Kainic acid induces apoptosis in neurons

Oxidative Stress and Redox Imbalance: Common Mechanisms in Cancer Stem Cells and Neurodegenerative Diseases

Oxidative stress (OS) is an established hallmark of cancer and neurodegenerative disorders (NDDs), which contributes to genomic instability and neuronal loss. This review explores the contrasting role of OS in cancer stem cells (CSCs) and NDDs. Elevated levels of reactive oxygen species (ROS) contribute to genomic instability and promote tumor initiation and progression in CSCs, while in NDDs such as Alzheimer's and Parkinson's disease, OS accelerates neuronal death and impairs cellular repair mechanisms. Both scenarios involve disruption of the delicate balance between pro-oxidant and antioxidant systems, which leads to chronic oxidative stress. Notably, CSCs and neurons display alterations in redox-sensitive signaling pathways, including Nrf2 and NF-κB, which influence cell survival, proliferation, and differentiation. Mitochondrial dynamics further illustrate these differences: enhanced function in CSCs supports adaptability and survival, whereas impairments in neurons heighten vulnerability. Understanding these common mechanisms of OS-induced redox imbalance may provide insights for developing interventions, addressing aging hallmarks, and potentially mitigating or preventing both cancer and NDDs.

The Chemistry of Phytoplankton

Phytoplankton have a high potential for CO2 capture and conversion. Besides being a vital food source at the base of oceanic and freshwater food webs, microalgae provide a critical platform for producing chemicals and consumer products. Enhanced nutrient levels, elevated CO2, and rising temperatures increase the frequency of algal blooms, which often have negative effects such as fish mortalities, loss of flora and fauna, and the production of algal toxins. Harmful algal blooms (HABs) produce toxins that pose major challenges to water quality, ecosystem function, human health, tourism, and the food web. These toxins have complex chemical structures and possess a wide range of biological properties with potential applications as new therapeutics. This review presents a balanced and comprehensive assessment of the roles of algal blooms in generating fixed carbon for the food chain, sequestering carbon, and their unique secondary metabolites. The structural complexity of these metabolites has had an unprecedented impact on structure elucidation technologies and total synthesis, which are highlighted throughout this review. In addition, the influence of biogeochemical environmental perturbations on algal blooms and their influence on biospheric environments is discussed. Lastly, we summarize work on management strategies and technologies for the control and treatment of HABs.

Replacement of Mouse Microglia With Human Induced Pluripotent Stem Cell (hiPSC)-Derived Microglia in Mouse Organotypic Slice Cultures

Microglia, the major immune cells in the brain, are reported to differ in gene expression patterns among species. Therefore, it would be preferable in some cases to use human microglia rather than mouse microglia in microglia-targeted disease research. In the past half a decade, researchers have developed in vivo transplantation methods in which human induced pluripotent stem cell-derived microglia (hiPSC-MG) are transplanted into a living mouse brain. However, in vivo transplantation methods are not necessarily accessible to all researchers due to the difficulty of obtaining the materials needed and the transplantation technique itself. In addition, for in vivo systems for microglia-targeted drug screening, it is difficult to control the pharmacokinetics, especially blood-brain barrier permeability. Therefore, in addition to existing in vivo transplantation systems, the development of an ex vivo transplantation system would help to further evaluate the properties of hiPSC-MG. In this study, we aimed to establish a method to efficiently transplant hiPSC-MG into cultured mouse hippocampal slices. We found that approximately 80% of the total microglia in a cultured slice were replaced by hiPSC-derived microglia when innate microglia were pharmacologically removed prior to transplantation. Furthermore, when neuronal death was induced by applying Kainic acid (KA) to slice cultures, transplanted hiPSC-MG changed their morphology and phagocytosed cell debris. Thus, this study provides a method to transplant hiPSC-MG into the mouse hippocampal slice cultures with a high replacement rate. Because the transplanted microglia survived and exerted phagocytic functions, this method will be useful for evaluating the properties of hiPSC-MG ex vivo.

Neuroprotective effects of combined trimetazidine and progesterone on cerebral reperfusion injury

Cerebral ischemia-reperfusion injury induces multi-dimensional damage to neuronal cells through exacerbation of critical protective mechanisms.

Targeting more than one mechanism simultaneously namely, inflammatory responses and metabolic energy homeostasis could provide additional benefits to restrict or manage cerebral injury. Being proven neuroprotective agents both, progesterone (PG) and trimetazidine (TMZ) has the potential to add on the individual therapeutic outcomes.

We hypothesized the simultaneous administration of PG and TMZ could complement each other to synergize, or at least enhance neuroprotection in reperfusion injury. We investigated the combination of PG and TMZ on middle cerebral artery occlusion (MCAO) induced cerebral reperfusion injury in rats. Molecular docking on targets of energy homeostasis and apoptosis assessed the initial viability of PG and TMZ for neuroprotection. Animal experimentation with MCA induced ischemia-reperfusion (I/R) injury in rats was performed on five randomized groups.

Sham operated control group received vehicle (saline) while the other four I-R groups were pre-treated with vehicle (saline), PG (8 ​mg/kg), TMZ treated (25 ​mg/kg), and PG ​+ ​TMZ (8 and 25 ​mg/kg) for 7 days by intraperitoneal route. Neurological deficit, infarct volume, and oxidative stress were evaluated to assess the extent of injury in rats. Inflammatory reactivity and apoptotic activity were determined with alterations in myeloperoxidase (MPO) activity, blood-brain barrier (BBB) permeability, and DNA fragments. Reperfusion injury inflicted cerebral infarct, neurological deficit, and shattered BBB integrity.

The combination treatment of PG and TMZ restricted cellular damage indicated by significant (p ​< ​0.05) decrease in infarct volume and improvement in free radical scavenging ability (SOD activity and GSH level). MPO activity and LPO decreased which contributed in improved BBB integrity in treated rats. We speculate that inhibition of inflammatory and optimum energy utilization would critically contribute to observed neuroprotection with combined PG and TMZ treatment. Further exploration of this neuroprotective approach for post-recovery cognitive improvement is worth investigating.

•

Molecular docking study.

•

Drug repurposing.

•

Combinatorial approach.

•

Network Pharmacology.

The Perils of Navigating Activity-Dependent Alternative Splicing of Neurexins

Neurexins are presynaptic cell-adhesion molecules essential for synaptic function that are expressed in thousands of alternatively spliced isoforms. Recent studies suggested that alternative splicing at splice site 4 (SS4) of Nrxn1 is tightly regulated by an activity-dependent mechanism. Given that Nrxn1 alternative splicing at SS4 controls NMDA-receptor-mediated synaptic responses, activity-dependent SS4 alternative splicing would suggest a new synaptic plasticity mechanism. However, conflicting results confound the assessment of neurexin alternative splicing, prompting us to re-evaluate this issue. We find that in cortical cultures, membrane depolarization by elevated extracellular K+-concentrations produced an apparent shift in Nrxn1-SS4 alternative splicing by inducing neuronal but not astroglial cell death, resulting in persistent astroglial Nrxn1-SS4+ expression and decreased neuronal Nrxn1-SS4- expression. in vivo, systemic kainate-induced activation of neurons in the hippocampus produced no changes in Nrxn1-SS4 alternative splicing. Moreover, focal kainate injections into the mouse cerebellum induced small changes in Nrxn1-SS4 alternative splicing that, however, were associated with large decreases in Nrxn1 expression and widespread DNA damage. Our results suggest that although Nrxn1-SS4 alternative splicing may represent a mechanism of activity-dependent synaptic plasticity, common procedures for testing this hypothesis are prone to artifacts, and more sophisticated approaches will be necessary to test this important question.

Envisioning the neuroprotective effect of Metformin in experimental epilepsy: A portrait of molecular crosstalk

Epilepsy is a neurological disorder characterized by an enduring predisposition to generate and aggravate epileptic seizures affecting around 1% of global population making it a serious health concern. Despite the recent advances in epilepsy research, no disease-modifying treatment able to terminate epileptogenesis have been reported yet reflecting the complexity in understanding the disease pathogenesis. To overcome the current treatment gap against epilepsy, one effective approach is to explore anti-epileptic effects from a drug that are approved to treat non-epileptic diseases. In this regard, Metformin emerged as an ideal candidate which is a first line treatment option for type 2 diabetes mellitus (T2DM), has conferred neuroprotection in several in vivo neurological disorders such as Alzheimer's diseases (AD), Parkinson's disease (PD), Stroke, Huntington's diseases (HD) including epilepsy. In addition, Metformin has ameliorated cognitive alteration, learning and memory induced by epilepsy as well as in animal model of AD. Herein, we review the promising findings demonstrated upon Metformin treatment against animal model of epilepsy however, the precise underlying mechanism of anti-epileptic potential of Metformin is not well understood. However, there is a growing understanding that Metformin demonstrates its anti-epileptic effect mainly via ameliorating brain oxidative damage, activation of AMPK, inhibition of mTOR pathway, downregulation of α-synuclein, reducing apoptosis, downregulation of BDNF and TrkB level. These reflects that Metformin being non-anti-epileptic drug (AED) has a potential to ameliorate the cellular pathways that were impaired in epilepsy reflecting its therapeutical potential against epileptic seizure that might plausibly overcome the limitations of today epilepsy treatment.

