Oestradiol and insulin-like growth factor-1 reduce cell loss after global ischaemia in middle-aged female rats

Aucubin Exerts Neuroprotection against Forebrain Ischemia and Reperfusion Injury in Gerbils through Antioxidative and Neurotrophic Effects

Aucubin is an iridoid glycoside that displays various pharmacological actions including antioxidant activity. However, there are few reports available on the neuroprotective effects of aucubin against ischemic brain injury. Thus, the aim of this study was to investigate whether aucubin protected against damage to hippocampal function induced by forebrain ischemia-reperfusion injury (fIRI) in gerbils, and to examine whether aucubin produced neuroprotection in the hippocampus against fIRI and to explore its mechanisms by histopathology, immunohistochemistry, and Western analysis. Gerbils were given intraperitoneal injections of aucubin at doses of 1, 5, and 10 mg/kg, respectively, once a day for seven days before fIRI. As assessed by the passive avoidance test, short-term memory function following fIRI significantly declined, whereas the decline in short-term memory function due to fIRI was ameliorated by pretreatment with 10 mg/kg, but not 1 or 5 mg/kg, of aucubin. Most of the pyramidal cells (principal cells) of the hippocampus died in the Cornu Ammonis 1 (CA1) area four days after fIRI. Treatment with 10 mg/kg, but not 1 or 5 mg/kg, of aucubin protected the pyramidal cells from IRI. The treatment with 10 mg/kg of aucubin significantly reduced IRI-induced superoxide anion production, oxidative DNA damage, and lipid peroxidation in the CA1 pyramidal cells. In addition, the aucubin treatment significantly increased the expressions of superoxide dismutases (SOD1 and SOD2) in the pyramidal cells before and after fIRI. Furthermore, the aucubin treatment significantly enhanced the protein expression levels of neurotrophic factors, such as brain-derived neurotrophic factor and insulin-like growth factor-I, in the hippocampal CA1 area before and after IRI. Collectively, in this experiment, pretreatment with aucubin protected CA1 pyramidal cells from forebrain IRI by attenuating oxidative stress and increasing neurotrophic factors. Thus, pretreatment with aucubin can be a promising candidate for preventing brain IRI.

Anti-Mutagenicity and Apoptotic Effects of Teucrium polium L. Essential Oil in HT29 Cell Line

Objectives: Regarding the high prevalence of cancer in Iran and the cytotoxic properties of T. polium, the current study aimed to investigate the cytotoxic and anti-mutagenicity effect of T. polium essential oil (TpEO) on human colon adenocarcinoma cell line (HT29). Methods: HT29 cells were cultured in L-glutamine, RPMI Sigma (1640), with 10% of FBS (fetal bovine serum). Then, the cultures were incubated with 5% CO2 at 37°C, and MTT assay was used to recognize cell proliferation under the inhibitory influence of TpEO. The cell cycle progression was monitored by Sub-G1 apoptosis assay using flow cytometry. Eventually, the anti-mutagenicity property was evaluated using the Ames test employing TA100 and exposure to sodium azide as the carcinogenic substance. Results: The cytotoxic effect of TpEO on HT29 cells was 66.867 ± 1.37 µg/mL. Cultured HT29 cells treated with TpEO exhibited morphological features of apoptosis. TpEO preventive effect was about 78.18%. Conclusions: This study showed that TpEO may be useful for treating colon cancer.

Pretreatment of Populus tomentiglandulosa protects hippocampal CA1 pyramidal neurons from ischemia-reperfusion injury in gerbils via increasing SODs expressions and maintaining BDNF and IGF-I expressions

To examine the effects of Populus tomentiglandulosa (PT) extract on the expressions of antioxidant enzymes and neurotrophic factors in the cornu ammonis 1 (CA1) region of the hippocampus at 5 min after inducing transient global cerebral ischemia (TGCI) in gerbils, TGCI was induced by occlusion of common carotid arteries for 5 min. Before ischemic surgery, 200 mg·kg^-1 PT extract was orally administrated once daily for 7 d. We performed neuronal nuclear antigen immunohistochemistry and Fluoro-Jade B staining. Furthermore, we determined in situ production of superoxide anion radical, expression levels of SOD1 and SOD2 as antioxidant enzymes and brain-derived neurotrophic factor (BDNF) and insulin-like growth factor I (IGF-I) as neurotrophic factors. Pretreatment with 200 mg·kg^-1 PT extract prevented neuronal death (loss). Furthermore, pretreatment with 200 mg·kg^-1 PT extract significantly inhibited the production of superoxide anion radical, increased expressions of SODs and maintained expressions of BDNF and IGF-I. Such increased expressions of SODs were maintained in the neurons after IRI. In summary, pretreated PT extract can significantly increase levels of SODs and protect the neurons against TGCI, suggesting that PT can be a useful natural agent to protect against TGCI.

