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This paper presents a discussion of the biochemical and physiological processes of oxidation reactions occurring in ageing neurons, specifically those of the brain's dopaminergic system.
The correlation between the dopaminergic system and the process of ageing became evident with the discovery that the brain’s striatum dopamine content declines rapidly beyond the age of 45 years
About 80% of dopamine in the human brain is located in the basal ganglia. An age-dependent decrease in the dopamine content of the basal ganglia was first detected in 1961, and later, widely corroborated.
It has been experimentally detected that the dopamine content of the human caudate-nucleus in the basal ganglia, decreases by 13% per decade over the age 45. The age-related progressive decline of dopaminergic control in the brain seems to be by now the first firmly established biochemical lesion of ageing.
Dopamine is a stimulatory neurotransmitter of the regulation of human growth hormone secretion. It has been widely postulated that the firing of the tubero-infundibular dopamine neurons enhances growth hormone release via the peptidergic somatoliberin neurons of the median eminence. Administration of L-Dopa, stimulates the hypothalamus secretion of growth hormone releasing hormone (GHRH), which interacts with the anterior lobe of the pituitary to stimulate the secretion of growth hormone. (Colour Plate 13, Page 86)
A wide amount of clinical research has been recently published to establish the direct association between growth hormone deficiency and the onset of several, old age representative features, like
decreased bone and muscular density and increases in cholesterol, adipose tissues, and thickness of the skin. A fundamental effect growth hormone has in relation to ageing, is its crucial control over the period of growth. A decrease in growth hormone to a certain threshold, at a specific period of life, is the main physiological signal for the closure of the epiphyses and cessation of bone growth.
In the beginning of the century, a theory of ageing was formulated stating that the period of cessation of growth is directly related to the period of initiation of senescence. In my research project and dissertation I suggest that cessation of growth is the main factor in entropy, which signals the initiation of a cascade of physiological events conducive to irreversible ageing, with all the cellular and molecular changes appearing thereafter.
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