Gender differences in methamphetamine-induced mRNA associated with neurodegeneration in the mouse nigrostriatal dopaminergic system

Sex differences and Tat expression affect dopaminergic receptor expression and response to antioxidant treatment in methamphetamine-sensitized HIV Tat transgenic mice

Methamphetamine (Meth) abuse is a common HIV comorbidity. Males and females differ in their patterns of Meth use, associated behaviors, and responses, but the underlying mechanisms and impact of HIV infection are unclear. Transgenic mice with inducible HIV-1 Tat protein in the brain (iTat) replicate many neurological aspects of HIV infection in humans. We previously showed that Tat induction enhances the Meth sensitization response associated with perturbation of the dopaminergic system, in male iTat mice. Here, we used the iTat mouse model to investigate sex differences in individual and interactive effects of Tat and Meth challenge on locomotor sensitization, brain expression of dopamine receptors (DRDs) and regulatory adenosine receptors (ADORAs). Because Meth administration increases the production of reactive oxygen species (ROS), we also determined whether the effects of Meth could be rescued by concomitant treatment with the ROS scavenger N-acetyl cysteine (NAC). After Meth sensitization and a 7-day abstinence period, groups of Tat+ and Tat-male and female mice were challenged with Meth in combination with NAC. We confirmed that Tat expression and Meth challenge suppressed DRD mRNA and protein in males and females' brains, and showed that females were particularly susceptible to the effects of Meth on D1-like and D2-like DRD subtypes and ADORAs. The expression of these markers differed strikingly between males and females, and between females in different phases of the estrous cycle, in a Tat -dependent manner. NAC attenuated Meth-induced locomotor sensitization and preserved DRD expression in all groups except for Tat + females. These data identify complex interactions between sex, Meth use, and HIV infection on addiction responses, with potential implications for the treatment of male and female Meth users in the context of HIV, especially those with cognitive disorders.

Methamphetamine administration increases hepatic CYP1A2 but not CYP3A activity in female guinea pigs

Methamphetamine use has increased over the past decade and the first use of methamphetamine is most often when women are of reproductive age. Methamphetamine accumulates in the liver; however, little is known about the effect of methamphetamine use on hepatic drug metabolism. Methamphetamine was administered on 3 occassions to female Dunkin Hartley guinea pigs of reproductive age, mimicking recreational drug use. Low doses of test drugs caffeine and midazolam were administered after the third dose of methamphetamine to assess the functional activity of cytochrome P450 1A2 and 3A, respectively. Real-time quantitative polymerase chain reaction was used to quantify the mRNA expression of factors involved in glucocorticoid signalling, inflammation, oxidative stress and drug transporters. This study showed that methamphetamine administration decreased hepatic CYP1A2 mRNA expression, but increased CYP1A2 enzyme activity. Methamphetamine had no effect on CYP3A enzyme activity. In addition, we found that methamphetamine may also result in changes in glucocorticoid bioavailability, as we found a decrease in 11β-hydroxysteroid dehydrogenase 1 mRNA expression, which converts inactive cortisone into active cortisol. This study has shown that methamphetamine administration has the potential to alter drug metabolism via the CYP1A2 metabolic pathway in female guinea pigs. This may have clinical implications for drug dosing in female methamphetamine users of reproductive age.

Sex Differences in Neurotoxicogenetics

A major development in biomedical research is the recognition that the sex of an individual plays a key role in susceptibility, treatment, and outcomes of most diseases. In this contribution, we present evidence that sex is also important in the toxicity of many environmental toxicants and contributes to the effect of genetics. Thus, individual differences in response to toxicants includes genetic makeup, the environment and sex; in fact, sex differences may be considered a part of genetic constitution. In this review, we present evidence for sex contribution to susceptibility for a number of toxicants.

Effects of HIV and Methamphetamine on Brain and Behavior: Evidence from Human Studies and Animal Models

Methamphetamine (Meth) use is frequent among HIV-infected persons. Combined HIV and Meth insults may exacerbate neural injury in vulnerable neuroanatomic structures or circuitries in the brain, leading to increased behavioral disturbance and cognitive impairment. While acute and chronic effects of Meth in humans and animal models have been studied for decades, the neurobehavioral effects of Meth in the context of HIV infection are much less explored. In-depth understanding of the scope of neurobehavioral phenotypes and mechanisms in HIV/Meth intersection is needed. The present report summarizes published research findings, as well as unpublished data, in humans and animal models with regard to neurobehavioral disturbance, neuroimaging, and neuropathology, and in vitro experimental systems, with an emphasis on findings emerging from the National Institute on Drug Abuse (NIDA) funded Translational Methamphetamine AIDS Research Center (TMARC). Results from human studies and animal (primarily HIV-1 gp120 transgenic mouse) models thus far suggest that combined HIV and Meth insults increase the likelihood of neural injury in the brain. The neurobehavioral effects include cognitive impairment and increased tendencies toward impaired behavioral inhibition and social cognition. These impairments are relevant to behaviors that affect personal and social risks, e.g. worse medication adherence, riskier behaviors, and greater likelihood of HIV transmission. The underlying mechanisms may include electrochemical changes in neuronal circuitries, injury to white matter microstructures, synaptodendritic damage, and selective neuronal loss. Utilization of research methodologies that are valid across species is instrumental in generating new knowledge with clinical translational value.