Time dependent impact of perinatal hypoxia on growth hormone, insulin-like growth factor 1 and insulin-like growth factor binding protein-3

Hypoxic-ischemia (HI) is a widely used animal model to mimic the preterm or perinatal sublethal hypoxia, including hypoxic-ischemic encephalopathy. It causes diffuse neurodegeneration in the brain and results in mental retardation, hyperactivity, cerebral palsy, epilepsy and neuroendocrine disturbances. Herein, we examined acute and subacute correlations between neuronal degeneration and serum growth factor changes, including growth hormone (GH), insulin-like growth factor 1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-3) after hypoxic-ischemia (HI) in neonatal rats. In the acute phase of hypoxia, brain volume was increased significantly as compared with control animals, which was associated with reduced GH and IGF-1 secretions. Reduced neuronal survival and increased DNA fragmentation were also noticed in these animals. However, in the subacute phase of hypoxia, neuronal survival and brain volume were significantly decreased, accompanied by increased apoptotic cell death in the hippocampus and cortex. Serum GH, IGF-1, and IGFBP-3 levels were significantly reduced in the subacute phase of HI. Significant retardation in the brain and body development were noted in the subacute phase of hypoxia. Here, we provide evidence that serum levels of growth-hormone and factors were decreased in the acute and subacute phase of hypoxia, which was associated with increased DNA fragmentation and decreased neuronal survival.

Neuroprotective effects of enriched environment housing after transient global cerebral ischaemia are associated with the upregulation of insulin-like growth factor-1 signalling

Aims

Use of enriched environment (EE) housing has been shown to promote recovery from cerebral ischaemic injury but the underlying mechanisms of their beneficial effects remains unclear. Here we examined whether the beneficial effects of EE housing on ischaemia‐induced neurodegeneration and cognitive impairment are associated with increased insulin‐like growth factor‐1 (IGF‐1) signalling in the hippocampus.

Methods

Forty‐two adult male Wistar rats were included in the study and received either ischaemia or sham surgery. Rats in each group were further randomized to either: EE or standard laboratory cage housing (control). Rats were placed in their assigned housing condition immediately after recovery from anaesthesia. Behavioural testing in the cued learning and discrimination learning tasks were conducted 2 weeks after ischaemia. Rats were euthanized after behavioural testing and the hippocampus was analysed for IGF‐1 level, IGF‐1 receptor (IGF‐1R) activation, protein kinase B (Akt) pathway activation, neurone loss and caspase 3 expression.

Results

Our data showed that EE housing: (1) mitigated ischaemia‐induced neuronal loss; (2) attenuated ischaemia‐induced increase in caspase 3 immunoreactivity in the hippocampus; (3) ameliorated ischaemia‐induced cognitive impairments; and (4) increased IGF‐1R activation and signalling through the Akt pathway after ischaemic injury.

Conclusion

Ultimately, these findings suggest the possibility that IGF‐1 signalling may be one of the underlying mechanisms involved in the beneficial effects of EE in optimizing recovery following cerebral ischaemic injury.

The comparison of anticancer activity of thymoquinone and nanothymoquinone on human breast adenocarcinoma

Cancer is one of the main causes of mortality in the world which is created by the effect of enviromental physico-chemical mutagen and carcinogen agents. The identification of new cytotoxic drugs with low side effects on immune system has developed as important area in new studies of pharmacology. Thymoquinone (TQ), derived from the medicinal spice Nigella sativa (also calledt black cumin) exhibit anti-inflammatory and anti-cancer activities. In this study we employed nanogel-based nanoparticle approach to improve upon its effectiveness. Myristic acid-chitosan (MA-chitosan) nanogels were prepared by the technique of self-assembly. Thymoquinone was loaded into the nanogels. The surface morphology of the prepared nanoparticles was determined using SEM and TEM. The other objective of this study was to examine the in-vitro cytotoxic activity of cell death of Thymoquinone and nanothymoquinone on human breast adenocarcinoma cell line (MCF7). Cytotoxicity and viability of Thymoquinone and nanothymoquinone were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and dye exclusion assay. Transmission electron microscopy confirmed the particle diameter was between 150 to 200 nm. Proliferation of MCF7 cells was significantly inhibited by Thymoquinone and nanothymoquinone in a concentration-dependent manner in defined times. There were significant differences in IC50 Thymoquinone and nanothymoquinone. TQ-loaded nanoparticles proved more effective compared to TQ solution. The high drug-targeting potential and efficiency demonstrates the significant role of the anticancer properties of TQ-loaded nanoparticles.

