Article

Local Estrogen Synthesis Regulates Parallel Fiber-Purkinje Cell Neurotransmission Within the Cerebellar Cortex

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Abstract

Estrogens affect cerebellar activity and cerebellar-based behaviors. Within the adult rodent cerebellum, the best-characterized action of estradiol is to enhance glutamatergic signaling. However, the mechanism(s) by which estradiol promotes glutamatergic neurotransmission remain unknown. Within the mouse cerebellum, we find that estrogen receptor activation of mGluR1a strongly enhances neurotransmission at the parallel fiber-Purkinje cell synapse. The blockade of local estrogen synthesis within the cerebellum results in a diminution of glutamatergic neurotransmission. Correspondingly, decreased estrogen availability via gonadectomy or blockade of aromatase activity negatively impacts locomotor performance. These data indicate that local- and not just gonadal-derived estrogens affect cerebellar physiology and function. In addition, estrogens were found to facilitate parallel fiber-Purkinje cell synaptic transmission in both sexes. As such, the actions of estradiol to support cerebellar neurotransmission and cerebellar-based behaviors may be fundamental to understanding the normal processing of activity within the cerebellar cortex.

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... Neuroactive steroids, including peripheric-derived hormones and locally synthesized neurosteroids in the central nervous system (CNS), which modulate cerebellar cortex synapse transmission, plasticity, and structure over the life span (Andreescu et al., 2007;Dieni, Ferraresi, et al., 2018;Hedges et al., 2018;Mancino et al., 2021;Sasahara et al., 2007;Tsutsui, 2019), may play a central role in mediating cerebellar function involved in regulating behavior (Dieni et al., 2020;Perez-Pouchoulen et al., 2016). Besides classical longterm actions on genomic mechanisms during development (Haraguchi et al., 2012;Sakamoto et al., 2003;Sasahara et al., 2007;Tsutsui, 2012), neuroactive steroids may also exert rapid nonclassical effects on cerebellar physiology (Andreescu et al., 2007;Dieni et al., 2020;Hedges et al., 2012). ...
... Besides classical longterm actions on genomic mechanisms during development (Haraguchi et al., 2012;Sakamoto et al., 2003;Sasahara et al., 2007;Tsutsui, 2012), neuroactive steroids may also exert rapid nonclassical effects on cerebellar physiology (Andreescu et al., 2007;Dieni et al., 2020;Hedges et al., 2012). The best-known rapid effect is related to estradiol activation of estrogen receptors, which impacts synaptic activity and cerebellar-dependent behaviors such as locomotion and adaptation of the vestibuloocular reflex (VOR), a gaze stabilizing reflex that makes possible clear vision during head movements (Andreescu et al., 2007;Dieni, Ferraresi, et al., 2018;Hedges et al., 2018;Smith et al., 1988). ...
... It has been observed that estradiol impacts glutamatergic neurotransmission between parallel fiber and Purkinje cells (PCs) in the cerebellar cortex, thereby potentially mediating cerebellar processes whereby input-output information processing adapts to influence behaviors (Andreescu et al., 2007;Dean & McCarthy, 2008;Dieni et al., 2020;Hedges et al., 2018;Smith, 1995). However, the cerebellum also contains androgens receptors (Ars) and the enzymatic machinery to locally synthesize androgens, leaving open the possibility that these steroids (locally synthesized and circulating) may be involved in the control of the cerebellar functioning (Mancino et al., 2021;Munetomo et al., 2015;Perez-Pouchoulen et al., 2016;Simerly et al., 1990;Tsutsui, 2019;Ukena et al., 1999). ...
Article
Cerebellar-dependent learning is essential for the adaptation of motor and no motor behaviors to changing contexts, and neuroactive steroids—mainly referred to as estrogens—may regulate this process. However, the role of androgens in this process has not been established, although they may affect cerebellar physiology. Thus, this study aims to determine whether the activation of androgenic neural pathways may take part in controlling the vestibuloocular (VOR) and optokinetic reflexes (OKR), which depend on a defined cerebellar circuitry. To answer this question, we acutely blocked the activation of androgen receptors (Ars) using systemic administration of the Ars antagonist flutamide (FLUT; 20 mg/Kg) in peripubertal male rats. Then, we evaluated the FLUT effect on general oculomotor performance in the VOR and OKR as well as VOR adaptive gain increases and decreases. We used a paradigm causing fast VOR adaptation that combined in phase/out phase visuo-vestibular stimulations. We found that FLUT impaired the gain increase and decrease in VOR adaptation. However, FLUT altered neither acute nor overtime basal ocular-motor performance in the VOR or OKR. These findings indicate that the activation of androgenic neural pathways participates in phenomena leading to fast VOR adaptation, probably through the modulation of plasticity mechanisms that underlie adaptation of this reflex. Conversely, androgens may not be essential for neural information processing demands in basal ocular-motor reflexes. Moreover, our results suggest that androgens, possibly testosterone and dihydrotestosterone, could rapidly regulate motor memory encoding in the VOR adaptation, acting at both cerebellar and extracerebellar plasticity sites.
... Experiments conducted in the brainstem and cerebellum indicate that despite the supposed low synthesis in the experimental models used, nE2 may contribute to rapidly modulating neurotransmission via dynamic change of its availability at a synaptic level [38][39][40][41][42]. It has already been demonstrated that modifications in local estradiol synthesis may be achieved by changes in aromatase activity. ...
... Nevertheless, the age-related maintenance of a low level of aromatase expression in the cerebellum seems to have a cardinal physiological significance in the contribution of controlling the cerebellar function. Recent reports showed that nE2 synthesis rapidly influences the glutamatergic transmission between the parallel fibers and Purkinje cells in the cerebellar cortex and acutely impact cerebellar dependent behaviors in adult rodents [39,40,74,87]. Furthermore, the high level of estrogen receptors found in the cerebellum of adults is supportive of cerebellar responsiveness even to a minute and localized nE2 synthesis [88][89][90]. ...
... Other synaptic plasticity sites that may play a late role in VOR memory consolidation could be present in the direct pathway in vestibular nuclei (Figure 4) [117,118,124,125]. Notably, as mentioned above, it has recently been shown that in adult rodents, nE2, as well as a high plasma concentration of estrogen, may similarly modulate the neuronal transmission at specific synapses into the VOR network as it is the case of the synapse between parallel fibers and PCs [39][40][41][42]87,91,97,126]. Moreover, the evidence that nE2 synthesis may also rapidly regulate the encoding of VOR adaptation and some other motor behavior controlled by the cerebellum is consistent with a nE2 modulation upon the cerebellar network [39,40,74,122]. ...
Article
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The estrogen estradiol is a potent neuroactive steroid that may regulate brain structure and function. Although the effects of estradiol have been historically associated with gonadal secretion, the discovery that this steroid may be synthesized within the brain has expanded this traditional concept. Indeed, it is accepted that de novo synthesized estradiol in the nervous system (nE2) may modulate several aspects of neuronal physiology, including synaptic transmission and plasticity, thereby influencing a variety of behaviors. These modulations may be on a time scale of minutes via non-classical and often membrane-initiated mechanisms or hours and days by classical actions on gene transcription. Besides the high level, recent investigations in the cerebellum indicate that even a low aromatase expression can be related to the fast nE2 effect on brain functioning. These pieces of evidence point to the importance of an on-demand and localized nE2 synthesis to rapidly contribute to regulating the synaptic transmission. This review is geared at exploring a new scenario for the impact of estradiol on brain processes as it emerges from the nE2 action on cerebellar neurotransmission and cerebellum-dependent learning.
... This finding observed in males as well as in females may be ascribed to local synthesis of estrogen in cerebellum. Previous human and animal studies have evidenced that estradiol is synthesized locally within the cerebellum (44)(45)(46)(47)(48)(49). The local synthesis of estradiol in cerebellum 287 5 Fig. 5. A: Immunoblot analysis of a1-3 subunits of the Na,K-ATPase in female cerebral cortex (F cortex), in female cerebellum (F cere), male cerebral cortex (M cortex) and in male cerebellum (M cere). ...
... So the cerebellar Na,K-ATPase is probably subjected to estradiol more intensively than the enzyme in males. The involvement of estradiol in regulation of local protein synthesis (47,50) may be responsible for higher presence of all 3 isoforms of catalytic a-subunit of Na,K-ATPase in cerebellum when compared to cerebral cortex. However, our studies of enzyme kinetics showed that the higher presence of a-subunit in cerebellum was not manifested in increased activity of the enzyme when compared to cortex. ...
Article
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Na,K-ATPase is the main system effectively excluding the superfluous sodium out of the cells on the expense of energy derived from hydrolysis of ATP. In brain 3 different isoforms of the catalytic α-subunit are known. The present study was focused to energy utilization and ability to bind sodium by the Na,K-ATPase as well as expression of all 3 isoforms of the catalytic α-subunit concerning its sex specificity in two selected regions of the brain, in cortex and in cerebellum of rats. Western blot analysis showed higher expression of all 3 catalytic α-subunits of Na,K-ATPase in cerebellum when compared to cortex which was not followed by higher activity. On contrary the total activity of the enzyme was lower in cerebellum comparing with cortex in females with no significant localization dependent differences of activities in males. Concerning sex dependence only the expression of α3 isoform was higher in cortex of male rats with no differences in the levels of α1 and α2 isoforms. However, the total activity of Na,K-ATPase in cortex was similar in male and female groups. On the other hand in cerebellum of females the total activity of Na,K-ATPase was significantly lower as compared with males. The obtained data indicate localization and sex dependent variations in maintenance of sodium homeostasis in the brain.
... L'activation de ces récepteurs mène à l'activation de mGluR1a et promeut la neurotransmission au niveau de la synapse entre les FP et les PC. En conséquence, cela potentialise l'activité glutamatergique dans le cervelet (Hedges et al. 2018 ...
Thesis
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Les troubles du spectre autistique (TSA) sont des troubles neurodéveloppementaux, touchant 3,7 hommes pour 1 femme en France, qui se traduisent principalement par des déficits persistants dans les comportements sociaux ainsi que par des comportements, intérêts et activités restreints et répétés. L’exposition à des facteurs environnementaux, notamment durant la période périnatale, serait majoritairement impliquée dans l’étiologie des TSA. On retrouve parmi ces facteurs, des composés pharmacologiques comme l’acide valproïque (VPA) (Dépakine®), dont l’exposition in utero augmente la probabilité de développer des TSA. Le cervelet, par ses fonctions cognitives et motrices, représente l’une des structures les plus impliquées dans la physiopathologie des TSA par des modifications anatomiques, cellulaires et moléculaires chez des patients et modèles animaux de TSA. Une supplémentation en acides gras polyinsaturés à longue chaîne n-3 (AGPI-LC n-3) sur plusieurs mois permet de réduire les symptômes de TSA chez des enfants. L’objectif de cette thèse a donc été de déterminer si une alimentation supplémentée en AGPI-LC n-3 en période périnatale pouvait protéger des symptômes de TSA induits par une exposition in utero au VPA chez la souris. Nous avons réalisé une étude longitudinale portant sur l’évolution des symptômes sociaux et moteurs ainsi que sur les corrélats cellulaires et moléculaires cérébelleux chez des souris mâles et femelles. Ces travaux ont permis de mettre en évidence qu’une alimentation équilibrée en AGPI n-3 et n-6 permet de protéger contre l’apparition de symptômes comportementaux, la perte de neurones cérébelleux et la dysbiose du microbiote intestinal.
