The effect of increased longevity, produced by dietary restriction, on the neuronal population of area 17 in rat cerebral cortex.
Area 17 of the brains of Sprague-Dawley derived rats, maintained on a limited ration of food to maintain their weights at the levels attained by two months of age, was compared with area 17 in control groups of rats fed ad lib. The oldest rats in the diet restricted group were sacrificed at 46 and 48 months of age, by which time their life spans had been extended about 12 months beyond the oldest age that rats fed ad lib achieve, for only few of the latter live as long as 33 months. In this study, the rats which were compared consisted of two groups of ad lib fed rats, one 3 and 6 months of age, and the other 33 months old, and two groups of diet restricted rats, one 26 months old and the other 46 to 48 month old rats (designated as 47 month old rats). Two indices were used to assess whether age affects the volume of area 17. One, the number of clusters of apical dendrites of layer V pyramidal cells per unit area of tangential sections, was the same in all groups, indicating that the lateral spread of area 17 did not alter with age. However, the other index, the thickness of area 17, did change with age, for area 17 was significantly thinner in the 47 month old diet restricted rats than in the other three groups. It was also found that the number of neuronal profiles in strips of sections passing through the entire depth of area 17 is decreased in the 47 month old rats, indicating that neurons had been lost from their cortices. This decrease in the number of neuronal profiles in the 47 month old rats was not due to nuclear shrinkage since the sizes of neuronal nuclei were not significantly different in the older ad lib and diet restricted rats. Determinations of neuronal packing densities in layers II/III, IV, V and VIa suggest that neurons are most frequently lost from the deeper cortical layers of the 47 month old rats, and in these layers large vacuolated spaces, the sizes of neuronal cell bodies, have been encountered. It is suggested that these spaces represent places from which neurons have been lost. It is concluded, therefore, that neurons are lost from area 17 in rats whose longevity is increased by diet restriction.
D000818:Animals; D002467:Cell Nucleus / Q000648:ultrastructure; D002470:Cell Survival; D003712:Dendrites / Q000648:ultrastructure; D004032:Diet; D002479:Inclusion Bodies / Q000648:ultrastructure; D008136:Longevity; D008854:Microscopy, Electron; D009474:Neurons / Q000166:cytology; D051381:Rats; D011919:Rats, Inbred Strains; D014793:Visual Cortex / Q000166:cytology* / Q000648:ultrastructure