Detection of estrogen receptor (ER) in the rat brain using rat anti-ER monoclonal IgG with the unlabeled antibody method

Puberty onset in female rats: relationship with fat intake, ovarian steroids and the peptides, galanin and enkephalin, in the paraventricular and medial preoptic nuclei

Puberty is a time of rapid change, including a marked increase in fat consumption and body fat accrual, particularly in females. The mechanisms underlying these changes are unknown. Building on the results obtained in adult rats, the present study in pubertal rats focused on the orexigenic peptides, galanin (GAL) and enkephalin (ENK), in the paraventricular nucleus (PVN) and medial preoptic nucleus (MPN), which are known to be responsive to female steroids and have a role in both energy balance and reproductive function. The present study examined female rats maintained on pure macronutrient diets from before weaning (day 15) to day 70. After an initial burst in protein intake (days 21-35), rats showed an increase, specifically in preference for fat, from 15% to 30%. In rats examined at different ages before (day 30) and after (days 45 and 60) puberty, this rise in fat intake was associated with a marked increase, from days 30-45, in levels of oestradiol and progesterone and in GAL and ENK mRNA or peptide levels, specifically in the PVN and MPN, but not other hypothalamic areas examined. This positive relationship with increased fat intake, steroids and peptides across ages was also observed when comparing pubertal rats that naturally preferred fat (> 25% of total diet) with those consuming little fat (< 15%) or rats that reached puberty at an early age (days 30-34) with those that were late (days 37-40). These rats with early puberty onset exhibited a strong fat preference 3-4 days before vaginal opening, which was positively related to steroid levels, GAL, fat intake and body fat accrual after puberty. These findings suggest that, in addition to providing a signal for puberty onset, early fat ingestion acting through mechanisms involving the steroids and orexigenic peptides may be related to long-term patterns of eating and body weight regulation.

Increased caloric intake on a fat-rich diet: role of ovarian steroids and galanin in the medial preoptic and paraventricular nuclei and anterior pituitary of female rats

Previous studies in male rats have demonstrated that the orexigenic peptide galanin (GAL), in neurones of the anterior parvocellular region of the paraventricular nucleus (aPVN) projecting to the median eminence (ME), is stimulated by consumption of a high-fat diet and may have a role in the hyperphagia induced by fat. In addition to confirming this relationship in female rats and distinguishing the aPVN-ME from other hypothalamic areas, the present study identified two additional extra-hypothalamic sites where GAL is stimulated by dietary fat in females but not males. These sites were the medial preoptic nucleus (MPN), located immediately rostral to the aPVN, and the anterior pituitary (AP). The involvement of ovarian steroids, oestradiol (E(2)) and progesterone (PROG), in this phenomenon was suggested by an observed increase in circulating levels of these hormones and GAL in MPN and AP with fat consumption and an attenuation of this effect on GAL in ovariectomised (OVX) rats. Furthermore, in the same four areas affected by dietary fat, levels of GAL mRNA and peptide immunoreactivity were stimulated by E(2) and further by PROG replacement in E(2)-primed OVX rats and were higher in females compared to males. Because both GAL and PROG stimulate feeding, their increase on a fat-rich diet may have functional consequences in females, possibly contributing to the increased caloric intake induced by dietary fat. This is supported by the findings that PROG administration in E(2)-primed OVX rats reverses the inhibitory effect of E(2) on total caloric intake while increasing voluntary fat ingestion, and that female rats with higher GAL exhibit increased preference for fat compared to males. Thus, ovarian steroids may function together with GAL in a neurocircuit, involving the MPN, aPVN, ME and AP, which coordinate feeding behaviour with reproductive function to promote consumption of a fat-rich diet at times of increased energy demand.