... Estrogen plays an important role in masculinizing the brain (39), and rapid estradiol signaling occurs in adult males, including through mGluRs. Estradiol activation of mGluR1a through ERb modulates sexual behavior in male quails (40,41), and rodent studies have confirmed rapid mER-mGluR signaling in both the male and female adult cerebellum (42). In females, though, rapid signaling of estradiol, including through mGluRs, has been shown to be incredibly important in driving reproduction, including in the development of the luteinizing hormone surge which stimulates ovulation, the central event in female reproduction. ...
Article
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Estrogen receptors were initially identified in the uterus, and later throughout the brain and body as intracellular, ligand-regulated transcription factors that affect genomic change upon ligand binding. However, rapid estrogen receptor signaling initiated outside of the nucleus was also known to occur via mechanisms that were less clear. Recent studies indicate that these traditional receptors, estrogen receptor-α and estrogen receptor-β, can also be trafficked to act at the surface membrane. Signaling cascades from these membrane-bound estrogen receptors (mERs) not only rapidly effect cellular excitability, but can and do ultimately affect gene expression, as seen through the phosphorylation of CREB. A principal mechanism of neuronal mER action is through glutamate-independent transactivation of metabotropic glutamate receptors (mGluRs), which elicits multiple signaling outcomes. The interaction of mERs with mGluRs has been shown to be important in many diverse functions in females, including, but not limited to, reproduction and motivation. Here we review membrane-initiated estrogen receptor signaling in females, with a focus on the interactions between these mERs and mGluRs.
... In turn, estrogens such as 17-beta-estradiol (E2) can have rapid (i.e. within minutes) effects on neuronal firing in many brain areas (Wong and Moss 1992;Smith et al. 2002;Remage-Healey 2004;Remage-Healey and Bass 2007;Meitzen et al. 2012;Rudolph et al. 2016;Hedges et al. 2018;Soutar et al. 2022). ...
Article
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Sensory neurons parse millisecond-variant sound streams like birdsong and speech with exquisite precision. The auditory pallial cortex of vocal learners like humans and songbirds contains an unconventional neuromodulatory system: neuronal expression of the estrogen synthesis enzyme aromatase. Local forebrain neuroestrogens fluctuate when songbirds hear a song, and subsequently modulate bursting, gain, and temporal coding properties of auditory neurons. However, the way neuroestrogens shape intrinsic and synaptic properties of sensory neurons remains unknown. Here, using a combination of whole-cell patch clamp electrophysiology and calcium imaging, we investigate estrogenic neuromodulation of auditory neurons in a region resembling mammalian auditory association cortex. We found that estradiol rapidly enhances the temporal precision of neuronal firing via a membrane-bound G-protein coupled receptor and that estradiol rapidly suppresses inhibitory synaptic currents while sparing excitation. Notably, the rapid suppression of intrinsic excitability by estradiol was predicted by membrane input resistance and was observed in both males and females. These findings were corroborated by analysis of in vivo electrophysiology recordings, in which local estrogen synthesis blockade caused acute disruption of the temporal correlation of song-evoked firing patterns. Therefore, on a modulatory timescale, neuroestrogens alter intrinsic cellular properties and inhibitory neurotransmitter release to regulate the temporal precision of higher-order sensory neurons.
... One possible explanation is that estrogen has a protective effect against ASD since estrogen was found to ameliorate ASD-like behaviors in zebrafish larva (Hoffman et al., 2016). Meanwhile, the interaction between estrogen receptors and mGluR1 could facilitate the glutamatergic neurotransmission at parallel fiber-Purkinje cell synapses (Hedges et al., 2018). However, the exact mechanism underlying the male-specific social defects in necab2 −/− zebrafish warrants further investigations. ...
Article
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Background De novo deletion of the neuronal calcium-binding protein 2 (NECAB2) locus is associated with idiopathic autism spectrum disorders (ASDs). The in vivo function of NECAB2 in the brain remains largely elusive.Methods We investigated the morphological and behavioral profiles of both necab2 knock-out and overexpression zebrafish models. The expression pattern and molecular role of necab2 were probed through a combination of in vitro and in vivo assays.ResultsWe show that Necab2 is a neuronal specific, cytoplasmic, and membrane-associated protein, abundantly expressed in the telencephalon, habenula, and cerebellum. Necab2 is distributed peri-synaptically in subsets of glutamatergic and GABAergic neurons. CRISPR/Cas9-generated necab2 knock-out zebrafish display normal morphology but exhibit a decrease in locomotor activity and thigmotaxis with impaired social interaction only in males. Conversely, necab2 overexpression yields behavioral phenotypes opposite to the loss-of-function. Proteomic profiling uncovers a role of Necab2 in modulating signal transduction of G-protein coupled receptors. Specifically, co-immunoprecipitation, immunofluorescence, and confocal live-cell imaging suggest a complex containing NECAB2 and the metabotropic glutamate receptor 1 (mGluR1). In vivo measurement of phosphatidylinositol 4,5-bisphosphate further substantiates that Necab2 promotes mGluR1 signaling.Conclusions Necab2 regulates psychomotor and social behavior via modulating a signaling cascade downstream of mGluR1.
... The anatomical evidence strongly indicates projections of aromatase nuclei that synthesize and release estradiol in a synaptic fashion to impact post-synaptic cellular physiology. Although difficult to test sensu strictu, this 'synaptocrine' anatomical arrangement (Saldanha et al., 2011) is also consistent with rapid neuromodulatory estrogen synthesis in pre-synaptic terminals during social and reproductive contexts (Remage-Healey et al., 2009Cornil et al., 2012), and the rapid effects of estradiol on neuronal firing (Wong and Moss, 1992;Smith et al., 2002;Remage-Healey and Bass, 2007;Rudolph et al., 2016;Hedges et al., 2018). The presence of pre-synaptic terminal aromatase in a network of brain regions, and their interconnectivity (see below), raises the specter of whether aromatase neurons themselves preferentially target downstream neurons in social and sensory brain regions that are in turn also aromatase positive. ...
Article
This review explores the role of aromatase in the brain as illuminated by a set of conserved network-level connections identified in several vertebrate taxa. Aromatase-expressing neurons are neurochemically heterogeneous but the brain regions in which they are found are highly-conserved across the vertebrate lineage. During development, aromatase neurons have a prominent role in sexual differentiation of the brain and resultant sex differences in behavior and human brain diseases. Drawing on literature primarily from birds and rodents we delineate brain regions that express aromatase and that are strongly interconnected, and suggest that, in many species, aromatase expression essentially defines the Social Behavior Network. Moreover, in several cases the inputs to and outputs from this core social behavior network also express aromatase. Recent advances in molecular and genetic tools for neuroscience now enable in-depth and taxonomically diverse studies of the function of aromatase at the neural circuit level.
... Chiefly, the CBLM is susceptible to the effects of estrogen. Estrogen receptors are present in the CBLM (McEwen, 2002) and local estrogen synthesis regulates CBLM neurotransmission (Hedges et al., 2018(Hedges et al., , 2012. Postmenopausal females undergoing estrogen (which was not certified by peer review) is the author/funder. ...
Preprint
Sex-specific differences in the aging cerebellum may be related to hormone changes with menopause. We evaluated the influence of reproductive stage on lobular cerebellar network connectivity using data from the Cambridge Centre for Ageing and Neuroscience repository. We used raw structural and resting state neuroimaging data and information regarding age, sex, and menopause-related variables. Crus I and II and Lobules V and VI were our cerebellar seeds of interest. We characterized reproductive stage using the Stages of Reproductive Aging Workshop criteria. Results show that postmenopausal females have lower cerebello-striatal and cerebello-cortical connectivity, particularly in frontal regions, along with lower connectivity within the cerebellum, compared to reproductive females. Postmenopausal females also exhibit greater connectivity in some brain areas as well. Differences begin to emerge across transitional stages of menopause. Further, results reveal sex-specific differences in connectivity between female reproductive groups and age-matched male control groups. This suggests that menopause may influence cerebellar network connectivity in aging females, and sex differences in the aging brain may be related to this biological process. Highlights Lobular analysis of cerebellar network connectivity across reproductive stages Postmenopausal females show lower cerebellar connectivity, compared to reproductive Connectivity differences begin to emerge in transitional stages of menopause Age-matched male control groups show distinct patterns of cerebellar connectivity Reproductive stage influences cerebellar network connectivity in aging females
... Furthermore, endogenous E 2 has been shown to affect microglial phagocytosis during the sensitive window of postnatal development of the CER (Perez-Pouchoulen et al., 2019). E 2 also regulates the neurotransmission of parallel fibers to Purkinje cells in the CER (Hedges et al., 2018). E 2 is expressed in cerebellar granule cells (Belcher, 1999) and has a trophic effects on these cells in both, males and females (Montelli et al., 2017). ...
Article
Full-text available
The sex steroid hormones (SSHs) play roles in regulation of various processes in the cardiovascular, immune, muscular and neural systems. SSHs affect prenatal and postnatal development of various brain structures, including regions associated with important physiological, behavioral, cognitive, and emotional functions. This action can be mediated by either intracellular or transmembrane receptors. While the classical mechanisms of SSHs action are relatively well examined, the physiological importance of non-classical mechanism of SSHs action through membrane-associated and transmembrane receptors in the brain remains unclear. The most recent summary describing the role of SSHs in different body systems is lacking. Therefore, the aim of this review is to discuss classical and non-classical signaling pathways of testosterone and estradiol action via their receptors at functional, cellular, tissue level and to describe the effects on various body systems and behavior. Particular emphasis will be on brain regions including the hippocampus, hypothalamus, frontal cortex and cerebellum.
... All serum was assayed at the same time. Hormone extraction and enzyme-linked immunosorbent assay protocols were modified from previously described protocols (Chao et al. 2011;Hedges et al. 2018;Krentzel et al. 2020;Tuscher et al. 2016). Briefly, 250 L of serum were extracted twice with a 10:1 ratio of diethyl ether followed by snap freeze with liquid nitrogen. ...
... Estrogen level in tissues, including the cerebellum, maintained through extra-gonadal secretion to ensure the sufficient availability of estrogen for normal functioning of steroid-dependent organs (Barakat, Oakley, Kim, Jin, & Ko, 2016). It has been revealed that cerebellum was an organ that could produce steroid hormones de novo where astrocytes can convert testosterone into estrogen through aromatization ( Hedges et al., 2018). Therefore, the sig- nificant increase in number of astrocytes in OVX-group in this study could be a compensatory response of the cerebellum to maintain cerebellar estrogen level which in turn protects the neurons in face of the peripheral estrogen deficiency. ...
