The effect of ageing on the posterior medial and posterior lateral subnuclei of the bed nucleus of the stria terminalis in the mouse.

The posterior medial and posterior lateral subnuclei of the bed nucleus of the stria terminalis were examined in male ASH/TO mice aged 6, 15, 25, 28 and 31 months using quantitative histological techniques. Neuron number in the posterior lateral subnucleus remained constant from 6 to 31 months (mean 1918 +/- 60) whereas in the posterior medial subnucleus neuron number fell from 5165 +/- 145 at 25 months to 4197 +/- 172 at 28 months. There was no further decrease in neuron number at 31 months (4034 +/- 55).

Stability of neuron number in the lateral part of the nucleus of the solitary tract in the ageing mouse brain.

Neuron number was estimated in the lateral part of the nucleus of the solitary tract of the mouse brain at 6, 15, 22, 25, 28 and 31 months of age. There was no significant variation in neuron number with age with an overall mean of 8500.

Stability of neuron number in the ageing mouse paraventricular nucleus.

The number of neurons in the paraventricular nucleus was estimated in brains from male mice aged 6, 25, 28 and 31 months. There was no significant variation with age in neuron number (mean 2715). At all ages most neurons were parvocellular neurons and the neurosecretory magnocellular neurons made up only 10% of the total. There was no significant variation in neuronal nuclear diameter (mean 9.4 microns) with age. The nuclear diameter of both parvocellular and magnocellular neurons was identical. The difference in size between the two types of neurons was due to the difference in volume of their perikarya.

Stability of neuron number in the subthalamic and entopeduncular nuclei of the ageing mouse brain.

The subthalamic and entopeduncular nuclei of mice aged 6, 15, 25, 28 and 31 months were examined in parasagittal 6 microns sections using quantitative histological techniques. The mean number of neurons in the subthalamic (overall mean 5366) and entopeduncular (overall mean 1101) nuclei did not vary significantly with age. The number of sections containing the subthalamic nucleus increased progressively in number with age with the increase beginning between 15 and 25 months. The increase in size of the nucleus was accompanied by a decrease in neuron packing density. No similar changes were observed in the entopeduncular nucleus despite its close anatomical and functional relationships to the subthalamic nucleus.

Stability of motor neuron number in the oculomotor and trochlear nuclei of the ageing mouse brain.

The total number of neurons in the oculomotor and trochlear nuclei of the mouse brain was estimated in three sets of serial sections at 6, 25, 28 and 31 months of age. Due to the oculomotor nucleus being completely intact in only one side of the brain, in each set of sections some counts were carried out in sagittal sections from the right half of the brain and other counts were carried out in coronal sections from the left half of the brain. It proved impossible to identify the boundary between the oculomotor nucleus and trochlear nucleus in the coronal sections so that in such sections the combined total of neurons in both nuclei was estimated. The oculomotor nucleus could be clearly identified in sagittal sections and therefore the total number of oculomotor neurons was estimated in eight brains (three at 6 months, two at 25 and 28 months and one at 31 months). The trochlear nucleus was intact in all but one of the sets of sagittal sections and trochlear neuron number was estimated separately in eleven brains. The total number of neurons in both nuclei did not vary significantly with age (mean 432). The mean number of oculomotor neurons in the eight brains was 341 and the mean number of trochlear neurons was 77. There was no variation in nuclear diameter at different ages nor was there any marked loss of Nissl substance or lipofuscin accumulation in the motor neurons with age.

An ultrastructural study of ependymal cell differentiation during lizard (Gallotia galloti) midbrain development.

Ependymal cell differentiation was examined in the lizard Gallotia galloti from E31 to adult. From E31 to E34 only one type of cell could be identified making up the pseudostratified columnar neuroepithelium but by E35 to E37 three types of ependymal cell were present. The first type was a narrow, elongated, columnar cell containing rough endoplasmic reticulum filled with an amorphous ground substance similar to that of astrocytes. The second type was broader with the nucleus close to the ventricular surface with numerous lipid droplets of varying sizes in the cytoplasm. The third type had an irregularly shaped apical nucleus and a broad basal process probably extending to the pial surface. The process contained numerous microtubules, glycogen granules and a few filaments. From E38 to hatching the ependyma showed marked regional variation. Much of it was formed by a single layer of moderately dark cuboidal cells but parts were made up of a low columnar epithelium in which the cells had elongated nuclei, frequently indented on the ventricular side. Cilia were common and often cells had cytoplasmic protrusions into the ventricle. Lipid was present in the form of small apical droplets or a large basal droplet. Ependymal cells in the region of the sulcus limitans were packed with lipid as were cells of the adjacent subventricular layer. In the adult the ependymal lining varied from cuboidal to low columnar with nuclear chromatin usually arranged in a reticulated pattern. Two types of ependymal process extending to the pia could be identified. One type was packed with microfilaments whilst the other contained a core of microtubules and scattered glycogen granules. Lipid was still present in the cells of the sulcus limitans.

