Analysis of arsenic-modulated expression of hypothalamic estrogen receptor, thyroid receptor, and peroxisome proliferator-activated receptor gamma mRNA and simultaneous mitochondrial morphology and respiration rates in the mouse

Arsenic has been identified as an environmental toxicant acting through various mechanisms, including the disruption of endocrine pathways. The present study assessed the ability of a single intraperitoneal injection of arsenic, to modify the mRNA expression levels of estrogen- and thyroid hormone receptors (ERα,β; TRα,β) and peroxisome proliferator-activated receptor gamma (PPARγ) in hypothalamic tissue homogenates of prepubertal mice in vivo. Mitochondrial respiration (MRR) was also measured, and the corresponding mitochondrial ultrastructure was analyzed. Results show that ERα,β, and TRα expression was significantly increased by arsenic, in all concentrations examined. In contrast, TRβ and PPARγ remained unaffected after arsenic injection. Arsenic-induced dose-dependent changes in state 4 mitochondrial respiration (St4). Mitochondrial morphology was affected by arsenic in that the 5 mg dose increased the size but decreased the number of mitochondria in agouti-related protein- (AgRP), while increasing the size without affecting the number of mitochondria in pro-opiomelanocortin (POMC) neurons. Arsenic also increased the size of the mitochondrial matrix per host mitochondrion. Complex analysis of dose-dependent response patterns between receptor mRNA, mitochondrial morphology, and mitochondrial respiration in the neuroendocrine hypothalamus suggests that instant arsenic effects on receptor mRNAs may not be directly reflected in St3-4 values, however, mitochondrial dynamics is affected, which predicts more pronounced effects in hypothalamus-regulated homeostatic processes after long-term arsenic exposure.

Functional Aspects of Hypothalamic Asymmetry

Anatomically, the brain is a symmetric structure. However, growing evidence suggests that certain higher brain functions are regulated by only one of the otherwise duplicated (and symmetric) brain halves. Hemispheric specialization correlates with phylogeny supporting intellectual evolution by providing an ergonomic way of brain processing. The more complex the task, the higher are the benefits of the functional lateralization (all higher functions show some degree of lateralized task sharing). Functional asymmetry has been broadly studied in several brain areas with mirrored halves, such as the telencephalon, hippocampus, etc. Despite its paired structure, the hypothalamus has been generally considered as a functionally unpaired unit, nonetheless the regulation of a vast number of strongly interrelated homeostatic processes are attributed to this relatively small brain region. In this review, we collected all available knowledge supporting the hypothesis that a functional lateralization of the hypothalamus exists. We collected and discussed findings from previous studies that have demonstrated lateralized hypothalamic control of the reproductive functions and energy expenditure. Also, sporadic data claims the existence of a partial functional asymmetry in the regulation of the circadian rhythm, body temperature and circulatory functions. This hitherto neglected data highlights the likely high-level ergonomics provided by such functional asymmetry.

Metabolic Lateralization in the Hypothalamus of Male Rats Related to Reproductive and Satiety States

The hypothalamus is the main regulatory center of many homeostatic processes, such as reproduction, food intake, and sleep-wake behavior. Recent findings show that there is a strongly interdependent side-linked localization of hypothalamic functions between the left and right hemispheres. The goal of the present study was to trace functional asymmetry of the hypothalamus related to the regulation of food intake and reproduction, in male rodents. Subjects were examined through measurements of mitochondrial metabolism ex vivo. Impact of gonadectomy and scheduled feeding was tested on the modulation of hypothalamic metabolic asymmetry. Results show that in male rats, functional lateralization of the hypothalamus can be attributed to the satiety state rather than to reproductive control. Fasting caused left-sided metabolic dominance, while satiety was linked to the right hemisphere; trends and direction in sided dominance gradually followed the changes in satiety state. Our findings revealed satiety state-dependent metabolic differences between the two hypothalamic hemispheres. It is therefore concluded that, at least in male rats, the hypothalamic hemispheres control the satiety state-related functions in an asymmetric manner.

Thyroid hormone- and estrogen receptor interactions with natural ligands and endocrine disruptors in the cerebellum

Although the effects of phytoestrogens on brain function is widely unknown, they are often regarded as "natural" and thus as harmless. However, the effects of phytoestrogens or environmental pollutants on brain function is underestimated. Estrogen (17beta-estradiol, E2) and thyroid hormones (THs) play pivotal roles in brain development. In the mature brain, these hormones regulate metabolism on cellular and organismal levels. Thus, E2 and THs do not only regulate the energy metabolism of the entire organism, but simultaneously also regulate important homeostatic parameters of neurons and glia in the CNS. It is, therefore, obvious that the mechanisms through which these hormones exert their effects are pleiotropic and include both intra- and intercellular actions. These hormonal mechanisms are versatile, and the experimental investigation of simultaneous hormone-induced mechanisms is technically challenging. In addition, the normal physiological settings of metabolic parameters depend on a plethora of interactions of the steroid hormones. In this review, we discuss conceptual and experimental aspects of the gonadal and thyroid hormones as they relate to in vitro models of the cerebellum.

