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102
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Chen Y, Su Y, Run X, Sun Z, Wang T, Sun S, Liang Z. Pretreatment of PC12 Cells with 17β-estradiol Prevents Aβ-Induced Down-Regulation of CREB Phosphorylation and Prolongs Inhibition of GSK-3β. J Mol Neurosci 2012; 50:394-401. [DOI: 10.1007/s12031-012-9938-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2012] [Accepted: 12/05/2012] [Indexed: 10/27/2022]
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103
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Nebieridze N, Zhang XL, Chachua T, Velíšek L, Stanton PK, Velíšková J. β-Estradiol unmasks metabotropic receptor-mediated metaplasticity of NMDA receptor transmission in the female rat dentate gyrus. Psychoneuroendocrinology 2012; 37:1845-54. [PMID: 22541715 PMCID: PMC3432293 DOI: 10.1016/j.psyneuen.2012.03.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2011] [Revised: 02/13/2012] [Accepted: 03/26/2012] [Indexed: 02/08/2023]
Abstract
Loss of estrogen in women following menopause is associated with increased risk for cognitive decline, dementia and depression, all of which can be prevented by estradiol replacement. The dentate gyrus plays an important role in cognition, learning and memory. The gatekeeping function of the dentate gyrus to filter incoming activity into the hippocampus is modulated by estradiol in a frequency-dependent manner and involves activation of metabotropic glutamate receptors (mGluR). In the present study, we investigated whether estradiol (EB) modulates the metaplastic effect of inducing synaptic long-term potentiation (LTP) on subsequent propensity for expression of LTP in the dentate gyrus. At medial perforant path-dentate granule cell synapses in hippocampal slices of ovariectomized female rats, EB replacement was critical for an initial induction of LTP to enhance the magnitude of subsequent LTP elicited by a second high-frequency stimulation, metaplasticity, which was not present in slices from oil-treated control animals. EB enhanced expression of group I mGluRs, and the metaplastic effect of EB on LTP required activation of group I mGluRs that led to Src-family tyrosine kinase-mediated phosphorylation of NR2B subunits of N-methyl-d-aspartate receptors (NMDAR) that enhanced the magnitude of NMDAR-dependent LTP. Our data show that EB effects on LTP in the hippocampal dentate gyrus require activation of group I mGluRs, which in turn leads to functional metaplastic regulation of NR2B subunit-containing NMDARs, as opposed to direct effects of EB on NMDARs.
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Affiliation(s)
- Nino Nebieridze
- Department of Cell Biology & Anatomy, New York Medical College, Valhalla, New York, USA
| | - Xiao-lei Zhang
- Department of Cell Biology & Anatomy, New York Medical College, Valhalla, New York, USA
| | - Tamar Chachua
- Department of Cell Biology & Anatomy, New York Medical College, Valhalla, New York, USA
| | - Libor Velíšek
- Department of Cell Biology & Anatomy, New York Medical College, Valhalla, New York, USA,Department of Pediatrics, New York Medical College, Valhalla, New York, USA
| | - Patric K. Stanton
- Department of Cell Biology & Anatomy, New York Medical College, Valhalla, New York, USA,Department of Neurology, New York Medical College, Valhalla, New York, USA
| | - Jana Velíšková
- Department of Cell Biology & Anatomy, New York Medical College, Valhalla, New York, USA,Department of Obstetrics & Gynecology, New York Medical College, Valhalla, New York, USA,Correspondence: Jana Velíšková, MD, PhD, New York Medical College, Department of Cell Biology & Anatomy, Basic Medical Sciences Bldg., Room #A21, Valhalla, NY 10595, USA, , Phone: (914) 594-4840, Fax: (914) 594-4653
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104
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Kramár EA, Babayan AH, Gall CM, Lynch G. Estrogen promotes learning-related plasticity by modifying the synaptic cytoskeleton. Neuroscience 2012; 239:3-16. [PMID: 23103216 DOI: 10.1016/j.neuroscience.2012.10.038] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2012] [Revised: 10/11/2012] [Accepted: 10/18/2012] [Indexed: 01/04/2023]
Abstract
Estrogen's acute, facilitatory effects on glutamatergic transmission and long-term potentiation (LTP) provide a potential explanation for the steroid's considerable influence on behavior. Recent work has identified mechanisms underlying these synaptic actions. Brief infusion of 17ß-estradiol (E2) into adult male rat hippocampal slices triggers actin polymerization within dendritic spines via a signaling cascade beginning with the GTPase RhoA and ending with inactivation of the filament-severing protein cofilin. Blocking this sequence, or actin polymerization itself, eliminates E2's effects on synaptic physiology. Notably, the theta burst stimulation used to induce LTP activates the same signaling pathway as E2 plus events that stabilize the reorganization of the sub-synaptic cytoskeleton. These observations suggest that E2 elicits a partial form of LTP, resulting in an increase of fast excitatory postsynaptic potentials (EPSPs) and a reduction in the threshold for lasting synaptic changes. While E2's effects on the cytoskeleton could be direct, results described here indicate that the hormone activates synaptic tropomyosin-related kinase B (TrkB) receptors for brain-derived neurotrophic factor (BDNF), a releasable neurotrophin that stimulates the RhoA to cofilin pathway. It is therefore possible that E2 acts via transactivation of neighboring receptors to modify the composition and structure of excitatory contacts. Finally, there is the question of whether a loss of acute synaptic actions contributes to the memory problems associated with estrogen depletion. Initial tests found that ovariectomy in middle-aged rats disrupts RhoA signaling, actin polymerization, and LTP consolidation. Acute applications of E2 reversed these defects, a result consistent with the idea that disturbances to actin management are one cause of behavioral effects that emerge with reductions in steroid levels.
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Affiliation(s)
- E A Kramár
- Department of Anatomy and Neurobiology, University of California, Irvine, CA 92697, USA.
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105
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Liu SB, Zhao MG. Neuroprotective effect of estrogen: role of nonsynaptic NR2B-containing NMDA receptors. Brain Res Bull 2012; 93:27-31. [PMID: 23085545 DOI: 10.1016/j.brainresbull.2012.10.004] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Revised: 10/07/2012] [Accepted: 10/09/2012] [Indexed: 01/19/2023]
Abstract
Excessive activation of N-methyl-D-aspartate receptors (NMDARs) has been implicated in the pathophysiology of chronic neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and Huntington's disease. Some studies reported that NR2A and NR2B play different roles in the central nervous system (CNS). The NR2A subunit is primarily found in the synapses and is required for glutamate-mediated neuronal survival. On the other hand, the NR2B subunit is primarily found in the extrasynaptic sites and is required for glutamate-mediated neuronal death in both in vitro and in vivo experiments. Estrogen is a steroid hormone well known for its widespread effects such as neuroprotection in the brain. Classically, estrogen can bind to two kinds of nuclear receptors, namely, estrogen receptor α (ERα) and estrogen receptor β (ERβ), and produce physiological and neuroprotective effects. Aside from nuclear receptors, estrogen has one membrane receptor, which can either be G-protein-coupled receptor 30 (GPR30), Gq-mER, or ER-X. NMDA exposure clearly promotes NR2B subunit phosphorylation at Ser-1303 and causes neuronal cell death. GPR30 mediates rapid non-genomic effects to protect neurons against injury by inhibiting p-DAPK1 dephosphorylation, which inhibits NR2B subunit phosphorylation at Ser-1303. In addition, NMDA exposure and global ischemia activate the autophagy pathway and induce cell death, which are markedly blocked by the NR2B antagonist Ro 25-6981. Thus, NR2B signaling, autophagy induction and cell death may be closely related. Ro 25-6981 inhibits the dissociation of the NR2B-Beclin-1 signaling complex and delays autophagy in vivo, thus confirming the link between NR2B signaling and autophagy. In short, ERα, ERβ, and GPR30 are involved in the neuroprotection of estrogen in the CNS. Additional research must be conducted to reveal the mechanism of estrogen action fully and to identify better targets for the development of more effective drugs. This article is part of a Special Issue entitled 'Extrasynaptic ionotropic receptors'.
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Affiliation(s)
- Shui-bing Liu
- Department of Pharmacology, School of Pharmacy, Fourth Military Medical University, Xi'an 710032, Shaanxi, China
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106
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Abstract
Inhibitors of aromatase, the final enzyme of estradiol synthesis, are suspected of inducing memory deficits in women. In previous experiments, we found hippocampal spine synapse loss in female mice that had been treated with letrozole, a potent aromatase inhibitor. In this study, we therefore focused on the effects of letrozole on long-term potentiation (LTP), which is an electrophysiological parameter of memory and is known to induce spines, and on phosphorylation of cofilin, which stabilizes the spine cytoskeleton and is required for LTP in mice. In acute slices of letrozole-treated female mice with reduced estradiol serum concentrations, impairment of LTP started as early as after 6 h of treatment and progressed further, together with dephosphorylation of cofilin in the same slices. Theta-burst stimulation failed to induce LTP after 1 week of treatment. Impairment of LTP was followed by spine and spine synapse loss. The effects were confirmed in vitro by using hippocampal slice cultures of female mice. The sequence of effects in response to letrozole were similar in ovariectomized female and male mice, with, however, differences as to the degree of downregulation. Our data strongly suggest that impairment of LTP, followed by loss of mushroom spines and spine synapses in females, may have implications for memory deficits in women treated with letrozole.
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107
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Vedder LC, Smith CC, Flannigan AE, McMahon LL. Estradiol-induced increase in novel object recognition requires hippocampal NR2B-containing NMDA receptors. Hippocampus 2012; 23:108-15. [PMID: 22965452 DOI: 10.1002/hipo.22068] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/30/2012] [Indexed: 11/11/2022]
Abstract
17β-estradiol (E2), at high circulating levels, enhances learning and memory in many women, making it a clinical treatment for hormone-related cognitive decline in aging. However, the mechanisms stimulated by E2, which are responsible for its cognitive enhancing effects, remain incompletely defined. Using an ovariectomized rat model, we previously reported that increasing plasma E2 enhances the magnitude of long-term potentiation (LTP) at hippocampal CA3-CA1 synapses, which is caused by a selective increase in current mediated by NR2B-containing NMDARs, leading to an increase in the NMDAR/AMPAR ratio. Whether the increase in NR2B current is causally related to the ability of E2 to enhance hippocampal dependent learning and memory has yet to be tested. Here, we find that E2 enhances performance in the novel object recognition (NOR) task with the same time course we previously showed E2 enhances the LTP magnitude, temporally linking the increase in LTP to enhanced learning and memory. Furthermore, using the selective NR2B subunit antagonist Ro25-6981, we find that the E2-enhanced NOR, like the enhanced LTP, requires hippocampal NR2B-containing NMDARs, specifically in area CA1. Finally, using whole-cell recordings and the phosphatase inhibitor orthovanadate, we investigated whether the E2-induced increase in NMDAR current is caused by an increase in the density of synaptic NMDARs and/or an increase in NMDAR subunit phosphorylation. We find that both mechanisms are responsible for the enhanced NMDAR current in E2-treated rats. Our results show that the E2-enhanced NOR requires a functional increase in NR2B-containing NMDARs, a requirement shared with the E2-enhanced LTP magnitude at CA3-CA1 synapses, supporting the hypothesis that the increase in LTP likely contributes to the enhanced learning and memory following an increase in plasma E2 levels.
