Effects of gonadal hormones on central nitric oxide producing systems

Reward of tactile genital stimulation is sexually equivalent, but mechanistically differentiated in mice

Gonadal steroid hormones are thought to activate sexual behavior by actions on multiple organ systems, including the nervous system and genitalia. We previously characterized ovarian hormone dependent behavioral and neural responses to clitoral stimulation in female mice. Here we investigate whether sex differences exist in the responses to tactile genital stimulation, and whether these might depend on gonadal androgens. We measured conditioned place preference (CPP) in response to manual tactile stimulation of either the prepuce or dorsum and subsequently measured neural activation. Behavioral and neural responses to genital stimulation were sexually equivalent in gonadally intact mice, with males exhibiting CPP and neural activation responses similar to those previously reported in females, with the exception of the Arcuate nucleus, which was activated to a greater extent in females. An unexpected sex difference in response to dorsal stimulation was observed, with only males developing CPP and increased FOS expression in the nucleus accumbens. Unlike females, the reward value of tactile stimulation was unaffected by gonadectomy in males. However, neural responses to tactile stimulation were disrupted by gonadectomy in both sexes. Testosterone treatment was only partially effective in restoring neural responses to genital stimulation and did so in a sexually diffentiated manner. We conclude that behavioral and neural responses of sexually-naïve mice to genital stimulation are largely similar between males and females, but that non-genital tactile stimulation is more reinforcing to males. Further, the relationship between gonadal steroid hormones and genital reward is sexually differentiated.

The hypothalamic paraventricular nucleus as a central hub for the estrogenic modulation of neuroendocrine function and behavior

Estradiol and hypothalamic paraventricular nucleus (PVN) help coordinate reproduction with body physiology, growth and metabolism. PVN integrates hormonal and neural signals originating in the periphery, generating an output mediated both by its long-distance neuronal projections, and by a variety of neurohormones produced by its magnocellular and parvocellular neurosecretory cells. Here we review the cyto-and chemo-architecture, the connectivity and function of PVN and the sex-specific regulation exerted by estradiol on PVN neurons and on the expression of neurotransmitters, neuromodulators, neuropeptides and neurohormones in PVN. Classical and non-classical estrogen receptors (ERs) are expressed in neuronal afferents to PVN and in specific PVN interneurons, projecting neurons, neurosecretory neurons and glial cells that are involved in the input-output integration and coordination of neurohormonal signals. Indeed, PVN ERs are known to modulate body homeostatic processes such as autonomic functions, stress response, reproduction, and metabolic control. Finally, the functional implications of the estrogenic modulation of the PVN for body homeostasis are discussed.

Hypothalamic cellular and molecular plasticity linked to sexual experience in male rats and mice

Male sexual behavior is subject to learning, resulting in increased efficiency of experienced males compared to naive ones. The improvement in behavioral parameters is underpinned by cellular and molecular changes in the neural circuit controlling sexual behavior, particularly in the hypothalamic medial preoptic area. This review provides an update on the mechanisms related to the sexual experience in male rodents, emphasizing the differences between rats and mice.

Nitric oxide synthase genotype interacts with stressful life events to increase aggression in male subjects in a population-representative sample

Nitric oxide signalling has been implicated in impulsive and aggressive traits and behaviours in both animals and humans. In the present study, we investigated the effects of a functional variable number of tandem repeats (VNTR) polymorphism in exon 1f (ex1f) of the nitric oxide synthase 1 (NOS1) gene (NOS1 ex1f-VNTR) and stressful life events on aggressive behaviour in population representative sample of adolescents followed up from third grade to 25 years of age. We studied the younger cohort of the longitudinal Estonian Children Personality, Behaviour and Health Study (subjects in the last study wave n = 437, males n = 193; mean age 24.8 ± 0.5 years). Aggressive behaviour was rated at age 25 with the Illinois Bully Scale and Buss-Perry Aggression Questionnaire. Life history of aggression was evaluated in a structured interview. Stressful life events and family relationships were self-reported at age 15. The hypothesized risk genotype (homozygosity for the short allele) was associated with higher levels of aggression in males (statistical significance withstanding the multiple correction procedure). Exposure to stressful life events or adverse family relationships was associated with increased aggressive behaviour in subjects homozygous for either of the alleles, and these associations were mostly observed in males. However, these associations in these stratified analyses did not survive correction for multiple testing. Aggressiveness was relatively unaffected by the NOS1 ex1f-VNTR genotype in the female subjects even when taking exposure to childhood adversity into account. Our findings support the hypothesized involvement of a functional NOS1 polymorphism on aggression in a population representative sample of young adults.

Cynomorium songaricum Extract Alleviates Memory Impairment through Increasing CREB/BDNF via Suppression of p38MAPK/ERK Pathway in Ovariectomized Rats

Cynomorium songaricum Rupr is a very important traditional Chinese medicine for tonifying the kidney, which has a significant effect on improving estrogen level on the long term. In many studies, it can improve the learning and memory function of ovariectomized (OVX) model animals. 10 of the 50 rats received only bilateral back surgery and were harvested with the same amount of fat as the ovaries without removing the ovaries as sham group; remains underwent bilateral ovariectomy and equally randomized into five groups: sham group, with OVX as model group, estradiol valerate (EV, 0.2 mg/kg) as positive control, with 3.3 and 33 mg/kg body weight/day of ethyl acetate extract of Cynomorium songaricum extract (CSE) as low and high dosage groups, respectively. The orally administered CSE to ovariectomized rats exerted an ameliorative effect on learning and memory in the Morris water maze tests. All rats were sacrificed after 8 weeks of treatment, and tissue was analyzed using histopathology and electron microscopy. To comprehensively examine the mechanism, brain derived neurotrophic factor (BDNF), p-p38 mitogen-activated protein kinase (p-p38MAPK), extracellular regulated protein kinases (ERK), p-extracellular regulated protein kinases (p-ERK), and p-cAMP-response element binding protein (p-CREB) were detected by Western blotting. Using histopathology and electron microscopy, it was clearly observed that the pyramidal neurons of the hippocampal CA1 area were reduced in the OVX groups, indicating that CSE could attenuate the loss of pyramidal neurons in hippocampal CA1 and revert the synaptic morphological variations produced by ovariectomy. Mechanistically, the expressions of p-p38MAPK and p-ERK levels were significantly downregulated by CSE intervention, whereas the BDNF and p-CREB were significantly upregulated by CSE as compared to the control. Concisely, Cynomorium songaricum Rupr exhibited potential therapeutic effect on Neuroprotection of ovariectomized rats, and its effect was possibly exerted by p-CREB/BDNF mediated down regulation of ERK/p38MAPK.