Article
Cerebellum seems to be a specific target for both the decrease of estrogen and hypertension in menopause. The aim of this study was to investigate the hypertension and menopause-induced changes in rat's cerebellar cortex and the possible mechanisms of these changes. Rats were divided into four groups: the sham-operated control (SC-group), the ovariectomized (OVX-group), the hypertensive (H-group), and the ovariectomized-hypertensive (OVX-H-group) group. The mean arterial pressure (MAP), serum nitric oxide (NO), lipid peroxides and antioxidant catalase enzyme levels were assayed. Cerebellar tissue homogenization for analysis of lipid peroxides, antioxidant catalase enzyme, tumor necrosis factor-α (TNF-α), and estradiol was done. Quantification of adrenomedullin (AM) and interleukin-10 (IL-10) mRNA was also done. Cerebella were processed for histological, immunohistochemical and transmission electron microscopic examination. In the OVX-group, insignificant structural and biochemical changes were observed compared with the SC-group apart from the significantly increased lipid peroxides and decreased NO and catalase levels in serum. The H-group showed an elevated lipid peroxides and TNF-α levels, reduced catalase level, numerous degenerated Purkinje cells, vacuolations of the neuropil, some axonal degeneration, and few ghosts in the granular cell layer (GL). However, in OVX-H-group, oxidative stress, inflammation, and cerebellar damage were exacerbated and cerebellar estrogen was reduced associated with reduction in GL thickness and decreased Purkinje cells number. Most axoplasms had degenerated neurofilaments with abnormal myelination. The immunoexpression of glial fibrillary acidic protein were significantly increased in both OVX-group and H-group and significantly decreased in OVX-H group. Gene expression of AM and IL-10 were increased in cerebellar tissues of H-group compared with the SC-group but it was significantly decreased in OVX-H-group compared with H-group. Taken together, postmenopausal rats with hypertension suffered from structural cerebellar changes than rats with only hypertension or estrogen deficiency separately due to augmentation of the increased oxidative stress markers and the proinflammatory cytokines (TNF-α) with down regulation of the anti-inflammatory cytokine (IL-10) and the blood pressure regulator, AM. These suggested that high blood pressure is a critical factor for postmenopausal cerebellum. K E Y W O R D S adrenomedullin, cerebellum, GFAP, hypertension, IL-10, postmenopause J Cell Physiol. 2018;1-15. wileyonlinelibrary.com/journal/jcp
... Estrogen level in tissues, including the cerebellum, maintained through extra-gonadal secretion to ensure the sufficient availability of estrogen for normal functioning of steroid-dependent organs (Barakat, Oakley, Kim, Jin, & Ko, 2016). It has been revealed that cerebellum was an organ that could produce steroid hormones de novo where astrocytes can convert testosterone into estrogen through aromatization (Hedges et al., 2018). Therefore, the significant increase in number of astrocytes in OVX-group in this study could be a compensatory response of the cerebellum to maintain (Laouafa et al., 2017). ...
Article
Full-text available
Cerebellum seems to be a specific target for both the decrease of estrogen and hypertension in menopause. The aim of this study was to investigate the hypertension and menopause‐induced changes in rat’s cerebellar cortex and the possible mechanisms of these changes. Rats were divided into four groups: the sham‐operated control (SC‐group), the ovariectomized (OVX‐group), the hypertensive (H‐group), and the ovariectomized‐hypertensive (OVX‐H‐group) group. The mean arterial pressure (MAP), serum nitric oxide (NO), lipid peroxides and antioxidant catalase enzyme levels were assayed. Cerebellar tissue homogenization for analysis of lipid peroxides, antioxidant catalase enzyme, tumor necrosis factor‐α (TNF‐α), and estradiol was done. Quantification of adrenomedullin (AM) and interleukin‐10 (IL‐10) mRNA was also done. Cerebella were processed for histological, immunohistochemical and transmission electron microscopic examination. In the OVX‐group, insignificant structural and biochemical changes were observed compared with the SC‐group apart from the significantly increased lipid peroxides and decreased NO and catalase levels in serum. The H‐group showed an elevated lipid peroxides and TNF‐α levels, reduced catalase level, numerous degenerated Purkinje cells, vacuolations of the neuropil, some axonal degeneration, and few ghosts in the granular cell layer (GL). However, in OVX‐H‐group, oxidative stress, inflammation, and cerebellar damage were exacerbated and cerebellar estrogen was reduced associated with reduction in GL thickness and decreased Purkinje cells number. Most axoplasms had degenerated neurofilaments with abnormal myelination. The immunoexpression of glial fibrillary acidic protein were significantly increased in both OVX‐group and H‐group and significantly decreased in OVX‐H group. Gene expression of AM and IL‐10 were increased in cerebellar tissues of H‐group compared with the SC‐group but it was significantly decreased in OVX‐H‐group compared with H‐group. Taken together, postmenopausal rats with hypertension suffered from structural cerebellar changes than rats with only hypertension or estrogen deficiency separately due to augmentation of the increased oxidative stress markers and the proinflammatory cytokines (TNF‐α) with down regulation of the anti‐inflammatory cytokine (IL‐10) and the blood pressure regulator, AM. These suggested that high blood pressure is a critical factor for postmenopausal cerebellum.
... Although 17-β-estradiol inhibits T and B cell development, it enhances B cell function in ERα-dependent manner, involving both genomic and non-genomic ER signaling in B lymphocytes [39,40]. Moreover, the brain of both sexes is a major target of estradiol and a site of estrogen synthesis [41,42]. ERβ is a dominant ER subtype in the adult cerebellum. ...
Article
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Estrogen is a steroid hormone that has critical roles in reproductive development, bone homeostasis, cardiovascular remodeling and brain functions. However, estrogen also promotes mammary, ovarian and endometrial tumorigenesis. Estrogen antagonists and drugs that reduce estrogen biosynthesis have become highly successful therapeutic agents for breast cancer patients. The effects of estrogen are largely mediated by estrogen receptor (ER) α and ERβ, which are members of the nuclear receptor superfamily of transcription factors. The mechanisms underlying the aberrant expression of ER in breast cancer and other types of human tumors are complex, involving considerable alternative splicing of ERα and ERβ, transcription factors, epigenetic and post-transcriptional regulation of ER expression. Elucidation of mechanisms for ER expression may not only help understand cancer progression and evolution, but also shed light on overcoming endocrine therapy resistance. Herein, we review the complex mechanisms for regulating ER expression in human cancer.
... Neuronal ER/mGluR signaling in females underlies the effects of estradiol on learning and memory, nociception, motor control, sexual receptivity, and heightened responses to drugs of abuse (8). Recent findings also implicate ER/mGluR signaling in the male quail brain (9,10), and the male and female rodent cerebellum (11). The ERs that signal through mGluRs are the same proteins that regulate gene expression in the nuclei of cells, except they have undergone palmitoylation, thereby promoting their trafficking to the plasma membrane (12,13). ...
Article
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Palmitoylation is a reversible posttranslational addition of a 16-carbon lipid chain involved in trafficking and compartmentalizing target proteins. It is important for many cellular functions, including signaling via membrane-localized estrogen receptors (ERs). Within the nervous system, palmitoylation of ERα is necessary for membrane surface localization and mediation of downstream signaling through the activation of metabotropic glutamate receptors (mGluRs). Substitution of the single palmitoylation site on ERα prevents its physical association with the integral membrane protein caveolin-1 (CAV1), required for the formation of the ER/mGluR signaling complex. Interestingly, siRNA knockdown of either of two palmitoyl acyltransferases, zinc finger DHHC type-containing 7 (DHHC7) or DHHC21, also eliminates this signaling mechanism. As ERα has only one palmitoylation site, we hypothesized that one of these DHHCs palmitoylates CAV1. We investigated this possibility by using an acyl-biotin exchange assay in HEK293 cells in conjunction with DHHC overexpression and found that DHHC7 increases CAV1 palmitoylation. Substitution of the palmitoylation sites on CAV1 eliminated this effect, but did not disrupt the ability of the DHHC enzyme to associate with CAV1. In contrast, siRNA-mediated knockdown of DHHC7 alone was not sufficient to decrease CAV1 palmitoylation, but rather required simultaneous knockdown of DHHC21. These findings provide additional information about the overall influence of palmitoylation on the membrane-initiated estrogen signaling pathway, and highlight the importance of considering the influence of palmitoylation on other CAV1-dependent processes.
... In addition, synaptic activity and neurotransmitters, such as glutamate and dopamine, exert a regulation of aromatase activity (Balthazart et al. 2002;Remage-Healey et al. 2008;Rudolph et al. 2016;Di Mauro et al. 2017;de Bournonville et al. 2017), further suggesting a role for local brain synthesis in neurotransmission. Indeed, there is evidence that aromatase activity is involved in the regulation of synaptic transmission in specific types of synapses, such as the synapse between the parallel fibers and the dendritic spines of cerebellar Purkinje cells (Dieni et al. 2018;Hedges et al. 2018). In addition, aromatase activity regulates structural and functional synaptic plasticity Hajszan et al. 2004;Grassi et al. 2009Grassi et al. , 2011Zhou et al. 2010;Scarduzio et al. 2013;Tozzi et al. 2015;Azcoitia et al. 2018), the expression of synaptic proteins (Liu et al. 2015), and the levels of neurotransmitters (Kokras et al. 2018) in different brain regions, including the hippocampus, the amygdala, and the vestibular nuclei. ...
Article
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The modulation of brain function and behavior by steroid hormones was classically associated with their secretion by peripheral endocrine glands. The discovery that the brain expresses the enzyme aromatase, which produces estradiol from testosterone, expanded this traditional concept. One of the best-studied roles of brain estradiol synthesis is the control of reproductive behavior. In addition, there is increasing evidence that estradiol from neural origin is also involved in a variety of non-reproductive functions. These include the regulation of neurogenesis, neuronal development, synaptic transmission, and plasticity in brain regions not directly related with the control of reproduction. Central aromatase is also involved in the modulation of cognition, mood, and non-reproductive behaviors. Furthermore, under pathological conditions aromatase is upregulated in the central nervous system. This upregulation represents a neuroprotective and likely also a reparative response by increasing local estradiol levels in order to maintain the homeostasis of the neural tissue. In this paper, we review the non-reproductive functions of neural aromatase and neural-derived estradiol under physiological and pathological conditions. We also consider the existence of sex differences in the role of the enzyme in both contexts.
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Estradiol, the most potent and prevalent member of the estrogen class of steroid hormones and is expressed in both sexes. Functioning as a neuroactive steroid, it plays a crucial role in modulating neurotransmitter systems affecting neuronal circuits and brain functions including learning and memory, reward and sexual behaviors. These neurotransmitter systems encompass the serotonergic, dopaminergic, and glutamatergic signaling pathways. Consequently, this review examines the pivotal role of estradiol and its receptors in the regulation of these neurotransmitter systems in the brain. Through a comprehensive analysis of current literature, we investigate the multifaceted effects of estradiol on key neurotransmitter signaling systems, namely serotonin, dopamine, and glutamate. Findings from rodent models illuminate the impact of hormone manipulations, such as gonadectomy, on the regulation of neuronal brain circuits, providing valuable insights into the connection between hormonal fluctuations and neurotransmitter regulation. Estradiol exerts its effects by binding to three estrogen receptors: estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and G protein-coupled receptor (GPER). Thus, this review explores the promising outcomes observed with estradiol and estrogen receptor agonists administration in both gonadectomized and/or genetically knockout rodents, suggesting potential therapeutic avenues. Despite limited human studies on this topic, the findings underscore the significance of translational research in bridging the gap between preclinical findings and clinical applications. This approach offers valuable insights into the complex relationship between estradiol and neurotransmitter systems. The integration of evidence from neurotransmitter systems and receptor-specific effects not only enhances our understanding of the neurobiological basis of physiological brain functioning but also provides a comprehensive framework for the understanding of possible pathophysiological mechanisms resulting to disease states. By unraveling the complexities of estradiol's impact on neurotransmitter regulation, this review contributes to advancing the field and lays the groundwork for future research aimed at refining understanding of the relationship between estradiol and neuronal circuits as well as their involvement in brain disorders.
