Debating the cause of a neurological disorder.
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Amino Acids, Diamino↗
Biomedical subjects
Ann M Marini
Publications and source records attributed to Ann M Marini.
Inhibition of N-methyl-D-aspartate receptors increases paraoxon-induced apoptosis in cultured neurons.
Organophosphorus (OP) compounds, used as insecticides and chemical warfare agents, are potent neurotoxins. We examined the neurotoxic effect of paraoxon (O,O-diethyl O-p-nitrophenyl phosphate), an organophosphate compound, and the role of NMDA receptors as a mechanism of action in cultured cerebellar granule cells. Paraoxon is neurotoxic to cultured rat cerebellar granule cells in a time- and concentration-dependent manner. Cerebellar granule cells are less sensitive to the neurotoxic effects of paraoxon on day in vitro (DIV) 4 than neurons treated on DIV 8. Surprisingly, the N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801, enhances paraoxon-mediated neurotoxicity suggesting that NMDA receptors may play a protective role. Pretreatment with a subtoxic concentration of N-methyl-D-aspartate (NMDA) [100 microM] protects about 40% of the vulnerable neurons that would otherwise die from paraoxon-induced neurotoxicity. Moreover, addition of a neuroprotective concentration of NMDA 3 h after treatment with paraoxon provides the same level of protection. Because paraoxon-mediated neuronal cell death is time-dependent, we hypothesized that apoptosis may be involved. Paraoxon increases apoptosis about 10-fold compared to basal levels. The broad-spectrum caspase inhibitor (Boc-D-FMK) and the caspase-9-specific inhibitor (Z-LEHD-FMK) protect against paraoxon-mediated apoptosis, paraoxon-stimulated caspase-3 activity and neuronal cell death. MK-801 increases, whereas NMDA blocks paraoxon-induced apoptosis and paraoxon-stimulated caspase-3 activity. These results suggest that activation of NMDA receptors protect neurons against paraoxon-induced neurotoxicity by blocking apoptosis initiated by paraoxon.
Amino Acid Chloromethyl Ketones↗
The excitoprotective effect of N-methyl-D-aspartate receptors is mediated by a brain-derived neurotrophic factor autocrine loop in cultured hippocampal neurons.
The neuroprotective effect and molecular mechanisms underlying preconditioning with N-methyl-D-aspartate (NMDA) in cultured hippocampal neurons have not been described. Pre-incubation with subtoxic concentrations of the endogenous neurotransmitter glutamate protects vulnerable neurons against NMDA receptor-mediated excitotoxicity. As a result of physiological preconditioning, NMDA significantly antagonizes the neurotoxicity resulting from subsequent exposure to an excitotoxic concentration of glutamate. The protective effect of glutamate or NMDA is time- and concentration-dependent, suggesting that sufficient agonist and time are required to establish an intracellular neuroprotective state. In these cells, the TrkB ligand, brain-derived neurotrophic factor (BDNF) attenuates glutamate toxicity. Therefore, we tested the hypothesis that NMDA protects neurons via a BDNF-dependent mechanism. Exposure of hippocampal cultures to a neuroprotective concentration of NMDA (50 microM) evoked the release of BDNF within 2 min without attendant changes in BDNF protein or gene expression. The accumulated increase of BDNF in the medium is followed by an increase in the phosphorylation (activation) of TrkB receptors and a later increase in exon 4-specific BDNF mRNA. The neuroprotective effect of NMDA was attenuated by pre-incubation with a BDNF-blocking antibody and TrkB-IgG, a fusion protein known to inhibit the activity of extracellular BDNF, suggesting that BDNF plays a major role in NMDA-mediated survival. These results demonstrate that low level stimulation of NMDA receptors protect neurons against glutamate excitotoxicity via a BDNF autocrine loop in hippocampal neurons and suggest that activation of neurotrophin signaling pathways plays a key role in the neuroprotection of NMDA.
6-Cyano-7-nitroquinoxaline-2,3-dione↗
N-methyl-D-aspartate and TrkB receptors protect neurons against glutamate excitotoxicity through an extracellular signal-regulated kinase pathway.
