resulting from high (>2.5mg/kg) doses of amphetamine is established in rats; there is less evidence for the role of estradiol in locomotor effects elicited by lower doses, which are less aversive, increase incentive motivation, involve different neural mechanisms than higher doses, and often more readily reveal group differences than do higher doses. Further, the extent to which estradiol is required for the induction versus the expression of sensitization is unknown. To establish a protocol, we replicated the effects of estradiol on locomotor sensitization to amphetamine reported in a previous study that involved a high locomotor-activating dose (1.5mg/kg) of amphetamine, but with a lower dose. Ovariectomized female rats received 5μg of estradiol benzoate (EB) or OIL 30min before each of 5 treatments of 1.0mg/kg amphetamine or saline; all received a 0.5mg/kg challenge dose three days later. Compared with results for OIL, EB enhanced the locomotor-activating effects of repeated 1.0mg/kg amphetamine across treatment days. In contrast, on challenge day, there was no difference between EB-saline and EB-amphetamine to the lower dose (i.e., no sensitization). Experiments 2 and 3 involved a shorter induction (2days) and a lengthier withdrawal (9days) before the challenge test for the expression of sensitization to better differentiate the induction phase from the expression phase. In Expt2, EB-, and not OIL-, treated rats showed sensitization to 0.5mg/kg amphetamine; neither group showed sensitization to 1.5mg/kg amphetamine (ceiling effect?). In Expt3, rats were treated with EB either in both the induction and expression phases, in one of the phases only, or in neither phase. There was an effect of hormone treatment on challenge day and not on induction day; rats given EB on Challenge day showed sensitization to 0.5mg/kg amphetamine; OIL rats did not. The results suggest rapid effects of estradiol on amphetamine sensitization consistent with rapid effects of estradiol reported for other behaviours.

Long-term effects of methamphetamine exposure in adolescent mice on the future ovarian reserve in adulthood

Currently, there is an increasing prevalence of adolescent exposure to methamphetamine (MA). However, there is a paucity of information concerning the long-term impact of early exposure to MA upon female fertility and ovarian reserve. The aim of this study was to investigate the effect of long-term MA exposure in adolescents on their ovarian reserve in adulthood. Adolescent mice received intraperitoneal injections of MA (5mg/kg, three times per week) or saline from the 21st postnatal day for an 8 week period. Morphological, histological, biochemical, hormonal and ethological parameters were evaluated. An impaired ovarian reserve and vitality was found in the group treated with MA, manifesting in morphological-apparent mitochondrial damage, an activated apoptosis pathway in the ovarian tissue, a downward expression of ovarian anti-Mullerian hormone (AMH), a decreased number of primordial and growing follicles, an increased number of atretic follicles, and a depressed secretion of AMH, estradiol and progesterone from granulosa cells. However, no significant difference was noticed regarding the estrous cycle, the mating ability and the fertility outcome in the reproductive age of the mice after a period of non-medication. The present results confirmed that a long term exposure to methamphetamine in adolescent mice does have an adverse impact on their ovarian reserve, which indicates that such an early abuse of MA might influence the fertility lifespan of the female mouse.

Rescue from Sexually Dimorphic Neuronal Cell Death by Estradiol and PI3 Kinase Activity

Responses of primary hippocampal and cortical neurons derived from male and female rats to cellular stressors were studied. It is demonstrated that 17β-estradiol (E2), a potent neuroprotectant, protected the female neurons but had no effects on the male neurons from CoCl2- and glutamate-induced toxicity. Agonists of the estrogen receptor (ER) subtypes ERα and ERβ, DPN and PPT, respectively, had similar effects to E2. By contrast, effects of E2 were abolished by the ER antagonist ICI-182780, further corroborating the neuroprotective role of ERs. In male neurons, CoCl2 predominately activated the apoptosis-inducing factor (AIF)-dependent pathway and AIF translocation from the cytosol to the nucleus. In comparison, CoCl2 activated the caspase pathway and cytochrome c release in female neurons. The inhibitors of these pathways, namely DiQ for AIF and zVAD for caspase, specifically rescued CoCl2-induced cell death in male and female neurons, respectively. When zVAD and ICI-182780, and E2 were applied in combination, it was demonstrated E2 acted on the caspase pathway leading to female-specific neuroprotection. Furthermore, the PI3 kinase (PI3K) inhibitor blocked the rescue effects of DiQ and zVAD on the male and female neurons, respectively, suggesting that PI3K is a common upstream regulator for both pathways. The present study suggested that both sex-specific and nonspecific mechanisms played a role in neuronal responses to stressors and protective reagents.