Effects of GLP-1 Receptor Activation on a Pentylenetetrazole-Kindling Rat Model

Objectives: To study the possible anti-seizure and neuroprotective effect of glucagon like peptide 1 (GLP1) analogue (liraglutide) in a pentylenetetrazole (PTZ) induced kindled rat model and its underlying mechanisms. Methods: Thirty Sprague Dawley rats were allocated into 3 equal groups; i) Normal group: normal rats received normal saline, ii) PTZ (kindling) group: received PTZ (50 mg/Kg intraperitoneally (i.p.)) every other day for 2 weeks and iii) PTZ + GLP1 group: same as the PTZ group but rats received liraglutide (75 µg/kg i.p. daily) for 2 weeks before PTZ injection. Seizure severity score, seizure latency and duration were assessed. Also, the expression of caspase-3 (apoptotic marker) and β-catenin (Wnt pathway) by western blotting, markers of oxidative stress (GSH, CAT and MDA) by biochemical assay and the expression of LC3 (marker of autophagy) and heat shock protein 70 (Hsp70) by immunostaining were assessed in hippocampal regions of brain tissues. Results: PTZ caused a significant increase in Racine score and seizure duration with a significant decrease in seizure latency. These effects were associated with a significant increase in MDA, β-catenin, caspase-3, Hsp70 and LC3 in brain tissues (p < 0.05). Meanwhile, liraglutide treatment caused significant attenuation in PTZ-induced seizures, which were associated with significant improvement in markers of oxidative stress, reduction in LC3, caspase-3 and β-catenin and marked increase in Hsp70 in hippocampal regions (p < 0.05). Conclusion: Activation of GLP1R might have anticonvulsant and neuroprotective effects against PTZ-induced epilepsy. These effects could be due to suppression of oxidative stress, apoptosis and autophagy and upregulation of Hsp70.

Effects of metformin on apoptosis and α-synuclein in a rat model of pentylenetetrazole-induced epilepsy

The present study was designed to examine the possible neuroprotective and antiepileptic effects of metformin (Metf) in a rat model of pentylenetetrazole (PTZ)-induced epilepsy and its possible underlying mechanisms. Forty male albino rats were assigned to 4 groups of equal size: (1) normal control (NC) group, (2) Metf group: daily treatment with Metf (200 mg/kg, i.p.) for 2 weeks, (3) PTZ group: treatment with PTZ (50 mg/kg, i.p.) every other day for 2 weeks, and (4) Metf + PTZ group: daily treatment with PTZ and metformin (200 mg/kg, i.p.) for 2 weeks. Administration of PTZ caused a significant increase in seizure score and duration, induced a state of oxidative stress (high malondialdehyde, low reduced glutathione and catalase activity), and led to the upregulation of β-catenin, caspase-3, and its cleavage products, Hsp70 and α-synuclein, in hippocampal regions as well as a significant reduction in seizure latency. While Metf treatment significantly ameliorated PTZ-induced seizures, attenuated oxidative stress, and upregulated α-synuclein and β-catenin expression, it also inhibited caspase-3 activation and the release of the cleavage product and caused more upregulation in Hsp70 expression in hippocampal regions (p < 0.05). In conclusion, the antiepileptic and neuroprotective effects of Metf in PTZ-induced epilepsy might be due to the inhibition of apoptosis, attenuation of oxidative stress and α-synuclein expression, and upregulation of Hsp70.

Glial loss of the metallo β-lactamase domain containing protein, SWIP-10, induces age- and glutamate-signaling dependent, dopamine neuron degeneration

Across phylogeny, glutamate (Glu) signaling plays a critical role in regulating neural excitability, thus supporting many complex behaviors. Perturbed synaptic and extrasynaptic Glu homeostasis in the human brain has been implicated in multiple neuropsychiatric and neurodegenerative disorders including Parkinson's disease, where theories suggest that excitotoxic insults may accelerate a naturally occurring process of dopamine (DA) neuron degeneration. In C. elegans, mutation of the glial expressed gene, swip-10, results in Glu-dependent DA neuron hyperexcitation that leads to elevated DA release, triggering DA signaling-dependent motor paralysis. Here, we demonstrate that swip-10 mutations induce premature and progressive DA neuron degeneration, with light and electron microscopy studies demonstrating the presence of dystrophic dendritic processes, as well as shrunken and/or missing cell soma. As with paralysis, DA neuron degeneration in swip-10 mutants is rescued by glial-specific, but not DA neuron-specific expression of wildtype swip-10, consistent with a cell non-autonomous mechanism. Genetic studies implicate the vesicular Glu transporter VGLU-3 and the cystine/Glu exchanger homolog AAT-1 as potential sources of Glu signaling supporting DA neuron degeneration. Degeneration can be significantly suppressed by mutations in the Ca2+ permeable Glu receptors, nmr-2 and glr-1, in genes that support intracellular Ca2+ signaling and Ca2+-dependent proteolysis, as well as genes involved in apoptotic cell death. Our studies suggest that Glu stimulation of nematode DA neurons in early larval stages, without the protective actions of SWIP-10, contributes to insults that ultimately drive DA neuron degeneration. The swip-10 model may provide an efficient platform for the identification of molecular mechanisms that enhance risk for Parkinson's disease and/or the identification of agents that can limit neurodegenerative disease progression.

l-Carnitine Modulates Epileptic Seizures in Pentylenetetrazole-Kindled Rats via Suppression of Apoptosis and Autophagy and Upregulation of Hsp70

l-Carnitine is a unique nutritional supplement for athletes that has been recently studied as a potential treatment for certain neuropsychiatric disorders. However, its efficacy in seizure control has not been investigated. Sprague Dawley rats were randomly assigned to receive either saline (Sal) (negative control) or pentylenetetrazole (PTZ) 40 mg/kg i.p. × 3 times/week × 3 weeks. The PTZ group was further subdivided into two groups, the first received oral l-carnitine (l-Car) (100 mg/kg/day × 4 weeks) (PTZ + l-Car), while the second group received saline (PTZ + Sal). Daily identification and quantification of seizure scores, time to the first seizure and the duration of seizures were performed in each animal. Molecular oxidative markers were examined in the animal brains. l-Car treatment was associated with marked reduction in seizure score (p = 0.0002) that was indicated as early as Day 2 of treatment and continued throughout treatment duration. Furthermore, l-Car significantly prolonged the time to the first seizure (p < 0.0001) and shortened seizure duration (p = 0.028). In addition, l-Car administration for four weeks attenuated PTZ-induced increase in the level of oxidative stress marker malondialdehyde (MDA) (p < 0.0001) and reduced the activity of catalase enzyme (p = 0.0006) and increased antioxidant GSH activity (p < 0.0001). Moreover, l-Car significantly reduced PTZ-induced elevation in protein expression of caspase-3 (p < 0.0001) and β-catenin (p < 0.0001). Overall, our results suggest a potential therapeutic role of l-Car in seizure control and call for testing these preclinical results in a proof of concept pilot clinical study.

