Response of the three main types of glial cells of cortex nad corpus callosum in rats handled during suckling or exposed to enriched, control and impoverished environments following weaning

Abstract

The cell populations of the occipital cortex were examined in young rats subjected to different sensory experiences. In one series recently weaned animals were reared in enriched, impoverished or control environments. The enriched environment was obtained by keeping the animals among "toys" and other rats; the impoverished environment, by rearing the animals one per cage in a darkened, quiet room; and the control environment, by housing the animals three per cage under usual animal room conditions. Six recently weaned rats were kept in each environment for 30 days and ten, for 80 days. In a second series suckling rats were handled daily. Handling consisted of touching, holding and rubbing rat pups for 15 minutes per day during the first ten days after birth; twelve rats were studied, six handled and six unhandled controls. In the two series, the animals were sacrificed under anesthesia by perfusion with mixed aldehydes. Semithin epon sections of occipital cortex were stained with toluidine blue; neurons and the three main types of glia were enumerated. In addition, the thickness of the cortex was measured and the glial cells of corpus callosum counted in the animals exposed to the three environments for 80 days. Under the influence of the enriched environment, the occipital cortex enlarged, the number of oligodendrocytes increased over the controls by 27-33% in the 30- and 80-day groups and the number of astrocytes, by 13% in the 80-day group. Within the cortex, only certain layers showed the increase in glial numbers. In the corpus callosum, however, the numbers of glial cells did not differ from those in controls. In the animals exposed to the impoverished environment, neither the size of the cortex nor the number of oligodendrocytes and astrocytes differed from controls. The animals subjected to handling also showed evidence of cortical enlargement, but the only significant change in glial cells was a 12% increase in astrocytes. It is concluded that handling and enrichment produce changes in anatomical indices of neural function including depth of cortex and numbers of glial cells. The glial response was specific to the type.of manipulation since astrocytes were predominantly affected by handling and oligodendrocytes, by enrichment. The effect of handling on astrocytes may be attributed to the stimulation being applied at a time of astrocyte proliferation, whereas the effect of enriched environment on oligodendrocytes occurred at a time of active production of these cells. The differences in cell numbers were explained by changes in the rate of cell population growth; since the impoverished did not differ from the control animals, the changes probably consisted of growth acceleration in the enriched animals rather than diminution in the impoverished ones.

Effects of Environmental Complexity and Deprivation on Brain Anatomy and Histology: A Review

“…Microscopy provided an affirmative answer with the finding that changes in cortical depth paralleled those of weight (Diamond et a/., 1964(Diamond et a/., , 1966(Diamond et a/., , 1972(Diamond et a/., , 1976Diamond, , 1976Walsh et al, 1972;Szeligo & Leblond, 1977). Following differential rearing from weaning the cortex is deeper in EC than IC animals.…”

Experience-driven brain plasticity: beyond the synapse

“…Exposure to EC, which was originally designed to investigate the relationship between neuronal and behavioral changes, was also shown in some early studies to induce changes in astroyctic morphology Szeligo and Leblond, 1977). However, limitations in quantification techniques available at the time resulted in inconsistent findings that made subsequent interpretation difficult.…”

“…However, it should be noted that not all studies find a relationship between early visual experience and myelination in the optic nerve (Moore et al, 1976;Fukui et al, 1991). Szeligo and Leblond (1977), who were the first to examine the influence of rearing environment on brain fiber tracts, found increases in oligodendrocytes in the visual cortex of EC rats. Subsequently, Sirevaag and Greenough (1987) also found the volume fraction of oligodendrocyte nuclei in the visual cortex to be greater among EC-raised rats, compared with their IC littermates.…”

Response threshold to aversive stimuli in stimulated early protein-malnourished rats

“…In addition, considering that early social or environmental isolation alters the emotional response in a fashion similar to that described after early protein malnutrition and that these changes in emotionality are enhanced by isolation and decreased by environmental stimulation in malnourished rats (25), the interactions between malnutrition and environmental stimulation represented another interesting point to investigate. In fact, it has been reported that environmental stimulation produces changes in structural, neurochemical and functional parameters in the central nervous system of the rat (26)(27)(28)(29). It has been suggested that these effects of early protein malnutrition may be partially reversed by environmental stimulation offered during malnutrition, or later during the nutritional recovery period (26,(30)(31)(32)(33).…”