Bisphenol A influences oestrogen- and thyroid hormone-regulated thyroid hormone receptor expression in rat cerebellar cell culture

Thyroid hormones (THs) and oestrogens are crucial in the regulation of cerebellar development. TH receptors (TRs) mediate these hormone effects and are regulated by both hormone families. We reported earlier that THs and oestradiol (E₂) determine TR levels in cerebellar cell culture. Here we demonstrate the effects of low concentrations (10^-10 M) of the endocrine disruptor (ED) bisphenol A (BPA) on the hormonal (THs, E₂) regulation of TRα,β in rat cerebellar cell culture. Primary cerebellar cell cultures, glia-containing and glia-destroyed, were treated with BPA or a combination of BPA and E₂ and/or THs. Oestrogen receptor and TH receptor mRNA and protein levels were determined by real-time qPCR and Western blot techniques. The results show that BPA alone decreases, while BPA in combination with THs and/or E₂ increases TR mRNA expression. In contrast, BPA alone increased receptor protein expressions, but did not further increase them in combination with THs and/or E₂. The modulatory effects of BPA were mediated by the glia; however, the degree of changes also depended on the specific hormone ligand used. The results signify the importance of the regulatory mechanisms interposed between transcription and translation and raise the possibility that BPA could act to influence nuclear hormone receptor levels independently of ligand-receptor interaction.

Estrogen-Induced Hypothalamic Synaptic Plasticity and Pituitary Sensitization in the Control of the Estrogen-Induced Gonadotrophin Surge

Proper gonadal function requires coordinated (feedback) interactions between the gonads, adenohypophysis, and brain: the gonads elaborate sex steroids (progestins, androgens, and estrogens) and proteins (inhibin-activin family) during gamete development. In both sexes, the brain-pituitary gonadotrophin-regulating interaction is coordinated by estradiol through its opposing actions on pituitary gonadotrophs (sensitization of the response to gonadotrophin-releasing hormone [GnRH]) versus hypothalamic neurons (inhibition of GnRH secretion). This dynamic tension between the gonadotrophs and the GnRH cells in the brain regulates the circulating gonadotrophins and is termed reciprocal/negative feedback. In females, reciprocal/negative feedback dominates approximately 90% of the ovarian cycle. In a spectacular exception, the dynamic tension is broken during the surge of circulating estrogen that marks follicle and oocyte(s) maturation. The cause is an estradiol-induced disinhibition of the GnRH neurons that releases GnRH secretion to the highly sensitized pituitary gonadotrophs that in turn release the gonadotrophin surge (the estrogen-induced gonadotrophin surge [EIGS], also known as positive feedback). Studies during the past 4 decades have shown this disinhibition to result from estrogen-induced synaptic plasticity (EISP), including a reversible approximately 50% loss in arcuate nucleus synapses. The disinhibited GnRH secretion occurs during maximal gonadotroph sensitization and results in the EIGS. Specific immunoneutralization of estradiol blocks the EISP and EIGS. The EISP is accompanied by increases in insulinlike growth factor 1, polysialylated neural cell adhesion molecule, and ezrin, 3 proteins that the authors believe are the links between estrogen-induced astroglial extension and the EISP that releases GnRH secretion at the moment of maximal sensitization of the pituitary gonadotrophs. The result is the paradoxical surge of gonadotrophins at the peak of ovarian estrogen secretion and the triggering of ovulation. This enhanced understanding of the mechanics of gonadotrophin control clarifies elements of the involved feedback loops and opens the way to a better understanding of the neurobiology of reproduction.

Preparation of purified perikaryal and synaptosomal mitochondrial fractions from relatively small hypothalamic brain samples

In order to measure the activity of neuronal mitochondria, a representative proof of neuronal processes, physiologically relevant mitochondrial samples need to be gained as simply as possible. Existing methods are, however, either for tissue samples of large size and/or homogenous microstructures only, or are not tested for mitochondrial function measurements. In the present article we describe a gradient fractionation method to isolate viable and well-coupled mitochondria from relatively heterogeneous histological microstructures such as the hypothalamus. With this new method, we are able to isolate a sufficient amount of functional mitochondria for determination of respiratory activity, in a short period of time, using affordable equipment. •Verified by electron microscopy, our method separates highly enriched and well-preserved perikaryal and synaptosomal mitochondria. Both fractions contain minimal cell debris and no myelin. Respiratory measurements (carried out by Clark-type electrode) confirmed undisturbed mitochondrial function providing well-evaluable records. The demonstrated protocol yields highly viable mitochondrial subfractions within 3 h from small brain areas for high-precision examinations. Using this procedure, brain regions with relatively heterogeneous histological microstructure (hypothalamus) can also be efficiently sampled.•Up to our present knowledge, our method is the shortest available procedure with the lowest sample size to gain debris-free, fully-viable mitochondria.

Role of mitochondrial uncoupling protein-2 (UCP2) in higher brain functions, neuronal plasticity and network oscillation

Background/Purpose

Major psychiatric illnesses, affecting 36% of the world's population, are profound disorders of thought, mood and behavior associated with underlying impairments in synaptic plasticity and cellular resilience. Mitochondria support energy demanding processes like neural transmission and synaptogenesis and are thus points of broadening interest in the energetics underlying the neurobiology of mental illness. These experiments interrogated the importance of mitochondrial flexibility in behavior, synaptic and cortical activity in a mouse model.

Methods

We studied mice with ablated uncoupling protein-2 expression (UCP2 KO) and analyzed cellular, circuit and behavioral attributes of higher brain regions.

Results

We found that mitochondrial impairment induced by UCP2 ablation produces an anxiety prone, cognitively impaired behavioral phenotype. Further, NMDA receptor blockade in the UCP2 KO mouse model resulted in changes in synaptic plasticity, brain oscillatory and sensory gating activities.

Conclusions

We conclude that disruptions in mitochondrial function may play a critical role in pathophysiology of mental illness. Specifically, we have shown that NMDA driven behavioral, synaptic, and brain oscillatory functions are impaired in UCP2 knockout mice.

