Changes with age in cerebral capillary morphology

Regional density of perfused capillaries and cerebral blood flow in untreated short-term and long-term streptozotocin diabetes

The regional density of perfused cerebral capillaries (rDPC) and regional cerebral blood flow (rCBF) were measured in 12 selected brain regions in rats after 3 and 20 weeks of streptozotocin-induced diabetes and in control groups. After 3 weeks of diabetes, both rCBF and rDPC were unchanged in the diabetic group compared to the control group. A diabetes duration of 20 weeks causing bilateral cataracts induced a significant (p less than 0.05) reduction in rCBF in two structures in the visual system compared to the control group (visual cortex: 105 versus 129 ml 100 g-1 min-1; lateral geniculate body: 106 versus 128 ml 100 g-1 min-1) and in the pontine reticular nucleus (82 versus 128 ml 100 g min-1), whereas rDPC remained unchanged. A highly significant correlation between rCBF and rDPC was found in both control groups (r = 0.8, p less than 0.005) whereas the correlation was more scattered in the diabetic groups (r = 0.6, p less than 0.05). The present results show that during chronic diabetes, a reduction of rCBF does not affect the number of perfused capillaries.

Age related changes in the effect of electroconvulsive shock on the blood brain barrier permeability in rats

Age-related changes in blood-brain barrier permeability to macromolecules were investigated during electrically induced seizures. Evans-blue was used as the barrier tracer. There was no change in the permeability of the blood brain barrier associated with aging in the rats. However, the extravasation of Evans-blue albumin was most pronounced in the brain after ten repeated electroshocks in old rats. In the adult group that was given a single electroconvulsive shock, there was no coloration of the brain tissue, whereas the group given ten repeated electroconvulsive seizures showed slight staining of the thalamic nuclei, hypothalamus, and midbrain in 5 out of 13 rats. In 30-day-old rats, Evans-blue leakage was similar to that of adults, except that the frequency and intensity of blood-brain barrier breakdown was less after ten repeated electroshocks. In 15-day-old rats, the blood-brain barrier breakdown to Evans-blue albumin was the same after a single and ten electroshocks and the same in control and electroshocked rats. According to our results ten repeated electroshocks have a more pronounced effect on the old animals and have less effect on the young animals in comparison to adult ones.

Aging and sex influence the permeability of the blood-brain barrier in the rat

The aim of the present study was to investigate the existence of aging- and sex-related alterations in the permeability of the blood-brain barrier (BBB) in the rat, by calculating a unidirectional blood-to-brain transfer constant (Ki) for the circulating tracer [14C]-alpha-aminoisobutyric acid. We observed that: a) the permeability of the BBB significantly increased within the frontal and temporo-parietal cortex, hypothalamus and cerebellum in 28-30 week old rats, in comparison with younger animals; b) in several brain areas of female intact rats higher Ki values (even though not significantly different) were calculated at oestrus than at proestrus; c) in 1-week ovariectomized rats there was a marked increase of Ki values at the level of the frontal, temporo-parietal and occipital cortex, cerebellum and brain-stem. One can speculate that aging- and sex-related alterations in the permeability of the BBB reflect respectively changes in brain neurochemical system activity and in plasma steroid hormone levels.

Morphometric studies on the microvasculature of pre- and paravertebral sympathetic ganglia in the adult and aged rat by light and electron microscopy