Normoxic resuscitation after cardiac arrest protects against hippocampal oxidative stress, metabolic dysfunction, and neuronal death

Resuscitation and prolonged ventilation using 100% oxygen after cardiac arrest is standard clinical practice despite evidence from animal models indicating that neurologic outcome is improved using normoxic compared with hyperoxic resuscitation. This study tested the hypothesis that normoxic ventilation during the first hour after cardiac arrest in dogs protects against prelethal oxidative stress to proteins, loss of the critical metabolic enzyme pyruvate dehydrogenase complex (PDHC), and minimizes subsequent neuronal death in the hippocampus. Anesthetized beagles underwent 10 mins ventricular fibrillation cardiac arrest, followed by defibrillation and ventilation with either 21% or 100% O2. At 1 h after resuscitation, the ventilator was adjusted to maintain normal blood gas levels in both groups. Brains were perfusion-fixed at 2 h reperfusion and used for immunohistochemical measurements of hippocampal nitrotyrosine, a product of protein oxidation, and the E1alpha subunit of PDHC. In hyperoxic dogs, PDHC immunostaining diminished by approximately 90% compared with sham-operated dogs, while staining in normoxic animals was not significantly different from nonischemic dogs. Protein nitration in the hippocampal neurons of hyperoxic animals was 2-3 times greater than either sham-operated or normoxic resuscitated animals at 2 h reperfusion. Stereologic quantification of neuronal death at 24 h reperfusion showed a 40% reduction using normoxic compared with hyperoxic resuscitation. These results indicate that postischemic hyperoxic ventilation promotes oxidative stress that exacerbates prelethal loss of pyruvate dehydrogenase and delayed hippocampal neuronal cell death. Moreover, these findings indicate the need for clinical trials comparing the effects of different ventilatory oxygen levels on neurologic outcome after cardiac arrest.

Sex differences in cytochrome P450 1B1, an estrogen-metabolizing enzyme, in the rhesus monkey telencephalon

The metabolic enzyme CYP1B1 is a recently cloned member of the cytochrome P450 superfamily, expressed widely throughout primate tissue, including the CNS. Although CYP1B1 protein is known to metabolize estradiol to catecholestrogens in the uterus, its localization and function in brain have not yet been described. To better understand CYP1B1 distribution, we have combined in situ hybridization (ISH) for its mRNA with immunohistochemistry (IHC) for the CYP1B1 protein in selected brain regions of male and female adult rhesus monkeys (Macaca mulatta). Blocks of formalin-fixed tissue obtained from the frontal cortex, hippocampus, thalamus, and amygdala were processed and embedded in paraffin. They were then sectioned and stained as described for human tissue [Muskhelishvili, L., Thompson, P.A., Kusewitt, D.F., Wang, C., Kadlubar, F.F., 2001. In situ hybridization and immunohistochemical analysis of cytochrome P450 1B1 expression in human normal tissues. J. Histochem. Cytochem. 49, 229-236]. Results indicated widespread distribution of CYP1B1 mRNA in both male and female monkey frontal cortex, hippocampus, thalamus, and amygdala. In contrast, although CYP1B1 protein was co-localized with its mRNA in the female brains, it was primarily restricted to hippocampal pyramidal neurons in the male brains. These results suggest that CYP1B1 may subserve widespread metabolic functions in the female primate brain but have more restricted actions within the hippocampal pyramidal neurons of the male.

Colocalization of estrogen receptor alpha and NMDA-2D mRNAs in amygdaloid and hypothalamic nuclei of the mouse brain

Interactions between gonadal steroid hormones and glutamatergic neurons participate in limbic and hypothalamic functions. Glutamate receptors are divided into metabotropic and ionotropic receptors. Among ionotropic receptors, N-methyl-D-aspartate (NMDA) is involved in a variety of neurophysiological processes. In turn, NMDA receptors are composed of subunits from two families: NR1 and NR2. Recently, molecular studies have shown that the expression of NMDA-2D receptor is regulated by estrogen. Although the expression patterns of NMDA-2D and ERalpha in the rodent brain appear to overlap, it remained to be determined whether or not these two receptors co-exist, in vivo, at the level of single neurons. To test the hypothesis that NMDA-2D and ERalpha messenger ribonucleic acid (mRNA) are co-expressed in the same neurons of the adult mouse brain, we used a dual-label in situ hybridization technique. Neuronal populations were identified with digoxigenin-tagged complementary RNA probes for NMDA-2D and 35S-labeled cRNA probes for ERalpha. Our results demonstrate that a majority of the ERalpha-positive neurons also express NMDA-2D mRNA. Quantitative examination of the cellular expression in the ventromedial and arcuate nuclei of the hypothalamus (VMH and Arc) showed that 52.5% and 61.5%, respectively, of the neurons endowed with ERalpha mRNA also contain NMDA-2D mRNA. In the amygdala, 51% of ERalpha-positive cells also contain NMDA-2D mRNA. These findings provide the first anatomical evidence that ER and NMDA-2D receptors can be found in the same hypothalamic and amygdaloid neurons. Co-expression of ERalpha and NMDA-2D receptors supports the hypothesis of the interactions between glutamate receptors and estrogens in brain regions where estrogens control female reproductive behaviors and neuroendocrine functions.

