Journal of Neuroscience, Vol 12, 1936-1944, Copyright © 1992 by Society for Neuroscience
Cholinergic cell loss and hypertrophy in the medial septal nucleus of the behaviorally characterized aged rhesus monkey
HM Stroessner-Johnson, PR Rapp and DG Amaral
Salk Institute, San Diego, CA 92186-5800.
Quantitative studies were conducted to determine the number and size of
cholinergic neurons in the medial septal nucleus of four aged (23-25 years
old) and four young (10-12 years old) rhesus monkeys. All of the animals
had been tested on an extensive battery of learning and memory tasks prior
to these experiments. Two of the aged monkeys displayed a pattern of
recognition memory deficits that resembled the effects of medial temporal
lobe damage. The postmortem anatomical data were analyzed in relation to
both the age and behavioral status of the animals. Across all rostrocaudal
levels of the medial septal nucleus, there was a 19.3% decrease in the
number of cholinergic neurons in the aged monkeys. The loss was regionally
selective, however, and ranged from a low of 6.2% rostrally to 40.9%
caudally. The degree of cell loss was similar in both memory-impaired and
memory-unimpaired aged animals. Morphological analysis also revealed that
the mean cross-sectional area of cholinergic neurons was significantly
larger in the aged animals. At caudal levels, the increase in average cell
size was at least partly due to a disproportionate loss of small to medium
size neurons. At rostral levels of the medial septal nucleus, however,
where there was minimal cell loss, a clear hypertrophy of cholinergic
neurons was evident. Interestingly, the cell hypertrophy observed at these
rostral levels was present only in brains from the behaviorally impaired
aged monkeys. These findings represent the first morphological
demonstration of alterations in cholinergic neurons in the aged nonhuman
primate.(ABSTRACT TRUNCATED AT 250 WORDS)