N-Methyl-D-aspartate (NMDA) at a subtoxic concentration (100 microM) promotes neuronal survival against glutamate-mediated excitotoxicity via a brain-derived neurotrophic factor (BDNF) autocrine loop in cultured cerebellar granule cells. The signal transduction mechanism(s) underlying NMDA neuroprotection, however, remains elusive. The mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3 kinase (PI3-K) pathways alter gene expression and are involved in synaptic plasticity and neuronal survival. This study tested whether neuroprotective activation of NMDA receptors, together with TrkB receptors, coactivated the MAPK or PI3-K pathways to protect rat cerebellar neurons. NMDA receptor activation caused a concentration- and time-dependent activation of MAPK lasting 24 hr. This activation was blocked by the NMDA receptor antagonist MK-801 but was attenuated only partially by the tyrosine kinase inhibitor k252a, suggesting that activation of both NMDA and TrkB receptors are required for maximal neuroprotection. The MAPK kinase (MEK) inhibitor U0126 (10 microM) partially blocked NMDA neuroprotection, whereas LY294002, a selective inhibitor of the PI3-K pathway, did not affect the neuroprotective activity of NMDA. Glutamate excitotoxicity decreased bcl-2, bcl-X(L), and bax mRNA levels,. NMDA increases Bcl-2 and Bcl-X(L) protein levels and decreases Bax protein levels. NMDA and TrkB receptor activation thus converge on the extracellular signal-regulated kinase (ERK) 1/2 signaling pathway to protect neurons against glutamate-mediated excitotoxicity. By increasing antiapoptotic proteins of the Bcl-2 family, NMDA receptor activation may also promote neuronal survival by preventing apoptosis.
Animals↗
BDNF variation and mood disorders: a novel functional promoter polymorphism and Val66Met are associated with anxiety but have opposing effects.
The brain-derived neurotrophic factor (BDNF) gene is critical for neuronal function and survival, and is likely to be important in psychiatric disorders. In this study, we used single-nucleotide polymorphism (SNP) discovery, functional analyses, and genetic association studies to better understand the potential role of BDNF sequence variation in behavior. Screening 480 unrelated individuals for SNPs and genotyping was performed in US Caucasian, American Indian, and African American populations. Lifetime DSM-III-R psychiatric diagnoses were assigned and the Tridimensional Personality Questionnaire (TPQ) was administered to measure anxious temperament (harm avoidance (HA)) and novelty seeking (NS). A novel SNP (-281 C>A) in promoter 1 was discovered that had decreased DNA binding in vitro and decreased basal reporter gene activity in transfected rat hippocampal neurons. The frequency of the -281 A allele was 0.03 in a Caucasian sample, but was virtually absent in other populations. Association analyses in a community-based sample showed that individuals with the -281 A allele (13 heterozygotes) had lower TPQ HA (F=4.8, p<0.05). In contrast, the Met 66 allele was associated with increased HA (F=4.1, p=0.02) and was most abundant in individuals with both anxiety disorders and major depression (p<0.05). Among the Val66Val homozygotes, individuals who were -281 CA heterozygotes had significantly lower HA than the -281 CC homozygotes (p<0.01). Our results suggest that in this population, the low activity -281 A allele may be protective against anxiety and psychiatric morbidity, whereas Met 66 may be a risk allele.
Adult↗
Delineating and understanding cerebellar neuroprotective pathways: potential implication for protecting the cortex.
The cerebellum is a brain region that is resistant to many of the neurodegenerative disorders such as stroke and Alzheimer's disease. In contrast, the neocortex (cerebrum, cerebral cortex) is vulnerable to these disorders. While there may be many reasons for the differences in vulnerability to acute and chronic neurodegenerative disorders, the cerebellum appears to be equipped with the tools necessary to protect itself against these types of insults. Over the last century, evidence has accumulated to suggest that the cerebellum is also involved in memory and higher cognitive function. We have discovered that intrinsic survival pathways exist in cerebellar granule cells that are regulated by low level stimulation of N-methyl-d-aspartate (NMDA) receptors. Activation of NMDA receptors protects vulnerable neurons against glutamate-mediated excitotoxicity acting on NMDA receptors. This report focuses on how modulation of neuronal survival by NMDA receptors through a brain-derived neurotrophic factor (BDNF)-mediated pathway may be incorporated into a network of cerebellar function, particularly in light of recent findings suggesting that the cerebellum plays a vital role in learning, memory, fear conditioning, and cognitive processing.