Estrogen-IGF-1 interactions in neuroprotection: ischemic stroke as a case study

The steroid hormone 17b-estradiol and the peptide hormone insulin-like growth factor (IGF)-1 independently exert neuroprotective actions in neurologic diseases such as stroke. Only a few studies have directly addressed the interaction between the two hormone systems, however, there is a large literature that indicates potentially greater interactions between the 17b-estradiol and IGF-1 systems. The present review focuses on key issues related to this interaction including IGF-1 and sex differences and common activation of second messenger systems. Using ischemic stroke as a case study, this review also focuses on independent and cooperative actions of estrogen and IGF-1 on neuroprotection, blood brain barrier integrity, angiogenesis, inflammation and post-stroke epilepsy. Finally, the review also focuses on the astrocyte, a key mediator of post stroke repair, as a local source of 17b-estradiol and IGF-1. This review thus highlights areas where significant new research is needed to clarify the interactions between these two neuroprotectants.

Comparison of different quantification methods to determine hippocampal damage after cerebral ischemia

BACKGROUND

Experimental stroke studies use multiple techniques to evaluate histopathological damage. Unfortunately, sensitivity and reproducibility of these techniques are poorly characterized despite pivotal influence on results.

METHOD

The present study compared several quantification methods to differentiate between two severities of global cerebral ischemia and reperfusion. Male Sprague-Dawley rats were randomized to moderate (10min) or severe (14min) ischemia by bilateral carotid occlusion (BCAO) with hemorrhagic hypotension. Neuronal cell count was determined in hippocampus at bregma -3.14mm and -3.8mm on day 3 and 28 post insult by counting neurons in the whole CA1 or in one to three defined regions of interest (ROI) placed in NeuN and Fluoro-Jade B stained sections.

RESULTS

In healthy rats hippocampal neurons were arranged uniformly, while distribution became inhomogeneous after ischemia. The number of NeuN and Fluoro-Jade B positive cells was dependent on localization. Differences between ischemia severities became more prominent at 28 days compared to 3 days. Fluoro-Jade B positive cell count increased at 28 days, staining rather injured not dying neurons.

COMPARISON WITH EXISTING METHODS

Placement of counting windows has a major influence on extent of differences between degree of neuronal injury and variations within groups.

CONCLUSIONS

The investigated quantification methods result in inconsistent information on the degree of damage. To obtain consistent and reliable results observation period should be extended beyond 3 days. Due to inhomogeneous distribution of viable neurons in CA1 after ischemia neuronal counting should not be performed in a single ROI window, but should be performed in multiple ROIs or the whole CA1 band.

Activation of the G-protein coupled receptor 30 (GPR30) has different effects on anxiety in male and female mice

The GPR30, a former orphan GPCR, is a putative membrane estrogen receptor that can activate rapid signaling pathways such as extracellular regulated kinase (ERK) in a variety of cells and may contribute to estrogen's effects in the central nervous system. The distribution of GPR30 in the limbic system predicts a role for this receptor in the regulation of learning and memory and anxiety by estrogens. Though acute G-1 treatment is reported to be anxiogenic in ovariectomised female mice and in gonadally intact male mice, the effect of GPR30 activation is unknown in gonadectomised male mice. In this study, we show that an acute administration of G-1 to gonadectomised male mice, but not female mice, was anxiolytic on an elevated plus maze task, without affecting locomotor activity. In addition, though G-1 treatment did not regulate ERK, it was associated with increased estrogen receptor (ER)α phosphorylation in the ventral, but not dorsal, hippocampus of males. In the female, G-1 increased the ERK activation solely in the dorsal hippocampus, independent of state anxiety. This is the first study to report an anxiolytic effect of GPR30 activation in male mice, in a rapid time frame that is commensurate with non-genomic signaling by estrogen.

