Sensitivity to ageing of the limbic dopaminergic system: a review

The limbic system includes the complex of brain centres, nuclei and connect ions that provide the anatomical substrate for emotions. Although the prese nce of small amounts of dopamine (DA) in several limbic structures has been recognized for a long time, for many years it was thought that limbic DA. represented a precursor of noradrenaline in the biosynthetic pathway of cat echolamines. More recent evidence has shown that limbic centres and nuclei are supplied with a dopaminergic innervation arising from the ventral tegme ntal area (field A10) and in smaller amounts from the mesencephalic A9 fiel d. The dopaminergic limbic system is sensitive to ageing. Parameters of dop aminergic neurotransmission (DA levels, biosynthetic and catabolic markers and DA receptors) undergo age-related changes which depend on the structure and species investigated and are characterized mainly by a decline of diff erent parameters examined. In this paper, the influence of ageing on DA bio synthesis, levels, metabolism and receptors are reviewed in laboratory rode nts, monkeys and humans as well as in cases of Alzheimer's disease and Park inson's disease. The possibility that changes of dopaminergic neurotransmis sion markers in the limbic system are associated with cognitive impairment and psychotic symptoms affecting the elderly is discussed. Better knowledge of dopaminergic neurotransmission mechanisms in the so-called physiologica l ageing and in senile dementia may provide new insights in the treatment o f behavioural alterations frequently occurring in old age. (C) 1998 Elsevie r Science Ireland Ltd. All rights reserved.