Journal of Alzheimer's disease : JAD
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The neurodegeneration that occurs in sporadic Alzheimer's disease (AD) is consistently associated with a number of characteristic histopathological, molecular, and biochemical abnormalities, including cell loss, abundant neurofibrillary tangles and dystrophic neurites, amyloid-beta deposits, increased activation of pro-death genes and signaling pathways, impaired energy metabolism/mitochondrial function, and evidence of chronic oxidative stress. The general inability to convincingly link these phenomena has resulted in the emergence and propagation of various heavily debated theories that focus on the role of one particular element in the pathogenesis of all other abnormalities. However, the accumulating evidence that reduced glucose utilization and deficient energy metabolism occur early in the course of disease, suggests a role for impaired insulin signaling in the pathogenesis of AD. ⋯ These abnormalities were associated with reduced levels of insulin receptor substrate (IRS) mRNA, tau mRNA, IRS-associated phosphotidylinositol 3-kinase, and phospho-Akt (activated), and increased glycogen synthase kinase-3beta activity and amyloid precursor protein mRNA expression. The strikingly reduced CNS expression of genes encoding insulin, IGF-I, and IGF-II, as well as the insulin and IGF-I receptors, suggests that AD may represent a neuro-endocrine disorder that resembles, yet is distinct from diabetes mellitus. Therefore, we propose the term, "Type 3 Diabetes" to reflect this newly identified pathogenic mechanism of neurodegeneration.
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Several epidemiological studies have found an association between low educational level (or low cognitively demanding occupations) and dementia. Although other studies have not found evidence to support such an association, there has been a general trend toward a "use it or lose it" concept which attempts to promote a neuroprotective role of intellectual activity against the development of dementia. Formation of amyloid-beta peptide (Abeta) in the brain plays a key role in the development of Alzheimer's disease whilst glutamate has been implicated in the pathophysiology of a number of neurological disorders including Alzheimer's disease and vascular dementia. ⋯ Long-term potentiation (LTP, a biological correlate of learning and memory) increases the sensitivity of hippocampal neurons to synaptically released glutamate whilst decreasing responses of neurons to bath applied glutamate receptor agonists and to hypoxia/ischemia in vitro. The effects of LTP are likely to involve changes in intracellular Ca2+ concentration. Based on these findings we are proposing that the LTP-induced neuroprotection in vitro may help explain the epidemiological evidence of a possible neuroprotective role of high intellectual activity against dementia.