•

Impairment of mitochondrial functions by removal of UCP2 has multiple behavioral and circuit impairments of animals.

Estrogen- and Satiety State-Dependent Metabolic Lateralization in the Hypothalamus of Female Rats

Hypothalamus is the highest center and the main crossroad of numerous homeostatic regulatory pathways including reproduction and energy metabolism. Previous reports indicate that some of these functions may be driven by the synchronized but distinct functioning of the left and right hypothalamic sides. However, the nature of interplay between the hemispheres with regard to distinct hypothalamic functions is still unclear. Here we investigated the metabolic asymmetry between the left and right hypothalamic sides of ovariectomized female rats by measuring mitochondrial respiration rates, a parameter that reflects the intensity of cell and tissue metabolism. Ovariectomized (saline injected) and ovariectomized+estrogen injected animals were fed ad libitum or fasted to determine 1) the contribution of estrogen to metabolic asymmetry of hypothalamus; and 2) whether the hypothalamic asymmetry is modulated by the satiety state. Results show that estrogen-priming significantly increased both the proportion of animals with detected hypothalamic lateralization and the degree of metabolic difference between the hypothalamic sides causing a right-sided dominance during state 3 mitochondrial respiration (St3) in ad libitum fed animals. After 24 hours of fasting, lateralization in St3 values was clearly maintained; however, instead of the observed right-sided dominance that was detected in ad libitum fed animals here appeared in form of either right- or left-sidedness. In conclusion, our results revealed estrogen- and satiety state-dependent metabolic differences between the two hypothalamic hemispheres in female rats showing that the hypothalamic hemispheres drive the reproductive and satiety state related functions in an asymmetric manner.

Hypothalamic sidedness in mitochondrial metabolism: new perspectives

Morphofunctional changes in hypothalamic neurons are highly energy dependent and rely on mitochondrial metabolism. Therefore, mitochondrial adenosine triphosphate production plays a permissive role in hypothalamic regulatory events. Here, we demonstrated that in the female rat hypothalamus, mitochondrial metabolism and tissue oxygenation show an asymmetric lateralization during the estrous cycle. This asymmetry was not detected in males. The observed sidedness suggests that estrous cycle-linked hypothalamic functions in females are based on hemispheric distinction. The novel concept of hypothalamic asymmetry necessitates the revision of hypothalamic neural circuits, synaptic reorganization, and the role of hypothalamic sides in the regulation of integrated homeostatic functions.

Ligand-induced changes in Oestrogen and thyroid hormone receptor expression in the developing rat cerebellum: A comparative quantitative PCR and Western blot study

Oestrogen (E2) and thyroid hormones (THs) are key regulators of cerebellar development. Recent reports implicate a complex mechanism through which E2 and THs influence the expression levels of each other's receptors (ERs and TRs) to precisely mediate developmental signals and modulate signal strength. We examined the modulating effects of E2 and THs on the expression levels of their receptor mRNAs and proteins in cultured cerebellar cells obtained from 7-day-old rat pups. Cerebellar granule cell cultures were treated with either E2, THs or a combination of these hormones, and resulting receptor expression levels were determined by quantitative PCR and Western blot techniques. The results were compared to non-treated controls and to samples obtained from 14-day-old in situ cerebella. Additionally, we determined the glial effects on the regulation of ER-TR expression levels. The results show that (i) ER and TR expression depends on the combined presence of E2 and THs; (ii) glial cells mediate the hormonal regulation of neuronal ER-TR expression and (iii) loss of tissue integrity results in characteristic changes in ER-TR expression levels. These observations suggest that both E2 and THs, in adequate amounts, are required for the precise orchestration of cerebellar development and that alterations in the ratio of E2/THs may influence signalling mechanisms involved in neurodevelopment. Comparison of data from in vitro and in situ samples revealed a shift in receptor expression levels after loss of tissue integrity, suggesting that such adjusting/regenerative mechanisms may function after cerebellar tissue injury as well.

NTPDases in the neuroendocrine hypothalamus: possible energy regulators of the positive gonadotrophin feedback

BACKGROUND

Brain-derived ectonucleoside triphosphate diphosphohydrolases (NTPDases) have been known as plasma membrane-incorporated enzymes with their ATP-hydrolyzing domain outside of the cell. As such, these enzymes are thought to regulate purinergic intercellular signaling by hydrolyzing ATP to ADP-AMP, thus regulating the availability of specific ligands for various P2X and P2Y purinergic receptors. The role of NTPDases in the central nervous system is little understood. The two major reasons are the insufficient knowledge of the precise localization of these enzymes in neural structures, and the lack of specific inhibitors for the various NTPDases. To fill these gaps, we recently studied the presence of neuron-specific NTPDase3 in the mitochondria of hypothalamic excitatory neurons by morphological and functional methods. Results from those studies suggested that intramitochondrial regulation of ATP levels may play a permissive role in the neural regulation of physiological functions by tuning the level of ATP-carried energy that is needed for neuronal functions, such as neurotransmission and/or intracellular signaling.

PRESENTATION OF THE HYPOTHESIS

In the lack of highly specific inhibitors, the determination of the precise function and role of NTPDases is hardly feasable. Yet, here we attempt to find an approach to investigate a possible role for hypothalamic NTPDase3 in the initiation of the midcycle luteinizing hormone (LH) surge, as such a biological role was implied by our recent findings. Here we hypothesize that NTPDase-activity in neurons of the AN may play a permissive role in the regulation of the estrogen-induced pituitary LH-surge.

