Apoptosis In Neocortex Research Articles

Quintessential Risk Factors: Their Role in Promoting Cognitive Dysfunction and Alzheimer’s Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder. The human brain is extremely sensitive to hypoxia, ischemia, and glucose depletion. Impaired delivery of oxygen in obstructive sleep apnea (OSA) alters neuronal homeostasis, induces pathology, and triggers neuronal degeneration/death. This article systematically delineates the steps in the complex cascade leading to AD, focusing on pathology caused by chronic intermittent hypoxia, hypertension, brain hypoperfusion, glucose dysmetabolism, and endothelial dysfunction. Hypoxia/hypoxemia underpins several pathological processes including sympathetic activation, chemoreflex activity, neuroinflammation, oxidative stress, and a host of perturbations leading to neurodegeneration. The arterial blood flow reduction in OSA is profound, being about 76 % in obstructive hypopneas and 80 % in obstructive apneas; this leads to cerebral ischemia promoting neuronal apoptosis in neocortex and brainstem. OSA pathology also includes gray matter loss in the frontal, parietal, temporal, and occipital cortices, the thalamus, hippocampus, and key brainstem nuclei including the nucleus tractus solitarius. (18)F-FDG PET studies on OSA and AD patients, and animal models of AD, have shown reduced cerebral glucose metabolism in the above mentioned brain regions. Owing to the pathological impact of hypoxia, hypertension, hypoperfusion and impaired glucose metabolism, the adverse cardiovascular, neurocirculatory and metabolic consequences upregulate amyloid beta generation and tau phosphorylation, and lead to memory/cognitive impairment-culminating in AD. The framework encompassing these factors provides a pragmatic neuropathological approach to explain onset of Alzheimer's dementia. The basic tenets of the current paradigm should influence the design of therapeutic strategies to ameliorate AD.

Neurodevelopmental Consequences of Sub-Clinical Carbon Monoxide Exposure in Newborn Mice

Carbon monoxide (CO) exposure at high concentrations results in overt neurotoxicity. Exposure to low CO concentrations occurs commonly yet is usually sub-clinical. Infants are uniquely vulnerable to a variety of toxins, however, the effects of postnatal sub-clinical CO exposure on the developing brain are unknown. Apoptosis occurs normally within the brain during development and is critical for synaptogenesis. Here we demonstrate that brief, postnatal sub-clinical CO exposure inhibits developmental neuroapoptosis resulting in impaired learning, memory, and social behavior. Three hour exposure to 5 ppm or 100 ppm CO impaired cytochrome c release, caspase-3 activation, and apoptosis in neocortex and hippocampus of 10 day old CD-1 mice. CO increased NeuN protein, neuronal numbers, and resulted in megalencephaly. CO-exposed mice demonstrated impaired memory and learning and reduced socialization following exposure. Thus, CO-mediated inhibition of neuroapoptosis might represent an important etiology of acquired neurocognitive impairment and behavioral disorders in children.

Control of postnatal apoptosis in the neocortex by RhoA-subfamily GTPases determines neuronal density.

Apoptosis of neurons in the maturing neocortex has been recorded in a wide variety of mammals, but very little is known about its effects on cortical differentiation. Recent research has implicated the RhoA GTPase subfamily in the control of apoptosis in the developing nervous system and in other tissue types. Rho GTPases are important components of the signaling pathways linking extracellular signals to the cytoskeleton. To investigate the role of the RhoA GTPase subfamily in neocortical apoptosis and differentiation, we have engineered a mouse line in which a dominant-negative RhoA mutant (N19-RhoA) is expressed from the Mapt locus, such that all neurons of the developing nervous system are expressing the N19-RhoA inhibitor. Postnatal expression of N19-RhoA led to no major changes in neocortical anatomy. Six layers of the neocortex developed and barrels (whisker-related neural modules) formed in layer IV. However, the density and absolute number of neurons in the somatosensory cortex increased by 12-26% compared with wild-type littermates. This was not explained by a change in the migration of neurons during the formation of cortical layers but rather by a large decrease in the amount of neuronal apoptosis at postnatal day 5, the developmental maximum of cortical apoptosis. In addition, overexpression of RhoA in cortical neurons was seen to cause high levels of apoptosis. These results demonstrate that RhoA-subfamily members play a major role in developmental apoptosis in postnatal neocortex of the mouse but that decreased apoptosis does not alter cortical cytoarchitecture and patterning.

Transplanted human embryonic germ cell‐derived neural stem cells replace neurons and oligodendrocytes in the forebrain of neonatal mice with excitotoxic brain damage

Stem cell therapy is a hope for the treatment of some childhood neurological disorders. We examined whether human neural stem cells (hNSCs) replace lost cells in a newborn mouse model of brain damage. Excitotoxic lesions were made in neonatal mouse forebrain with the N-methyl-D-aspartate (NMDA) receptor agonist quinolinic acid (QA). QA induced apoptosis in neocortex, hippocampus, striatum, white matter, and subventricular zone. This degeneration was associated with production of cleaved caspase-3. Cells immunopositive for inducible nitric oxide synthase were present in damaged white matter and subventricular zone. Three days after injury, mice received brain parenchymal or intraventricular injections of hNSCs derived from embryonic germ (EG) cells. Human cells were prelabeled in vitro with DiD for in vivo tracking. The locations of hNSCs within the mouse brain were determined through DiD fluorescence and immunodetection of human-specific nestin and nuclear antigen 7 days after transplantation. hNSCs survived transplantation into the lesioned mouse brain, as evidenced by human cell markers and DiD fluorescence. The cells migrated away from the injection site and were found at sites of injury within the striatum, hippocampus, thalamus, and white matter tracts and at remote locations in the brain. Subsets of grafted cells expressed neuronal and glial cell markers. hNSCs restored partially the complement of striatal neurons in brain-damaged mice. We conclude that human EG cell-derived NSCs can engraft successfully into injured newborn brain, where they can survive and disseminate into the lesioned areas, differentiate into neuronal and glial cells, and replace lost neurons. (c) 2005 Wiley-Liss, Inc.