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Affiliation(s)
- Lindsey C Vedder
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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108
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Abstract
Brain injury during development can have severe, long-term consequences. Using an array of animal models, we have an understanding of the etiology of perinatal brain injury. However, we have only recently begun to address the consequences of endogenous factors such as genetic sex and developmental steroid hormone milieu. Our limited understanding has sometimes led researchers to make over-generalizing and potentially dangerous statements regarding treatment for brain injury. Therefore this review acts as a cautionary tale, speaking to our need to understand the effects of sex and steroid hormone environment on the response to brain trauma in the neonate.
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Affiliation(s)
- Joseph Nuñez
- Neuroscience Program, Michigan State University, 108 Giltner Hall, East Lansing, MI 48824, USA.
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109
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Zhang Y, Xiao X, Zhang XM, Zhao ZQ, Zhang YQ. Estrogen facilitates spinal cord synaptic transmission via membrane-bound estrogen receptors: implications for pain hypersensitivity. J Biol Chem 2012; 287:33268-81. [PMID: 22869379 DOI: 10.1074/jbc.m112.368142] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Recent evidence suggests that estrogen is synthesized in the spinal dorsal horn and plays a role in nociceptive processes. However, the cellular and molecular mechanisms underlying these effects remain unclear. Using electrophysiological, biochemical, and morphological techniques, we here demonstrate that 17β-estradiol (E2), a major form of estrogen, can directly modulate spinal cord synaptic transmission by 1) enhancing NMDA receptor-mediated synaptic transmission in dorsal horn neurons, 2) increasing glutamate release from primary afferent terminals, 3) increasing dendritic spine density in cultured spinal cord dorsal horn neurons, and 4) potentiating spinal cord long term potentiation (LTP) evoked by high frequency stimulation (HFS) of Lissauer's tract. Notably, E2-BSA, a ligand that acts only on membrane estrogen receptors, can mimic E2-induced facilitation of HFS-LTP, suggesting a nongenomic action of this neurosteroid. Consistently, cell surface biotinylation demonstrated that three types of ERs (ERα, ERβ, and GPER1) are localized on the plasma membrane of dorsal horn neurons. Furthermore, the ERα and ERβ antagonist ICI 182,780 completely abrogates the E2-induced facilitation of LTP. ERβ (but not ERα) activation can recapitulate E2-induced persistent increases in synaptic transmission (NMDA-dependent) and dendritic spine density, indicating a critical role of ERβ in spinal synaptic plasticity. E2 also increases the phosphorylation of ERK, PKA, and NR2B, and spinal HFS-LTP is prevented by blockade of PKA, ERK, or NR2B activation. Finally, HFS increases E2 release in spinal cord slices, which can be prevented by aromatase inhibitor androstatrienedione, suggesting activity-dependent local synthesis and release of endogenous E2.
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Affiliation(s)
- Yan Zhang
- Institute of Neurobiology, Institutes of Brain Science and State Key Laboratory of Medical Neurobiology, Fudan University, Shanghai 200032, China
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110
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Ooishi Y, Kawato S, Hojo Y, Hatanaka Y, Higo S, Murakami G, Komatsuzaki Y, Ogiue-Ikeda M, Kimoto T, Mukai H. Modulation of synaptic plasticity in the hippocampus by hippocampus-derived estrogen and androgen. J Steroid Biochem Mol Biol 2012; 131:37-51. [PMID: 22075082 DOI: 10.1016/j.jsbmb.2011.10.004] [Citation(s) in RCA: 103] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Revised: 09/27/2011] [Accepted: 10/12/2011] [Indexed: 12/29/2022]
Abstract
The hippocampus synthesizes estrogen and androgen in addition to the circulating sex steroids. Synaptic modulation by hippocampus-derived estrogen or androgen is essential to maintain healthy memory processes. Rapid actions (1-2h) of 17β-estradiol (17β-E2) occur via synapse-localized receptors (ERα or ERβ), while slow genomic E2 actions (6-48h) occur via classical nuclear receptors (ERα or ERβ). The long-term potentiation (LTP), induced by strong tetanus or theta-burst stimulation, is not further enhanced by E2 perfusion in adult rats. Interestingly, E2 perfusion can rescue corticosterone (stress hormone)-induced suppression of LTP. The long-term depression is modulated rapidly by E2 perfusion. Elevation of the E2 concentration changes rapidly the density and head structure of spines in neurons. ERα, but not ERβ, drives this enhancement of spinogenesis. Kinase networks are involved downstream of ERα. Testosterone (T) or dihydrotestosterone (DHT) also rapidly modulates spinogenesis. Newly developed Spiso-3D mathematical analysis is used to distinguish these complex effects by sex steroids and kinases. It has been doubted that the level of hippocampus-derived estrogen and androgen may not be high enough to modulate synaptic plasticity. Determination of the accurate concentration of E2, T or DHT in the hippocampus is enabled by mass-spectrometric analysis in combination with new steroid-derivatization methods. The E2 level in the hippocampus is approximately 8nM for the male and 0.5-2nM for the female, which is much higher than that in circulation. The level of T and DHT is also higher than that in circulation. Taken together, hippocampus-derived E2, T, and DHT play a major role in modulation of synaptic plasticity.
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Affiliation(s)
- Yuuki Ooishi
- Department of Biophysics and Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo, Japan
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111
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Xiao X, Yang Y, Zhang Y, Zhang XM, Zhao ZQ, Zhang YQ. Estrogen in the Anterior Cingulate Cortex Contributes to Pain-Related Aversion. Cereb Cortex 2012; 23:2190-203. [DOI: 10.1093/cercor/bhs201] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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112
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Stelly CE, Cronin J, Daniel JM, Schrader LA. Long-term oestradiol treatment enhances hippocampal synaptic plasticity that is dependent on muscarinic acetylcholine receptors in ovariectomised female rats. J Neuroendocrinol 2012; 24:887-96. [PMID: 22313316 DOI: 10.1111/j.1365-2826.2012.02287.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Short-term oestradiol treatment modulates hippocampus-dependent memory and synaptic plasticity in the hippocampus. Long-term oestradiol treatment can also enhance hippocampus- dependent memory, although the effects of long-term oestradiol treatment on synaptic plasticity are unknown. We investigated the effects of long-term oestradiol treatment on synaptic plasticity at the Schaeffer Collateral/CA1 synapse in 8-month-old female rats. In addition, we determined the role of endogenous activation of muscarinic acetylcholine receptors (mAChRs) in synaptic transmission and plasticity using scopolamine (1 μm), an antagonist of mAChRs. Hippocampus slices from ovariectomised rats that were treated with oestradiol-containing capsules for 5 months were compared with slices from ovariectomised rats that received cholesterol-containing capsules. Unexpectedly, scopolamine application significantly increased the baseline field excitatory postsynaptic potentials (fEPSP) and decreased paired pulse facilitation (PPF) in slices from cholesterol-treated rats. Baseline fEPSPs and PPF were not significantly modulated in slices from oestradiol-treated rats by scopolamine. Slices from oestradiol-treated rats showed enhanced long-term potentiation relative to slices from cholesterol-treated rats. Scopolamine significantly reduced the magnitude of plasticity in slices from oestradiol-treated rats. Taken together, these results suggest that mAChRs have a significant effect on baseline synaptic transmission through a decrease in the probability of glutamate release in slices from cholesterol-treated rats. Long-term oestradiol treatment blocks this effect and enhances theta-burst stimulation-induced synaptic plasticity in the middle-aged female rat, and this effect is mediated by activation of mAChRs.
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Affiliation(s)
- C E Stelly
- Neuroscience Program, Tulane University, New Orleans, LA, USA
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113
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G-protein-coupled receptor 30 mediates rapid neuroprotective effects of estrogen via depression of NR2B-containing NMDA receptors. J Neurosci 2012; 32:4887-900. [PMID: 22492045 DOI: 10.1523/jneurosci.5828-11.2012] [Citation(s) in RCA: 124] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
17-β-estradiol (E2) is a steroid hormone involved in neuroprotection against excitotoxicity and other forms of brain injury. Through genomic and nongenomic mechanisms, E2 modulates neuronal excitability and signal transmission by regulating NMDA and non-NMDA receptors. However, the mechanisms and identity of the receptors involved remain unclear, even though studies have suggested that estrogen G-protein-coupled receptor 30 (GPR30) is linked to protection against ischemic injury. In the culture cortical neurons, treatment with E2 and the GPR30 agonist G1 for 45 min attenuated the excitotoxicity induced by NMDA exposure. The acute neuroprotection mediated by GPR30 is dependent on G-protein-coupled signals and ERK1/2 activation, but independent on transcription or translation. Knockdown of GPR30 using short hairpin RNAs (shRNAs) significantly reduced the E2-induced rapid neuroprotection. Patch-clamp recordings revealed that GPR30 activation depressed exogenous NMDA-elicited currents. Short-term GPR30 activation did not affect the expression of either NR2A- or NR2B-containing NMDARs; however, it depressed NR2B subunit phosphorylation at Ser-1303 by inhibiting the dephosphorylation of death-associated protein kinase 1 (DAPK1). DAPK1 knockdown using shRNAs significantly blocked NR2B subunit phosphorylation at Ser-1303 and abolished the GPR30-mediated depression of exogenous NMDA-elicited currents. Lateral ventricle injection of the GPR30 agonist G1 (0.2 μg) provided significant neuroprotection in the ovariectomized female mice subjected to middle cerebral artery occlusion. These findings provide direct evidence that fast neuroprotection by estradiol is partially mediated by GPR30 and the subsequent downregulation of NR2B-containing NMDARs. The modulation of DAPK1 activity by GPR30 may be an important mediator of estradiol-dependent neuroprotection.
