The present study was undertaken to assess age-related changes in the Purkinje's cells in the rat cerebellar cortex. The cellular and nucleolar volumes and the volume percentage of lipofuscin per cytoplasma were measured in six age groups. The number of Purkinje's cells was also counted. The cellular volume of rats aged 18, 24 and 30 months decreased significantly as compared with that of 3-month-old rats. The nucleolar volume of rats aged 12, 18, 24 and 30 months decreased significantly as compared with that of 3-month-old rats. The accumulation of lipofuscin in the cytoplasma of the Purkinje's cells was observed more or less in all ages. The degree of accumulation of lipofuscin in the Purkinje's cells increased with aging. The number of Purkinje's cells at the ages of 24 and 30 months decreased significantly as compared with that of 3-month-old rats.

Six age groups, each composed of four animals from each of the following ages, were used to assess age-related ultrastructural changes in the neuropil of the 111 layer of the frontal cortex in rats: 3, 6, 12, 18, 24 and 30 months old. Random samplings within the neuropil were taken to produce 40 electron micrographs in each rat (totaling 960). The profiles of axon terminals, dendrites and astroglial processes in the neuropil of each micrograph were traced. Then the percentage of their areas for the area of neuropil (relative volume fraction) was examined using the image analyzer system.The relative volume fractions of both the axon terminals and dendrites for the neuropil were found to have decreased in the aged rats. On the contrary, the relative volume fraction of astroglial processes for the neuropil had progressively increased with aging.

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Nerve terminals in the lateral septum were studied by electron microscopy in the rat after lesions of the suprachiasmatic nuclei (SCN). The results were as follows: 1) The electron‐lucent degenerations showed a reduction in the number of vesicles and the swelling of terminals and/or vesicles. These degenerating terminals predominated at two days of survival period. The electron‐dense degenerations which showed a darkening and shrinkage of the terminals mainly appeared at four days of survival period. 2) Most of the degenerating terminals contained large core vesicles of a diameter in the range of 800–1500 A. 3) The percentage of the degenerating terminals to all the terminals on the electron micrographs was about 7%. 4) The F‐type synapses were not found in the lateral septum of the normal and SCN lesion rats. These data confirmed the existence of the projection which reached the lateral septum from the SCN and suggested to us that these synapses were so‐called peptidergic synapses.