Neurotransmitter systems in aging and senile dementia.

Abstract 1. 1. Reported changes in neurotransmitter systems with aging in human and animal brain are briefly reviewed. The effects of age appear to vary from region to region in brain, as well as from system to system. Considerable evidence is available that dopaminergic activity decreases with age, particularly in the striatum and nucleus accumbens; this loss may be important to age-related losses in agility and increases in the incidence and severity of tardive dyskinesia. Lesser, but still convincing, evidence indicates decreases with age in noradrenergic, GABAergic and cholinergic systems, with the most marked effects being found, respectively, in the hypothalamus, thalamus and cortex-hippocampus. The cortical and hippocampal losses in cholinergic activity are markedly accentuated in senile dementia of the Alzheimer type and are probably related to memory defects in aging and dementia. 2. 2. Serotonin and met-enkephalin systems in the hypothalamus are probably relatively unchanged by age and little or no information is available on numerous other putative transmitters. 3. 3. Brief consideration is also given to age-related changes in the density of specific binding sites, possible reasons for lack of therapeutic effect of choline analogs in senile dementia, and the question of whether cell death, loss of nerve endings and/or decreased neuronal vitality underlie the deficits found.