A study on the effect of aging on the organization of the septal region in the brain of mice

Abstract EN

The septal region is an important part of the limbic system through wide connections with several brain areas.

It is involved in the control of a variety of behavioral processes related to higher cognitive functions (learning and memory), emotions and autonomic regulation.

The aim of the present study is to demonstrate the structure of the septal region in the young adult mice and to emphasize the aging changes in it using combined qualitative and quantitative methods.

In this study, a total number of 40 male mice was used.

They were divided into two groups.

Group I composed of 20 young adult male mice (3 months old) which considered as a control group.

Group II composed of 20 male aged mice (20-24 months old).

Animals were sacrificed and the septal region was dissected.

In each group, 5 animals were processed for the study by Einarson's Gallocyanine stain, 5 animals were processed for the study by Golgi-Cox method and other 10 animals were prepared for the ultrastructural study by transmission electron microscope.

The total number of cells and the numerical density in the septal nuclei were measured both in the young adult and aged mice.

It was found that the septal region is formed of the lateral septal nucleus, medial septal nucleus, the nucleus of the diagonal band of Broca, septofimbrial nucleus and the triangular septal nucleus.

In the young auult mice, Golgi stain revealed the presence of different types of neurons in the septal nuclei.

The dendrites of these neurons appeared to have long extensions with many arborizations.

The ultrastructural study showed the presence of several types of neurons in the septal nuclei.

Each type of these neurons had distinct ultrastructural features.

In the aged mice, neurons of the septal nuclei appeared to be faint by Gallocyanine stain indicating loss of Nissl granules.

Golgi stain showed apparent tortuosity, decrease in the extension and arborization of dendrites of the neurons together with marked loss of spines.

The ultrastructural study revealed the presence of various degenerative changes involving both the nucleus and cytoplasmic organelles in the different types of neurons of the septal nuclei.

The presynaptic terminals on the cell bodies and dendrites of the neurons showed decrease in the amount of synaptic vesicles.

Measuring the total number of cells and numerical density in all septal nuclei showed highly significant decrease in the aged mice as compared to those of the young adult mice.

In conclusion, this study clearly demonstrates the presence of many morphological differences in neurons of the septal nuclei which reflect differences in the processing of informations.

This can explain the wide variety of functions of this region.

It also demonstrates that neurons of the septal nuclei suffered from the occurrence of many degenerative changes with aging.

These changes may account for the age-related decline in the cognitive functions.