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114
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He S, Shao LR, Rittase WB, Bausch SB. Increased Kv1 channel expression may contribute to decreased sIPSC frequency following chronic inhibition of NR2B-containing NMDAR. Neuropsychopharmacology 2012; 37:1338-56. [PMID: 22218089 PMCID: PMC3327840 DOI: 10.1038/npp.2011.320] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/26/2011] [Revised: 10/21/2011] [Accepted: 11/29/2011] [Indexed: 12/20/2022]
Abstract
Numerous studies have documented the effects of chronic N-methyl-D-aspartate receptor (NMDAR) blockade on excitatory circuits, but the effects on inhibitory circuitry are not well studied. NR2A- and NR2B-containing NMDARs play differential roles in physiological processes, but the consequences of chronic NR2A- or NR2B-containing NMDAR inhibition on glutamatergic and GABAergic neurotransmission are unknown. We investigated altered GABAergic neurotransmission in dentate granule cells and interneurons following chronic treatment with the NR2B-selective antagonist, Ro25,6981, the NR2A-prefering antagonist, NVP-AAM077, or the non-subunit-selective NMDAR antagonist, D-APV, in organotypic hippocampal slice cultures. Electrophysiological recordings revealed large reductions in spontaneous inhibitory postsynaptic current (sIPSC) frequency in both granule cells and interneurons following chronic Ro25,6981 treatment, which was associated with minimally altered sIPSC amplitude, miniature inhibitory postsynaptic current (mIPSC) frequency, and mIPSC amplitude, suggesting diminished action potential-dependent GABA release. Chronic NVP-AAM077 or D-APV treatment had little effect on these measures. Reduced sIPSC frequency did not arise from downregulated GABA(A)R, altered excitatory or inhibitory drive to interneurons, altered interneuron membrane properties, increased failure rate, decreased action potential-dependent release probability, or mGluR/GABA(B) receptor modulation of GABA release. However, chronic Ro25,6981-mediated reductions in sIPSC frequency were occluded by the K+ channel blockers, dendrotoxin, margatoxin, and agitoxin, but not dendrotoxin-K or XE991. Immunohistochemistry also showed increased Kv1.2, Kv1.3, and Kv1.6 in the dentate molecular layer following chronic Ro25,6981 treatment. Our findings suggest that increased Kv1 channel expression/function contributed to diminished action potential-dependent GABA release following chronic NR2B-containing NMDAR inhibition and that these Kv1 channels may be heteromeric complexes containing Kv1.2, Kv1.3, and Kv1.6.
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Affiliation(s)
- Shuijin He
- Department of Pharmacology, Uniformed Services University School of Medicine, Bethesda, MD, USA
- Graduate Program in Neuroscience, Uniformed Services University School of Medicine, Bethesda, MD, USA
| | - Li-Rong Shao
- Department of Pharmacology, Uniformed Services University School of Medicine, Bethesda, MD, USA
| | - W Bradley Rittase
- Department of Pharmacology, Uniformed Services University School of Medicine, Bethesda, MD, USA
| | - Suzanne B Bausch
- Department of Pharmacology, Uniformed Services University School of Medicine, Bethesda, MD, USA
- Graduate Program in Neuroscience, Uniformed Services University School of Medicine, Bethesda, MD, USA
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115
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Chronic nicotine exposure inhibits estrogen-mediated synaptic functions in hippocampus of female rats. Neurosci Lett 2012; 517:41-6. [PMID: 22521583 DOI: 10.1016/j.neulet.2012.04.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Revised: 03/24/2012] [Accepted: 04/05/2012] [Indexed: 11/24/2022]
Abstract
Nicotine, the addictive agent in cigarettes, reduces circulating estradiol-17β (E₂) and inhibits E₂-mediated intracellular signaling in hippocampus of female rats. In hippocampus, E₂-signaling regulates synaptic plasticity by phosphorylation of the N-methyl-D-aspartic acid receptor subunit NR2B and cyclic-AMP response element binding protein (pCREB). Therefore, we hypothesized that chronic nicotine exposure induces synaptic dysfunction in hippocampus of female rats. Female rats were exposed to nicotine or saline for 16 days followed by electrophysiological analysis of hippocampus. Briefly, population measurements of excitatory post-synaptic field potentials (fEPSPs) were recorded from stratum radiatum of the CA1 hippocampal slice subfield. A strict software-controlled protocol was used which recorded 30 min of baseline data (stimulation rate of 1/min), a paired-pulse stimulation sequence followed by tetanic stimulation, and 1h of post-tetanus recording. EPSP amplitude and the initial EPSP slope were measured off-line. We then investigated by Western blot analysis the effects of nicotine on hippocampal estrogen receptor-beta (ER-β), NR2B and pCREB. The results demonstrated significantly decreased post-tetanic potentiation and paired-pulse facilitation at the 40, and 80 ms interval in nicotine-exposed rats compared to the saline group. Western blot analysis revealed that nicotine decreased protein levels of ER-β, NR2B, and pCREB. We also confirmed the role of E₂ in regulating NR2B and pCREB phosphorylation by performing Western blots in hippocapmal tissue obtained from E₂-treated ovariectomized rats. In conclusion, chronic nicotine exposure attenuates short-term synaptic plasticity, and the observed synaptic defects might be a consequence of loss of estradiol-17β-signaling. However, determining the exact molecular mechanisms of chronic nicotine exposure on synaptic plasticity specific to the female brain require further investigation.
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116
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Fiocchetti M, Ascenzi P, Marino M. Neuroprotective effects of 17β-estradiol rely on estrogen receptor membrane initiated signals. Front Physiol 2012; 3:73. [PMID: 22493583 PMCID: PMC3319910 DOI: 10.3389/fphys.2012.00073] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2011] [Accepted: 03/13/2012] [Indexed: 12/15/2022] Open
Abstract
Besides its crucial role in many physiological events, 17β-estradiol (E2) exerts protective effects in the central nervous system. The E2 effects are not restricted to the brain areas related with the control of reproductive function, but rather are widespread throughout the developing and the adult brain. E2 actions are mediated through estrogen receptors (i.e., ERα and ERβ) belonging to the nuclear receptor super-family. As members of the ligand-regulated transcription factor family, classically, the actions of ERs in the brain were thought to mediate only the E2 long-term transcriptional effects. However, a growing body of evidence highlighted rapid, membrane initiated E2 effects in the brain that are independent of ER transcriptional activities and are involved in E2-induced neuroprotection. The aim of this review is to focus on the rapid effects of E2 in the brain highlighting the specific role of the signaling pathway(s) of the ERβ subtype in the neuroprotective actions of E2.
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117
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Tanaka M, Sokabe M. Continuous de novo synthesis of neurosteroids is required for normal synaptic transmission and plasticity in the dentate gyrus of the rat hippocampus. Neuropharmacology 2012; 62:2373-87. [PMID: 22365983 DOI: 10.1016/j.neuropharm.2012.02.007] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Revised: 02/07/2012] [Accepted: 02/08/2012] [Indexed: 11/28/2022]
Abstract
Both in vivo and in vitro studies have shown that neurosteroids promote learning and memory by modulating synaptic functions in the hippocampus. However, we do not know to what degree endogenously synthesized neurosteroids contribute to the hippocampal synaptic functions. Cytochrome P450scc is the enzyme that converts cholesterol to pregnenolone (PREG), which is required for the biosynthesis of all other neurosteroids. To investigate the physiological roles of endogenous neurosteroids in synaptic functions, we electrophysiologically examined the effects of aminoglutethimide (AG), a selective inhibitor of P450scc, on the synaptic transmission and plasticity in the dentate gyrus of rat hippocampal slices. The application of AG (100 μM) decreased the slope of the field excitatory postsynaptic potentials (fEPSPs) in granule cells by 20-30% in 20 min through the modulation of postsynaptic AMPA receptors, while it did not affect the presynaptic properties, including the paired-pulse ratio and the probability of glutamate release from presynaptic terminals. The AG-induced depression was nearly completely rescued by exogenously applied 500 nM PREG or by 1 nM dehydroepiandrosterone sulfate (DHEAS), one of the neurosteroids synthesized from PREG, suggesting that the AG-induced depression was caused by the loss of DHEAS. AG also reduced NMDA receptor activity, and suppressed high-frequency stimulation (HFS)-induced long-term potentiation (LTP). These findings provide novel evidence that the endogenous neurosteroids locally synthesized in the brain are required to maintain the normal excitatory synaptic transmission and plasticity in the dentate gyrus of the rat hippocampus.
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Affiliation(s)
- Motoki Tanaka
- Department of Physiology, Nagoya University Graduate School of Medicine, 65 Tsurumai, Showa, Nagoya 466-8550, Japan.
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118
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Lebron-Milad K, Milad MR. Sex differences, gonadal hormones and the fear extinction network: implications for anxiety disorders. BIOLOGY OF MOOD & ANXIETY DISORDERS 2012; 2:3. [PMID: 22738383 PMCID: PMC3384233 DOI: 10.1186/2045-5380-2-3] [Citation(s) in RCA: 191] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/27/2011] [Accepted: 02/07/2012] [Indexed: 01/11/2023]
Abstract
Convergent data from rodents and human studies have led to the development of models describing the neural mechanisms of fear extinction. Key components of the now well-characterized fear extinction network include the amygdala, hippocampus, and medial prefrontal cortical regions. These models are fueling novel hypotheses that are currently being tested with much refined experimental tools to examine the interactions within this network. Lagging far behind, however, is the examination of sex differences in this network and how sex hormones influence the functional activity and reactivity of these brain regions in the context of fear inhibition. Indeed, there is a large body of literature suggesting that sex hormones, such as estrogen, do modulate neural plasticity within the fear extinction network, especially in the hippocampus.After a brief overview of the fear extinction network, we summarize what is currently known about sex differences in fear extinction and the influence of gonadal hormones on the fear extinction network. We then go on to propose possible mechanisms by which sex hormones, such as estrogen, may influence neural plasticity within the fear extinction network. We end with a discussion of how knowledge to be gained from developing this line of research may have significant ramifications towards the etiology, epidemiology and treatment of anxiety disorders.
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Affiliation(s)
- Kelimer Lebron-Milad
- Department of Psychiatry, Harvard Medical School & Massachusetts General Hospital, Boston, MA, USA.
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Briz V, Parkash J, Sánchez-Redondo S, Prevot V, Suñol C. Allopregnanolone prevents dieldrin-induced NMDA receptor internalization and neurotoxicity by preserving GABA(A) receptor function. Endocrinology 2012; 153:847-60. [PMID: 22166974 DOI: 10.1210/en.2011-1333] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Dieldrin is an endocrine disruptor that accumulates in mammalian adipose tissue and brain. It induces convulsions due to its antagonism of the γ-aminobutyric acid A receptor (GABA(A)R). We have previously reported that long-term exposure to dieldrin causes the internalization of the N-methyl-D-aspartate receptor (NMDAR) as a result of persistent GABA(A)R inhibition. Because the neurosteroids 17β-estradiol (E2) and allopregnanolone are known to modulate the function and trafficking of GABA(A)R and NMDAR, we examined the effects of E2 and allopregnanolone on dieldrin-induced GABA(A)R inhibition, NMDAR internalization, and neuronal death in cortical neurons. We found that 1 nM E2 increased the membrane expression of NR1/NR2B receptors and postsynaptic density 95 but did not induce their physical association. In contrast, 10 nM E2 had no effect on these proteins but reduced NR2A membrane expression. We also found that exposure to 60 nM dieldrin for 6 d in vitro caused the internalization of NR1 and NR2B but not NR2A. Treatment with either 1 nM E2 or 10 μM allopregnanolone prevented the dieldrin-induced reduction in membrane levels of the NR1/NR2B receptors. Furthermore, prolonged exposure to 200 nM dieldrin down-regulated the expression of NR2A; this was inhibited only by allopregnanolone. Although both hormones restored NMDAR function, as measured by the NMDA-induced rise in intracellular calcium, allopregnanolone (but not E2) reversed the inhibition of GABA(A)R and neuronal death caused by prolonged exposure to dieldrin. Our results indicate that allopregnanolone protects cortical neurons against the neurotoxicity caused by long-term exposure to dieldrin by maintaining GABA(A)R and NMDAR functionality.