Animals↗
Inhibition of protein kinase C promotes neuronal survival in low potassium through an Akt-dependent pathway.
Cerebellar granule cell neurons undergo apoptotic cell death when subjected to serum-free conditions at physiological concentrations of potassium (5 mM). Protein kinase C (PKC) is known to play a role in preventing neuronal apoptosis under trophic factor deprivation, but its role in protecting cerebellar neurons from cell death under conditions of low potassium is unknown. This study sought to determine the involvement of PKC in neuronal survival and to determine if PKC regulated the phosphatidylinositol 3-kinase (PI 3-K)/Akt pathway in low physiologic concentrations of potassium. Incubation with a pan-PKC inhibitor, Ro-31-8220 (2 microm), or a specific PKCAlpha inhibitor, Gö6976, protected cerebellar granule cell neurons from low potassium-mediated cell death. In contrast, phorbol ester (TPA, 100 nm), a PKC activator, increased cell death. Incubation with, Ro-31-8220 rescued neurons from cell death induced by the PI 3-K inhibitor, LY294002, suggesting that Ro-31-8220 may affect Akt phosphorylation. Western blot analysis showed that serum-free, low potassium conditions decreased Akt phosphorylation, which was exacerbated by treatment with LY294002. In contrast, PKC inhibitors, Gö6976 or Ro-31-8220, increased Akt phosphorylation approximately two and four-fold, respectively in low potassium conditions. Because Akt activation appears to be critical in promoting neuronal survival under these culture conditions, increased Akt phosphorylation brought about by inhibiting PKC promotes neuronal survival.
Animals↗
AMPA protects cultured neurons against glutamate excitotoxicity through a phosphatidylinositol 3-kinase-dependent activation in extracellular signal-regulated kinase to upregulate BDNF gene expression.
The signal transduction and molecular mechanisms underlying alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-mediated neuroprotection are unknown. In the present study, we determined a major AMPA receptor-mediated neuroprotective pathway. Exposure of cerebellar granule cells to AMPA (500 microM) + aniracetam (1 microM), a known blocker of AMPA receptor desensitization, evoked an accumulation of brain-derived neurotropic factor (BDNF) in the culture medium and enhanced TrkB-tyrosine phosphorylation following the release of BDNF. AMPA also activated the src-family tyrosine kinase, Lyn, and the downstream target of the phosphatidylinositol 3-kinase (PI3-K) pathway, Akt. Extracellular signal regulated kinase (ERK), a component of the mitogen-activated protein kinase (MAPK) pathway, was also activated. K252a, a selective inhibitor of neurotrophin signaling, blocked the AMPA-mediated neuroprotection. The involvement of BDNF release in protecting neurons by AMPA was confirmed using a BDNF-blocking antibody. AMPA-mediated neuroprotection is blocked by PP1, an inhibitor of src family kinases, LY294002, a PI3-K inhibitor, or U0126, a MAPK kinase (MEK) inhibitor. Neuroprotective concentrations of AMPA increased BDNF mRNA levels that was blocked by the AMPA receptor antagonist, 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX). The increase in BDNF gene expression appeared to be the downstream target of the PI3-K-dependent activation of the MAPK cascade since MEK or the PI3-K inhibitor blocked the AMPA receptor-mediated increase in BDNF mRNA. Thus, AMPA receptors protect neurons through a mechanism involving BDNF release, TrkB receptor activation, and a signaling pathway involving a PI3-K dependent activation of MAPK that increases BDNF expression.
Animals↗
Role of brain-derived neurotrophic factor and NF-kappaB in neuronal plasticity and survival: From genes to phenotype.
