Seizures increase trkC mRNA expression in the dentate gyrus of rat hippocampus. Role of glutamate receptor activation

Early Induction of Neurotrophin Receptor and miRNA Genes in Mouse Brain after Pentilenetetrazole-Induced Neuronal Activity

Neurotrophin receptors regulate neuronal survival and network formation, as well as synaptic plasticity in the brain via interaction with their ligands. Here, we examined early changes in the expression of neurotrophin receptor genes Ntk1 (TrkA), Ntrk2 (TrkB), Ntrk3 (TrkC), Ngfr (p75NTR) and miRNAs that target theses gens in the mouse brain after induction of seizure activity by pentylenetetrazol. We found that expression of Ntrk3 and Ngfr was upregulated in the cortex and the hippocampus 1-3 hours after the seizures, while Ntrk2 expression increased after 3-6 hours in the anterior cortex and after 1 and 6 hours in the hippocampus. At the same time, the ratio of Bcl-2/Bax signaling proteins increased in the anterior and posterior cortex, but not in the hippocampus, suggesting the activation of anti-apoptotic signaling. Expression of miRNA-9 and miRNA-29a, which were predicted to target Ntrk3, was upregulated in the hippocampus 3 hours after pentylenetetrazol injection. Therefore, early cellular response to seizures in the brain includes induction of the Ntrk2, Ntrk3, Ngfr, miRNA-9, and miRNA-29a expression, as well as activation of Bcl-2 and Bax signaling pathways, which may characterize them as important mediators of neuronal adaptation and survival upon induction of the generalized brain activity.

Anti-inflammatory and cognitive effects of interferon-β1a (IFNβ1a) in a rat model of Alzheimer's disease

Background

Aβ_1-42 peptide abnormal production is associated with the development and maintenance of neuroinflammation and oxidative stress in brains from Alzheimer disease (AD) patients. Suppression of neuroinflammation may then represent a suitable therapeutic target in AD. We evaluated the efficacy of IFNβ1a in attenuating cognitive impairment and inflammation in an animal model of AD.

Methods

A rat model of AD was obtained by intra-hippocampal injection of Aβ_1-42 peptide (23 μg/2 μl). After 6 days, 3.6 μg of IFNβ1a was given subcutaneously (s.c.) for 12 days. Using the novel object recognition (NOR) test, we evaluated changes in cognitive function. Measurement of pro-inflammatory or anti-inflammatory cytokines, reactive oxygen species (ROS), and SOD activity levels was performed in the hippocampus. Data were evaluated by one-way ANOVA with Fisher’s Protected Least Significant Difference (PLSD) test.

Results

We showed that treatment with IFNβ1a was able to reverse memory impairment and to counteract microglia activation and upregulation of pro-inflammatory cytokines (IL-6, IL-1β) in the hippocampus of Aβ_1-42-injected rats. The anti-inflammatory cytokine IL-10, significantly reduced in the Aβ_1-42 animals, recovered to control levels following IFNβ1a treatment. IFNβ1a also reduced ROS and lipids peroxidation and increased SOD1 protein levels in the hippocampus of Aβ_1-42-injected rats.

Conclusion

This study shows that IFNβ1a is able to reverse the inflammatory and cognitive effects of intra-hippocampal Aβ_1-42 in the rat. Given the role played by inflammation in AD pathogenesis and the established efficacy of IFNβ1a in the treatment of inflammatory diseases of the central nervous system such as multiple sclerosis, its use may be a viable strategy to inhibit the pro-inflammatory cytokine and oxidative stress cascade associated with Aβ deposition in the hippocampus of AD patients.

Identification of calcium sensing receptor (CaSR) mRNA-expressing cells in normal and injured rat brain

Calcium sensing receptor (CaSR), isolated for the first time from bovine and human parathyroid, is a G-protein-coupled receptors that has been involved in diverse physiological functions. At present a complete in vivo work on the identification of CaSR mRNA-expressing cells in the adult brain lacks and this investigation was undertaken in order to acquire more information on cell type expressing CaSR mRNA in the rat brain and to analyse for the first time its expression in different experimental models of brain injury. The expression of CaSR mRNAs was found mainly in scattered cells throughout almost all the brain regions. A double labeling analysis showed a colocalization of CaSR mRNA expression in neurons and oligodendrocytes, whereas it was not found expressed both in the microglia and in astrocytes. One week after kainate-induced seizure CaSR was found in the injured CA3 region of the hippocampus and very interestingly it was found up-regulated in the neurons of CA1-CA2 and dentate gyrus. Similarly, 1 week following ibotenic acid injection in the hippocampus, CaSR mRNA expression was increased in oligodendrocytes both in the lesioned area and in the contralateral CA1-CA3 pyramidal cell layers and dentate gyrus. One week after needle-induced mechanical lesion an increase of labeled cells expressing CaSR mRNA was observed along the needle track. In conclusion, the present results contribute to extend available data on cell type-expressing CaSR in normal and injured brain and could spur to understand the role of CaSR in repairing processes of brain injury.