Low Non-NMDA Receptor Current Density as Possible Protection Mechanism from Neurotoxicity of Circulating Glutamate on Subfornical Organ Neurons in Rats

The subfornical organ (SFO) is one of circumventricular organs characterized by the lack of a normal blood brain barrier. The SFO neurons are exposed to circulating glutamate (60~100 µM), which may cause excitotoxicity in the central nervous system. However, it remains unclear how SFO neurons are protected from excitotoxicity caused by circulating glutamate. In this study, we compared the glutamate-induced whole cell currents in SFO neurons to those in hippocampal CA1 neurons using the patch clamp technique in brain slice. Glutamate (100 µM) induced an inward current in both SFO and hippocampal CA1 neurons. The density of glutamate-induced current in SFO neurons was significantly smaller than that in hippocampal CA1 neurons (0.55 vs. 2.07 pA/pF, p<0.05). To further identify the subtype of the glutamate receptors involved, the whole cell currents induced by selective agonists were then compared. The current densities induced by AMPA (0.45 pA/pF) and kainate (0.83 pA/pF), non-NMDA glutamate receptor agonists in SFO neurons were also smaller than those in hippocampal CA1 neurons (2.44 pA/pF for AMPA, p<0.05; 2.34 pA/pF for kainate, p< 0.05). However, the current density by NMDA in SFO neurons was not significantly different from that of hippocampal CA1 neurons (1.58 vs. 1.47 pA/pF, p>0.05). These results demonstrate that glutamate-mediated action through non-NMDA glutamate receptors in SFO neurons is smaller than that of hippocampal CA1 neurons, suggesting a possible protection mechanism from excitotoxicity by circulating glutamate in SFO neurons.

Oxidative stress associated with neuronal apoptosis in experimental models of epilepsy

Epilepsy is considered one of the most common neurological disorders worldwide. Oxidative stress produced by free radicals may play a role in the initiation and progression of epilepsy; the changes in the mitochondrial and the oxidative stress state can lead mechanism associated with neuronal death pathway. Bioenergetics state failure and impaired mitochondrial function include excessive free radical production with impaired synthesis of antioxidants. This review summarizes evidence that suggest what is the role of oxidative stress on induction of apoptosis in experimental models of epilepsy.

Rosiglitazone synergizes the neuroprotective effects of valproic acid against quinolinic acid-induced neurotoxicity in rats: targeting PPARγ and HDAC pathways

Huntington's disease (HD) is an autosomal dominant progressive neurodegenerative disorder which affects medium spiny GABAergic neurons mainly in the striatum. Oxidative damage, neuro-inflammation, apoptosis, protein aggregation, and signaling of neurotrophic factors are some of the common cellular pathways involved in HD. Quinolinic acid (QA) causes excitotoxicity by stimulating N-methyl-D-aspartate receptors via calcium overload leading to neurodegeneration. Neuroprotective potential of peroxisome proliferator activated receptor-γ (PPARγ) agonists and histone deacetylase (HDAC) inhibitors have been well documented in experimental models of neurodegenerative disorders; however, their exact mechanisms are not clear. Therefore, present study has been designed to explore possible neuroprotective mechanism of valproic acid (VPA) and its interaction with rosiglitazone against QA induced HD-like symptoms in rats. Single bilateral intrastriatal QA (200 nmol/2 μl saline) administration significantly caused motor incoordination, memory impairment, oxidative damage, mitochondrial dysfunction (complex I, II, II and IV), cellular alterations [tumor necrosis factor-alpha (TNF-α), caspase-3, brain derived neurotrophic factor, acetylcholinesterase], and striatal neurodegeneration as compared to sham group. Treatment with rosiglitazone (5, 10 mg/kg) and VPA (100, 200 mg/kg) for 21 days significantly attenuated these behavioral, biochemical, and cellular alterations as compared to control (QA 200 nmol) group. However, VPA (100 mg/kg) treatment in combination with rosiglitazone (5 mg/kg) for 21 days synergized their neuroprotective effect, which was significant as compared to their effects per se in QA-treated animals. The present study provides an evidence of possible interplay of PPARγ agonists and HDAC inhibitors as a novel therapeutic strategy in the management of HD.

Uncaria rhynchophylla (Miq) Jack Plays a Role in Neuronal Protection in Kainic Acid-Treated Rats

Uncaria rhynchophylla (Miq) Jack (UR) is one of many Chinese herbs. Our previous studies have shown that UR has both anticonvulsive and free radical-scavenging activities in kainic acid (KA)-treated rats. The aim of the present study was to use the effect of UR on activated microglia, nitric oxide synthase, and apoptotic cells to investigate its function in neuroproction in KA-treated rats. UR of 1.0 or 0.5 g/kg was orally administered for 3 days (first day, second day, and 30 min prior to KA administration on the third day), or 10 mg/kg (intraperitoneal injection, i.p.) N-nitro-L-arginine methyl ester (L-NAME) 30 min prior to KA (2 μg/2 μl) was injected into the right hippocampus region of Sprague-Dawly rats. ED1 (mouse anti rat CD68), neuronal nitric oxide synthase (nNOS), inducible nitric oxide synthase (iNOS) immunoreactive cells and apoptotic cells were observed in the hippocampus region. The results indicated that 1.0 g/kg, 0.5 g/kg of UR and 10 mg/kg of L-NAME reduced the counts of ED1, nNOS, iNOS immunoreactive cells and apoptotic cells in KA-treated rats. This study demonstrates that UR can reduce microglia activation, nNOS, iNOS and apoptosis, suggesting that UR plays a neuro-protective role against neuronal damage in KA-treated rats.

Gastrodia elata BL Mediates the Suppression of nNOS and Microglia Activation to Protect Against Neuronal Damage in Kainic Acid-Treated Rats

Our previous studies showed that Gastrodia elata (GE), an herb used in traditional Chinese medicine, has both anti-convulsive and free radical-scavenging activities in kainic acid (KA)-treated rats. The aim of the present study was to further investigate possible physiological mechanisms of GE against activities of neuronal nitric oxide synthase (nNOS) and microglia in KA-treated rats; 0.5 g/kg and 1.0 g/kg of GE extract were administered orally, whereas 20 mg/kg of N-nitro-L-arginine methyl ester (L-NAME) was administered intraperitoneally (ip), both at 30 minutes prior to KA (2 μg/2 μl) being injected into the right hippocampus region of rats. ED1-staining, apoptotic, inducible nitric oxide synthase (iNOS), and nNOS-staining cells were observed in the hippocampus region. The results indicated that 1.0 g/kg of GE and 20 mg/kg of L-NAME reduced the counts of ED1-stained cells, and 0.5 g/kg and 1.0 g/kg of GE, and 20 mg/kg of L-NAME reduced the numbers of apoptotic cells and nNOS-staining cells. In addition, 20 mg/kg of L-NAME also reduced the numbers of iNOS-staining cells, but 0.5 g/kg and 1.0 g/kg of GE did not. This study demonstrated that GE was able to reduce nNOS, microglia activation and apoptosis, suggesting that GE has a protective effect against neuronal damage in KA-treated rats.

Anti-oxidant activity mediated neuroprotective potential of trimetazidine on focal cerebral ischaemia-reperfusion injury in rats

1. The present study was designed to investigate the neuroprotective effect of trimetazidine (TMZ) following focal cerebral ischaemia-reperfusion (I/R) injury in rat forebrain. 2. Cerebral I/R injury was induced in rats by middle cerebral artery occlusion (MCAO) for 2 h, followed by reperfusion for 22 h. Trimetazidine (5 and 25 mg/kg, i.p.) was administered 1 h after induction of MCAO. The effects of TMZ were investigated by measuring neurological deficit, volume of infarct and brain swelling after 22 h reperfusion. Oxidative stress and inflammatory reactivity were assessed by estimating anti-oxidant markers and myeloperoxidase (MPO) activity in brain homogenates. Rectal temperature was measured during the study. The effects of TMZ on blood-brain barrier (BBB) permeability and apoptosis were also investigated in rat brain. Apoptosis was observed by DNA fragmentation studies using agarose gel electrophoresis. 3. Treatment with TMZ significantly (P < 0.01) reduced infarct volume and brain swelling. Superoxide dismutase (SOD) activity was reduced in ipsilateral hemispheres of vehicle (saline)-treated reperfused (RI) animals. Treatment with TMZ significantly restored SOD activity (P < 0.01) and glutathione levels (P < 0.05) after reperfusion compared with RI animals. Lipid peroxidation, MPO activity, BBB permeability and rectal temperature were all significantly (P < 0.01, P < 0.05 and P < 0.001, respectively) reduced in TMZ-treated animals compared with RI animals. 4. These results suggest that TMZ protects the brain against cerebral I/R injury and that this neuroprotective activity could be mediated by its anti-oxidant properties. The reduction in rectal temperature by TMZ treatment may be responsible for maintaining the delicate energy balance during I/R injury in rat brain and could have contributed to the neuroprotective activity of TMZ.

