Elevation of striatal dopamine receptors by estrogen: dose and time studies

The impact of biological clock and sex hormones on the risk of disease

Molecular clocks are responsible for defining 24-h cycles of behaviour and physiology that are called circadian rhythms. Several structures and tissues are responsible for generating these circadian rhythms and are named circadian clocks. The suprachiasmatic nucleus of the hypothalamus is believed to be the master circadian clock receiving light input via the optic nerve and aligning internal rhythms with environmental cues. Studies using both in vivo and in vitro methodologies have reported the relationship between the molecular clock and sex hormones. The circadian system is directly responsible for controlling the synthesis of sex hormones and this synthesis varies according to the time of day and phase of the estrous cycle. Sex hormones also directly interact with the circadian system to regulate circadian gene expression, adjust biological processes, and even adjust their own synthesis. Several diseases have been linked with alterations in either the sex hormone background or the molecular clock. So, in this chapter we aim to summarize the current understanding of the relationship between the circadian system and sex hormones and their combined role in the onset of several related diseases.

Differential effects of chronic adolescent glucocorticoid or methamphetamine on drug-induced locomotor hyperactivity and disruption of prepulse inhibition in adulthood in mice

Sensitization of dopaminergic activity has been suggested as an underlying mechanism in the psychotic symptoms of schizophrenia. Adolescent stress and chronic abuse of methamphetamine (Meth) are well-known risk factors for psychosis and schizophrenia; however it remains unknown how these factors compare in terms of dopaminergic behavioural sensitization in adulthood. In addition, while Brain-Derived Neurotrophic Factor (BDNF) has been implicated in dopaminergic activity and schizophrenia, its role in behavioural sensitization remains unclear. In this study we therefore compared the effect of chronic adolescent treatment with the stress hormone, corticosterone (Cort), or with Meth, on drug-induced locomotor hyperactivity and disruption of prepulse inhibition in adulthood in BDNF heterozygous mice and their wild-type controls, as well as on dopamine receptor gene expression. Between 6 and 9 weeks of age, the animals either received Cort in the drinking water or were treated with an escalating Meth dose protocol. In adulthood, Cort-pretreated mice showed significantly reduced Meth-induced locomotor hyperactivity compared to vehicle-pretreated mice. In contrast, Meth hyperlocomotion was significantly enhanced in animals pretreated with the drug in adolescence. There were no effects of either pretreatment on prepulse inhibition. BDNF Het mice showed greater Meth-induced hyperlocomotion and lower prepulse inhibition than WT mice. There were no effects of either pretreatment on D1 or D2 gene expression in either the dorsal or ventral striatum, while D3 mRNA was shown to be reduced in male mice only irrespective of genotype. These results suggest that in adolescence, chronically elevated glucocorticoid levels, a component of chronic stress, do not cause dopaminergic sensitization adulthood, in contrast to the effect of chronic Meth treatment in the same age period. BDNF does not appear to be involved in the effects of chronic Cort or chronic Meth.

The therapeutic effect of bromocriptine as mesylate and estradiol valerate on serum and blood biochemistry of common quails

Hematology and serum biochemistry study may provide antique knowledge about the physical status of individuals, making them a valuable tool to differentiate healthy animals from affected animals. We aimed to investigate Steroid safety levels in birds through ex-situ studies at regular therapeutic doses. A total of 100 birds were used for hematology and serum biochemistry. This study was designed into 2 trials over the summer and winter, each comprised 5, 10, 15, and 20 d. Each study group was based on 5 control group birds and 20 experimental group birds. A sum of 2 groups representing 2 different steroids trial groups was treated with therapeutic doses to the stretch of 5, 10, 15, and 20 d each season. A therapeutic dose of each of the steroids was given at the rate of 3 drops 2 times a day to each bird. Analysis of data reveals that steroids had severe effects on bird's (Coturnix coturnix) hematological parameters. In most trials, the hematological effects of bromocriptine as mesylate showed an increase in red blood cell count and white blood cell count. On the other hand, steroid estradiol valerate showed a decrease in these parameters. Effect of steroids on serum biochemistry profile indicate acute damage to vital organs, especially to liver and kidney, indicating an increase in cholesterol, total protein, albumin, urea, and uric acid. The overall effect of steroids on the bird's serum and biochemistry of quails were nearly similar but different only in their intensity.

Striatal dopamine D2-type receptor availability and peripheral 17β-estradiol

Research using rodent models has established a relationship between the steroid hormone estrogen and dopamine function, by revealing changes throughout the estrous cycle and by directly manipulating neuroendocrine signaling through ovariectomy and administration of estrogen. However, a direct link between estrogen levels and dopamine signaling had not been established in humans. The goal of this study, therefore, was to assess the relationship between circulating 17β-estradiol and dopamine signaling in the human brain by testing for a relationship between two proxies for these variables: peripheral 17β-estradiol and striatal dopamine D₂-type receptor availability, measured with [¹⁸F]fallypride and positron emission tomography (PET). Sixteen (23-45 years of age) women were tested on 2 days of the menstrual cycle estimated prospectively to occur during (a) the early follicular phase, when estrogen levels are near their nadir, and (b) the periovulatory phase, when estrogen levels peak. PET scans with [¹⁸F]fallypride were performed on these 2 days, and serum 17β-estradiol was measured using radioimmunoassay. Dopamine D₂-type receptor availability did not differ significantly in the whole striatum or the caudate, putamen, or accumbens subregions during the high-estrogen vs. the low-estrogen phases of the menstrual cycle. We conclude that circulating estrogen levels do not affect dopamine D₂-type receptor availability in the human striatum although other indices of dopaminergic function may be affected.

Female Reproductive Behavior

Reproductive behavior is the behavior related to the production of offspring and includes all aspects from the establishment of mating systems, courtship, sexual behavior, and parturition to the care of young. In this chapter, I outline the hormonal regulation of the estrous cycle, followed by a description of the neural regulation of female sexual behavior. Ovarian hormones play an important role in the induction of ovulation and behavioral estrus, in which they interact closely with several neurotransmitters and neuropeptides to induce sexual behavior. This chapter discusses the latest research on the role of estrogen, progesterone, serotonin, dopamine, noradrenaline, oxytocin, and GABA in female mating behavior. In addition, the most relevant brain areas, such as the preoptic area and the ventromedial nucleus of the hypothalamus, in which these regulations take place, are discussed.

Ovarian steroids alter dopamine receptor populations in the medial preoptic area of female rats: implications for sexual motivation, desire, and behaviour

Dopamine (DA) transmission in the medial preoptic area (mPOA) plays a critical role in the control of appetitive sexual behaviour in the female rat. We have shown previously that a DA D1 receptor (D1R)-mediated excitatory state appears to occur in females primed with estradiol benzoate (EB) and progesterone (P), whereas a DA D2 receptor (D2R)-mediated inhibitory state appears to occur in females primed only with EB. The present experiment employed three techniques to better understand what changes occur to DA receptors (DARs) in the mPOA under different hormonal profiles. Ovariectomized females were randomly assigned to one of three steroid treatment groups: EB + P (10 and 500 μg, respectively), EB + Oil, or the control (Oil + Oil), with hormone injections administered at 48 and 4 h prior to euthanizing. First, the number of neurons in the mPOA that contained D1R or D2R was assessed using immunohistochemistry. Second, the mPOA and two control areas (the prelimbic cortex and caudate putamen) were analysed for DAR protein levels using western blot, and DAR functional binding levels using autoradiography. Ovarian steroid hormones affected the two DAR subtypes in opposite ways in the mPOA. All three techniques supported previous behavioural findings that females primed with EB have a lower D1R : D2R ratio, and thus a D2R-mediated system, and females primed with EB + P have a higher D1R : D2R ratio, and thus a D1R-mediated system. This provides strong evidence for a DA-driven pathway of female sexual motivation, desire, and behaviour that is modified by different hormone priming regimens.