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Affiliation(s)
- Víctor Briz
- Department of Neurochemistry and Neuropharmacology, Consejo Superior de Investigaciones Científicas-Institut d'Investigacions Biomèdiques August Pi i Sunyer (IIBB-CSIC-IDIBAPS), Centro de Investigación Biomédica en Red Epidemiology and Public Health (CIBERESP), E-08036, Barcelona, Spain
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Uteshev VV. α7 nicotinic ACh receptors as a ligand-gated source of Ca(2+) ions: the search for a Ca(2+) optimum. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:603-38. [PMID: 22453962 DOI: 10.1007/978-94-007-2888-2_27] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The spatiotemporal distribution of cytosolic Ca(2+) ions is a key determinant of neuronal behavior and survival. Distinct sources of Ca(2+) ions including ligand- and voltage-gated Ca(2+) channels contribute to intracellular Ca(2+) homeostasis. Many normal physiological and therapeutic neuronal functions are Ca(2+)-dependent, however an excess of cytosolic Ca(2+) or a lack of the appropriate balance between Ca(2+) entry and clearance may destroy cellular integrity and cause cellular death. Therefore, the existence of optimal spatiotemporal patterns of cytosolic Ca(2+) elevations and thus, optimal activation of ligand- and voltage-gated Ca(2+) ion channels are postulated to benefit neuronal function and survival. Alpha7 nicotinic -acetylcholine receptors (nAChRs) are highly permeable to Ca(2+) ions and play an important role in modulation of neurotransmitter release, gene expression and neuroprotection in a variety of neuronal and non-neuronal cells. In this review, the focus is placed on α7 nAChR-mediated currents and Ca(2+) influx and how this source of Ca(2+) entry compares to NMDA receptors in supporting cytosolic Ca(2+) homeostasis, neuronal function and survival.
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Affiliation(s)
- Victor V Uteshev
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, 3500 Camp Bowie Blvd, Fort Worth, TX 76107, USA.
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121
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Grassi S, Frondaroli A, Scarduzio M, Dieni CV, Brecchia G, Boiti C, Pettorossi VE. Influence of sex and estrous cycle on synaptic responses of the medial vestibular nuclei in rats: role of circulating 17β-estradiol. Brain Res Bull 2011; 87:319-27. [PMID: 22127323 DOI: 10.1016/j.brainresbull.2011.11.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2011] [Revised: 11/08/2011] [Accepted: 11/15/2011] [Indexed: 11/30/2022]
Abstract
We investigated the possible influence of sex and estrous cycle on the synaptic responses of neurons in the medial vestibular nucleus (MVN) and their long-term modifications. In brain stem slices of male and female rats during proestrus (PE) and diestrus (DE), we evaluated the field potential evoked in the MVN by vestibular afferent stimulation. Here we find that in PE females the field potential had a lower threshold and higher amplitude than in DE females and in males and also that the stimulus-response curve was shifted to the left. Such difference is related to the level and cyclic fluctuation of circulating 17β-estradiol (E(2)). This is supported by the exogenous administration of E(2) in DE females and males, with low levels of circulating E(2) that enhanced the field potential amplitude to values close to those of PE females. Sex and estrous cycle also influence the MVN synaptic plasticity. This has been shown by investigating the effect of testosterone (T) on the induction of long-term effects, since T is the precursor for the neural synthesis of E(2) (estrogenic pathway), which is involved in the induction of fast long-term potentiation (LTP), or of 5α-dihydrotestosterone (DHT, androgenic pathway) which mediates slow LTP and long-term depression (LTD). We found that T mostly induced LTD in PE females and no effect in DE females, while it only provoked fast LTP in males. We suggest that high level of circulating E(2) may interfere with the conversion of T, by inhibiting the neural estrogenic pathway and facilitating the androgenic one. On the whole these results demonstrate an influence of circulating E(2) on vestibular synaptic transmission and plasticity that in some cases may contribute to the sex and menstrual cycle dependence of symptoms in human vestibular pathology.
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Affiliation(s)
- Silvarosa Grassi
- Dipartimento di Medicina Interna, Sezione di Fisiologia Umana, Università di Perugia, Via del Giochetto, I-06126 Perugia, Italy.
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Spencer-Segal JL, Tsuda MC, Mattei L, Waters EM, Romeo RD, Milner TA, McEwen BS, Ogawa S. Estradiol acts via estrogen receptors alpha and beta on pathways important for synaptic plasticity in the mouse hippocampal formation. Neuroscience 2011; 202:131-46. [PMID: 22133892 DOI: 10.1016/j.neuroscience.2011.11.035] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2011] [Revised: 10/25/2011] [Accepted: 11/15/2011] [Indexed: 01/07/2023]
Abstract
Estradiol affects hippocampal-dependent spatial memory and underlying structural and electrical synaptic plasticity in female mice and rats. Using estrogen receptor (ER) alpha and beta knockout mice and wild-type littermates, we investigated the role of ERs in estradiol effects on multiple pathways important for hippocampal plasticity and learning. Six hours of estradiol administration increased immunoreactivity for phosphorylated Akt throughout the hippocampal formation, whereas 48 h of estradiol increased immunoreactivity for phosphorylated TrkB receptor. Estradiol effects on phosphorylated Akt and TrkB immunoreactivities were abolished in ER alpha and ER beta knockout mice. Estradiol also had distinct effects on immunoreactivity for post-synaptic density 95 (PSD-95) and brain derived-neurotrophic factor (BDNF) mRNA in ER alpha and beta knockout mice. Thus, estradiol acts through both ERs alpha and beta in several subregions of the hippocampal formation. The different effects of estradiol at 6 and 48 h indicate that several mechanisms of estrogen receptor signaling contribute to this female hormone's influence on hippocampal synaptic plasticity. By further delineating these mechanisms, we will better understand and predict the effects of endogenous and exogenous ovarian steroids on mood, cognition, and other hippocampal-dependent behaviors.
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Affiliation(s)
- J L Spencer-Segal
- Laboratory of Neuroendocrinology, The Rockefeller University, New York, NY, USA.
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Smith JA, Hilton ECY, Saulsberry L, Canning BJ. Antitussive effects of memantine in guinea pigs. Chest 2011; 141:996-1002. [PMID: 22016492 DOI: 10.1378/chest.11-0554] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
BACKGROUND The treatment of cough is a significant clinical unmet need because there is little evidence that current therapies are effective. Based on evidence supporting a role for N-methyl D-aspartate receptors (NMDARs) in cough, we hypothesized that memantine, a low-affinity, uncompetitive NMDAR channel blocker in routine use for the treatment of Alzheimer disease, could be an effective, well-tolerated, antitussive therapy. The aim of this study was to establish preclinical evidence that memantine has antitussive effects. METHODS We studied the influence of memantine on experimentally induced coughing in response to citric acid and bradykinin inhalation in guinea pigs. We also compared the potency and efficacy of memantine as an antitussive to other NMDAR antagonists, dextromethorphan and ketamine, and to the γ-aminobutyric acid class B receptor agonist baclofen. RESULTS Compared with control subjects, 10 mg/kg memantine significantly reduced the cumulative number of coughs evoked by both citric acid (median, 24.0 [interquartile range (IQR), 13.0-25.5] vs 1.5 [IQR, 0.3-10.3] coughs; P = .012) and bradykinin aerosols (median, 16.0 [IQR, 9.5-18.5] vs 0.0 [IQR, 0-0.75] coughs; P = .002). Memantine 10 mg/kg produced a similar reduction in the cumulative number of coughs to baclofen 3 mg/kg and demonstrated comparatively greater cough suppression than 30 mg/kg dextromethorphan or 30 mg/kg ketamine. This dose of memantine produced no sedative or respiratory depressive effects. CONCLUSIONS This study illustrates that memantine has marked antitussive effects in guinea pigs, most likely mediated through NMDAR channel blockade. Memantine, therefore, has the potential to be a safe, effective, and well-tolerated antitussive agent.
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Affiliation(s)
- Jaclyn A Smith
- Department of Medicine, Division of Allergy and Clinical Immunology, Johns Hopkins Asthma and Allergy Center, Baltimore, MD; Respiratory Research Group, The University of Manchester, University Hospital of South Manchester, Manchester, England
| | - Emma C Y Hilton
- Respiratory Research Group, The University of Manchester, University Hospital of South Manchester, Manchester, England
| | - Loren Saulsberry
- Department of Medicine, Division of Allergy and Clinical Immunology, Johns Hopkins Asthma and Allergy Center, Baltimore, MD
| | - Brendan J Canning
- Department of Medicine, Division of Allergy and Clinical Immunology, Johns Hopkins Asthma and Allergy Center, Baltimore, MD.
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Snyder MA, Cooke BM, Woolley CS. Estradiol potentiation of NR2B-dependent EPSCs is not due to changes in NR2B protein expression or phosphorylation. Hippocampus 2011; 21:398-408. [PMID: 20082293 DOI: 10.1002/hipo.20756] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The hormone, 17β-estradiol (E2), influences the structure and function of synapses in the CA1 region of the hippocampus. E2 increases the density of dendritic spines and excitatory synapses on CA1 pyramidal cells, increases CA1 cells' sensitivity to excitatory synaptic input mediated by the NMDA receptor (NMDAR), enhances NMDAR-dependent long-term potentiation, and improves hippocampus-dependent working memory. Smith and McMahon (2006 J Neurosci 26:8517-8522) reported that the larger NMDAR-mediated excitatory postsynaptic currents (EPSCs) recorded after E2 treatment are due primarily to an increased contribution of NR2B-containing NMDARs. We used a combination of electrophysiology, Western blot, and immunofluorescence to investigate two potential mechanisms by which E2 could enhance NR2B-dependent EPSCs: An increase in NMDAR subunit protein levels and/or a change(s) in NR2B phosphorylation. Our studies confirmed the E2-induced increase in NR2B-dependent EPSC amplitude, but we found no evidence that E2 affects protein levels for the NR1, NR2A, or NR2B subunit of the NMDAR, nor that E2 affects phosphorylation of NR2B. Our findings suggest that the effects of E2 on NMDAR-dependent synaptic physiology in the hippocampus likely result from recruitment of NR2B-containing NMDARs to synapses rather than from increased expression of NMDARs or changes in their phosphorylation state.