Post-finasteride syndrome and post-SSRI sexual dysfunction: two sides of the same coin?

Sexual dysfunction is a clinical condition due to different causes including the iatrogenic origin. For instance, it is well known that sexual dysfunction may occur in patients treated with antidepressants like selective serotonin reuptake inhibitors (SSRI). A similar side effect has been also reported during treatment with finasteride, an inhibitor of the enzyme 5alpha-reductase, for androgenetic alopecia. Interestingly, sexual dysfunction persists in both cases after drug discontinuation. These conditions have been named post-SSRI sexual dysfunction (PSSD) and post-finasteride syndrome (PFS). In particular, feeling of a lack of connection between the brain and penis, loss of libido and sex drive, difficulty in achieving an erection and genital paresthesia have been reported by patients of both conditions. It is interesting to note that the incidence of these diseases is probably so far underestimated and their etiopathogenesis is not sufficiently explored. To this aim, the present review will report the state of art of these two different pathologies and discuss, on the basis of the role exerted by three different neuromodulators such as dopamine, serotonin and neuroactive steroids, whether the persistent sexual dysfunction observed could be determined by common mechanisms.

Early postnatal genistein administration permanently affects nitrergic and vasopressinergic systems in a sex-specific way

Genistein (GEN) is a natural xenoestrogen (isoflavonoid) that may interfere with the development of estrogen-sensitive neural circuits. Due to the large and increasing use of soy-based formulas for babies (characterized by a high content of GEN), there are some concerns that this could result in an impairment of some estrogen-sensitive neural circuits and behaviors. In a previous study, we demonstrated that its oral administration to female mice during late pregnancy and early lactation induced a significant decrease of nitric oxide synthase-positive cells in the amygdala of their male offspring. In the present study, we have used a different experimental protocol mimicking, in mice, the direct precocious exposure to GEN. Mice pups of both sexes were fed either with oil, estradiol or GEN from birth to postnatal day 8. Nitric oxide synthase and vasopressin neural systems were analyzed in adult mice. Interestingly, we observed that GEN effect was time specific (when compared to our previous study), sex specific, and not always comparable to the effects of estradiol. This last observation suggests that GEN may act through different intracellular pathways. Present results indicate that the effect of natural xenoestrogens on the development of the brain may be highly variable: a plethora of neuronal circuits may be affected depending on sex, time of exposure, intracellular pathway involved, and target cells. This raises concern on the possible long-term effects of the use of soy-based formulas for babies, which may be currently underestimated.

NADPH-Diaphorase Colocalizes with GPER and Is Modulated by the GPER Agonist G1 in the Supraoptic and Paraventricular Nuclei of Ovariectomized Female Rats

Nitric oxide is produced in the brain by the neuronal nitric oxide synthase (nNOS) and carries out a wide range of functions by acting as a neurotransmitter-like molecule. Gonadal hormones are involved in the regulation of the brain nitrergic system. We have previously demonstrated that estradiol, via classical estrogen receptors (ERs), regulates NOS activity in the supraoptic (SON) and paraventricular (PVN) nuclei of the hypothalamus, acting through both ERα and ERβ. Magnocellular and parvocellular neurons in the SON and PVN also express the G protein-coupled ER (GPER). In this study, we have assessed whether GPER is also involved in the regulation of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase in the SON and PVN. Adult female ovariectomized rats were treated with G1, a selective GPER agonist, or with G1 in combination with G15, a selective GPER antagonist. G1 treatment decreased NADPH-diaphorase expression in the SON and in all PVN subnuclei. The treatment with G1 + G15 effectively rescued the G1-dependent decrease in NADPH-diaphorase expression in both brain regions. In addition, the activation of extracellular signal-regulated kinase (ERK) 1/2, one of the kinases involved in the GPER-dependent intracellular signaling pathway and in NOS phosphorylation, was assessed in the same brain nuclei. Treatment with G1 significantly decreased the number of p-ERK 1/2-positive cells in the SON and PVN, while the treatment with G1 + G15 significantly recovered its number to control values. These findings suggest that the activation of GPER in the SON and PVN inhibits the phosphorylation of ERK 1/2, which induces a decrease in NADPH-diaphorase expression.

The Female Sexual Response: Current Models, Neurobiological Underpinnings and Agents Currently Approved or Under Investigation for the Treatment of Hypoactive Sexual Desire Disorder