Nicotine-induced fibroblast growth factor-2 restores the age-related decline of precursor cell proliferation in the subventricular zone of rat brain

Precursor cell proliferation is present in the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus of the hippocampus of adult rat and persists during aging although at reduced levels. Previous studies have shown that acute intermittent nicotine treatment significantly increases fibroblast growth factor-2 (FGF-2) expression in several brain regions of aged rats. The aim of the present investigation was to test the hypothesis that nicotine-induced expression of FGF-2 may restore the age-related decline of precursor cell proliferation. It was first demonstrated that nicotine treatment increases both mRNA and protein FGF-2 in the SVZ of aged male rats (18 months old). The effect of nicotine on precursor cell proliferation in the SVZ was studied by i.p. injection of 5-bromo-2'-deoxyuridine (BrdU) 40 mg/kg to label dividing cells. The nicotine treatment was found to significantly enhance precursor cell proliferation in the SVZ. This increase was sufficiently large to restore the age-related decline of proliferating precursor cells observed in aged rats to that found in young adult rats (3 months old). FGF-2 was expressed in GFAP-positive cells and may act via its receptor FGFR1 that was found expressed in nestin-positive cells of the SVZ. The data obtained demonstrated that the age-related decline of precursor cell proliferation may be counteracted by activating a trophic mechanism mediated by FGF-2.

Cellular localization of mGluR3 and mGluR5 mRNAs in normal and injured rat brain

In order to understand the role of metabotropic glutamate receptors (mGluRs) in the brain, it is important to know how the mGluRs are differentially expressed among the different cell types. At present, the cellular expression of mGluR3 and mGluR5 has been mostly studied in terms of proteins with observations suggesting the expression of both mGluR3 and mGluR5 in neuronal and in glial cells. In order to verify the brain cell type-expressing mGluR3 and mGluR5 mRNAs, both in normal and injured brain, we performed a double labeling analysis, by in situ hybridization for mGluR3 or mGluR5 mRNA and immunohistochemistry for specific cellular markers. This approach allowed us to find mGluR3 mRNA expressed in neurons (NeuN-positive cells), and in glial cells, such as astrocytes (GFAP-positive cells) and oligodendrocytes (CNPase-positive cells). The same analysis showed that only NeuN-positive cells express mGluR5 mRNA. The time course of mGluR3 mRNA expression in two models of hippocampal formation lesion, kainate-induced seizures or ibotenic acid injection, showed an increased expression of mGluR3 in the area of lesion. This effect appears 1 week after the injury and was localized in GFAP- and CNPase-positive cells. In contrast, mGluR5 was not found expressed in the area of lesion. The present results contribute to extend available data on cell type-expressing mGluR3 and mGluR5 in normal and injured brain and could be relevant to understand the mechanisms that drive neuron-glial cells interaction both in normal and repairing processes.

Endoplasmic reticulum stress inhibition protects against excitotoxic neuronal injury in the rat brain

Elevated brain glutamate with activation of neuronal glutamate receptors accompanies neurological disorders, such as epilepsy and brain trauma. However, the mechanisms by which excitotoxicity triggers neuronal injury are not fully understood. We have studied the glutamate receptor agonist kainic acid (KA) inducing seizures and excitotoxic cell death. KA caused the disintegration of the endoplasmic reticulum (ER) membrane in hippocampal neurons and ER stress with the activation of the ER proteins Bip, Chop, and caspase-12. Salubrinal, inhibiting eIF2alpha (eukaryotic translation initiation factor 2 subunit alpha) dephosphorylation, significantly reduced KA-induced ER stress and neuronal death in vivo and in vitro. KA-induced rise in intracellular calcium was not affected by Salubrinal. The results show that ER responses are essential parts of excitotoxicity mediated by glutamate receptor activation and that Salubrinal decreases neuronal death in vivo. Inhibition of ER stress by small molecular compounds may be beneficial for treatment of various neuronal injuries and brain disorders.