Sex differences in impulsivity and brain morphometry in methamphetamine users

Methamphetamine (METH) is an addictive stimulant, and METH users have abnormal brain structures and function. The aims of this study were to investigate the relationships between impulsivity, brain structures, and possible sex-specific differences between METH users and non-drug using Controls. Structural MRI and the Barratt Impulsiveness Scale (BIS) questionnaire were completed in 124 subjects: 62 METH (ages 41.2 ± 1.4 years, 34 males) and 62 Controls (ages 43.3 ± 2.3 years, 36 males). Independent and interactive effects of METH use status and sex were evaluated. Relationships between METH usage characteristics, brain morphometry, and impulsivity scores were examined. METH users had higher impulsivity scores, on both the Cognitive and Behavioral Factors from the BIS (p < 0.0001-0.0001). Compared with same-sex Controls, male METH users had larger, while female METH users had smaller, right superior frontal cortex (interaction-p = 0.0005). The male METH users with larger frontal volumes and female METH users with smaller or thinner frontal cortices had greater Cognitive impulsivity (interaction-p ≤ 0.05). Only female METH users showed relatively larger nucleus accumbens (interaction-p = 0.03). Greater impulsivity and thinner frontal cortices in METH users are validated. Larger superior frontal cortex in male METH users with greater cognitive impulsivity suggest decreased dendritic pruning during adolescence might have contributed to their impulsive and drug use behaviors. In the female METH users, smaller frontal cortices and the associated greater impulsivity suggest greater neurotoxicity to these brain regions, while their relatively larger nucleus accumbens suggest an estrogen-mediated neuroprotective glial response. Men and women may be affected differently by METH use.

Nomifensine alters sex differences in striatal dopaminergic function

A series of three experiments are presented in which the acute effects of the catecholamine reuptake inhibitor, nomifensine, upon striatal dopaminergic function are compared in female and male mice. In Experiment 1, treatment with nomifensine (5 mg kg⁻¹), at 30 min prior to injection of methamphetamine (40 mg kg⁻¹) significantly decreased the amount of striatal dopamine depletion in male, but not female, mice, thereby abolishing the sex difference in methamphetamine-induced neurotoxicity (males > females). In Experiment 2, the methamphetamine-evoked sex differences in dopamine and DOPAC output from superfused striatal tissue (males > females) were abolished in mice treated with nomifensine at 30 min prior to tissue removal. In Experiment 3, the potassium chloride-evoked sex differences in dopamine and DOPAC output from superfused striatal tissue (females > males) were reversed in mice treated with nomifensine at 30 min prior to tissue removal. Taken together these results demonstrate the critical role played by catecholamine transporters in sex differences of dopaminergic function and suggest that this may involve the dopamine transporter, due to its high concentrations within the striatum. Such findings highlight the need for gender-specific considerations in use of treatments that target reuptake transporters function.

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.

Markers associated with sex differences in methamphetamine-induced striatal dopamine neurotoxicity

Three different approaches were employed to assess various markers associated with sex differences in responses to methamphetamine (MA). Bioassay measures reveal that MA treatment results in significantly greater reductions in body weight and increases in body temperature in male mice. Protein and mRNA determinations show significant increases in Bcl-2 and PAI-1 in male mice, while females show significant increases in GFAP and decreases in IGF-1R following treatment with MA. In mice with a heterozygous mutation of their dopamine transporter (+/- DAT), only female mice show significant differences in dopamine transporter binding and mRNA and associated reductions in striatal dopamine content along with increases in MA-evoked striatal dopamine output. The identification of these sex-dependent differences in markers provides a foundation for more exhaustive evaluation of their impact upon, and treatment of, disorders/neurotoxicity of the nigrostriatal dopaminergic system and the bases for the differences that exist between females and males.

Effects of the genotoxic agent 5-bromo-2'-deoxyuridine with or without pre-pubertal gonadectomy on brain monoamines and their metabolites in female rats

A nucleotide analog 5-bromo-2'-deoxyuridine (BrdU) is a genotoxic compound. Previous studies have demonstrated that prenatal treatment of rodents with BrdU affects the development of cortical neurons, reduces dopamine levels, and elevates serotonin (5-HT) levels in the striatum in adult male offspring from BrdU-treated dams. Moreover, prenatal BrdU-treated rats show locomotor hyperactivity in both males and females. This study investigated sexual dimorphism in the effect of prenatal BrdU on monoamine metabolism. Sprague-Dawley rats were treated with BrdU on gestational days 9-15 (50mg/kg, i.p.) and monoamine metabolism was examined in female rats at 10 weeks of age. The influence of pre-pubertal gonadectomy on the effects of BrdU was also investigated. BrdU-treated females showed elevations of dopamine and 5-HT levels in the striatum; reductions in dopamine, dihydroxyphenylacetic acid, or homovanillic acid (HVA) in the hypothalamus or the midbrain; and elevated HVA and 5-HT in the hippocampus. Pre-pubertal gonadectomy had a suppressive effect on striatal dopamine levels in prenatal BrdU-treated females. The present data indicate sexual dimorphic effects of prenatal BrdU-treatment in striatal dopamine metabolism but not in serotonergic metabolism and suggest a contribution of the increasing gonadal hormones that accompany puberty to this sex difference.