PURPOSE: Brain-derived neurotrophic factor (BDNF) is a member of the family of neurotrophins and promotes diverse effects in neurons including development, maintenance of function, synaptic plasticity, and survival in different animal models. We present advances in our understanding of the genomics of the BDNF gene (bdnf) and its regulation by calcium-activated transcription factors, including cAMP response element binding protein (CREB) and more recently, nuclear factor kappaB (NF-kappaB) and discuss these findings in the context of neuronal plasticity and survival. METHODS: We used amplified bdnf complementary DNAs (cDNAs) and genomic DNA templates for direct sequencing and sequence variant discovery, information mining of public databases, and conventional molecular and cellular biology approaches to screen bdnf for novel regulatory elements, alternatively spliced exons, and functional sequence variants. RESULTS: We discovered a candidate NF-kappaB site in promoter 3 of bdnf and showned that activation of N-methyl-D-aspartate (NMDA) inotropic glutamate receptors increased bdnf expression through an NF-kappaB-dependent pathway and extended the finding to show that NF-kappaB was required for NMDA neuroprotection in vitro. In addition, sequence analysis of bdnf cDNAs from different brain regions predicted at least three pre-pro-BDNF protein isoforms, two of which were previously unknown. Each isoform differs at the amino terminus and may have functional importance. CONCLUSIONS: Given the central role that BDNF plays in the developing and adult nervous system, understanding how BDNF is regulated and how it functions will enhance our knowledge of its diverse effects, which may lead to more effective treatments for neurodegenerative disorders and reveal the role of BDNF in complex phenotypes related to behavior.
Animals↗
N-methyl-D-aspartate and TrkB receptor activation in cerebellar granule cells: an in vitro model of preconditioning to stimulate intrinsic survival pathways in neurons.
Delineating the mechanisms of survival pathways that exist in neurons will provide important insight into how neurons utilize intracellular proteins as neuroprotectants against the causes of acute neurodegeneration. We have employed cultured rat cerebellar granule cells as a model for determining the mechanisms of these intraneuronal survival pathways. Glutamate has long been known to kill neurons by an N-methyl-d-aspartate (NMDA) receptor-mediated mechanism. Paradoxically, subtoxic concentrations of NMDA protect neurons against glutamate-mediated excitotoxicity. Because NMDA protects neurons in physiologic concentrations of glucose and oxygen, we refer to this phenomenon as physiologic preconditioning. One of the major mechanisms of NMDA neuroprotection involves the activation of NMDA receptors leading to the rapid release of brain-derived neurotrophic factor (BDNF). BDNF then binds to and activates its cognate receptor, receptor tyrosine kinase B (TrkB). The efficient utilization of these two receptors confers remarkable resistance against millimolar concentrations of glutamate that kill more than eighty percent of the neurons in the absence of preconditioning the neurons with a subtoxic concentration of NMDA. Exactly how the neurons mediate neuroprotection by activation of both receptors is just beginning to be understood. Both NMDA and TrkB receptors activate nuclear factor kappaB (NF-kappaB), a transcription factor known to be involved in protecting neurons against many different kinds of toxic insults. By converging on survival transcription factors, such as NF-kappaB, NMDA and TrkB receptors protect neurons. Thus, crosstalk between these very different receptors provides a rapid means of neuronal communication to upregulate survival proteins through release and transcriptional activation of messenger RNA.
Animals↗
Antihistamine terfenadine inhibits calcium influx, cGMP formation, and NMDA receptor-dependent neurotoxicity following activation of L-type voltage sensitive calcium channels.
We have investigated the actions of the H1 receptor antagonist terfenadine on voltage sensitive calcium channels and calcium-mediated pathways. We found that terfenadine prevented N-methyl-D-aspartate (NMDA)-mediated excitotoxicity following stimulation of L-type voltage sensitive calcium channels by the specific agonist BayK8644. The neuroprotective effect of terfenadine was concentration-dependent, 10 and 100 nM terfenadine providing 50 and 100% neuroprotection, respectively. Neuroprotection was associated with a decrease in calcium influx via L-voltage sensitive calcium channels. Terfenadine fully reversed the increase in intracellular calcium induced by BayK8644, and delayed significantly the time necessary for this agonist to induce maximum intracellular calcium levels. Calcium-mediated biochemical pathways coupled to voltage sensitive calcium channels activation were also affected by terfenadine. This drug inhibited intracellular cGMP formation by BayK8644 in a concentration-dependent manner, 100 nM terfenadine reducing cGMP formation by 50% and 1 micro M terfenadine fully inhibiting cGMP synthesis. Terfenadine reduced NMDA receptor-mediated cGMP formation due to the release of glutamate following activation of calcium channels by BayK8644. Finally, we also show that terfenadine effectively reduced steady-state concentrations of both intracellular calcium and cGMP in unstimulated cultures in their usual growing conditions.
