Age-related Changes Of Capillaries In Rat Cortex And White Matter

Aging is associated with a deterioration of memory and cognitive function. There are many factors that might negatively affect cognitive function during aging. Among of them, the cerebral vascular system has a major impact on brain function. The cerebral capillaries represent the finest branches of the cerebrovascular tree, and they form anastomoses, create a three-dimensional vascular network and play a crucial role in regulating the surrounding microenvironment and maintaining local brain perfusion. The normal functional activities of neurons and the effective conduction of nerve impulse are all dependent on the morphological and functional integrity of the capillary network. Lots of qualitative studies on age-related changes of the capillaries in the brain indicated the global morphological changes in microvascular structure (e.g., glomerular loops and twisted capillaries) in different regions of the aged brain, and age-related alterations of the microvascular ultrastructure (e.g., atrophy of endothelium, basement membrane thickening, and pericyte degeneration). However, there are only a few quantitative studies in brain capillaries, which are always limited in the cortical and hippocampal regions. Recently, lots of studies using the new stereological methods found that there was no significant loss of cortical neurons. Although a few researchers studied the age-related changes of cortical capillaries, they reported different conclusions, and none of them used design-based stereology principle. Therefore, whether the cortical capillary degenerated during aging needs to be further investigated. Besides, the studies using the unbiased stereological methods indicated the significant atrophy of white matter and the decrease of the total length of myelinated fibers in white matter during aging. Until now, there were no studies investigating the capillary changes in aged white matter. Therefore, in order to obtain an accurate assessment of age-related changes in the cortical capillary network and obtain first information about the age-related changes of capillary in white matter, we investigated the age-related changes of the capillaries in the cortex and white matter of female Long-Evans rats by means of immunohistochemistry and stereological techniques.PARTⅠAGE-RELATED CHANGES OF CAPILLARIES IN RAT CORTEX1. Materials and methods1.1 Ten young (7-month-old) and ten aged (27-month-old) female Long-Evans rats were used.1.2 The rats were anaesthetized and perfusion-fixed. One hemisphere was sampled from each rat brain and then cut into 2-mm-thick consecutive slabs. A 4-μm isotropic, uniform random section was cut from each slab. The sections were stained with immunohistochemistry technique. Under an oil objective lens (100×), 3-5 fields of vision were randomly captured from the cortical region on each section. There were 30 photographs from each rat.1.3 The volume of the cerebral cortex, the volume shrinkage of cortex induced by tissue processing, the length density, the total length, the volume density, the total volume, the surface area density and the total surface area of the capillaries in the cerebral cortex were investigated with the new stereological methods.2. Results2.1 The volume shrinkage of cortex induced by tissue processing was 53.9± 7.3% in young female group and 48.8±8.8% in aged female group. There were no significant differences in the cortex volume between young female group (457.5±37 mm3) and aged female group (426.3±63.6 mm3) (p>0.05).2.2 The total length of the capillaries in the cerebral cortex was 331.9±62.2 m in the young group and 281.6±61.5 m in the aged group, with no significant differences between the two groups (p>0.05).2.3 The total volume of the capillaries in the cerebral cortex was 6.7±1.2 mm3 in the young group and 6.0±1.2 mm3 in the aged group, with no significant differences between the two groups (p>0.05).2.4 The total surface area of the capillaries in the cerebral cortex was 46.5±9.8 cm~2 in the young group and 41.7±9.4 cm2 in the aged group, with no significant differences between the two groups (p>0.05).PARTⅡAGE-RELATED CHANGES OF CAPILLARIES IN RAT WHITE MATTER1. Materials and methods1.1 Ten young (7-month-old) and ten aged (27-month-old) female Long-Evans rats were used.1.2 The rats were anaesthetized and perfusion-fixed. One hemisphere was sampled from each rat brain and then cut into 2-mm-thick consecutive slabs. A 4-μm isotropic, uniform random section was cut from each slab. The sections were stained with immunohistochemistry technique. Under an oil objective lens (100×), the entire white matter region on each section was photograghed. 4-6 fields of vision were captured from each section. There were 30 photographs from each rat. 1.3 The volume of the white matter, the volume shrinkage of white matter induced by tissue processing, the length density, the total length, the volume density, the total volume, the surface area density and the total surface area of the capillaries in white matter were investigated with the new stereological methods.2. Results2.1 The volume shrinkage of white matter induced by tissue processing was 46.4±8.8% in the young female group and 46.1±7.3% in the aged female group. The white matter volume in the aged rats (78.0±16.4 mm~3) was significantly decreased by 14.9% when compared to the young rats (91.7±12.1 mm~3) (p<0.05).2.2 The total length of the capillaries in the white matter of aged rats (23.3±5.1 m) was significantly decreased by 32.2% when compared to the young rats (34.4±7.8 m) (p<0.01).2.3 The total volume of the capillaries in the white matter of aged rats (0.54±0.14 mm~3) was significantly decreased by 33.2% when compared to the young rats (0.81±0.13 mm~3) (p<0.01).2.4 The total surface area of the capillaries in the white matter of aged rats (3.8±0.89 cm2) was significantly decreased by 31.7% when compared to the young rats (5.6±1.0 cm2) (p<0.01).GENERAL CONCLUSIONS1. The present study for the first time combined the new stereological techniques and immunohistochemistry technique to quantitatively study the age-related changes of the capillaries in the cortex and white matter of rat.2. There was no significant alteration in the total length, the total volume and the total surface area of the capillaries in the cortex during aging. 3. The total length, the total volume and the total surface area of the capillaries in the white matter were significantly decreased during normal aging.4. Our study provided the normal data of the total length, total volume and total surface area of the capillaries in the cortex and white matter of female Long-Evans rats. These data will provide the important baseline value to compare with future studies of the effects of the neurodegenerative diseases in CNS on the capillaries in cortex and white matter of this animal model.