Co-expression of estrogen and thyroid hormone receptors in individual hypothalamic neurons

Estrogen receptors (ER) and thyroid hormone receptors (TR) are members of the nuclear receptor family of transcription factors that induce or repress the expression of target genes. Previous behavioral studies in female rodents have demonstrated that thyroid hormones can antagonize the effects of estrogen in the central nervous system (CNS), particularly by attenuating estrogen's ability to facilitate reproductive behaviors. Additional molecular studies have suggested a mechanism for this antagonism by showing that ligand-activated ER alpha and TRs have the potential to interact in their transcriptional controls. Although the expression patterns of ER alpha and TRs in the rodent brain appear to overlap in behaviorally relevant areas, it remained to be determined whether these two classes of proteins coexist in vivo at the level of single neurons. To address this possibility, we employed a highly sensitive double-label in situ hybridization technique using digoxigenin and (35)S-labeled cRNA probes to analyze, in detail, the expression of ER alpha mRNA with TR alpha 1 and TR alpha 2 mRNAs in the same neurons of the ovariectomized (OVX) adult mouse brain. Our results demonstrate that a large majority of the ER alpha-positive neurons also expresses TR alpha 1 and TR alpha 2 mRNAs. Quantitative examination of the cellular expression in the ventromedial and arcuate nuclei of the hypothalamus (VMH and Arc) showed that 81.5% and 80.5% of the neurons endowed with ER alpha mRNA also contain TR alpha 1 and TR alpha 2 mRNAs, respectively. In the amygdala, more than 60.5% and 67% of ER alpha-positive cells also contain TR alpha 1 and TR alpha 2 mRNAs, respectively. These findings provide the first anatomical evidence that ER and TR can be found in the same neurons, including hypothalamic neurons. This coexpression of ER alpha and TR provides the cellular basis for a new level of neuronal integration in a brain region where estrogens control female reproductive behaviors.

Estrogens: neuroprotective or neurotoxic?

The present paper reviews the major modes of action of estrogen on the molecular, cellular, tissue, and neurobehavioral levels of mammalian physiology, with an emphasis on the brain as an estrogen target tissue. We draw a distinction between receptor- and nonreceptor-mediated actions, as well as delineate the range of different signal transduction pathways that might be available within a given tissue to mediate estrogenic effects. We consider species differences relevant to understanding the predictability of effects in humans from data obtained in rats or monkeys. Finally, we emphasize the importance of developmental stage in determining whether estrogenic effects are beneficial or harmful; "neuroprotective" or "neurotoxic."

Characterization and implications of estrogenic down-regulation of human catechol-O-methyltransferase gene transcription

Catechol-O-methyltransferase (COMT, EC 2.1.1.6) is a ubiquitous enzyme that is crucial to the metabolism of carcinogenic catechols and catecholamines. Regulation of human COMT gene expression may be important in the pathophysiology of various human disorders including estrogen-induced cancers, Parkinson's disease, depression, and hypertension. The gender difference in human COMT activity and variations in rat COMT activity during the estrous cycle led us to explore whether estrogen can regulate human COMT gene transcription. Our Northern analyses showed that physiological concentrations of 17-beta-estradiol (10(-9)-10(-7) M) could decrease human 1. 3-kilobase COMT mRNA levels in MCF-7 cells in a time- and dose-dependent manner through an estrogen receptor-dependent mechanism. Two DNA fragments immediately 5' to the published human COMT gene proximal and distal promoters were cloned. Sequence analyses revealed several half-palindromic estrogen response elements and CCAAT/enhancer binding protein sites. By cotransfecting COMT promoter-chloramphenicol acetyltransferase reporter genes with human estrogen receptor cDNA and pSV-beta-galactosidase plasmids into COS-7 cells, we showed that 17-beta-estradiol could down-regulate chloramphenicol acetyltransferase activities, and COMT promoter activities dose-dependently. Functional deletion analyses of COMT promoters also showed that this estrogenic effect was mediated by a 280 base pair fragment with two putative half-palindromic estrogen response elements in the proximal promoter and a 323-base pair fragment with two putative CCAAT/enhancer binding protein sites in the distal promoter. Our findings provide the first evidence and molecular mechanism for estrogen to inhibit COMT gene transcription, which may shed new insight into the role of estrogen in the pathophysiology of different human disorders.