Relationships among gender, age, time, and temperature in methamphetamine-induced striatal dopaminergic neurotoxicity

A neurotoxic regimen of methamphetamine (MA-40 mg/kg ip) administered at 0 (control-MA vehicle), 0.5 and 72 h prior to determinations of striatal dopamine (DA) and DOPAC (3,4-dihydroxyphenylacetic acid)/DA ratios were compared among juvenile and adult female and male mice. Adult females and males showed similar depletions in striatal DA at 0.5 h post-MA, but males showed greater DA depletions and DOPAC/DA ratios at 72 h post-MA. Juvenile mice showed neither sex differences, nor any MA neurotoxicity upon striatal DA or DOPAC/DA ratios. Following MA, body temperatures increased in all mice, but increases in adult males were greater than adult females; juveniles showed no sex differences and body temperature increases were similar to that of adult males. MA-evoked DA output was greater in adult compared to juvenile males and a biologically effective regimen of testosterone to juvenile males neither increased MA-evoked DA output nor decreased MA-induced striatal DA like that observed in adult males. These results demonstrate: (1) Unlike adults, juvenile mice show neither a sex difference for MA-induced neurotoxicity or body temperature increases, nor MA neurotoxicity, (2) Initial effects of MA (0.5 h) in adult females and males are similar, but at 72 h post-MA females show no further striatal DA depletion, (3) Increased striatal DA depletion within adult versus juvenile males may be related to initially higher MA-evoked DA responses, and (4) Testosterone fails to convert juvenile males into adults with regard to MA effects.

The impact of age and gender on the striatal astrocytes activation in murine model of Parkinson's disease

OBJECTIVE

The aim of the present study was to determine how aging and gender influence the response of astrocytes to 1-methyl-4-phenyl-1,2,3,6-tetrahydropiridine (MPTP) intoxication.

MATERIALS AND METHODS

To asses the MPTP-induced astrocytes activation in nigro-striatal system, we measured the temporal changes in mRNA and protein expression of the specific astrocytic marker, glial fibrillary acidic protein (GFAP; by RT-PCR and Western blot), in the striatum of male and female C57BL/6 mice (2 and 12-month old) after 6 h and 1, 3, 7, 14 and 21 days post-intoxication.

RESULTS

We observed the increases of GFAP mRNA level post-MPTP intoxication in both young and aging males only at early time points, whereas in females (both ages) also at later time points. We noticed maximal increase of GFAP protein content on the 3rd day post-intoxication in young and aged males, whereas in females at the 7-daytime point.

CONCLUSIONS

The present results provide additional information of potential relevance to understand the mechanisms of gender and age-related difference in susceptibility of nigro-striatal system to MPTP insult.

Independent influences of sex steroids of systemic and central origin in a rat model of Parkinson's disease: A contribution to sex-specific neuroprotection by estrogens

This review considers evidence which reveals considerable complexity and sex differences in the response of the nigrostriatal dopaminergic (NSDA) system to hormonal influences. This pathway degenerates in Parkinson's disease (PD) and sex hormones contribute to sex differences in PD, where men fare worse than women. Here we discuss evidence from animal studies which allows us to hypothesize that, contrary to expectations, the acclaimed neuroprotective property of physiological concentrations of estradiol arises not by promoting NSDA neuron survival, but by targeting powerful adaptive responses in the surviving neurons, which restore striatal DA functionality until over 60% of neurons are lost. Estrogen generated locally in the NSDA region appears to promote these adaptive mechanisms in females and males to preserve striatal DA levels in the partially injured NSDA pathway. However, responses to systemic steroids differ between the sexes. In females there is general agreement that gonadal steroids and exogenous estradiol promote striatal adaptation in the partially injured NSDA pathway to protect against striatal DA loss. In contrast, the balance of evidence suggests that in males gonadal factors and exogenous estradiol have negligible or even harmful effects. Sex differences in the organization of NSDA-related circuitry may well account for these differences. Compensatory mechanisms and sexually dimorphic hard-wiring are therefore likely to represent important biological substrates for sex dimorphisms. As these processes may be targeted differentially by systemic steroids in males and females, further understanding of the underlying processes would provide valuable insights into the potential for hormone-based therapies in PD, which would need to be sex-specific. Alternatively, evidence that estrogen generated locally is protective in the injured male NSDA pathway indicates the great therapeutic potential of harnessing central steroid synthesis to ameliorate neurodegenerative disorders. A clearer understanding of the relative contributions and inter-relationships of central and systemic steroids within the NSDA system is an important goal for future studies.