Effects of SCH-23390 in combination with a low dose of 17β-estradiol on anxiety-like behavior in ovariectomized rats

The aim of this study was to explore effects on anxiety-like behavior of D₁ dopamine receptor agonist, SKF-38393, and of D₁ dopamine receptor antagonist, SCH-23390, given alone or in combination with a low dose of 17β-estradiol (17β-E₂) to ovariectomized (OVX) rats. Two weeks after surgery, OVX rats began 14 days of treatment with the vehicle, a low dose of 17β-E₂ (5.0 μg/rat, s.c.), SKF-38393 (0.1 mg/kg, i.p.), SCH-23390 (0.1 mg/kg, i.p.), SKF-38393 plus 17β-E₂, or SCH-23390 plus 17β-E₂. The animals were tested in the black and white model (BWM) and the open field test (OFT). SCH-23390 (0.1 mg/kg, i.p.) alone or in a combination with a low dose of 17β-E₂ (5.0 μg/rat, s.c.) resulted in anxiolytic-like effect in OVX rats in the BWM. Repeated treatment with SCH-23390 and 17β-E₂ profoundly increased anxiolytic-like effect of single substances exerted per se. Coadministration of SCH-23390 with 17β-E₂ increased frequency of rearing and grooming in OVX rats in OFT. SKF-38393 (0.1 mg/kg, i.p.) treatment failed to alter anxiety-like behavior in OVX rats in the BWM. The results of the present study suggest that 17β-E₂ and SCH-23390 interact to exert anxiolytic-like action and that each of these drugs can potentiate effects of each other.

Reproductive experience does not persistently alter prefrontal cortical-dependent learning but does alter strategy use dependent on estrous phase

Reproductive experiences in females comprise substantial hormonal and experiential changes and can exert long lasting changes in cognitive function, stress physiology, and brain plasticity. The goal of this research was to determine whether prior reproductive experience could alter a prefrontal-cortical dependent form of learning (strategy set shifting) in an operant box. In this study, female Sprague-Dawley rats were mated and mothered once or twice to produce either primiparous or biparous dams, respectively. Age-matched nulliparous controls (reproductively-naïve females with no exposure to pup cues) were also used. Maternal behaviors were also assessed to determine whether these factors would predict cognitive flexibility. For strategy set shifting, rats were trained in a visual-cue discrimination task on the first day and on the following day, were required to switch to a response strategy to obtain a reward. We also investigated a simpler form of behavioral flexibility (reversal learning) in which rats were trained to press a lever on one side of the box the first day, and on the following day, were required to press the opposite lever to obtain a reward. Estrous phase was determined daily after testing. Neither parity nor estrous phase altered total errors or trials to reach criterion in either the set-shifting or reversal-learning tasks, suggesting that PFC-dependent cognitive performance remains largely stable after 1 or 2 reproductive experiences. However, parity and estrous phase interacted to alter the frequency of particular error types, with biparous rats in estrus committing more perseverative but fewer regressive errors during the set-shifting task. This suggests that parity and estrous phase interfere with the ability to disengage from a previously used, but no longer relevant strategy. These data also suggest that parity alters the behavioral sensitivity to ovarian hormones without changing overall performance.

Immunology and the menstrual cycle

Sex and gender differences in disease prevalence, pathogenesis and modulation have been frequently reported. The menstrual cycle represents the opportunity to study the physiological effect of hormonal fluctuations in vivo on the immune function and chronic disease modulation. Reports on the effect of the cycle on immune cell numbers and activity fluctuations are scarce, but recent publications demonstrate an increasing interest in the subject. The menstrual cycle might affect immune cell numbers and modulate their activity throughout the 4-week cycle, as demonstrated in the case of regulatory T cells. The implications of these fluctuations are particularly relevant in the field of chronic diseases affecting women of reproductive age. In fact, baseline inflammation and immune cell activation in association with other mechanisms, such as regulation of receptor expression, modulation of muscular contraction and behavioral aspects might explain the menstrual-associated fluctuations described in chronic and acute diseases. In the following review the current knowledge about the modulatory effects of the menstrual cycle on both immune cells and systemic diseases, such as autoimmune diseases, asthma, diabetes, cardiac arrhythmia and schizophrenia, is reported. Most of these diseases display worsening of symptoms premenstrually or during menses due to physiologic effects on the target tissue mediated by progesterone and estrogen fluctuations and, thus, display paradigmatic changes potentially relevant to numerous other conditions.

Acquisition of cocaine self-administration in ovariectomized female rats: effect of estradiol dose or chronic estradiol administration

This study was conducted to investigate whether the dose of estradiol (E) administered acutely, or chronic delivery of one dose of E impacts acquisition and subsequent cocaine self-administration in ovariectomized (OVX) female rats. Five groups of female rats were compared: OVX females treated with 0, 1, 2, or 5 microg 17beta-E, 30 min prior to the self-administration session, and OVX rats that received a 1.5mg E pellet (designed to chronically release 25 microg E/day X 60 days) implanted 1 week before cocaine self-administration initiation. Rats were tested in 1h sessions on a FR1 schedule with the dose of cocaine increasing every week (testing occurred 5 day/week; doses: 0.2, 0.3, 0.4, 0.5 and 0.75 mg/(kg infusion)). We report that OVX rats treated with 2 microg E acquired self-administration more rapidly than all of the other groups, and animals that received 1 or 2 microg E self-administered significantly more cocaine compared to OVX+vehicle at 0.3 and 0.4 mg/(kg infusion). In contrast, OVX rats given 5 microg E acutely, or chronic E via slow-release pellets did not take more cocaine than the OVX+vehicle group at any time point. Physiological serum concentrations of E were seen with 1 or 2 microg E, but 5 microg E and the E pellet produced supra-physiological concentrations. These results suggest an inverted U-shaped dose-response curve for the effect of E on acquisition of cocaine self-administration.

Gonadal steroids mediate the opposite changes in cocaine-induced locomotion across adolescence in male and female rats

Evidence from both human studies and animal models indicates that cocaine elicits more behavioral stimulation in females than males. The present study sought to determine whether sex-specific responses to cocaine emerge during adolescence and to determine if gonadal steroid action during puberty affects adult responsiveness to cocaine. We administered cocaine using an escalating dose model in male and female rats at ages postnatal (PN) 28, 42, and 65 days. To assess the effects of pubertal gonadal steroid action, we compared the effects of binge cocaine administration on intact and prepubertally gonadectomized male and female rats in adulthood. Cocaine responses changed in opposite directions in males and females as they progressed through adolescence. At most doses, adolescent males were more responsive than adult males whereas adult females were more responsive than adolescent females. Ambulatory activity was age-dependent in males whereas non-ambulatory activity was age-dependent in females. Prepubertal gonadectomy increased behavioral responsiveness to the highest dose of cocaine in males whereas it decreased behavioral responsiveness to lower doses of cocaine in females. We conclude that sex differences in behavioral responses to cocaine arise during adolescence from a concurrent decrease in male responsiveness and increase in female responsiveness. Our results suggest that gonadal steroids exert lasting and opposing effects on the sensitivity of males and females to psychostimulants during development.

Neonatal immune system activation with lipopolysaccharide enhances behavioural sensitization to the dopamine agonist, quinpirole, in adult female but not male rats

Administration of the bacterial cell wall component, lipopolysaccharide (LPS), stimulates the immune and endocrine systems inducing an acute phase of sickness and stress responses in adult and neonatal rats. Neonatal LPS exposure has been shown to alter a variety of behavioural and physiological processes in the adult animal. Early developmental stress, such as maternal separation, causes similar acute as well as long-term behavioural changes in adults, including altered sensitivity to drugs of abuse. Moreover, results of studies have shown evidence of a direct link between immune activation and sensitivity to dopamine-based drugs of abuse. The current study examined the effects of neonatal LPS treatment on subsequent locomotor sensitization to the dopamine (D(2)/D(3)) agonist, quinpirole, in adult rats as an index of drug sensitivity. Male and female Long-Evans rats were treated systemically with either LPS (50microg/kg) or saline (0.9%) on postnatal days 3 and 5. Locomotor sensitization was then examined in the adult rats (postnatal day 70). Animals were injected with quinpirole (0.5mg/kg, s.c.) or saline every other day for a total of 10 injections and locomotor activity was assessed for 60min immediately following injections 1, 2, 4, 6, and 10. Animals also received a 'challenge' injection of 0.5mg/kg quinpirole 28 days after injection 10, to assess persistence of behavioural sensitization. Locomotor activity progressively increased with repeated administration of quinpirole, indicating locomotor sensitization in all of the drug-treated groups. There was an overall sex difference, with females showing significantly greater sensitization than males. Moreover, neonatal LPS treatment potentiated both the level and the rate of development of locomotor sensitization to quinpirole administration in females, but not in males. Thus, the current study revealed that neonatal exposure to bacterial infection increases dopamine (D(2)/D(3)) agonist sensitivity in a sex-specific manner. These findings have important implications for the sexually dimorphic development of addictions to both natural and artificial rewards.