Differential expression of estrogen receptor mRNA and protein in the female rat preoptic area

The expression of estrogen receptor (ER) mRNA and ER protein in the medial preoptic area of ovariectomized rat was investigated at both cellular and regional levels using non-isotopic in situ hybridization and immunohistochemistry. ER mRNA was localized in the cytoplasm, while both liganded and unliganded forms of the ER protein were confined to the nucleus. Furthermore, ER mRNA containing cells were evenly distributed throughout the medial preoptic area, showing a homogeneous staining pattern compared to that of ER protein. ER immunoreactive cells were highly distributed in the medial, moderately in the lateral aspect of the medial preoptic area, showing a heterogeneous staining pattern with strongly and weakly labeled cells. These results suggest that ER protein levels are controlled by cellular posttranscriptional mechanisms.

Roles of steroid hormones and their receptors in structural organization in the nervous system

Due to their chemical properties, steroid hormones cross the blood-brain barrier where they have profound effects on neuronal development and reorganization both in invertebrates and vertebrates, including humans mediated through their receptors. Steroids play a crucial role in the organizational actions of cellular differentiation representing sexual dimorphism and apoptosis, and in the activational effects of phenotypic changes in association with structural plasticity. Their sites of action are primarily the genes themselves but some are coupled with membrane-bound receptor/ion channels. The effects of steroid hormones on gene transcription are not direct, and other cellular components interfere with their receptors through cross-talk and convergence of the signaling pathways in neurons. These genomic and non-genomic actions account for the divergent effects of steroid hormones on brain function as well as on their structure. This review looks again at and updates the tremendous advances made in recent decades on the study of the role of steroid (gonadal and adrenal) hormones and their receptors on developmental processes and plastic changes in the nervous system.

Estrogen receptor-immunoreactive neurons contain calcitonin gene-related peptide, methionine-enkephalin or tyrosine hydroxylase in the female rat preoptic area

We have shown in our previous studies that estrogen treatment selectively influences calcitonin gene-related peptide (CGRP)-, methionine-enkephalin (Met-Enk)- and tyrosine hydroxylase (TH)-immunoreactive (IR) intensities in the neurons of the periventricular preoptic nucleus (PPN) and the medial preoptic area (MPA) of the female rat. In the present study, we examined whether estrogen receptor (ER)-IR neurons in the PPN and MPA contain CGRP, Met-Enk, or TH using a double-labeling immunohistochemical method and investigated changes in the number of double-labeling cells upon treatment with estrogen. Brain sections of ovariectomized rats and ovariectomized and estrogen-treated rat were stained using the avidin-biotin-peroxidase complex method followed by the peroxidase-anti-peroxidase method. The sections were first incubated with an anti-ER antibody in conjunction with nickel diaminobenzidine which produces a dark blue reaction product in the nucleus. Subsequently, CGRP, Met-Enk or TH antisera were applied to these sections and the resulting brown diaminobenzidine reaction product in the cytoplasm was examined. Neurons that were double-labeled for ER and CGRP, Met-Enk or TH were investigated in the PPN and MPA. The number of doubly labeled ER/CGRP- and ER/TH-IR neurons was large, whereas the number of ER/Met-Enk-IR neurons was small. These results suggest that ER in the PPN and MPA may be more closely related to the mechanism of changes in CGRP- and TH-IR intensities upon estrogen treatment than that in Met-Enk-IR intensity.