Cytochrome C is tyrosine 97 phosphorylated by neuroprotective insulin treatment

Recent advancements in isolation techniques for cytochrome c (Cytc) have allowed us to discover post-translational modifications of this protein. We previously identified two distinct tyrosine phosphorylated residues on Cytc in mammalian liver and heart that alter its electron transfer kinetics and the ability to induce apoptosis. Here we investigated the phosphorylation status of Cytc in ischemic brain and sought to determine if insulin-induced neuroprotection and inhibition of Cytc release was associated with phosphorylation of Cytc. Using an animal model of global brain ischemia, we found a ∼50% decrease in neuronal death in the CA1 hippocampal region with post-ischemic insulin administration. This insulin-mediated increase in neuronal survival was associated with inhibition of Cytc release at 24 hours of reperfusion. To investigate possible changes in the phosphorylation state of Cytc we first isolated the protein from ischemic pig brain and brain that was treated with insulin. Ischemic brains demonstrated no detectable tyrosine phosphorylation. In contrast Cytc isolated from brains treated with insulin showed robust phosphorylation of Cytc, and the phosphorylation site was unambiguously identified as Tyr97 by immobilized metal affinity chromatography/nano-liquid chromatography/electrospray ionization mass spectrometry. We next confirmed these results in rats by in vivo application of insulin in the absence or presence of global brain ischemia and determined that Cytc Tyr97-phosphorylation is strongly induced under both conditions but cannot be detected in untreated controls. These data suggest a mechanism whereby Cytc is targeted for phosphorylation by insulin signaling, which may prevent its release from the mitochondria and the induction of apoptosis.

Stroke neuroprotection: oestrogen and insulin-like growth factor-1 interactions and the role of microglia

Oestrogen has been shown to be neuroprotective for stroke and other neural injury models. Oestrogen promotes a neuroprotective phenotype through myriad actions, including stimulating neurogenesis, promoting neuronal differentiation and survival, suppressing neuroinflammation and maintaining the integrity of the blood-brain barrier. At the molecular level, oestrogen directly modulates genes that are beneficial for repair and regeneration via the canonical oestrogen receptor. Increasingly, evidence indicates that oestrogen acts in concert with growth factors to initiate neuroprotection. Oestrogen and insulin-like growth factor (IGF)-1 act cooperatively to influence cell survival, and combined steroid hormone/growth factor interaction has been well documented in the context of neurones and astrocytes. Here, we summarise the evidence that oestrogen-mediated neuroprotection is critically dependent on IGF-1 signalling, and specifically focus on microglia as the source of IGF-1 and the locus of oestrogen-IGF-1 interactions in stroke neuroprotection.

Neuroprotective action of acute estrogens: animal models of brain ischemia and clinical implications

The ovarian hormone 17β-estradiol (E2) exerts profound neuroprotective actions against ischemia-induced brain damage in rodent models of global and focal ischemia. This review focuses on the neuroprotective efficacy of post-ischemic administration of E2 and non-feminizing estrogen analogs in the aging brain, with an emphasis on studies in animals subjected to a long-term loss of circulating E2. Clinical findings from the Women's Health Initiative study as well as data from animal studies that used long-term, physiological levels of E2 treatment are discussed in this context. We summarize major published findings that highlight the effective doses and timing of E2 treatment relative to onset of ischemia. We then discuss recent findings from our laboratory showing that under some conditions the aging hippocampus remains responsive to E2 and some neuroprotective non-feminizing estrogen analogs even after prolonged periods of hormone withdrawal. Possible membrane-initiated signaling mechanisms that may underlie the neuroprotective actions of acutely administered E2 are also discussed. Based on these findings, we suggest that post-ischemic treatment with high doses of E2 or certain non-feminizing estrogen analogs may have great therapeutic potential for treatment of brain damage and neurodegeneration associated with ischemia.

Revisiting the timing hypothesis: biomarkers that define the therapeutic window of estrogen for stroke

Significantly extended life expectancy coupled with contemporary sedentary lifestyles and poor nutrition has created a global epidemic of cardiovascular disease and stroke. For women, this issue is complicated by the discrepant outcomes of hormone therapy (HT) for stroke incidence and severity as well as the therapeutic complications for stroke associated with advancing age. Here we propose that the impact of estrogen therapy cannot be considered in isolation, but should include age-related changes in endocrine, immune, and nucleic acid mediators that collaborate with estrogen to produce neuroprotective effects commonly seen in younger, healthier demographics. Due to their role as modulators of ischemic cell death, the post-stroke inflammatory response, and neuronal survival and regeneration, this review proposes that Insulin-like Growth Factor (IGF)-1, Vitamin D, and discrete members of the family of non-coding RNA peptides called microRNAs (miRNAs) may be crucial biochemical markers that help determine the neuroprotective "window" of HT. Specifically, IGF-1 confers neuroprotection in concert with, and independently of, estrogen and failure of the insulin/IGF-1 axis is associated with metabolic disturbances that increase the risk for stroke. Vitamin D and miRNAs regulate and complement IGF-1 mediated function and neuroprotective efficacy via modulation of IGF-1 availability and neural stem cell and immune cell proliferation, differentiation and secretions. Together, age-related decline of these factors differentially affects stroke risk, severity, and outcome, and may provide a novel therapeutic adjunct to traditional HT practices.

