Estrogen modulates stimulation of inositol phospholipid hydrolysis by norepinephrine in rat brain slices

Aging alters the expression of genes for neuroprotection and synaptic function following acute estradiol treatment

This study used microarray analysis to examine age-related changes in gene expression 6 and 12 h following a single estradiol injection in ovariectomized mice. Estradiol-responsive gene expression at the 6 h time point was reduced in aged (18 months) animals compared with young (4 months) and middle-aged (MA, 12 months) mice. Examination of gene clustering within biological and functional pathways indicated that young and MA mice exhibited increased expression of genes for cellular components of the synapse and decreased expression of genes related to oxidative phosphorylation and mitochondrial dysfunction. At the 12 h time point, estradiol-responsive gene expression increased in aged animals and decreased in young and MA mice compared with the 6 h time point. Gene clustering analysis indicated that aged mice exhibited increased expression of genes for signaling pathways that are rapidly influenced by estradiol. The age differences in gene expression for rapid signaling pathways may relate to disparity in basal pathway activity and estradiol mediated activation of rapid signaling cascades.

Expression of estrogen receptor GPR30 in the rat spinal cord and in autonomic and sensory ganglia

The G protein-coupled receptor GPR30 has recently been identified as a nonnuclear estrogen receptor. Reverse transcriptase-polymerase chain reaction revealed expression of GPR30 mRNA in varying quantities in the rat spinal cord, dorsal root ganglia, nodose ganglia, trigeminal ganglia, hippocampus, brain stem, and hypothalamus. Immunohistochemical studies that used a rabbit polyclonal antiserum against the human GPR30 C-terminus revealed a fine network of GPR30-immunoreactive (irGPR30) cell processes in the superficial layers of the spinal cord; some of which extended into deeper laminae. A population of neurons in the dorsal horn and ventral horn were irGPR30. Dorsal root, nodose, and trigeminal ganglionic neurons displayed varying intensities of irGPR30. Positively labeled neurons were detected in the major pelvic ganglion, but not in the superior cervical ganglion. A population of chromaffin cells in the adrenal medulla was irGPR30, so were cells of the zona glomerulosa. Double-labeling the adrenal medulla with GPR30 antiserum and tyrosine hydroxylase antibody or phenylethanolamine-N-methyltransferase antiserum revealed that irGPR30 is expressed in the majority of tyrosine hydroxylase-positive chromaffin cells. Last, some of the myenteric ganglion cells were irGPR30. Tissues processed with preimmune serum resulted in no staining. Voltage-sensitive dye imaging studies showed that the selective GPR30 agonist G-1 (1, 10, and 100 nM) depolarized cultured spinal neurons in a concentration-dependent manner. Collectively, our result provides the first evidence that GPR30 is expressed in neurons of the dorsal and ventral horn as well as in sensory and autonomic neurons, and activation of GPR30 by the selective agonist G-1 depolarizes cultured spinal neurons.

Glutamate-mediated excitotoxicity in neonatal hippocampal neurons is mediated by mGluR-induced release of Ca++ from intracellular stores and is prevented by estradiol

Hypoxic/ischemic (HI) brain injury in newborn full-term and premature infants is a common and pervasive source of life time disabilities in cognitive and locomotor function. In the adult, HI induces glutamate release and excitotoxic cell death dependent on NMDA receptor activation. In animal models of the premature human infant, glutamate is also released following HI, but neurons are largely insensitive to NMDA or AMPA/kainic acid (KA) receptor-mediated damage. Using primary cultured hippocampal neurons we have determined that glutamate increases intracellular calcium much more than kainic acid. Moreover, glutamate induces cell death by activating Type I metabotropic glutamate receptors (mGluRs). Pretreatment of neurons with the gonadal steroid estradiol reduces the level of the Type I metabotropic glutamate receptors and completely prevents cell death, suggesting a novel therapeutic approach to excitotoxic brain damage in the neonate.