Long-term use of methamphetamine disrupts the menstrual cycles and hypothalamic-pituitary-ovarian axis

OBJECTIVES

Long-term use of methamphetamine (MA) induces the neuron damage and leads to multiple neuropsychiatric disorders. However, the effect of MA on the female reproductive functions has not yet been evaluated. The objective of this study was to determine the prevalence of abnormal menstrual cycling in female MA users.

METHODS

Female MA users (N = 113) were recruited from the Zhangjiang Isolated Compulsory Detoxification Center. Gynecologic history and drug use history were recorded, and serum levels of follicle-stimulating hormone, luteinizing hormone, prolactin, estrogen, progesterone, and testosterone were measured.

RESULTS

Long-term use of MA significantly altered the menstrual cycle, and 33.6% women suffered from abnormal uterine bleeding while using MA. Deregulation of sex hormones was observed in 73.3% of participants during abstinence. The most common patterns were simple anovular menstruation, which was caused mainly by a hypothalamic deregulation and pituitary suppression with or without ovarian suppression. Normal hormone levels were observed more frequently in participants abstinent for more than 10 months (39.5%) than in participants who were abstinent for less than 10 months (18.6%). However, no relationship was found between hormone deregulation and age or history of MA use.

CONCLUSIONS

The present data demonstrate that long-term use of MA results in the disruption of menstrual cycles and dysfunction of hypothalamic-pituitary-gonadal axis in women.

Estrogen receptor agonists for attenuation of neuroinflammation and neurodegeneration

Recent results from laboratory investigations and clinical trials indicate important roles for estrogen receptor (ER) agonists in protecting the central nervous system (CNS) from noxious consequences of neuroinflammation and neurodegeneration. Neurodegenerative processes in several CNS disorders including spinal cord injury (SCI), multiple sclerosis (MS), Parkinson's disease (PD), and Alzheimer's disease (AD) are associated with activation of microglia and astrocytes, which drive the resident neuroinflammatory response. During neurodegenerative processes, activated microglia and astrocytes cause deleterious effects on surrounding neurons. The inhibitory activity of ER agonists on microglia activation might be a beneficial therapeutic option for delaying the onset or progression of neurodegenerative injuries and diseases. Recent studies suggest that ER agonists can provide neuroprotection by modulation of cell survival mechanisms, synaptic reorganization, regenerative responses to axonal injury, and neurogenesis process. The anti-inflammatory and neuroprotective actions of ER agonists are mediated mainly via two ERs known as ERα and ERβ. Although some studies have suggested that ER agonists may be deleterious to some neuronal populations, the potential clinical benefits of ER agonists for augmenting cognitive function may triumph over the associated side effects. Also, understanding the modulatory activities of ER agonists on inflammatory pathways will possibly lead to the development of selective anti-inflammatory molecules with neuroprotective roles in different CNS disorders such as SCI, MS, PD, and AD in humans. Future studies should be concentrated on finding the most plausible molecular pathways for enhancing protective functions of ER agonists in treating neuroinflammatory and neurodegenerative injuries and diseases in the CNS.

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.

