Biomedical subjects

A M Sirevaag

Publications and source records attributed to A M Sirevaag.

9 recordsLinked to original sources

PubMed1993

A method for quantification of astrocytic processes reveals laminar differences in the dentate gyrus but not in CA1 of the hippocampal formation.

The distribution of astrocytic processes in the dentate gyrus molecular layer and CA1 subregion of the hippocampal formation was examined in 8-microns frozen sections from adult male rats. The stereological cycloid intersection method (Baddeley et al., 1986) was used to estimate surface density of glial fibrillary acidic protein-immunoreactive astrocytic processes. A distinct lamination pattern was delineated in the dentate gyrus which corresponds to the afferent input to this region. No such pattern was detectable in s. radiatum of CA1. By using this relatively new stereological method which utilizes a sensitive sampling scheme, it was possible to increase the reliability in reporting the distribution of fine processes while at the same time greatly reducing the amount of time necessary to estimate the amount of astrocytic processes in a given region.

Animals↗

PubMed1991

Plasticity of GFAP-immunoreactive astrocyte size and number in visual cortex of rats reared in complex environments.

Previous studies have indicated effects of postweaning rearing environment complexity on astrocyte nuclei. This study examined the effects of rearing for 10, 30 or 67 days in a complex (EC), social (SC) or individual cage (IC) environment upon glial fibrillary acidic protein (GFAP) immunoreactive astrocytes of the occipital cortex. EC rats exposed to their environment for 30 days or longer had a greater surface density of astrocytic processes (Sv) than SC or IC rats. The greater surface density of EC cortical astrocytes appeared to be due to an increase in the mean size of astrocytes after 30 days of differential environmental exposure. After 67 days of environmental exposure, however, the greater Sv appeared to be due to an increase in the number of astrocytes. Astrocytic plasticity appears to develop rather slowly during exposure to a complex environment and appears to involve two stages. The first stage is a hypertrophy of existing astrocytes and the second stage involves proliferation or retarded death of astrocytes. These changes may be related to brain information processing since astrocytes are known modulators of synaptic activity and may possibly serve as regulators of synaptic density.

Analysis of Variance↗

PubMed1991

Astrocyte hypertrophy in the dentate gyrus of young male rats reflects variation of individual stress rather than group environmental complexity manipulations.

Glial hypertrophy is associated with synaptogenesis in visual cortex and with stress-induced damage in the hippocampus. This study examined astrocytes in the dentate gyrus of male weanling rats exposed to complex or standard laboratory environments. No group differences in astrocytic surface density were observed, as expected in this brain region where group differences in synaptogenesis in male rats are reportedly minimal. Similarly, no group differences in adrenal weight were observed. Across all treatment groups, however, a significant positive correlation (r = 0.57) between adrenal weight and surface density of astrocytic processes was found. Considerable variation in responses of individual rats to their environments occurs in both the complex and the laboratory cage environments, and animals responding poorly may have had heavier adrenals and greater astrocyte reactivity in the dentate gyrus. Thus astrocyte hypertrophy in the dentate gyrus reflects the stress history of the individual rat and not any differential effects of rearing in a complex or a laboratory cage environment.

Adrenal Glands↗

PubMed1989

Effects of complex experience on somatic growth and organ development in rats.

Rats kept in complex environments (EC) show an array of brain changes relative to animals housed individually (IC). These effects have been explained as due to (a) information storage, (b) chronic stress that causes brain damage, or (c) neuroendocrine effects on brain maturation. Complex experience also affects somatic growth and organ development, and these may be related to the EC/IC brain differences. We have compared somatic growth and internal organs of 315 weanling and adult rats with various histories. (a) Young EC rats showed slower skeletal and visceral growth, while many brain components expand. (b) Although thymus and spleen were lighter in young ECs, immunocompetence was nonsignificantly (p less than .07) higher than in ICs. (c) Somatic growth of adult rats was slow and not very responsive to experience, whereas studies have shown EC/IC brain effects similar to those in young rats. (d) Males had slightly greater EC/IC somatic and visceral differences. (e) The stress index, adrenal weight, varied across age and experience, so chronic stress can not explain EC/IC brain differences. Training paradigms show brain changes similar to those from complex experience, occurring specifically with learning and in brain regions using the information. Learning and memory, therefore remain the best explanation of the EC brain effects.

Adrenal Glands↗

PubMed1988

Direct evidence that complex experience increases capillary branching and surface area in visual cortex of young rats.