Genetic alteration in the dopamine transporter differentially affects male and female nigrostriatal transporter systems

Female mice with a heterozygous mutation of their dopamine transporter (+/- DAT) showed relatively robust reductions in striatal DAT specific binding (38-50%), while +/- DAT males showed modest reductions (24-32%). Significant decreases in substantia nigra DAT specific binding (42%) and mRNA (24%) were obtained in +/- DAT females, but not +/- DAT males (19% and 5%, respectively). The effects of this DAT perturbation upon vesicular monoamine transporter-2 (VMAT-2) function revealed significantly greater reserpine-evoked DA output from +/+ and +/- DAT female as compared to male mice and the DA output profile differed markedly between +/+ and +/- DAT females, but not males. No changes in VMAT-2 protein or mRNA levels were present among these conditions. On the basis of these data, we propose: (1) a genetic mutation of the DAT does not exert equivalent effects upon the DAT in female and male mice, with females being more affected; (2) an alteration in the DAT may also affect VMAT-2 function; (3) this interaction between DAT and VMAT-2 function is more prevalent in female mice; and (4) the +/- DAT mutation affects VMAT-2 function through an indirect mechanism, that does not involve an alteration in VMAT-2 protein or mRNA. Such DAT/VMAT-2 interactions can be of significance to the gender differences observed in drug addiction and Parkinson's disease.

Sex differences in dopamine- and vesicular monoamine-transporter functions

Men and women differ with regard to their use of, and responses to, methamphetamine (MA). Analogous sex differences with regard to MA are observed in animal models. In this report, data from a series of experiments that focus upon dopamine transporter (DAT) and vesicular monoamine transporter2 (VMAT2) function are reviewed by way of providing some understanding for these sex differences to MA. The amount of dopamine (DA) recovered after infusion of DA into superfused striatal tissue was greater in females and an accentuated amount of extracellular DA was obtained from females after infusion of the DAT-blocking drug, nomifensine. These data suggest a higher level of DAT activity in females. To evaluate the implications of this sex difference in DAT function as related to MA, the amount of DA evoked by an infusion of MA into superfused striatal tissue was tested and found to be significantly greater in males. In contrast, potassium chloride-stimulated DA release was greater in females. The results of these DA-evoked experiments imply that the greater DAT activity of females, by itself, cannot explain the sex differences observed with MA, and our attention was then directed to the VMAT2. Administration of the VMAT2 blocker, reserpine, in vivo resulted in a significantly greater amount of striatal DA depletion within female mice and infusion of reserpine in vitro into striatal tissue produced significantly greater levels of extracellular DA in females. The data of these reserpine experiments suggest that females possess a more active/efficient VMAT2 function. Collectively, the data provide evidence for sex differences in both DAT and VMAT2 functioning, and we propose that the interaction of these two transporter systems contributes to the differences in response to MA between males and females.

Differences in reserpine-induced striatal dopamine output and content between female and male mice: implications for sex differences in vesicular monoamine transporter 2 function

In this report a series of six in vitro experiments in which reserpine-evoked dopamine output and two in vivo experiments in which the effects of reserpine injections upon dopamine content from striatal tissue of female and male mice were performed as a means to assess possible sex differences in vesicular monoamine transporter 2 (VMAT2) function. Significantly greater amounts of dopamine were obtained from striatal tissue of female mice in response to either a brief (experiment 1) or continuous (experiment 2) infusion of reserpine. Similarly, reserpine-evoked dopamine output from striatal tissue of gonadectomized females was significantly greater that that of gonadectomized males (experiment 3). When reserpine-evoked dopamine responses were compared directly between intact versus gonadectomized females (experiment 4) or males (experiment 5) no statistically significant differences were obtained. Finally, comparisons of gonadectomized females treated or not with estrogen revealed no statistically significant differences in reserpine-evoked dopamine output (experiment 6). Injections of reserpine produced significantly greater depletions of striatal dopamine content within intact female versus male mice (experiment 7). Dopamine contents of gonadectomized females treated or not with estrogen did not differ following treatment with reserpine, but were significantly greater than that of gonadectomized males (experiment 8). Taken together, these results show that female striatal tissue is more responsive to reserpine-evoked dopamine output, and this sex difference appears to be estrogen independent. Similarly, the dopamine depleting effects of reserpine are greater in intact female mice, however, gonadectomy reverses this effect in an estrogen independent manner. The data suggest that female mice may have a greater amount/activity of VMAT2 function as revealed by the increased responsiveness to the VMAT2 blocking drug, reserpine. Such differences in VMAT2 function may be related to the gender differences observed in conditions like Parkinson's disease and drug addiction.

Methamphetamine-induced neurotoxicity and microglial activation are not mediated by fractalkine receptor signaling