How a woman responds to sexual cues is highly dependent on a number of distinct, yet related, factors. Researchers have attempted to explain the female sexual response for decades, but no single model reigns supreme. Proper female sexual function relies on the interplay of somatic, psychosocial and neurobiological factors; misregulation of any of these components could result in sexual dysfunction. The most common sexual dysfunction disorder is hypoactive sexual desire disorder (HSDD). HSDD is a disorder affecting women across the world; a recent in-person diagnostic interview study conducted in the USA found that an estimated 7.4% of US women suffer from HSDD. Despite the disorder's prevalence, it is often overlooked as a formal diagnosis. In a survey of primary care physicians and obstetrics/gynaecology specialists, the number one reason for not assigning an HSDD diagnosis was the lack of a safe and effective therapy approved by the US Food and Drug Administration (FDA). This changed with the recent FDA approval of flibanserin (Addyi™) for the treatment of premenopausal women with acquired, generalized HSDD; there are still, however, no treatments approved outside the USA. HSDD is characterized by a marked decrease in sexual desire, an absence of motivation (also known as avolition) to engage in sexual activity, and the condition's hallmark symptom, marked patient distress. Research suggests that HSDD may arise from an imbalance of the excitatory and inhibitory neurobiological pathways that regulate the mammalian sexual response; top-down inhibition from the prefrontal cortex may be hyperactive, and/or bottom-up excitation to the limbic system may be hypoactive. Key neuromodulators for the excitatory pathways include norepinephrine, oxytocin, dopamine and melanocortins. Serotonin, opioids and endocannabinoids serve as key neuromodulators for the inhibitory pathways. Evolving treatment strategies have relied heavily on these crucial research findings, as many of the agents currently being investigated as treatment options for HSDD target and influence key players within these excitatory and inhibitory pathways, including various hormone therapies and centrally acting drugs, such as buspirone, bupropion and bremelanotide.

Striatal NOS1 has dimorphic expression and activity under stress and nicotine sensitization

Nicotine exerts its addictive influence through the meso-cortico-limbic reward system, where the striatum is essential. Nicotine addiction involves different neurotransmitters, nitric oxide (NO) being especially important, since it triggers the release of the others by positive feedback. In the nervous system, NO is mainly produced by nitric oxide synthase 1 (NOS1). However, other subtypes of synthases can also synthesize NO, and little is known about the specific role of each isoform in the process of addiction. In parallel, NOS activity and nicotine addiction are also affected by stress and sexual dimorphism. To determine the specific role of this enzyme, we analyzed both NOS expression and NO synthesis in the striatum of wild-type and NOS1-knocked out (KO) mice of both sexes in situations of nicotine sensitization and stress. Our results demonstrated differences between the caudate-putamen (CP) and nucleus accumbens (NA). With respect to NOS1 expression, the CP is a dimorphic region (27.5% lower cell density in males), but with a stable production of NO, exclusively due to this isoform. Thus, the nitrergic system of CP may not be involved in stress or nicotine addiction. Conversely, the NA is much more variable and strongly involved in both situations: its NO synthesis displays dimorphic variations at both basal (68.5% reduction in females) and stress levels (65.9% reduction in males), which disappear when nicotine is infused. Thus, the KO animals showed an increase in NO production (21.7%) in the NA, probably by NOS3, in an attempt to compensate the lack of NOS1.

Schizandrin ameliorates ovariectomy-induced memory impairment, potentiates neurotransmission and exhibits antioxidant properties

BACKGROUND AND PURPOSE

Schizandrin (SCH) has been reported to prevent or reduce learning and memory defects. However, it is not known whether SCH ameliorates cognitive impairments induced by oestrogen deficiency. In the present study, we investigated the effect of SCH on memory in ovariectomized (OVX) and non-OVX rats.

EXPERIMENTAL APPROACH

A passive avoidance test was used to evaluate the effect of SCH on memory. Field EPSPs were recorded in hippocampal slices using an electrophysiological method. In OVX rats, biochemical parameters in the bilateral hippocampus were measured; these included superoxide dismutase (SOD), malondialdehyde (MDA) and AChE. Also, the number of NADPH-diaphorase (NADPH-d) positive neurons was counted by NADPH-d histochemistry staining technique.

KEY RESULTS

Oral SCH improved the memory and facilitated the induction of long-term potentiation in non-OVX and OVX rats; this effect was more obvious in OVX rats. Similarly, SCH perfusion enhanced synaptic transmission in hippocampal slices from both non-OVX and OVX rats. However, SCH perfusion reduced the ratio of paired-pulse facilitation only in OVX but not in non-OVX rats. In addition, SCH decreased AChE activity and MDA level and increased SOD activity and the number of NADPH-d-positive neurons in OVX rats.

CONCLUSIONS AND IMPLICATIONS

SCH improves memory in OVX rats and its potential mechanisms may include a reduction in the loss of hippocampal NADPH-d positive neurons, an increase of antioxidant properties and a potentiation of synaptic transmission that possibly involves to enhance cholinergic function. Overall, our findings indicate that SCH has potential as a therapeutic strategy for the cognitive dysfunctions associated with the menopause.

Estrous cycle and sex affect cocaine-induced behavioural changes in CD1 mice

RATIONALE

Several findings on sex differences in cocaine response suggest a role for hormonal milieu in modulating the subjective effects of cocaine. Nitric oxide (NO) has been involved in the neurochemical, hormonal, and behavioral changes related to stress and anxiety. Within the brain, the anteroventral subdivision of the medial amygdala (MeAV) is an important area involved in processing emotional responses such as anxiety and a high density of NO-producing neurons is observed in this area.

OBJECTIVES

In this study, we hypothesize the possibility of sex/hormonal differences in response to cocaine and that these differences may reflect a change in the MeAV nitrergic system. We have examined cocaine's acute effects on nicotinamide adenine dinucleotide phosphate diaphorase (nadph-d) expression, as well as its effect on motor activity and anxiety in male and estrus and diestrus females.

RESULTS

Our results show that acute cocaine administration produces an increase in both anxiety behaviors and nadph-d expression in the MeAV. Male and diestrus female mice were more susceptible to these effects of cocaine than estrus female mice in which no differences were detected. In addition, we examined individual differences in male and female mice responding to intravenous cocaine reinforcement in a self-administration paradigm. Female mice acquired cocaine self-administration at a faster rate than males and showed a higher motivation to self-administer cocaine under a progressive ratio schedule of reinforcement.

CONCLUSIONS

Our data suggest a complex interaction between hormonal milieu and the behavioral and reinforcing effects of cocaine.

