Impact of circadian nuclear receptor REV-ERBα on midbrain dopamine production and mood regulation.

The circadian nature of mood and its dysfunction in affective disorders is well recognized, but the underlying molecular mechanisms are still unclear. Here, we show that the circadian nuclear receptor REV-ERBα, which is associated with bipolar disorder, impacts midbrain dopamine production and mood-related behavior in mice. Genetic deletion of the Rev-erbα gene or pharmacological inhibition of REV-ERBα activity in the ventral midbrain induced mania-like behavior in association with a central hyperdopaminergic state. Also, REV-ERBα repressed tyrosine hydroxylase (TH) gene transcription via competition with nuclear receptor-related 1 protein (NURR1), another nuclear receptor crucial for dopaminergic neuronal function, thereby driving circadian TH expression through a target-dependent antagonistic mechanism. In conclusion, we identified a molecular connection between the circadian timing system and mood regulation, suggesting that REV-ERBα could be targeting in the treatment of circadian rhythm-related affective disorders.

Methyl Yellow: A Potential Drug Scaffold for Parkinson's Disease.

Parkinson's disease (PD) is an age-related neurodegenerative disease affecting movement. To date, there are no currently available therapeutic agents which can prevent or slow disease progression. Here, we evaluated an azobenzene derivative, methyl yellow (MY), as a potential drug scaffold for PD; its inhibitory activity toward monoamine oxidase B (MAO-B) as well as drug-like properties were investigated. The inhibitory effect of MY on MAO activity was determined by a MAO enzyme inhibition assay. In addition, the in vitro properties of MY as a drug candidate (e.g., blood-brain barrier (BBB) permeability, serum albumin binding, drug efflux through P-glycoprotein (P-gp), drug metabolism by P450, and mitochondrial toxicity) were examined. In vivo effectiveness of MY was also evaluated in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) Parkinsonian mouse model. MY selectively inhibited MAO-B in a dose-dependent and reversible manner. MY was BBB-permeable, bound relatively weakly to serum albumin, was an unlikely substrate for both systems of P-gp and P450, and did not cause mitochondrial toxicity. Results from the MPTP Parkinsonian mouse model indicated that, upon treatment with MY, neurotoxicity induced by MPTP was mitigated. Investigations of MY demonstrate its inhibitory activity toward MAO-B, compliant properties for drug consideration, and its neuroprotective capability in the MPTP Parkinsonian mouse model. These data provide insights into potential use, optimization, and new design of azobenzene derivatives for PD treatment.

Signaling pathways mediating the neuroprotective effects of sex steroids and SERMs in Parkinson's disease.

Studies with the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of Parkinson's disease have shown the ability of 17ß-estradiol to protect the nigrostriatal dopaminergic system. This paper reviews the signaling pathways mediating the neuroprotective effect of 17ß-estradiol against MPTP-induced toxicity. The mechanisms of 17ß-estradiol action implicate activation of signaling pathways such as the phosphatidylinositol-3 kinase/Akt and the mitogen-activated protein kinase pathways. 17ß-estradiol signaling is complex and integrates multiple interactions with signaling molecules that act to potentiate a protective effect. 17ß-estradiol signaling is mediated via estrogen receptors, including GPER1, but others receptors, such as the IGF-1 receptor, are implicated in the neuroprotective effect. Glial and neuronal crosstalk is a critical factor in the maintenance of dopamine neuronal survival and in the neuroprotective action of 17ß-estradiol. Compounds that stimulate GPER1 such as selective estrogen receptor modulators and phytoestrogens show neuroprotective activity and are alternatives to 17ß-estradiol.

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.

Structure-activity relationship and docking studies of thiazolidinedione-type compounds with monoamine oxidase B.

The neuroprotective activity of pioglitazone and rosiglitazone in the MPTP parkinsonian mouse prompted us to evaluate a set of thiazolidinedione (TZD) type compounds for monoamine oxidase A and B inhibition activity. These compounds were able to inhibit MAO-B over several log units of magnitude (82 nM to 600 µM). Initial structure-activity relationship studies identified key areas to modify the aromatic substituted TZD compounds. Primarily, substitutions on the aromatic group and the TZD nitrogen were key areas where activity was enhanced within this group of compounds.