Gender specific effect of progesterone on myocardial ischemia/reperfusion injury in rats

The study was designed to investigate the effect of progesterone and its gender based variation on myocardial ischemia/reperfusion (I/R) injury in rats. Adult Sprague Dawley rats were divided into vehicle treated reperfusion injury group male (I/R-M), female (I/R-F), ovariectomised (I/R-OVR) and progesterone treatment (I/R-M+PG, I/R-F+PG, I/R-OVR+PG) groups, respectively. I/R injury was produced by occluding the left descending coronary artery (LCA) for 1 h and followed by re-opening for 1 h. Progesterone (2 mg kg(-1) i.p.) was administered 30 min after induction of ischemia. Hemodynamic parameters (+/-dp/dt, MAP), heart rate, ST-segment elevation and occurrence of ventricular tachycardia (VT) were measured during the I/R period. The myocardial infarct area, oxidative stress markers, activities of myeloperoxidase (MPO) and creatine kinase (CK) were determined after the experiment along with the assessment of the effect on apoptotic activity by using DNA fragmentation analysis. Histological observations were carried out on heart tissue. Treatment with progesterone significantly (P<0.05) reduced infarct area, lipid peroxidation (LPO) level and activity of MPO in females (I/R-F+PG) as compared to ischemic females (I/R-F). Progesterone significantly (P<0.001, P<0.05) inhibited serum CK activity and incidences of VT in female rats. Superoxide dismutase (SOD) activity, reduced glutathione (GSH) levels were significantly elevated (P<0.05) in I/R-F+PG group. Internucleosomal DNA fragmentation was less in I/R-F+PG group when compared to I/R-F group. The ischemic male and ovariectomised (I/R-M and I/R-OVR) counterparts did not show any significant change after progesterone treatment. In conclusion, the cardioprotective effect of progesterone on myocardial I/R injury induced damage is based on gender of the animal. The protective effect could be mediated by attenuation of inflammation and its possible interaction with endogenous estrogen.

Metabotropic glutamate receptor subtype 5 antagonists MPEP and MTEP

Glutamate regulates the function of central nervous system (CNS), in part, through the cAMP and/or IP3/DAG second messenger-associated metabotropic glutamate receptors (mGluRs). The mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) has been extensively used to elucidate potential physiological and pathophysiological functions of mGluR5. Unfortunately, recent evidence indicates significant non-specific actions of MPEP, including inhibition of NMDA receptors. In contrast, in vivo and in vitro characterization of the newer mGluR5 antagonist 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) indicates that it is more highly selective for mGluR5 over mGluR1, has no effect on other mGluR subtypes, and has fewer off-target effects than MPEP. This article reviews literature on both of these mGluR5 antagonists, which suggests their possible utility in neurodegeneration, addiction, anxiety and pain management.

Lysosomal enzyme cathepsin B is involved in kainic acid-induced excitotoxicity in rat striatum

The present study investigated the role of lysosomal enzymes in excitotoxic neuronal damage induced by excessive stimulation of non-NMDA glutamate receptors with kainic acid (KA). Internucleosomal DNA fragmentation was induced after intrastriatal administration of KA 1.25-5.0 nmol to rats. Increased expression of cathepsin B (P < 0.01, n = 6) but not cathepsin L in KA-injected striatum was observed 12 to 24 h after intrastriatal infusion of KA (2.5 nmol). Treatment with intrastriatal infusion of the cathepsin B inhibitor Z-FA-FMK (5-10 microg) 10 min prior to or 3 h after KA injection robustly attenuated KA-induced (2.5 nmol) DNA fragmentation. Z-FA-FMK (10 microg) also significantly reduced the size of striatal lesions induced by KA (P < 0.01, n = 6). These results suggest that lysosomal enzyme cathepsin B plays an important role in excitotoxic neuronal injury.

Ketogenic diet protects the hippocampus from kainic acid toxicity by inhibiting the dissociation of bad from 14-3-3

The ketogenic diet (KD) is often effective for intractable epilepsy, but its antiepileptic mechanisms remain largely unknown. Within the cell death/survival pathway, Akt and its downstream protein Bad play an important role in kainic acid (KA)-induced cell death. Therefore, we investigated the effects of a KD on KA-induced changes in the Akt/Bad/14-3-3 signaling pathway by evaluating Akt, Bad, 14-3-3, and cleaved caspase-3 expression levels as well as their relative interactions. Our results showed that a KD did not affect the expression levels of Akt, Bad, Bcl-xL, Bax, and 14-3-3 but increased phospho-Akt [serine 473; p-Akt (Ser473)] and phospho-Bad [serine 136; p-Bad (Ser136)] expression levels as well as decreased cleaved caspase-3 levels following a KA-induced seizure in the hippocampus. Furthermore, we found that a KD increased the protein-protein interaction between 14-3-3 and p-Bad (Ser136), which might be phosphorylated by p-Akt (Ser473), and decreased interaction of Bad and Bcl-xL. These results suggest that a KD might protect, at least partially, the hippocampus from KA-induced cell death via inhibiting the dissociation of Bad from 14-3-3.

Gene profiling the response to kainic acid induced seizures

Kainic acid activates non-N-methyl-d-aspartate (NMDA) glutamate receptors where it increases synaptic activity resulting in seizures, neurodegeneration, and remodeling. We performed microarray analysis on rat hippocampal tissue following kainic acid treatment in order to study the signaling mechanisms underlying these diverse processes in an attempt to increase our current understanding of mechanisms contributing to such fundamental processes as neuronal protection and neuronal plasticity. The kainic acid-treated rats used in our array experiments demonstrated severe seizure behavior that was also accompanied by neuronal degeneration which is suggested by fluoro-jade B staining and anti-caspase-3 immunohistochemistry. The gene profile revealed 36 novel kainic acid regulated genes along with additional genes previously reported. The functional roles of these novel genes are discussed. These genes mainly have roles in transcription and to a lesser extent have roles in cell death, extracellular matrix remodeling, cell cycle progression, neuroprotection, angiogenesis, and synaptic signaling. Gene regulation was confirmed via quantitative real time polymerase chain reaction and in situ hybridization.

Ketogenic diet increases calbindin-D28k in the hippocampi of male ICR mice with kainic acid seizures

The ketogenic diet (KD) increased the expression of calbindin-D(28k) (CB) in the interneurons of the hippocampus compared with the normal diet (ND)-fed mice. Also, 2 days after kainic acid (KA) administration, numerous CB-expressing astrocytes were found in the KD-fed mice compared with those of the ND-fed mice. These results suggest that the neuroprotective effect of the KD on the KA-induced toxicity may be, in part, mediated via an increased expression of CB.

Ketogenic diet prevents clusterin accumulation induced by kainic acid in the hippocampus of male ICR mice

We investigated the effect of ketogenic diet (KD) on clusterin accumulation in the kainic acid (KA)-induced seizure model. Two days after KA administration, strong clusterin-like immunoreactivity (IR) was detected in the hippocampus in the normal diet (ND)-fed mice. But in the KD-fed mice, few clusterin-like IR was detected. These results indicate that KD has neuroprotective effects throughout diminishing nuclear clusterin accumulation that is involved in caspase-3 independent cell death mechanism.

Kainate down-regulates a subset of GABAA receptor subunits expressed in cultured mouse cerebellar granule cells

The effect of kainate, an agonist selective for ionotropic AMPA/kainate type of glutamate receptors, on GABAA receptor subunit expression in cultured mouse cerebellar granule cells was studied using quantitative RT-PCR, ligand binding and electrophysiology. Chronic kainate treatment, without producing excitotoxicity, resulted in preferential, dose- and time-dependent down-regulation of alpha1, alpha6 and beta2 subunit mRNA expression, the expression of beta3, gamma2 and delta subunit mRNAs being less affected. The down-regulation was reversed by DNQX, an AMPA/kainate-selective glutamate receptor antagonist. A 14-day kainate treatment resulted in 46% decrease of total [3H]Ro 15-4513 binding to the benzodiazepine sites. Diazepam-insensitive [3H]Ro 15-4513 binding was decreased by 89% in accordance with very low amount of alpha6 subunit mRNA present. Diazepam-sensitive [3H]Ro 154513 binding was decreased only by 40%, contrasting >90% decrease in alpha1 subunit mRNA expression. However, this was consistent with lower potentiation of GABA-evoked currents in kainate-treated than control cells by the alpha1-selective benzodiazepine site ligand zolpidem, suggesting compensatory expression of alpha5 (and/or alpha2 or alpha3) subunits producing diazepam-sensitive but zolpidem-insensitive receptor subtypes. In conclusion, chronic kainate treatment of cerebellar granule cells selectively down-regulates oil, alpha6 and beta2 subunits resulting in altered GABAA receptor pharmacology.