Markers associated with testosterone enhancement of methamphetamine-induced striatal dopaminergic neurotoxicity

Intact male CD-1 mice received an injection of testosterone propionate (TP--5 ug), progesterone (P--5 mg), the oil vehicle or remained untreated (control). At 24 hours after hormonal treatments the mice received an injection of methamphetamine (MA--40 mg/kg) and rectal temperatures were measured. At 5 days post-MA, assays were performed to assess effects of these treatments. Maximal increases in body temperatures, that were significantly greater than oil-treated controls, were obtained in TP-treated mice. At 5 days post-MA, maximal weight reductions were obtained with TP-treated mice, while P-treated mice showed no significant decrease between the pre- versus post-MA determinations. Striatal dopamine concentrations showed maximal reductions and heat-shock protein-70 maximal increases in the TP group, with both differing significantly as compared with all other groups. Protein levels of dopamine transporters were significantly decreased in P-treated mice, while vesicular monoamine transporter-2 was significantly decreased in TP-treated mice. Taken together, these results suggest that testosterone exacerbates the deleterious effects of MA within male mice as indicated by a number of markers related to neurotoxicity. The changes in markers as associated with this enhanced neurotoxicity suggest that TP may increase thermal/energy responses and/or oxidative stress to produce this effect.

Selective estrogen receptor modulators regulate dendritic spine plasticity in the hippocampus of male rats

Some selective estrogen receptor modulators, such as raloxifene and tamoxifen, are neuroprotective and reduce brain inflammation in several experimental models of neurodegeneration. In addition, raloxifene and tamoxifen counteract cognitive deficits caused by gonadal hormone deprivation in male rats. In this study, we have explored whether raloxifene and tamoxifen may regulate the number and geometry of dendritic spines in CA1 pyramidal neurons of the rat hippocampus. Young adult male rats were injected with raloxifene (1 mg/kg), tamoxifen (1 mg/kg), or vehicle and killed 24 h after the injection. Animals treated with raloxifene or tamoxifen showed an increased numerical density of dendritic spines in CA1 pyramidal neurons compared to animals treated with vehicle. Raloxifene and tamoxifen had also specific effects in the morphology of spines. These findings suggest that raloxifene and tamoxifen may influence the processing of information by hippocampal pyramidal neurons by affecting the number and shape of dendritic spines.

Antidepressive and anxiolytic activity of selective estrogen receptor modulators in ovariectomized mice submitted to chronic unpredictable stress

Estradiol has antidepressive and anxiolytic actions. However, its therapeutic use is limited by its peripheral effects. Selective estrogen receptor modulators may represent an alternative to estradiol for the treatment of depressive symptoms. Here we report that tamoxifen and raloxifene decrease immobility time in the forced swim test and increases the time spent in open arms in the elevated plus maze in ovariectomized mice submitted to chronic unpredictable stress.

Parity decreases methamphetamine-induced striatal dopaminergic perturbation

The role of parity upon methamphetamine-induced neurotoxicity of the striatal dopaminergic system was assessed. Female CD-1 mice either remained nulliparous or underwent one or three complete pregnancies and were designated as the 0, 1 or 3 pregnancy groups. The mice were then treated with a neurotoxic regimen of methamphetamine (MA--40 mg/kg) or its saline vehicle (control) and striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) levels were measured at 7-days post-MA. Basal levels of striatal DA, DOPAC and the DOPAC/DA ratio were similar among the saline (control) 0, 1 and 3 pregnancy groups. In response to MA, striatal DA and DOPAC were significantly decreased in the 0 and 1 pregnancy as compared with the control group. Mice with 3 pregnancies showed DA and DOPAC levels that did not differ from controls and were significantly greater than the 0 pregnancy group. The DOPAC/DA ratios of the 0 pregnancy group were significantly greater than all other groups (control, 1 and 3 pregnancy) which failed to differ among each other. These results demonstrate that parity decreases MA-induced striatal dopaminergic neurotoxicity, and the degree of this neuroprotection is related to the number of pregnancies experienced.