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.

Testosterone enhances dopamine depletion by methamphetamine in male, but not female, mice.

We examined the effects of varying concentrations of testosterone propionate (T) treatment within intact and gonadectomized male and female mice with regard to its capacity to alter striatal dopamine (DA) depletion in response to a neurotoxic regimen of methamphetamine (MA). Administration of T at 24h prior to MA significantly increased striatal DA depletion in intact and gonadectomized male mice. Similar treatments administered to intact and gonadectomized female mice failed to alter striatal DA concentrations in response to MA. These results demonstrate that T can enhance MA-induced neurotoxicity in male, but not in female, mice. Such findings have important implications with regard to sex differences in nigrostriatal dopaminergic function, in general, and, in specific, to sex differences related to nigrostriatal dopaminergic neurotoxicity and neurodegeneration like that in response to MA and in Parkinson's disease, where a greater incidence is typically reported for males.

Gender differences in methamphetamine use and responses: a review.

BACKGROUND: Men and women differ markedly with regard to their use of, and responses to, methamphetamine (MA) and related amphetamines. However, these gender differences oftentimes are given only a cursory consideration in the analyses of these MA effects. OBJECTIVE: In this brief review, we summarize the data on gender differences in various parameters of MA use and responses. Such information on the pattern of male versus female differences in the use and responses to this psychostimulant can aid in tailoring gender-dependent treatment strategies. METHODS: English-language articles were identified from MEDLINE as well as from reference lists of identified articles for the years 1966 to 2007. Search terms included various combinations of men/male, women/female, methamphetamine, and gender/sex differences. Only studies with human subjects were reviewed. RESULTS: Women tend to begin MA use at earlier ages, appear more dependent on MA, but also respond better to treatment than do men. MA use appears to be associated with depression in women, and women seem more committed to MA, whereas men are more likely to use other drugs in the absence of access to MA. Female MA abusers had both larger volumes within the corpus callosum and more hyperperfused regions in the parietal and occipital areas of the brain, along with more genetic alterations but less MA-induced toxicity. Amphetamine-stimulated dopamine release was greater in men. CONCLUSIONS: When considered in total, women seem more dependent on and committed to MA but show diminished (amphetamine-stimulated) dopamine responses and a decreased degree of toxicity, as indicated by a lower incidence of emergency department-related deaths involving MA. A pervasive comorbidity of depression or depression-related characteristics were present in women MA users, suggesting that MA may serve as a type of self-medication for their depression. These findings not only highlight the need for consideration of gender when assessing MA use, but also can serve to direct efforts at prevention and treatment programs that address the specific needs of men and women.

Estrogen prevents neuroprotection by caffeine in the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson's disease.

Epidemiological studies have strongly linked caffeine consumption with a reduced risk of developing Parkinson's disease (PD) in men. Interestingly, in women, this inverse association is present only in those who have not taken postmenopausal estrogens, suggesting an interaction between the influences of estrogen and caffeine use on the risk of PD. To explore a possible biological basis for this interaction, we systematically investigated how the neuroprotective effect of caffeine is influenced by gender, ovariectomy (OVX), and then exogenous estrogen in the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD. (1) Caffeine treatment produced a dose-dependent attenuation of MPTP-induced striatal dopamine loss in both young and retired breeder (RB) male, but not female, mice. (2) In female mice (both young and RB), caffeine was less potent or altogether ineffective as a neuroprotectant after sham surgery compared to OVX or after OVX plus estrogen replacement compared to OVX plus placebo treatment. (3) Estrogen treatment also prevented the protection of caffeine against dopamine loss in young male mice. (4) Consistent with the putative protective effect of estrogen, female and OVX plus estrogen mice were relatively resistant to MPTP toxicity compared to male and OVX plus placebo mice, respectively. (5) There was no overall difference in brain levels of caffeine and its metabolites between OVX plus placebo and OVX plus estrogen mice. Together, these results suggest that estrogen can occlude and thereby prevent the neuroprotective effect of caffeine in a model of PD neurodegeneration, supporting a biological basis for the interaction between estrogen and caffeine in modifying the risk of PD.