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Affiliation(s)
- Melissa A Snyder
- Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois, USA
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125
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Fester L, Prange-Kiel J, Jarry H, Rune GM. Estrogen synthesis in the hippocampus. Cell Tissue Res 2011; 345:285-94. [DOI: 10.1007/s00441-011-1221-7] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2011] [Accepted: 07/17/2011] [Indexed: 12/31/2022]
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Ooishi Y, Mukai H, Hojo Y, Murakami G, Hasegawa Y, Shindo T, Morrison JH, Kimoto T, Kawato S. Estradiol rapidly rescues synaptic transmission from corticosterone-induced suppression via synaptic/extranuclear steroid receptors in the hippocampus. ACTA ACUST UNITED AC 2011; 22:926-36. [PMID: 21725036 DOI: 10.1093/cercor/bhr164] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We investigated rapid protection effect by estradiol on corticosterone (CORT)-induced suppression of synaptic transmission. Rapid suppression by 1 μM CORT of long-term potentiation (LTP) at CA3-CA1 synapses was abolished via coperfusion of 1 nM estradiol. N-methyl-D-aspartate (NMDA) receptor-derived field excitatory postsynaptic potential (NMDA-R-fEPSP) was used to analyze the mechanisms of these events. Estradiol abolished CORT-induced suppression of NMDA-R-fEPSP slope. This CORT-induced suppression was abolished by calcineurin inhibitor, and the rescue effect by estradiol on the CORT-induced suppression was inhibited by mitogen-activated protein (MAP) kinase inhibitor. The CORT-induced suppressions of LTP and NMDA-R-fEPSP slope were abolished by glucocorticoid receptor (GR) antagonist, and the restorative effects by estradiol on these processes were mimicked by estrogen receptor α (ERα) and ERβ agonists. Taken together, estradiol rapidly rescued LTP and NMDA-R-fEPSP slope from CORT-induced suppressions. A GR→calcineurin pathway is involved in these suppressive effects. The rescue effects by estradiol are driven via ERα or ERβ→MAP kinase pathway. Synaptic/extranuclear GR, ERα, and ERβ probably participate in these rapid events. Mass-spectrometric analysis determined that acute hippocampal slices used for electrophysiological measurements contained 0.48 nM estradiol less than exogenously applied 1 nM. In vivo physiological level of 8 nM estradiol could protect the intact hippocampus against acute stress-induced neural suppression.
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Affiliation(s)
- Yuuki Ooishi
- Department of Biophysics and Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
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Grassi S, Tozzi A, Costa C, Tantucci M, Colcelli E, Scarduzio M, Calabresi P, Pettorossi VE. Neural 17β-estradiol facilitates long-term potentiation in the hippocampal CA1 region. Neuroscience 2011; 192:67-73. [PMID: 21749911 DOI: 10.1016/j.neuroscience.2011.06.078] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 06/23/2011] [Accepted: 06/28/2011] [Indexed: 10/18/2022]
Abstract
In the hippocampal formation many neuromodulators are possibly implied in the synaptic plasticity such as the long-term potentiation (LTP) induced by high-frequency stimulation (HFS) of afferent fibers. We investigated the involvement of locally synthesized neural 17β-estradiol (nE(2)) in the induction of HFS-LTP in hippocampal slices from male rats by stimulating the Schaffer collateral fibers and recording the evoked field excitatory postsynaptic potential (fEPSP) in the CA1 region. We demonstrated that either the blockade of nE(2) synthesis by the aromatase inhibitor letrozole, or the antagonism of E(2) receptors (ERs) by ICI 182,780 did not prevent the induction of HFS-LTP, but reduced its amplitude by ∼60%, without influencing its maintenance. Moreover, letrozole and ICI 182,780 did not affect the first short-term post-tetanic component of LTP and the paired-pulse facilitation (PPF). These findings demonstrate that nE(2) plays an important role in the induction phase of HFS-dependent LTP. Since the basal responses were not affected by the blocking agents, we suggest that the synthesis of nE(2) is induced or enhanced by HFS through aromatase activation. In this context, the local production of nE(2) seems to be a very effective mechanism to modulate the amplitude of LTP.
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Affiliation(s)
- S Grassi
- Dipartimento di Medicina Interna, Sezione di Fisiologia Umana, Università di Perugia, Via del Giochetto, I-06126 Perugia, Italy.
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McCombe PA, Henderson RD. Effects of gender in amyotrophic lateral sclerosis. ACTA ACUST UNITED AC 2011; 7:557-70. [PMID: 21195356 DOI: 10.1016/j.genm.2010.11.010] [Citation(s) in RCA: 247] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/18/2010] [Indexed: 12/28/2022]
Abstract
BACKGROUND There is evidence that amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND), is more common in men than in women and that gender influences the clinical features of the disease. The causes of this are unknown. OBJECTIVE This review examines the gender differences that are found in ALS and postulates reasons for these differences. METHODS A literature review of PubMed (with no date limits) was performed to find information about gender differences in the incidence, prevalence, and clinical features of ALS, using the search terms ALS or MND and gender or sex, ALS prevalence, and SOD1 mice and gender. Articles were reviewed for information about gender differences, together with other articles that were already known to the authors. RESULTS The incidence and prevalence of ALS are greater in men than in women. This gender difference is seen in large studies that included all ALS patients (sporadic and familial), but is not seen when familial ALS is studied independently. Men predominate in the younger age groups of patients with ALS. Sporadic ALS has different clinical features in men and women, with men having a greater likelihood of onset in the spinal regions, and women tending to have onset in the bulbar region. Gender appears to have no clear effect on survival. In animals with superoxide dismutase 1 (sod1) mutations, sex does affect the clinical course of disease, with earlier onset in males. Possible reasons for the differences in ALS between men and women include different exposures to environmental toxins, different biological responses to exogenous toxins, and possibly underlying differences between the male and female nervous systems and different abilities to repair damage. CONCLUSIONS There is a complex interaction between gender and clinical phenotypes in ALS. Understanding the causes of the gender differences could give clues to processes that modify the disease.
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Affiliation(s)
- Pamela A McCombe
- The University of Queensland Centre for Clinical Research, Department of Neurology, Royal Brisbane and Women's Hospital, Herston, Australia.
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Barron AM, Hojo Y, Mukai H, Higo S, Ooishi Y, Hatanaka Y, Ogiue-Ikeda M, Murakami G, Kimoto T, Kawato S. Regulation of synaptic plasticity by hippocampus synthesized estradiol. Horm Mol Biol Clin Investig 2011; 7:361-75. [PMID: 25961274 DOI: 10.1515/hmbci.2011.118] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2011] [Accepted: 07/21/2011] [Indexed: 01/29/2023]
Abstract
Estradiol is synthesized from cholesterol in hippocampal neurons of adult rats by cytochrome P450 and hydroxysteroid dehydrogenase enzymes. These enzymes are expressed in the glutamatergic neurons of the hippocampus. Surprisingly, the concentration of estradiol and androgen in the hippocampus is significantly higher than that in circulation. Locally synthesized estradiol rapidly and potently modulates synaptic plasticity within the hippocampus. E2 rapidly potentiates long-term depression and induces spinogenesis through synaptic estrogen receptors and kinases. The rapid effects of estradiol are followed by slow genomic effects mediated by both estrogen receptors located at the synapse and nucleus, modulating long-term potentiation and promoting the formation of new functional synaptic contacts. Age-related changes in hippocampally derived estradiol synthesis and distribution of estrogen receptors may alter synaptic plasticity, and could potentially contribute to age-related cognitive decline. Understanding factors which regulate hippocampal estradiol synthesis could lead to the identification of alternatives to conventional hormone therapy to protect against age-related cognitive decline.
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130
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Yun SH, Trommer BL. Fragile X mice: reduced long-term potentiation and N-Methyl-D-Aspartate receptor-mediated neurotransmission in dentate gyrus. J Neurosci Res 2010; 89:176-82. [PMID: 21162125 DOI: 10.1002/jnr.22546] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2010] [Revised: 09/28/2010] [Accepted: 10/08/2010] [Indexed: 02/04/2023]
Abstract
Fragile X syndrome (FXS) is a monogenic mental retardation syndrome that frequently includes autism. The Fmr1-knockout (Fmr1-KO) mouse, like FXS-affected individuals, lacks the fragile X mental retardation protein (FMRP) and models autism as well as FXS. Limited human data and several mouse models have implicated the hippocampal dentate gyrus (DG) in autism. We therefore investigated whether the Fmr1-KO mouse exhibited functional changes in DG. We found diminished medial perforant path-granule cell long-term potentiation (LTP), complementing previous investigations of synaptic plasticity in Fmr1-KO demonstrating impaired LTP in CA1, neocortex, and amygdala and exaggerated long-term depression in CA1. We also found that peak amplitude of NMDA receptor-mediated excitatory postsynaptic currents (EPSCs) was smaller in Fmr1-KO than control. AMPA receptor-mediated EPSCs were comparable in the two strains, yielding a lower NMDA/AMPA ratio in Fmr1-KO mice and suggesting one mechanism by which absent FMRP might contribute to diminished LTP. The clinical hallmarks of autism include both excessive adherence to patterns and impaired detection of socially important patterns. The DG has a putative role in pattern separation (for time, space, and features) that has been attributed to granule cell number, firing rates, adult neurogenesis, and even perforant path LTP. DG also contributes to pattern completion in CA3 via its mossy fiber efferents, whose terminals include abundant FMRP in "fragile X granules." Together with the present data, these observations suggest that DG is a candidate region for further investigation in autism and that the Fmr1-KO model may be particularly apt.