Perinatal exposure to genistein affects the normal development of anxiety and aggressive behaviors and nitric oxide system in CD1 male mice

Genistein is a phytoestrogen, particularly abundant in soybeans, that is able to bind estrogen receptors exerting both estrogenic and antiestrogenic activities. Genistein is largely present in the human diet even during pregnancy. Embryos and fetuses are therefore, commonly exposed to genistein during the development and after birth. In the present study, we used a murine model as a test end-point to investigate the effects of early exposure to genistein on adult male behavior and related neural circuits. Daily exposure of dams to genistein (100 μg/g of body weight) during late pregnancy and early lactation, produced in male offspring, when adults, significant changes in anxiety and aggressive behaviors. Moreover, we found statistically significant variations in the number of neuronal nitric-oxide synthase positive cells in the amygdala. In conclusions, these data indicate that early exposure to phytoestrogens may induce life-long effects on the differentiation of brain structures and behaviors.

Tenuigenin ameliorates learning and memory impairments induced by ovariectomy

Estrogen deficiency is associated with cognitive impairment. Hormone replacement therapy (HRT) has proven to be effective in preventing and reversing the memory and learning deficiencies. However, conventional estrogenic treatment could increase the risks of breast cancer and venous thromboembolism. Tenuigenin (TEN) is putatively believed as the active component extracted from a Chinese herb Polygala tenuifolia root. Although TEN has been shown to enhance learning and memory in healthy mice, it remains unknown whether or not TEN could ameliorate learning and memory impairments. In the present study, mice were divided into four groups: sham-operated (sham), ovariectomized (OVX), OVX+estradiol benzoate (EB) and OVX+TEN groups. Step-through passive avoidance and Y-maze tests were used to assess learning and memory abilities, and the number of nitric oxide synthase (NOS) positive neurons and the synaptic measurement of hippocampal CA1 area were examined. The results showed that TEN was given orally to OVX mice, leading to the improvement of learning and memory in step-through passive avoidance and Y-maze tests. TEN could reduce the loss of NOS positive neurons and prevent the synaptic morphological changes induced by ovariectomy. Our results suggest that TEN may exert a potential therapeutic value for menopause cognitive dysfunction.

Role of oestrogen receptors on the modulation of NADPH-diaphorase-positive cell number in supraoptic and paraventricular nuclei of ovariectomised female rats

Modulation of the nitric oxide producing system (demonstrated via the NADPH-diaphorase histochemical reaction) by oestradiol has been established in several structures of the rat brain. The present study aimed to explore the possible regulation of NADPH-diaphorase activity by oestradiol in neurones of the supraoptic (SON) and paraventricular (PVN) nuclei and the role of oestrogen receptors (ERα and ERβ) in this regulation. Adult ovariectomised rats were divided into six groups and injected either with vehicle or a single dose of oestradiol, a selective ERα agonist-PPT [4,4',4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol], a selective ERβ agonist-DPN [2,3-bis(4-hydroxyphenyl)-propionitrile], a selective ERα antagonist-MPP [1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1H-pyrazole dihydrochloride] or a selective ERβ antagonist-PHTPP (4-[2-phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol). The number of NADPH-diaphorase positive elements in the SON and the PVN was modulated by both ERs but, depending on the nucleus, ERα and ERβ ligands induced different effects. These results suggest that the regulation of nitrergic system by ERs may play a role in the control of oestrogen-dependent physiological mechanisms regulated by the SON and the PVN.

Estradiol reduces depressive-like behavior through inhibiting nitric oxide/cyclic GMP pathway in ovariectomized mice

Estradiol decline has been associated with depressive-like behavior in female mice and NO has been suggested to play a major role in the pathogenesis of major depression. This study was conducted to investigate the antidepressant-like effects of acute estradiol administration in female ovariectomized (OVX) mice and the possible role of nitric oxide (NO)/cyclic GMP (cGMP) pathway. To this end, bilateral ovariectomy was performed in female mice and different doses of estradiol were injected alone or in combination with non-specific NO synthase (NOS) inhibitor (L-NAME), selective neural NOS (nNOS) inhibitor (7-NI), an NO precursor (L-arginine) or selective phosphodiesterase type 5 inhibitor (sildenafil). The duration of immobility was recorded in the forced swimming test (FST) to assess the depressive behavior. Moreover, hippocampal levels of NO were determined in select groups. 10 days following the procedure, OVX mice showed significantly prolonged immobility time in comparison with the sham group. Estradiol (3, 10, and 30 μg/kg, s.c.), when injected 1 h prior to FST, exerted antidepressant-like effects in OVX mice. Both L-NAME (30 mg/kg, i.p.), and 7-NI (50 mg/kg, i.p.) significantly reduced the immobility times of OVX mice. Administration of a sub-effective dose of L-NAME (10mg/kg), 15 min after a sub-effective dose of estradiol (1 μg/kg, s.c.) had a robust antidepressant-like effect in OVX mice. Also a sub-effective dose of 7-NI (25 mg/kg), 30 min after a sub-effective dose of estradiol (1 μg/kg, s.c.) showed antidepressant-like effect in OVX mice. Both the NO precursor L-arginine (750 mg/kg, i.p.) and the cGMP-specific phosphodiesterase type 5 inhibitor sildenafil (5 mg/kg, i.p.), 30 min before estradiol treatment, prevented the antidepressant-like effect of a potent dose of estradiol (10 μg/kg, s.c.) in OVX mice. The present findings suggest that suppression of the NO synthase/NO/cGMP pathway may be involved in the antidepressant-like effects of estradiol in OVX mice.

Testostérone et contrôle central de l’érection

La testostérone orchestre l’organisation périnatale et l’activation adulte des structures nerveuses cérébrales et spinales impliquées dans l’expression du comportement sexuel mâle. Cette revue décrit brièvement les différents effets de la testostérone dans la régulation de la motivation sexuelle et de l’érection, et les modèles génétiques générés, jusqu’à présent, dans le but d’élucider ses mécanismes d’action centraux.