Tamoxifen protects male mice nigrostriatal dopamine against methamphetamine-induced toxicity.

The selective estrogen receptor modulator tamoxifen and estradiol were shown to protect nigrostriatal dopamine concentration loss by methamphetamine in female mice whereas male mice were protected only by tamoxifen. The present study examined the protective properties of tamoxifen in male mice on several nigrostriatal dopaminergic markers and body temperature. Intact male mice were administered 12.5 or 50 microg tamoxifen 24 h before methamphetamine treatment. Basal body temperatures of male mice remained unchanged by the tamoxifen treatment. Methamphetamine reduced striatal dopamine and its metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid concentrations, striatal and substantia nigra dopamine and vesicular monoamine transporter specific binding as well substantia nigra dopamine and vesicular monoamine transporter mRNA levels and increased striatal preproenkephalin mRNA levels. These methamphetamine effects were not altered by 12.5 microg tamoxifen except for increased striatal dopamine metabolites and turnover. Tamoxifen at 50 microg reduced the methamphetamine effect on striatal dopamine concentration, dopamine transporter specific binding and prevented the increase in preproenkephalin mRNA levels; in the substantia nigra tamoxifen prevented the decrease of dopamine transporter mRNA levels. The present results show a tamoxifen dose-dependent prevention of loss of various dopaminergic markers against methamphetamine-induced toxicity in male mice. Since this is the only known hormonal protection of male mice against methamphetamine toxicity, these findings provide important new information on specific parameters of nigrostriatal dopaminergic function preserved by tamoxifen.

Gender differences in Parkinson's disease.

OBJECTIVE: To investigate gender differences in basic disease characteristics, motor deterioration and nigrostriatal degeneration in Parkinson's disease (PD). METHODS: We studied 253 consecutive PD patients who were not receiving levodopa or dopamine agonists (disease duration < or = 10 years). We investigated the influence of gender and oestrogen status on: (1) age at onset, (2) presenting symptom, (3) severity and progression of motor symptoms (Unified Parkinson's Disease Rating Scale III (UPDRS-III) scores) and (4) amount and progression of nigrostriatal degeneration ([123I]FP-CIT single photon emission computed tomography measurements). RESULTS: Age at onset was 2.1 years later in women (53.4 years) than in men (51.3 years). In women, age at onset correlated positively with parity, age at menopause and fertile life span. Women more often presented with tremor (67%) than men (48%). Overall, patients presenting with tremor had a 3.6 year higher age at onset and a 38% slower UPDRS-III deterioration. Mean UPDRS-III scores at disease onset were equal for both genders, as was the rate of deterioration. Women had a 16% higher striatal [123I]FP-CIT binding than men at symptom onset and throughout the course of PD. CONCLUSIONS: Our results suggest that, in women, the development of symptomatic PD may be delayed by higher physiological striatal dopamine levels, possibly due to the activity of oestrogens. This could explain the epidemiological observations of a lower incidence and higher age at onset in women. Women also presented more often with tremor which, in turn, is associated with milder motor deterioration and striatal degeneration. Taken together, these findings suggest a more benign phenotype in women with PD.

Protective effects of ginsenoside Rg2 against glutamate-induced neurotoxicity in PC12 cells.