Evidence for the involvement of ERbeta and RGS9-2 in 17-beta estradiol enhancement of amphetamine-induced place preference behavior

Estrogen enhances dopamine-mediated behaviors, which make women and female rats more sensitive to the effects of the psychostimulant drugs, cocaine and amphetamine. How cocaine and amphetamine elicit more robust behavioral responses in females remains unclear, but studies have shown that the Regulator of G-protein Signaling 9-2 (RGS9-2) protein is an important modulator of the behavioral responses to these drugs. Previously, we reported that 17-beta estradiol reduced RGS9-2 mRNA expression in the shell of the nucleus accumbens, but not the core. The present studies were designed to further evaluate the involvement of RGS9-2 in estradiol enhancement of amphetamine-induced place preference behavior and to examine which estrogen receptor subtype mediates the effect of estradiol. Female Sprague-Dawley rats were ovariectomized and treated for 14 days with an inert vehicle or 17-beta estradiol (by Silastic implant or injection [80 microg/kg]). 17-beta-Estradiol-treated female rats had enhanced amphetamine-induced conditioned place preference behavior compared to vehicle-treated, ovariectomized female rats. In situ hybridization histochemistry and Western blotting identified an inverse relationship between RGS9-2 protein expression in the nucleus accumbens shell and the hormonal enhancement of amphetamine-induced place preference behavior. A similar relationship was not found between place preference behavior and RGS9-2 expression in the accumbens core. Moreover, treatment of ovariectomized female rats with the selective estrogen receptor-beta agonist, diarylpropionitrile (1 mg/kg), for 2 weeks also facilitated amphetamine-induced place preference behavior and selectively reduced nucleus accumbens shell RGS9-2 protein expression. These data provide insight into a potential mechanism by which estrogen and/or sex modulate mesoaccumbal dopamine receptor signaling and possibly, addictive behaviors.

Estrous cycle-dependent changes in basal and ethanol-induced activity of cortical dopaminergic neurons in the rat

The influence of the estrous cycle on dopamine levels in the rat medial prefrontal cortex under basal and ethanol-stimulated conditions was evaluated by microdialysis. The basal dopamine concentration in the dialysate varied markedly during the estrous cycle, being highest in estrus and lowest in proestrus. Furthermore, a challenge intraperitoneal administration of ethanol (0.5 g/kg) induced a significant increase in dopaminergic output (+50%) during estrus but had no effect in diestrus or proestrus. Ovariectomy or pretreatment with either finasteride (a 5alpha-reductase inhibitor) or clomiphene (an estrogen receptor antagonist) prevented this ethanol-induced increase in dopamine concentration. The effect of ethanol was restored in ovariectomized rats by pretreatment with estrogen but not by that with progesterone. Our results thus show that the basal levels of dopamine in the prefrontal cortex are dependent on the phase of the estrous cycle. Furthermore, this dependence appears to be attributable to the effects of ovarian steroid hormones and results in a differential sensitivity of the dopaminergic neurons to ethanol. The hormone-induced changes in the activity of these neurons might contribute to the differences in drug sensitivity and mood state apparent among phases of the estrous cycle and between the sexes.

Administration of estrogen to ovariectomized rats promotes conditioned place preference and produces moderate levels of estrogen in the nucleus accumbens

Estrogen (E2) can modulate a variety of functional processes, including conditioning. However, the precise relationship between E2 and these processes is not entirely understood. Indeed, the nature of E2's effects on conditioning may depend upon several factors, including, but not limited to, the task examined, route of E2 administration, bioavailability of E2 administered, and/or duration of E2 exposure. The present studies examined the effects of E2 on conditioned place preference (CPP), and E2 levels produced in plasma and the nucleus accumbens. In Experiment 1, ovariectomized, Long-Evans rats were subcutaneously (SC) administered sesame oil vehicle (n = 12), 10 microg (n = 12), or 1 mg (n = 10), E2 immediately prior to placement in the CPP apparatus on conditioning days. Only rats administered 10 microg E2 exhibited a CPP. This regimen of E2 (n = 5/group) also produced moderate levels of E2 in the nucleus accumbens (significantly greater than vehicle and less than 1 mg E2). In Experiment 2, ovariectomized rats were SC administered propylene glycol vehicle (n = 11), 10 microg (n = 13), or 1 mg (n = 14), E2 immediately prior to conditioning. Administration of 1 mg E2 in propylene glycol produced a CPP. Notably, 1 mg E2 in propylene glycol produced moderate levels of E2 in the nucleus accumbens (significantly greater than vehicle or 10 microg E2) that were similar to those produced by 10 microg E2 in sesame oil (n = 5/group). Together, these data suggest that regimen of E2 that can produce a CPP result in moderate levels of E2 in the nucleus accumbens.

Effect of short- vs. long-term estrogen on reinstatement of cocaine-seeking behavior in female rats

Estrogen effects on cocaine-induced reinstatement of lever responding were examined in sham-operated, vehicle-treated (SH+VEH), ovariectomized (OVX+VEH), and OVX female Wistar rats with estrogen replacement (OVX+EB). The effect of long- (64+/-1.56 days) and short-term (9 days) EB treatment on reinstatement of cocaine-seeking behavior was compared in Experiment 1 and 2, respectively, in order to compare the effect of EB when it was present during the development vs. expression of reinstatement of cocaine-seeking behavior. Rats were trained to self-administer 0.4 mg/kg/inf cocaine. After the acquisition criteria were met, rats continued to respond for cocaine for 2 h/day for a 14-day maintenance period. Cocaine was then replaced with saline and the 21-day extinction period commenced. Subsequently, rats were tested for reinstatement of lever responding on the previously drug-paired lever after alternating daily injections of saline or cocaine. In both experiments, there were no differences between groups in self-administration behavior during training, maintenance, or extinction. In Experiment 1, SH+VEH and chronically treated OVX+EB rats had greater cocaine-induced reinstatement than OVX+VEH rats. In Experiment 2, short-term treated OVX+EB rats also showed enhanced cocaine-induced reinstatement compared to OVX+VEH rats. The results indicate that EB-mediated enhancement of cocaine-induced reinstatement is dependent on EB presence during the expression of reinstatement but not during the formation of stimulus-reward associations during the development of cocaine-reinforced behavior.

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.

Estrogen modulates RGS9 expression in the nucleus accumbens

Estrogen enhances psychostimulant-induced dopamine receptor-mediated behaviors. One possible mechanism for this enhancement is modulation of the expression of the regulators of G-protein signaling (RGS) proteins. Ovariectomized (OVX) rats received empty s.c. implants or implants packed with 17beta estradiol. Two weeks later the rats were given a single injection of various dopaminergic agents or saline. Estrogen administration to OVX rats selectively reduced RGS9 mRNA expression in the nucleus accumbens shell, but not core. Treating rats with D1 and D2 dopamine receptor agonists or amphetamine failed to change RGS9 mRNA expression in either OVX or OVX rats receiving estrogen. Our findings provide evidence for estrogen as a factor that enhances dopamine receptor signaling by altering RGS9 mRNA expression which could underlie gender specific patterns of psychostimulant abuse.