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Affiliation(s)
- Sung Hwan Yun
- Department of Pediatrics, Maimonides Medical Center, Brooklyn, New York 11219, USA
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Sarkar SN, Smith LT, Logan SM, Simpkins JW. Estrogen-induced activation of extracellular signal-regulated kinase signaling triggers dendritic resident mRNA translation. Neuroscience 2010; 170:1080-5. [PMID: 20691769 PMCID: PMC3026564 DOI: 10.1016/j.neuroscience.2010.07.035] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2010] [Revised: 06/22/2010] [Accepted: 07/20/2010] [Indexed: 11/25/2022]
Abstract
Activated extracellular signal-regulated kinase (ERK) signaling mediated plasticity-related gene transcription has been proposed for one possible mechanism by which 17β-estradiol (E2) enhances synaptic plasticity and memory. Because activated ERK also enhances plasticity-related mRNA translation in the dendrites of neurons, we sought to determine the effects of E2 on activation of ERK, phosphorylation of translation initiation factors, and dendritic mRNA translation in hippocampal neurons. Acute E2 application resulted in a rapid, transient increase in phosphorylation of translation initiation factors, ribosomal protein (S6) and eIF4E binding protein1 (4EBP1), in an activated ERK-dependent manner. Since phosphorylation of these translation factors enhance mRNA translation, we tested E2's effect on dendritic mRNA translation. Using a green fluorescent protein (GFP)-based dendritic mRNA translation reporter (reporter plasmid construct consisted of a GFP gene fused to the 3' untranslated region (UTR) from CAMKIIα, which contains dendritic resident mRNA targeting and mRNA translational regulatory elements) we showed that E2 treatment resulted in increased somatic and dendritic GFP mRNA translation in GFP-reporter transfected hippocampal neurons. Translation inhibitor anisomycin and ERK inhibitor U0126 blocked E2 effects. Taken together, our results provide a novel mechanism by which E2 may trigger local protein synthesis of α-CaMKII in the dendrites, which is necessary for modulation of synaptic plasticity.
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Affiliation(s)
- S N Sarkar
- Department of Pharmacology and Neuroscience, University of North Texas, Health Science Center at Fort Worth, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107, USA
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Duration of estrogen deprivation, not chronological age, prevents estrogen's ability to enhance hippocampal synaptic physiology. Proc Natl Acad Sci U S A 2010; 107:19543-8. [PMID: 20974957 DOI: 10.1073/pnas.1009307107] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Whether estrogen replacement is beneficial to cognitive health is controversial. Some studies have shown that estrogen replacement therapy (ERT) relieves memory impairment associated with menopause in women, whereas others suggest that estrogen not only is incapable of providing a benefit, but actually can be detrimental. One possible explanation for this discrepancy in study findings could be the varying time after menopause at which ERT is initiated. It has been proposed that a critical period exists during which ERT must be administered to enhance cognitive function. This idea has yet to be tested directly using functional synaptic studies, however. Here we investigated whether prolonged hormone deprivation caused by ovariectomy (OVX) in young adult rats prevents the ability of estrogen replacement to increase synaptic function in the hippocampus to a degree necessary for estrogen-induced improvement in learning and memory. Remarkably, estrogen replacement was found to increase long-term potentiation, the current mediated by NR2B-containing NMDA receptors, and the dendritic spine density at CA3-CA1 synapses up to 15 months post-OVX. However, by 19 months post-OVX, the same estrogen replacement was unable to induce these changes. Importantly, this loss of estrogen's effectiveness was seen to be a consequence of the duration of deprivation. In female rats aged with their ovaries intact and examined at the same chronological age as the 19-month post-OVX group, estrogen replacement significantly increased synaptic function and spine density. These data clearly demonstrate that a critical period exists during which ERT must be administered, and that once this period passes, the beneficial effects are lost.
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133
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Mukai H, Kimoto T, Hojo Y, Kawato S, Murakami G, Higo S, Hatanaka Y, Ogiue-Ikeda M. Modulation of synaptic plasticity by brain estrogen in the hippocampus. Biochim Biophys Acta Gen Subj 2010; 1800:1030-44. [DOI: 10.1016/j.bbagen.2009.11.002] [Citation(s) in RCA: 117] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2009] [Revised: 10/15/2009] [Accepted: 11/02/2009] [Indexed: 12/31/2022]
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134
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Mitterling KL, Spencer JL, Dziedzic N, Shenoy S, McCarthy K, Waters EM, McEwen BS, Milner TA. Cellular and subcellular localization of estrogen and progestin receptor immunoreactivities in the mouse hippocampus. J Comp Neurol 2010; 518:2729-43. [PMID: 20506473 DOI: 10.1002/cne.22361] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Estrogen receptor-alpha (ERalpha), estrogen receptor-beta (ERbeta), and progestin receptor (PR) immunoreactivities are localized to extranuclear sites in the rat hippocampal formation. Because rats and mice respond differently to estradiol treatment at a cellular level, the present study examined the distribution of ovarian hormone receptors in the dorsal hippocampal formation of mice. For this, antibodies to ERalpha, ERbeta, and PR were localized by light and electron immunomicroscopy in male and female mice across the estrous cycle. Light microscopic examination of the mouse hippocampal formation showed sparse nuclear ERalpha and PR immunoreactivity (-ir) most prominently in the CA1 region and diffuse ERbeta-ir primarily in the CA1 pyramidal cell layer as well as in a few interneurons. Ultrastructural analysis additionally revealed discrete extranuclear ERalpha-, ERbeta-, and PR-ir in neuronal and glial profiles throughout the hippocampal formation. Although extranuclear profiles were detected in all animal groups examined, the amount and types of profiles varied with sex and estrous cycle phase. ERalpha-ir was highest in diestrus females, particularly in dendritic spines, axons, and glia. Similarly, ERbeta-ir was highest in estrus and diestrus females, mainly in dendritic spines and glia. Conversely, PR-ir was highest during proestrus, mostly in axons. Except for very low levels of extranuclear ERbeta-ir in mossy fiber terminals in mice, the labeling patterns in the mice for all three antibodies were similar to the ultrastructural labeling found previously in rats, suggesting that regulation of these receptors is well conserved across the two species.
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Affiliation(s)
- Katherine L Mitterling
- Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology, The Rockefeller University, New York, New York 10065, USA
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135
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BDNF upregulation rescues synaptic plasticity in middle-aged ovariectomized rats. Neurobiol Aging 2010; 33:708-19. [PMID: 20674095 DOI: 10.1016/j.neurobiolaging.2010.06.008] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2010] [Revised: 04/30/2010] [Accepted: 06/12/2010] [Indexed: 01/31/2023]
Abstract
Brain-derived neurotrophic factor (BDNF) has emerged as a possible broad-spectrum treatment for the plasticity losses found in rodent models of human conditions associated with memory and cognitive deficits. We have tested this strategy in the particular case of ovariectomy. The actin polymerization in spines normally found after patterned afferent stimulation was greatly reduced, along with the stabilization of long-term potentiation, in hippocampal slices prepared from middle-aged ovariectomized rats. Both effects were fully restored by a 60-minute infusion of 2 nM BDNF. Comparable rescue results were obtained after elevating endogenous BDNF protein levels in hippocampus with 4 daily injections of a short half-life ampakine (positive modulator of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate [AMPA]-type glutamate receptors). These results provide the first evidence that minimally invasive, mechanism-based drug treatments can ameliorate defects in spine plasticity caused by depressed estrogen levels.
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136
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Ma XM, Huang JP, Kim EJ, Zhu Q, Kuchel GA, Mains RE, Eipper BA. Kalirin-7, an important component of excitatory synapses, is regulated by estradiol in hippocampal neurons. Hippocampus 2010; 21:661-77. [PMID: 20333733 DOI: 10.1002/hipo.20780] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/04/2010] [Indexed: 12/13/2022]
Abstract
Estradiol enhances the formation of dendritic spines and excitatory synapses in hippocampal neurons in vitro and in vivo, but the underlying mechanisms are not fully understood. Kalirin-7 (Kal7), the major isoform of Kalirin in the adult hippocampus, is a Rho GDP/GTP exchange factor localized to postsynaptic densities. In the hippocampus, both Kal7 and estrogen receptor α (ERα) are highly expressed in a subset of interneurons. Over-expression of Kal7 caused an increase in spine density and size in hippocampal neurons. To determine whether Kalirin might play a role in the effects of estradiol on spine formation, Kal7 expression was examined in the hippocampus of ovariectomized rats. Estradiol replacement increased Kal7 staining in both CA1 pyramidal neurons and interneurons in ovariectomized rats. Estradiol treatment of cultured hippocampal neurons increased Kal7 levels at the postsynaptic side of excitatory synapses and increased the number of excitatory synapses along the dendrites of pyramidal neurons. These increases were mediated via ERα because a selective ERα agonist, but not a selective ERβ agonist, caused a similar increase in both Kal7 levels and excitatory synapse number in cultured hippocampal neurons. When Kal7 expression was reduced using a Kal7-specific shRNA, the density of excitatory synapses was reduced and estradiol was no longer able to increase synapse formation. Expression of exogenous Kal7 in hippocampal interneurons resulted in decreased levels of GAD65 staining. Inhibition of GABAergic transmission with bicuculline produced a robust increase in Kal7 expression. These studies suggest Kal7 plays a key role in the mechanisms of estradiol-mediated synaptic plasticity.
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Affiliation(s)
- Xin-Ming Ma
- Department of Neuroscience, University of Connecticut Health Center, Farmington, 06030, USA.
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137
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Zhou L, Fester L, von Blittersdorff B, Hassu B, Nogens H, Prange-Kiel J, Jarry H, Wegscheider K, Rune GM. Aromatase inhibitors induce spine synapse loss in the hippocampus of ovariectomized mice. Endocrinology 2010; 151:1153-60. [PMID: 20097718 DOI: 10.1210/en.2009-0254] [Citation(s) in RCA: 104] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Recently, inhibition of estrogen synthesis by aromatase inhibitors has become a favored therapy for breast cancer in postmenopausal women. Estrogen is, however, important for synapse formation in the hippocampus. Inhibition of aromatase induces spine synapse loss in organotypic hippocampal slice cultures. We therefore studied the effect of systemic treatment with the potent aromatase inhibitor letrozole on spine synapse formation and synaptic proteins in the hippocampi of female mice for periods of 7 d and 4 wk. In cyclic, letrozole-treated females and in ovariectomized, letrozole-treated females, the number of spine synapses was significantly reduced in the hippocampus but not in the prefrontal or cerebellar cortex. Consequently, the expression of the N-methyl-D-aspartate receptor NR1 was significantly down-regulated after treatment with letrozole. In cyclic animals the expression of the synaptic proteins synaptophysin and spinophilin was down-regulated in response to letrozole. In ovariectomized animals, however, protein expression was down-regulated after 7 d of treatment, whereas the expression was up-regulated after 4 wk of treatment. Our results indicate that systemic inhibition of aromatase in mice affects structural synaptic plasticity in the hippocampus. This may contribute to cognitive deficits in postmenopausal women treated with aromatase inhibitors.