Stability of neuronal glial number in the aging mouse supraoptic nucleus.

The numbers of neurons and glia in the supraoptic nucleus were estimated in mice aged 6, 25, 28 and 31 months. There were no significant variations in the number of neurons or in the number of glia with age. Measurement of neuronal and glial nuclear diameters at 6, 12, 15, 22, 25, 28, and 31 months showed a steady decrease in neuronal nuclear diameter from 9.2 +/- 0.3 microns at 6 months to 8.3 +/- 0.1 microns at 22 months followed by an increase in diameter between 25 and 31 months to 9.8 +/- 0.1 microns. There was no significant variation in glial nuclear diameter (mean 6 microns) with age. Neuronal Nissl substance decreased with age but lipofuscin accumulation was not a prominent feature of ageing supraoptic neurons.

Stability of motor neuron and interneuron number in the hypoglossal nucleus of the ageing mouse brain.

The number of motor neurons and interneurons in the hypoglossal nucleus was estimated in mice aged 6, 15, 25, 28 and 31 months. The number of motor neurons (overall mean 974) and interneurons (overall mean 125) did not vary significantly with age. Possible reasons for neuron number remaining stable with age were discussed.

Age related changes in neuron number in the tegmental nuclei of Gudden of the mouse.

The number of neurons was estimated in the ventral part of the dorsal tegmental nucleus and in the ventral tegmental nucleus of Gudden in brains of male ASH/TO strain mice aged 6, 15, 25, 28 and 31 months. In both nuclei there was a significant decrease in neuron number after 28 months of age. The possible significance of these results was considered in relation to the connection of Gudden's tegmental nuclei with the mammillary nuclei in which neuron number is stable with age, and with the vestibulocerebellar system which loses neurons with age.

Variation with age in neuron number in the bed nucleus of the mouse anterior commissure.

The number of neurons in the bed nucleus of the anterior commissure (BAC) was estimated at 6, 12, 15, 22, 25, 28 and 31 months. There was a highly significant (p less than 0.001) decline in neuron number with age. Neuron loss was, however, restricted to the period between 15 and 22 months of age with no significant change in neuron number occurring either between 6 and 15 months or between 22 and 31 months of age.

A comparison of age-related changes in neuron number in the dorsal motor nucleus of the vagus and the nucleus ambiguus of the mouse.

The numbers of preganglionic parasympathetic neurons in the dorsal motor nucleus of the vagus and of branchiomotor neurons in the nucleus ambiguus were estimated in mice aged 6, 15, 25, 28 and 31 months. The number of preganglionic neurons fell from 1318 at 6 months to 820 at 31 months with neuron number remaining stable until after 25 months. The number of branchiomotor neurons in the nucleus amgiguus fell from 587 at 6 months to 351 at 31 months, the significant decline in number beginning after 15 months. The retrofacial nucleus, or compact formation of the nucleus ambiguus, did not lose neurons until after 25 months whereas significant neuron loss from the remainder of the nucleus began after 15 months.

An ultrastructural study of the development of astrocytes in the midbrain of the lizard.

Astrocyte development was investigated electron microscopically in the midbrain of the lizard Gallotia galloti from E32 to adult. At E32 only very immature (early) glioblasts were present in the midbrain and similar cells could be found until hatching. From E34 two other types of glioblast could be identified--dark glioblasts which had a slightly greater amount of cytoplasm than early glioblasts and light glioblasts, in which cytoplasmic organelles were more abundant. Both dark and light glioblasts were present in very small numbers in the adults. Astroblasts, which could be identified by the characteristic appearance of their rough endoplasmic reticulum, first appeared at E35, at which stage a few very immature astrocytes containing small quantities of gliofilaments were also present. With increasing age the quantity of gliofilaments in astrocyte cytoplasm increased. Astrocytes in the adult white matter contained very large amounts of gliofilaments whereas those in grey matter contained many fewer gliofilaments and had glycogen granules in their cytoplasm which were rarely present in mature fibrous astrocytes.

An ultrastructural study of the development of oligodendrocytes in the midbrain of the lizard.

Oligodendrocyte development was investigated in the midbrain of the lizard Gallotia galloti using the electron microscope. Oligodendroblasts, which had a pale cytoplasm containing numerous microtubules in the perikaryon and processes, were present from E35. Active oligodendrocytes had a pale nucleus, usually containing a nucleolus, and an electron-dense cytoplasm with long parallel stacks of rough endoplasmic reticulum. These were present from E37 to hatching which coincides with the period of rapid myelination. The three types of oligodendrocyte (light, medium and dark) first classified by Mori & Leblond (1970) in the rat could be identified in the lizard. Light oligodendrocytes were present at all ages from E37 to adult. Medium oligodendrocytes first appeared at E40 and dark oligodendrocytes were present at all ages from hatching onwards.