Neurotrophins in the dentate gyrus

Since the discovery of nerve growth factor (NGF) in the 1950s and brain-derived neurotrophic factor (BDNF) in the 1980s, a great deal of evidence has mounted for the roles of neurotrophins (NGF; BDNF; neurotrophin-3, NT-3; and neurotrophin-4/5, NT-4/5) in development, physiology, and pathology. BDNF in particular has important roles in neural development and cell survival, as well as appearing essential to molecular mechanisms of synaptic plasticity and larger scale structural rearrangements of axons and dendrites. Basic activity-related changes in the central nervous system (CNS) are thought to depend on BDNF modulation of synaptic transmission. Pathologic levels of BDNF-dependent synaptic plasticity may contribute to conditions such as epilepsy and chronic pain sensitization, whereas application of the trophic properties of BDNF may lead to novel therapeutic options in neurodegenerative diseases and perhaps even in neuropsychiatric disorders. In this chapter, I review neurotrophin structure, signal transduction mechanisms, localization and regulation within the nervous system, and various potential roles in disease. Modulation of neurotrophin action holds significant potential for novel therapies for a variety of neurological and psychiatric disorders.

Acute intermittent nicotine treatment induces fibroblast growth factor-2 in the subventricular zone of the adult rat brain and enhances neuronal precursor cell proliferation

Over the past years, evidence has accumulated that stem cells are present in the adult brain, and generate neurons and/or glia from two active germinal zones: the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the dentate gyrus of the hippocampus. This study shows that acute intermittent nicotine treatment significantly enhances neuronal precursor cell proliferation in the SVZ of adult rat brain, but not in the SGZ of the hippocampus, and pre-treatment with mecamylamine, a nonselective nAChR antagonist, blocks the enhanced precursor proliferation by nicotine. This effect is supported by up-regulation of fibroblast growth factor-2 (FGF-2) mRNA in the SVZ and the expression of its receptor FGFR-1 in cells of SVZ showing precursor cells profile. It is also demonstrated that the nicotine effect on neuronal precursor proliferation is mediated by FGF-2 via fibroblast growth factor receptor 1 (FGFR-1) activation by showing that i.c.v. pre-treatment with anti-FGF-2 antibodies or with FGFR-1 inhibitor 3-[(3-(2-carboxyethyl)-4-methylpyrrol-2-yl)methylene]-2-indolinone (SU5402) blocks nicotine-induced precursor cell proliferation. This nicotine enhancement of neuronal precursor cell proliferation was not accompanied by an increase in the number of apoptotic cells. Taken together the present findings revealed the existence in the SVZ of the adult rat brain of a trophic mechanism mediated by FGF-2 and its receptor and regulated by nAchR activation. This possibility of in vivo regulation of neurogenesis in the adult brain by exogenous factors may aid to develop treatments stimulating neurogenesis with potential therapeutic implications.

Increase in Bcl-2 phosphorylation and reduced levels of BH3-only Bcl-2 family proteins in kainic acid-mediated neuronal death in the rat brain

Kainic acid induces excitotoxicity and nerve cell degeneration in vulnerable regions of rat brain, most markedly in hippocampus and amygdala. Part of the cell death following kainic acid is apoptotic as shown by caspase 3 activation and chromatin condensation. Here we have studied the regulation of pro- and anti-apoptotic proteins belonging to the Bcl-2 family in rat hippocampus and amygdala by kainic acid in relationship to ensuing neuronal death. The pro-apoptotic protein Bax was up-regulated in hippocampus 6 h after kainic acid administration. The increase in Bax was followed by the appearance of TdT-mediated dUTP nick end labelling-positive cells which were prominent at 24 h. Immunohistochemistry for active Bax revealed a punctuated labelling of neurons in the CA3 and hilar regions of hippocampus as well as in amygdala. Double staining for NeuN, a marker for nerve cells, and TdT-mediated dUTP nick end labelling showed that mainly neurons undergo degeneration after kainic acid treatment. In contrast to Bax, the pro-apoptotic BH3-only Bcl-2 proteins Bim and Harakiri/DP5 were down-regulated by kainic acid. This was also observed for the anti-apoptotic proteins Bcl-x and Bcl-w. Immunoreactive Bcl-2 was up-regulated in hippocampus after kainic acid together with an increase in the phosphorylation of serine-87 in Bcl-2, suggesting a post-transcriptional modification of the protein. This was confirmed using immunoprecipitation of total Bcl-2 from hippocampus and amygdala which revealed an increase in serine-87 phospho-Bcl-2 after kainic acid. Inhibition of the c-jun N-terminal protein kinase pathway reduced both serine-87 phosphorylation and cell death after kainic acid. This indicates an important role of Bcl-2 phosphorylation in controlling neuronal death after kainic acid. In contrast to the situation in trophic factor-deprived neurons, no up-regulation of Bim or Harakiri/DP5 proteins occurred after kainic acid, suggesting alternative pathways for regulation of cell death in excitotoxicity. The results indicate that not only the relative levels of Bcl-2 family proteins but also conformation changes and post-translational modifications contribute to neuronal death following kainic acid.