Differential effects of intraspecific interactions on the striatal dopamine system in social and non-social voles

We used in vivo microdialysis to examine the responses to intraspecific social interactions in the striatal dopamine systems of females of two vole species displaying vastly different social structures. Both highly social prairie voles and asocial meadow voles had similar increases in extracellular dopamine associated with mating. There was a species-specific effect of social condition on extracellular dihydroxyphenylacetic acid (DOPAC). Exposure to a conspecific male significantly decreased extracellular DOPAC in female prairie voles isolated for approximately 18 h during surgical recovery. Such decrease in DOPAC was not seen if females experienced continued isolation or if they were housed with a sibling during surgical recovery. No changes in extracellular DOPAC were seen in meadow voles after manipulations of social environment. Together, our data indicate that mating-associated dopamine release is independent from mating systems. However, species-specific patterns of extracellular DOPAC suggest that social isolation may be a more stressful stimulus for the social prairie vole than for the asocial meadow vole.

Comparative behavioral changes between male and female postpubertal rats following neonatal excitotoxic lesions of the ventral hippocampus

Neonatal ventral hippocampal (nVH) lesioned male rat has been used as a model to test the hypothesis that early neurodevelopmental abnormalities lead to behavioral changes putatively linked to schizophrenia. There are significant gender differences in schizophrenia with male and female individuals differing in the age of onset, course and outcome of the disorder. In order to assess whether the behavioral effects of nVH lesions extend to or are different in female rats, we investigated spontaneous locomotion, grooming, social interactions and spatial memory in male and female rats post-pubertally at postnatal day (P) 56 following bilateral ibotenic acid of the ventral hippocampus at P7. The spontaneous locomotor activity in a novel environment of both male and female nVH lesioned rats was significantly enhanced compared to their respective sham-operated controls. In tests of social interactions, the number of encounters was significantly decreased in female lesioned rats, whereas the male nVH lesioned rats showed a significantly reduced duration of active social interactions. Furthermore, Morris water maze test showed a deficit of spatial learning/memory in only male lesioned rats with significant decrease in the latency to find hidden platform. These results suggest that while nVH lesions affect post-pubertal behavior in both sexes of rats, the males appear to be affected to a greater extent than the females underscoring the influence of sex differences in the development of behaviors in the nVH lesioned animals.

Gender differences in schizophrenia

Sex differences in schizophrenia can be caused by the disease process itself, by genetic and hormonal differences, by differences in the maturation and morphology of the brain and in age- and gender-specific behavioural patterns. These hypotheses will be tested on the major results reported in the literature as well as on different levels (epidemiology, risk factors, animal experiments, a controlled clinical study) on data from the ABC Schizophrenia Study. Symptomatology, lifetime risk and symptom-related course of illness-the latter without consideration of age-show no gender differences. However, until menopause illness onset is delayed and severity of illness is reduced by oestrogen on the level of gene expression and transmitter functioning. Oestrogen has an antagonistic effect on the-familial or exogenous-predisposition to illness. As a result, the age distribution of onset and the severity of first-episode illness in young men and post-menopausal women differ from the normal. First intervention trials with oestrogen substitution of neuroleptic therapy have demonstrated antipsychotic effects. The poorer social course of schizophrenia in men than in premenopausal women is accounted for by men's lower level of social development at illness onset and the subsequent impediment of their further development. Men's socially adverse illness behaviour, too, is a contributing factor. Scarcity of the knowledge of differences in the development, morphology and functioning of the male and female brain does not yet allow any definitive conclusions about gender differences in schizophrenia.

Effects of sex and estrogen on behavioral sensitization to cocaine in rats

Estrogen rapidly enhances dopamine (DA) activity in the striatum and nucleus accumbens as well as behavioral responses to psychomotor stimulants in female rats but not males. This experiment was conducted to investigate the role of pulsatile estrogen treatment on and sex differences in the development and expression of sensitization of cocaine-induced rotational behavior in rats with unilateral striatal DA denervation. Four groups were tested: ovariectomized (OVX) females treated with 5 microg of estradiol benzoate (OVX+E), OVX females, castrated (CAST) males, and intact males. Animals received estrogen or vehicle 30 min before cocaine (0, 5, 10, or 20 mg/kg, i.p.) on 4 consecutive days, followed by 3 d without treatment for 3 weeks. At the conclusion of the experiment, animals were withdrawn from hormone and/or cocaine for 10 d, and all groups underwent a challenge test with 10 mg/kg cocaine. We report here that OVX+E females exhibit significantly greater sensitization of rotational behavior with a faster rate of sensitization than the three other groups. There is also a sex difference independent of gonadal hormones: OVX females exhibit a greater magnitude of sensitization of rotational behavior than do CAST males at 20 mg/kg cocaine. Furthermore, on the challenge test, OVX+E animals tested without estrogen treatment continue to exhibit greater rotational behavior than do all other groups. Thus, estrogen enhances sensitization to cocaine, there are sex differences in behavioral sensitization, and sensitization that develops under conditions with estrogen persists even when estrogen levels are low.

Estrogen regulation of gene expression in the brain: a possible mechanism altering the response to psychostimulants in female rats

Acute behavioral responses to cocaine are more pronounced in female than in male rats. We have shown that 3 weeks of treatment with 17beta-estradiol (E(2)) implants significantly enhanced the hyperactivity induced by cocaine in ovariectomized (OVX) rats. The ligand-bound estrogen receptor (ER) functions as a transcription factor to regulate the expression of E-responsive genes. Thus, we hypothesized that estrogen (E) modulates the behavioral response to cocaine via regulation of expression of components of dopamine (DA) and serotonin (5-HT) systems in mesolimbic nuclei important in the response to cocaine as well as the hypothalamus, a brain area known to be E-responsive. Adult female Sprague-Dawley rats were OVX; half of them then received E(2) implant (OVX+E) (n=8/group, two groups). Twenty-seven days later, brain tissue was collected to study E(2) effects on mRNA expression for DA D(1)-like (D(1)) and D(2)-like (D(2S), D(2L), D(3)) receptors, DA transporter (DAT), 5-HT(1A), 5-HT(1B), 5-HT(2A), 5-HT(2C) receptors, and 5-HT transporter (SERT) as well as ERalpha and ERbeta in amygdala, hypothalamus, nucleus accumbens, midbrain, and ventral tegmental area (VTA). We found that E(2) implants in OVX rats increased mRNA levels for D(1) receptor in hypothalamus, D(2L) receptor in midbrain, and D(3) receptor in VTA, and decreased D(3) receptor mRNA levels in midbrain relative to OVX controls. E(2) also increased 5-HT(2C) receptor mRNA levels in midbrain and hypothalamus. In addition, E(2) decreased mRNA levels for ERalpha in amygdala and hypothalamus and ERbeta in amygdala. The present study demonstrates that E can regulate mRNA expression for specific DA and 5-HT receptors in a region-specific manner and suggests that such modifications may contribute to the behavioral response to cocaine.

Endocrinological basis of sex differences in cocaine-induced behavioral responses

Currently, 1.8 million Americans use cocaine, 30% of whom are females. Sex differences in the pattern of cocaine abuse may reside in neuroendocrinological modulations that affect the use of and/or dependence on cocaine. This review discusses sex differences in cocaine-induced behavioral and molecular alterations in the central nervous system, with emphasis on the role of endocrine responses in the neuronal modulations of this drug. Mechanisms and data supporting the role of the hypothalamic-gonadal axis in the modulation of cocaine-induced behavioral and molecular alterations are also provided.

Increased sensitivity of dopamine systems following reproductive experience in rats

Several studies have suggested that alterations in forebrain dopamine activity during the postpartum period may result in the onset of postpartum psychosis in women [J. Psychosom. Obstet. Gynecol. 19 (1998) 104; Prog. Neuro-Psychopharmacol. Biol. Psychiatry 17 (1993) 571; J. Clin. Psychiatry 51 (1990) 365.]. The present study investigated whether increased dopamine activity in these forebrain regions is a normal consequence of reproductive experience in rodents. Both intact and ovariectomized parous and nulliparous females were tested for their responses to the dopamine agonist apomorphine using two behavioral measures, prepulse inhibition (PPI) and oral stereotypy. In addition, dopamine and DOPAC levels were measured in tissue from the striatum and nucleus accumbens together with circulating plasma prolactin levels. The results of the behavioral studies demonstrate an increased response to apomorphine in parous females. Parous subjects also had increased levels of dopamine and DOPAC in striatal tissue and lower levels of circulating prolactin. Ovariectomy in nulliparous females resulted in a potentiated response to apomorphine with regard to the disruption of PPI, as well as a significant decrease in the plasma prolactin levels, as compared with intact nulliparous females. These data suggest that increased dopamine activity in forebrain regions occurs as a consequence of parity, which persists for a minimum of several weeks postpartum. These findings support the hypothesis that increased dopamine sensitivity in forebrain dopamine regions may be one potential mechanism underlying the development of postpartum psychosis in women.

