Microarray analysis of rat hippocampus exposed to excitotoxicity: reversal Na(+)/Ca(2+) exchanger NCX3 is overexpressed in glial cells.

Multiple factors are involved in the glutamate-induced excitotoxicity phenomenon, such as overload of ionotropic and metabotropic receptors, excess Ca(2+) influx, nitric oxide synthase activation, oxidative damage due to increase in free radicals, and release of endogenous polyamine, among others. In order to attempt a more integrated approach to address this issue, we established, by microarray analysis, the hippocampus gene expression profiles under glutamate-induced excitotoxicity conditions. Increased gene expression is mainly related to excitotoxicity (CaMKII, glypican 2, GFAP, NCX3, IL-2, and Gmeb2) or with cell damage response (dynactin and Ecel1). Several genes that augmented their expression are related to glutamatergic system modulation, in particular with NMDA receptor modulation and calcium homeostasis (IL-2, CaMKII, acrosin, Gmeb2, hAChE, Slc83a, and SP1 factor). Conversely, among genes that diminished their expression, we found the Syngap 1, which is downregulated by CaMKII, and the MHC II, which is downregulated by glutamate. Changes observed in gene expression induced by monosodium glutamate (MSG) neonatal treatment in the hippocampus are consistent with the activation of the mechanisms that modulate NMDA receptor function as well as with the implementation of plastic response to cell damage and intracellular calcium homeostasis. Regarding this aspect, we report here that NCX3/Slc8a3, a Na(+)/Ca(2+) membrane exchanger, is highly expressed in astrocytes, both in vitro and in vivo, in response to glutamate-induced excitotoxicity. Hence, the results of this analysis present a broad view of the expression profile elicited by MSG neonatal treatment, and lead us to suggest the possible molecular pathways of action and reaction involved under this experimental model of excitotoxicity.

Selective estrogen receptor modulators regulate dendritic spine plasticity in the hippocampus of male rats.

Some selective estrogen receptor modulators, such as raloxifene and tamoxifen, are neuroprotective and reduce brain inflammation in several experimental models of neurodegeneration. In addition, raloxifene and tamoxifen counteract cognitive deficits caused by gonadal hormone deprivation in male rats. In this study, we have explored whether raloxifene and tamoxifen may regulate the number and geometry of dendritic spines in CA1 pyramidal neurons of the rat hippocampus. Young adult male rats were injected with raloxifene (1 mg/kg), tamoxifen (1 mg/kg), or vehicle and killed 24 h after the injection. Animals treated with raloxifene or tamoxifen showed an increased numerical density of dendritic spines in CA1 pyramidal neurons compared to animals treated with vehicle. Raloxifene and tamoxifen had also specific effects in the morphology of spines. These findings suggest that raloxifene and tamoxifen may influence the processing of information by hippocampal pyramidal neurons by affecting the number and shape of dendritic spines.

Current Evidence on the Protective Effects of Recombinant Human Erythropoietin and Its Molecular Variants against Pathological Hallmarks of Alzheimer's Disease.

Substantial evidence in the literature demonstrates the pleiotropic effects of the administration of recombinant human erythropoietin (rhEPO) and its molecular variants in different tissues and organs, including the brain. Some of these reports suggest that the chemical properties of this molecule by itself or in combination with other agents (e.g., growth factors) could provide the necessary pharmacological characteristics to be considered a potential protective agent in neurological disorders such as Alzheimer's disease (AD). AD is a degenerative disorder of the brain, characterized by an aberrant accumulation of amyloid ß (Aß) and hyperphosphorylated tau (tau-p) proteins in the extracellular and intracellular space, respectively, leading to inflammation, oxidative stress, excitotoxicity, and other neuronal alterations that compromise cell viability, causing neurodegeneration in the hippocampus and the cerebral cortex. Unfortunately, to date, it lacks an effective therapeutic strategy for its treatment. Therefore, in this review, we analyze the evidence regarding the effects of exogenous EPOs (rhEPO and its molecular variants) in several in vivo and in vitro Aß and tau-p models of AD-type neurodegeneration, to be considered as an alternative protective treatment to this condition. Particularly, we focus on analyzing the differential effect of molecular variants of rhEPO when changes in doses, route of administration, duration of treatment or application times, are evaluated for the improved cellular alterations generated in this disease. This narrative review shows the evidence of the effectiveness of the exogenous EPOs as potential therapeutic molecules, focused on the mechanisms that establish cellular damage and clinical manifestation in the AD.