Methamphetamine (METH) damages dopamine (DA) nerve endings by a process that has been linked to microglial activation but the signaling pathways that mediate this response have not yet been delineated. Cardona et al. [Nat. Neurosci. 9 (2006), 917] recently identified the microglial-specific fractalkine receptor (CX3CR1) as an important mediator of MPTP-induced neurodegeneration of DA neurons. Because the CNS damage caused by METH and MPTP is highly selective for the DA neuronal system in mouse models of neurotoxicity, we hypothesized that the CX3CR1 plays a role in METH-induced neurotoxicity and microglial activation. Mice in which the CX3CR1 gene has been deleted and replaced with a cDNA encoding enhanced green fluorescent protein (eGFP) were treated with METH and examined for striatal neurotoxicity. METH depleted DA, caused microglial activation, and increased body temperature in CX3CR1 knockout mice to the same extent and over the same time course seen in wild-type controls. The effects of METH in CX3CR1 knockout mice were not gender-dependent and did not extend beyond the striatum. Striatal microglia expressing eGFP constitutively show morphological changes after METH that are characteristic of activation. This response was restricted to the striatum and contrasted sharply with unresponsive eGFP-microglia in surrounding brain areas that are not damaged by METH. We conclude from these studies that CX3CR1 signaling does not modulate METH neurotoxicity or microglial activation. Furthermore, it appears that striatal-resident microglia respond to METH with an activation cascade and then return to a surveying state without undergoing apoptosis or migration.

Sex differences in striatal dopaminergic function within heterozygous mutant dopamine transporter knock-out mice

The issue of whether a deletion of the dopamine transporter (DAT) allele (+/- DAT) would differentially alter striatal dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) concentrations and DA release upon potassium and methamphetamine (MA) stimulation between male and female mice was examined. Striatal DA and DOPAC concentrations of female +/- DAT mice were significantly decreased as compared with wild type (+/+) controls and male +/- DAT mice. No such changes were obtained from the olfactory tubercle suggesting that these effects might be specific for the striatum. Potassium-stimulated DA was increased in male and female +/- DAT mice and maximally stimulated DA was obtained from +/- DAT females, although these mice showed the lowest DA concentrations. MA-evoked DA was increased in male and female +/- mice. While MA-evoked DA was significantly increased in +/+ males versus +/+ females, the +/- females showed the highest DA responses, thereby showing a reversal in the results seen in wild-type conditions. These findings indicate: (1) that a deficiency in the DAT interacts with the sex of the subject, (2)+/- DAT females show more extreme changes in dopaminergic responses, and (3) the importance for considering such variables such as sex when examining differences among knock-out conditions.

Decreased frontal white-matter integrity in abstinent methamphetamine abusers

This study explored differences in frontal white-matter (WM) integrity between methamphetamine (MA) abusers and healthy comparison subjects using diffusion tensor imaging (DTI). Fractional anisotropy (FA) values, which indicate WM integrity, were calculated for regions-of-interest in frontal WM on diffusion tensor images of 32 MA abusers and 30 healthy comparison subjects. Frontal executive functions were also assessed by the Wisconsin Card Sorting test (WCST). MA abusers had significantly lower FA values in bilateral frontal WM at the anterior commissure-posterior commissure (AC-PC) plane and the right frontal WM 5 mm above the AC-PC plane relative to healthy comparison subjects. MA abusers had more total, perseveration and non-perseveration errors in the WCST relative to healthy comparison subjects. FA values of the right frontal WM 5 mm above the AC-PC plane negatively correlated with the number of total and non-perseveration errors in the WCST in MA abusers. In the sub-analysis for gender differences, lower FA values in frontal WM and more errors in the WCST were found only in male MA abusers, not in female MA abusers, relative to comparison subjects of the respective gender. We report that frontal WM integrity of MA abusers is compromised. This finding may also be related to impairment in frontal executive function. In addition, the neurotoxic effect of MA on frontal WM may be less prominent in women than in men, possibly due to oestrogen's neuroprotective effect.

Effects of gender on nigral gene expression and parkinson disease

To identify gene expression patterns in human dopamine (DA) neurons in the substantia nigra pars compacta (SNc) of male and female control and Parkinson disease (PD) patients, we harvested DA neurons from frozen SNc from 16 subjects (4 male PDs, 4 female PDs, 4 male and 4 female controls) using Laser Capture microdissection and microarrays. We assessed for enrichment of functional categories with a hypergeometric distribution. The data were validated with QPCR. We observed that gender has a pervasive effect on gene expression in DA neurons. Genes upregulated in females relative to males are mainly involved in signal transduction and neuronal maturation, while in males some of the upregulated genes (alpha-synuclein and PINK1) were previously implicated in the pathogenesis of PD. In females with PD we found alterations in genes with protein kinase activity, genes involved in proteolysis and WNT signaling pathway, while in males with PD there were alterations in protein-binding proteins and copper-binding proteins. Our data reveal broad gender-based differences in gene expression in human dopaminergic neurons of SNc that may underlie the predisposition of males to PD. Moreover, we show that gender influences the response to PD, suggesting that the nature of the disease and the response to treatment may be gender-dependent.

Influence of age and gender on cytokine expression in a murine model of Parkinson's disease

OBJECTIVE

The neuroinflammatory reaction has been linked with Parkinson's disease. One of the hypotheses to explain the significance of age and gender (male predominance) effects on neurodegeneration in Parkinson's disease may result from a link between these risk factors and the inflammatory processes. Here, we investigated the expression of inflammatory mediators in relation to 1-methyl-4-phenyl-1,2,3,6-tetrahydropiridine (MPTP)-induced neurodegenerative processes in nigrostriatal pathway in young and aged male and female mice.