Estrogen improves motor disability in parkinsonian postmenopausal women with motor fluctuations

OBJECTIVE

To test the efficacy, tolerance, and safety of low-dose oral estrogen in postmenopausal women with PD associated with motor fluctuations.

BACKGROUND

Motor fluctuations in PD may be predictable or unpredictable, and eventually affect most patients after long-term levodopa therapy. Although estrogen can modulate nigrostriatal dopamine levels, its effects on PD are unclear.

METHODS

Patients were randomized to receive conjugated estrogen (oral Premarin 0.625 mg daily; n = 20) or placebo (n = 20) in a double-blind, parallel-group, prospective study over 8 weeks. Existing antiparkinsonian drug regimes were kept unchanged. Changes in "on" and "off" periods using patient diaries, Unified Parkinson's Disease Rating Scale (UPDRS) score, timed tapping score, and Hamilton Depression Scale score were determined by one rater. Subgroup analyses were also performed on patients with only predictable motor fluctuations.

RESULTS

Both treatment groups were similar in age, duration of disease and menopause, antiparkinsonian medication, and compliance with test medication and diary assessments. "On" and "off" times, and motor score (UPDRS subscale III) improved with estrogen, using the Mann-Whitney U test (p < 0.05 after Bonferroni adjustment). Mean "on" time improved by 7% (9 hours/week of awake time) in estrogen-treated patients versus a deterioration of 0.5% (1.4 hours) in placebo-treated patients (95% confidence interval, [CI] of mean difference, 5.73 to 14.9). Mean "off" time improved by 4% (4.4 hours/week of awake time) in estrogen-treated patients versus no change in placebo-treated patients (95% CI, 1.54 to 7.16). Mean subscale III score improved by 3.5 points in estrogen-treated patients versus 0.4 in placebo-treated patients (95% CI, 1.02 to 5.18). No other significant changes were observed (p > 0.05). Subgroup analyses in patients with only predictable motor fluctuations showed similar results, except improvement in mean subscale III score was marginally not significant (p = 0.07; 95% CI, 1.06 to 6.24). Five patients on estrogen had facial flushing, three had lower abdominal discomfort, and two had mild withdrawal vaginal bleeding. The adverse events were mild and resolved without sequelae.

CONCLUSION

Low-dose estrogen is a safe and effective adjunct therapy to existing antiparkinsonian treatment in reducing motor disability in postmenopausal women with PD associated with motor fluctuations.

Estrogen reduces acute striatal dopamine responses in vivo to the neurotoxin MPP+ in female, but not male rats

The effects of in vivo estrogen treatment upon MPP(+)-induced dopamine (DA) release were determined using in vivo microdialysis in female and male rats. Ovariectomized female rats were implanted or not with an estrogen pellet (0.1 mg, 17beta estradiol) and subjected to microdialysis 6 days later. After baseline DA release was determined, 5 mM MPP(+) was infused through the microdialysis probe for one 20-min interval. Perfusion resumed with normal medium for the duration of the experiment. A significant attenuation of MPP(+)-induced DA release was obtained in estrogen-treated females. One week later, striatal DA and dihydroxyphenylacetic acid (DOPAC) concentrations were determined for the lesioned and non-lesioned striata of each animal. MPP(+) infusion significantly decreased striatal DA concentrations, however, there was no effect of estrogen treatment on striatal DA depletion. This experiment was repeated using orchidectomized male rats treated with 0, 0.1, or 5 mg estradiol. In contrast to the females, no differences in MPP(+)-induced DA release were seen among these males, and there was no significant effect of the varying estrogen treatments on striatal DA or DOPAC concentrations. These results demonstrate that in vivo estrogen treatment attenuates MPP(+)-induced striatal DA release in gonadectomized female, but not male, rats.

Regulation of striatal dopamine receptors by estrogen

The ability of estrogen to modulate the expression of ventral and dorsal striatal dopamine receptors D(1), D(2,) and D(3) was examined in vivo using semi-quantitative in situ hybridization and ligand binding autoradiography. Two-week treatment with subcutaneous pellets of 17beta-estradiol (25 mg) downregulated D(2) dopamine receptor mRNA in both dorsal and ventral striatum (shell and core regions of nucleus accumbens). No significant changes in D(1) or D(3) mRNA expression were detected. Ligand binding autoradiography did not reveal changes in D(1), D(2,) or D(3) receptor protein expression. We also assessed the ability of 17beta-estradiol to regulate D(2) gene promoter activity in NB41A3 neuroblastoma cells that express this gene endogenously using co-transfections with an estrogen receptor expression vector. While a small fragment of the D(2) promoter could be activated 2.5-fold by estrogen, a larger portion of the D(2) gene was not regulated by this treatment. Estrogens do not appear to have a net effect on striatal dopamine receptor expression. The observed downregulation of D(2) receptor mRNA in the dorsal and ventral striatum in vivo could be secondary to the increased striatal dopamine release induced by estrogen. Synapse 34:222-227, 1999. Published 1999 Wiley-Liss, Inc.

Gender differences in dopaminergic function in striatum and nucleus accumbens

In female rats the gonadal hormones estrogen and progesterone modulate dopamine (DA) activity in the striatum and nucleus accumbens. For example, there is estrous cycle-dependent variation in basal extracellular concentration of striatal DA, in amphetamine (AMPH)-stimulated DA release, and in striatal DA-mediated behaviors. Ovariectomy attenuates basal extracellular DA, AMPH-induced striatal DA release, and behaviors mediated by the striatal DA system. Estrogen rapidly and directly acts on the striatum and accumbens, via a G-protein-coupled external membrane receptor, to enhance DA release and DA-mediated behaviors. In male rats, estrogen does not affect striatal DA release, and removal of testicular hormones is without effect. These effects of estrogen also result in gender differences in sensitization to psychomotor stimulants. The effects of the gonadal hormones on the striatum and ascending DA systems projecting to the striatum and nucleus accumbens are hypothesized to occur as follows: estrogen induces a rapid change in neuronal excitability by acting on membrane receptors located in intrinsic striatal GABAergic neurons and on DA terminals. The effect of these two actions results in enhanced stimulated DA release through modulation of terminal excitability. These effects of gonadal hormones are postulated to have important implications for gender differences in susceptibility to addiction to the psychomotor stimulants. It is suggested that hormonal modulation of the striatum may have evolved to facilitate reproductive success in female rats by enhancing pacing behavior.

Interactive effects of tamoxifen and oestrogen upon the nigrostriatal dopaminergic system: long-term treatments

In the present report adult female rats were ovariectomized (OVX) and assigned to one of four treatment conditions. Treatments consisted of administering pellets containing 17beta-oestradiol (E), tamoxifen (TMX), a combination of TMX and E or no further treatment (OVX). Animals received these treatments immediately following OVX and were maintained in these conditions for a 40-day period. Subsequently, the corpus striatum (CS) was dissected from each animal and prepared for determinations of basal and amphetamine stimulated DA output using in-vitro superfusion. No statistically significant differences among the four treatment groups were obtained for basal dopamine output. The highest levels of amphetamine-stimulated dopamine responses were obtained from E treated rats. These values were significantly greater than that obtained from OVX rats and rats treated with a combination of TMX+E. The significance of these findings is that they indicate both a non-traditional central nervous system site and mechanism of action through which tamoxifen-oestrogen interactions can function. Such data may have important implications for administration of tamoxifen to premenopausal women as this anti-oestrogen may compromise nigrostriatal dopaminergic function under conditions where oestrogenic modulation is present.