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Affiliation(s)
- Lepu Zhou
- Institute of Anatomy I, Cellular Neurobiology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany
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138
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Prange-Kiel J, Fester L, Zhou L, Jarry H, Rune GM. Estrus cyclicity of spinogenesis: underlying mechanisms. J Neural Transm (Vienna) 2010; 116:1417-25. [PMID: 19730783 PMCID: PMC3085745 DOI: 10.1007/s00702-009-0294-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2009] [Accepted: 08/06/2009] [Indexed: 11/09/2022]
Abstract
Hippocampal spine density varies with the estrus cycle. The cyclic change in estradiol levels in serum was hypothesized to underlie this phenomenon, since treatment of ovariectomized animals with estradiol induced an increase in spine density in hippocampal dendrites of rats, as compared to ovariectomized controls. In contrast, application of estradiol to hippocampal slice cultures did not promote spinogenesis. In addressing this discrepancy, we found that hippocampal neurons themselves are capable of synthesizing estradiol de novo. Estradiol synthesis can be suppressed by aromatase inhibitors and by knock-down of Steroid Acute Regulatory Protein (StAR) and enhanced by substrates of steroidogenesis. Expression of estrogen receptors (ERs) and synaptic proteins, synaptogenesis, and long-term potentiation (LTP) correlated positively with aromatase activity in hippocampal cultures without any difference between genders. All effects due to inhibition of aromatase activity were rescued by application of estradiol to the cultures. Most importantly, gonadotropin-releasing hormone (GnRH) increased estradiol synthesis dose-dependently via an aromatase-mediated mechanism and consistently increased spine synapse density and spinophilin expression. As a consequence, our data suggest that cyclic fluctuations in spine synapse density result from pulsative release of GnRH from the hypothalamus and its effect on hippocampal estradiol synthesis, rather than from varying levels of serum estradiol. This hypothesis is further supported by higher GnRH receptor (GnRH-R) density in the hippocampus than in the cortex and hypothalamus and the specificity of estrus cyclicity of spinogenesis in the hippocampus, as compared to the cortex.
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Affiliation(s)
- Janine Prange-Kiel
- Department of Cell Biology, UT Southwestern Medical Center, Dallas, TX 75390, USA
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139
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Jover-Mengual T, Miyawaki T, Latuszek A, Alborch E, Zukin RS, Etgen AM. Acute estradiol protects CA1 neurons from ischemia-induced apoptotic cell death via the PI3K/Akt pathway. Brain Res 2010; 1321:1-12. [PMID: 20114038 DOI: 10.1016/j.brainres.2010.01.046] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2009] [Revised: 12/03/2009] [Accepted: 01/18/2010] [Indexed: 11/28/2022]
Abstract
Global ischemia arising during cardiac arrest or cardiac surgery causes highly selective, delayed death of hippocampal CA1 neurons. Exogenous estradiol ameliorates global ischemia-induced neuronal death and cognitive impairment in male and female rodents. However, the molecular mechanisms by which a single acute injection of estradiol administered after the ischemic event intervenes in global ischemia-induced apoptotic cell death are unclear. Here we show that acute estradiol acts via the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) signaling cascade to protect CA1 neurons in ovariectomized female rats. We demonstrate that global ischemia promotes early activation of glycogen synthase kinase-3beta (GSK3beta) and forkhead transcription factor of the O class (FOXO)3A, known Akt targets that are related to cell survival, and activation of caspase-3. Estradiol prevents ischemia-induced dephosphorylation and activation of GSK3beta and FOXO3A, and the caspase death cascade. These findings support a model whereby estradiol acts by activation of PI3K/Akt signaling to promote neuronal survival in the face of global ischemia.
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Affiliation(s)
- Teresa Jover-Mengual
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY, USA.
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140
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Mans RA, Chowdhury N, Cao D, McMahon LL, Li L. Simvastatin enhances hippocampal long-term potentiation in C57BL/6 mice. Neuroscience 2009; 166:435-44. [PMID: 20040368 DOI: 10.1016/j.neuroscience.2009.12.062] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2009] [Revised: 12/23/2009] [Accepted: 12/23/2009] [Indexed: 12/28/2022]
Abstract
Statins inhibit 3-hydroxy-3-methylglutaryl CoA reductase, the rate-limiting enzyme in the cholesterol biosynthetic pathway, and they are widely used to control plasma cholesterol levels and prevent cardiovascular disease. However, emerging evidence indicates that the beneficial effects of statins extend to the CNS. Statins have been shown to improve the outcome of stroke and traumatic brain injury, and statin use has been associated with a reduced prevalence of Alzheimer's disease (AD) and dementia. However, prospective studies with statins in AD have produced mixed results. Recently, we reported that simvastatin, a widely used statin in humans, enhances learning and memory in non-transgenic mice as well as in transgenic mice with AD-like pathology on a mixed genetic background. However, the cellular and molecular mechanisms underlying the beneficial effects of simvastatin on learning and memory remain elusive. The present study was undertaken to investigate the effect of acute simvastatin treatment on hippocampal long-term potentiation (LTP), a cellular model of learning and memory, in brain slices from C57BL/6 mice. Our results demonstrate that a prolonged in vitro simvastatin treatment for 2-4 h, but not a short-term 20-min exposure, significantly increases the magnitude of LTP at CA3-CA1 synapses without altering basal synaptic transmission or the paired-pulse facilitation ratio in hippocampal slices. Furthermore, we show that phosphorylation of Akt (protein kinase B) is increased significantly in the CA1 region following 2-hour treatment with simvastatin, and that inhibition of Akt phosphorylation suppresses the simvastatin-induced enhancement of LTP. These findings suggest activation of Akt as a molecular pathway for augmented hippocampal LTP by simvastatin treatment, and implicate enhancement of hippocampal LTP as a potential cellular mechanism underlying the beneficial effects of simvastatin on cognitive function.
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Affiliation(s)
- R A Mans
- Department of Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294-0012, USA
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141
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Fester L, Zhou L, Voets C, Ossig C, Disteldorf E, Bläute F, Prange-Kiel J, Dudzinski D, Jarry H, Rune GM, Rune GM. The opposing roles of estradiol on synaptic protein expression in hippocampal cultures. Psychoneuroendocrinology 2009; 34 Suppl 1:S123-9. [PMID: 19781860 DOI: 10.1016/j.psyneuen.2009.08.013] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2009] [Revised: 08/13/2009] [Accepted: 08/22/2009] [Indexed: 11/29/2022]
Abstract
Estrogen-induced synaptic plasticity was frequently shown by an increase of spines at apical dendrites of CA1 pyramidal neurons after systemic application of estradiol to ovariectomized rats. Surprisingly, exogenous application of estradiol to hippocampal cultures had no effect on spines and on spine synapses, although quantitative immunohistochemistry revealed an upregulation of spinophilin and of synaptophysin, in these cultures. The role of synaptophysin as a presynaptic marker and of spinophilin as a postsynaptic marker, appears questionable from these discrepancies. In contrast, synaptopodin, a marker protein of "mature" mushroom-shaped spines, was downregulated after treatment of hippocampal cultures with estradiol. Synaptopodin is strongly associated to the spine apparatus, a spine-specific cell organelle, which is present in 80% of all mushroom-shaped spines. Consistently, we found a reduction in the number of spines, containing a spine apparatus in response to estradiol, suggesting that the presence of a spine apparatus in many but not all spines is very likely a result of their dynamic character. In summary, synaptic proteins appear to be regulated by estradiol, independent of its function on spine and spine synapse formation.
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Affiliation(s)
- Lars Fester
- Institute of Anatomy I: Cellular Neurobiology, University Medical Center, Martinistr. 52, 20246 Hamburg, Germany
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142
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Smith CC, Vedder LC, McMahon LL. Estradiol and the relationship between dendritic spines, NR2B containing NMDA receptors, and the magnitude of long-term potentiation at hippocampal CA3-CA1 synapses. Psychoneuroendocrinology 2009; 34 Suppl 1:S130-42. [PMID: 19596521 PMCID: PMC2796081 DOI: 10.1016/j.psyneuen.2009.06.003] [Citation(s) in RCA: 98] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2009] [Revised: 06/03/2009] [Accepted: 06/04/2009] [Indexed: 11/24/2022]
Abstract
When circulating estrogen levels decline as a natural consequence of menopause and aging in women, there is an increased incidence of deficits in working memory. In many cases, these deficits are rescued by estrogen replacement therapy. These clinical data therefore highlight the importance of defining the biological pathways linking estrogen to the cellular substrates of learning and memory. It has been known for nearly two decades that estrogen enhances dendritic spine density on apical dendrites of CA1 pyramidal cells in hippocampus, a brain region required for learning. Interestingly, at synapses between CA3-CA1 pyramidal cells, estrogen has also been shown to enhance synaptic NMDA receptor current and the magnitude of long-term potentiation, a cellular correlate of learning and memory. Given that synapse density, NMDAR function, and long-term potentiation at CA3-CA1 synapses in hippocampus are associated with normal learning, it is likely that modulation of these parameters by estrogen facilitates the improvement in learning observed in rats, primates and humans following estrogen replacement. To facilitate the design of clinical strategies to potentially prevent or reverse the age-related decline in learning and memory during menopause, the relationship between the estrogen-induced morphological and functional changes in hippocampus must be defined and the role these changes play in facilitating learning must be elucidated. The aim of this report is to provide a summary of the proposed mechanisms by which this hormone increases synaptic function and in doing so, it briefly addresses potential mechanisms contributing to the estrogen-induced increase in synaptic morphology and plasticity, as well as important future directions.
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143
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Grassi S, Frondaroli A, Scarduzio M, Dutia MB, Dieni C, Pettorossi VE. Effects of 17beta-estradiol on glutamate synaptic transmission and neuronal excitability in the rat medial vestibular nuclei. Neuroscience 2009; 165:1100-14. [PMID: 19944747 DOI: 10.1016/j.neuroscience.2009.11.039] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2009] [Accepted: 11/17/2009] [Indexed: 10/20/2022]
Abstract
We investigated the effects of the neurosteroid 17beta-estradiol (E(2)) on the evoked and spontaneous activity of rat medial vestibular nucleus (MVN) neurons in brainstem slices. E(2) enhances the synaptic response to vestibular nerve stimulation in type B neurons and depresses the spontaneous discharge in both type A and B neurons. The amplitude of the field potential, as well as the excitatory post-synaptic potential (EPSP) and current (EPSC), in type B neurons, are enhanced by E(2). Both effects are long-term phenomena since they outlast the drug washout. The enhancement of synaptic response is mainly due to facilitation of glutamate release mediated by pre-synaptic N-methyl-D-aspartate receptors (NMDARs), since the reduction of paired pulse ratio (PPR) and the increase of miniature EPSC frequency after E(2) are abolished under D-(-)-2-amino-5-phosphonopentanoic acid (AP-5). E(2) also facilitates post-synaptic NMDARs, but it does not affect directly alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) and group I-metabotropic glutamate receptors (mGluRs-I). In contrast, the depression of the spontaneous discharge of type A and type B neurons appears to depend on E(2) modulation of intrinsic ion conductances, as the effect remains after blockade of glutamate, GABA and glycine receptors (GlyRs). The net effect of E(2) is to enhance the signal-to-noise ratio of the synaptic response in type B neurons, relative to resting activity of all MVN neurons. These findings provide evidence for a novel potential mechanism to modulate the responsiveness of vestibular neurons to afferent inputs, and so regulate vestibular function in vivo.