We investigated the effect of ginsenoside Rg2 on neurotoxic activities induced by glutamate in PC12 cells. The cells were incubated with glutamate (1 mmol/L), glutamate and ginsenoside Rg2 (0.05, 0.1, 0.2 mmol/L) or nimodipine (5 micromol/L) for 24 h. The cellular viability was assessed by MTT assay. The lipid peroxidation products malondialdehyde (MDA) and nitrogen oxide (NO) were measured by a spectrophotometric method. Fura-2/AM, as a cell permeable fluorescent probe for Ca2+, was used to detect intracellular Ca2+ concentration ([Ca2+]i) using a monespectrofluorometer. Immunocytochemical techniques were employed to check the protein expression levels of calpain II, caspase-3 and beta-amyloid (Abeta)1-40 in PC12 cells. The results showed that glutamate decreased the cell viability, increased [Ca2+]i, lipid peroxidation (the excessive production of MDA, NO) and the protein expression levels of calpain II, caspase-3 and Abeta1-40 in PC12 cells. Ginsenoside Rg2 significantly attenuated glutamate-induced neurotoxic effects upon these parameters at all doses tested. Our study suggests that ginsenoside Rg2 has a neuroprotective effect against glutamate-induced neurotoxicity through mechanisms related to anti-oxidation and anti-apoptosis. In addition, the inhibitory effect of ginsenoside Rg2 against the formation of Abeta1-40 suggests that ginsenoside Rg2 may also represent a potential treatment strategy for Alzheimer's disease.

Unconventional effects of estrogen uncovered.

The nigrostriatal dopamine system shows marked gender differences that, in many cases, can be attributable to estrogen. However, the virtual absence of conventional estrogen receptors within the nigrostriatal dopamine system has made it difficult to understand how estrogen can function within this system. Recent findings have helped to uncover how estrogen can affect a discrete function of striatal dopamine-containing neurons--transporter activity--in a manner similar to that achieved through alterations in dopamine D(2) receptors and their associated G protein. These findings suggest that the effects of estrogen on dopamine transporter function could result from a signal transduction interaction involving D(2) receptor-G protein coupling.

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.

Rotenone produces opposite effects upon mouse striatal dopamine function as a result of environmental temperature.

Rotenone is a commonly used pesticide that can function as an environmental neurotoxin. Rotenone is a known mitochondrial complex I inhibitor which can lead to oxidative stress and results in dopaminergic cell death. Another environmental factor known to exacerbate oxidative stress and result in striatal dopaminergic cell death is elevated environmental temperature. In this study we evaluated the effects of a single injection of various doses of rotenone (0.65, 1.3 and 2.6 mg/kg) on striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations in CD-1 mice and compared this with a single injection of two doses of methamphetamine (MA - 10 or 20 mg/kg), a known striatal DA depleting agent, as administered to mice maintained at 21 degrees C (Experiment 1). These results were then compared to striatal DA and DOPAC concentrations of mice treated with rotenone (1.3 or 2.6 mg/kg) or MA (10 or 20 mg/kg) administered to mice maintained at 28 degrees C (Experiment 2). A single injection of rotenone to mice maintained at 21 degrees C resulted in a significant increase in DA and decrease in DOPAC concentrations for all doses tested compared to controls, whereas a single injection of MA at the same temperature resulted in a significant decrease in DA and no change in DOPAC concentrations. At a temperature of 28 degrees C, a single injection of rotenone resulted in a significant decrease in both DA and DOPAC concentrations similar to that seen with the MA-treated mice. Collectively, these results indicate that rotenone interacts with environmental temperature to produce opposite effects upon striatal DA concentrations -- significantly increasing striatal DA when administered at 21 degrees C and significantly decreasing striatal DA when administered at 28 degrees C, while producing similar decreases in striatal DOPAC under both temperatures.

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.

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.

Gender differences in modulatory effects of tamoxifen upon the nigrostriatal dopaminergic system.

It has been demonstrated that the gonadal steroid hormone estrogen can exert neuroprotective effects upon the nigrostriatal dopaminergic (NSDA) system against methamphetamine (MA)-induced neurotoxicity in female, but not male, mice. In contrast, the anti-estrogen, tamoxifen (TMX) can function as a NSDA neuroprotectant within both female and male mice. In an attempt to understand these effects of TMX, the effects of this anti-estrogen upon both behavioral and neurochemical indices of NSDA function were examined within female and male mice following treatment with MA. In general, TMX exerted markedly different (bi-directional) effects upon NSDA function between female and male mice. Notably, treatment with TMX resulted in a relative decrease in striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations within male mice and a relative increase in female mice when treated with MA to produce a significant gender difference. Similar effects were obtained for locomotor behaviors related with NSDA function. That is, TMX produced increases in horizontal activity, number of movements and total distance traveled within MA-treated female mice resulting in statistically significant gender differences for the two former parameters. For non-locomotor behaviors, like time occupying the center and margin of the cage, TMX-treated male mice showed statistically significant increases and decreases compared within TMX-treated female mice, respectively. These results show that in contrast to the similar neuroprotective effects of TMX upon MA-induced NSDA neurotoxicity, a number of other NSDA indices induced by MA show markedly different response profiles between TMX-treated female and male mice.