Regulation of striatal dopamine receptors by corticosterone: an in vivo and in vitro study

The effects of chronic corticosterone administration and adrenalectomy on the expression of brain dopamine receptors were studied in rats. In situ hybridization and receptor binding autoradiography were carried out to determine D1, D2 and D3 receptor expression in dorsal and ventral striata. Except for down-regulation of D2 mRNA in dorsal striatum after 2 week corticosterone treatment, no other significant changes were detected. In addition, the transcriptional regulation of D1 and D2 gene promoters by glucocorticoids was studied in neuroblastoma cell lines using transient transfections. While a small segment of the D2-promoter could be activated three-fold by dexamethasone, large fragments of neither D1 or D2 promoters were regulated by this treatment. Glucocorticoids do not appear to have direct overall effects on striatal dopamine receptor expression. The observed down-regulation of D2 receptor mRNA in the dorsal striatum in vivo is likely secondary to increased striatal dopamine release induced by corticosterone.

Estrous cycle differences in cocaine-induced stereotypic and locomotor behaviors in Fischer rats

This study was conducted to characterize female behavioral response to acute 'binge' pattern cocaine administration (15 mg kg(-1) i.p., three times a day, at 1 h intervals) during the different stages of the estrous cycle in Fischer rats. Cocaine administration significantly increased stereotypic behavior and locomotion in females. Animals in estrus showed significantly higher cocaine-induced stereotypic and locomotive behavioral responses than those in other stages of the cycle. Plasma levels of the cocaine metabolite benzoylecgonine during metestrus diestrus were significantly higher than during estrus and proestrus probably reflecting more rapid biotransformation of cocaine. Therefore, it is likely that the hormonal fluctuations associated with the estrous cycle modulate both cocaine metabolism and the behavioral responses to cocaine in female rats. This in turn may have important implications in gender differences in behavioral responses to cocaine.

Gonadal steroids and neuronal function

Gonadal steroid hormones may affect, simultaneously, a wide variety of neuronal targets, influencing the way the brain reacts to many external and internal stimuli. Some of the effects of these hormones are permanent, whereas others are short lasting and transitory. The ways gonadal steroids affect brain function are very versatile and encompass intracellular, as well as, membrane receptors. In some cases, these compounds can interact with several neurotransmitter systems and/or transcription factors modulating gene expression. Knowledge about the mechanisms implicated in steroid hormone action will facilitate the understanding of brain sexual dimorphism and how we react to the environment, to drugs, and to certain disease states.

Estrogen decreases corpus striatal neurotoxicity in response to 6-hydroxydopamine

Ovariectomized rats treated or not with an estradiol pellet were subjected to an unilateral intrastriatal infusion of 6-hydroxydopamine (6-OHDA). Various parameters of nigrostriatal dopaminergic function as derived from measurements of dopamine and dihydroxyphenylacetic acid (DOPAC) concentrations were determined from the 6-OHDA lesioned and non-lesioned sides of the corpus striatum in these animals. Dopamine concentrations within the 6-OHDA lesioned striatum of estrogen-treated rats were significantly greater than non-estrogen-treated rats. There were no differences in striatal dopamine concentrations between estrogen- versus non-estrogen-treated rats on their non-lesioned side. In contrast to that of dopamine, no differences in DOPAC concentrations between estrogen and non-estrogen-treated rats were obtained within the 6-OHDA-lesioned side. The DOPAC concentrations on the non-lesioned side of the striatum were significantly greater in the non-estrogen-treated rats. These results demonstrate that estrogen significantly diminishes the depletion of striatal dopamine resulting from the neurotoxin 6-OHDA. The data obtained from the DOPAC determinations imply that this capacity of estrogen may be exerted through actions upon uptake processes of striatal dopaminergic neurons. Such findings suggest that estrogen may function as an important modulatory factor capable of attenuating degeneration within the corpus striatum, and in this way serve as a neuroprotectant of the nigrostriatal dopaminergic system.

Gonadal steroid modulation of neuroendocrine transduction: a transynaptic view

1. Steroid hormones act on neuronal communication through different mechanisms, ranging from transynaptic modulation of neurotransmitter synthesis and release to development and remodeling of synaptic circuitry. Due the wide distribution of putative brain targets for steroid hormones, acute or sustained elevations of their circulating levels may affect, simultaneously, a variety of neuronal elements. In an elementary mode of interaction, steroids are able to modulate both the synthesis and release of a neurotransmitter at a particular synapse, and the response of its target postsynaptic cells. Using two neuroendocrine transducing systems-the rat pineal gland and the GT1-7 cell line-we have examined these interactions and the following findings are discussed in this article. 2. In the rat, pineal melatonin production is partially controlled by gonadal hormones. In females, melatonin synthesis and secretion is reduced during the night of proestrus, apparently as a consequence of elevated estradiol and progesterone levels. In males, circulating testosterone seems to be necessary to maintain the amplitude of the nocturnal melatonin peak. 3. Some gonadal effects on pineal activity are exerted on its noradrenergic input, since changes in circulating steroid hormone levels are able to induce acute modifications of tyrosine hydroxylase activity in pineal sympathetic nerve terminals. 4. Gonadal steroids are also able to regulate the response of pineal cells to adrenergic stimulation, since in vivo treatment of both male and female rats with steroid hormone blockers induces profound modifications in adrenergically-induced accumulation of cyclic AMP (cAMP) in dispersed pinealocytes. 5. Direct exposure of pineal cells from gonadectomized female and male rats to estradiol (E2) or testosterone (T), respectively, potentiates pinealocyte response to adrenergic activation. In addition, short-term (15 min) exposure to either progesterone (Pg) or progesterone coupled to bovine serum albumin (P-3-BSA) suppresses the E2-dependent potentiation of adrenergic response in female rat pinealocytes. 6. Exposure of GT1-7 cells to E2 completely blocked the norepinephrine (NE)-induced elevation of cAMP content. In E2-treated GT1-7 cells, additional exposure (15 min) to either Pg or P-3-BSA abolished E2-dependent inhibition of NE responsiveness. In addition, P-3-BSA alone increased basal cAMP levels in GT1-7 cells, regardless previous exposure to E2. 7. In conclusion, there are evidences, both from the current literature and from the present results, supporting the view that in some neuroendocrine systems gonadal hormones modulate neurotransmission by acting, simultaneously, at pre- and postsynaptic sites. The models presented here constitute appropriate examples of this transynaptic mode of steroid and, therefore, may offer a useful approach to investigate steroid hormone actions on the brain.

Effects of testosterone upon MPTP-induced neurotoxicity of the nigrostriatal dopaminergic system of C57/B1 mice

We have recently reported that treatment of gonadectomized female and male C57/B1 mice with the gonadal steroid hormone, estrogen, reduced nigrostriatal dopaminergic neurotoxicity resulting from the Parkinson's-like inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In the present report we examined whether the predominantly male gonadal steroid hormone, testosterone, would similarly modulate MPTP-induced neurotoxicity. Male C57/B1 mice were assigned to one of the following five treatment conditions: (1) Intact, (2) Orchidectomized, (3) Intact + MPTP, (4) Orchidectomized + Testosterone + MPTP and (5) Orchidectomized + MPTP. Corpus striatal and olfactory tubercle dopamine. DOPAC and norepinephrine concentrations were determined from the animals within each of the five treatment conditions. Orchidectomy alone failed to alter striatal dopamine and DOPAC concentrations, with levels obtained being similar to that of Intact animals. MPTP treatment significantly reduced striatal reduced striatal dopamine and DOPAC concentrations, regardless of hormonal condition of the animal. Similar results were obtained for olfactory tubercle determinations, with the exception that DOPAC levels from Orchidectomized mice were significantly greater than Intact males. No significant differences were obtained for norepinephrine within either brain area sampled. These results show that unlike estrogen, testosterone is devoid of any capacity to modulate nigrostriatal dopaminergic neurotoxicity resulting from MPTP. These findings may be related to the gender differences which exist in the prevalence of Parkinson's disease.