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Affiliation(s)
- S Grassi
- Department of Internal Medicine, Section of Human Physiology, University of Perugia, Perugia, Italy.
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144
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Cytoskeletal changes underlie estrogen's acute effects on synaptic transmission and plasticity. J Neurosci 2009; 29:12982-93. [PMID: 19828812 DOI: 10.1523/jneurosci.3059-09.2009] [Citation(s) in RCA: 211] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Estrogen, in addition to its genomic effects in brain, causes rapid and reversible changes to synaptic operations. We report here that these acute actions are due to selective activation of an actin-signaling cascade normally used in the production of long-term potentiation (LTP). Estrogen, or a selective agonist of the steroid's beta-receptor, caused a modest increase in fast glutamatergic transmission and a pronounced facilitation of LTP in adult hippocampal slices; both effects were completely eliminated by latrunculin, a toxin that prevents actin filament assembly. Estrogen also increased spine concentrations of filamentous actin and strongly enhanced its polymerization in association with LTP. A search for the origins of these effects showed that estrogen activates the small GTPase RhoA and phosphorylates (inactivates) the actin severing protein cofilin, a downstream target of RhoA. Moreover, an antagonist of RhoA kinase (ROCK) blocked estrogen's synaptic effects. Estrogen thus emerges as a positive modulator of a RhoA>ROCK>LIM kinase>cofilin pathway that regulates the subsynaptic cytoskeleton. It does not, however, strongly affect a second LTP-related pathway, involving the GTPases Rac and Cdc42 and their effector p21-activated kinase, which may explain why its acute effects are reversible. Finally, ovariectomy depressed RhoA activity, spine cytoskeletal plasticity, and LTP, whereas brief infusions of estrogen rescued plasticity, suggesting that the deficits in plasticity arise from acute, as well as genomic, consequences of hormone loss.
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145
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Fester L, Zhou L, Bütow A, Huber C, von Lossow R, Prange-Kiel J, Jarry H, Rune GM. Cholesterol-promoted synaptogenesis requires the conversion of cholesterol to estradiol in the hippocampus. Hippocampus 2009; 19:692-705. [PMID: 19156851 DOI: 10.1002/hipo.20548] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Cholesterol of glial origin promotes synaptogenesis (Mauch et al., (2001) Science 294:1354-1357). Because in the hippocampus local estradiol synthesis is essential for synaptogenesis, we addressed the question of whether cholesterol-promoted synapse formation results from the function of cholesterol as a precursor of estradiol synthesis in this brain area. To this end, we treated hippocampal cultures with cholesterol, estradiol, or with letrozole, a potent aromatase inhibitor. Cholesterol increased neuronal estradiol release into the medium, the number of spine synapses in hippocampal slice cultures, and immunoreactivity of synaptic proteins in dispersed cultures. Simultaneous application of cholesterol and letrozole or blockade of estrogen receptors by ICI 182 780 abolished cholesterol-induced synapse formation. As a further approach, we inhibited the access of cholesterol to the first enzyme of steroidogenesis by knock-down of steroidogenic acute regulatory protein, the rate-limiting step in steroidogenesis. A rescue of reduced synaptic protein expression in transfected cells was achieved by estradiol but not by cholesterol. Our data indicate that in the hippocampus cholesterol-promoted synapse formation requires the conversion of cholesterol to estradiol.
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Affiliation(s)
- Lars Fester
- Institute of Anatomy I: Cellular Neurobiology, Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany
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146
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Cairns BE, Dong X. The Role of Peripheral Glutamate and Glutamate Receptors in Muscle Pain. ACTA ACUST UNITED AC 2009. [DOI: 10.1080/10582450801960388] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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147
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Abstract
The age of an experimental animal can be a critical variable, yet age matters are often overlooked within neuroscience. Many studies make use of young animals, without considering possible differences between immature and mature subjects. This is especially problematic when attempting to model traits or diseases that do not emerge until adulthood. In this commentary we discuss the reasons for this apparent bias in age of experimental animals, and illustrate the problem with a systematic review of published articles on long-term potentiation. Additionally, we review the developmental stages of a rat and discuss the difficulty of using the weight of an animal as a predictor of its age. Finally, we provide original data from our laboratory and review published data to emphasize that development is an ongoing process that does not end with puberty. Developmental changes can be quantitative in nature, involving gradual changes, rapid switches, or inverted U-shaped curves. Changes can also be qualitative. Thus, phenomena that appear to be unitary may be governed by different mechanisms at different ages. We conclude that selection of the age of the animals may be critically important in the design and interpretation of neurobiological studies.
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Affiliation(s)
- James Edgar McCutcheon
- Department of Cellular and Molecular Pharmacology, Rosalind Franklin University of Medicine and Science, The Chicago Medical School, 3333 Green Bay Road, North Chicago, IL 60064, USA
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148
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Stephan KE, Friston KJ, Frith CD. Dysconnection in schizophrenia: from abnormal synaptic plasticity to failures of self-monitoring. Schizophr Bull 2009; 35:509-27. [PMID: 19155345 PMCID: PMC2669579 DOI: 10.1093/schbul/sbn176] [Citation(s) in RCA: 821] [Impact Index Per Article: 54.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Over the last 2 decades, a large number of neurophysiological and neuroimaging studies of patients with schizophrenia have furnished in vivo evidence for dysconnectivity, ie, abnormal functional integration of brain processes. While the evidence for dysconnectivity in schizophrenia is strong, its etiology, pathophysiological mechanisms, and significance for clinical symptoms are unclear. First, dysconnectivity could result from aberrant wiring of connections during development, from aberrant synaptic plasticity, or from both. Second, it is not clear how schizophrenic symptoms can be understood mechanistically as a consequence of dysconnectivity. Third, if dysconnectivity is the primary pathophysiology, and not just an epiphenomenon, then it should provide a mechanistic explanation for known empirical facts about schizophrenia. This article addresses these 3 issues in the framework of the dysconnection hypothesis. This theory postulates that the core pathology in schizophrenia resides in aberrant N-methyl-D-aspartate receptor (NMDAR)-mediated synaptic plasticity due to abnormal regulation of NMDARs by neuromodulatory transmitters like dopamine, serotonin, or acetylcholine. We argue that this neurobiological mechanism can explain failures of self-monitoring, leading to a mechanistic explanation for first-rank symptoms as pathognomonic features of schizophrenia, and may provide a basis for future diagnostic classifications with physiologically defined patient subgroups. Finally, we test the explanatory power of our theory against a list of empirical facts about schizophrenia.
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Affiliation(s)
- Klaas E. Stephan
- Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, 12 Queen Square, London WC1N 3BG, UK,Laboratory for Social and Neural Systems Research, Institute for Empirical Research in Economics, University of Zurich, Zurich, Switzerland,To whom correspondence should be addressed; tel: +44-207-8337472, fax: +44-207-8131420, e-mail:
| | - Karl J. Friston
- Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, 12 Queen Square, London WC1N 3BG, UK
| | - Chris D. Frith
- Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, 12 Queen Square, London WC1N 3BG, UK,Centre of Functionally Integrative Neuroscience (CFIN), Aarhus University Hospital, 8000-Aarhus, Denmark
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149
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Frye CA. Hormonal influences on seizures: basic neurobiology. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2009; 83:27-77. [PMID: 18929075 DOI: 10.1016/s0074-7742(08)00003-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
There are sex differences and effects of steroid hormones, such as androgens, estrogens, and progestogens, that influence seizures. Androgens exert early organizational and later activational effects that can amplify sex/gender differences in the expression of some seizure disorders. Female-typical sex steroids, such as estrogen (E2) and progestins, can exert acute activational effects to reduce convulsive seizures and these effects are mediated in part by the actions of steroids in the hippocampus. Some of these anticonvulsive effects of sex steroids are related to their formation of ligands which have agonist-like actions at gamma-aminobutyric acid (GABAA) receptors or antagonist actions at glutamatergic receptors. Differences in stress, developmental phase, reproductive status, endocrine status, and treatments, such as anti-epileptic drugs (AEDs), may alter levels of these ligands and/or the function of target sites, which may mitigate differences in sensitivity to, and/or tolerance of, steroids among some individuals. The evidence implicating sex steroids in differences associated with hormonal, reproductive, developmental, stress, seizure type, and/or therapeutics are discussed.
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Affiliation(s)
- Cheryl A Frye
- Department of Psychology, The University at Albany-State University of New York, New York 12222, USA
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150
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Kramár EA, Chen LY, Rex CS, Gall CM, Lynch G. Estrogen's Place in the Family of Synaptic Modulators. MOLECULAR AND CELLULAR PHARMACOLOGY 2009; 1:258-262. [PMID: 20419049 PMCID: PMC2858427] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Estrogen, in addition to its genomic effects, triggers rapid synaptic changes in hippocampus and cortex. Here we summarize evidence that the acute actions of the steroid arise from actin signaling cascades centrally involved in long-term potentiation (LTP). A 10-min infusion of E2 reversibly increased fast EPSPs and promoted theta burst-induced LTP within adult hippocampal slices. The latter effect reflected a lowered threshold and an elevated ceiling for the potentiation effect. E2's actions on transmission and plasticity were completely blocked by latrunculin, a toxin that prevents actin polymerization. E2 also caused a reversible increase in spine concentrations of filamentous (F-) actin and markedly enhanced polymerization caused by theta burst stimulation (TBS). Estrogen activated the small GTPase RhoA, but not the related GTPase Rac, and phosphorylated (inactivated) synaptic cofilin, an actin severing protein targeted by RhoA. An inhibitor of RhoA kinase (ROCK) thoroughly suppressed the synaptic effects of E2. Collectively, these results indicate that E2 engages a RhoA >ROCK> cofilin> actin pathway also used by brain-derived neurotrophic factor and adenosine, and therefore belongs to a family of 'synaptic modulators' that regulate plasticity. Finally, we describe evidence that the acute signaling cascade is critical to the depression of LTP produced by ovariectomy.
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Affiliation(s)
- Enikö A. Kramár
- Department of Psychiatry and Human Behavior, University of California, Irvine, California
| | - Lulu Y. Chen
- Department of Anatomy and Neurobiology, University of California, Irvine, California
| | - Christopher S. Rex
- Department of Psychiatry and Human Behavior, University of California, Irvine, California
| | - Christine M. Gall
- Department of Anatomy and Neurobiology, University of California, Irvine, California
| | - Gary Lynch
- Department of Psychiatry and Human Behavior, University of California, Irvine, California
- Department of Anatomy and Neurobiology, University of California, Irvine, California
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