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Spectral analysis of stable isotope ratios in readily available tissues such as hair and tooth enamel could help researchers monitor the effects of neuroprotective drugs or even track neurodegenerative disease, according to research published in PLoS One. The same approach might also be used to analyse archaeological specimens and provide new insights into the physiology of ancient people and animals. Otto Appenzeller of the New Mexico Health Enhancement and Marathon Clinics Research Foundation, in Albuquerque, USA, and colleagues there and at the Universita degli Studi di Milano, in Italy, explain how biological rhythms can provide insights into normal physiology and disease, but tracking them over time normally requires constant, potentially invasive, monitoring. Such monitoring is obviously impossible for a preserved, or mummified, body long dead. However, biological rhythms do leave traces. The brain contains a master timekeeper within the anterior part of the hypothalamus its rhythmic chemical oscillations and the changes in gene expression from this region might, the researchers thought, be traced remotely by examining the effects on proteins and other biomolecules in peripheral tissues, such as the hair and tooth enamel. The changes in these tissues will reflect the pulsations of cell cycles, circadian period, and thermoregulation profoundly. As such, the team explains, that hair grows throughout life but the rate of growth changes depending on diet, age, blood flow to the skin, hormonal and metabolic changes. The structure of teeth, similarly, is affected. The researchers have now demonstrated that analyses of stable isotope ratios along the length of a hair and along growth lines in teeth can reveal the inner biological rhythms and how they are controlled by the autonomic nervous system (ANS). To demonstrate how this research might be exploited in understanding ourselves, our ancestors, and animals, the team examined hair from mummified humans from South America, extinct mammals and modern animals and people, both healthy and diseased, and the teeth of hominins. For living subjects, the team also used power spectra to monitor heart-rate variability, which is itself a measure of a biological rhythm. Their analysis of the data showed recurring periods of slow and fast rhythms in the hydrogen isotope ratios in hair and carbon and oxygen isotope ratios in teeth with a cycle of around a year. The power spectra revealed the range of heart rate variability in living subjects. Additionally, by comparing these results with data from patients with neurodegeneration they could also demonstrate how such an analysis of hair might become a powerful diagnostic tool in tracking the effects of emerging treatments for neurodegenerative disease and neuroprotective drugs. Previously, Appenzeller and his colleagues have looked for the telltale signs of neurological problems in paintings of the ancient Egyptians and identified cases of progressive facial hemiatrophy, a disfiguring disease, based on distortions of facial features reproduced in the paintings. Such studies coupled with hair and teeth analysis from ancient samples could provide important clues about our past that would otherwise remain hidden. Related links:
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