Inhibition of cell cycle pathway by flavopiridol promotes survival of cerebellar granule cells after an excitotoxic treatment

Kainic acid (KA)-induced neuronal damage and the protective effects of flavopiridol were studied in primary cultures of rat cerebellar granule cells (CGNs). When neurons were treated with 500 microM KA, the percentage of cells with condensed nuclei measured by nuclear counting increased by up to 55%. After flavopiridol treatment, an antitumoral drug that is a broad inhibitor of cyclin-dependent kinases, the percentage of condensed nuclei decreased by up to 26%. Furthermore, this KA-mediated cell death was only partially dependent on the activation of the initiator caspase-9 and the effector caspases-3 and -6. This argues for a minor role of caspases in the intracellular pathway leading to KA-induced programmed cell death in CGNs. We examined the possible implication of cell cycle proteins in KA-induced neurotoxicity. We found an increase in the expression of proliferating cell nuclear antigen and E2F-1, two proteins implicated in S-phase, by Western blot. KA increased bromodeoxyuridine incorporation in CGNs, a marker of cell proliferation, and flavopiridol attenuated this effect. These results indicated that flavopiridol decreased the expression of cell cycle markers in CGNs after KA treatment. Flavopiridol might thus be used as a preventive agent against neurodegenerative diseases associated with cell cycle activation.

Down-regulation of GluR2 is associated with Ca2+-dependent protease activities in kainate-induced apoptotic cell death in cultured [correction of culturd] rat hippocampal neurons

In the present study, the molecular mechanisms underlying kainate-induced neurotoxicity were characterized in cultured rat hippocampal neurons. Long-term exposure to kainate caused typically apoptotic cell death, which was accompanied by the accumulation of calcium, marked down-regulation of GluR2 subunit, and the activation of calpain and caspase-3. All these alterations were prevented by alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionic acid (AMPA) receptor antagonist CNQX, but not by NMDA receptor antagonist MK801 and membrane L-type calcium channel antagonist nifedipine. In the presence of cyclothiazide, kainate-induced neurotoxicity was significantly enhanced. Inhibition of either caspases by zVAD-fmk or calpains by calpeptin protected neurons from neurotoxicity. These results suggest that long-term exposure of hippocampal neurons to kainate causes apoptosis, whose mechanisms involve multiple Ca(2+)-dependent cascades, in which AMPA receptor subunits may be targets for Ca(2+)-activated protease-mediated degradation during kainate-induced neuron apoptosis.

3-Amino thioacridone, a selective cyclin-dependent kinase 4 inhibitor, attenuates kainic acid-induced apoptosis in neurons

The mechanisms underlying selective neuronal cell death in kainic acid-mediated neurodegeneration are not fully understood. We have recently demonstrated that in cerebellar granule neurons, kainic acid induces the expression of proteins associated with cell-cycle progression. In the present study we show that 3-amino thioacridone (3-ATA), a selective cyclin-dependent kinase 4 inhibitor, attenuates kainic acid-induced apoptosis in cerebellar granule neurons. When neurons were pre-treated with 3-ATA 10 microM for 24 h, they were less susceptible to damage induced by kainic acid 500 microM, since the number of dead cells decreased significantly. In flow cytometry studies using propidium iodide staining, 3-ATA also reduced the ratio of apoptotic cells induced by kainic acid. Moreover, 3-ATA decreased the proportion of cells with a condensed nucleus from 55% to 22%. Our data suggest that the cell cycle pathway is involved in the mechanism of apoptosis mediated by kainic acid and that cyclin-dependent kinase 4 plays a prominent role in this process. 3-ATA may to prevent the apoptosis associated with neurodegenerative disorders without the over-activation of excitatory amino acid receptors.

Temporal and spatial distribution of activated caspase-3 after subdural kainic acid infusions in rat spinal cord

The molecular events initiating apoptosis following traumatic spinal cord injury (SCI) remain poorly understood. Soon after injury, the spinal cord is exposed to numerous secondary insults, including elevated levels of glutamate, that contribute to cell dysfunction and death. In the present study, we attempted to mimic the actions of glutamate by subdural infusion of the selective glutamate receptor agonist, kainic acid, into the uninjured rat spinal cord. Immunohistochemical colocalization studies revealed that activated caspase-3 was present in ventral horn motor neurons at 24 hours, but not 4 hours or 96 hours, following kainic acid treatment. However, at no time point examined was there evidence of significant neuronal loss. Kainic acid resulted in caspase-3 activation in several glial cell populations at all time points examined, with the most pronounced effect occurring at 24 hours following infusion. In particular, caspase-3 activation was observed in a significant number of oligodendroglia in the dorsal and ventral funiculi, and there was a pronounced loss of oligodendroglia at 96 hours following treatment. The results of these experiments indicate a role for glutamate as a mediator of oligodendroglial apoptosis in traumatic SCI. In addition, understanding the apoptotic signaling events activated by glutamate will be important for developing therapies targeting this cell death process.

Profound increase in sensitivity to glutamatergic- but not cholinergic agonist-induced seizures in transgenic mice with astrocyte production of IL-6

Transgenic mice with glial fibrillary acidic protein (GFAP) promoter driven-astrocyte production of the cytokines interleukin-6 (IL-6) and tumor necrosis factor (TNF) were used to determine whether the pre-existing production of these cytokines in vivo might modulate the sensitivity of neurons to excitotoxic agents. Low doses of kainic acid (5 mg/kg) that produced little or no behavioral or electroencephalogram (EEG) alterations in wild type or glial fibrillary acidic protein (GFAP)-TNF animals induced severe tonic-clonic seizures and death in GFAP-IL6 transgenic mice of 2 or 6 months of age. GFAP-IL6 mice were also significantly more sensitive to N-methyl-D-aspartate (NMDA)- but not pilocarpine-induced seizures. Kainic acid uptake in the brain of the GFAP-IL6 mice was higher in the cerebellum but not in other regions. Kainic acid binding in the brain of GFAP-IL6 mice had a similar distribution and density as wild type controls. In the hippocampus of GFAP-IL6 mice that survived low dose kainic acid, there was no change in the extent of either neurodegeneration or astrocytosis. Immunostaining revealed degenerative changes in gamma aminobutyric acid (GABA)- and parvalbumin-positive neurons in the hippocampus of 2-month-old GFAP-IL6 mice which progressed to the loss of these cells at 6 months of age. Thus, GFAP-IL6 but not GFAP-TNF mice showed markedly enhanced sensitivity to glutamatergic- but not cholinergic-induced seizures and lethality. This may relate, in part, to a compromise of inhibitory interneuron function. Therefore, pre-existing IL-6 production and inflammation in the central nervous system (CNS) not only causes spontaneous neurodegeneration but also synergizes with other neurotoxic insults to induce more severe acute functional neurological impairment.

Inflammatory mechanisms associated with brain damage induced by kainic acid with special reference to the interleukin-1 system

The evidence of inflammatory processes in the clinical manifestations and neuropathological sequelae of epilepsy have accumulated in the last decade. Administration of kainic acid, an analogue of the excitatory amino acid glutamate, induces a characteristic behavioural syndrome and a reproducible pattern of neurodegeneration in several brain areas, closely resembling human temporal lobe epilepsy. Results from studies using the kainic acid model indicate that manipulation of pro- and anti-inflammatory cytokines can modify the outcome with regard to the behavioural syndrome as well as the neuropathological consequences. Interleukin-1 is one of the most important cytokines and has several actions in the brain that are critical for the host defense against injury and infection, and it is involved in the initiation of early stages of inflammation. It is believed that interleukin-1 plays a pivotal role in the neuroinflammation associated with certain forms of neurodegeneration, including cerebral ischemia, trauma and excitotoxic brain injury. In this review, we have summarized the experimental data available with regard to the involvement of the interleukin-1 system in kainic acid-induced changes in the brain and emphasized the modulatory role of interleukin-1beta in this model of epilepsy

The protective effect of a ketogenic diet on kainic acid-induced hippocampal cell death in the male ICR mice

This study was designed to evaluate the antiapoptotic effects of a ketogenic diet (KD) through histological (cresyl violet staining, TUNEL staining and immunohistochemistry) and behavioral studies using kainic acid (KA, 25mg/kg i.p.)-induced seizures in male ICR mice. KA-induced seizure in rodents is widely used as an experimental model for human temporal lobe epilepsy because of their behavioral and pathological similarities. A KA-induced seizure causes neuronal damage in hippocampal pyramidal neurons and involves a caspase-3-mediated apoptotic pathway. In this study, the seizure onset time of the KD-fed group was delayed compared to that of the group fed a normal diet (ND) after a systemic KA injection. Histological studies revealed that KA caused pyknosis in most of the hippocampal areas in the ND-fed group, however, well-preserved pyramidal neurons were detected in the hippocampus of mice that had been on KD for 1 month, which began on postnatal day 21. The number of TUNEL-positive cells and caspase-3-positive cells in the hippocampus of the KD-fed group was lower than that of the ND-fed group. These findings indicate that KD has an antiepileptic effect via a neuroprotective action that involves the inhibition of caspase-3-mediated apoptosis of hippocampal neurons.