Synthesis and biological evaluation of SERMs with potent nongenomic estrogenic activity

We have synthesized novel SERMs that activate a rapid response in CNS neurons, but which lack the ability to bind to the nuclear estrogen receptors (ERalpha and ERbeta). These compounds are analogues of 4-hydroxytamoxifen, but unlike 4-hydroxytamoxifen, they do not exist as a mixture of E/Z isomers. They contain a carboxamide insertion between the olefin and basic phenyl side chain, which results in more stable geometric isomers. The amide insertion also eliminates their ability to bind to the nuclear estrogen receptors, and hence, they are unable to modulate ER-mediated gene transcription as do classical estrogens and SERMs. We show that one of these analogues, ST-X, elicits a potent nongenomic estrogen response in the CNS by rapidly inhibiting GIRK activation in hypothalamic gamma-aminobutyric acid (GABA) and proopiomelanocortin (POMC) neurons. To our knowledge, ST-X is the only SERM that modulates rapid estrogen responses, but which lacks nuclear ER activity.

Neurotrophic Factors and Estradiol Interact To Control Axogenic Growth in Hypothalamic Neurons

Previous work from our laboratory has shown that in cultures of hypothalamic neurons obtained from male fetuses at embryonic day 16, the axogenic response to estrogen (E2) is contingent on coculture with target glia or target glia-conditioned media (CM). Neither the estrogen receptor blockers tamoxifen nor ICI 182,780 prevented the axogenic effects of the hormone. Estradiol made membrane-impermeable by conjugation to a protein of high molecular weight (E2-BSA) preserved its axogenic capacity, suggesting the possibility of a membrane effect responsible for the action of E2. Western blot analysis of extracts from homogenates of cultured neurons grown with E2 and CM from target glia had more TrkB than cultures with CM alone or E2 alone. To further investigate the interaction between E2 and the neurotrophin receptors, we used a specific antisense oligonucleotide (AS) to prevent the estradiol-induced increase of TrkB. The effect of E2 was suppressed in cultures in which TrkB was down-regulated by the AS, showing decreased axonal elongation when compared with neurons treated with E2 without AS or with sense TrkB. In cultures grown with AS, the axonal length of E2-treated cultures was not different from cultures without E2. Evidence suggesting cross-talk between E2 and neurotrophic factor(s) prompted investigation of signaling along the MAPK cascade. Immuno blotting of E2-treated cultures showed increased levels of phosphorylated ERK1 and ERK2. UO126 but not LY294002 blocked E2-induced axonal elongation, suggesting that the MAPKs are involved in this response.

Nongenomic steroid action: controversies, questions, and answers

Steroids may exert their action in living cells by several ways: 1). the well-known genomic pathway, involving hormone binding to cytosolic (classic) receptors and subsequent modulation of gene expression followed by protein synthesis. 2). Alternatively, pathways are operating that do not act on the genome, therefore indicating nongenomic action. Although it is comparatively easy to confirm the nongenomic nature of a particular phenomenon observed, e.g., by using inhibitors of transcription or translation, considerable controversy exists about the identity of receptors that mediate these responses. Many different approaches have been employed to answer this question, including pharmacology, knock-out animals, and numerous biochemical studies. Evidence is presented for and against both the participation of classic receptors, or proteins closely related to them, as well as for the involvement of yet poorly understood, novel membrane steroid receptors. In addition, clinical implications for a wide array of nongenomic steroid actions are outlined.