A novel biomechanical analysis of gait changes in the MPTP mouse model of Parkinson's disease.

Parkinson's disease (PD) is an age-associated neurodegenerative disorder hallmarked by a loss of mesencephalic dopaminergic neurons. Accurate recapitulation of the PD movement phenotype in animal models of the disease is critical for understanding disease etiology and developing novel therapeutic treatments. However, most existing behavioral assays currently applied to such animal models fail to adequately detect and subsequently quantify the subtle changes associated with the progressive stages of PD. In this study, we used a video-based analysis system to develop and validate a novel protocol for tracking locomotor performance in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. We anticipated that (1) treated mice should use slower, shorter, and less frequent strides and (2) that gait deficits should monotonically increase following MPTP administration, as the effects of neurodegeneration become manifest. Video-based biomechanical analyses, utilizing behavioral measures motivated by the comparative biomechanics literature, were used to quantify gait dynamics over a seven-day period following MPTP treatment. Analyses revealed shuffling behaviors consistent with the gait symptoms of advanced PD in humans. Here we also document dramatic gender-based differences in locomotor performance during the progression of the MPTP-induced lesion, despite male and female mice showing similar losses of striatal dopaminergic cells following MPTP administration. Whereas female mice appeared to be protected against gait deficits, males showed multiple changes in gait kinematics, consistent with the loss of locomotor agility and stability. Overall, these data show that the novel video analysis protocol presented here is a robust method capable of detecting subtle changes in gait biomechanics in a mouse model of PD. Our findings indicate that this method is a useful means by which to easily and economically screen preclinical therapeutic compounds for protecting against or reversing neuropathology associated with PD neurodegeneration.

Modulation of olfactory bulb tyrosine hydroxylase and catecholamine transporter mRNA by estrogen.

Since estrogen exerts wide ranging effects within the central nervous system, it is important to investigate the sites and actions of this gonadal steroid hormone at extra-hypothalamic locations. In the present report, the effects of estrogen upon catecholaminergic function within the olfactory bulb were examined. To assess the role of estrogen at this site, ovariectomized mice received either no further hormonal treatment or were treated with estrogen, the anti-estrogen, tamoxifen, or a combination of estrogen and tamoxifen as administered in a 21-day release pellet. At 14 days post-hormonal treatment, the olfactory bulbs were assayed for mRNA levels of tyrosine hydroxylase, dopamine transporter and norepinephrine transporter using competitive-PCR. Tyrosine hydroxylase mRNA levels in either estrogen or estrogen+tamoxifen treated females were significantly decreased compared with non-hormonally treated controls. In addition, tyrosine hydroxylase mRNA levels of tamoxifen-treated mice were significantly greater than that of estrogen-treated mice. Dopamine transporter mRNA levels of tamoxifen-treated females were significantly greater than that of non-hormonally treated controls and estrogen treated mice. The combination of estrogen+tamoxifen significantly increased dopamine transporter mRNA levels compared to that of estrogen treated mice. No overall statistically significant differences in norepinephrine transporter mRNA levels were obtained among the four treatment groups. The data demonstrate that estrogen can exert significant modulatory effects upon olfactory bulb catecholaminergic function. Therefore, events which alter estrogen levels (menstrual/estrogen cycle, pregnancy/lactation, menopause, tamoxifen treatment) can modulate olfactory bulb catecholaminergic functions which may be involved with the detection and processing of olfactory stimuli.