The ageing of many populations in recent years has directed increasing attention to the social, medical and biological problems of senescence. The psychological changes associated with ageing occupy a central position in inquiries in this field. The expectation of mental disorder shows a steep increase with advancing chronological age, and beyond 75 years a large part of this increase is accounted for by disorders associated with degenerative changes in the central nervous system for which we lack remedies at the present time. Larsson et al. (1963) have estimated that the aggregate morbidity risk for these disorders up to the age of 70 is 0·4 per cent., up to age 75, 1·2 per cent. and up to age 80, 5 per cent. For higher ages estimates were probably less reliable, but the calculated risk up to the age of 90 was 5·2 per cent. In a survey of a random sample of elderly people aged 65 and over in the general population, Kay et al. (1964), found a total of 4·2 per cent. of elderly subjects to be suffering from senile dementia, 2·9 per cent. being mild cases. The condition is generally recognized as being a major cause of serious infirmity among the elderly in psychiatric, geriatric, general medical and community practice alike.

Summary and conclusionsNecropsy brain tissue from normal (control) patients and patients with depression and dementia was examined for activities of various cholinergic components, and these related to the degree of senile plaque formation and extent of intellectual impairment. Choline acetyltransferase and acetylcholinesterase activities decreased significantly as the mean plaque count rose, and in depressed and demented subjects the reduction in choline acetyltransferase activity correlated with the extent of intellectual impairment as measured by a memory information test; muscarinic cholinergic receptor binding activity remained unchanged with increasing senile plaque formation but butyrylcholinesterase activity increased.The results suggest a close relation between changes in the cholinergic system and Alzheimer's dementia, but the precise role of the system in this disease remains to be elucid'ated.

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Acetyl- and butyryl-cholinesterase activities have been measured biochemically in normal brain tissue, in senile dementia of Alzheimer type and in mental disorders without Alzheimer-type abnormalities. Acetylcholinesterase was significantly reduced and butyrylcholinesterase significantly increased, compared with the normal, in the hippocampus and temporal cortex of the Alzheimer cases. No significant enzyme changes were seen in the other diseases investigated including multi-infarct dementia, schizophrenia and depression. There was no correlation between age and acetylcholinesterase activity, but a significant positive correlation between the butyrylcholinesterase activities with increasing age (60-90 years) was found in the hippocampus. The possible connection between cholinergic system pathology and these cholinesterase abnormalities in Alzheimer dementia is discussed.

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