Sexual differentiation of the brain: genes, estrogen, and neurotrophic factors

Based on evidence obtained during the past 50 years, the current hypothesis to explain the sexual dimorphism of structure and function in the brain of vertebrates maintains that these differences are produced by the epigenetic action of gonadal hormones. However, evidence has progressively accumulated suggesting that genetic mechanisms controlling sexual-specific neuronal characteristics precede, or occur in parallel with, hormonal effects. 1. In cultures of hypothalamic neurons taken from gestation day 16 (GD16) embryos, treatment of sexually segregated cultures with estradiol (E2) induces axon growth in neurons from male neurons, but not from female neurons. In these cultures treatment with E2 increased the levels of tyrosine kinase type B (TrkB) and insulin-like growth factor I (IGF-I) receptors in male but not in female neurons. This and other sex differences cannot be explained by differences in hormonal environment, because the donor embryos were obtained when gonadal secretion of steroids is just beginning, before the perinatal surge of testosterone that determines development of the male brain beginning at GD17/18. 2. The response to estrogen is contingent upon coculture with heterotopic glia (mostly astrocytes) from a target region (amygdala) harvested from same-sex fetuses at GD16, whereas in the presence of homotopic glia or in cultures without glia, E2 had no effect. It was concluded that the axogenic effect of E2 depends on interaction between neurons and glia from a target region and that neurons from fetal male donors appear to mature earlier than neurons from females, a differentiated response that takes place prior to divergent exposure to gonadal secretions. 3. The effects of target and nontarget glia-conditioned media (CM) on the E2-induced growth of neuronal processes of hypothalamic neurons obtained from sexually segregated fetal donors were also studied. Estrogen added to media conditioned by target glia modified the number of primary neurites and the growth of axons of hypothalamic neurons of males but not of females. 4. Neither the Type III steroidal receptor blocker tamoxifen nor Type I antiestrogen ICI 182,780 prevented the axogenic effects of the hormone. Estradiol made membrane-impermeable by conjugation to a protein of high molecular weight (E2-BSA) preserved its axogenic capacity, suggesting the possibility of a membrane effect responsible for the action of E2. 5. Western blot analysis of the tyrosine kinase type A (TrkA), type B (TrkB), type C (TrkC), and insulin-like growth factor (IGF-I R) receptors in extracts from homogenates of cultured hypothalamic neurons showed that in cultures of male-derived neurons grown with E2 and CM from target glia, the amounts of TrkB and IGF-I R increased notably. Densitometric quantification showed that these cultures had more TrkB than cultures with CM alone or E2 alone. On the contrary, in cultures of female-derived neurons, the presence of CM alone induced maximal levels of TrkB, which were not further increased by E2; female-derived neurons in all conditions did not contain IGF-I R. Levels of TrkC were not modified by any experimental condition in male- or female-derived cultures and Trk A was not found in the homogenates. These results are compared with similar data from other laboratories and integrated in a model for the confluent interaction of estrogen and neurotrophic factors released by glia that may contribute to the sexual differentiation of the brain.

Effects of chronic restraint stress and estradiol on open field activity, spatial memory, and monoaminergic neurotransmitters in ovariectomized rats

Twenty-one days of chronic restraint stress impairs male rat performance on the radial arm maze [Luine et al. (1994) Brain Res. 639, 167-170], but enhances female rat performance [Bowman et al. (2001) Brain Res. 904, 279-289]. To assess possible ovarian hormone mechanisms underlying this sexually dimorphic response to stress, we examined chronic stress effects in ovariectomized rats. Ovariectomized rats received Silastic capsule implants containing cholesterol or estradiol and were assigned to a daily restraint stress (21 days, 6 h/day) or non-stress group. Following the stress period, subjects were tested for open field activity and radial arm maze performance. Stress and estradiol treatment affected open field activity. All stressed animals, with or without estradiol treatment, made fewer total outer sector crossings. In contrast, estradiol-treated animals, with or without stress, made more inner sector visits, an indication that estradiol decreased anxious behavior on the open field across time. As measured by the total number of visits required to complete the task, stress did not affect radial arm maze performance in ovariectomized rats, but estradiol-treated animals, with or without stress, performed better than non-treated animals on the radial arm maze. Stressed subjects receiving estradiol showed the best radial arm maze performance. Following killing, tissue samples were obtained from various brain regions known to contribute to learning and memory, and monoamine and metabolite levels were measured. Several changes were observed in response to both stress and estradiol. Most noteworthy, stress treatment decreased homovanillic acid levels in the prefrontal cortex, an effect not previously observed in stressed intact females. Estradiol treatment increased norepinephrine levels in CA3 region of the hippocampus, mitigating stress-dependent changes. Both stress and estradiol decreased dentate gyrus levels of 5-hydroxyindole acetic acid. In summary, the current study provides novel information showing that estradiol alters behavioral and neurochemical responses to stress in ovariectomized rats. Estradiol treatment decreased anxious behavior on the open field and stressed animals receiving estradiol had enhanced radial arm maze performance. In relation to interactions between stress and estradiol on cognition and anxiety, changes in the prefrontal cortex dopaminergic system, dentate gyrus serotonergic system, and norepinephrine levels in the CA3 region appear important. Results show that estradiol may moderate stress effects on cognition and anxiety through both organizational and activation effects.

