Aging, neurodegenerative disease and the brain

The brain undergoes many changes in chemistry and structure during normal aging. For example, it dries and shrinks. Neurons are lost from some regions and there is also neuronal atrophy and loss of synaptic branching. The extent of such losses remains controversial for all but a few subcortical regions of the brain. Decreases in glucose metabolism and in some pre- and post-synaptic neurotransmitter indices have also been reported. Many systems, however, remain entirely unexplored. The evidence to date also indicates that there is great regional specificity in the effects, and that humans show considerable variability between individuals. Of interest is the fact that some of the changes most clearly demonstrated in normal aging - such as loss of dopaminergic neurons of the substantia nigra and cholinergic neurons of the medial basal forebrain - also occur in a much accentuated form in neurodegenerative diseases such as Parkinson's disease and Alzheimer disease. The small loss of these systems in normal aging may account for the shuffling gait, stooped posture and memory loss in the elderly. A phenomenon seen in neurodegenerative diseases, but not in normal aging, is the appearance of chronic inflammation in the brain. The suggestion that the progress of such diseases might be slowed by treatment with anti-inflammatory agents has, in the case of Alzheimer disease, gained some support from 19 epidemiological studies and one very small clinical trial. Clearly more detailed clinical trials are required, and caution must be used because of the undesirable side effects of currently available anti-inflammatory agents.