Region-specific changes of tyrosine hydroxylase-immunoreactivity by estrogen treatment in female rat hypothalamus

The effect of 17 beta-estradiol (E2) treatment for 28 days on tyrosine hydroxylase-immunoreactive (TH-IR) neurons in the periventricular preoptic nucleus (PPN) and medial preoptic area (MPA) of ovariectomized (OVX) rats was examined by morphometric analysis. The number of TH-IR neurons in the PPN of the E2-treated group was smaller than that of the OVX group, whereas the opposite result was found in the MPA; the number of TH-IR neurons in the MPA of the E2-treated group was larger than that of the OVX group. Numerous TH-IR neurons were found in the ventromedial portion of the MPA of the E2-treated group. In both the OVX and E2-treated groups, TH-IR neurons contained many short processes up to 40 microns in length. E2 treatment caused a significant decrement of the number of neurons containing the processes in the range of 10-40 microns length in the PPN, however it caused a significant increment of the number of neurons containing the processes in the range of 5-10 microns length in the MPA. These results suggested that immunoreactivity of TH in the PPN and MPA neuron are affected by E2 treatment and that E2 might modulate the production of TH in a region-specific pattern within the hypothalamus of the female rat.

Estrogen-receptor immunoreactivity in hamster brain: preoptic area, hypothalamus and amygdala

The distribution of estrogen-receptor containing cells in the preoptic area, hypothalamus and amygdala of female Syrian hamster brain was studied by immunocytochemical methods. Dense populations of estrogen-receptor immunoreactive (ER-IR) cells were found in the medial preoptic area, the bed nucleus of the stria terminalis, amygdala, ventral and lateral parts of the hypothalamus, and the arcuate nucleus. Injection of estradiol caused a decrease in estrogen-receptor immunoreactivity (ERIR) containing cells within one hour, a decrease that may reflect a change in the ability of the occupied estrogen receptor to bind the particular antibody (H222) used rather than down-regulation of the estrogen receptor. Our findings on the distribution of estrogen-receptor containing cells in these areas using an immunocytochemical technique are consistent with and extend the findings of others using autoradiographic and in vitro binding techniques to study estrogen receptor distribution in hamster brain.

Time-course analysis of changes in calcitonin gene-related peptide-and methionine-enkephalin-immunoreactivity in the female rat preoptic area after estrogen treatment

The time-course effects of one month of estrogen upon calcitonin gene-related peptide - and methionine-enkephalin-immunoreactivity in the periventricular preoptic nucleus and medial preoptic nucleus were semi-quantitatively investigated with a computer-based image analysis system. Female Wistar rats were ovariectomized and implanted subcutaneously with a 10-mm-long silastic capsule containing estradiol-17 beta, or with a blank capsule, as a control. Estradiol-17 beta-treated rats were killed at days 1, 4, 7, 10, 14 and 28 after the implantation of estradiol-17 beta. To investigate the details of changes in calcitonin gene-related peptide- and methionine-enkephalin-immunoreactive fibers in the periventricular preoptic nucleus and medial preoptic nucleus, a grid, made up of 8 x 16 squares (one square corresponding to 50 x 50 microns in the true section), was set on the wall of the third ventricle, and immunoreactivity within each square was measured with an image analyser. In the control rats, calcitonin gene-related peptide- and methionine-enkephalin-immunoreactive fibers were distributed in the periventricular preoptic nucleus and medial preoptic nucleus. In the estradiol-17 beta-treated rats, calcitonin gene-related peptide-immunoreactive fibers increased prominently at day 1, day 7 and day 10 in the periventricular preoptic nucleus, whereas methionine-enkephalin-immunoreactive fibers increased at day 1, day 14 and day 28 in the periventricular preoptic nucleus and medial preoptic nucleus. These findings suggest that the mechanism underlying the increases in these calcitonin gene-related peptide- and methionine-enkephalin-immunoreactive fibers after estrogen treatment might be different.

Nuclear localization of estrogen receptor-immunoreactivity in the preoptic area of female rats and its reduction by intraventricular colchicine treatment

The subcellular localization of estrogen receptor (ER) was investigated in the preoptic area of ovariectomized female rats by electron microscopic immunohistochemistry, using a monoclonal antibody to ER. ER-immunoreactivity was localized in the nuclei of neurons of the periventricular preoptic nucleus (Pe) and the medial preoptic area (MPA). ER-immunoreactivity had a speckled pattern in the nucleus, but was not observed in the nucleolus or cytoplasm. After intraventricular colchicine treatment, ER-immunoreactivity within the nucleus was reduced drastically in neurons of the Pe and the MPA. The possible mechanism by which colchicine alters ER-immunoreactivity is mentioned.