Nongenomic regulation of the kinetics of exocytosis by estrogens

The role of nongenomic action of estrogens on elicited catecholamine secretion and exocytosis kinetics was studied in perfused rat adrenals and in cultured bovine chromaffin cells. 17beta-Estradiol as well as the estrogen receptor modulators raloxifene and LY117018, but not 17alpha-estradiol, inhibited at the micromolar range the catecholamine output elicited by acetylcholine or high potassium. However, these agents failed to modify the secretion elicited by high Ca(2+) in glands treated with the ionophore A-23187 (calcimycin), suggesting that estrogens did not directly act on the secretory machinery. At the single cell level, estrogens modified the kinetics of exocytosis at nanomolar range. All of the drugs tested except 17alpha-estradiol produced a profound slowing down of the exocytosis as measured by amperometry. LY117018 also reduced the granule content of catecholamines. 17beta-Estradiol reduced the intracellular free Ca(2+) but only at micromolar concentrations, whereas nanomolar concentrations increased the cAMP levels. These effects were reproduced with the nonpermeable drug 17beta-estradiol-horseradish peroxidase and antagonized with nanomolar concentrations of the antiestrogen ICI 182,780 (fulvestrant). Our data suggest the presence of membrane sites that regulate both the exocytotic phenomenon and the total catecholamine release with high and low affinity, respectively.

Estradiol-induced nongenomic calcium signaling regulates genotropic signaling in macrophages

Estradiol (E(2)) exerts not only genotropic but also nongenomic actions through nuclear estrogen receptors (ER). Here, we provide a novel paradigm for nongenomic E(2) signaling independent of nuclear ER. E(2) induces a rapid rise in the intracellular free Ca(2+) concentration ([Ca(2+)](i)) through membrane estrogen receptors in murine RAW 264.7 macrophages. This E(2)-induced Ca(2+) signaling is not prevented by different ER blockers and cannot directly activate stably transfected c-fos promoter or the mitogen-activated protein kinases p38, ERK1/2, and SAPK/JNK, or NO production. However, the E(2)-induced rise in [Ca(2+)](i) specifically down-regulates the serum-stimulated activation of c-fos promoter and ERK1/2, and conversely, it specifically up-regulates lipopolysaccharide-stimulated activation of c-fos promoter, p38, and NO production. The E(2)-changed activation of c-fos promoter can be prevented by an intracellular Ca(2+) chelator. Our data indicate that E(2)-induced nongenomic Ca(2+) signaling through membrane ER is able to specifically modulate genotropic signaling pathways with impact on macrophage activation.

Nongenomic mechanism mediates estradiol stimulation of axon growth in male rat hypothalamic neurons in vitro

The purpose of the present work was to investigate the participation of estradiol receptors (ER) in estrogen-induced axon growth in vitro. Hypothalamic neurons from 16 day (E16) male rat fetuses were cultured with or without 17-beta-estradiol at 1 x 10(-7) M in basal medium or medium conditioned by astroglia derived from ventral mesencephalon (CM). After 48 hr in vitro, neurite outgrowth was quantified by morphometric analysis. An axogenic effect could be demonstrated for estradiol added to CM. With RT-PCR, the mRNA transcript for ERalpha was found in the donor tissues as well as in the neuron cultures. In this model two specific nuclear ER blockers (tamoxifen and ICI 182,780) were ineffective in blocking the neuritogenic effect, and a membrane-impermeable estrogen-albumin construct (E2-BSA) was as effective as estradiol. These results indicate that the axogenic effect of estradiol at E16 is not exerted through the classical intracellular receptor signal transduction system and suggest the possibility of a membrane-mediated mechanism. The data are discussed in light of our previous findings pointing to the interdependent activation of the estrogenic and the trophic factor signaling pathways that mediate stimulated axon growth.

