Stereological study on the hippocampal neurons of ageing rats

In this study, nuclear diameters and numerical densities of granule and pyramidal cells were determined using stereological formulae. The granule- to pyramidal cell ratio was also estimated. Data obtained from the hippocampal of two, five, twelve and twenty-four months old rats were statistically analyzed. The nuclear diameter was observed to show significant decrease between twelve and twenty-four months in granule cells. In pyramidal cells, it showed a significant increase from two through to twelve months, followed by a significant decrease. The numerical density of granule cells showed a significant decrease between two and five months, followed by stability through to twenty- four months. The numerical density of pyramidal cells showed similar change up to twelve months of age followed by significant increase. This difference between the changes in the granule and pyramidal neurons reflected an increase in the granule-to pyramidal cell ratio with ageing. This was attributed to the difference in the nature of development between the two cell types. The post-natal origin and further adding of granule cells was suggested to result in this difference. It was concluded that the period between five and twelve months of age could be considered a period of structural stability. Between 12 and 24 months, the pyramidal cells were suggested to show ageing manifestation while the granule cells are still enjoying the period of adulthood stability. The increase in the granule-to- pyramidal cell ratio in this period was suggested to manifest deterioration in the information processing mechanisms of the hippocampal neurons

Changes with age in the volume proportions of the hippocampal components

Stereological techniques were employed to examine changes with age in the volume proportions of different hippocampal components. The adult values were compared with those recorded in previous literatures. A significant decrease was observed in the volume proportions of the granular layer in the dorsal lip of dentate gyrus between two and five months of age. Comparing this results with the observed stability in the volume proportions of the granular layer in the whole dentate gyrus led to a conclusion that ventral lip of dentate gyrus showed a stage of increasing growth rate compared with the dorsal lip during this period of life. Stability of the volume proportions of dentate gyrus components was observed between five through to twenty-four months of age. An increase in the volume proportions of the pyramidal layer in the hippocampus between two and five months was attributed to an increase in the volume of the pyramidal neurons in this period. The dentate-to-Ammon's horn volume ratio showed a significant decrease between twelve and fourteen months which was suggested to reflect hippocampal functional change with ageing