New Aspects of VEGF, GABA, and Glutamate Signaling in the Neocortex of Human Temporal Lobe Pharmacoresistant Epilepsy Revealed by RT-qPCR Arrays.

In the epilepsy spectrum, temporal lobe epilepsy (TLE) is the most common and devastating focal and symptomatic epilepsy form in adults, where more than 30% of patients develop pharmacoresistance. It is not fully understood how the gene expression contributes to establishing an epileptic phenotype. Cerebrovascular remodeling directed by VEGF (vascular endothelial growth factor) signaling might modulate the synaptic neurotransmission in the epileptic brain. To address this question, the gene expression was profiled in biopsies of the temporal cortex from diagnosed patients with pharmacoresistant TLE that underwent surgical resection to seizure control. One hundred sixty-eight genes related to VEGF signaling and GABA and glutamate neurotransmissions were evaluated. Genes related to downstream signaling -phosphoinositide 3-kinase (PI3K), mitogen-activated protein kinases (MAPK), and Janus-activated kinase/signal transducer and activator of transcription (JAK/STAT) pathways- and neurotransmitters metabolism were evaluated too. Thirty-nine genes were upregulated. The genes encoding for G protein q polypeptide, serine racemase, gephyrin, and glutamate/cystine antiporter system xCT appeared as novel upregulated genes in the pharmacoresistant TLE. ClueGO, a Cytoscape plugin, was used to build a gene network associated using Gene Ontology (GO) terminology. Enrichment analysis by ClueGO retrieves that positive regulation of endothelial cell proliferation, nerve development, and neuronal apoptosis were over-represented categories. In conclusion, VEGF signaling is confirmed as a relevant mediator in the pharmacoresistant TLE. In addition, the enrichment analysis applied to differentially expressed genes suggests new pharmacological targets to be assessed in the treatment of pharmacoresistant TLE. Results make up an approximation to better understand the epileptic brain and complement the available data.

Neuroprotective and Neurorestorative Effects of Epo and VEGF: Perspectives for New Therapeutic Approaches to Neurological Diseases.

BACKGROUND: Erythropoietin (Epo) and vascular endothelial growth factor (VEGF) are two vasoactive molecules with essential trophic effects for brain development. The expression and secretion of both molecules increase in response to neuronal damage and they exert protective and restorative effects, which may also be accompanied by adverse side effects. OBJECTIVE: We review the most relevant evidence on the neuroprotective and neurorestorative effects of Epo and VEGF in three of the most frequent neurological disorders, namely, stroke, epilepsy and Alzheimer's disease, to develop new therapeutic approaches. METHODS: Several original scientific manuscripts and reviews that have discussed the evidence in critical way, considering both the beneficial and adverse effects of Epo and VEGF in the selected neurological disorders, were analysed. In addition, throughout this review, we propose several considerations to take into account in the design of therapeutic approaches based on Epo and VEGF signalling. RESULTS: Although the three selected disorders are triggered by different mechanisms, they evolve through similar processes: excitotoxicity, oxidative stress, neuroinflammation, neuronal death, glial reactivity and vascular remodelling. Epo and VEGF exert neuroprotective and neurorestorative effects by acting on these processes due to their pleiotropism. In general, the evidence shows that both Epo and VEGF reduce neuronal death but that at the vascular level, their effects are contradictory. CONCLUSION: Because the Epo and VEGF signalling pathways are connected in several ways, we conclude that more experimental studies, primarily studies designed to thoroughly assess the functional interactions between Epo and VEGF in the brain under both physiological and pathophysiological conditions, are needed.

Interactions Between Epilepsy and Plasticity.

Undoubtedly, one of the most interesting topics in the field of neuroscience is the ability of the central nervous system to respond to different stimuli (normal or pathological) by modifying its structure and function, either transiently or permanently, by generating neural cells and new connections in a process known as neuroplasticity. According to the large amount of evidence reported in the literature, many stimuli, such as environmental pressures, changes in the internal dynamic steady state of the organism and even injuries or illnesses (e.g., epilepsy) may induce neuroplasticity. Epilepsy and neuroplasticity seem to be closely related, as the two processes could positively affect one another. Thus, in this review, we analysed some neuroplastic changes triggered in the hippocampus in response to seizure-induced neuronal damage and how these changes could lead to the establishment of temporal lobe epilepsy, the most common type of focal human epilepsy.

From neurogenesis to neuroprotection in the epilepsy: signalling by erythropoietin.