Nongenomic effects of oestrogen: embryonic mouse midbrain neurones respond with a rapid release of calcium from intracellular stores

Evidence is emerging that oestrogen, besides acting via classical nuclear receptors, can rapidly influence the physiology of nerve cells through other mechanisms. Oestrogens have been shown to modulate the differentiation and function of embryonic midbrain dopaminergic neurones by stimulating neurite outgrowth, expression of tyrosine hydroxylase mRNA, dopamine uptake and release in spite of the fact that dopaminergic cells in the prenatal midbrain do not express the classical oestrogen receptor. This study therefore intended to unravel possible signal transduction pathways activated by oestrogen which might be associated with the above oestrogen effects. As a physiological second-messenger mechanism, we studied the influence of oestrogen on fluctuations of intracellular Ca2+ levels [Ca2+]i by microspectrofluorimetry of the Ca2+-sensitive indicator Fura-2, in primary cultures from embryonic mouse midbrains. 17Beta-estradiol (10 nM-1 pM) but not 17alpha-estradiol increased [Ca2+]i within 1-3 s in a dose-dependent way. Removal of extracellular Ca2+ abrogated K+-stimulated Ca2+ rise but did not affect 17beta-estradiol stimulation. Pretreatment of cells with thapsigargin (1 microM, 10 min), an inhibitor of Ca2+-pumping ATPases in the endoplasmic reticulum, abolished the 17beta-estradiol effect but not the K+-stimulated [Ca2+]i rise. Oestrogen effects on [Ca2+]i were completely mimicked by using a membrane-impermeant oestrogen-BSA construct. In order to identify oestrogen-sensitive cells, some cultures were subsequently immunostained for microtubule-associated protein II, tyrosine hydroxylase, or GABA. All oestrogen-sensitive cells were immunocytochemically characterized as neurones, and about half of these responsive neurones was found to be dopaminergic or GABAergic. These results demonstrate that 17beta-estradiol is capable of rapidly modulating physiological parameters of developing midbrain neurones by directly interacting with specific membrane binding sites coupled to a signal transduction mechanism that causes a calcium release from intracellular Ca2+ stores. It is suggested that oestrogen effects on differentiation and function of midbrain dopaminergic neurones are mediated by intracellular Ca2+ signalling.

17 beta-Estradiol potentiates kainate-induced currents via activation of the cAMP cascade

Evidence for nongenomic actions of steroids is now coming from a variety of fields of steroid research. Mechanisms of steroid action are being studied with regard to the membrane receptors and the activation of second messengers. The present study investigated the mechanism for the rapid effect of estrogen on acutely dissociated hippocampal CA1 neurons by using the whole-cell, voltage-clamp recording. Under the perforated patch configuration, 17 beta-estradiol potentiated kainate-induced currents in 38% of tested neurons. The potentiation was stereospecific, rapid in onset, and reversible after the removal of the steroid. Dose-response curves show that the potentiation by 17 beta-estradiol was evident at a concentration as low as 10 nM and saturated at 10 microM. 17 beta-Estradiol did not affect the kinetics (i.e., affinity and cooperativity) and reversal potential of kainate-induced currents. This suggests that the potentiation did not result from direct interaction with kainate receptors nor the activation of ion channels other than kainate receptor-channels. The potentiation by 17 beta-estradiol was similar to the enhancement of kainate-induced currents evoked by 8-bromo-cAMP, and was modulated by an inhibitor of phosphodiesterase (IBMX). The estrogen potentiation was blocked by a specific blocker of PKA (Rp-cAMPS). Under standard recording configuration, the effect was significantly affected by intracellular perfusing with GDP-beta-S or GTP-gamma-S. The data suggest that the potentiation of kainate-induced currents by 17-beta-estradiol was likely a G-protein(s) coupled, cAMP-dependent phosphorylation event. By involvement of this non-genomic mechanism, estrogen may play a role in the modulation of excitatory synaptic transmission in the hippocampus.

