Neurobiology of disease
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Neurobiology of disease · Apr 2006
Traumatic mechanical injury to the hippocampus in vitro causes regional caspase-3 and calpain activation that is influenced by NMDA receptor subunit composition.
Apoptotic or necrotic cell death in the hippocampus is a major factor underlying the cognitive impairments following traumatic brain injury. In this study, we examined if traumatic mechanical injury would produce regional activation of calpain and caspase-3 in the in vitro hippocampus and studied how the mechanically induced activation of NR2A and NR2B containing N-methyl-d-aspartate receptors (NMDARs) affects the activation of these proteases following mechanical injury. Following a 75% stretch, significant levels of activated caspase-3 and calpain-mediated spectrin breakdown products were evident only in cells within the dentate gyrus, and little co-localization of the markers was identified within individual cells. ⋯ At moderate injury levels, both caspase-3 and calpain activation was attenuated by blocking NR2B containing NMDARs prior to stretch or by blocking all NMDARs prior to stretch injury. Treatment with an NR2A selective NMDAR antagonist had little effect on either activated caspase-3 or Ab38 immunoreactivity following moderate injury but resulted in the appearance of activated caspase-3 in the dentate gyrus following severe mechanical stretch. Together, these studies suggest that the injury induced activation of NR2A containing NMDARs functions as a pro-survival signal, while the activation of NR2B containing NMDARs is a competing, anti-survival, signal following mechanical injury to the hippocampus.
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Neurobiology of disease · Mar 2006
Melatonin reduces the severity of anesthesia-induced apoptotic neurodegeneration in the developing rat brain.
General anesthetics cause widespread apoptotic neurodegeneration in many regions of the developing rat brain. The activation of mitochondria-dependent apoptotic pathway is important in the early stages of anesthesia-induced developmental neuroapoptosis. ⋯ When 7-day-old rats (the peak of synaptogenesis) were exposed to a commonly used and highly pro-apoptotic anesthesia cocktail (midazolam, isoflurane, nitrous oxide) in combination with the escalating doses of melatonin (from 1 to 20 mg/kg, s.c.), the severity of anesthesia-induced damage was reduced in a dose-dependent manner in two most vulnerable brain regions--the cerebral cortex and anterior thalamus. Melatonin-induced neuroprotection was mediated, at least in part, via the inhibition of mitochondria-dependent apoptotic pathway since melatonin caused an up-regulation of the anti-apoptotic protein, bcl-X(L), reduction in anesthesia-induced cytochrome c release into the cytoplasm and a decrease in anesthesia-induced activation of caspase-3, an important step in the activation of DNAses and the formation of the apoptotic bodies.
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Neurobiology of disease · Feb 2006
Locomotor hyperactivity and alterations in dopamine neurotransmission are associated with overexpression of A53T mutant human alpha-synuclein in mice.
Genetic and biochemical abnormalities associated with alpha-synuclein are implicated in the etiology of Parkinson's disease (PD). In this study, altered locomotor behavior linked to the expression of mutant or wildtype human alpha-synuclein was investigated. A53T alpha-synuclein transgenic (A53T-tg) mice exhibited normal activity at 5 months of age; however, by 7 months, they developed marked hyperactivity that remained evident until 19 months. ⋯ Hyperactivity in A53T-tg mice was also associated with increased D1 receptor expression in the substantia nigra and decreased dopamine transporter expression in the nucleus accumbens and striatum. Finally, striatal dopamine uptake measured by high-speed chronoamperometry was reduced by 40% in A53T-tg mice. Thus, expression of A53T mutant human alpha-synuclein in mice results in adult-onset hyperactivity associated with D1 receptor and dopamine transporter-mediated alterations in dopamine neurotransmission.
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Neurobiology of disease · Feb 2006
In vivo imaging of microglial activation with [11C](R)-PK11195 PET in idiopathic Parkinson's disease.
Idiopathic Parkinson's disease (PD) is a neurodegenerative disorder associated with akinesia, tremor and rigidity. While the characteristic Lewy body pathology targets pigmented and other brainstem nuclei at post-mortem, activated microglia are found in both subcortical and cortical areas. [11C](R)-PK11195 is a positron emission tomography (PET) marker of peripheral benzodiazepine sites (PBBS), which are selectively expressed by activated microglia. We examined 18 PD patients clinically and with [11C](R)-PK11195 and [18F]-dopa PET. ⋯ Levels of microglial activation did not correlate with clinical severity or putamen [18F]-dopa uptake. Our in vivo findings confirm that widespread microglial activation is associated with the pathological process in PD. The absence of significant longitudinal changes suggests that microglia are activated early in the disease process, and levels then remain relatively static, possibly driving the disease via cytokine release.
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Neurobiology of disease · Dec 2005
Apolipoprotein E4 enhances brain inflammation by modulation of the NF-kappaB signaling cascade.
Apolipoprotein E4 (apoE4), the major genetic risk factor of Alzheimer's disease (AD), is associated with enhanced brain inflammation. Genome-wide gene expression profiling was employed to study the effects of apoE genotype on hippocampal gene expression in LPS-treated mice, transgenic for either apoE4 or the AD benign allele, apoE3. This revealed that the expression of inflammation-related genes following intracerebroventricular injection of LPS was significantly higher and more prolonged in apoE4 than in apoE3 transgenic mice. ⋯ Direct measurement of NF-kappaB-regulated genes revealed that their extent of activation was greater in the apoE4 mice. Immunohistochemistry experiments revealed that microglial and NF-kappaB activation were more pronounced in apoE4 than in apoE3 mice. These findings suggest that the increased brain inflammation in apoE4 mice is related to disregulation of NF-kappaB signaling pathway.