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Estradiol, the most potent and prevalent member of the estrogen class of steroid hormones and is expressed in both sexes. Functioning as a neuroactive steroid, it plays a crucial role in modulating neurotransmitter systems affecting neuronal circuits and brain functions including learning and memory, reward and sexual behaviors. These neurotransmitter systems encompass the serotonergic, dopaminergic, and glutamatergic signaling pathways. Consequently, this review examines the pivotal role of estradiol and its receptors in the regulation of these neurotransmitter systems in the brain. Through a comprehensive analysis of current literature, we investigate the multifaceted effects of estradiol on key neurotransmitter signaling systems, namely serotonin, dopamine, and glutamate. Findings from rodent models illuminate the impact of hormone manipulations, such as gonadectomy, on the regulation of neuronal brain circuits, providing valuable insights into the connection between hormonal fluctuations and neurotransmitter regulation. Estradiol exerts its effects by binding to three estrogen receptors: estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and G protein-coupled receptor (GPER). Thus, this review explores the promising outcomes observed with estradiol and estrogen receptor agonists administration in both gonadectomized and/or genetically knockout rodents, suggesting potential therapeutic avenues. Despite limited human studies on this topic, the findings underscore the significance of translational research in bridging the gap between preclinical findings and clinical applications. This approach offers valuable insights into the complex relationship between estradiol and neurotransmitter systems. The integration of evidence from neurotransmitter systems and receptor-specific effects not only enhances our understanding of the neurobiological basis of physiological brain functioning but also provides a comprehensive framework for the understanding of possible pathophysiological mechanisms resulting to disease states. By unraveling the complexities of estradiol’s impact on neurotransmitter regulation, this review contributes to advancing the field and lays the groundwork for future research aimed at refining understanding of the relationship between estradiol and neuronal circuits as well as their involvement in brain disorders.
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The association of hypogonadism and cerebellar ataxia was first recognized in 1908 by Gordon Holmes. Since the seminal description, several heterogeneous phenotypes have been reported, differing for age at onset, associated features, and gonadotropins levels. In the last decade, the genetic bases of these disorders are being progressively uncovered. Here, we review the diseases associating ataxia and hypogonadism and the corresponding causative genes. In the first part of this study, we focus on clinical syndromes and genes (RNF216, STUB1, PNPLA6, AARS2, SIL1, SETX) predominantly associated with ataxia and hypogonadism as cardinal features. In the second part, we mention clinical syndromes and genes (POLR3A, CLPP, ERAL1, HARS, HSD17B4, LARS2, TWNK, POLG, ATM, WFS1, PMM2, FMR1) linked to complex phenotypes that include, among other features, ataxia and hypogonadism. We propose a diagnostic algorithm for patients with ataxia and hypogonadism, and we discuss the possible common etiopathogenetic mechanisms.
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Contribution to Special Issue on Fast effects of steroids. Estrogen receptors α and β (ERα and ERβ) have a unique relationship with metabotropic glutamate receptors (mGluRs) in the female rodent brain such that estradiol is able to recruit intracellular G-protein signaling cascades to influence neuronal physiology, structure, and ultimately behavior. While this association between ERs and mGluRs exists in many cell types and brain regions, its effects are perhaps most striking in the nucleus accumbens (NAc). This review will discuss the original characterization of ER/mGluR signaling and how estradiol activity in the NAc confers increased sensitivity to drugs of abuse in females through this mechanism.
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Our laboratory has demonstrated that 17β-estradiol (E2) enhances hippocampal memory consolidation via rapid activation of multiple intracellular signaling cascades, including the ERK/MAPK cascade (Fernandez et al., 2008; Fan et al., 2010). However, the receptor mechanisms responsible for these effects of E2 remain unclear. In vitro, estrogen receptor α (ERα) signaling through metabotropic glutamate receptor 1a (mGluR1a) leads to ERK-dependent CREB phosphorylation (Boulware et al., 2005), suggesting that interactions between ERs and mGluR1a may be vital to the memory-enhancing effects of E2. As such, the present study tested the roles of classical estrogen receptors (ERα and ERβ) and mGluR1a in mediating the effects of E2 on hippocampal memory consolidation. Dorsal hippocampal (DH) infusion of ERα (PPT) or ERβ (DPN) agonists enhanced novel object recognition and object placement memory in ovariectomized female mice in an ERK-dependent manner, suggesting that these receptors influence memory by rapidly activating hippocampal cell signaling. Next, DH infusion of the mGluR1a antagonist LY367385 blocked the object and spatial memory facilitation induced by E2, PPT, and DPN, demonstrating that ER/mGluR1a signaling is critical for the memory-enhancing effects of E2. Finally, we show that ERα, ERβ, mGluR1, and ERK all reside within specialized membrane microdomains of the DH, and that ERα and ERβ physically interact with mGluR1, providing a means through which ERs may activate mGluRs and downstream signaling. Together, these findings provide the first in vivo evidence demonstrating that ER/mGluR signaling can mediate the beneficial effects of E2 on hippocampal memory consolidation.
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Estrogens have profound actions on the structure of the nervous system during development and in adulthood. One of the signature actions of estradiol is to alter the morphology of neural processes. In the hippocampus, estradiol modulates spines and cellular excitability that affect cognitive behaviors. In the hypothalamus, estradiol increases spine density in mediobasal hypothalamic nuclei that regulate reproduction. The hypothalamic arcuate nucleus (ARH), an important site for modulation of female sexual receptivity, has a sexual dimorphism in dendritic spine density that favors females. In the present study, we used both β-actin immunostaining and Golgi staining to visualize estradiol-induced changes in spine density in Long-Evans rats. Golgi impregnation was used to visualize spine shape, and then β-actin immunoreactivity was used as a semiquantitative measure of spine plasticity since actin forms the core of dendritic spines. At 4 h after estradiol treatment, both β-actin immunofluorescence and filopodial spines were increased (from 70.57 ± 1.09% to 78.01 ± 1.05%, p < 0.05). Disruption of estradiol-induced β-actin polymerization with cytochalasin D attenuated lordosis behavior, indicating the importance of estradiol-mediated spinogenesis for female sexual receptivity (81.43 ± 7.05 to 35.00 ± 11.76, p < 0.05). Deactivation of cofilin, an actin depolymerizing factor is required for spinogenesis. Membrane-initiated estradiol signaling involving the metabotropic glutamate receptor 1a was responsible for the phosphorylation and thereby deactivation of cofilin. These data demonstrate that estradiol-induced spinogenesis in the ARH is an important cellular mechanism for the regulation of female sexual behavior.
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Rapid actions of estrogens were first described >40 years ago. However, the importance of rapid estrogen-mediated actions in the CNS is only now becoming apparent. Several lines of evidence demonstrate that rapid estrogen-mediated signaling elicits potent effects on molecular and cellular events, resulting in the "fine-tuning" of neuronal circuitry. At an ultrastructural level, the details of estrogen receptor localization and how these are regulated by the circulating hormone and age are now becoming evident. Furthermore, the mechanisms that allow membrane-associated estrogen receptors to couple with intracellular signaling pathways are also now being revealed. Elucidation of complex actions of rapid estrogen-mediated signaling on synaptic proteins, connectivity, and synaptic function in pyramidal neurons has demonstrated that this neurosteroid engages specific mechanisms in different areas of the brain. The regulation of synaptic properties most likely underlies the fine-tuning of neuronal circuitry. This in turn may influence how learned behaviors are encoded by different circuitry in male and female subjects. Importantly, as estrogens have been suggested as potential treatments of a number of disorders of the CNS, advancements in our understanding of rapid estrogen signaling in the brain will serve to aid in the development of potential novel estrogen-based treatments.
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Accuracy in quantifying brain-derived steroid hormones ("neurosteroids") has become increasingly important for understanding the modulation of neuronal activity, development, and physiology. Relative to other neuroactive compounds and classical neurotransmitters, steroids pose particular challenges with regard to isolation and analysis, owing to their lipid solubility. Consequently, anatomical studies of the distribution of neurosteroids have relied primarily on the expression of neurosteroid synthesis enzymes. To evaluate the distribution of synthesis enzymes vis-à-vis the actual steroids themselves, traditional steroid quantification assays, including radioimmunoassays, have successfully employed liquid extraction methods (e.g., ether, dichloromethane, or methanol) to isolate steroids from microdissected brain tissue. Due to their sensitivity, safety, and reliability, the use of commercial enzyme-immunoassays (EIA) for laboratory quantification of steroids in plasma and brain has become increasingly widespread. However, EIAs rely on enzymatic reactions in vitro, making them sensitive to interfering substances in brain tissue and thus producing unreliable results. Here, we evaluate the effectiveness of a protocol for combined, two-stage liquid/solid-phase extraction (SPE) as compared to conventional liquid extraction alone for the isolation of estradiol (E(2)) from brain tissue. We employ the songbird model system, in which brain steroid production is pronounced and linked to neural mechanisms of learning and plasticity. This study outlines a combined liquid-SPE protocol that improves the performance of a commercial EIA for the quantification of brain E(2) content. We demonstrate the effectiveness of our optimized method for evaluating the region specificity of brain E(2) content, compare these results to established anatomy of the estrogen synthesis enzyme and estrogen receptor, and discuss the nature of potential EIA interfering substances.
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Estradiol attenuates the ATP-induced increase of intracellular calcium concentration ([Ca(2+)](i)) in rat dorsal root ganglion (DRG) neurons by blocking the L-type voltage gated calcium channel (VGCC). Because ATP is a putative nociceptive signal, this action may indicate a site of estradiol regulation of pain. In other neurons, 17β-estradiol (E(2)) has been shown to modulate L-type VGCC through a membrane estrogen receptor-group II metabotropic glutamate receptor (mGluR(2/3)). The present study investigated whether the rapid estradiol attenuation of the ATP-induced increase in [Ca(2+)](i) requires mGluR(2/3). Previously we showed that DRG (L(1)-S(3)) express ERα, P2X(3), and mGluR(2/3) receptors. DRG were acutely dissociated by enzyme digestion and grown in short-term culture for imaging analysis. DRG neurons were stimulated twice, once with ATP (50 μM) for 5 sec and then again in the presence of E(2) (100 nM) or E(2) (100 nM) + LY341495 (100 nM), an mGluR(2/3) inhibitor. ATP induced a transient increase in [Ca(2+)](i) (216.3 ± 41.2 nM). This transient increase could be evoked several times in the same DRG neurons if separated by a 5-min washout. Treatment with estradiol significantly attenuated the ATP-induced [Ca(2+)](i) increase in 60% of the DRG neurons, to 163.3 ± 20.9 nM (P < 0.001). Coapplication of E(2) and the mGluR(2/3) inhibitor LY341495 blocked the 17β-estradiol attenuation of the ATP-induced [Ca(2+) ](i) transient (209.1 ± 32.2 nM, P > 0.05). These data indicate that the rapid action of E(2) in DRG neurons is dependent on mGluR(2/3) and demonstrate that membrane estrogen receptor-α-initiated signaling involves interaction with mGluRs.