Male/Female differences in neuroprotection and neuromodulation of brain dopamine

The existence of a sex difference in Parkinson's disease (PD) is observed as related to several variables, including susceptibility of the disease, age at onset, and symptoms. These differences between men and women represent a significant characteristic of PD, which suggest that estrogens may exert beneficial effects against the development and the progression of the disease. This paper reviews the neuroprotective and neuromodulator effects of 17β-estradiol and progesterone as compared to androgens in the nigrostriatal dopaminergic (NSDA) system of both female and male rodents. The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mice model of PD and methamphetamine toxicity faithfully reproduce the sex differences of PD in that endogenous estrogen levels appear to influence the vulnerability to toxins targeting the NSDA system. Exogenous 17β-estradiol and/or progesterone treatments show neuroprotective properties against NSDA toxins while androgens fail to induce any beneficial effect. Sex steroid treatments show male and female differences in their neuroprotective action against methamphetamine toxicity. NSDA structure and function, as well as the distribution of estrogen receptors, show sex differences and may influence the susceptibility to the toxins and the response to sex steroids. Genomic and non-genomic actions of 17β-estradiol converge to promote survival factors and the presence of both estrogen receptors α and β are critical to 17β-estradiol neuroprotective action against MPTP toxicity.

Agonistic behavior in males and females: effects of an estrogen receptor beta agonist in gonadectomized and gonadally intact mice

Affiliative and agonistic social interactions are mediated by gonadal hormones. Research with estrogen receptor alpha (ERalpha) or beta (ERbeta) knockout (KO) mice show that long-term inactivation of ERalpha decreases, while inactivation of ERbeta increases, male aggression. Opposite effects were found in female alphaERKO and betaERKO mice. The role of acute activation of ERalpha or ERbeta in the agonistic responses of adult non-KO mice is unknown. We report here the effects of the ERbeta selective agonist WAY-200070 on agonistic and social behavior in gonadally intact and gonadectomized (gonadex) male and female CD-1 mice towards a gonadex, same-sex intruder. All 15min resident-intruder tests were videotaped for comprehensive behavioral analysis. Separate analyses assessed: (1) effects of WAY-200070 on each sex and gonadal condition; (2) differences between sexes, and between gonadally intact and gonadex mice, in untreated animals. Results show that in gonadally intact male and female mice, WAY-200070 increased agonistic behaviors such as pushing down the intruder and aggressive grooming, while leaving attacks unaffected. In untreated mice, males attacked more than females, and gonadex animals showed less agonistic behavior than same-sex, gonadally intact mice. Overall, our detailed behavioral analysis suggested that in gonadally intact male and female mice, ERbeta mediates patterns of agonistic behavior that are not directly involved in attacks. This suggests that specific aspects of aggressive behavior are acutely mediated by ERbeta in adult mice. Our results also showed that, in resident-intruder tests, female mice spend as much time in intrasexual agonistic interactions as males, but use agonistic behaviors that involve extremely low levels of direct attacks. This non-attack aggression in females is increased by acute activation of ERbeta. Thus, acute activation of ERbeta similarly mediates agonistic behavior in adult male and female CD-1 mice.

Neuroprotective actions of selective estrogen receptor modulators

Decreasing levels of sex hormones with aging may have a negative impact on brain function, since this decrease is associated with the progression of neurodegenerative disorders, increased depressive symptoms and other psychological disturbances. Extensive evidence from animal studies indicates that sex steroids, in particular estradiol, are neuroprotective. However, the potential benefits of estradiol therapy for the brain are counterbalanced by negative, life-threatening risks in the periphery. A potential therapeutic alternative to promote neuroprotection is the use of selective estrogen receptor modulators (SERMs), which may be designed to act with tissue selectivity as estrogen receptor agonists in the brain and not in other organs. Currently available SERMs act not only with tissue selectivity, but also with cellular selectivity within the brain and differentially modulate the activation of microglia, astroglia and neurons. Finally, SERMs may promote the interaction of estrogen receptors with the neuroprotective signaling of growth factors, such as the phosphatidylinositol 3-kinase/glycogen synthase kinase 3 pathway.