TESTING THE HYPOTHESIS

We propose to test our hypothesis on ovariectomized rats, by stereotaxically injecting 17beta-estradiol and/or an NTPDase-inhibitor into the arcuate nucleus and determine the consequential levels of blood LH, mitochondrial respiration rates from arcuate nucleus synaptosomal preparations, NTPDase3-expression from arcuate nucleus tissue samples, all compared to sham and intact controls.

IMPLICATIONS OF THE HYPOTHESIS

Results from these studies may lead to the conclusion that estrogen may modulate the activity of mitochondrial, synapse-linked NTPDase3, and may show a correlation between mitochondrial NTPDase3-activity and the regulation of LH-release by estrogen.

Effects of energy restriction on thyroid hormone metabolism in chickens

Energy restriction induces changes in thyroid hormone economy in the form of a complex adaptation mechanism, in order to conserve energy storage and protein reserves. In the present work, thyroid hormone serum concentrations, hepatic deiodinase enzyme activities and hepatic deiodinase mRNA expression were examined after feed restriction and fasting. We demonstrate that during energy restriction, T 3 concentration is lowered due to a decreased T 4 activation and increased T 3 inactivation. We show that hepatic type-I deiodinase (D1) is not affected by energy restriction, however, hepatic D2 is decreased on both transcriptional and enzyme activity levels. Furthermore, hepatic D3 is increased after feed restriction in the liver. We also show that the hypothalamic feedback is not involved in the changes in serum T 3 and T 4 concentrations. Our data indicate that D2 enzyme contributes to the special hormone-exporting role of the chicken liver and this enzyme can be modulated by feed restriction.

Ecto-nucleoside triphosphate diphosphohydrolase 3 in the ventral and lateral hypothalamic area of female rats: morphological characterization and functional implications

BACKGROUND

Based on its distribution in the brain, ecto-nucleoside triphosphate diphosphohydrolase 3 (NTPDase3) may play a role in the hypothalamic regulation of homeostatic systems, including feeding, sleep-wake behavior and reproduction. To further characterize the morphological attributes of NTPDase3-immunoreactive (IR) hypothalamic structures in the rat brain, here we investigated: 1.) The cellular and subcellular localization of NTPDase3; 2.) The effects of 17beta-estradiol on the expression level of hypothalamic NTPDase3; and 3.) The effects of NTPDase inhibition in hypothalamic synaptosomal preparations.

METHODS

Combined light- and electron microscopic analyses were carried out to characterize the cellular and subcellular localization of NTPDase3-immunoreactivity. The effects of estrogen on hypothalamic NTPDase3 expression was studied by western blot technique. Finally, the effects of NTPDase inhibition on mitochondrial respiration were investigated using a Clark-type oxygen electrode.

RESULTS

Combined light- and electron microscopic analysis of immunostained hypothalamic slices revealed that NTPDase3-IR is linked to ribosomes and mitochondria, is predominantly present in excitatory axon terminals and in distinct segments of the perikaryal plasma membrane. Immunohistochemical labeling of NTPDase3 and glutamic acid decarboxylase (GAD) indicated that gamma-amino-butyric-acid- (GABA) ergic hypothalamic neurons do not express NTPDase3, further suggesting that in the hypothalamus, NTPDase3 is predominantly present in excitatory neurons. We also investigated whether estrogen influences the expression level of NTPDase3 in the ventrobasal and lateral hypothalamus. A single subcutaneous injection of estrogen differentially increased NTPDase3 expression in the medial and lateral parts of the hypothalamus, indicating that this enzyme likely plays region-specific roles in estrogen-dependent hypothalamic regulatory mechanisms. Determination of mitochondrial respiration rates with and without the inhibition of NTPDases confirmed the presence of NTPDases, including NTPDase3 in neuronal mitochondria and showed that blockade of mitochondrial NTPDase functions decreases state 3 mitochondrial respiration rate and total mitochondrial respiratory capacity.

CONCLUSION

Altogether, these results suggest the possibility that NTPDases, among them NTPDase3, may play an estrogen-dependent modulatory role in the regulation of intracellular availability of ATP needed for excitatory neuronal functions including neurotransmission.

Glycogenic induction of thyroid hormone conversion and leptin system activation in the liver of postpartum dairy cows

In the regulation of energy metabolism, the liver plays an important role in the reinforcement of energy production. In periparturient cows the energy homeostasis turns into a negative energy balance that may shift the physiological regulation of energy balance towards pathological processes. Propylene glycol (PG), as a complementary source of energy used in the nutrition of dairy cows, alters systemic thyroid hormone economy; however, the exact mechanism through which highly glycogenic feed supplements impact liver metabolism is little known. Previous studies showed that only leptin receptors are expressed in the liver of cows, and now we report that leptin mRNA is expressed in the liver of cows as well. The present results show that the mRNA of leptin and its receptors are differentially modulated by the increased energy content of the feed consumed. Simultaneous changes in hepatic type I deiodinase activity suggest that hepatic modulation of the leptin system by PG supplementation may be mediated by an increased local thyroxine-triiodothyronine conversion. Since PG supplementation with simultaneous T4-T3 turnover and increased hepatic leptin- and short-form leptin receptor mRNA were not associated with a significant change in hepatic total lipid levels, it is suggested that the leptin system, directly or indirectly modulated by thyroid hormones, may represent a local defence mechanism to prevent fatty liver formation.