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The parallel fibers (PFs) in the cerebellar cortex extend several millimeters along a folium in the mediolateral direction. The PFs are orthogonal to and cross several parasagittal zones defined by the olivocerebellar and corticonuclear pathways and the expression of molecular markers on Purkinje cells (PCs). The functions of these two organizations remain unclear, including whether the bands respond similarly or differentially to PF input. By using flavoprotein imaging in the anesthetized mouse in vivo, this study demonstrates that high-frequency PF stimulation, which activates a beamlike response at short latency, also evokes patches of activation at long latencies. These patches consist of increased fluorescence along the beam at latencies of 20-25 s with peak activation at 35 s. The long-latency patches are completely blocked by the type 1 metabotropic glutamate receptor (mGluR(1)) antagonist LY367385. Conversely, the AMPA and NMDA glutamate receptor antagonists DNQX and APV have little effect. Organized in parasagittal bands, the long-latency patches align with zebrin II-positive PC stripes. Additional Ca(2+) imaging demonstrates that the patches reflect increases in intracellular Ca(2+). Both the PLCβ inhibitor U73122 and the ryanodine receptor inhibitor ryanodine completely block the long-latency patches, indicating that the patches are due to Ca(2+) release from intracellular stores. Robust, mGluR(1)-dependent long-term potentiation (LTP) of the patches is induced using a high-frequency PF stimulation conditioning paradigm that generates LTP of PF-PC synapses. Therefore, the parasagittal bands, as defined by the molecular compartmentalization of PCs, respond differentially to PF inputs via mGluR(1)-mediated release of internal Ca(2+).
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Premenstrual dysphoric disorder (PMDD) is a debilitating cyclic disorder that is characterized by affective symptoms, including irritability, depression, and anxiety, which arise in the luteal phase of the menstrual cycle and resolve soon after the onset of menses. Despite a prevalence of up to 8% in women of reproductive age, few studies have investigated the brain mechanisms that underlie this disorder. We used positron emission tomography with [(18)F] fluorodeoxyglucose and self-report questionnaires to assess cerebral glucose metabolism and mood in 12 women with PMDD and 12 healthy comparison subjects in the follicular and late luteal phases of the menstrual cycle. The primary biological end point was incorporated regional cerebral radioactivity (scaled to the global mean) as an index of glucose metabolism. Relationships between regional brain activity and mood ratings were assessed. Blood samples were taken before each session for assay of plasma estradiol and progesterone concentrations. There were no group differences in hormone levels in either the follicular or late luteal phase, but the groups differed in the effect of menstrual phase on cerebellar activity. Women with PMDD but not comparison subjects showed an increase in cerebellar activity (particularly in the right cerebellar vermis) from the follicular phase to the late luteal phase (p = .003). In the PMDD group, this increase in cerebellar activity was correlated with worsening of mood (p = .018). These findings suggest that the midline cerebellar nuclei, which have been implicated in other mood disorders, also contribute to negative mood in PMDD.
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Sex steroids assist adult neural tissue in the protection from and repair of damage resulting from neural injury; some steroids may be synthesized in the brain. Songbirds are especially useful models to explore steroidal neuroprotection and repair. First, the full suite of cholesterol transporters and steroidogenic enzymes are expressed in the zebra finch (ZF) brain. Second, estrogens promote recovery of behavioral function after damage to the adult ZF cerebellum. Third, the estrogen synthetic enzyme aromatase is rapidly upregulated in reactive glia following neural injury, including in the ZF cerebellum. We hypothesized that cerebellar injury would locally upregulate steroidogenic factors upstream of aromatase, providing the requisite substrate for neuroestrogen synthesis. We tested this hypothesis by lesioning the cerebellum of adult songbirds using both males and females that peripherally synthesize steroids in different amounts. We then used quantitative PCR to examine expression of mRNAs for the neurosteroidogenic factors TSPO, StAR, SCC, 3β-HSD, CYP17, and aromatase, at 2 and 8 days post-lesion. Compared to sham lesions, cerebellar lesions significantly upregulated mRNA levels of TSPO and aromatase. Sex differences in response to the lesions were detected for TSPO, StAR, and aromatase. All birds responded to experimental conditions by showing time-dependent changes in the expression of TSPO, SCC, and aromatase, suggesting that acute trauma or stress may impact neurosteroidogensis for many days. These data suggest that the cerebellum is an active site of steroid synthesis in the brain, and each steroidogenic factor likely provides neuroprotection and promotes repair.
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Despite the benefit of adjuvant hormonal therapy (HT) on mortality among women with breast cancer (BC), many women are non-adherent with its use. We investigated the effects of early discontinuation and non-adherence to HT on mortality in women enrolled in Kaiser Permanente of Northern California (KPNC). We identified women diagnosed with hormone-sensitive stage I-III BC, 1996-2007, and used automated pharmacy records to identify prescriptions and dates of refill. We categorized patients as having discontinued HT early if 180 days elapsed from the prior prescription. For those who continued, we categorized patients as adherent if the medication possession ratio was ≥80%. We used Cox proportional hazards models to estimate the association between discontinuation and non-adherence with all-cause mortality. Among 8,769 women who filled at least one prescription for HT, 2,761 (31%) discontinued therapy. Of those who continued HT, 1,684 (28%) were non-adherent. During a median follow-up of 4.4 years, 813 women died. Estimated survival at 10 years was 80.7% for women who continued HT versus 73.6% for those who discontinued (P < 0.001). Of those who continued, survival at 10 years was 81.7 and 77.8% in women who adhered and non-adhered, respectively (P < 0.001). Adjusting for clinical and demographic variables, both early discontinuation (HR 1.26, 95% CI 1.09-1.46) and non-adherence (HR 1.49, 95% CI 1.23-1.81), among those who continued, were independent predictors of mortality. Both early discontinuation and non-adherence to HT were common and associated with increased mortality. Interventions to improve continuation of and adherence to HT may be critical to improve BC survival.
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To evaluate the influence of adjuvant tamoxifen and exemestane on cognitive functioning in postmenopausal patients with breast cancer (BC). Neuropsychological assessments were performed before the start (T1) and after 1 year of adjuvant endocrine treatment (T2) in Dutch postmenopausal patients with BC, who did not receive chemotherapy. Patients participated in the international Tamoxifen and Exemestane Adjuvant Multinational trial, a prospective randomized study investigating tamoxifen versus exemestane as adjuvant therapy for hormone-sensitive BC. Participants included 80 tamoxifen users (mean age, 68.7 years; range 51 to 84), 99 exemestane users (mean age, 68.3 years; range, 50 to 82), and 120 healthy controls (mean age, 66.2 years; range, 49 to 86). At T2, after adjustment for T1 performance, exemestane users did not perform statistically significantly worse than healthy controls on any cognitive domain. In contrast, tamoxifen users performed statistically significantly worse than healthy controls on verbal memory (P < .01; Cohen's d = .43) and executive functioning (P = .01; Cohen's d = .40), and statistically significantly worse than exemestane users on information processing speed (P = .02; Cohen's d = .36). With respect to visual memory, working memory, verbal fluency, reaction speed, and motor speed, no significant differences between the three groups were found. After 1 year of adjuvant therapy, tamoxifen use is associated with statistically significant lower functioning in verbal memory and executive functioning, whereas exemestane use is not associated with statistically significant lower cognitive functioning in postmenopausal patients with BC. Our results accentuate the need to include assessments of cognitive effects of adjuvant endocrine treatment in long-term safety studies.
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This study aimed to identify medical and psychological predictors for cognitive performance of breast cancer (BC) patients before the start of adjuvant systemic treatment and to compare cognitive performance between BC patients and healthy controls adjusting for medical and psychological variables. 205 postmenopausal BC patients underwent pre-treatment neuropsychological tests and provided medical and psychological data. 124 healthy controls underwent the same assessment. 'Treatment for diabetes mellitus' and/or 'hypertension', 'less hours spent on cognitively stimulating activities', 'fewer days since surgery' and 'more reproductive years' were associated with worse cognitive performance in the BC patients, independent of age and IQ. Cognitive differences between BC patients and healthy controls could partly be explained by the evaluated variables. The results stress the need for adjustment for pre-treatment cognitive differences between study groups, and also indicate that further research into pre-treatment cognitive dysfunction is warranted.
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Does the cerebellum influence nonmotor behavior? Recent anatomical studies demonstrate that the output of the cerebellum targets multiple nonmotor areas in the prefrontal and posterior parietal cortex, as well as the cortical motor areas. The projections to different cortical areas originate from distinct output channels within the cerebellar nuclei. The cerebral cortical area that is the main target of each output channel is a major source of input to the channel. Thus, a closed-loop circuit represents the major architectural unit of cerebro-cerebellar interactions. The outputs of these loops provide the cerebellum with the anatomical substrate to influence the control of movement and cognition. Neuroimaging and neuropsychological data supply compelling support for this view. The range of tasks associated with cerebellar activation is remarkable and includes tasks designed to assess attention, executive control, language, working memory, learning, pain, emotion, and addiction. These data, along with the revelations about cerebro-cerebellar circuitry, provide a new framework for exploring the contribution of the cerebellum to diverse aspects of behavior.
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Several prospective studies into the effects of adjuvant systemic therapy on cognitive functioning suggest that a proportion of breast cancer patients show cognitive deficits already before the start of systemic therapy. Owing to, among others, methodological inconsistency, studies report different rates of this pre-treatment cognitive impairment. We examined the impact of four different criteria of cognitive impairment and two types of reference groups (a study-specific healthy reference group versus published normative data) on the prevalence of cognitive impairment. Two hundred and five postmenopausal breast cancer patients underwent a battery of neuropsychological tests before the start of endocrine therapy, 124 healthy subjects underwent the same tests. Proportions of cognitive impaired patients were calculated for each of four criteria for cognitive impairment, using (1) study-specific healthy controls and (2) published norms of healthy controls as reference groups. The prevalence of cognitive impairment varied greatly with the strictness of the criterion, as expected, but also was dependent on the reference group used. Cognitive impairment, relative to published norms, ranged from 1% for the strictest to 36.6% for the less strict criterion, cognitive impairment relative to study-specific healthy controls, ranged from 13.7 to 45.4% for the same criteria. This study highlights contrasting proportions of cognitive impairment by using different criteria for cognitive impairment and different reference groups. (Dis)advantages of the methods using a criterion for cognitive impairment, and of the use of published norms versus a study-specific reference group are discussed.
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Our understanding of estrogen signaling in the nervous system has undergone a significant shift in recent years. For over three decades, the idea that all estradiol actions were explained by direct regulation of transcription held sway. Within the past decade, the idea that in addition to classical effects, membrane-initiated actions of estradiol are important has gained traction. While several novel putative membrane estrogen receptors (ERs) have been described, a large fraction of measured responses appear to be due to membrane-localized estrogen receptor-alpha (ER alpha) and estrogen receptor-beta (ER beta), the same proteins that regulate gene expression. These membrane-localized ERs participate in the regulation of the synthesis of neuroprogesterone, dorsal root ganglion (DRG) neuron excitation, and female sexual receptivity. This is achieved by the modulation of intracellular cell signaling pathways usually associated with the activation of G protein-coupled receptors (GPCRs). ER alpha and ER beta are themselves not GPCRs that directly activate G proteins to regulate physiological responses, but rather interact with traditional GPCRs to initiate cell signaling. This review presents results that support a direct protein-protein interaction between ER alpha and ER beta with metabotropic glutamate receptors (mGluRs), allowing estradiol to signal through mGluRs. This ER/mGluR hypothesis explains how estradiol can activate a wide-range of intracellular pathways and provides an underlying mechanism for the hitherto seemingly unrelated rapid membrane actions in the nervous system.