Neuroprotective actions of sex steroids in Parkinson's disease

The sex difference in Parkinson's disease, with a higher susceptibility in men, suggests a modulatory effect of sex steroids in the brain. Numerous studies highlight that sex steroids have neuroprotective properties against various brain injuries. This paper reviews the protective effects of sex hormones, particularly estradiol, progesterone and androgens, in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson's disease as compared to methamphetamine toxicity. The molecular mechanisms underlying beneficial actions of sex steroids on the brain have been investigated showing steroid, dose, timing and duration specificities and presently focus is on the dopamine signaling pathways, the next frontier. Both genomic and non-genomic actions of estrogen converge to promote survival factors and show sex differences. Neuroprotection by estrogen involves activation of signaling molecules such as the phosphatidylinositol-3 kinase/Akt and the mitogen-activated protein kinase pathways. Interaction with growth factors, such as insulin-like growth factor 1, also contributes to protective actions of estrogen.

The antimanic-like effect of tamoxifen: Behavioural comparison with other PKC-inhibiting and antiestrogenic drugs

Protein kinase C (PKC) is an important cellular target for mood stabilizers such as lithium and valproate, and tamoxifen, an antiestrogenic drug with PKC inhibition activity, also demonstrates an antimanic effect. Thus, the aim of the present study was to evaluate whether the antimanic effect of tamoxifen is mediated through the PKC inhibitory and/or the antiestrogenic action(s) of the drug. In the present study, the effects of tamoxifen, chelerythrine (a PKC inhibitor) and medroxyprogesterone (an antiestrogenic drug) were investigated in amphetamine-induced hyperlocomotion of mice, an animal model of a manic state. Lithium carbonate (100 and 150 mg/kg, i.p.), tamoxifen (1.0 mg/kg, i.p.) and chelerythrine (1 microg/site, i.c.v.) completely blocked the amphetamine-induced hyperlocomotion. However, while the intermediate medroxyprogesterone dose (3.0 mg/kg, i.p.) partially reduced the amphetamine-induced hyperlocomotion, lower (1.0 mg/g) and higher (6.0 mg/kg) doses produced no effect. Our results indicate a major role for PKC inhibition in the antimanic-like effect of tamoxifen, although its antiestrogenic action may also contribute to this effect.

Circuit-based framework for understanding neurotransmitter and risk gene interactions in schizophrenia

Many risk genes interact synergistically to produce schizophrenia and many neurotransmitter interactions have been implicated. We have developed a circuit-based framework for understanding gene and neurotransmitter interactions. NMDAR hypofunction has been implicated in schizophrenia because NMDAR antagonists reproduce symptoms of the disease. One action of antagonists is to reduce the excitation of fast-spiking interneurons, resulting in disinhibition of pyramidal cells. Overactive pyramidal cells, notably those in the hippocampus, can drive a hyperdopaminergic state that produces psychosis. Additional aspects of interneuron function can be understood in this framework, as follows. (i) In animal models, NMDAR antagonists reduce parvalbumin and GAD67, as found in schizophrenia. These changes produce further disinhibition and can be viewed as the aberrant response of a homeostatic system having a faulty activity sensor (the NMDAR). (ii) Disinhibition decreases the power of gamma oscillation and might thereby produce negative and cognitive symptoms. (iii) Nicotine enhances the output of interneurons, and might thereby contribute to its therapeutic effect in schizophrenia.

More than a decade of estrogen neuroprotection

Considerable evidence has emerged through more than a decade of research supporting the neuroprotective and cognition-preserving effects of estrogens. Such basic research coupled with various epidemiological studies led quickly to the assessment of Premarin for the treatment of mild to moderate Alzheimer's disease (AD), initiated by the Alzheimer's Disease Cooperative Study Group and headed by Dr. Leon Thal. While this and subsequent trials with Premarin (Wyeth Research, Monmouth Junction, New Jersey) and PremPro (Wyeth Research), a conjugated equine estrogen preparation plus medoxyprogresterone acetate, have not supported the use of estrogens in treating advanced AD, considerable inferences have been made from these placebo controlled trials of estrogens. Here, we aimed to put these AD trials of estrogens in perspective by considering the potential mechanisms of these potent neuroprotective estrogens, the role of estrogens in other neurodegenerative conditions, such as cerebral ischemia, and based on our current understanding of estrogen neurobiology, offer insight into the design of future clinical trails of estrogens for neuronal protection.