Morphometric measurements have been made by light and electron microscopy on sections of perfused sympathetic ganglia from rats of 6-24 months of age with special reference to the microvascular bed. Capillaries, postcapillary venules and small venules comprised the majority of the vessels studied but small arterioles were, in addition, included in the light microscopical part of the study. Light microscopical measurements using image analysis showed that there was a decrease in the density of the microvascular bed (number of vascular profiles/area) and in the total vascular luminal area with age in both ganglia. The ratio of neurons to microvessels remained constant in the superior cervical ganglion (SCG) but decreased with age in the coeliac-superior mesenteric ganglion (CSMG). However, the distribution of microvessels in relation to individual neurons remained unchanged throughout life in both ganglia. Ultrastructural studies revealed fenestrations in 12% of SCG microvessel profiles and in 38% of CSMG microvessels at 6 months, but the percentage of fenestrated profiles in the CSMG had declined by 24 months. There were no significant differences in the number of fenestrations per fenestrated profile. The basal lamina surrounding the microvessels increased significantly (almost doubling) in thickness with age. The range and distribution of microvessel wall thicknesses, expressed as harmonic mean wall thickness, were comparable in both ganglia at both ages and increased linearly according to the amount of pericyte covering present. No consistently significant relationships could be discerned between the microvessel wall thickness and luminal diameter or between the wall thickness and the area available to a given volume of blood for exchange of metabolites (luminal perimeter/luminal area). We conclude that the ganglionic capillary bed is similar in both ganglia and, in old age, accommodates structural changes that occur in the ganglion by maintaining its structure and relationship to individual neurons.

Progressive failure of cerebral angiogenesis supporting neural plasticity in aging rats

Previous work has demonstrated substantial formation of new synapses and capillary branches in visual cortex of young rats provided with complex experience. Synaptogenesis appears greatly weakened in old rats, however, perhaps because of an age-associated impairment of metabolic support. We have examined capillaries in visual cortex from eight 14-month-old and nine 24-month-old rats that had been kept for 50 days in either a complex environment with toys and other rats or in the standard laboratory condition they had been raised in. In spite of tissue expansion that increased cortical thickness and spread apart existing blood vessels in 14-month-old rats that received complex experience, the density of capillaries was not affected. These results indicate that new capillaries infiltrated the expanding tissue. These rats also had significantly more small-diameter capillaries, possibly reflecting the immaturity of new vessels and effectively reducing the maximum amount of blood available to the tissue. Similar but nonsignificant trends were observed in the 24-month-old animals given complex experience. These results suggest that angiogenesis, while it does occur, is substantially impaired in middle-aged animals, and a failure of angiogenesis in old rats may explain their reduced capacity for synaptogenesis.

In vivo [31P]NMR studies on the influence of age on rat brain hypoxia

In this paper the response of cerebral phosphate metabolism to mild hypoxia in young, medium and old rats has been studied via in-vivo [31P]nuclear magnetic resonance (NMR). It was found that the young adults (5-6 months) were more sensitive to this mild stress than either the mature adult (11-12 months) or senescent (23-24 months) rats even though the depth of hypoxia (paO2 = 45-55 mm Hg) was equal for all age groups. They displayed an earlier onset of acidosis, a greater fall in PCr and larger rise in Pi. This response is presumably an attempt to maintain adequate adenosine triphosphate (ATP) levels via anaerobic glycolysis. In contrast, mature adults and senescent adults appear to be able to maintain ATP levels by increasing mitochondrial rates. Acidosis is less severe as are drops in PCr and rises in Pi. Recovery is less complete for the young rats: Pi levels remain high while PCr and pHi levels stay low after normoxia has been reinstigated. All metabolite levels in the mature and senescent adults return to within 10% of control levels. All the data were analyzed and differences were found to be statistically significant. This study reveals that, contrary to popular belief, mature and old rats respond more favorably to reduced O2 than younger individuals. This is due to a more severe anaerobic acidosis in the latter age group. Speculations to explain this disparity are based on the fact that previous in-vitro studies involve systems that are totally or partially disconnected from the organism will not account for important feedback control present in an in-vivo system as studied here.