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This paper will outline the history of study of the cerebellum from its beginnings to relatively recent times. Although there is no unanimous agreement about what the cerebellum does or how it does it, some principles of its structure and function are well understood. The historical approach can help to identify remaining questions and point the way to future progress. We make no effort to separate anatomical, physiological and clinical studies; rather, we hope to emphasize their interrelation. The cerebellum has always been seen as a distinct subdivision of the brain. Over the years there was an increasingly accurate description of its gross appearance and major subdivisions. By the beginning of the 19th century, the classical descriptive anatomical work was completed, and experimental study of the functions of the cerebellum began. Lesions were made in the cerebellum of experimental animals, and the behavioral deficits that were caused by the lesion were studied and described. These early animal studies powerfully influenced clinical interpretation of the symptoms seen in patients with cerebellar disease. Several questions are implicit in the anatomical and clinical studies of the nineteenth and early twentieth centuries, some of which remain incompletely answered. Many of these are addressed in other chapters in this volume. 1. Do different parts of the cerebellum do different things? The uniformity of the neuronal architecture of the cerebellar cortex suggests that each small region must operate in a similar way, but it is also clear that different regions control different functions. Is there a systematic sensory and/or body representation? 2. What are the functions of the cerebellar hemispheres? Massive in humans and very large in primates, their functions remain in dispute. Because the size of the cerebellar hemispheres parallels the development of the cerebral cortex, some have suggested that the hemispheres in humans and the higher primates may play a role in cognitive functions. 3. If one part of the cerebellum is damaged, can another part take over? A related question is whether normal motor function is possible in cases of complete or near-complete agenesis of the cerebellum. 4. What are the functions of the two distinctly different afferent systems to the cerebellum; the climbing and mossy fibers?
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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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Increasing duration of tamoxifen therapy improves survival in women with breast cancer but the impact of adherence to tamoxifen on mortality is unclear. This study investigated whether women prescribed tamoxifen after surgery for breast cancer adhered to their prescription and whether adherence influenced survival. A retrospective cohort study of all women with incident breast cancer in the Tayside region of Scotland between 1993 and 2002 was linked to encashed prescription records to calculate adherence to tamoxifen. Survival analysis was used to determine the effect of adherence on all-cause mortality. In all 2080 patients formed the study cohort with 1633 (79%) prescribed tamoxifen. The median duration of use was 2.42 years (IQR=1.04-4.89 years). Longer duration was associated with better survival but this varied over time. The hazard ratio for mortality in relation to duration at 2.4 years was 0.85, 95% CI=0.83-0.87. Median adherence to tamoxifen was 93% (interquartile range=84-100%). Adherence <80% was associated with poorer survival, hazard ratio 1.10, 95% CI=1.001-1.21. Persistence with tamoxifen was modest with only 49% continuing therapy for 5 years of those followed up for 5 years or more. Increased duration of tamoxifen reduces the risk of death, although one in two women do not complete the recommended 5-year course of treatment. A significant proportion of women have low adherence to tamoxifen and are at increased risk of death.
Article
PURPOSE: To identify predictors of adjuvant tamoxifen use, side effects, and discontinuation in older women. PATIENTS AND METHODS: We followed a cohort of 303 women ≥ 55 years of age diagnosed with stage I or stage II breast cancer for nearly 3 years. Data were collected from women’s surgical records and from computer-assisted telephone interviews at 5, 21, and 33 months after primary tumor therapy. RESULTS: Two hundred ninety-two (96%) of 303 patients in the study provided information about tamoxifen use. Tamoxifen use was reported by 189 patients (65%); 26 (15%) discontinued use during the follow-up period. Patients who were 65 to 74 years of age (relative to those 55 to 64 years of age), had stage II disease, were estrogen receptor–positive, saw a greater number of breast cancer physicians, and had better perceptions of their abilities to discuss treatment options with physicians had greater odds of tamoxifen use. Those who had better physical function, had received standard primary tumor therapy, and had obtained helpful breast cancer information from books or magazines had lesser odds of tamoxifen use. Patients ≥ 75 years of age (relative to those 55 to 64 years of age) and patients with better emotional health had significantly lesser odds of reporting side effects. Patients who were estrogen receptor–positive were less likely to stop taking tamoxifen; patients who experienced side effects were more likely to stop taking tamoxifen. CONCLUSION: Deviations from a prescribed course of adjuvant tamoxifen occur relatively frequently. The clinical consequences of this deviation need to be identified.
Article
578 Background: Adjuvant hormonal therapy reduces mortality among women with hormone-sensitive breast cancer (BC). We investigated the effects of early discontinuation and nonadherence to hormonal therapy on mortality in women enrolled in Kaiser Permanente of Northern California. Methods: We identified women diagnosed with hormone-sensitive stage I-III BC, 1996-2006, and used automated pharmacy records to identify hormonal therapy prescriptions and dates of refill. We categorized patients as having discontinued therapy if 180 days elapsed from the prior prescription. Of those who continued therapy, we categorized patients as adherent if the number of pills dispensed from the date of the first prescription to the date of treatment completion covered ≥ 80%. We used Cox proportional hazards models to estimate the association between discontinuation and non-adherence with all-cause mortality controlling for socio-demographic and clinical variables. Results: Among 8,769 women, median age 62 (24-99), who filled...
Article
The basic principles of cerebellar function were originally described by Flourens, Cajal, and Marr/Albus/Ito, and they constitute the pillars of what can be considered to be the classic cerebellar doctrine. In their concepts, the main cerebellar function is to control motor behavior, Purkinje cells are the only cortical neuron receiving and integrating inputs from climbing fiber and mossy-parallel fiber pathways, and plastic modification at the parallel fiber synapses onto Purkinje cells constitutes the substrate of motor learning. Yet, because of recent technical advances and new angles of investigation, all pillars of the cerebellar doctrine now face regular re-examination. In this review, after summarizing the classic concepts and recent disputes, we attempt to synthesize an integrated view and propose a revisited version of the cerebellar doctrine.
Article
Accumulating evidence from human and rodent studies suggests that females are more sensitive to the motivating and rewarding properties of drugs of abuse. Numerous reports implicate estradiol in enhancing drug-related responses in females, yet the neurobiological mechanisms underlying this effect of estradiol are unknown. Because dendritic spine plasticity in the nucleus accumbens (NAc) is linked to the addictive effects of drugs, we examined the influence of estradiol on dendritic spines in this region. Previously our laboratory demonstrated that in female medium spiny neurons, estradiol activates metabotropic glutamate receptor subtype five (mGluR5), a G protein-coupled receptor already implicated in the etiology of drug addiction. Thus, we sought to determine whether mGluR5 is a part of the mechanism by which estradiol affects dendritic spine density in the NAc. To test this hypothesis, ovariectomized female rats were treated with the mGluR5 antagonist, MPEP, or vehicle prior to estradiol (or oil) treatment and 24 h later dendritic spine density was evaluated by DiI labeling and confocal microscopy. We found that estradiol decreased dendritic spine density in the NAc core and that pretreatment with MPEP blocked this effect. In contrast, MPEP had no effect on dendritic spine density in the NAc shell or CA1 region of the hippocampus, two regions in which estradiol increased the density of dendritic spines. As dendritic spine plasticity in the NAc core has behavioral consequences for drug addiction, these data provide a clue as to how estradiol acts in females to enhance behavioral responses to drugs of abuse.
Article
This chapter develops a specific perspective regarding the interrelation- ship of the cerebellum, motor behaviors, and cognitive processes. The advent of the proposals regarding the cerebellum and cognition has challenged many investigators to examine this issue aggressively and to address the extent to which current concepts, definitions, and experimental approaches are adequate for deriving new insights into the interfaces between the domains of motor execution and adaptive modifications in behavior. This chapter contends that the dichotomy often made between motor processes and cognitive processes is inconsistent with the organization of behaviors in general and that, when a broader, more integrative view is adopted, a role of the cerebellum in “cognitive” processes is not only expected but also necessary given this structure's contribution to motor coordination and behavioral adaptations.
Article
The CACNA1A gene, encoding the voltage-gated calcium channel subunit α1A, is involved in pre- and postsynaptic Ca(2+) signaling, gene expression, and several genetic neurological disorders. We found that CACNA1A coordinates gene expression using a bicistronic mRNA bearing a cryptic internal ribosomal entry site (IRES). The first cistron encodes the well-characterized α1A subunit. The second expresses a transcription factor, α1ACT, which coordinates expression of a program of genes involved in neural and Purkinje cell development. α1ACT also contains the polyglutamine (polyQ) tract that, when expanded, causes spinocerebellar ataxia type 6 (SCA6). When expressed as an independent polypeptide, α1ACT-bearing an expanded polyQ tract-lacks transcription factor function and neurite outgrowth properties, causes cell death in culture, and leads to ataxia and cerebellar atrophy in transgenic mice. Suppression of CACNA1A IRES function in SCA6 may be a potential therapeutic strategy.
Article
Background and purpose: Anti-histaminergic drugs have been widely used in the clinical treatment of vestibular disorders and most studies concentrate on their presynaptic actions. The present study investigated the postsynaptic effect of histamine on medial vestibular nucleus (MVN) neurons and the underlying mechanisms. Experimental approach: Histamine-induced postsynaptic actions on MVN neurons and the corresponding receptor and ionic mechanisms were detected by whole-cell patch-clamp recordings on rat brain slices. The distribution of postsynaptic histamine H₁, H₂ and H₄ receptors was mapped by double and single immunostaining. Furthermore, the expression of mRNAs for H₁, H₂ and H₄ receptors and for subtypes of Na⁺ -Ca²⁺ exchangers (NCXs) and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels was assessed by quantitative real-time RT-PCR. Key results: A marked postsynaptic excitatory effect, co-mediated by histamine H₁ and H₂ receptors, was involved in the histamine-induced depolarization of MVN neurons. Postsynaptic H₁ and H₂ rather than H₄ receptors were co-localized in the same MVN neurons. NCXs contributed to the inward current mediated by H₁ receptors, whereas HCN channels were responsible for excitation induced by activation of H₂ receptors. Moreover, NCX1 and NCX3 rather than NCX2, and HCN1 rather than HCN2-4 mRNAs, were abundantly expressed in MVN. Conclusion and implications: NCXs coupled to H₁ receptors and HCN channels linked to H₂ receptors co-mediate the strong postsynaptic excitatory action of histamine on MVN neurons. These results highlight an active role of postsynaptic mechanisms in the modulation by central histaminergic systems of vestibular functions and suggest potential targets for clinical treatment of vestibular disorders.
Article
An attempt to analyze the "behavior" of the cerebellum by integrating structure and neuronal functions. Harvard Book List (edited) 1971 #140 (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Article
This review focuses on the effects of estrogens upon the cerebellum, a brain region long ignored as a site of estrogen action. Highlighted are the diverse effects of estradiol within the cerebellum, emphasizing the importance of estradiol signaling in cerebellar development, modulation of synaptic neurotransmission in the adult, and the potential influence of estrogens on various health and disease states. We also provide new data, consistent with previous studies, in which locally synthesized estradiol modulates cerebellar glutamatergic neurotransmission, providing one underlying mechanism by which the actions of estradiol can affect this brain region.