OESTROGEN AND NIGROSTRIATAL DOPAMINERGIC NEURODEGENERATION: ANIMAL MODELS AND CLINICAL REPORTS OF PARKINSON'S DISEASE

1. The exact nature of oestrogen (positive, negative or no effect) in the dopaminergic neurodegenerative disorder Parkinson's disease is controversial. 2. In the present review, we summarize the data on oestrogen and nigrostriatal dopaminergic neurodegeneration in animal models and clinical reports of Parkinson's disease. 3. Most animal studies support the ability of oestrogen to function as a neuroprotectant against neurotoxins that target the nigrostriatal dopaminergic system. 4. Retrospective and prospective clinical studies generally support the findings from animal studies that oestrogen exerts a positive, or, at worst, no effect, in Parkinson's disease. 5. Oestrogen was chosen as one of the 12 neuroprotective compounds to be attractive candidates for further clinical trials (Phase II or III) in 2003.

Blockade of MCH1 receptor signalling ameliorates obesity and related hepatic steatosis in ovariectomized mice

BACKGROUND AND PURPOSE

Melanin-concentrating hormone (MCH) is a cyclic orexigenic neuropeptide predominantly expressed in the lateral hypothalamus. We investigated the roles of MCH1 receptor signalling in ovariectomy (OVX)-induced obesity in female C57BL/6J mice, an animal model of postmenopausal obesity.

EXPERIMENTAL APPROACH

The effects of blocking signalling via the MCH1 receptor on OVX-induced obesity was investigated by using Mch1r deficient (KO) mice and chronic treatment with a selective MCH1 receptor antagonist.

KEY RESULTS

OVX induced body weight gain and increases in the weight of visceral fat and of liver; these effects were attenuated following OVX in Mch1r KO mice. OVX-induced triglyceride (TG) accumulation and elevated expression of lipogenic genes were significantly ameliorated in the liver of Mch1r KO mice. In agreement with these results, chronic i.c.v. infusion of a selective MCH1 receptor antagonist significantly reduced body weight gain, visceral fat and liver weights in OVX mice, and hepatic TG contents and lipogenic gene expression levels were normalized.

CONCLUSION AND IMPLICATIONS

Our results indicate that MCH1 receptor signalling is involved in the development of fatty liver, as well as obesity, in OVX mice, and suggest a therapeutic potential for MCH1 receptor antagonists in the treatment of obesity and fatty liver.

In search of neuroprotective therapies based on the mechanisms of estrogens

Although estradiol is a neuroprotective factor, estrogen therapy in older women increases the risk of adverse cognitive outcomes and poses additional peripheral risks, requiring careful use of estrogenic compounds as treatments for neurodegenerative conditions or neural injury. Potential alternatives to estrogen therapy to promote neuroprotection might include treatment with molecules that are able to interact with estrogen receptors, with alternative mechanisms of action, or with molecules that induce local estradiol synthesis in the brain, or a combination of all. However, before considering the broad clinical applications, more basic research is required to clarify the mechanisms of action and potential risks of some of these estrogen-based treatments.

Gender dimorphism in the DAT1 -67 T-allele homozygosity and predisposition to bipolar disorder

Linkage and association studies implicate the dopamine transporter gene (DAT1) in the etiopathophysiology of bipolar disorder. We have recently reported the association between the DAT1 core promoter -67A/T polymorphism and this disorder in a sample of Iranian patients. For the first time, these data support sex dimorphism in the homozygosity for the -67 T-allele between male and female affected cases. The present study was undertaken with a larger sample size of cases (N=240) and controls (N=213) to determine whether there is consistent difference between male and female patients and homozygosity for this allele. The results confirm and strengthen our preliminary observation that homozygosity for the T-allele is a predisposing factor in male patients, but not in females (chi2=8.825, df=1, p=0.003). Moreover, Hardy-Weinberg disequilibrium was observed in the female cases studied (chi2=12.9, df=1, p=0.0003), which may reflect the underlying biology. These findings imply gender dimorphism with respect to the DAT1 -67 alleles and susceptibility to disease.