Acute and chronic effects of estrogenic compounds on glutamate-stimulated phosphatidylinositol metabolism in primary neuronal cultures

Glutamate (Glu)-stimulated phosphatidylinositol (PI) metabolism in primary neuronal cultures was found to be modulated by acute and chronic treatment with two estrogenic compounds. 17 beta-Estradiol 3-benzoate (0.1 and 1 microM), when applied with Glu, significantly reduced Glu (40 microM)-stimulated PI metabolism by 20-36%, an effect not seen with 17 alpha-estradiol. The weak estrogen phenol red (20 microM), had no effect when added immediately before Glu stimulations. Two-week pretreatment with 17 beta-estradiol 3-benzoate (1 microM) resulted in a significant decrease in Glu-stimulated PI metabolism (10-100 microM). Chronic treatment with 20 microM phenol red, at a concentration commonly found in culture medium, resulted in parallel but not statistically significant effects to those observed with chronic estradiol treatment. Estrogenic compounds may modulate the excitatory responses of neurons by both genomic and non-genomic means.

Noradrenaline-induced inositol phosphate formation in rat striatum is mediated by alpha 1A-adrenoceptors

The aim of this study was to assess the contribution of alpha 1-adrenoceptor subtypes to noradrenaline (NA)-induced inositol phosphate formation in rat striatum. In cross-chopped slices and in the presence of 10 mM LiCl, NA stimulated the accumulation of [3H]inositol phosphates. After 60-min incubation with 100 microM NA, [3H]IP1 was the major product detected (82 +/- 3% of total [3H]inositol phosphates). Best-fit values for the concentration-response curve for NA-induced [3H]IP1 accumulation yielded an EC50 of 9.4 +/- 1.1 microM, maximum effect of 210 +/- 3% of basal, and Hill coefficient (nH) of 1.1 +/- 0.1. Pre-treatment of the slices for 30 min with the alkylating agent chloroethylclonidine (100 microM) failed to decrease significantly the response to 100 microM NA. Inhibition curves for four alpha 1-antagonists, (+)-niguldipine, prazosin, WB-4101 and 5-methylurapidil (5-MU), best-fit to a single-site model with pKi values of 9.4 ((+)-niguldipine), 9.2 (prazosin and WB-4101) and 8.8 (5-MU). The putative alpha 1 D-selective antagonist BMY 7378 reduced the response to NA only partially (30 +/- 3% inhibition at 1 microM: pKi 7.24). NA-induced [3H]IP1 accumulation was significantly reduced (to 20 +/- 9% of controls) by Ca2+ removal and increased as the extracellular Ca2+ concentration was raised from nominally zero (no added Ca2+) to 1 mM Ca2+. NA-induced [3H]IP1 accumulation was reduced by both the non-selective Ca2+ channel blocker Ni2+ (58 +/- 3% inhibition at 2 mM) and nimodipine, an antagonist of L-type voltage-operated Ca2+ channels (77 +/- 4% inhibition at 3 microM). Taken together these results indicate that NA-induced inositol phosphate formation in striatal slices is mediated by activation of alpha 1A-adrenoceptors coupled to Ca2+ entry and Ca2+ activation of phospholipase C.

Brain Stem Auditory Evoked Potentials: Effects of Ovarian Steroids Correlated with Increased Incidence of Bell's Palsy in Pregnancy

To investigate the effect of ovarian steroids on the brain stem during changes of estrogen and progesterone blood levels, we recorded brain stem auditory evoked potentials with increased stimulus rates from 26 women treated for sterility by menotropins (Pergonal and Metrodin). These women were divided into three groups according to their estrogen and progesterone blood levels. The brain stem auditory evoked potential results revealed a significant delay of peak III only, with an increased stimulus rate in the group with the highest estrogen level. Estrogen may cause a brain stem synaptic impairment, presumably because of ischemic changes, and thus also may be responsible for a higher incidence of Bell's palsy during pregnancy.