Effect of aging on the blood-brain barrier

Aging is commonly associated with progressive deterioration in central nervous system (CNS) function. Nutritional factors or environmental toxins have important effects on CNS degenerative changes. The blood-brain barrier (BBB) is a major modulator of nutrient delivery to the CNS. The tight junctions and the paucity of pinocytosis or fenestrations in brain capillary endothelium act as an effective barrier between the CNS and the circulating toxic agents. Senescence is associated with significant, though often subtle, changes in BBB. Conditions which are commonly associated with aging, such as hypertension and cerebrovascular ischemia, aggravate the age-related alterations in BBB function. The histologic changes in brain vasculature with aging is region selective and species specific. The common age-related histologic changes include loss of capillary endothelial cells, elongation of the remaining endothelial cells, and decreased capillary diameter in rat cortex, but not in the monkey or human cortex, and a decrease in the number of mitochondria in endothelial cells of the brain capillaries in the monkey but not in the rat. The age-related alterations in BBB transport function include a decrease in BBB choline transport with aging and decreased brain glucose influx. The BBB neutral amino acid transport appears to be unaltered in the aged mice. Most of the studies reported so far have failed to show a significant age-related alteration in BBB permeability to water-soluble substances and high molecular weight solutes in the absence of neurological disease. A more profound change in BBB permeability appears to be associated with Alzheimer's disease. Immunohistological studies have demonstrated the presence of serum proteins in the cerebrovascular amyloid in patients with Alzheimer's disease.(ABSTRACT TRUNCATED AT 250 WORDS)

The ultrastructural features of secretory cells of some endocrine glands in aging

In the electron microscopic investigation of the secretory cells of adenohypophysis, adrenal cortex, adrenal medulla and pancreatic islets from the adult and old Wistar male rats, certain age-related ultrastructural features have been found. Age changes appeared to be more pronounced in the thyrotrophs, somatotrophs and gonadotrophs of the adenohypophysis and in zona glomerulosa and zona reticularis spongiocytes of the adrenal cortex. They consisted of atrophy of the Golgi apparatus, appearance of the cytoplasmic vacuoles, lipid and lipofuscin granules, secondary lysosomes and damage of the inner mitochondrial membrane. Parallel to these, hypertrophy of the Golgi apparatus and rough endoplasmic reticulum, formation of giant mitochondria and presence of a great number of secretory cells in the cellular cytoplasm were noted in zona fasciculata spongiocytes and chromaffin cells of the adrenal medulla, and in beta cells of the pancreatic islets during aging thus evidencing for the adaptive changes in the ultrastructure of these cells. However, no appreciable age changes have been observed in the ultrastructure of the adrenocorticotropic cells of the adenohypophysis.

Aging in the rat medial nucleus of the trapezoid body. III. Alterations in capillaries

The medial nucleus of the trapezoid body (MTB), a large cell group in the rat brainstem auditory pathway, undergoes significant cell loss and loss of synapses with advancing age [5,6]. The purpose of the present study was to examine the microvasculature of the MTB in rats of the following ages: 3 months (MO), 6 MO, 24 MO, 27 MO, and 33 MO. In rats aged 24 to 33 MO, the following ultrastructural changes were observed in MTB capillaries: (1) large cavitations or spaces within capillary basal laminae, and (2) membranous debris, indicative of cellular degeneration within leaflets of capillary basal lamina. The volume density ratio (VDR) of capillaries decreases significantly between 6 and 33 MO of age.

Integrity of blood-brain barrier to peroxidase in senescent mice

The brain distribution of systemically-administered horseradish peroxidase was studied in senescent mice and compared with the distribution in a group of young mice. The distribution of HRP was surveyed in both the experimental and control groups by light and electron microscopy by an observer unaware of the source of the material. No qualitative differences were observed in the brain distribution of systemically-administered HRP in old mice compared to young mice. The results of this study suggest that the blood-brain barrier to HRP is preserved in senescent mice.

Cerebellar capillaries. Qualitative and quantitative observations in young and senile rats

Ultrastructural changes including reduced electron density, reduction in polysomes and cisternae of rough endoplasmic reticulum occur in tthe cytoplasm of endothelial cells and pericytes in the cerebellar cortex of senile virgin female Han: WIST-rats in comparison to 3-month old virgin rats. processes of pericytes cover less of the capillary surface in the cerebellar cortex of senile rats; moreover, arithmetic and harmonic mean thickness of the endothelium and relative volume of mitochondria in endothelial cells and pericytes are reduced, whereas he luminal diameter of the capillaries, harmonic and arithmetic mean thickness of pericytes and their processes and of the basal laminae between endothelial cells and astrocytes (abbreviated BAL 1), pericytes and astrocytes (BAL 2) and endothelial cells and pericytes (BAL 3) increase. The increase in harmonic mean thickness of the basal laminae is statistically significant (alpha less than or equal to 0.05) and compensates for a decrease in thickness of capillary endothelium. Consequently, the total barrier mass and thickness of cerebellar cortical capillaries in senile animals is higher than in young individuals.