METHODS AND RESULTS

We simultaneously assessed striatal tyrosine hydroxylase (TH) protein concentrations (Western blotting) and cytokine (TNFalpha, IFNgamma, IL-1beta, IL-6 and TGFbeta(1)) mRNA levels (RT-PCR) in young and aged (2- and 12-month-old) C57BL/6 male and female mice after 6 h, 1, 3, 7, 14, 21 days after MPTP intoxication. Western blotting analysis showed that at the early time points, males showed a greater reduction in striatal TH versus females. Additionally, in contrast to the aged mice, in young males and females the TH concentration gradually increased between the 7th and the 21st day after intoxication. The increases in TNFalpha, IL-1beta and IFNgamma after intoxication were faster in both young and aged males than females. In males (both ages), we observed an increase in TGFbeta(1) at the early time points. In contrast, in females (both ages) TGFbeta(1) was elevated at later time points. MPTP caused an increase in IL-6 in males and females, but this increase was significantly higher in females.

CONCLUSIONS

A gender and age skewing of the cytokine gene expression in the striatum after intoxication may be related to the greater susceptibility in males as well as older animals to the detrimental effects of MPTP.

Sex differences in methamphetamine-evoked striatal dopamine of mice are reversed by nomifensine

Male mice show more severe striatal dopamine depletions to the psychostimulant, methamphetamine (MA). To gain some understanding for this sex difference, we examined MA-evoked dopamine (DA) responses from superfused striatal tissue fragments of male and female mice under conditions of a dopamine transporter which was either unaltered (Experiment 1) or inhibited, with use of the drug, nomifensine (Experiment 2). In Experiment 1, MA-evoked DA was significantly greater in male versus female mice. In Experiment 2, diminished, albeit statistically significant, DA responses to MA infusion in the presence of nomifensine were obtained from striatal tissue of female, but not male, mice. In Experiment 3, potassium-evoked DA responses and sex differences were abolished in the presence of nomifensine. These data demonstrate a clear sex difference in DA responses to MA. Interestingly, under conditions where dopamine transporter function is inhibited, MA retains its ability to evoke DA. However, this capacity was only observed within striatal tissue fragments of female mice and not under conditions of potassium-evoked DA. These results indicate an additional component for the bases of sex differences in nigrostriatal dopaminergic function in health and in disease. In particular, the present findings have important implications in suggesting an alternative, non-traditional, mechanism for MA effects and indicate that such a function is limited to females.

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.

Sex differences in striatal dopamine release in healthy adults

BACKGROUND

Sex differences in addictive disorders have been described. Preclinical studies have implicated the striatal dopamine system in these differences, but human studies have yet to substantiate these findings.

METHODS

Using positron emission tomography (PET) scans with high-specific-activity [11C] raclopride and a reference tissue approach, we compared baseline striatal dopamine binding potential (BP) and dopamine release in men and women following amphetamine and placebo challenges. Subjective drug effects and plasma cortisol and growth hormone responses were also examined.

RESULTS

Although there was no sex difference in baseline BP, men had markedly greater dopamine release than women in the ventral striatum. Secondary analyses indicated that men also had greater dopamine release in three of four additional striatal regions. Paralleling the PET findings, men's ratings of the positive effects of amphetamine were greater than women's. We found no sex difference in neuroendocrine hormone responses.

CONCLUSIONS

We report for the first time a sex difference in dopamine release in humans. The robust dopamine release in men could account for increased vulnerability to stimulant use disorders and methamphetamine toxicity. Our findings indicate that future studies should control for sex and may have implications for the interpretation of sex differences in other illnesses involving the striatum.

Association between dopamine receptor D1 A-48G polymorphism and methamphetamine abuse

Several lines of evidence have suggested that substance abuse is mediated by the dopaminergic rewarding system, primarily through the activity of the dopamine receptor D1 (DRD1). The purpose of the present study was to evaluate the association of DRD1 A-48G polymorphism with methamphetamine (MAP) abusers and MAP-induced psychosis patients. A total of 363 MAP abusers and 425 healthy normal controls were enrolled. The structural Diagnostic Interview for Genetic Study was used to evaluate all MAP abusers. The MAP abusers were classified into psychosis (n = 135) and non-psychosis (n = 228) groups. A-48G polymorphism was determined by polymerase chain reaction-restriction fragment length polymorphism. The results show that male sex and a higher frequency of MAP abuse were the predisposing factors in the development of MAP psychosis. The DRD1 -48G allele frequency in the MAP psychosis group, non-psychosis group and the healthy normal controls was 0.14, 0.18 and 0.16, respectively. No association was found between DRD1 A-48G polymorphism and MAP abuse and MAP psychosis. However, the data provided additional evidence of ethnicity-related differences in the distribution of polymorphism in comparison to previous studies.

Testosterone modulation of striatal dopamine output in orchidectomized mice

Three experiments are presented in which dopamine (DA) responses from superfused striatal tissue of orchidectomized (ORCH) mice treated or not with testosterone (T) are compared. In experiment 1, potassium-stimulated DA output was significantly greater in ORCH vs. ORCH+T mice. This profile was reversed when reserpine was infused in experiment 2, with DA output being significantly greater in ORCH+T vs. ORCH mice. In experiment 3, the amount of DA recovered following infusion of DA indicated no statistically significant differences in DA recoveries between ORCH and ORCH+T mice as tested in this paradigm. The findings that both potassium- and reserpine-induced DA responses are altered significantly by T suggests that one potential site of T action might involve the storage/uptake of DA within the vesicles of these neurons. Such results have important implications with regard to understanding the sex differences that are present in nigrostriatal dopaminergic function within health and diseased states.