Molecular aspects of glutamate dysregulation: implications for schizophrenia and its treatment

The glutamate system is involved in many aspects of neuronal synaptic strength and function during development and throughout life. Synapse formation in early brain development, synapse maintenance, and synaptic plasticity are all influenced by the glutamate system. The number of neurons and the number of their connections are determined by the activity of the glutamate system and its receptors. Malfunctions of the glutamate system affect neuroplasticity and can cause neuronal toxicity. In schizophrenia, many glutamate-regulated processes seem to be perturbed. Abnormal neuronal development, abnormal synaptic plasticity, and neurodegeneration have been proposed to be causal or contributing factors in schizophrenia. Interestingly, it seems that the glutamate system is dysregulated and that N-methyl-D-aspartate receptors operate at reduced activity. Here we discuss how the molecular aspects of glutamate malfunction can explain some of the neuropathology observed in schizophrenia, and how the available treatment intervenes through the glutamate system.

Neuroprotective synergy of N-methyl-D-aspartate receptor antagonist (MK801) and protein synthesis inhibitor (cycloheximide) on spinal cord ischemia-reperfusion injury in rats

Thoraco-abdominal aortic surgery requiring temporal cross clamping of the aorta results in a high incidence of paraplegia due to temporary ischemia of the spinal cord. Both excitotoxicity and apoptosis are implicated in the pathogenesis of spinal cord ischemia-reperfusion injury. We propose that the N-methyl-D-aspartate receptor antagonist dizocilpine maleate (MK801) and the protein synthesis inhibitor cycloheximide produce a synergic effect in a rodent model of spinal cord ischemia-reperfusion injury. Injury was induced by 20 min of temporal thoracic aorta occlusion and distal blood volume reduction. After injury, the animals were treated with vehicle, MK801, cycloheximide or MK801 and cycloheximide. Hind limb motor function recovery was better in the MK801 and combined therapy groups than in the control and cycloheximide groups. The mean neuronal survival rate of the control group was 45.3 +/- 3.2% on the 7(th) day after injury. In the MK801 and cycloheximide treatment groups, neuronal survival increased to 62.4 +/- 3.6% and 54.1 +/- 2.4%, respectively. For the combined therapy group, neuronal survival increased to 75.6 +/- 2.5%. The number of apoptotic cells in the control group was 211.4 +/- 8.8 per section on the 7th day after ischemic insult, while apoptosis was significantly reduced in the cycloheximide (96.8 +/- 6.7 cells) and combined (84.8 +/- 8.5 cells) groups. It was unchanged in the MK801 group (209.8 +/- 5.4 cells). These results suggest that combined treatments directed at blocking both N-methyl-D-aspartate receptor-mediated excitotoxic necrosis and caspase-mediated apoptosis might have synergic therapeutic potential in reducing spinal cord ischemia-reperfusion injury.

The exacerbation of hippocampal excitotoxicity by glucocorticoids is not mediated by apoptosis

Both endogenous and exogenous glucocorticoids (GCs) are known to cause apoptosis in a number of peripheral tissues and in some cases in the CNS. Additionally, GCs can exacerbate the neuron loss associated with such acute neurological insults as hypoxia-ischemia, excitotoxicity, and metabolic disruption. This exacerbation is accompanied by increased accumulation of glutamate in the synapse, excessive cytosolic calcium, and increased oxygen radical activity, markers usually attributed to pathways of necrotic cell death. It is also known that acute insults can involve apoptotic mediators. In this context, one outstanding question that has received little attention is whether the exacerbation of insult-mediated cell death in neurons is apoptotic in mechanism. In this study we investigate whether the GC-mediated exacerbation of hippocampal excitotoxicity in culture involves apoptosis. Specifically, we show that while the magnitude of hippocampal neuron death caused by the excitotoxin kainic acid is indeed worsened in the presence of GCs, there is no evidence of increased markers of apoptosis. Specifically, we show that neither kainic acid nor GCs alone, or in combination, cause activation of caspase 3, a critical executor of insult-induced apoptosis. Furthermore, while kainic acid causes a significant incidence of apoptotic nuclear condensation, the incidence of this morphological indicator of apoptosis is not worsened by GCs. Thus, GCs appear to augment excitotoxic death in hippocampal neurons without augmenting the occurrence of apoptosis. We suggest that this finding is to be expected, given some energetic features of GC action and the energetic demands of apoptosis.

In vivo role of caspases in excitotoxic neuronal death: generation and analysis of transgenic mice expressing baculoviral caspase inhibitor, p35, in postnatal neurons

Caspases, a family of cysteine proteases, are thought to be critical mediators of apoptosis. To examine the role of neuronal caspases in excitotoxic neurodegeneration in vivo, we have generated transgenic mice expressing the baculovirus protein p35, a potent viral caspase inhibitor, using the neuron-specific calmodulin dependent kinase-II alpha (CaMKII-alpha) promoter. The expression of p35 was confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting and immunohistochemistry. We analyzed caspase activation and cell death by employing an experimental paradigm, in which the excitotoxin kainate (KA) was injected into CA1 of hippocampus and the distribution of the caspase-generated actin fragment was detected immunohistochemically. While kainate treatment led to selective neuronal death in the CA1, CA3 and CA4 of non-transgenic control mice, we observed restricted caspase activation only in the CA3 sector. The transgenic expression of p35 consistently inhibited the kainate-induced caspase activation, but failed to influence the death of neurons to any extent. In addition, we observed concomitant early calpain activation in the specific areas where neurons underwent degeneration in both the transgenic and non-transgenic mice. These results indicate that p35-inhibitable caspases play rather minor roles in the kainate-induced excitotoxicity and that the relative contribution of calpain is likely to be greater than that of caspases.

Kainate-induced excitotoxicity is dependent upon extracellular potassium concentrations that regulate the activity of AMPA/KA type glutamate receptors

In addition to well-known N-methyl-d-aspartate (NMDA) receptor-mediated excitotoxicity, recent studies suggest that non-NMDA type ionotropic glutamate receptors are also important mediators of excitotoxic neuronal death, and that their functional expression can be regulated by the cellular environment. In this study, we used cerebellar granule cells (CGCs) in culture to investigate kainate (KA)-induced excitotoxicity. Although previous reports indicated that KA induces apoptosis of CGCs in culture, no KA-induced excitotoxic cell death was observed in CGCs treated with KA when cells were maintained in high potassium media (24 mm K+). In contrast, when mature CGCs were shifted into low potassium media (3 mm K+), KA produced significant excitotoxicity. In electrophysiological studies, the KA-induced inward current density was significantly elevated in CGCs shifted into low K+ media compared with those maintained in high K+ media. Non-desensitizing aspects of KA currents observed in this study suggest that these responses were mediated by AMPA rather than KA receptors. In immunofluorescence studies, the surface expression of GluR1 subunits increased when mature CGCs were shifted into a low K+ environment. This study suggests that KA-induced excitotoxicity in mature CGCs is dependent upon the extracellular potassium concentration, which modulates functional expression and excitability of AMPA/KA receptors.

Dantrolene protects neurons against kainic acid induced apoptosis in vitro and in vivo

Apoptotic cell death induced by kainic acid (KA) in cultures of rat cerebellar granule cells (CGC) and in different brain regions of Wistar rat pups on postnatal day 21 (P21) was studied. In vitro, KA (100-500 microM) induced a concentration-dependent loss of cell viability in MTT assay and cell death had apoptotic morphology as studied by chromatin staining with propidium iodide (PI). In vivo, twenty-four hours after induction of status epilepticus (SE) by an intraperitoneal KA injection (5 mg/kg) we quantified apoptotic cells in hippocampus (CA1 and CA3), parietal cortex and cerebellum using PI staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) technique. We report that dantrolene, a specific ryanodine receptor antagonist, was able to significantly reduce the apoptotic cell death in CGC cultures and in hyppocampal CA1 and parietal cortex regions. Our finding can be valuable for neuroprotective therapy strategies in patients with repeated generalized seizures or status epilepticus.