Rats housed in complex environments with toys and other rats generate new synapses, and the expanding neuropil tends to spread apart existing blood vessels. Previous work demonstrated that weanling rats kept in complex environments had more closely packed capillaries, suggesting that new capillaries had sprouted into the newly added neuropil. The present study directly investigates the issue of new branching by using india ink perfusions of weanling rats kept for 30 days in a complex environment (EC), paired in standard caging (SC), or individual cages (IC) to examine the density of capillary branch points and the capillary surface area per unit tissue volume. EC rats had a greater density of branch points than the SC and IC littermates, a finding consistent with increased capillary sprouting. Capillary surface area per unit tissue volume and the number of branch points per unit of capillary surface area were also higher for EC rats. This suggests that blood vessels of EC rats branch off more often than those of animals kept in more standard conditions, and provides further evidence that complex experience can increase angiogenesis in cerebral cortex of postweanling rats.

Animals↗

PubMed1988

A multivariate statistical summary of synaptic plasticity measures in rats exposed to complex, social and individual environments.

Multivariate analysis of variance, canonical discriminant analysis, factor analysis, and stepwise multiple regression were applied to 36 variables representing measures of occipital cortical synaptic, cellular, and vascular morphology in rats reared in complex, social, and individual housing environments. The results indicate differential expression of coordinated vascular and cellular metabolic processes across the three environments.

Analysis of Variance↗

PubMed1987

Complex experience promotes capillary formation in young rat visual cortex.

The metabolic support of neural plasticity was examined by comparing cerebral vasculature of weanling rats reared in complex environments (EC) to littermates reared individually (IC) or socially in pairs (SC). EC rats have a thicker occipital cortex, more synaptic contacts per neuron and larger dendritic arbors compared to SC or IC rats, potentially increasing local metabolic demands on microvasculature. Capillaries of EC rats were closer together than those of SC or IC rats and potentially filled a greater fraction of cortex with blood. The closer capillary spacing in young EC rats suggests compensatory angiogenesis in response to increased metabolic demand.

Animals↗

PubMed1987

Differential rearing effects on rat visual cortex synapses. III. Neuronal and glial nuclei, boutons, dendrites, and capillaries.

Morphological measures of neurons, astrocytes, oligodendrocytes, presynaptic boutons, dendrites and capillaries were examined in the upper 4 layers of occipital cortex in rats reared for 30 days postweaning in complex (EC), social (SC) or individual cage (IC) environments. EC rats had a lower numerical density of neuronal nuclei with a comparable volume fraction to SC and IC rats. The volume fraction of astrocyte and oligodendrocyte nuclei was significantly greater for EC rats than IC littermates, and IC rats also had more synapses and neurons/micron3 of glial nuclei. Environmental groups did not differ in the numerical density of presynaptic boutons but the number of boutons per neuron was greater in EC than in IC or SC rats. This result parallels the findings that EC rats have more synapses per neuron than IC rats. Electron microscopic estimates of dendritic volume fraction confirmed estimates from Golgi-impregnated neurons that there is more dendrite per neuron in the occipital cortex of EC rats than IC or SC rats. EC rats also had a larger capillary volume than SC or IC and these capillaries were closer together and had fewer synapses/micron3 of capillary in ECs. Another indicator of metabolic activity, mitochondria volume per neuron, gave similar results with ECs having a greater volume than ICs and SCs intermediate. These results indicate that not only are there more synapses per neuron in the visual cortex of rats from more complex environments but also that the brain appears to adjust to the metabolic requirements of its synapses or neurons, in terms of vascular, mitochondrial and glial support.

Animals↗

PubMed1985

Differential rearing effects on rat visual cortex synapses. II. Synaptic morphometry.

An array of morphological measurements was made upon spine synapses in the upper 4 layers of occipital cortex of rats reared for 30 days after weaning in complex (EC), social (SC) or isolated (IC) environments. The mean length of the synaptic contact zone (post-synaptic density plus interpolated non-impregnated regions) was greater in layer IV of EC rats than in IC rats. SC rats were intermediate, not differing from other groups. There were no differences in these measures in other layers, nor were there differences in the mean area or perimeter of presynaptic terminals or postsynaptic processes, the relative frequency of headed vs sessile shaped spines, the length of the apposition between pre- and postsynaptic processes, or the ratio of perimeter to area (inverse roundness) of postsynaptic processes. Cleft width was greater in regions of the contact zone where postsynaptic density was present than in regions where it was absent (perforations), but, aside from the previously described differences in the frequency of perforated synapses, there were no group differences in cleft width. The maximum length of synaptic contact zones and the maximum area of presynaptic terminals was greater in EC than in IC rats in layer IV, but not in other layers, with SC rats again intermediate. These results support previous findings of larger layer IV synaptic contacts in EC rats and suggest that the size of some synaptic components can change without changes in others, a population of very large synapses is seen in layer IV of EC rats that is not seen in IC rats, and perforations may be unlikely sites of synapse splitting, given that membranes are more closely apposed in these regions, rather than pulling apart.

Animals↗