Epilepsy as an example of neural plasticity

Epilepsy is a devastating disease affecting more than 1% of the population. Yet, if one considers the neurobiological substrates of this disease, what is revealed is an array of phenomenon that exemplify the remarkable capacity for the brain to change its basic structure and function, that is, neural plasticity. Some of these alterations are transient and merely impressive for their extent, or for their robust nature across animal models and human epilepsy. Others are notable for their persistence, often enduring for months or years. As an example, the dentate gyrus, and specifically the principal cell of the dentate gyrus, the granule cell, is highlighted. This area of the brain and this particular cell type, for reasons that are currently unclear, hold an uncanny capacity to change after seizures. For those interested in plasticity, it is suggested that perhaps the best examples for studying plasticity lie in the field of epilepsy.

Neuronal expression and regulation of rat inhibitor of apoptosis protein-2 by kainic acid in the rat brain

Inhibitors of apoptosis proteins (IAPs) define a protein family with the ability to counteract cell death by the inhibition of different caspases activated during apoptosis. These proteins are present in different cells, however, the function and roles of IAPs in brain tissue are not fully understood. We report here that RIAP-2, the rat homologue of human cIAP-1/HIAP-2, is expressed in different areas of rat brain as shown by in situ hybridization and immunohistochemistry. Brain regions with relatively high expression of RIAP-2 mRNA included cortex, cerebellum and different subregions of rat hippocampus. Double labelling using a specific anti-RIAP antibody and markers for neurons and glial cells, showed that RIAP-2 is predominantly expressed by nerve cells. Kainic acid treatment, which induces seizures, transiently up-regulated RIAP-2 mRNA levels in cerebral cortex, in the CA1 and dentate gyrus regions of hippocampus, which returned to normal levels at 24 h. However in the CA3 region, RIAP-2 mRNA was decreased at 6 h following an early up-regulation. This region contains neurons particularly vulnerable to kainic acid induced cell degeneration. The decrease in RIAP-2 following kainic acid was also observed using immunohistochemistry. RIAP-2 protein did not colocalize with TUNEL labelling present in cells undergoing cell death. The results show that in the adult rat brain RIAP-2 is expressed mainly by neurons, and that the levels are regulated by kainic acid, which activates glutamate receptors. The decrease in RIAP-2 in specific neuronal populations may contribute to cell degeneration in vulnerable brain regions observed after kainic acid treatment.

The role of cytokines and growth factors in seizures and their sequelae

Although the neuropathological changes caused by severe or repeated seizures have been well characterized, many questions about the molecular mechanisms involved remain unanswered. Neuronal cell death, reactive gliosis, enhanced neurogenesis, and axonal sprouting are four of the best-studied sequelae of seizures. In vitro, each of these pathological processes can be substantially influenced by soluble protein factors, including neurotrophins, cytokines, and growth factors. Furthermore, many of these proteins and their receptors are expressed in the adult brain and are up-regulated in response to neuronal activity and injury. We review the evidence that these intercellular signaling proteins regulate seizure activity as well as subsequent pathology in vivo. As nerve growth factor and brain derived neurotrophic factor are the best-studied proteins of this class, we begin by discussing the evidence linking these neurotrophins to epilepsy and seizure. More than a dozen additional cytokines, growth factors, and neurotrophins that have been examined in the context of epilepsy models are then considered. We discuss the effect of seizure on expression of cytokines and growth factors, and explore the regulation of seizure development and aftermath by exogenous application or antagonist perturbation of these proteins. The experimental evidence supports a role for these factors in each aspect of seizure and pathology, and suggests potential targets for future therapeutics.