Epilepsy is a disorder characterised by recurrent seizures and molecular events, including the activation of early expression genes and the post-translational modifications of functional proteins. These events lead to changes in neurogenesis, mossy fibre sprouting, network reorganisation and neuronal death. The role of these events is currently a matter of great debate, especially as they relate to protection, repair, or further brain injury. In recent years, accumulating data have supported the idea that erythropoietin (EPO) regulates biological processes including neuroprotection and neurogenesis in several diseases, such as epilepsy. This review summarises the role of EPO in some of the molecular mechanisms involved in these events that could direct a more detailed approach for its use as a therapeutic alternative in reducing epileptic seizures.

Excitotoxicity triggered by neonatal monosodium glutamate treatment and blood-brain barrier function.

It is likely that monosodium glutamate (MSG) is the excitotoxin that has been most commonly employed to characterize the process of excitotoxicity and to improve understanding of the ways that this process is related to several pathological conditions of the central nervous system. Excitotoxicity triggered by neonatal MSG treatment produces a significant pathophysiological impact on adulthood, which could be due to modifications in the blood-brain barrier (BBB) permeability and vice versa. This mini-review analyzes this topic through brief descriptions about excitotoxicity, BBB structure and function, role of the BBB in the regulation of Glu extracellular levels, conditions that promote breakdown of the BBB, and modifications induced by neonatal MSG treatment that could alter the behavior of the BBB. In conclusion, additional studies to better characterize the effects of neonatal MSG treatment on excitatory amino acids transporters, ionic exchangers, and efflux transporters, as well as the role of the signaling pathways mediated by erythropoietin and vascular endothelial growth factor in the cellular elements of the BBB, should be performed to identify the mechanisms underlying the increase in neurovascular permeability associated with excitotoxicity observed in several diseases and studied using neonatal MSG treatment.

NKCC1 and KCC2 protein expression is sexually dimorphic in the hippocampus and entorhinal cortex of neonatal rats.

Seizure susceptibility appears to be greater in males than females during the early developmental stages of the brain when the gamma-aminobutyric acid (GABA), acting through its GABA-A receptor, predominantly produces neuronal depolarization. GABA-mediated excitation has been observed when the NKCC1 (chloride importer) expression level is higher than KCC2 (chloride exporter). In this study, the relative protein expression of NKCC1 and KCC2 over ß-actin was evaluated in the hippocampus and entorhinal cortex of male and female rats during postnatal days (PND) 1, 3, 5, 7, 9, 11, 13 and 15 using Western blotting assays. For both cerebral regions in the females, the NKCC1/ß-actin expression ratio was constant during all evaluated ages, whereas the KCC2/ß-actin expression ratio increased gradually until reaching a maximal level at PND9 that was nearly three- and ten-fold higher in the hippocampus and entorhinal cortex, respectively, compared with the initial level. In males, the NKCC1/ß-actin expression ratio was constant during the first week, peaking almost three-fold higher than the initial level at PND9 in the hippocampus and at PND11 in the entorhinal cortex and then returning to the initial values at PND13, whereas the KCC2/ß-actin expression ratio increased gradually to reach a maximal and steady level at PND5, which were nearly two- and four-fold higher in the hippocampus and entorhinal cortex, respectively, compared with the intial level. In conclusion, the NKCC1/ß-actin and KCC2/ß-actin expression ratios displayed a specific expression profile for each gender and cerebral region, which could be related with the differences in seizure susceptibility observed between genders.

Prefrontal serotonin depletion impairs egocentric, but not allocentric working memory in rats.

Working memory is a cognitive ability chiefly organized by the prefrontal cortex. Working memory tests may be resolved based on allocentric or egocentric spatial strategies. Serotonergic neurotransmission is closely involved in working memory, but its role in spatial strategies for working memory performance is unknown. To address this issue, prefrontal serotonin depletion was induced to adult male rats, and three days after the behavioral expression of both allocentric and egocentric strategies were evaluated in the "Y" maze and in a crossed-arm maze, respectively. Serotonin depletion caused no effects on allocentric-related behavioral performance, but lesioned rats performed deficiently when the egocentric working memory was evaluated. These results suggest that serotonin may be more closely related with the organization of working memory that uses own movement-guided responses than with that involving the use of external visuospatial signals. Further neurochemical studies are needed to elucidate possible interactions between serotonergic activity and other neurotransmitter systems in the organization of working memory-related allocentric and egocentric strategies.