Oestrogens in the mammalian brain: from conception to adulthood--a review

Environmental and plant oestrogens have been identified as compounds that when ingested, disrupt the physiological pathways of endogenous oestrogen actions and thus, act as agonists or antagonists of oestrogen. Although the risks of exposure to exogenous oestrogens (ExEs) are subject to scientific debate, the question of how ExE exposure affects the central nervous system remains to be answered. We attempt to summarise the mechanisms of oestrogenic effects in the central nervous tissue with the purpose to highlight the avenues potentially used by ExEs. The genomic and rapid, non-genomic cellular pathways activated by oestrogen are listed and discussed together with the best known interneuronal mechanisms of oestrogenic effects. Because the effects of oestrogen on the brain seem to be age dependent, we also found it necessary to put the age-dependent oestrogenic effects in parallel to their intra- and intercellular mechanisms of action. Finally, considering the practical risks of human ExE exposure, we briefly discuss the human significance of this matter. We believe this short review of the topic became necessary because recent data suggest new fields and pathways for endogenous oestrogen actions and have generated the concern that the hidden exposure of humans and domestic animal species to ExEs may also exert its beneficial and/or adverse effects through these avenues.

Immunolocalization of ecto-nucleoside triphosphate diphosphohydrolase 3 in rat brain: Implications for modulation of multiple homeostatic systems including feeding and sleep–wake behaviors

Three anti-peptide antisera were raised against three distinct amino acid sequences of ecto-nucleoside triphosphate diphosphohydrolase 3 (NTPDase3), characterized by Western blot analyses, and used to determine the distribution of NTPDase3 protein in adult rat brain. The three antisera all yielded similar immunolocalization data, leading to increased reliability of the results obtained. Unlike NTPDase1 and NTPDase2, NTPDase3 immunoreactivity was detected exclusively in neurons. Immunoreactivity was localized primarily to axon-like structures with prominent staining of presynaptic elements. Specific perikaryal immunostaining was detected primarily in scattered neurons near the lateral hypothalamic area and the perifornical nucleus. High densities of immunoreactive axon-like fibers were present in midline regions of the forebrain and midbrain. Highly scattered NTPDase3 positive fibers were observed in the cerebral cortex, the hippocampal formation, and the basal ganglia. Moreover, very high densities of immunostained fibers were detected in the mediobasal hypothalamus, with the overall mesencephalic pattern of staining associated closely with hormone responsive nuclei. High densities of NTPDase3 positive terminals were also associated with noradrenergic neurons. However, co-immunolocalization studies revealed clearly that NTPDase3 immunoreactivity was not localized within the noradrenaline cells or terminals. In contrast, nearly all of the NTPDase3 immunopositive hypothalamic cells, and most fibers in the mid- and hindbrain, also expressed hypocretin-1/orexin-A. The overall pattern of expression and co-localization with hypocretin-1/orexin-A suggests that NTPDase3, by regulating the extracellular turnover of ATP, may modulate feeding, sleep-wake, and other behaviors through diverse homeostatic systems.

Ontogeny of rapid estrogen-mediated extracellular signal-regulated kinase signaling in the rat cerebellar cortex: potent nongenomic agonist and endocrine disrupting activity of the xenoestrogen bisphenol A

In addition to regulating estrogen receptor-dependent gene expression, 17beta-estradiol (E(2)) can directly influence intracellular signaling. In primary cultured cerebellar neurons, E(2) was previously shown to regulate growth and oncotic cell death via rapid stimulation of ERK1/2 signaling. Here we show that ERK1/2 signaling in the cerebellum of neonatal and mature rats was rapidly responsive to E(2) and during development to the environmental estrogen bisphenol A (BPA). In vivo dose-response analysis for each estrogenic compound was performed by brief (6-min) intracerebellar injection, followed by rapid fixation and phosphorylation-state-specific immunohistochemistry to quantitatively characterize changes in activated ERK1/2 (pERK) immunopositive cell numbers. Beginning on postnatal d 8, E(2) significantly influenced the number of pERK-positive cells in a cell-specific manner that was dependent on concentration and age but not sex. In cerebellar granule cells on postnatal d 10, E(2) or BPA increased pERK-positive cell numbers at low doses (10(-12) to 10(-10) M) and at higher (10(-7) to 10(-6) M) concentrations. Intermediate concentrations of either estrogenic compound did not modify basal ERK signaling. Rapid E(2)-induced increases in pERK immunoreactivity were specific to the ERK1/2 pathway as demonstrated by coinjection of the mitogen-activated, ERK-activating kinase (MEK)1/2 inhibitor U0126. Coadministration of BPA (10(-12) to 10(-10) M) with 10(-10) M E(2) dose-dependently inhibited rapid E(2)-induced ERK1/2 activation in developing cerebellar neurons. The ability of BPA to act as a highly potent E(2) mimetic and to also disrupt the rapid actions of E(2) at very low concentrations during cerebellar development highlights the potential low-dose impact of xenoestrogens on the developing brain.

Estrogen receptor expression in a human primitive neuroectodermal tumor cell line from the cerebral cortex: estrogen stimulates rapid ERK1/2 activation and receptor-dependent cell migration

Primitive neuroectodermal tumors (PNETs) are the most common form of pediatric brain tumor. Most often these malignant childhood brain tumors arise from neuroepithelial precursor cells in the cerebellum, and less frequently in the cerebral cortex. Because the normal PNET precursor cells from the cerebrum and cerebellum transiently express high levels of estrogen receptors (ERs), we hypothesized that the PNET cells of the cerebrocortical-derived cell line PFSK1 may also express ERs and would be responsive to estrogen. Results of immunoblot studies using ER-specific antiserum indicate that both ERalpha and ERbeta are expressed in PFSK1 cells. The ability of estrogen to rapidly activate MAPK signaling was tested; low physiological concentrations of E(2) stimulated ERK1/2 phosphorylation and nuclear translocation within 15min of exposure. Exogenously added 17beta-estradiol (E(2)) could not stimulate PFSK1 growth, however E(2) significantly increased PFSK1 cell migration, suggesting that rapid actions of E(2) and ER-mediated processes might contribute to the metastatic phenotype of some PNETs.