Alterations in brain monoamines and GABAA receptors in transgenic mice overexpressing TGF alpha

This study investigated the possibility that overexpression of transforming growth factor alpha (TGF alpha) changes those neurotransmitter systems that have been associated with behaviors found to be altered in the transgenic TGF alpha CD-1 mice. The female TGF alpha mice showed elevated levels of norepinephrine (NE) in the hypothalamus and serotonin (5-HT) in the cortex and brain stem when compared with nontransgenic CD-1 females. The concentrations of monoamines were not altered in the male transgenic brain. The 5-hydroxyindoleacitic acid (5-HIAA)/5-HT ratio was significantly reduced in the brain stem of the male TGF alpha mice and frontal cortex in the female transgenics. The binding of the [3H]GBR 12935-labeled DA transporter was lower in the frontal cortex in the transgenic male TGF alpha mice than in the female TGF alpha mice. No gender difference in dopamine (DA) transporter binding was noted between the nontransgenic male and female mice. Serotonin and GABAA receptors were measured only in males. No differences in the number of 5-HT1A and 5-HT2 receptors were found in the cortex or hippocampus. Maximal GABA stimulation of [3H]flunitrazepam binding in the forebrain hemispheres and cerebellar binding of an imidazobenzodiazepine, [3H]Ro 15-4513, were not different between transgenic and nontransgenic male mice. However, forebrain [35S]TBPS binding in male TGF alpha mice was less affected by the blockade of the GABA agonist sites by the specific GABAA antagonists SR 95531 and bicuculline than the binding of the controls, suggesting either altered endogenous GABA concentrations or a change in receptor populations.(ABSTRACT TRUNCATED AT 250 WORDS)

Activation of protein kinase C in the hypothalamic ventromedial nucleus or the midbrain central gray facilitates lordosis

Many neurotransmitters and neuropeptides can act through the hypothalamic ventromedial nucleus (VMN) or midbrain central gray (MCG) to facilitate lordosis. Since these lordosis-facilitating agents can also stimulate the phosphoinositide (PI) second-messenger pathway, it was hypothesized that direct activation of this pathway can also potentiate the behavior. To evaluate this possibility, a phorbol ester, TPA (12-O-tetradecanoyl phorbol 13-acetate), was used to activate a key enzyme, protein kinase C (PKC), of the PI pathway in ovariectomized (OVX) rats either primed or not primed with estrogen. These female rats were paired with males for mating tests before and after an intracerebral infusion of TPA, and both the lordosis quotient (LQ) and the lordosis strength (LS) were measured. Bilateral infusion of TPA (5 micrograms/0.5 microliter or 0.2 microgram/0.2 microliter, but not 0.1 microgram/0.2 microliter/side) into the VMN or MCG of estrogen-primed subjects facilitated both LQ and LS in 30 min, peaked at 60-90 min, and the facilitation lasted for more than 180 min. This facilitatory effect of TPA was: (1) not observed in OVX rats not primed with estrogen; (2) not observed if the infused TPA did not reach both sides of the VMN or MCG; (3) not mimicked by 4 alpha-phorbol 12,13-didecanoate, which does not activate PKC; (4) blocked by PKC inhibitors (H7 10 mM or staurosporine 1 microM, 0.2 microliter/side), which by themselves did not facilitate lordosis; and (5) was not affected by pretreatment of the progestin antagonist RU486.(ABSTRACT TRUNCATED AT 250 WORDS)

Roles of second-messenger systems and neuronal activity in the regulation of lordosis by neurotransmitters, neuropeptides, and estrogen: a review