Estrogen, Testosterone, and Methamphetamine Toxicity

The gonadal steroid hormone, estrogen, can diminish the degree of striatal dopamine depletion resulting from methamphetamine. In this article, we describe the conditions of this estrogen neuroprotection as well as the potential for estrogen and testosterone to enhance methamphetamine-induced neurodegeneration of the nigrostriatal dopaminergic system. When administered prior to a neurotoxic regimen of methamphetamine, estrogen significantly decreases the amount of striatal dopamine depletion in intact or gonadectomized female, but not male, mice. This capacity for estrogen to function as a neuroprotectant can occur quite rapidly, at 30 min prior to methamphetamine administration, and with relatively low doses of estrogen (1 microg estradiol benzoate). Estrogen remains an effective neuroprotectant in neonatally gonadectomized female mice treated with testosterone, but not in female mice that were gonadectomized prior to puberty. Nor does estrogen demonstrate any beneficial effects when administered after methamphetamine. Recent data have indicated some conditions where gonadal steroids can increase the extent of striatal neurodegeneration in response to methamphetamine. Specifically, when some existing perturbation is present in the nigrostriatal dopaminergic system, treatment with estrogen enhances the extent of striatal dopamine depletion to methamphetamine. Similarly, increased striatal dopamine depletion to methamphetamine is observed in gonadectomized male mice treated with testosterone.

Effects of estrogen and related agents upon methamphetamine-induced neurotoxicity within an impaired nigrostriatal dopaminergic system of ovariectomized mice

Estrogen increases methamphetamine (MA)-induced neurotoxicity within the impaired nigrostriatal dopaminergic (NSDA) system of ovariectomized female mice, as defined by enhanced striatal dopamine (DA) depletion. In this study we compared the effects of a lower dose of estradiol benzoate (EB, 1 microg) with related agents--tamoxifen (TMX, 12.5 microg), testosterone (5 microg) and dehydroepiandrosterone (DHEA, 3 mg) in this paradigm. In experiment 1, ovariectomized mice received an initial treatment with MA. At 1 week after MA, mice were treated with EB, TMX, testosterone, DHEA or oil vehicle and 24 h later a second MA treatment. Striatal DA and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations in the MA-treated groups were decreased compared to the non-MA-treated control. Neither EB nor any of the other agents tested showed enhanced neurodegenerative or neuroprotective effects against a second MA invasion. To verify that estrogen was capable of showing a neuroprotective effect under a condition of two administrations of MA, in experiment 2, EB was administered either once or twice prior to each of the two MA treatments. EB treatment prior to the first MA invasion or first and second MA protected the NSDA system against DA and DOPAC depletion. These results imply that a lower dose of EB, TMX, testosterone and DHEA cannot exert neurodegenerative or neuroprotective effects in the impaired NSDA model. However, EB administered prior to the introduction of neurotoxicity can protect the NSDA system. This study may provide an understanding of the variations in results on the effects of estrogen upon the NSDA neurodegenerative disorder, Parkinson's disease.

Effect of estrogen upon methamphetamine-induced neurotoxicity within the impaired nigrostriatal dopaminergic system

In the present study, we investigated whether estrogen remains effective as a neuroprotectant within an impaired nigrostriatal dopaminergic (NSDA) system of gonadectomized female and male mice. In Experiment 1, mice were treated with four different regimens of methamphetamine (MA) to establish a protocol for an impaired NSDA system to be used in subsequent experiments. Based upon the results of Experiment 1, in Experiment 2 gonadectomized female mice received a treatment with either control (saline), low- or high-dose of MA to produce an initial NSDA impairment. At one week post-MA, mice received either estradiol benzoate (10 microg) or vehicle followed 24 h later with low-MA or saline. Estrogen altered the toxic effects of the second invasion of MA as indicated by a significant decrease in striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations. In addition, DA and DOPAC depletion was greater in high- vs. low-dose MA. In gonadectomized male mice (Experiment 3), striatal DA and DOPAC concentrations showed greater decreases following high-, vs. low-doses of MA; however, estrogen did not alter these responses. These results demonstrate that the capacity for estrogen to protect or worsen MA-induced neurotoxicity of dopaminergic neurons is limited to female mice and depends on the condition of the NSDA system.