Spatial, temporal, and cellular distribution of the activated extracellular signal regulated kinases 1 and 2 in the developing and mature rat cerebellum

The extracellular signal regulated kinases 1 and 2 (ERK1/2) are important members of an intracellular signaling cascade that is involved in many aspects of the cellular physiology and development of neurons and glia. ERK1/2 are expressed in many brain regions including the cerebellum; however, their role during cerebellar development is poorly understood. Immunohistochemical approaches using phosphorylation-state specific antiserum that recognizes only the activated-ERK1/2 (pERK) were used to characterize the spatial and temporal patterns of activated-ERK in the developing and adult rat cerebellum. The distribution and cell type-specificity of pERK-immunoreactivity (IR) followed an age-related pattern, with the density of pERK-IR Purkinje cells decreasing between P6 and P15 and increasing at later times. Immunopositive granule cell neurons increased from P6 to P12, became decreased during much of late postnatal cerebellar development, and absent in adults. Co-localization of pERK with glial fibrillary acidic protein or the neuronal marker beta-tubulin revealed that activated ERK is present in maturing Purkinje and granule cells, and the soma of Bergmann glia on P4, P10 and P15; pERK was detected in astrocytes on P10 and P15. Associated with weaning, there was a general increase in activated-ERK in all cell types on P22. In adults, pERK-IR was confined to the Purkinje cell layer and scattered cells in the corpus medullare. In summary, a high degree of developmental plasticity was observed in the spatiotemporal distribution of cerebellar pERK-IR suggesting that the ERK-pathway plays a dynamic role in regulating neuronal and glial migration, proliferation and differentiation in the developing cerebellum. In the mature cerebellum, ERK signaling may also mediate postsynaptic information processing.

Estrogens and ICI182,780 (Faslodex) modulate mitosis and cell death in immature cerebellar neurons via rapid activation of p44/p42 mitogen-activated protein kinase

Estrogen influences the development and function of the nervous system through estrogen receptor-dependent changes in gene expression and by rapidly influencing diverse intracellular signaling pathways. We have investigated the influence of estradiol on developing neonatal rat cerebellar neurons in primary culture and found that low concentrations of 17beta-estradiol (17beta-E2), 17alpha-E2, 17beta-E2-BSA, and ICI182,780 stimulated phosphorylation of the extracellular signal-regulated kinases 1/2 (ERK1/2) mitogen-activated protein kinases (MAPK). Neither testosterone nor progesterone increased ERK1/2 phosphorylation. The effects of the estrogens were specific to the ERK1/2 MAPK pathway and were blocked by U0126, an inhibitor of the ERK1/2 MAPK kinase (MEK1/2). Compared with control cultures, significant MAPK-dependent decreases in viable granule cell numbers were observed in dissociated explant cultures of developing cerebellar neurons 24-96 hr after pulse treatment with 10 pm 17beta-E2 or 10 nm ICI182,780. In contrast, continuous exposure to 10 pm 17beta-E2 significantly increased granule cell numbers. Analysis of bromodeoxyuridine incorporation revealed that a 15 min pulsed treatment with 10 pm 17beta-E2 increased mitogenesis, whereas continuous exposure to the same concentration of 17beta-E2 was anti-mitotic. Estradiol did not increase caspase activity; however, significant increases in cellular permeability and lysis were observed. Cell lysis and death were independent of the pan-caspase inhibitor zVAD-fmk but were blocked fully by the irreversible calpain inhibitor PD150606. These results indicate that rapid activation of the ERK1/2 MAPK pathway by low concentrations of 17beta-E2 induces oncotic/necrotic, but not apoptotic, programmed cell death in a subpopulation of developing granule cells and increased mitogenesis of the granule cell neuroblasts refractory to estrogen-induced neurotoxicity.

Estradiol affects axo-somatic contacts of neuroendocrine cells in the arcuate nucleus of adult rats

It has been shown that gonadal steroids have the capacity to induce synaptic plasticity in certain areas of the nervous system. Previously we have demonstrated that due to the effect of estradiol there is a transient decrease in the number of GABAergic axo-somatic synapses in the arcuate nucleus. By using systemic application of the tracer Fluorogold we retrogradely labeled a subpopulation of arcuate neurons that project to the median eminence. We than applied the disector method for synapse quantification and found that these "hypophysiotropic neurons" receive less axo-somatic inputs. We found that 17beta-estradiol induced a decrease in the numerical density of axo-somatic contacts of these retrogradely-labeled neoroendocrine cells. Our data support the hypothesis that the hormonally driven morphological synaptic plasticity is neuron specific within the arcuate nucleus and plays a decisive role in the regulation of anterior pituitary.

