Marian C. Diamond

Morphologic cerebral cortical asymmetry in male and female rats

Abstract Our results indicate that specific regions in the right cerebral cortex of the young adult male rat are thicker than the corresponding regions on the left. The differences attain statistical significance in areas 17, 18a, and 39. In contrast, in the young adult female, specific regions in the left cortex are uniformly thicker than the right, though the differences are not statistically significant. However, if the female is ovariectomized at birth, by young adulthood the right-left cortical pattern is similar to that of the male.

Morphological changes in the young, adult and aging rat cerebral cortex, hippocampus, and diencephalon

This study was designed to serve as a standard for experiments studying effects of behavior or other variables on the anatomy of the rat brain. The depth of the cerebral cortex, the hippocampus, and the diencephalon were measured, as well as the width of the diencephalon, in male, Long-Evans rats in the following age groups: 6, 10, 14, 20, 26, 41, 55, 77, 90, 108, 185, 300, 400, and 650 days. In general, the depth of all the forebrain structures increases to 26 days of age at which time the cerebral cortex decreases while the hippocampus and diencephalon continue to increase until 650 days of age. A search for hemispheric dominance in the rat showed the right cerebral cortex to be thicker than the left in all age groups in 92 out of 98 areas measured. The body weights and endocrine organ weights were recorded.

Effects of differential environments on plasticity of dendrites of cortical pyramidal neurons in adult rats

Thickening of the frontal cortex and especially the occipital cortex was observed in adult rats after exposure to the “enriched” condition. An increase in branching and in length of terminal segments was found in the dendritic tree of pyramidal cells in layers II and III of the visual cortex of the adult rat after exposure to “standard” and enriched conditions. These exposures began at day 112 and continued 30 days. The increase observed in the basal dendritic tree of pyramidal cells in the superficial layers was significantly greater in the enriched conditions than in the standard condition. It appeared, furthermore, that branching occurred predominantly on basal terminal segments of all orders at a considerable distance from the tip. This mode of growth is similar to that observed in the cortex of normal immature rats. The differential conditions did not influence the bifurcation angles. The dendritic and cortical changes and changes reported in the literature indicate that the effects of differential experience are not limited to a short, “critical” period.

Quantitative Synaptic Changes With Differential Experience In Rat Brain

Significant differences in size and number of synaptic junctions were found between littcrmate rats assigned at weaning (25 days of age) to enriched or impoverished environments and kept there for 30 days. The synapses measured were asymmetrical axodendritic junctions in the neuropil of layer III of the occipital cortex. Rats given experience in the enriched condition (EC) showed, in comparison to littermates in the impoverished condition (1C). synapses that averaged 52% greater in length but that were only 67% as numerous. The EC rats had more large synapses as well as fewer small synapses than did IC rats, so the EC size distribution could not have been derived simply by loss of small synapses from the IC distribution. The total area of synapses in the EC group, taking both size and number of contacts into account, was 40% greater than in IC. Thickness of cortex was 4.0% greater in EC than in IC, a value that compares closely with the 4.6% found in several previous 25-to-55 day EC-1C experiments. Proble...

Environmental enrichment and the brain.

An intriguing capacity of the adult nervous system for structural and functional modification in response to external stimuli (plasticity) has been the focus of research efforts for decades. This review shows history of ideas about brain changes in relation to experiential factors and surveys experimental studies of the impact of enriched environment on the brain and behaviour, in adult, aged and injured nervous system.

Rat Brain: Effects of Environmental Enrichment on Wet and Dry Weights

Wet weight of rat cerebral cortex was increased by exposure to an enriched environment, as compared with standard colony or impoverished conditions. Dry weights and wet weights were compared and both yielded identical percentage differences between brains of animals experiencing enrichment and those experiencing impoverishment.

Morphologic hippocampal asymmetry in male and female rats

Abstract Our findings indicate that the hippocampus of the rat varies in structure in the right and left hemispheres and in males and females. A morphologic study of the thickness of the dorsal hippocampus was carried out on celloidin-embedded histologic sections from male, Long-Evans rats of the following ages: 6, 10, 14, 26, 41, 55, 77, 90, 108, 185, 300, 400, and 650 days. Between 15 and 25 rats per age group were used, a total of 225 male rats. In addition, the hippocampi were measured on 47 Long-Evans female, 90-day-old rats: 11 normal and 36 animals ovariectomized one day after birth. We found that in males the right hippocampus was significantly thicker than the left for some but not all age groups. In the female at 90 days of age, the left hippocampus was thicker than the right. This left-right pattern in the female hippocampus did not reverse, as it did in the cerebral cortex after ovariectomy at birth.

On the brain of a scientist: Albert Einstein

Neuron:glial ratios were determined in specific regions of Albert Einsteins cerebral cortex to compare with samples from 11 human male cortices. Cell counts were made on either 6- or 20-micron sections from areas 9 and 39 from each hemisphere. All sections were stained with the Klüver-Barrera stain to differentiate neurons from glia, both astrocytes and oligodendrocytes. Cell counts were made under oil immersion from the crown of the gyrus to the white matter by following a red line drawn on the coverslip. The average number of neurons and glial cells was determined per microscopic field. The results of the analysis suggest that in left area 39, the neuronal: glial ratio for the Einstein brain is significantly smaller than the mean for the control population (t = 2.62, df 9, p less than 0.05, two-tailed). Einsteins brain did not differ significantly in the neuronal:glial ratio from the controls in any of the other three areas studied.

Chemical and Anatomical Plasticity of Brain: Replications and Extensions, 1970

The search for changes in the brain resulting from experience dates back at least two centuries. Only in the last few years, however, has it become clear that environmental variables, including learning and memory, can produce neurochemical and anatomical changes in the brain. In the present volume many of the chapters discuss experiments in which variables in the environment are shown to cause measurable changes in the synthesis and/or composition of neurochemicals.

Age-related morphologic differences in the rat cerebral cortex and hippocampus: Male-female; right-left

This paper is one of a series presenting right-left differences in the morphology of the rat forebrain, but this presentation differs from the previous ones by offering age-related changes in both sexes. Long-Evans rats were housed with the dam prior to weaning at 21 days of age and three to a cage thereafter. The ages of the animals studied were 6 to 7, 14, 21, 90, 180 to 185, 390 to 400, and 870 to 876 days. The thicknesses of the cerebral cortex and of the hippocampus were measured on microslide-projected images of thionin-stained sections. We learned that the cerebral cortex of the male rat was thicker on the right side than on the left at all ages in 41 of 42 measures, being statistically significant in 30 of 42 measures. Areas 10, 3 and 17 showed the most marked differences at all ages. In the female rat, laterality was not so well defined, but, in general, the left cerebral cortex was thicker than the right in 33 of 54 measures, but in only 5 of the 54 were statistically significant differences found. The right-left differences in the hippocampus followed the pattern of the cortical differences in the male and female rats. The right male hippocampus was thicker than the left at all ages, with greater differences noted in the younger than in the older groups. The female left hippocampus was thicker than the right, but only in the 90-day group was the difference significant.