Effects of global ischemia and estradiol pretreatment on phosphorylation of Akt, CREB and STAT3 in hippocampal CA1 of young and middle-aged female rats

Transient global ischemia induces selective, delayed neuronal death of pyramidal neurons in the hippocampal CA1. Whereas long term treatment of middle-aged female rats with estradiol at physiological doses ameliorates neuronal death, the signaling pathways that mediate the neuroprotection are, as yet, unknown. Protein kinase B (Akt) and downstream transcription factors, the cAMP response element binding protein (CREB) and signal transducer and activator of transcription (STAT3) are critical players in cellular survival following injury. The present study was undertaken to determine whether long term estradiol alters the phosphorylation status and activity of Akt, STAT3 and CREB in ovariohysterectomized, middle-aged and young female rats subjected to global ischemia. Irrespective of either hormone or ischemic condition, middle-aged females exhibited lower levels of p-CREB and higher levels of Akt and STAT3 in CA1 than young females, as assessed by Western blot. In middle-aged animals, ischemia increased the phosphorylation status/activity of Akt and STAT3, and decreased the phosphorylation status/activity of CREB in the hippocampal CA1. Whereas estradiol did not detectably alter the phosphorylation status/activity of Akt or STAT3, it prevented the ischemia-induced decrease in nuclear p-CREB. Similar results were observed for the young females. Collectively, these data demonstrate that CREB, STAT3, and Akt are involved in the molecular response to global ischemia and that age influences the status of CREB, STAT3 and Akt activity in CA1 under physiological as well as pathological conditions, further emphasizing the importance of including older rodents in neuroprotection studies.

Neuroprotective actions of estradiol and novel estrogen analogs in ischemia: translational implications

This review highlights our investigations into the neuroprotective efficacy of estradiol and other estrogenic agents in a clinically relevant animal model of transient global ischemia, which causes selective, delayed death of hippocampal CA1 neurons and associated cognitive deficits. We find that estradiol rescues a significant number of CA1 pyramidal neurons that would otherwise die in response to global ischemia, and this is true when hormone is provided as a long-term pretreatment at physiological doses or as an acute treatment at the time of reperfusion. In addition to enhancing neuronal survival, both forms of estradiol treatment induce measurable cognitive benefit in young animals. Moreover, estradiol and estrogen analogs that do not bind classical nuclear estrogen receptors retain their neuroprotective efficacy in middle-aged females deprived of ovarian hormones for a prolonged duration (8weeks). Thus, non-feminizing estrogens may represent a new therapeutic approach for treating the neuronal damage associated with global ischemia.

Mechanisms of estrogens' dose-dependent neuroprotective and neurodamaging effects in experimental models of cerebral ischemia

Ever since the hypothesis was put forward that estrogens could protect against cerebral ischemia, numerous studies have investigated the mechanisms of their effects. Despite initial studies showing ameliorating effects, later trials in both humans and animals have yielded contrasting results regarding the fundamental issue of whether estrogens are neuroprotective or neurodamaging. Therefore, investigations of the possible mechanisms of estrogen actions in brain ischemia have been difficult to assess. A recently published systematic review from our laboratory indicates that the dichotomy in experimental rat studies may be caused by the use of insufficiently validated estrogen administration methods resulting in serum hormone concentrations far from those intended, and that physiological estrogen concentrations are neuroprotective while supraphysiological concentrations augment the damage from cerebral ischemia. This evidence offers a new perspective on the mechanisms of estrogens’ actions in cerebral ischemia, and also has a direct bearing on the hormone replacement therapy debate. Estrogens affect their target organs by several different pathways and receptors, and the mechanisms proposed for their effects on stroke probably prevail in different concentration ranges. In the current article, previously suggested neuroprotective and neurodamaging mechanisms are reviewed in a hormone concentration perspective in an effort to provide a mechanistic framework for the dose-dependent paradoxical effects of estrogens in stroke. It is concluded that five protective mechanisms, namely decreased apoptosis, growth factor regulation, vascular modulation, indirect antioxidant properties and decreased inflammation, and the proposed damaging mechanism of increased inflammation, are currently supported by experiments performed in optimal biological settings.