Astrocyte-derived transforming growth factor-{beta} mediates the neuroprotective effects of 17{beta}-estradiol: involvement of nonclassical genomic signaling pathways

17beta-Estradiol (E2) and selective estrogen receptor modulators (SERMs), such as tamoxifen, mediate numerous effects in the brain, including neurosecretion, neuroprotection, and the induction of synaptic plasticity. Astrocytes, the most abundant cell type in the brain, influence many of these same functions and thus may represent a mediator of estrogen action. The present study examined the regulatory effect and underlying cell signaling mechanisms of E2-induced release of neurotropic growth factors from primary rat cortical astrocyte cultures. The results revealed that E2 (0.5, 1, and 10 nm) and tamoxifen (1 mum) increased both the expression and release of the neuroprotective cytokines, TGF-beta1 and TGF-beta2 (TGF-beta), from cortical astrocytes. The stimulatory effect of E2 was attenuated by the estrogen receptor (ER) antagonist, ICI182,780, suggesting ER dependency. The effect of E2 also appeared to involve mediation by the phosphotidylinositol 3-kinase (PI3K)/Akt signaling pathway, because E2 rapidly induced Akt phosphorylation, and pharmacological or molecular inhibition of the PI3K/Akt pathway prevented E2-induced release of TGF-beta. Additionally, the membrane-impermeant conjugate, E2-BSA, stimulated the release of TGF-beta, suggesting the potential involvement of a membrane-bound ER. Finally, E2, tamoxifen, and E2-BSA were shown to protect neuronal-astrocyte cocultures from camptothecin-induced neuronal cell death, effects that were attenuated by ICI182,780, Akt inhibition, or TGF-beta immunoneutralization. As a whole, these studies suggest that E2 induction of TGF-beta release from cortical astrocytes could provide a mechanism of neuroprotection, and that E2 stimulation of TGF-beta expression and release from astrocytes occurs via an ER-dependent mechanism involving mediation by the PI3K/Akt signaling pathway.

Sex differences in methamphetamine-evoked striatal dopamine output are abolished following gonadectomy: comparisons with potassium-evoked output and responses in prepubertal mice

Sex differences are reported for methamphetamine (MA)-induced neurotoxicity of the nigrostriatal dopaminergic system. In an attempt to understand some of the bases for these differences, we investigated MA-evoked dopamine (DA) responses from superfused striatal tissue fragments of intact and male and female CD-1 mice. These responses were compared with that of gonadectomized mice, potassium-evoked DA responses in intact mice and responses in prepubertal mice. In experiment 1, DA responses were tested using infusion of MA at doses of 1, 10, 100 and 1,000 microM. In intact mice, mean peak MA-evoked DA responses were consistently increased and significantly greater in male vs. female mice at the 1,000 microM dose. No such significant differences were observed between gonadectomized male vs. female mice (experiment 2). In contrast to MA, potassium-stimulated DA responses were increased in intact female mice, with statistically significant differences at doses of 30 and 60 mM (experiment 3). No statistically significant differences between intact prepubertal male and female mice were obtained in response to a 1,000 microM dose of MA (experiment 4) or to a 60 mM dose of potassium (experiment 5). These results indicate that intact male mice show greater sensitivity to MA-evoked DA output. This sex difference is abolished following gonadectomy, is not observed with potassium, nor is it present in prepubertal mice. The increased sensitivity to MA shown by intact males may be related to the greater degree of striatal dopaminergic neurotoxicity observed in male mice in response to this psychostimulant and appears to be attributable to differences in gonadal steroid hormones between male and female mice.