Estrogen regulates GFAP-expression in specific subnuclei of the female rat interpeduncular nucleus: a potential role for estrogen receptor beta

We previously demonstrated that in rat, astrocytic glial fibrillary acidic protein- (GFAP) expression in the interpeduncular nucleus (IPN) was responsive to testosterone and in females the intensity of GFAP-immunoreactivity (IR) followed the periodic hormonal changes of the estrous cycle. The aim of this study was to test whether 17beta-estradiol (E(2)), in the absence of other ovarian hormones, can influence GFAP-expression within individual subnuclei of the IPN and to determine the cellular distribution of estrogen receptor beta (ERbeta) in the IPN. Quantitative surface-density analysis was used to compare the intensity of GFAP-IR at different anterio-posterior (AP) levels of the IPN in ovariectomized female rats 24 h after treatment with E(2) or vehicle. Estrogen-treatment resulted in a significant increase in GFAP-IR in the rostrolateral subnucleus of the IPN at AP: -5.60, in the lateral-, dorsolateral-, dorsomedial- and central subnuclei at -6.04 and in the lateral subnucleus at -6.72. No significant differences were observed at -5.80 and -6.30. These results indicate that E(2), in the absence of other ovarian hormones, modulates GFAP-expression within select IPN subnuclei and that these affects are dependent on position along the AP axis. To determine whether ERbeta was a possible mediator of the observed estrogenic effects, adjacent section pairs of the IPN were immunostained for ERbeta or GFAP. Using the 'mirror' method, ERbeta-IR was detected in the cytoplasm of GFAP-immunopositive astroglia and in the nuclei of GFAP-immunonegative neurons. These findings suggest that in the IPN, E(2) may directly modulate GFAP-expression through ERbeta-mediated mechanisms.

Meningeal allografts of the 6-day-old rat pineal: a model for a pineal deprived of intracerebral innervation

Pineals from 6-day-old rats were transplanted into an incised bed of the parietal cortex of adult rats, of which 29 survived 4-5 weeks after transplantation. The pinealocytes and capillaries in the grafts were comparable in structure to those in the control. Grafts were demarcated from the host cortical tissue by a double, meninx plus gland-capsule sheath through which no nerve ingrowth was seen into the graft from the host brain. On the other hand, sympathetic nerves originating from the cervical ganglia reached the grafted pineal along the perivascular spaces of blood vessels, as is the case in situ. On this basis. the present meningeal graft is thought to be a model of the pineal gland surviving without its intracerebral neural control.

Estrogenic actions in the brain: estrogen, phytoestrogens, and rapid intracellular signaling mechanisms

The endogenous gonadal steroid 17beta-estradiol (E2) plays an important role in the development, maturation, and function of a wide variety of reproductive and nonreproductive tissues, including those of the nervous system. The actions of E2 at target tissues can be divided into 1) long-term "genomic" actions that are mediated by intracellular estrogen receptor-induced changes in gene expression and 2) rapid actions that modulate a diverse array of intracellular signal transduction cascades. Environmental estrogens are compounds present in the environment that can mimic, and in some cases antagonize, the effects of endogenous estrogens. As a result of these actions, there is currently much interest within the scientific community regarding the relative benefits or threats associated with exposure to different environmental estrogens. Within the general public there is considerable acceptance of the benefits associated with increased use of "natural" estrogens as a component of a healthy diet and in postmenopausal women as an alternative to estrogen replacement therapies. First, this review will focus attention on the role of estrogens in the central nervous system by briefly discussing some of the known mechanisms through which estrogen's effects are mediated, focusing on rapid intracellular signaling mechanisms during neurodevelopment. Second, with the hope of bringing attention to an area of study that until recently has received little consideration, we will briefly discuss phytoestrogens and suggest that these compounds have the potential to influence rapid E2-induced mechanisms in the nervous system in ways that may result in modified brain functions.

Identification of a developmental gradient of estrogen receptor expression and cellular localization in the developing and adult female rat primary somatosensory cortex

Immunohistochemistry was used to investigate the spatiotemporal distribution of estrogen receptor alpha and beta (ER alpha, ER beta) in the posteromedial barrel subfield (PMBS) of the cerebral cortex in developing and adult female rats. Counting of immunopositive cells in predefined areas from each layer of the PMBS showed that at PN3, ER alpha immunoreactivity (IR) was present in every cell, whereas ER beta-IR was not detected. At PN6, about 59% of the cells were ER alpha immunopositive and low levels of ER beta-IR were observed in scattered cells. At PN18 the proportion of ER alpha-IR cells decreased to 49%; however, ER beta-IR became widespread and was detected in 39% of cells. By PN25 only faint ER alpha-IR was observed and in the adults ER alpha-IR was not detected. In contrast, at PN25 and in adults, ER beta-IR was detected in about half the cells of the PMBS. Regarding the cellular localization of ER-IR, at PN3 an outside-in gradient of cytoplasmic to nuclear localization of ER alpha-IR was observed. At PN18 and in adults ER beta-IR was preferentially localized to the nucleus of principal neurons, and to the cytoplasm of small, stellate-shaped interneurons. Together, these observations reveal a developmental transition of ER expression in the PMBS; ER alpha is expressed during early development, ER alpha and ER beta are co-expressed at later developmental times, and only ER beta is expressed in adults. These changes in ER expression and localization suggest that ER alpha and ER beta may play important, but different roles in the formation and function of the PMBS region of the primary somatosensory cortex.

Retarded myelination in the lumbar spinal cord of piglets born with spread-leg syndrome

Piglets born with spread-leg syndrome, a congenital weakness of the hindlimb adductors, were investigated to determine the site of lesion leading to limb impairment. Histological and immunohistochemical studies of the motor neuron unit showed no alterations but quantitative analysis revealed a reduction of axonal diameter and myelin sheath-thickness of the fibres innervating the adductors of the affected limbs. In the lumbar spinal cord a lack of myelination was observed in the tracts descending to the lower motor neurons. Recovery from the syndrome was accompanied by a catching-up of myelination with that of the controls. The spread-leg syndrome is due to a nutritional deficiency in the sow; thus it is assumed that the deficient maternal substances, mainly choline and methionine, are essential for the normal myelin production by spinal white matter oligodendrocytes of the fetus.