Comparison between PACAP- and enriched environment-induced retinal protection in MSG-treated newborn rats

Pituitary adenylate cyclase activating polypeptide (PACAP) and its receptors occur throughout the nervous system, including the retina. PACAP exerts diverse actions in the eye: it influences ocular blood flow, contraction of the ciliary muscle, and has retinoprotective effects. This effect has been proven in different models of retinal degeneration. We have previously shown that PACAP protects against monosodium-glutamate (MSG)-induced damage in neonatal rats. The beneficial effects of enriched environment, another neuroprotective strategy, have long been known. Environmental enrichment has been shown to decrease different neuronal injuries. It also influences the development of the visual system. We have recently demonstrated that significant neuroprotection can be achieved in MSG-induced retinal degeneration in animals kept in an enriched environment. Combination of neuroprotective strategies often results in increased protection. Therefore, the aim of the present study was to compare the two neuroprotective strategies alone and in combination therapy. We found that both PACAP and environmental enrichment led to a similar degree of retinal protection, but the two treatments together did not lead to increased protection: their effects were not additive.

Acute administration of non-classical estrogen receptor agonists attenuates ischemia-induced hippocampal neuron loss in middle-aged female rats

Background

Pretreatment with 17β-estradiol (E2) is profoundly neuroprotective in young animals subjected to focal and global ischemia. However, whether E2 retains its neuroprotective efficacy in aging animals, especially when administered after brain insult, is largely unknown.

Methodology/Principal Findings

We examined the neuroprotective effects of E2 and two agonists that bind to non-classical estrogen receptors, G1 and STX, when administered after ischemia in middle-aged rats after prolonged ovarian hormone withdrawal. Eight weeks after ovariectomy, middle-aged female rats underwent 10 minutes of global ischemia by four vessel occlusion. Immediately after reperfusion, animals received a single infusion of either E2 (2.25 µg), G1 (50 µg) or STX (50 µg) into the lateral ventricle (ICV) or a single systemic injection of E2 (100 µg/kg). Surviving pyramidal neurons in the hippocampal CA1 were quantified 1 week later. E2 and both agonists that target non-classical estrogen receptors (G1 and STX) administered ICV at the time of reperfusion provided significant levels of neuroprotection, with 55–60% of CA1 neurons surviving vs 15% survival in controls. A single systemic injection of a pharmacological dose of E2 also rescued approximately 50% of CA1 pyramidal neurons destined to die. To determine if E2 and G1 have similar mechanisms of action in hippocampal neurons, we compared the ability of E2 and G1 to modify CA1 pyramidal neuron responses to excitatory inputs from the Schaffer collaterals recorded in hippocampal slices derived from female rats not subjected to global ischemia. E2 and G1 (10 nM) significantly potentiated pyramidal neuron responses to excitatory inputs when applied to hippocampal slices.

Conclusions/Significance

These findings suggest (1) that middle-aged female rats retain their responsiveness to E2 even after a long period of hormone withdrawal, (2) that non-classical estrogen receptors may mediate the neuroprotective actions of E2 when given after ischemia, and (3) that the neuroprotective efficacy of estrogens may be related to their modulation of synaptic activity in hippocampal slices.

Interactions of estradiol and insulin-like growth factor-I signalling in the nervous system: new advances

Estradiol and insulin-like growth factor-I (IGF-I) interact in the brain to regulate a variety of developmental and neuroplastic events. Some of these interactions are involved in the control of hormonal homeostasis and reproduction. However, the interactions may also potentially impact on affection and cognition by the regulation of adult neurogenesis in the hippocampus and by promoting neuroprotection under neurodegenerative conditions. Recent studies suggest that the interaction of estradiol and IGF-I is also relevant for the control of cholesterol homeostasis in neural cells. The molecular mechanisms involved in the interaction of estradiol and IGF-I include the cross-regulation of the expression of estrogen and IGF-I receptors, the regulation of estrogen receptor-mediated transcription by IGF-I and the regulation of IGF-I receptor signalling by estradiol. Current investigations are evidencing the role exerted by key signalling molecules, such as glycogen synthase kinase 3 and beta-catenin, in the cross-talk of estrogen receptors and IGF-I receptors in neural cells.