Ruth E. Johnson

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.

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.

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.

Occipital cortical morphology of the rat: alterations with age and environment.

Abstract With the use of Golgi impregnation, this study demonstrated dendritic proliferation in layers II and III in the medial occipital cortex of 444- and 630-day-old male rats. Increases occurred in animals housed in either enriched or standard colony conditions. Specifically, third- and fourth-order basal dendrites increased significantly in frequency from 414 to 444 to 630 days of age. This study approximated a longitudinal study because the different age groups were littermates. The finding of an increase in dendritic branching in old age was not new, but our study was the first to note this increase in the rats cerebral cortex. In a separate study the cortical morphology was examined in 90- and 630-day-old rats which had been living together in a single enriched environment for 30 days. The brains of these rats were compared with littermates living with their respective age groups in standard colony conditions. The dendritic pattern was similar in those two age groups irrespective of environment. Only the sixth order significantly differed, with the frequency of branching being greater in the 630-day-old animals. An increase in cortical thickness in the enriched animals was apparent compared with controls, but the differences were not significant. Because previous results showed the 60- to 90-day-old enriched rats without old companions developed a significantly thicker cortex than standard control littermates, it is possible that when young rats live with old rats they do not interact with their environment as musch as when living with other young rats.

Changes in neuron number and size and glia number in the young, adult, and aging rat medial occipital cortex.

We previously reported changes in the Long-Evans, male rat cerebral cortical thickness as a function of age between birth and 650 days of age [Diamond, M. C., Johnson, R. E., and Ingham, C. (1975). Behav. Biol. 14 , 163–174]. On the adjacent celloidin-embedded sections from the 26-, 41-, 108-, and 650-day age groups in that study, cell counts and measurements were taken in the present study. Neurons, astrocytes, and oligodendrocytes were counted in the medial occipital cortex sectioned at the level of the posterior commissure. In addition, comparisons were made between neuron density as a function of age in the upper and lower halves of the cortical samples. The greatest decrease in density in both neuron and astrocytes and oligodendrocytes occurs before 108 days of age, with a nonsignificant density decrease after this time until 650 days of age. The lower cortical layers indicate a greater decrease in density before 108 days of age than do the upper layers. The area of the perikarya and nuclei decreases significantly before 108 days of age but not between 108 and 650 days of age. These cell counts and neuron size measurements offer encouraging results regarding the aging mammalian cortex of an animal living in a standard laboratory environment.

A comparison of cortical thickness in male and female rats—normal and gonadectomized, young and adult

Removal of rat ovaries at Day 1 increases cortical thickness by Day 90 when compared with intact littermates (C. Pappas, 1977, Ph.D. Thesis, University of California, Berkeley, Calif.) . In the present experiments, using Day 1 sets of sextuplets, one male and one female were gonadectomized; one male and one female were sham-operated; one male and one female were left intact to serve as normal controls. After weaning at Day 21, the animals were separated three to a cage (20×20×32 cm) according to sex and condition. At 90 days of age all were ether-anesthetized and sacrificed. From Formalin-perfused and fixed frozen brains, transverse sections were cut from motor, somesthetic, and occipital regions. Projected, thionin-stained sections were outlined and the cortex was measured. Significant differences in cortical thickness were seen between ovariectomized rats compared with sham-operated littermates. There were no significant cortical thickness differences between normal intact males and females; or between rats ovariectomized at Day 90 and Day 300 compared 90 days later with sham-operated littermates.

Brain Plasticity Induced By Environment and Pregnancy

Histological studies of brains from rats experiencing enriched (EC) or impoverished (IQ environmental conditions were carried out. Cerebral cortical depth measurements, body weights and endocrine organ weights were taken from the following groups of animals: male rats in EC vs. IC, non-pregnant female rats in EC vs. IC, pregnant rats from EC and IC, and the offspring from EC and IC parents.Male and female rats lived separately in their EC and IC cages from 60 to 90 days of age. Then one EC male lived with one EC female, and one IC male with one IC female, in a small cage for five days. After mating, all animals were returned to their original conditions with slight alterations. After birth, the parents and offspring were weighed, anesthetized, and perfused with 10% formol-saline. Transverse sections from the frontal, somesthetic, and occipital cortex were takenA separate group of non-pregnant female rats was treated in a similar manner, except that instead of mating a male and female two females were plac...

A morphological study of male rat cerebral cortical asymmetry

Reports of morphologic asymmetry in the mammalian brain are becoming the rule rather than the exception. In a previous publication we noted that in the male Long-Evans rat the right cerebral cortex was generally thicker than the left cortex in all nine areas measured. In the present study, in the majority of cortical areas measured, the right hemisphere was also found to be thicker than the left in the S1 strain of rats for four age groups and under three experimental conditions. The ages at the commencement and termination of exposure to enriched, standard colony, and impoverished conditions were 25 to 55, 60 to 64, 60 to 90, and 25 to 105 days. In some areas the magnitude of the hemispheric asymmetry varied across the different age groups. The environmental conditions affected the degree of right-left difference in one cortical region, medial area 10.

Aging and environmental influences on two types of dendritic spines in the rat occipital cortex

Abstract The density of dendritic spines was determined by counting spines on 34-μm segments from basal branches of pyramidal cells in layers II and III of the rat occipital cortex. Counts began at the first bifurcation site from the soma, and one segment from each side of the neuron was studied. The results of this investigation indicated a marked decrease in spines with a lollipop (type L) configuration from 90 to 414 days of age. After this decrease, the density of type L spines increased to 630 days to the same density as they were at 90 days. The presence or absence of type L spines was not affected by housing the animals in an enriched environment. In contrast to the type L spines, another type of spine, those with a nubbin configuration (type N) increased in density at each age. The density of these type N spines also appeared subject to environmental influences in the oldest group. We conclude that type L spines, after decreasing to the adult level, increase as the animal approaches senescence perhaps as a compensatory mechanism. On the other hand, type N spines increase with age and are responsive to the environment in the old animals. Type N spines possibly represent degenerating spines.