Oestrogen-induced changes in the synaptology of the monkey (Cercopithecus aethiops) arcuate nucleus during gonadotropin feedback

To assess their role in the regulation of gonadotropin secretion in primates, we determined the number of synaptic connections on gondotropin releasing hormone (GnRH)- and non-GnRH neurones of the arcuate nucleus of ovariectomized (OVX) and OVX plus oestradiol benzoate-treated African green monkeys. After 24 h (day 1), 48 h (day 2) and 8 days (day 8), we performed immunostaining for GnRH. Using electron microscopy, synapses on GnRH- and randomly selected non-GnRH neurones were counted and characterized according to the classification of Gray (symmetric/inhibitory or asymmetric/excitatory). Serum concentrations of oestradiol (OVX) needed to 232 pg/ml on day 1, 63 pg/ml on day 2 and 45 pg/ml on day 8. Concentrations of luteinizing hormone (LH) fell after ovariectomy to 9 microg/ml on day 1, surged to 93 microg/ml on day 2 and declined again by day 8. (a) Ten days after ovariectomy, there were no synapses on GnRH neurones, whereas non-GnRH cells received substantial inhibitory innervation and moderate excitatory input. (b) On day 1, GnRH neurones had highest numbers of inhibitory synapses, while inhibitory synapses on non-GnRH neurones decreased, whereas numbers of excitatory synapses remained relatively unchanged compared to OVX monkeys. (c) By day 2, synapses on GnRH neurones decreased, while synapses increased on non-GnRH cells compared to day 1. (d) On day 8, the most pronounced alteration on GnRH cells was an elevated inhibitory input while non-GnRH neurones received the fewest synapses compared to day 2. We conclude that during an oestrogen-induced LH surge, synapses on GnRH- and mixed non-GnRH neurones are differentially regulated. These findings suggest that oestrogen modulation of arcuate nucleus synapses may be important in the regulation of gonadotropin secretion in monkeys.

AMPA receptors colocalize with neuropeptide-Y- and galanin-containing, but not with dopamine, neurons of the female rat arcuate nucleus: a semiquantitative immunohistochemical colocalization study

It is well established that excitatory amino acid (EAA) neurotransmission is an essential component in the regulation of the gonadotropin-releasing hormone (GnRH) delivery system. However, the morphological interconnection of these systems is not fully understood. The objective of the present study was to determine whether or not alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors--as indicators of aspartate/glutamatergic innervation--are present in the major neuronal populations, such as the neuropeptide-Y-(NPY), galanin- (GAL) and tyrosine-hydroxylase- (TH) containing neurons of the arcuate nucleus (AN) of the female rat. Colocalization experiments using the "mirror" technique demonstrated that: (1) AN neurons containing GluR1 are also immunoreactive (IR) for GluR2/3; (2) 38.32% of AMPA-IR cells contain NPY and 31.72% of AMPA-containing neurons are also IR for GAL; in turn, 79.41% of NPY- and 56.19% of GAL-containing neurons are IR for AMPA receptors; none of the neurons are IR for both AMPA receptors and TH. These data suggest that an excitatory aspartate/glutamatergic input is implicated in the regulation of the examined neuropeptide-containing AN neurons but not in that of TH-IR cells of the same area.

Estrogen effects on tyrosine hydroxylase-immunoreactive cells in the ventral mesencephalon of the female rat: further evidence for the two cell hypothesis of dopamine function

The present study was undertaken to examine the differential effect of estrogen (E) on the expression of tyrosine hydroxylase (TH) in the substantia nigra compacta (SNc) and in two subdivisions of the ventral tegmental area in ovariectomized (ovx) and ovx plus estradiol benzoate (ovx+E)-treated female rats. Cell counting of TH-immunoreactive perikarya of the SNc, paranigral (PN) and interfascicular (IF) nucleus was performed and compared. Our findings demonstrate that E eliminated TH immunoreactivity from a number of midbrain neurons, while it seemingly did not affect it in others. This signifies a differential effect of E on ventral mesencephalic dopaminergic neurons.

Modular distribution of vasoactive intestinal polypeptide in the rat barrel cortex: changes induced by neonatal removal of vibrissae

The distribution of vasoactive intestinal polypeptide-immunoreactive neuronal structures in the barrel cortex (posteromedial barrel subfield) of adult rats was analysed after unilateral removal of the vibrissal follicles of row C in neonatal rats. The hypothesis was tested whether the distribution of vasoactive intestinal polypeptide-immunoreactive structures depends on the normal anatomical organization of the specific sensory input. After three months survival the distribution of the vasoactive intestinal polypeptide-immunoreactive structures was morphometrically evaluated. This approach revealed alterations in the contralateral posteromedial barrel subfield, where the disappearance of barrel row C and a substantial increase in size mainly of barrel row D, but also of other rows could be detected. Increase in row D included both barrels and the interspace (septal segments between barrels in one row). As vasoactive intestinal polypeptide immunoreactivity of the barrel field was found previously to be localized in synaptic boutons involved in symmetric synapses, our present findings suggest that (i) the interspace is enriched in inhibitory vasoactive intestinal polypeptide-immunoreactive synapses as opposed to the excitatory thalamocortical input reaching the barrel hollow, (ii) the spatial distribution of the vasoactive intestinal polypeptide system in the barrel cortex is closely associated with the neuronal organization of the sensory input and reacts with a considerable plasticity to lesion-induced changes of the input, and (iii) the compensatory barrel hypertrophy in a row neighbouring the deafferented row involves an increasing number of vasoactive intestinal polypeptide-immunoreactive synapses per barrel.