Neuronal apoptosis after brief and prolonged seizures

Evidence has accumulated that apoptotic cell death contributes to brain damage following experimental seizures. A substantial number of degenerating neurons within limbic regions display morphological features of apoptosis following prolonged seizures evoked by systemic or local injections of kainic acid, systemic injections of pilocarpine and sustained stimulation of the perforant path. Although longer periods of seizures consistently result in brain damage, it has previously not been clear whether brief single or intermittent seizures lead to cell death. However, recent results indicate that also single seizures lead to apoptotic neuronal death. A brief, non-convulsive seizure evoked by kindling stimulation was found to produce apoptotic neurons bilaterally in the rat dentate gyrus. The mechanism triggering and mediating apoptotic degeneration is at present being studied. Alterations in the expression and activity of cell-death regulatory proteins such as members of the Bcl-2 family and the cysteinyl aspartate-specific proteinase (caspase) family occur in regions vulnerable to cell degeneration, suggesting an involvement of these factors in mediating apoptosis following seizures. Findings of decreased apoptotic cell death following administration of caspase inhibitors prior to and following experimentally induced status epilepticus, further suggest a role for caspases in seizure-evoked neuronal degeneration. Intermediate forms of cell death with both necrotic and apoptotic features have been found after seizures and investigation into the detailed mechanisms of the different forms of cell degeneration is needed before attempts to specific prevention can be made.

Traumatic brain injury: developmental differences in glutamate receptor response and the impact on treatment

Perinatal brain injury following trauma, hypoxia, and/or ischemia represents a substantial cause of pediatric disabilities including mental retardation. Such injuries lead to neuronal cell death through either necrosis or apoptosis. Numerous in vivo and in vitro studies implicate ionotropic (iGluRs) and metabotropic (mGluRs) glutamate receptors in the modulation of such cell death. Expression of glutamate receptors changes as a function of developmental age, with substantial implications for understanding mechanisms of post-injury cell death and its potential treatment. Recent findings suggest that the developing brain is more susceptible to apoptosis after injury and that such caspase mediated cell death may be exacerbated by treatment with N-methyl-D-aspartate receptor antagonists. Moreover, group I metabotropic glutamate receptors appear to have opposite effects on necrotic and apoptotic cell death. Understanding the relative roles of glutamate receptors in post-traumatic or post-ischemic cell death as a function of developmental age may lead to novel targeted approaches to the treatment of pediatric brain injury.

Cerebellar granule cells as a model to study mechanisms of neuronal apoptosis or survival in vivo and in vitro

Granule cells of the cerebellum constitute the largest homogeneous neuronal population of mammalian brain. Due to their postnatal generation and the feasibility of well characterized primary in vitro cultures, cerebellar granule cells are a model of election for the study of cellular and molecular correlates of mechanisms of survival/apoptosis and neurodegeneration/neuroprotection. The present review mainly deals with recent data on mechanisms and factors promoting survival or apoptotic elimination of cerebellar granule neurons, with a particular focus on the molecular correlates at the level of gene expression and induction of cellular signal pathways. The in vivo development is first analysed with particular reference to the role played by several neurotrophic factors and by the NMDA subtype of glutamate receptor. Then, mechanisms of survival/apoptosis are examined in the model of primary in vitro cultures, where the role of neurotrophins acting on cerebellar granule cells is followed by the large deal of data coming from the paradigm of potassium/serum withdrawal. The role of some key genes of the Bcl family, of some kinase systems and of transcriptional factors is primarily highlighted. Furthermore, the involvement of mitochondria, free radicals and proteases of the caspase family is considered. Finally, the use of cerebellar granule neurons in primary culture to experimentally address the issue of neurodegeneration and pharmacological neuroprotection is considered, with some comments on models at the borderline between necrosis and apoptosis, such as the excitotoxic neuronal damage. The overlapping of cellular signal pathways activated in granule neurons by apparently unrelated stimuli, such as neurotrophins and neurotransmitters/neuromodulators is stressed to put into light the special 'trophic' role played by activity in neurons. Finally, the advantage of designing and performing conceptually equivalent experiments on cerebellar granule neurons during development in vivo and in vitro, is stressed. On the basis of the reviewed material, it is concluded that cerebellar granule neurons have acquired a special position in modern neuroscience as one of the most reliable models for the study of neural development, function and pathology.

Neuroprotection with herpes simplex vectors expressing virally derived anti-apoptotic agents

A large body of literature dealing with neurotoxicity has focused on trying to define the exact nature of cell death following a neurological insult. While there is some debate in the field, it has been shown that a number of neurons in a given population can respond to an acute insult stimulus by activating the apoptotic cascade. To what extent, however, these insults result in the classical manifestations of either apoptosis or necrosis, or whether a mixture of the two results, is highly controversial, in part dependent on the particular system utilized. In this paper, we investigate the role of particular apoptotic signals in cultured rat hippocampal neurons, following acute excitotoxicity, metabolic poisoning, and heat stress. In particular, we examine these effects by utilizing a modified herpes simplex viral vector to specifically deliver viral anti-apoptotic genes. We have selected a battery of viral genes (crmA, p35, gamma34.5, KsBcl-2) that have evolved to suppress suicidal host responses to infection. We examine these inhibitors in the face of the above classes of insults and report that each viral agent tested has a unique profile in its ability to protect hippocampal neurons following acute neurological insults. Specifically, the effects of domoic acid excitotoxicity can be alleviated only with crmA, p35 and gamma34.5 whereas all genes tested can protect against heat stress. Conversely, no genes tested can protect against metabolic poisoning by cyanide. Such a study helps us to further understand the nature of apoptotic signals in different insults.

Alteration of Bcl-2 expression in the nigrostriatal system after kainate injection with or without melatonin co-treatment

In order to understand further the role of the anti-apoptotic Bcl-2 proto-oncogene protein in excitotoxin-induced brain injury and possible interaction between Bcl-2 and the antioxidant melatonin, the expression of Bcl-2 in various brain parts was studied after intrastriatal injection of kainate (KA, 2.5 nmol) with or without co-treatment of melatonin (10 mg/kg, intraperitoneally (i.p.)). Three days after unilateral injection of KA to the striatum in the rat, a dramatic direct cytotoxic effect was observed, as indicated an expression of Bcl-2 immunoreactivity in TUNEL- and OX-42-positive cells in the KA-injected striatum and traumatized cortical region. A less severe detrimental effect was also observed in the ipsilateral substantia nigra and peritraumatic cortex, as reflected by an upregulation of Bcl-2-immunostained neurons. Surprisingly, a reduction in Bcl-2-immunoreactive neurons that was accompanied by a less severe loss of tyrosine hydroxylase-immunoreactive neurons in the nigrostriatal pathway was observed after co-treatment with melatonin. Western blot analysis confirmed that Bcl-2 expression is elevated in striatum and cortex on the lesioned side, and that its expression was attenuated substantially after systemic administration of melatonin. The results showing an upregulation of Bcl-2 in nigral neurons and reactive microglia after KA lesion are consistent with the view that Bcl-2 is protective in function in the central nervous system.

Regulation of X-chromosome-linked inhibitor of apoptosis protein in kainic acid-induced neuronal death in the rat hippocampus

XIAP (X-chromosome-linked inhibitor of apoptosis protein) is an antiapoptotic protein which inhibits the activity of caspases and suppresses cell death. However, little is known about the presence and function of XIAP in the nervous system. Here we report that XIAP mRNA is expressed in developing and adult rat brain. Using a specific antibody, we observed XIAP-immunoreactive cells in different brain regions, among others, in the hippocampus and cerebral cortex. Kainic acid, which induces delayed cell death of specific neurons, increased the levels of XIAP in the CA3 region of hippocampus. XIAP was, however, largely absent in cells undergoing cell death, as shown by TUNEL labeling and staining for active caspase-3. In cultured hippocampal neurons, XIAP was initially upregulated by kainic acid and then degraded in a process blocked by the caspase-3 inhibitor DEVD. Similarly, recombinant XIAP is cleaved by active caspase-3 in vitro. The results show that there is biphasic regulation of XIAP in the hippocampus following kainic acid and that XIAP becomes a target for caspase-3 activated during cell death in the hippocampus. The degradation of XIAP by kainic acid contributes to neuronal cell death observed in vulnerable neurons of the hippocampus after caspase activation.