Influence of 17- alpha-estradiol on catecholamine secretion from the perfused rat adrenal gland

OBJECTIVES

It has been known that adrenal corticosteroids influence the expression of adrenomedullary catecholamine-synthetizing enzymes and also suppress the emission of axonal-like processes in cultured chromaffin cells. In the present study, it was attempted to investigate the effect of 17-alpha-estradiol on catecholamine (CA) secretion evoked by acetylcholine (ACh). DMPP. McN-A-343, excess K+ and Bay-K-8644 from the isolated perfused rat adrenal gland.

METHODS

Mature male Sprague-Dawley rats were anesthetized with ether. The adrenal gland was isolated by the method of WaKade. A cannula used for perfusion of the adrenal gland was inserted into the distal end of the renal vein. The adrenal gland, along with ligated blood vessels and the cannula, was carefully removed from the animal and placed on a platform of a leucite chamber.

RESULTS

The perfusion of 17-alpha-estradiol (1-100 uM) into an adrenal vein for 20 min produced relatively dose-dependent inhibition in CA secretion evoked by ACh (5.32 mM). DMPP (100 uM for 2 min). McN-A-343 (100 uM for 2 min) and Bay-K-8644 (10 uM for 4 min), while it did not affect the CA secretory effect of high K+ (56 mM). Also, in the presence of 17-beta-estradiol. CA secretion of ACh. DMPP and McN-A-343, without any effect on excess K(+)-evoked CA sectretion was depressed. However, in adrenal glands pre-loaded with 17-alpha-estradiol (10 uM) plus tamoxifen (2 uM), which is known to be a selective antagonist of estrogen receptors (for 20 min). CA secretory responses evoked by ACh. DMPP and McN-A-343 were condiderably recovered as compared to that of 17-alpha-estradiol only, but excess K(+)-induced CA secretion was not affected. However, pre-treatment with 17-alpha-estradiol in the presence of meclopramide (dopaminergic antagonist) did not affect the secretory effect of CA evoked by ACh. DMPP, McN-A-343 and high potassium.

CONCLUSIONS

These results suggest that 17-alpha-estradiol causes the marked inhibition of CA secretion evoked by cholinergic receptor stimulation, but not that by excess K+, indicating strongly that this effect may be mediated by inhibiting the influx of extracellular calcium into the rat adrenomedullary chromaffin cells through the activation of inhibitory estrogen receptors, and it also plays a modulatory role in regulating CA secretion.

Complex effects of age and gender on hypothermic, adrenocorticotrophic hormone and cortisol responses to ipsapirone challenge in normal subjects

The effects of a challenge dose of the 5-HT1A agonist, ipsapirone (0.3 mg per kg body weight), or placebo on body temperature and on adrenocorticotrophic hormone (ACTH) and cortisol release, were examined in 30 normal subjects (14 males, 19-74 years and 16 females, 22-69 years) using a randomized, double blind design. Irrespective of age or gender, ipsapirone induced a significant reduction in body temperature relative to placebo and a significant increase in ACTH and cortisol release. Maximal temperature reduction by ipsapirone was significantly blunted in older subjects and was inversely related to age. There was no gender difference in the hypothermic response to ipsapirone. ACTH and cortisol responses showed an opposite impact of aging in males and females. Whereas both responses diminished with age in male subjects, they increased with age in females. The cortisol response of older females was significantly larger than that of all the other subjects. Adverse effects of ipsapirone were also more marked in elderly females and were correlated with ACTH and cortisol responses. These findings should be taken into consideration in the use of ipsapirone and other 5-HT1A agonists as challenge procedures for studying central serotonergic function in depression and other disorders. Careful matching of control and experimental subjects is indicated so as to avoid spurious results which reflect the effects of age and gender rather than the pathophysiology of the disorders being investigated.

Dopamine and sexual behavior

Among central neurotransmitters involved in the control of sexual behavior, dopamine is certainly one of the most extensively studied. Our attempt to review old and recent neuropharmacological, biochemical, electrophysiological, and psychobiological studies performed so far only in rats, monkeys, and humans, provides evidence that dopamine through its different neuronal systems and receptor subtypes plays different roles in the control of several aspects of sexual behavior. In fact, while the nigrostriatal system is necessary for the control of the sensory-motor coordination required for copulation, the mesolimbic-mesocortical system plays a key role in the preparatory phase of the behavior, mainly in sexual arousal, motivation and possibly reward. Conversely, the incertohypothalamic system plays a major role in the consummation of the behavior, mainly in seminal emission and erectile performance, but evidence for its involvement in sexual motivation also exists. The dopaminergic receptors playing the major role in the control of male sexual behavior belong to the D2 receptor subtype. However a D1/D2 receptor interaction is well established and an opposite role for D1 and D2 receptors in the preoptic area suggested. Despite some differences, most studies show that treatments that increase or decrease, respectively, brain dopaminergic activity improve or worsen, respectively, several parameters of copulatory activity, supporting a facilitatory role of dopamine in male sexual behavior. In contrast, no conclusion can be deduced from the available studies on the role of central dopaminergic systems in the control of proceptivity and receptivity, the two main components of female sexual behavior.

Cellular and molecular mechanisms of impaired dopaminergic function during aging

One important cause of impaired motor function during aging is deterioration of the dopamine system. Such motor deficits in experimental animals can be closely related to loss of striatal dopamine receptors, and similar observations have now been made in humans. Two mechanisms account for the age-related decrease in striatal dopamine receptor levels: loss of receptor-containing neurons and reduced rates of receptor synthesis. The striatal neurons affected by aging appear to reside in a kainic-acid-sensitive population. Attempts to mimic those death mechanisms which occur in vivo using cultured neurons suggest that large D2-dopamine-receptor-containing cells may be the most vulnerable. Whether dopamine itself, the endogenous neurotransmitter for the cells, may ultimately be toxic to these neurons remains to be determined. The levels of D2-receptor mRNA in the surviving neurons is reduced during aging. This decrement is apparently due to a decreased rate of mRNA biosynthesis. Future experiments must therefore focus on the regulatory elements of this gene in order to determine why its transcription is selectively affected by aging. Finally, various interventions have been shown to delay or reverse the age changes characteristic of the dopaminergic system. Both dopamine receptors and motor function have been manipulated by diet and exercise as well as 6-OH-dopamine lesions and estrogen and prolactin administration. The possibility that such treatments might eventually be utilized therapeutically has become increasingly real as our knowledge of the affected cellular and molecular processes continues to expand.

Sex differences in the rapid and acute effects of estrogen on striatal D2 dopamine receptor binding

Regional changes in striatal D2 dopamine (DA) receptor binding in castrated (CAST) or ovariectomized (OVX) rats were investigated following administration of a low dose of estradiol benzoate (EB), repeated treatment with EB followed by progesterone, or vehicle. In two separate experiments, there was a significant decrease in striatal D2 DA receptor binding in caudal striatum from OVX, but not CAST rats 30 min after a single injection of EB. In CAST rats, there was a significant increase in striatal D2 DA receptor binding in rostral striatum 4 h after injection of EB. There was no effect of EB plus progesterone treatment in either OVX or CAST rats. In addition, CAST rats had significantly lower D2 DA receptor binding in the lateral region of the rostral striatum than did OVX rats. These results show sexually dimorphic and regionally specific effects of estrogen on striatal D2 DA receptor binding, and a significant sex difference in striatal D2 DA receptor binding in the absence of circulating gonadal hormones. The present findings are discussed in light of previous reports of sex differences in gonadal hormone influences on striatal DA mediated behaviors.