Many neurotransmitters and neuropeptides can affect the rodent feminine sexual behavior, lordosis, when administered in the ventromedial hypothalamus (VMH), midbrain central gray (MCG), or other brain regions. A survey of the electrophysiological and biochemical actions of these neural agents revealed that there is a very consistent association between lordosis facilitation with both the activation of the phosphoinositide (PI) pathway and the excitation of VMH and MCG neurons. In contrast, lordosis inhibition is associated, less consistently, with alterations of the adenylate cyclase (AC) system and the inhibition of neuronal activity. The findings that lordosis could be facilitated by going beyond membrane receptors and directly activating the PI pathway, suggest that this second-messenger pathway is a common mediator for the lordosis-facilitating agents. Furthermore, as in the case of stimulating membrane receptors, direct activation of this common mediator also requires estrogen priming for lordosis facilitation. Therefore, it is likely that the PI pathway is modulated by estrogen in the permissive action of estrogen priming. Indeed, a literature review shows that estrogen can affect selective isozymes of key enzyme families of the PI pathway at various levels. Such selective modulations, at several levels, could easily alter the course of a PI cascade; thence, the eventual functional outcome. These findings prompt us to propose that estrogen enables lordosis to be facilitated by a selective modulation of the PI pathway.

α1-Adrenergic agonists act on the ventromedial hypothalamus to cause neuronal excitation and lordosis facilitation: electrophysiological and behavioral evidence

To see if activation of central alpha 1-adrenergic receptors can cause facilitation of lordosis in rats, the behavioral effects of centrally administered alpha 1-agonists, methoxamine (MA) and phenylephrine (PhE), and related agents were studied. In ovariectomized rats treated with estrogen, infusion of MA, PhE, or a beta-agonist isoproterenol, into the lateral ventricle, or bilateral infusions of MA or PhE into the ventromedial hypothalamus (VMH) facilitated lordosis. Conversely, intra-VMH infusion of the alpha 1-antagonist prazosin (PZ) inhibited lordosis. Intra-VMH infusion of isoproterenol or an alpha 2-agonist clonidine, had no effect. Neither was the intra-VMH infusion of MA effective if: (i) the rats were not primed with estrogen; (ii) the tips of the cannulae were outside the VMH; or (iii) it was preceded by an intra-VMH infusion of the alpha 1b-antagonist, chloroethylclonidine (CEC). These results not only verify implications from recent studies that alpha 1-receptors in the hypothalamus are important for lordosis facilitation, but further show that the adrenergic facilitatory effect are: (i) mediated specifically by alpha 1b-subtype of the alpha 1-receptor, (ii) estrogen-dependent, and (iii) site-specific to VMH. To investigate neural mechanisms potentially underlying the lordosis-facilitating effect of alpha 1-activation, the actions of MA and PhE on the electrical activity of single neurons of the ventromedial nucleus of the hypothalamus (VMN) in vitro were studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Ipriflavone inhibits phosphoinositide hydrolysis and Ca2+ uptake in the osteoblast-like UMR-106 cells

The mechanism of action of ipriflavone, an isoflavone derivative, was studied in the osteoblastic-like UMR-106 cell line. Ipriflavone affected both phosphoinositide hydrolysis and 45Ca2+ uptake. A repeated treatment of UMR-106 cells (once a day, for 3 days) with ipriflavone decreased, in a concentration-dependent manner, [3H]inositol monophosphate accumulation. This effect was also achieved after single addition of high concentrations of ipriflavone or 100 nM [Asu1,7]eel-calcitonin, a semi-synthetic analog of eel calcitonin. When repeatedly added to UMR-106 cells, 17 beta-estradiol produced a marked inhibition of [3H]inositol monophosphate accumulation, an effect which appeared significant only at a concentration of 1 microM and which was accompanied by a reduced incorporation of [3H]inositol into membrane phospholipids. A repeated treatment with ipriflavone reduced 45Ca2+ uptake as well. This effect was observed also after a single addition of [Asu1,7]eel-calcitonin but not following single or repeated treatment with 17 beta-estradiol. The present data indicate the osteoblast as a direct and specific target for ipriflavone and suggest that this compound may share intracellular transducing mechanisms with other antiosteoporotic hormones such as estrogen and calcitonin.