Increased blood--brain barrier transport of protein-bound anticonvulsant drugs in the newborn

The extraction of heroin, caffeine, diphenylhydantoin, and phenobarbital has been measured in the newborn, suckling, and adult brain. Anticonvulsant drugs such as diphenylhydantoin and phenobarbital are bound by plasma protein, and it is generally believed that only the fraction of drug that is free (dialyzable) in vitro is available for transport through the blood-brain barrier in vivo. In both the adult and neonatal rat or rabbit, lipid-mediated transport of free phenytoin occurs. In addition, a fraction of the drug that enters the capillary bound to plasma protein also gains access to the brain. A greater amount of protein-bound drug permeates the newborn brain, and this is ascribed to a longer capillary transit time in the neonate. With regard to phenobarbital, the total (i.e., both free and protein-bound) plasma drug enters the newborn brain. In contrast, no protein-bound phenobarbital permeates the adult brain, and it is only the free drug fraction that gains access to the brain. Since the blood-brain barrier permeability-surface area product for the two anticonvulsants is unchanged in newborn and older animals, the age-related differences in brain uptake of protein-bound drugs can be attributed to developmental changes in cerebral blood flow and capillary transit time. The increased transport of protein-bound drugs in the newborn may cause increased concentrations (i.e., brain:plasma ratios) of these anticonvulsants in the neonatal brain.

Age-associated changes in the effects of amphetamine on the blood-brain barrier of rats

The effects of varying doses of amphetamine on the permeability of the blood-brain barrier (BBB) to albumin were studied in young and aged Fischer 344 rats. There was no change in the permeability of the BBB associated with aging as revealed by saline-treated control experiments. The changes in the permeability of the BBB did not correlate with the changes in blood pressure produced by corresponding doses of amphetamine in the young or aged animals. In the dose range reported the young and aged rats showed similar pressor responses to amphetamine. The aged rats showed a greater increase in the permeability of the BBB than the young, and this effect was seen with a lower dose of amphetamine in the aged rats. At the highest doses tested the permeability was restored to control levels in both the young and the aged rats. The enhanced vulnerability of the BBB of the aged rats may be related to a deterioration of the noradrenergic control of cerebrovascular permeability.

Age-related changes in rat brain capillaries

We have measured several morphological parameters by electron microscopy of the frontal cortex (FC) and hippocampal CA1 (HC) capillaries in male Fischer 344 rats 3-, 9- and 24-months old. The results indicate that with increasing age there is an increase in the cross-sectional area of the basement membrane, increase in the fraction of endothelial cell and pericyte cytoplasmic area occupied by mitochondria in the FC, increase in the size of the pericyte mitochondria in both the FC and HC, increased capillary lumen area in the FC and decreased capillary lumen area in the HC. Also, the cytoplasmic area occupied by mitochondria in capillary pericytes is larger than in the endothelial cells of both FC and HC. These results suggest that there is regional variation in the age-associated changes in capillary morphometrics.

Capillaries in aging rat olfactory bulb: a quantitative light and electron microscopic analysis

Olfactory bulbs from Charles River (Crl) rats from 3 to 36 months have been examined with light and electron microscopy. Total capillary length, surface, and volume, as well as number of endothelial cells, increases during the twofold increase in olfactory bulb volume from 3 to 18 months, but the relative density of these parameters shows no change during this time; from 18 to 36 months when neuronal cell body and dendrites are decreasing markedly in size, the relative density of capillaries shows only a modest decrease. Capillary lumen size and capillary wall thickness remain the same throughout life, but basal lamina thickness doubles from 3 to 24 months and then remains constant from 24 to 36 months. The incidence of several unusual ultrastructural features of the outer capillary basal lamina has been shown to increase with age.