Neuropeptides and enzymes are targets for the action of endocrine disrupting chemicals in the vertebrate brain

Endocrine-disrupting chemicals (EDC) are molecules that interfere with endocrine signaling pathways and produce adverse consequences on animal and human physiology, such as infertility or behavioral alterations. Some EDC act through binding to androgen or/and estrogen receptors primarily operating through a genomic mechanism regulating gene expression. This mechanism of action may induce profound developmental adverse effects, and the major targets of the EDC action are the gene products, i.e., mRNAs inducing the synthesis of various peptidic molecules, which include neuropeptides and enzymes related to neurotransmitters syntheses. Available immunohistochemical data on some of the systems that are affected by EDC in lower and higher vertebrates are detailed in this review.

Effects of perinatal administration of Bisphenol A on the neuronal nitric oxide synthase expressing system in the hypothalamus and limbic system of CD1 mice

Bisphenol A (BPA) is a well-known plastic-derived pollutant that can bind to oestrogen receptors and is considered an endocrine-disrupting chemical. Its impact on different behaviours in rodents has been largely investigated, however, only a few data are available on its effects upon neural circuits. In the present study, we investigated the long-term effects of early exposure of mice of both sexes to BPA on the nitrinergic system, one of the neural systems involved in the control of sexual behaviour and under the control of gonadal hormones. Mice of both sexes were exposed for eight prenatal and eight postnatal days to BPA that was administered to the mothers. The maternally-exposed mice were sacrificed at the age of 2 months and their brains were sectioned and immunohistochemically treated for the detection of neuronal nitric oxide synthase (nNOS). Significant effects of BPA exposure were detected for the number of immunoreactive cells in the medial preoptic nucleus and in the ventromedial subdivision of the bed nucleus of the stria terminalis, in a sex-oriented and dose-dependent way. These results indicate that BPA has a powerful effect on specific portions of the nNOS-immunoreactive system belonging to the accessory olfactory system that are particularly important for the control of sexual behaviour. In addition, they confirm that perinatal exposure to endocrine-disrupting chemicals, in particular to BPA, may have a high impact on the organisation of specific neural pathways that can later affect complex behaviours and functions.

Estrogen regulates cytoskeletal flexibility, cellular metabolism and synaptic proteins: A proteomic study

Estrogen (E2) influences brain function to induce gender differences in neuronal processes. In contrast to its well-described effects on signaling systems and gene transcription factors, our knowledge of E2-regulated protein networks is rather limited. Thus, we examined changes in protein expression patterns in the whole brains of ovariectomized mice after 24h estrogen exposure using two-dimensional differential gel electrophoresis. Interpretation of our network-based hypothesis suggested that E2 regulates synaptic proteins and processes, increases cytoskeletal flexibility and alters glucose consumption in the brain. We verified the predicted reduced basal synaptic activity using in vivo microdialysis in conscious mice, showing that E2 decreases the extracellular concentrations of certain amino acids in two different brain areas (in the striatum and in the hypothalamus) and that this is independent from the E2 receptor densities. Our data reveal that E2 induces minor, but substantial changes to functionally different protein networks at the whole brain level, and as a cumulative effect, it adjusts the brain steady-state condition to a more flexible state.

Of mice and rats: key species variations in the sexual differentiation of brain and behavior

Mice and rats are important mammalian models in biomedical research. In contrast to other biomedical fields, work on sexual differentiation of brain and behavior has traditionally utilized comparative animal models. As mice are gaining in popularity, it is essential to acknowledge the differences between these two rodents. Here we review neural and behavioral sexual dimorphisms in rats and mice, which highlight species differences and experimental gaps in the literature, that are needed for direct species comparisons. Moving forward, investigators must answer fundamental questions about their chosen organism, and attend to both species and strain differences as they select the optimal animal models for their research questions.

Phosphorylation of N-methyl-D-aspartic acid receptor-associated neuronal nitric oxide synthase depends on estrogens and modulates hypothalamic nitric oxide production during the ovarian cycle

Within the preoptic region, nitric oxide (NO) production varies during the ovarian cycle and has the ability to impact hypothalamic reproductive function. One mechanism for the regulation of NO release mediated by estrogens during the estrous cycle includes physical association of the calcium-activated neuronal NO synthase (nNOS) enzyme with the glutamate N-methyl-d-aspartate (NMDA) receptor channels via the postsynaptic density 95 scaffolding protein. Here we demonstrate that endogenous variations in estrogens levels during the estrous cycle also coincide with corresponding changes in the state of nNOS Ser1412 phosphorylation, the level of association of this isoform with the NMDA receptor/postsynaptic density 95 complex at the plasma membrane, and the activity of NO synthase (NOS). Neuronal NOS Ser1412 phosphorylation is maximal on the afternoon of proestrus when both the levels of estrogens and the physical association of nNOS with NMDA receptors are highest. Estradiol mimicked these effects in ovariectomized (OVX) rats. In addition, the catalytic activity of NOS in membrane protein extracts from the preoptic region, i.e. independent of any functional protein-protein interactions or cell-cell signaling, was significantly increased in estradiol-treated OVX rats compared with OVX rats. Finally, lambda phosphatase-mediated nNOS dephosphorylation dramatically impaired NOS activity in preoptic region protein extracts, thus demonstrating the important role of phosphorylation in the regulation of NO production in the preoptic region. Taken together, these results yield new insights into the regulation of neuron-derived NO production by gonadal steroids within the preoptic region and raise the possibility that changes in nNOS phosphorylation during fluctuating physiological conditions may be involved in the hypothalamic control of key neuroendocrine functions, such as reproduction.