Journal Article↗
Cyclooxygenase-2 inhibition protects cultured cerebellar granule neurons from glutamate-mediated cell death.
Primary insults to the brain can initiate glutamate release that may result in excitotoxicity followed by neuronal cell death. This secondary process is mediated by both N-methyl-D-aspartate (NMDA) and non-NMDA receptors in vivo and requires new gene expression. Neuronal cyclooxygenase-2 (COX2) expression is upregulated following brain insults, via glutamatergic and inflammatory mechanisms. The products of COX2 are bioactive prostanoids and reactive oxygen species that may play a role in neuronal survival. This study explores the role of neuronal COX2 in glutamate excitotoxicity using cultured cerebellar granule neurons (day 8 in vitro). Treatment with excitotoxic concentrations of glutamate or kainate transiently induced COX2 mRNA (two- and threefold at 6 h, respectively, p < 0.05, Dunnett) and prostaglandin production (five- and sixfold at 30 min, respectively, p < 0.05, Dunnett). COX2 induction peaked at toxic concentrations of these excitatory amino acids. Surprisingly, NMDA, L-quisqualate, and trans-ACPD did not induce COX2 mRNA at any concentration tested. The glutamate receptor antagonist NBQX (5 microM, AMPA/kainate receptor) completely inhibited kainate-induced COX2 mRNA and partially inhibited glutamate-induced COX2 (p < 0.05, Dunnett). Other glutamate receptor antagonists, such as MK-801 (1 microM, NMDA receptor) or MCPG (500 microM, class 1 metabotropic receptors), partially attenuated glutamate-induced COX2 mRNA. These antagonists all reduced steady-state COX2 mRNA (p < 0.05, Dunnett). To determine whether COX2 might be an effector of excitotoxic cell death, cerebellar granule cells were pretreated (24 h) with the COX2-specific enzyme inhibitor, DFU (5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl) phenyl-2((5)H)-furanone) prior to glutamate challenge. DFU (1 to 1000 nM) completely protected cultured neurons from glutamate-mediated neurotoxicity. Approximately 50% protection from NMDA-mediated neurotoxicity, and no protection from kainate-mediated neurotoxicity was observed. Therefore, glutamate-mediated COX2 induction contributes to excitotoxic neuronal death. These results suggest that glutamate, NMDA, and kainate neurotoxicity involve distinct excitotoxic pathways, and that the glutamate and NMDA pathways may intersect at the level of COX2.
Animals↗
Transient neurologic deficits associated with carbamazepine-induced hypertension.
Carbamazepine is a well-established, effective treatment of complex partial seizures and is well tolerated in most patients. The adverse effects of carbamazepine include aplastic anemia, agranulocytosis, pancytopenia, bone marrow depression, thrombocytopenia, cardiac conduction abnormalities, congestive heart failure, and peripheral edema. Hypertension or hypotension has also rarely been documented in patients with either therapeutic or toxic blood levels of carbamazepine. It is possible that carbamazepine-induced hypertension in those with therapeutic blood levels is rarely seen because most of the patients who begin treatment are young and do not have baseline hypertension. The authors describe a patient of African-American descent with a history of controlled essential hypertension who developed severe uncontrolled hypertension when started on carbamazepine. Treatment with additional antihypertensive medications did not reduce his blood pressure. In addition, he developed two episodes of transient neurologic deficits, the symptoms of which consisted of dysarthria, vertigo, and unstable gait. A substantial reduction of his carbamazepine dose resulted in the control of his blood pressure and no recurrence of his symptoms.
Aged↗