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.

Frontal glucose hypometabolism in abstinent methamphetamine users

Changes in relative regional cerebral glucose metabolism (rCMRglc) and their potential gender differences in abstinent methamphetamine (MA) users were explored. Relative rCMRglc, as measured by (18)F-fluorodeoxyglucose positron emission tomography, and frontal executive functions, as assessed by Wisconsin card sorting test (WCST), were compared between 35 abstinent MA users and 21 healthy comparison subjects. In addition, male and female MA users and their gender-matched comparison subjects were compared to investigate potential gender differences. MA users had lower rCMRglc levels in the right superior frontal white matter and more perseveration and nonperseveration errors in the WCST, relative to healthy comparison subjects. Relative rCMRglc in the frontal white matter correlated with number of errors in the WCST in MA users. In the subanalysis for gender differences, lower rCMRglc in the frontal white matter and more errors in the WCST were found only in male MA users, not in female MA users, relative to their gender-matched comparison subjects. The current findings suggest that MA use causes persistent hypometabolism in the frontal white matter and impairment in frontal executive function. Our findings also suggest that the neurotoxic effect of MA on frontal lobes of the brain might be more prominent in men than in women.

Enlarged striatum in abstinent methamphetamine abusers: a possible compensatory response

BACKGROUND

Little is known about structural brain abnormalities associated with methamphetamine (METH) abuse; therefore, we aimed: 1) to evaluate possible morphometric changes, especially in the striatum of recently abstinent METH-dependent subjects; 2) to evaluate whether morphometric changes are related to cognitive performance; and 3) to determine whether there are sex-by-METH interactions on morphometry.

METHODS

Structural MRI was performed in 50 METH and 50 comparison subjects with the same age range and sex proportion; quantitative morphometric analyses were performed in the subcortical gray matter, cerebellum and corpus callosum. Neuropsychological tests were also performed in 44 METH and 28 comparison subjects.

RESULTS

METH users showed enlarged putamen (left: + 10.3%, p = .0007; right: + 9.6%, p = .001) and globus pallidus (left: + 9.3%, p = .002; right: + 6.6%, p = .01). Female METH subjects additionally showed larger mid-posterior corpus callosum (+ 9.7%, p = .05). Although METH users had normal cognitive function, those with smaller striatal structures had poorer cognitive performance and greater cumulative METH usage.

CONCLUSIONS

Since METH subjects with larger striatal structures had relatively normal cognitive performance and lesser cumulative METH usage, the enlarged putamen and globus pallidus might represent a compensatory response to maintain function. Possible mechanisms for the striatal enlargement include glial activation and inflammatory changes associated with METH-induced injury.

Dopamine transporter function differences between male and female CD-1 mice

It has been reported that male mice are more susceptible to the neurotoxic effects of methamphetamine (MA) upon the nigrostriatal dopaminergic (NSDA) system. Since MA utilizes the dopamine transporter (DAT) to exert its effects, in the present study, we tested for differences in the dynamics of DAT function between male and female mice as an approach to understand some of the bases for this sex difference in MA-induced NSDA neurotoxicity. To accomplish this goal, in Experiment 1, the amount of dopamine (DA) obtained following DA infusion into the superfused striatal tissue fragments of male and female mice was measured while in Experiment 2 responses to the DA uptake blocker, nomifensine (NMF), were assessed in these preparations. The differences obtained to these treatments demonstrate that marked differences in DA transporter activity exist between male and female mice. When combining the DA and DOPAC measures from these two experiments, the data suggest that the female mice show a more active and efficient recovery and vesicular packaging of extracellular DA. These findings have important implications for sex differences in NSDA functions and responses to neurotoxins which enter the neurons via the DAT.

Effects of neonatal and prepubertal hormonal manipulations upon estrogen neuroprotection of the nigrostriatal dopaminergic system within female and male mice

Estrogen (E) can function as a neuroprotectant of the nigrostriatal dopaminergic (NSDA) system against methamphetamine (MA) neurotoxicity in female, but not male, mice. In the present report we examined whether the organizational effects of gonadal steroid hormones, as exerted in the early postnatal period, or developmental effects, as exerted during the pubertal period, would contribute to this sexually dimorphic neuroprotectant action of E. Neonatal gonadectomy and treatment with testosterone of female mice, retained the ability to show an E neuroprotectant response when tested as adults. However, females not treated with gonadal steroids failed to show an E-dependent neuroprotectant response. Neonatal gonadectomy of male mice, failed to result in the display of an E neuroprotectant response when tested as adults. Prepubertal gonadectomy of female mice, with or without testosterone treatment, abolished the capacity for E to produce neuroprotection against MA-induced NSDA neurotoxicity. Nor did prepubertal gonadectomy enable male mice to show an E neuroprotectant response. Taken together these results demonstrate that none of the manipulations performed within male mice enabled them to show an E-dependent neuroprotective response against MA-induced neurotoxicity of the NSDA system when tested as adults. For the female, it appears that the presences of gonadal steroids at these two developmental periods are needed for the display of an E-dependent neuroprotectant response within the adult.