Protective actions of estrogen on angiotensin II-induced hypertension: role of central nitric oxide

The present study tested the hypotheses that 1) nitric oxide (NO) is involved in attenuated responses to ANG II in female mice, and 2) there is differential expression of neuronal NO synthase (nNOS) in the subfornical organ (SFO) and paraventricular nucleus (PVN) in response to systemic infusions of ANG II in males vs. females. Aortic blood pressure (BP) was measured in conscious mice with telemetry implants. N(G)-nitro-l-arginine methyl ester (l-NAME; 100 microg x kg(.-1)day(-1)), an inhibitor of NOS, was administrated into the lateral cerebral ventricle for 14 days before and during ANG II pump implantation. Central infusion of l-NAME augmented the pressor effects of systemic ANG II in females (Delta21.5 + or - 2.2 vs. Delta9.2 + or - 1.5 mmHg) but not in males (Delta29.4 + or - 2.5 vs. Delta30.1 + or - 2.5 mmHg). Central administration of N(5)-(1-imino-3-butenyl)-l-ornithine (l-VNIO), a selective nNOS inhibitor, also significantly potentiated the increase in BP induced by ANG II in females (Delta17.5 + or - 3.2 vs. Delta9.2 + or - 1.5 mmHg). In gonadectomized mice, central l-NAME infusion did not affect the pressor response to ANG II in either males or females. Ganglionic blockade after ANG II infusion resulted in a greater reduction in BP in central l-NAME- or l-VNIO-treated females compared with control females. Western blot analysis of nNOS protein expression indicated that levels were approximately 12-fold higher in both the SFO and PVN of intact females compared with those in intact males. Seven days of ANG II treatment resulted in a further increase in nNOS protein expression only in intact females (PVN, to approximately 51-fold). Immunohistochemical studies revealed colocalization of nNOS and estrogen receptors in the SFO and PVN. These results suggest that NO attenuates the increase in BP induced by ANG II through reduced sympathetic outflow in females and that increased nNOS protein expression associated with the presence of female sex hormones plays a protective role against ANG II-induced hypertension in female mice.

Estrous cycle influences the expression of neuronal nitric oxide synthase in the hypothalamus and limbic system of female mice

BACKGROUND

Nitric oxide plays an important role in the regulation of male and female sexual behavior in rodents, and the expression of the nitric oxide synthase (NOS) is influenced by testosterone in the male rat, and by estrogens in the female. We have here quantitatively investigated the distribution of nNOS immunoreactive (ir) neurons in the limbic hypothalamic region of intact female mice sacrificed during different phases of estrous cycle.

RESULTS

Changes were observed in the medial preoptic area (MPA) (significantly higher number in estrus) and in the arcuate nucleus (Arc) (significantly higher number in proestrus). In the ventrolateral part of the ventromedial nucleus (VMHvl) and in the bed nucleus of the stria terminalis (BST) no significant changes have been observed. In addition, by comparing males and females, we observed a stable sex dimorphism (males have a higher number of nNOS-ir cells in comparison to almost all the different phases of the estrous cycle) in the VMHvl and in the BST (when considering only the less intensely stained elements). In the MPA and in the Arc sex differences were detected only comparing some phases of the cycle.

CONCLUSION

These data demonstrate that, in mice, the expression of nNOS in some hypothalamic regions involved in the control of reproduction and characterized by a large number of estrogen receptors is under the control of gonadal hormones and may vary according to the rapid variations of hormonal levels that take place during the estrous cycle.

Estrous cycle influences the expression of neuronal nitric oxide synthase in the hypothalamus and limbic system of female mice

BACKGROUND

Nitric oxide plays an important role in the regulation of male and female sexual behavior in rodents, and the expression of the nitric oxide synthase (NOS) is influenced by testosterone in the male rat, and by estrogens in the female. We have here quantitatively investigated the distribution of nNOS immunoreactive (ir) neurons in the limbic hypothalamic region of intact female mice sacrificed during different phases of estrous cycle.

RESULTS

Changes were observed in the medial preoptic area (MPA) (significantly higher number in estrus) and in the arcuate nucleus (Arc) (significantly higher number in proestrus). In the ventrolateral part of the ventromedial nucleus (VMHvl) and in the bed nucleus of the stria terminalis (BST) no significant changes have been observed. In addition, by comparing males and females, we observed a stable sex dimorphism (males have a higher number of nNOS-ir cells in comparison to almost all the different phases of the estrous cycle) in the VMHvl and in the BST (when considering only the less intensely stained elements). In the MPA and in the Arc sex differences were detected only comparing some phases of the cycle.

CONCLUSION

These data demonstrate that, in mice, the expression of nNOS in some hypothalamic regions involved in the control of reproduction and characterized by a large number of estrogen receptors is under the control of gonadal hormones and may vary according to the rapid variations of hormonal levels that take place during the estrous cycle.

Brain sex differences and hormone influences: a moving experience?

Sex differences in the nervous system come in many forms. Although a majority of sexually dimorphic characteristics in the brain have been described in older animals, mechanisms that determine sexually differentiated brain characteristics often operate during critical perinatal periods. Both genetic and hormonal factors likely contribute to physiological mechanisms in development to generate the ontogeny of sexual dimorphisms in brain. Relevant mechanisms may include neurogenesis, cell migration, cell differentiation, cell death, axon guidance and synaptogenesis. On a molecular level, there are several ways to categorize factors that drive brain development. These range from the actions of transcription factors in cell nuclei that regulate the expression of genes that control cell development and differentiation, to effector molecules that directly contribute to signalling from one cell to another. In addition, several peptides or proteins in these and other categories might be referred to as 'biomarkers' of sexual differentiation with undetermined functions in development or adulthood. Although a majority of sex differences are revealed as a direct consequence of hormone actions, some may only be revealed after genetic or environmental disruption. Sex differences in cell positions in the developing hypothalamus, and steroid hormone influences on cell movements in vitro, suggest that cell migration may be one target for early molecular actions that impact brain development and sexual differentiation.