Modifications of mesolimbic and nigrostriatal dopaminergic activities after intracerebroventricular administration of prolactin

In the present study we examined the effects of intracerebroventricular (i.c.v.) injections of prolactin (PRL) on the presynaptic activity and post-synaptic sensitivity of mesolimbic and nigrostriatal dopaminergic neurons. In addition, the effects of PRL on in vitro release of dopamine (DA) from perifused striatal fragments were examined. Tyrosine hydroxylase (TH) activity and D2 receptor density in the striatum decreased after i.c.v. PRL administration; this was accompanied by an increase in D2 receptor affinity. These effects occurred after i.c.v. administration of PRL to normoprolactinemic rats, although normally they did not appear after administration to animals with pituitary grafting-induced hyperprolactinemia. Thus, in these animals, i.c.v. PRL failed to decrease TH activity and D1 and D2 receptor densities to a significant extent. In the case of D2 receptors, this was probably due to the fact that pituitary grafting-induced hyperprolactinemia itself was able to reduce the density of this receptor. No changes were observed in DA or L-3, 4-dihydroxyphenylacetic acid (DOPAC) contents after i.c.v. administration of PRL to both normo-and hyperprolactinemic animals. Basal and K(+)-evoked DA release in vitro from perifused striatal fragments of normoprolactinemic rats were not affected by the addition of PRL, whereas this hormone enhanced K(+)-evoked DA release when added to perifused striatal fragments from hyperprolactinemic animals. In the limbic forebrain, i.c.v. administration of PRL to normoprolactinemic animals produced a decrease in DA and DOPAC contents and D1 receptor density. Interestingly, none of these effects appeared when PRL was injected to hyperprolactinemic animals. In summary, our results suggest a possible inhibitory role of PRL on the activity of both the nigrostriatal and mesolimbic dopaminergic neuronal systems. These inhibitory effects were reflected in the decreases elicited in a set of neurochemical parameters, indicating either presynaptic activity or postsynaptic sensitivity, after i.c.v.-administered PRL. This observation supports the hypothesis of a possible neuromodulatory role for an extrapituitary PRL on the activity of these neurons, although the fact that most of these effects did not appear when i.c.v. administration was performed in hyperprolactinemic rats also suggests that they are influenced by peripheral PRL levels.

Men are more inhibited than women by weak prepulses

The acoustic startle reflex is normally inhibited when the startling stimulus is preceded by a weak prepulse. We studied "prepulse inhibition" (PPI) to assess potential gender differences in this operational measure of sensorimotor gating. A review of data from our previously published studies in psychiatric patients and normal controls indicated that startle in women was less inhibited by weak prepulses than was startle in men, and that this gender difference narrowed when stronger prepulses were used to elicit maximal levels of PPI. Based on these observations, new subjects were selected for study using our established criteria to exclude individuals with psychiatric disorders, substance abuse, or serious neurologic or medical illness. Replicating our preliminary observation, women exhibited significantly less PPI than men, with the gender difference being most notable under conditions with weak prepulses. Potentially confounding variables, including electrode impedance, startle amplitude, habituation and latency did not differ between men and women. PPI was then measured in male and female rats, where no gender differences were noted. These findings identify significant gender differences in PPI in humans, and suggest that inhibitory "gating" processes are more robust in men than in women, when assessed using a sensitive range of inhibitory stimuli.

Effect of chronic estradiol and progesterone treatments of ovariectomized rats on brain dopamine uptake sites

Dopamine released from brain nerve terminals is mainly removed from the synaptic cleft by an uptake mechanism. Despite their functional importance, modulation of the dopamine uptake sites is still not well known. Steroid hormones were shown to modulate brain dopamine transmission. The aim of this study was thus to investigate in ovariectomized rats the effects of 17 beta-estradiol and progesterone treatments on brain dopamine uptake sites. Treatments consisted of 17 beta-estradiol (10 micrograms/0.2 ml), progesterone (0.72 mg/0.2 ml), 17 beta-estradiol + progesterone, or the vehicle (0.3% gelatin in saline solution) twice daily for 2 weeks. The steroid treatments left the affinity of [3H]GBR 12935 binding to striatal homogenates unchanged (ovariectomized rats, 0.823 +/- 0.028 nM), whereas the density was increased by these steroids alone or in combination to a similar extent of 16-23%. Chronic treatment of ovariectomized rats with 17 beta-estradiol, progesterone, or their combination increased to the same extent and uniformly [3H]-GBR 12935 binding in the striatum as measured by autoradiography; the increase was similar in the substantia nigra pars compacta, whereas no steroid effect was observed in the nucleus accumbens and in the substantia nigra pars reticulata. In summary, chronic exposure to 17 beta-estradiol and/or progesterone increased dopamine uptake site density in the nigrostriatal dopaminergic system, whereas the nucleus accumbens and the substantia nigra pars reticulata were unaffected.

From an animal model of an attentional deficit towards new insights into the pathophysiology of schizophrenia

The paper presents an animal model of schizophrenic-like attentional deficit, consisting of an inability to ignore irrelevant stimuli. It is based on the paradigm of latent inhibition (LI), in which animals learn to ignore repeatedly presented stimuli not followed by meaningful consequences. In a series of experiments it was demonstrated that the capacity to ignore irrelevant stimuli is lost in rats treated with systemic or intra-accumbens injections of amphetamine, in normal volunteers given amphetamine, in high "psychosis-prone" persons, in acute schizophrenic patients and in untreated male adult rats that were raised until weaning under conditions of extremely restricted stimulation. In addition, LI is lost following the disruption of the hippocampal input to the nucleus accumbens. In all of the above conditions tested for antagonism by anti-psychotic drugs a loss of LI is reversed. On the basis of these results we propose an animal model which accommodates a neurodevelopmental dysfunction, hippocampal pathology, mesolimbic DA overactivity, vulnerability to stress, and gender differences, all of which have been postulated as factors in the pathophysiology of schizophrenia.

First onset and early symptomatology of schizophrenia. A chapter of epidemiological and neurobiological research into age and sex differences

In the frame of the ABC (Age, Beginning and Course) Schizophrenia Project we studied the influence of age and sex on first-ever onset, symptom manifestation and early course up to first admission in schizophrenia by using a large, representative sample of first-admitted schizophrenic patients. The results showed that the two variables had surprisingly little bearing upon the core symptoms, particularly on negative and other most frequent symptoms and on first-rank symptoms. In 70% of the cases schizophrenia started solely with negative symptoms, in 20% with negative and positive and in 10% with positive symptoms only. In most of the cases symptoms accumulated exponentially up to the first acute episode with positive symptoms appearing considerably later. The age differences observed concerned secondary phenomena associated with developmental factors. Such phenomena, i.e. anxiety, depression and the cognitive formation of delusions, can be interpreted as responses to the psychosis. Also the sex differences, which culminated in far more frequent socially negative disease behaviour in males, were limited to secondary phenomena. This positive and negative core symptomatology of schizophrenia seems to be astonishingly uniform and fairly independent of age and sex at this early stage of the disease. The only remarkable difference was a three to four years higher mean age of onset in females. We were able to show in animal experiments and to confirm in a clinical study that this finding is attributable to a neuromodulatory effect of estrogens on the sensitivity of D2 receptors in the brain. Apparently, estrogens raise the vulnerability threshold until menopause and have a slight neuroleptic-like effect on the symptomatology in acute schizophrenic episodes.

Nigrostriatal and mesolimbic dopaminergic activities were modified throughout the ovarian cycle of female rats

In this work, we have studied the changes in the functional state of nigrostriatal (NSDA) and mesolimbic (MLDA) dopaminergic neurons during the estrous cycle of the female rat. The activity of tyrosine hydroxylase (TH), the turnover rate (Kt) after inhibition of dopamine (DA) synthesis and the ratio between the contents of this amine and its metabolite, L-3,4 dihydroxyphenylacetic acid (DOPAC), were used as indices of neuronal activity. The neuronal activity of NSDA neurons rose during estrous and declined during proestrous, as reflected by the values of Kt and DOPAC/DA ratio measured during both phases. Interestingly, the course of variations in striatal TH activity was similar, although retarded in relation to the changes in neuronal activity. Thus, TH activity was high during diestrous, whereas it was low during estrous. The activity of MLDA neurons was reduced during proestrous. This can be concluded from the decreased Kt and DOPAC/DA ratio measured in this phase and it was accompanied by a low TH activity. Thereupon, both Kt and TH activity increased during estrous. These results indicate the existence of physiological changes in the functional state of both dopaminergic systems during the ovarian cycle, which are partially different for each neuronal pathway. This supports the existence of a specific regulation, and not indiscriminate effects, by the hormones involved in this cycle, mainly estradiol and progesterone.