A comparison of quantitative histological changes in different regions of the ageing mouse cerebellum.

The number of Purkinje cells per mm and the number of granule cells per mm3 were estimated in the lobus simplex of mice aged 6, 15, 22, 25, 28 and 31 months. The results were compared with similar estimations already carried out in the spinocerebellum and nodulus of the same cerebella. All regions showed a decrease of approximately 30% in Purkinje cell number between 6 and 31 months of age with the decrease occurring between 15 and 31 months. At each age examined the number of Purkinje cells per mm was similar in the spino- and pontocerebellum but significantly smaller in the nodulus. Granule cell density was identical in all parts of the cerebellum at all ages. Molecular layer thickness varied significantly with age in all cerebellar regions but this may be an artefactual variation. Granule layer thickness did not vary with age in either the nodulus or spinocerebellum but there was a significant variation in granule layer thickness, in the pontocerebellum due to a substantial decrease in thickness between 28 and 31 months of age. This might be the result of a loss of granule cells in this region which is not apparent in other parts of the cerebellum.

An electron microscopic study of the leptomeninx and associated cells of the aged mouse.

The ultrastructure of the leptomeninx was examined in mice aged 25, 28 and 31 months. Apart from occasional lipofuscin granules there were no obvious age related changes in the ultrastructure of leptomeningeal cells. Granular pial cells usually contained large honeycomb bodies and were a prominent feature of the ageing leptomeninx but in contrast leptomeningeal macrophages showed no evidence of phagocytic activity suggesting that cell death or degeneration was not a feature of cells of the leptomeninx even in extremely old mice.

An ultrastructural study of development of the leptomeninx of the rabbit spinal cord.

Development of the rabbit spinal cord leptomeninges was examined in embryos and fetuses aged 12 to 30 d post-conception. In the early stages of development all mesenchymal cells surrounding the neural tube were structurally similar, resembling immature fibroblasts. At 16 d post-conception cells adjacent to the glia limitans showed little structural change, apart from an increase in the amount of rough endoplasmic reticulum, but cells in the presumptive arachnoid became packed with glycogen. By E22 glycogen was present in pial cells but never in the amounts found in the arachnoid. As development proceeded the amount of glycogen in the leptomeninges declined. Pial collagen increased both in amount and in fibre diameter with age.

A morphological study of the development of the leptomeninx of the fetal rabbit cerebrum.

The development of the leptomeninx of the rabbit cerebrum is similar to that of the rabbit spinal cord. At E12 and E14 the leptomeningeal cells resemble immature fibroblasts. At E16 glycogen granules appear in the leptomeningeal cell cytoplasm and are present in pial as well as arachnoid cells. The amount of glycogen decreases from E22 until by E28 it is rarely found in leptomeningeal cells. Leptomeningeal macrophages are present from E12 but granular pial cells were not observed prior to E16. Initially collagen in the pial layer consists of scattered fine fibrils but by E20 collagen is present in larger amounts and the fibrils are of larger diameter and banded.

A quantitative histological study of Golgi II neurons and pale cells in different cerebellar regions of the adult and ageing mouse brain.

Two types of medium to large sized neurons are present in the granular layer of the mouse cerebellum. One type has a large nucleus with a prominent nucleolus and a moderate amount of cytoplasm containing Nissl substance. This type corresponds to the classical Golgi II neuron. The second type has a much smaller nucleus (mean diameter 8.4 microns) with a darkly staining nuclear envelope which is almost invariably deeply indented by cytoplasmic intrusions. The nucleolus is smaller and less conspicuous than in Golgi II neurons. These neurons are identical to the pale cells described by Altman and Bayer (1977). The numbers of both types of neuron were estimated in the spinocerebellum, lobus simplex and nodulus in mice aged 6, 15, 22, 25, 28 and 31 months. There was no significant variation in the number of either Golgi II neurons or pale cells with age in any part of the cerebellum. The number of Golgi II neurons per mm3 was similar in all parts of the cerebellum (mean 3560 mm3). This was identical to the mean number of pale cells per mm3 in the spinocerebellum and pontocerebellum but in the nodulus pale cells were much more numerous (mean 41,170 per mm3). It is postulated that pale cells are small Golgi II neurons.

Age related changes in neuron number in the combined ventral and lateral pontine nuclei of the mouse.

The ventral and lateral pontine nuclei of mice aged 6, 15, 22, 25, 28 and 31 months were examined in parasagittal 6 m sections using quantitative histological techniques. The total number of neurons in both nuclei declined from 13,983 +/- 326 at 6 months to 7,684 +/- 242 at 31 months. The decline in number began after 15 months at which age lipofuscin was first observed in the neuronal perikarya. The nuclear diameter of pontine neurons increased from 9.4 +/- 0.2 microns at 6 months to 10.9 +/- 0.1 microns at 31 months. The increase in nuclear diameter was first apparent at 25 months. The number of sections containing the nuclei did not change with age (mean 166 +/- 3).