Article
It is well known that many of the actions of estrogens in the central nervous system are mediated via intracellular receptor/transcription factors that interact with steroid response elements on target genes. However, there now exists compelling evidence for membrane estrogen receptors in hypothalamic and other brain neurons. But, it is not well understood how estrogens signal via membrane receptors, and how these signals impact not only membrane excitability but also gene transcription in neurons. Indeed, it has been known for sometime that estrogens can rapidly alter neuronal activity within seconds, indicating that some cellular effects can occur via membrane delimited events. In addition, estrogens can affect second messenger systems including calcium mobilization and a plethora of kinases to alter cell signaling. Therefore, this review will consider our current knowledge of rapid membrane-initiated and intracellular signaling by estrogens in the hypothalamus, the nature of receptors involved and how they contribute to homeostatic functions.
Article
The steroid 17β-estradiol (E2) is well known to influence hippocampal functions such as memory, affective behaviors, and epilepsy. There is growing awareness that in addition to responding to ovarian E2, the hippocampus of both males and females synthesizes E2 as a neurosteroid that could acutely modulate synaptic function. Previous work on acute E2 actions in the hippocampus has focused on excitatory synapses. Here, we show that E2 rapidly suppresses inhibitory synaptic transmission in hippocampal CA1. E2 acts through the α form of the estrogen receptor to stimulate postsynaptic mGluR1-dependent mobilization of the endocannabinoid anandamide, which retrogradely suppresses GABA release from CB1 receptor-containing inhibitory presynaptic boutons. Remarkably, this effect of E2 is sex specific, occurring in females but not in males. Acute E2 modulation of endocannabinoid tone and consequent suppression of inhibition provide a mechanism by which neurosteroid E2 could modulate hippocampus-dependent behaviors in a sex-specific manner.
Article
Ongoing studies in our laboratory have demonstrated that systematically administered sex steroids 17ß-estradiol (E2) and progesterone (P) alter cerebellar Purkinje cell responses to the amino acid neurotransmitter glutamate (Glu) in the urethane-anesthetized, ovariectomized adult rat. In the present study, we have examined the effects of locally pressure ejected E2 (0.5 μM) on Purkinje cell responsiveness to microiontophoretically applied Glu. The inactive stereoisomer of E2, 17α-E2 (0.5 μM), estradiol benzoate (EB, 0.5 μM), and estrone (E1, 0.5 μM) were also tested (vehicle: 0.01% propylene glycol-saline, pH 7.4). Extracellular activity of single Purkinje neurons was recorded using multibarrel glass micropipets. Spontaneous firing rate and neuronal responses to microiontophoretic pulses (10 s every 40 s at 10–50 nA) of Glu were examined before, during and after continuous local pressure application of the steroids (1–5 psi, 10–15 min). Local E2 administration increased Glu response by 86% within 2–3 min after the onset of steroid application, with no recovery apparent by 30 min after termination of steroid administration. As such, local E2 application mimicked the effect of systemic injection of this steroid. The inactive estrogen isomer, 17α-E2, failed to significantly enhance Glu responsiveness. Both EB and E1, however, significantly potentiated Glu responsiveness in a manner similar to locally applied E2. In addition, EB administration produced long-lasting increases in background discharge, unlike E2, and eventual recovery of Glu responses to control pre-steroid levels. In summary, this study provides a demonstration of local sex steroid actions on neuronal responsiveness in a model extrahypothalamic CNS area. These effects were specific, as the inactive 17α-E2 isomer did not alter neuronal physiology. The results presented here suggest that the neuronal effects of systemic estrogen may be mediated by local actions of E2 or E1.
Article
The purpose of this study was to test whether 17β-estradiol (E2) could alter neuronal activity or responsiveness to iontophoretically applied amino acid neurotransmitters in an area not reported to contain classical E2 receptors. Such a region is the cerebellum, which was selected as a model system for these studies because it has been well characterized electrophysiologically. Extracellular activity of cerebellar Purkinje neurons was recorded from urethane-anesthetized, adult, ovariectomized rats using multibarrel glass micropipets. Spontaneous firing rate and responses of single units to microiontophoretic pulses (10 s pulses every 40 s) of GABA (10–50 nA) or glutamate (GLUT, 3–40 nA) were examined before, during and after iontophoretic (0.25 mM 17β-estradiol hemisuccinate) or jugular i.v. (100, 300 or 1000 ng/kg 17β-estradiol) administration of E2. Both modes of E2 administration resulted in a significant increase in Purkinje cell excitatory responses to GLUT, independent of the direction of change in spontaneous firing rate. This effect was seen as early as one minute after iontophoretic application of E2 and 10–40 min following i.v. E2. In all cases, recovery to the control level of response was not observed by 2 h following E2 administration.17α-E2 (300ng/kg) resulted in a less pronounced, transient increase in GLUT response, while a lower dose (100 ng/kg) did not have any effect. Prior administration of the anti-estrogen tamoxifen did not prevent any of the observed E2 effects. In addition, estrogen-priming did not alter E2-induced potentiation of GLUT responses. In contrast to the effect of E2 on GLUT responsiveness, GABA-mediated inhibition of Purkinje cells was either increased, antagonized or unchanged following E2 application. In summary, this study suggests the hypothesis that circulating levels of E2 may alter neuronal sensitivity to specific neurotransmitter substances within the cerebellar circuitry.
Article
Ongoing studies from this laboratory have demonstrated marked potentiating actions of the sex steroid 17β-estradiol (E2) on glutamate-induced excitation. In the present study, systemic injection of a physiological dose fo E2 was demonstrated to augment significantly excitatory responses of cerebellar Purkinje (Pnj) cells to iontophoretic application of the specific excitatory amino acid (e.a.a.) agonists quisqualate and . Potentiation of e.a.a. responses was observed as rapidly as 5–10 min post E2, and was, in many cases, a persistent, non-decremental effect. These observed long-term actions of E2 may provide one mechanism for the activating effects of the steroid on sensorimotor function and acitivity.
Article
In female rats the gonadal hormones estrogen and progesterone modulate dopamine (DA) activity in the striatum and nucleus accumbens. For example, there is estrous cycle-dependent variation in basal extracellular concentration of striatal DA, in amphetamine (AMPH)-stimulated DA release, and in striatal DA-mediated behaviors. Ovariectomy attenuates basal extracellular DA, AMPH-induced striatal DA release, and behaviors mediated by the striatal DA system. Estrogen rapidly and directly acts on the striatum and accumbens, via a G-protein–coupled external membrane receptor, to enhance DA release and DA-mediated behaviors. In male rats, estrogen does not affect striatal DA release, and removal of testicular hormones is without effect. These effects of estrogen also result in gender differences in sensitization to psychomotor stimulants. The effects of the gonadal hormones on the striatum and ascending DA systems projecting to the striatum and nucleus accumbens are hypothesized to occur as follows: estrogen induces a rapid change in neuronal excitability by acting on membrane receptors located in intrinsic striatal GABAergic neurons and on DA terminals. The effect of these two actions results in enhanced stimulated DA release through modulation of terminal excitability. These effects of gonadal hormones are postulated to have important implications for gender differences in susceptibility to addiction to the psychomotor stimulants. It is suggested that hormonal modulation of the striatum may have evolved to facilitate reproductive success in female rats by enhancing pacing behavior.
Article
Adult female rats implanted with a microelectrode drive unit were trained to walk on a computer-controlled treadmill apparatus (10 s on every 20 s for 2 h) during recording of single Purkinje neurons in the paravermal area of the anterior cerebellum. Vigorous increases in the firing rate of individual units were found to be correlated with movement of specific limbs in particular stages of the step cycle during treadmill locomotion. Both spontaneous and motor-evoked discharge of individual Purkinje neurons were monitored before and after s.c. injection of either 17β estradiol (E2, 100 ng/kg) or progesterone (P, 50 μgs). The percent increase in firing rate during locomotion versus rest was determined as a measure of the evoked: spontaneous discharge ratio. Drug-induced changes in this ratio indicate differential effects on the individual parameters, rather than simple excitatory or inhibitory effects. For all neurons tested, E2 augmented the movement-evoked discharge over pre-E2 control levels. The onset for this effect occurred at 15 min post-steroid, with a peak response noted at 30–35 min post-steroid. By 60–90 min, a partial recovery of the evoked: spontaneous ratio was noted, although absolute increases in both parameters were still observed, indicating long-term effects on neuronal activity. These effects were independent of the stage of the estrous cycle. In contrast, P decreased absolute firing rates of Purkinje cells during stationary and locomotor phases. However, the evoked: spontaneous ratio was decreased to an even greater degree. The latency for this effect was 9–12 min, with recovery to control levels of response seen at 30 min post-steroid. This response was typical of cells tested on estrus and diestrus 1. Cells tested on proestrus or diestrus 2, when E2 levels are increasing, were not modulated by P using the above paradigm.
Article
Treatment with the selective estrogen receptor modulator (SERM) tamoxifen for 5 years has produced dramatic breast cancer-related benefits in (a) the adjuvant setting, with 30% to 50% reductions in recurrence, contralateral disease, and mortality and (b) the prevention setting of healthy high-risk women, where tamoxifen reduces the risk of invasive and noninvasive breast cancer by 50%. Despite these striking data, adherence to tamoxifen is low, and low adherence is associated with poor survival. Although toxicity is a major predictor of poor adherence after starting therapy, pretreatment (baseline) predictors of poor tamoxifen adherence have been minimally studied. The adherence-survival link underscores the critical need to identify early predictors of poor adherence, and recent work is beginning to address this need. A major baseline predictor of poor adherence to prevention is current smoking, which is interestingly absent from studies of adherence to adjuvant therapy. Other important prevention adherence factors include breast cancer risk, extremes of age, non-white ethnicity, low socioeconomic status, and alcohol use. The strongest adjuvant therapy predictors are age (especially very young), ethnicity, and socioeconomic status. Future studies involving prospective systematic evaluation of these and other potential predictors in endocrine chemoprevention (e.g., other SERMs and aromatase inhibitors) are critical, as is the development of effective/targeted interventions to improve adherence and thus treatment outcomes in at-risk women.
Article
Estrogens have been shown to have protective effects on a wide range of cell types and animal models for many neurodegenerative diseases. The present study demonstrates the cytoprotective effects of 17β-estradiol (E2) and estrogen-like compounds in an in vitro model of Friedreich's ataxia (FRDA) using human donor FRDA skin fibroblasts. FRDA fibroblasts are extremely sensitive to free radical damage and oxidative stress, produced here using l-buthionine (S,R)-sulfoximine to inhibit de novo glutathione synthesis. We have shown that the protective effect of E2 in the face of l-buthionine (S,R)-sulfoximine -induced oxidative stress is independent of estrogen receptor-α, estrogen receptor-β or G protein-coupled receptor 30 as shown by the inability of either ICI 182,780 or G15 to inhibit the E2-mediated protection. These cytoprotective effects appear to be dependent on antioxidant properties and the phenolic structure of estradiol as demonstrated by the observation that all phenolic compounds tested were protective, whereas all nonphenolic compounds were inactive, and the observation that the phenolic compounds reduced the levels of reactive oxygen species, whereas the nonphenolic compounds did not. These data show for the first time that phenolic E2-like compounds are potent protectors against oxidative stress-induced cell death in FRDA fibroblasts and are possible candidate drugs for the treatment and prevention of FRDA symptoms.
