Olfactory disorder: A loss in the ability to smell or a change in the way odors are perceived. Reduction of the sense of smell is termed hyposmia. Total inability to detect odors is termed anosmia. As for changes in the perception of odors, some people notice that familiar odors become distorted. Or, an odor that usually smells pleasant instead smells foul. Still other people may perceive a smell that is not present.Modern neurology has several important parts, and one of them is studying factors, causing neurodegeneration in brain. Alzheimer's disease is a bright example of neurodegeneration. This pathological process leads to total degradation of personality and memory loss in elderly people, as well as deterioration of spatial orientation. Modern medicine has over 10 theories, trying to explain the nature of this disease. Most popular theory links beginning of Alzheimer's disease with accumulation of a specific protein in brain. This protein, called amyloid beta peptide, is toxic for neurons – nervous cells.
This protein does exist in an organism under normal conditions, but its concentration is extremely low. When the disease starts, this protein accumulates in brain in the form of plaques, similar to those of atherosclerosis. Initial stage of Alzheimer's disease is often notable for olfaction disorders. Russian scientists decided to find out whether link between smell deterioration and neurodegeneration existed. Alzheimer's disease progresses very slowly, thus a reliable model of this disease would have been a great help to medics.
Researchers investigated consequences, appearing in animals, which olfactory bulbs were removed, and found that defects in olfactory system formed same symptoms as Alzheimer's disease. Scientists explain this effect with direct links of olfactory system with a hippocampus, an important part of brain. The fact that hippocampus deterioration is a central stage in Alzheimer's disease development, is beyond question. Experiments revealed that when a link between an olfactory bulb and hippocampus is broken, biochemical shifts appear, which increase the amount of beta amyloid plaques, thus promoting the disease.
Olfaction disorder is the very first sign of Alzheimer's disease. The model, created by Russian scientists, allows not only diagnosing this disease, but also performing search of new pharmaceuticals. Now medics can examine olfaction system of a patient, while there are no visible signs of Alzheimer's disease, and advise some preventive measures. At this stage a patient has about 3-4 years to cope with his disease.
The results, obtained by Russian scientists comply with previous researches outcomes. There have been scattered reports of evidence suggesting that a diminished sense of smell is associated with Alzheimer’s disease. In 1987, Rezek reported on olfactory deficits as a neurological sign in dementia of the Alzheimer type. Talamo and his group examined changes in olfactory neurons in patients with Alzheimer’s disease. They indicated that there were histopathological changes in olfactory epithelium. In 1991, Hyman and colleagues suggested that neuroanatomical and neurochemical changes related to Alzheimer’s disease occur in the olfactory bulb of the brain, confirming prior studies. Other areas that exhibited degeneration included the anterior olfactory nucleus, the olfactory tubercle, the uncus and the subiculum. These studies could be challenged on methodological grounds, but still carry some weight.
Finally, researchers at the University of Pennsylvania School of Medicine have linked smell loss in mice with excessive levels of a key protein associated with Alzheimer's and Parkinson's disease in 2004.
"The loss of smell – or olfactory dysfunction – has been known for more than a decade as an early sign of several neurodegenerative diseases, but we have never been able to link it to a pathological entity that is measurable over time," said Richard Doty, PhD, Professor and Director of Penn's Smell and Taste Center, who is also the team leader of the study. "By tying decrements in the ability to smell to the presence of key disease proteins, such as tau, we may well be able to assess the degree of progression of selected elements of Alzheimer's disease and related disorders by scores on quantitative smell tests."
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