Medial preoptic area interactions with dopamine neural systems in the control of the onset and maintenance of maternal behavior in rats

The medial preoptic area (MPOA) and dopamine (DA) neural systems interact to regulate maternal behavior in rats. Two DA systems are involved: the mesolimbic DA system and the incerto-hypothalamic DA system. The hormonally primed MPOA regulates the appetitive aspects of maternal behavior by activating mesolimbic DA input to the shell region of the nucleus accumbens (NAs). DA action on MPOA via the incerto-hypothalamic system may interact with steroid and peptide hormone effects so that MPOA output to the mesolimbic DA system is facilitated. Neural oxytocin facilitates the onset of maternal behavior by actions at critical nodes in this circuitry. DA-D1 receptor agonist action on either the MPOA or NAs can substitute for the effects of estradiol in stimulating the onset of maternal behavior, suggesting an overlap in underlying cellular mechanisms between estradiol and DA. Maternal memory involves the neural plasticity effects of mesolimbic DA activity. Finally, early life stressors may affect the development of MPOA-DA interactions and maternal behavior.

Restoration of female genital vasocongestive arousal responses in young and aged rats

INTRODUCTION

Treatments of aged, male hypertensive rats that induce vascular remodeling or that normalize endothelial function are known to produce sustained improvements in erectile function. Whether the treatments targeting these processes benefit female genital vasocongestive arousal (GVA) responses is currently not known.

AIM

To determine whether the actions of nitric oxide (NO) are critical to the apomorphine (APO)-generated GVA responses in both intact and ovariectomized OVX young adult female rats (before any aging-associated decreases in the responses). In addition, we also investigated whether the diminished GVA responses in aged rats could be restored, at least in part, using an antihypertensive treatment, which is known to enhance erectile responses and improve general vascular function in male rats.

METHODS

In female Wistar rats, APO-induced GVA responses (80 microg/kg, subcutaneously [sc], 30 minutes) were assessed by videomonitoring following various treatments. Young adult females were ovariectomized or were treated with the nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine methyl ester (30 mg/kg, iv), followed by an NO mimetic, sodium nitroprusside (10 microg/kg/minute, intravenous). Aged females (18 months) were treated for 2 weeks with the angiotensin converting enzyme (ACE) inhibitor, enalapril (30 mg/kg/day, orally) plus low sodium (0.04%).

MAIN OUTCOME MEASURES

APO-induced GVA responses in female rats.

RESULTS

There was an age-associated reduction in sexual responses in normotensive rats that was greatly enhanced (fourfold) by brief, aggressive antihypertensive treatment. The enhanced vasocongestive responses persisted for a 5-week off-treatment. Both OVX and NOS inhibition significantly decreased sexual responses by approximately 80% in young female rats. Systemic administration of an NO mimetic recovered vasocongestive responses in the NOS-blocked rats, but not in OVX animals.

CONCLUSIONS

Although mechanisms were not established, the major findings were that brief aggressive ACE inhibitor treatment markedly improved sexual responses in aged female rats, and systemic delivery of an NO mimetic recovered sexual responses in globally NOS-blocked animals.

Effects of neonatal handling on central noradrenergic and nitric oxidergic systems and reproductive parameters in female rats

Early-life environmental events that disrupt the mother-pup relationship may induce profound long-lasting changes on several behavioral and neuroendocrine systems. The neonatal handling procedure, which involves repeated brief maternal separations followed by experimental manipulations, reduces sexual behavior and induces anovulatory estrous cycles in female rats. On the afternoon of proestrus, neonatally handled females show a reduced surge of luteinizing hormone (LH) and an increased content of gonadotropin-releasing hormone in the medial preoptic area (MPOA). In order to detect the possible causes for the reduced ovulation and sexual behavior, the present study aimed to analyze the effects of neonatal handling on noradrenaline (NA) and nitric oxide (NO) levels in the MPOA on the afternoon of proestrus. Neonatal handling reduced MHPG (NA metabolite) levels and MHPG/NA ratio in the MPOA, indicating decreased NAergic activity. Additionally, neonatal handling decreased NO levels, as measured by the metabolites (NO(x)), nitrite and nitrate in the same period. We may conclude that the neonatal handling procedure decreased activity of the NAergic and NOergic systems in the MPOA during proestrus, which is involved in the control of LH and FSH secretion, and this may possibly explain the anovulatory estrous cycles and reduced sexual behavior of the neonatally handled female rats.

Nitric Oxide Synthase and NADPH Diaphorase Distribution in the Bullfrog (Rana catesbeiana) CNS: Pathways and Functional Implications

The gas nitric oxide (NO) is emerging as an important regulator of normal physiology and pathophysiology in the central nervous system (CNS). The distribution of cells releasing NO is poorly understood in non-mammalian vertebrates. Nitric oxide synthase immunocytochemistry (NOS ICC) was thus used to identify neuronal cells that contain the enzyme required for NO production in the amphibian brain and spinal cord. NADPH-diaphorase (NADPHd) histochemistry was also used because the presence of NADPHd serves as a reliable indicator of nitrergic cells. Both techniques revealed stained cells in all major structures and pathways in the bullfrog brain. Staining was identified in the olfactory glomeruli, pallium and subpallium of the telencephalon; epithalamus, thalamus, preoptic area, and hypothalamus of the diencephalon; pretectal area, optic tectum, torus semicircularis, and tegmentum of the mesencephalon; all layers of the cerebellum; reticular formation; nucleus of the solitary tract, octaval nuclei, and dorsal column nuclei of the medulla; and dorsal and motor fields of the spinal cord. In general, NADPHd histochemistry provided better staining quality, especially in subpallial regions, although NOS ICC tended to detect more cells in the olfactory bulb, pallium, ventromedial thalamus, and cerebellar Purkinje cell layer. NOS ICC was also more sensitive for motor neurons and consistently labeled them in the vagus nucleus and along the length of the rostral spinal cord. Thus, nitrergic cells were ubiquitously distributed throughout the bullfrog brain and likely serve an essential regulatory function.