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.

Developmental and Genetic Influences upon Gender Differences in Methamphetamine-Induced Nigrostriatal Dopaminergic Neurotoxicity

The gonadal steroid hormone estrogen (E) may play an important role in sex differences in methamphetamine (MA)-induced neurotoxicity of the nigrostriatal dopaminergic (NSDA) system because E can serve as a neuroprotectant in female, but not male, mice. Gonadal steroid hormones also exert important organizational/developmental effects upon the brain at critical developmental periods. In Part 1 we assessed whether organizational (neonatal) or developmental (prepubertal) effects of gonadal steroids would alter gender/E-dependent neuroprotection of MA-induced NSDA neurotoxicity. Attempts to feminize male mice by gonadectomy at either the neonatal or prepubertal period failed to enable E to function as a neuroprotectant within the adult male mouse. Attempts to masculinize the female by testosterone administration at the neonatal period did not abolish the capacity for E to function as a neuroprotectant. However, prepubertal gonadectomy of female mice did disrupt E's capacity to serve as a neuroprotectant. These results suggest that genetic sex may prove the primary determinant for the sex differences observed in response to MA-induced NSDA neurotoxicity. In Part 2 we examined whether gender differences in response to MA-induced NSDA neurotoxicity would interact with a specific genetic alteration in a neurotrophic factor, brain-derived neurotrophic factor (BDNF). Female and male mice that were either deficient (+/- BDNF) or overexpressing (DBH:BDNF+) BDNF were treated with MA. Sex differences in MA-induced NSDA neurotoxicity remained present in +/- BDNF mice and were less severe as compared with their wild-type controls. A similar result was obtained in mice that overexpress BDNF, with female and mutant mice showing less NSDA neurotoxicity. In both BDNF-deficient mice and mice that overexpress BDNF, the relative degree of MA-induced NSDA neurotoxicity was lower in males. Taken together, these results suggest that a selective alteration in BDNF expression offers some neuroprotective potential against MA-induced NSDA neurotoxicity, and the relative degree of this neuroprotection may interact with the gender of the subject.

The effect of gender and the neurotrophin, BDNF, upon methamphetamine-induced neurotoxicity of the nigrostriatal dopaminergic system in mice

The interactive effects between gender and a selective alteration in the neurotrophin, brain-derived neurotrophic factor (BDNF) upon methamphetamine (MA)-induced neurotoxicity of the nigrostriatal dopaminergic (NSDA) system were assessed. MA treatment produced a greater degree of NSDA neurotoxicity (indicated by greater reductions in corpus striatal dopamine levels) in wild type control BDNF male versus female mice. This sex difference was unaltered in heterozygous mutant BDNF (BDNF +/-) mice and in mice which overexpress BDNF (DBH:BDNF +). Both BDNF mutant conditions resulted in preservation of corpus striatal dopamine levels following MA treatment as compared with their respective MA-treated wild type controls. The relative amount of this preservation was greater in male BDNF mutants, with values being significantly greater than females in the BDNF +/- condition. These results suggest that alterations in BDNF do not alter basic gender differences in MA-induced NSDA neurotoxicity, but may produce a neuroprotection against MA which is relatively greater in males.

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

In the present experiment we evaluated the dose-response effects of estrogen (estradiol benzoate; EB) and tamoxifen (TMX) in modulating the acute behavioral and chronic effects of methamphetamine (MA) upon the nigrostriatal dopaminergic (NSDA) system in ovariectomized (OVX) mice. EB over a range of doses from 1-40 microg resulted in a neuroprotective effect upon the NSDA system as defined by both a preservation of striatal dopamine (DA) concentrations and a decrease in DOPAC/DA ratios. Interestingly, the neuroprotective effect of the 1-microg EB dose occurred in the absence of any statistically significant effect upon the bioassay parameter of uterine weight. With the exception of an increase in stereotypy time as a response to the 40-microg dose, EB at any of the doses tested failed to alter any acute behavioral responses evoked by MA. In response to TMX, a statistically significant NSDA neuroprotectant response was obtained for DOPAC/DA ratios, but not DA concentrations, to doses ranging from 12.5 to 500 microg. No statistically significant effects upon uterine weights were obtained for any of the doses of TMX tested. Behaviorally, TMX at 500 microg had the effect of increasing the amount of time spent in the center of the cage. Taken together these results demonstrate: (1) EB and TMX at relatively low doses can exert a neuroprotective effect against MA; (2) these neuroprotective effects of EB and TMX can occur in the absence of an effect upon the bioassay parameter--uterine weights; (3) the parameter of DOPAC/DA ratio may indicate a more sensitive index of NSDA neuroprotection, and (4) modulatory effects of EB and TMX upon acute behavioral responses of the NSDA system to MA can be distinguished from their neuroprotective actions.