Article
Flavoprotein autofluorescence imaging, an intrinsic mitochondrial signal, has proven useful for monitoring neuronal activity. In the cerebellar cortex, parallel fiber stimulation evokes a beam-like response consisting of an initial, short-duration increase in fluorescence (on-beam light phase) followed by a longer duration decrease (on-beam dark phase). Also evoked are parasagittal bands of decreased fluorescence due to molecular layer inhibition. Previous work suggests that the on-beam light phase is due to oxidative metabolism in neurons. The present study further investigated the metabolic and cellular origins of the flavoprotein signal in vivo, testing the hypotheses that the dark phase is mediated by glia activation and the inhibitory bands reflect decreased flavoprotein oxidation and increased glycolysis in neurons. Blocking postsynaptic ionotropic and metabotropic glutamate receptors abolished the on-beam light phase and the parasagittal bands without altering the on-beam dark phase. Adding glutamate transporter blockers reduced the dark phase. Replacing glucose with lactate (or pyruvate) or adding lactate to the bathing media abolished the on-beam dark phase and reduced the inhibitory bands without affecting the light phase. Blocking monocarboxylate transporters eliminated the on-beam dark phase and increased the light phase. These results confirm that the on-beam light phase is due primarily to increased oxidative metabolism in neurons. They also show that the on-beam dark phase involves activation of glycolysis in glia resulting in the generation of lactate that is transferred to neurons. Oxidative savings in neurons contributes to the decrease in fluorescence characterizing the inhibitory bands. These findings provide strong in vivo support for the astrocyte-neuron lactate shuttle hypothesis.
Article
Estradiol and other steroid hormones modulate the nervous system and behavior on both acute and long-term time scales. Though estradiol was originally characterized as a regulator of gene expression through the action of nuclear estrogen receptors (ERs) that directly bind DNA, research over the past thirty years has firmly established that estradiol can bind to extra-nuclear ERs associated with the cellular membrane, producing changes in neurons through stimulation of various intracellular signaling pathways. Several studies have determined that the classical ERs, ERα and ERβ, mediate some of these fast-acting signaling pathways through activation of G proteins. Since ERα and ERβ are not G protein-coupled receptors, the mechanisms by which ERs can stimulate signal transduction pathways are a focus of recent research. Here we discuss recent studies illustrating one mechanism by which ERα and ERβ initiate these pathways: through direct association with metabotropic glutamate receptors (mGluRs). Estradiol binding to these membrane-localized estrogen receptors results in mGluR signaling independent of glutamate. ERs are organized with mGluRs into functional signaling microdomains via caveolin proteins. The pairing of ERs to specific mGluRs via caveolins is region specific, with ERs being linked to different mGluRs in hippocampal, striatal, and other neurons. It is becoming clear that ER signaling through mGluRs is one important mechanism by which estrogens can modulate neuron and glial physiology, ultimately impacting various aspects of nervous system function.
Article
The absence of orexin results in narcolepsy-cataplexy. While the function of the central orexinergic system in sleep regulation has been well studied, the role of orexin in motor control is largely unknown. Here, we show that orexin-A acts via OX(1) and OX(2) receptors to directly depolarize neurons in the rat lateral vestibular nucleus (LVN), a subcortical motor center, and enhance their sensitivity. A dual ionic mechanism involving both Na+-Ca²+ exchangers and inward rectifier K+ channels underlies these effects. Furthermore, orexin-A regulates central vestibular-mediated posture, motor balance and negative geotaxis. Orexin is critical when an animal is facing a major motor challenge as opposed to during rest and general movements. Therefore, orexin participates not only in sleep and emotion (nonsomatic) but also in motor (somatic) regulation, suggesting that the central orexinergic system plays an important role in somatic-nonsomatic integration. These findings may account for why the absence of orexin results in narcolepsy-cataplexy.
Article
Estradiol biosynthesis is catalyzed by the enzyme aromatase, the product of the CYP19A1 gene. Aromatase is expressed in the brain, where it is involved not only in the control of neuroendocrine events and reproduction, but also in the regulation of neural development, synaptic plasticity and cell survival. In this review we summarize the existing data related with the detection of aromatase in human brain, with particular emphasis in the so-called "non-primary reproductive" areas. Besides hypothalamus, amygdala and preoptic/septal areas, aromatase is expressed in certain regions of basal forebrain, cerebral cortex, hippocampus, thalamus, cerebellum and brainstem of the human brain. Aromatase in human brain is produced by neurons, but there is also an astrocyte subpopulation that constitutively expresses the enzyme. The use of different methodological approaches, including the in vivo analysis by positron emission tomography of human subjects, has permitted to draw a general map of human brain aromatase, but the detailed distribution map is still far to be completed. On the other hand, despite the fact that there is only one aromatase protein, there are multiple mRNA transcripts that differ in the 5'-untranslated region, where regulatory elements reside. To date, some of the aromatase transcripts characteristic of cerebral cortex, as well as of human cell lines of neural origin, have been identified. This characteristic may confer tissue or even region-specific regulation of the expression and therefore it is conceivable to develop selective aromatase modulators to regulate the expression of the enzyme in the human brain. This article is part of a Special Issue entitled: Neuroactive Steroids: Focus on Human Brain.
Article
Acute and long-term complications can occur in patients receiving radiation therapy. It has been suggested that cytoprotection might decrease the incidence and severity of therapy-related toxicity in these patients. Developing cerebellum is highly radiosensitive and for that reason it is a useful structure to test potential neuroprotective substances to prevent radiation induced abnormalities. Recent studies have shown that estrogen can rapidly modulate intracellular signalling pathways involved in cell survival. Thus, it has been demonstrated that estrogens mediate neuroprotection by promoting growth, cell survival and by preventing axonal pruning. The aim of this work was to evaluate the effect of the treatment with 17-β-estradiol on the motor, structural and biochemical changes induced by neonatal ionizing radiation exposure, and to investigate the participation of nitric oxide and protein kinase C, two important intracellular messengers involved in neuronal activity. Our results show that perinatal chronic 17-β-estradiol treatment partially protects against radiation-induced cerebellar disorganization and motor abnormalities. PKC and NOS activities could be implicated in its neuroprotective mechanisms. These data provide new evidence about the mechanisms underlying estrogen neuroprotection, which could have therapeutic relevance for patients treated with radiotherapy.
Article
Aromatase catalyzes the last step in estrogen biosynthesis. Brain aromatase is involved in diverse neurophysiological and behavioral functions including sexual behavior, aggression, cognition, and neuroprotection. Using positron emission tomography (PET) with the radiolabeled aromatase inhibitor [N-methyl-(11)C]vorozole, we characterized the tracer distribution and kinetics in the living human brain. Six young, healthy subjects, three men and three women, were administered the radiotracer alone on two separate occasions. Women were scanned in distinct phases of the menstrual cycle. Specificity was confirmed by pretreatment with a pharmacological (2.5 mg) dose of the aromatase inhibitor letrozole. PET data were acquired over a 90-min period and regions of interest placed over selected brain regions. Brain and plasma time activity curves, corrected for metabolites, were used to derive kinetic parameters. Distribution volume (V(T)) values in both men and women followed the following rank order: thalamus > amygdala = preoptic area > medulla (inferior olive) > accumbens, pons, occipital and temporal cortex, putamen, cerebellum, and white matter. Pretreatment with letrozole reduced V(T) in all regions, though the size of the reduction was region-dependent, ranging from ∼70% blocking in thalamus andpreoptic area to ∼10% in cerebellum. The high levels of aromatase in thalamus and medulla (inferior olive) appear to be unique to humans. These studies set the stage for the noninvasive assessment of aromatase involvement in various physiological and pathological processes affecting the human brain.
Article
Along with its ability to directly regulate gene expression, estradiol influences cell signaling and brain functions via rapid, membrane-initiated events. In the female rat striatum, estradiol activates membrane-localized estrogen receptors to influence synaptic neurotransmission, calcium channel activity, and behaviors related to motor control. Yet, the mechanism by which estradiol acts to rapidly affect striatal physiology has remained elusive. Here we find that membrane estrogen receptors (ERs) couple to the metabotropic glutamate receptors mGluR5 and mGluR3, providing the framework to understand how membrane estrogen receptors affect striatal function. Using CREB phosphorylation as a downstream measure of ER/mGluR activation, membrane-localized estrogen receptor α (ERα) activates mGluR5 signaling to mediate mitogen-activated protein kinase (MAPK)-dependent CREB phosphorylation. Further, ERα and estrogen receptor β (ERβ) activate mGluR3 to attenuate L-type calcium channel-dependent CREB signaling. Interestingly, while this fundamental mechanism of ER/mGluR signaling was initially characterized in hippocampal neurons, estrogen receptors in striatal neurons are paired with a different set of mGluRs, resulting in the potential to functionally isolate membrane-initiated estrogen signaling across brain regions via use of specific mGluR modulators. These results provide both a mechanism for the rapid actions of estrogens within the female striatum, as well as demonstrate that estrogen receptors can interact with a more diverse set of surface membrane receptors than previously recognized.
Article
Long-term potentiation (LTP) of parallel fiber-Purkinje cell (PF-PC) synapses in the cerebellum has been suggested to underlie aspects of motor learning. Previous in vitro studies have primarily used low frequency PF stimulation conditioning paradigms to generate either presynaptic PF-PC LTP (4-8 Hz) or postsynaptic PF-PC LTP (1 Hz). Little is known about the conditions that evoke PF-PC LTP in vivo. High frequency stimulation in vivo increases PC responsiveness to peripheral stimuli; however, neither the site of action nor the signaling pathways involved have been examined. Using flavoprotein autofluorescence optical imaging in the FVB mouse in vivo, this report describes that a conditioning stimulation consisting of a high frequency burst of PF stimulation (100 Hz, 15 pulse trains every 3 s for 5 min) evokes a long-term increase in the response to PF stimulation. Following the conditioning stimulation, the response to PF stimulation increases over 20 min to approximately 130% above baseline and this potentiation persists for at least 2 h. Field potential recordings of the responses to PF stimulation show that the postsynaptic component is potentiated but the presynaptic, parallel fiber volley is not. Paired-pulse facilitation does not change after the conditioning stimulation, suggesting the potentiation occurs postsynaptically. Blocking non-NMDA (N-methyl-d-aspartic acid) ionotropic glutamate receptors with DNQX (6,7-dinitroquinoxaline-2,3-dione disodium salt, 50 muM, bath application) during the conditioning stimulation has no effect on the long-term increase in fluorescence. However, blocking subtype I metabotropic glutamate receptors (mGLuR(1)) with LY367385 (200 muM) during the conditioning stimulation abolishes the long-term increase in fluorescence. Blocking GABAergic neurotransmission is not required to evoke this long-term potentiation. Blocking GABA(A) receptors reduces but does not eliminate the long-term potentiation. Therefore, this study demonstrates that high frequency PF stimulation generates long-term potentiation of PF-PC synapses in vivo. This novel form of LTP is generated primarily postsynaptically and is mediated by mGluR(1) receptors.