Possible mechanism of acute effect of ethanol on intestinal IgA expression in rat

The purpose of this study was to investigate the possible mechanism of acute effect of ethanol on IgA expression in rat intestine. To this end, adult female Wistar rats showing diestrus day 1 were treated with (a) ethanol (2 or 4 g/kg, i.p.); (b) N omega-nitro-L-arginine-methyl ester (L-NAME), which inhibits the activity of all isoforms of nitric oxide synthase, (30 mg/kg, s.c.) followed by ethanol 3 h later; and (c) L-NAME (30 mg/kg, s.c.) followed by saline 3 h later. Saline-injected and untreated rats were used as controls. The animals were sacrificed 0.5 h after ethanol administration. Intestinal expression of IgA was evaluated by both immunohistochemistry and Western immunoblotting. Morphometric analysis showed that acute ethanol treatment increased the number of IgA-immunoreactive cells in a dose-dependent manner. Pretreatment with L-NAME abolished this action of alcohol. Injection of L-NAME followed by saline had no influence on the number of IgA+cells. The results, obtained by Western immunoblotting, paralleled our immunohistochemical findings. Taken together, these data suggest that acute effect of ethanol on intestinal IgA might be mediated by endogenous nitric oxide.

Regulation of soluble guanylyl cyclase activity by oestradiol and progesterone in the hypothalamus but not hippocampus of female rats

Oestradiol and progesterone act in the hypothalamus to coordinate the timing of lordosis and ovulation in female rats in part through regulation of nitric oxide (NO) and cyclic guanosine monophosphate (cyclic GMP) signalling pathways. Soluble guanylyl cyclase is an enzyme that produces cyclic GMP when stimulated by NO and plays a crucial role in the display of lordosis behaviour. We examined the effects of oestradiol and progesterone on the stimulation of cyclic GMP synthesis by NO-dependent and independent activators of soluble guanylyl cyclase in preoptic-hypothalamic and hippocampal slices. Ovariectomised Sprague-Dawley rats were injected with oestradiol (2 microg oestradiol benzoate, s.c.) or vehicle for 2 days. Progesterone (500 microg, s.c.) or vehicle was injected 44 h after the first dose of oestradiol. Rats were killed 48 h after the first oestradiol or vehicle injection, and hypothalamus and hippocampus were obtained. NO-dependent activation of soluble guanylyl cyclase was induced by NO donors, sodium nitroprusside or diethylamine NONOate; NO-independent activation of soluble guanylyl cyclase was induced with 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole and 5'-cyclopropyl-2-[1-2fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridine-3-yl]pyridine-4-ylamine. The NO-dependent activators of soluble guanylyl cyclase produced a concentration-dependent increase in cyclic GMP accumulation and induced significantly greater cyclic GMP accumulation in preoptic-hypothalamic slices from animals treated with oestradiol and progesterone than in slices from rats injected with vehicle, oestradiol or progesterone alone. Hormones did not modify soluble guanylyl cyclase activation by NO-independent stimulators or influence NO content in preoptic-hypothalamic slices. Oestradiol and progesterone did not affect activation of soluble guanylyl cyclase in hippocampal slices by any pharmacological agent, indicating a strong regional selectivity for the hormone effect. Thus, oestradiol and progesterone, administered in vivo, enhance the ability of NO to activate soluble guanylyl cyclase in brain areas modulating female reproductive function without an effect on production of NO itself.

Morphometrical and neurochemical changes in the anteroventral subdivision of the rat medial amygdala during estrous cycle

The anteroventral subdivision of the medial amygdala (MeAV) is one of the vomeronasal structures involved in the control of hormonally dependent behaviors such as sexual and agonistic behaviors in rats. The present study investigates some anatomical and neurochemical parameters of this nucleus (volume, number of neurons, number of glial elements, and of NADPH-diaphorase-positive neurons) in females in two estrous cycle phases (diestrous and estrous) and in males. We also investigate the possible existence of adult neurogenesis in this nucleus in the females. Results showed that volume and estimated number of Nissl-stained neurons in the MeAV vary with the estrous cycle phase: estrous females have greater values than diestrous females. As a consequence of these variations, there is a transient sex difference between males and diestrous females. Two subpopulations of NADPH-diaphorase-positive neurons were detected: intensely stained and medium stained. The intensely stained neurons were more numerous in the estrous than the diestrous females. Neither BrdU nor GFAP inmunostaining revealed significant differences between the two groups, suggesting that adult cell generation, i.e., increases in the number of glial elements, has no significant role in the changes detected in the number of Nissl-stained sections. In conclusion, the MeAV shows functional diergism, due to plastic changes in the female rat brain probably linked to the increase of estradiol during estrous. Finally, these changes are probably functionally related to changes in the behaviors that are controlled through this nucleus.

Nitric oxide involvement in estrous cycle-dependent changes of the behavioral responses of female rats in the elevated plus-maze test

Nitric oxide (NO)/cGMP pathway is known as a mediator in anxiety modulation. In this study, we assessed the involvement of NO pathway in the estrous cycle-related changes of anxiety level in rat. By using elevated plus-maze test, we studied the changes of serum nitrate and nitrite (NO(x)) levels in comparison to the estrous cycle-dependent changes of anxiety state. Then, we tested the effects of nitric oxide synthase (NOS) inhibitor, L-NAME (10, 60mg/kg, i.p.), and the NO precursor, l-arginine (100mg/kg, i.p.) on anxiety modulatory properties of exogenous ovarian hormones in ovariectomized (OVX) rats. Compared with other cycle phases and with OVX rats, cycling rats spent more time in open arms and had lower levels of serum NO(x) levels during metestrous while they spent less time in open arms and had lower levels of serum NO(x) levels during proestrous. In OVX rats, L-NAME (60mg/kg, i.p.) exerted anxiolytic effect while l-arginine showed no effect. In comparison with corn oil-treated controls, estradiol benzoate (10microg/kg, subcutaneously (s.c.)) significantly increased the serum NO(x) level and exerted anxiogenic effect, which was dose-dependently inhibited by L-NAME but was not changed by l-arginine. In contrast, progesterone (25mg/kg, s.c.) significantly decreased the serum NO(x) level and exerted anxiolytic effect, which was abolished by l-arginine but was not affected by L-NAME. These findings suggest that NO system might be involved in the estrous cycle-related changes of anxiety level, probably by mediating the effect of ovarian sex hormones.