Seizure-induced neuronal death is associated with induction of c-Jun N-terminal kinase and is dependent on genetic background

Previous studies have shown that expression of c-Jun protein, as well as the c-Jun amino-terminal kinase (JNK) group of mitogen-activated protein kinases, may play a critical role in the pathogenesis of glutamate neurotoxicity. In order to define the molecular cascade that leads to c-Jun activation following excitotoxic injury and delineate whether induction of protein synthesis is related to cell death signaling cascades or those changes associated with increased seizure activity, we examined the expression of JNK-1, as well as its substrate, c-Jun and N-terminal phosphorylated c-Jun following kainic acid (KA) administration in two strains of mice. In the present study, we assessed the immunohistochemical expression of these proteins at time points between 2 h and 7 days, in excitotoxic cell death-resistant (C57BL/6) and -susceptible (FVB/N) mouse strains that were systemically injected with saline or kainic acid. No strain-related differences in the immunohistochemical expression of any of the proteins were observed in intact control mice. However, following KA administration, the magnitude and period of induction of JNK-1 protein was associated with impending cell death, while increased phosphorylation of c-Jun protein was associated with resistance to cell death. In contrast, expression of c-Jun protein does not appear to be a reliable indicator of impending cell death, as it was expressed in resistant and vulnerable subfields in mice susceptible to kainate injury. These results provide the first evidence that JNK-1 expression may be involved in producing the neuronal cell death response following excitotoxin-induced injury.

Neuronal apoptosis after CNS injury: the roles of glutamate and calcium

While a role has been well established for excitotoxic necrosis in the pathogenesis of traumatic or ischemic damage to the CNS, accumulating evidence now suggests that apoptosis may also be a prominent contributor. In this review we focus on the role of glutamate and attendant intracellular calcium influx in triggering or modifying excitotoxic necrosis and apoptosis, raising the possibility that calcium influx may affect these two death pathways in opposite directions. Incorporating consideration of both pathways will probably be needed to develop the most effective neuroprotective treatments for CNS injury.

Role of desensitization of AMPA receptors on the neuronal viability and on the [Ca2+]i changes in cultured rat hippocampal neurons

We investigated the role of desensitization of alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) receptors on the neurotoxicity and on the [Ca2+]i changes induced by kainate or by AMPA in cultured rat hippocampal neurons. The neuronal viability was evaluated either by the 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, or by analysis of cell morphology. Short-term exposure of the neurons to kainate or AMPA (30 min) was not toxic, but the exposure for 24 h to the excitotoxic drugs caused a concentration-dependent neurotoxic effect which was prevented by LY 303070, a noncompetitive AMPA receptor antagonist. In the presence of cyclothiazide (CTZ), kainate or AMPA was toxic (30 min exposure), or the toxic effect was significantly enhanced (24 h exposure), but in this case LY 303070 did not completely protect the cells against kainate-induced toxicity. The alterations in the [Ca2+]i caused by kainate or AMPA showed a great cell-to-cell variability. LY 303070 completely or partially inhibited the responses stimulated by kainate. CTZ differentially affected the responses evoked by kainate or AMPA. In the majority of hippocampal neurons, CTZ did not potentiate, or only slightly potentiated, the kainate-stimulated responses but in 11% of neurons there was a great potentiation. In AMPA-stimulated neurons, the responses were slightly or greatly potentiated in the majority of neurons, but not in all of them. The results show that AMPA and kainate may be toxic, depending on the time of exposure and on the blockade of the desensitization of the AMPA receptors. Overall, our results clearly show that there exist different populations of hippocampal neurons with different sensitivities to kainate, AMPA, CTZ and LY 303070. Moreover, the effects of CTZ on both [Ca2+]i alterations and neurotoxicity are not fully correlated.

Seizures induce widespread upregulation of cystatin B, the gene mutated in progressive myoclonus epilepsy, in rat forebrain neurons

Loss of function mutations in the gene encoding the cysteine protease inhibitor, cystatin B (CSTB), are responsible for the primary defect in human progressive myoclonus epilepsy (EPM1). CSTB inhibits the cathepsins B, H, L and S by tight reversible binding, but little is known regarding its localization and physiological function in the brain and the relation between the depletion of the CSTB protein and the clinical symptoms in EPM1. We have analysed the expression of mRNA and protein for CSTB in the adult rat brain using in situ hybridization and immunocytochemistry. In the control brains, the CSTB gene was differentially expressed with the highest levels in the hippocampal formation and reticular thalamic nucleus, and moderate levels in amygdala, thalamus, hypothalamus and cortical areas. Detectable levels of CSTB were found in virtually all forebrain neurons but not in glial cells. Following 40 rapidly recurring seizures evoked by hippocampal kindling stimulations, CSTB mRNA expression showed marked bilateral increases in the dentate granule cell layer, CA1 and CA4 pyramidal layers, amygdala, and piriform and parietal cortices. Maximum levels were detected at 6 or 24 h, and expression had reached control values at 1 week post-seizures. The changes of mRNA expression were accompanied by transient elevations (at 6-24 h) of CSTB protein in the same brain areas. These findings demonstrate that seizure activity leads to rapid and widespread increases of the synthesis of CSTB in forebrain neurons. We propose that the upregulation of CSTB following seizures may counteract apoptosis by binding cysteine proteases.

Human Bcl-2 protects against AMPA receptor-mediated apoptosis

Dysfunctions of the (S)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) subtype of ionotropic receptor for the brain's major excitatory neurotransmitter, L-glutamate, occur in various neurological conditions. We have previously demonstrated that AMPA receptor-mediated excitotoxicity occurs by apoptosis and here examined the influence of the expression of cell death repressor gene Bcl-2 on this excitotoxic insult. Using neuronal cortical cultures prepared from transgenic mice expressing the human Bcl-2 gene, the influence of Bcl-2 on AMPA receptor-mediated neuronal death was compared with that seen with staurosporine and H2O2. At day 6 cultures were exposed to AMPA (0.1-100 microM), and cellular injury was analyzed 48 h after insult using phase-contrast microscopy, a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide viability assay, and DNA staining with 4,6-diamidino-2-phenylindole and Sytox Green. AMPA produced a concentration-dependent increase in cell death that was significantly attenuated by human Bcl-2. AMPA (3 microM) increased the number of apoptotic nuclei to 60% of control in wild-type cultures, and human Bcl-2 significantly decreased the number of apoptotic nuclei to 30% of AMPA-treated cultures. Human Bcl-2 only provided significant neuroprotection against neuronal injury induced by low concentrations of staurosporine (1-10 nM) and H2O2 (0.1-30 microM) and where neuronal death was by apoptosis, but not against H2O2-induced necrosis. Our findings indicate that overexpression of Bcl-2 in primary cultured neurons protects in an insult-dependent manner against AMPA receptor-mediated apoptosis, whereas protection was not seen against more traumatic insults. This study provides new insights into the molecular therapeutics of neurodegenerative conditions.

Aurintricarboxylic acid promotes survival and regeneration of axotomised retinal ganglion cells in vivo

Aurintricarboxylic acid (ATA) has been used as an anti-apoptotic drug to counteract ischemic or cytotoxic injury to neurons. We investigated whether ATA has a neuroprotective effect on axotomized, adult retinal ganglion cells (RGC) as a model for traumatic neuronal cell death. A solution of ATA was injected into the vitreous body of rat eyes whose optic nerves had been cut. In controls, 14% of RGC survived 14 days after axotomy, whereas 44% of RGC survived after a single injection of ATA solution, and 59% survived when the injection was repeated after 7 days. A single injection of ATA 1 day after axotomy rescued 58% of RGC. However, injection of ATA 4 days after axotomy did not influence the survival of RGC, indicating that crucial, irreversible cascades of death are initiated prior to this point in time. The TUNEL technique was used to visualise apoptotic ganglion cells and revealed that 4 days after axotomy their number was significantly less in retinas whose optic nerves were axotomized and treated with ATA, than those of controls. As a consequence of neuroprotection, more RGC were recruited to regenerate into a peripheral nerve graft used to replace the cut optic nerve. In this paradigm, ATA-treated RGC extended significantly more axons within the graft than control RGC. This number could be increased by a second injection of ATA 7 days after axotomy. These data show that ATA is not only able to delay post-traumatic neuronal death but also enhances the extent of axonal regeneration in vivo.