The effects of a lengthy period of environmental diversity on well‐fed and previously undernourished rats. I. Neurons and glial cells

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Abstract
Male rats undernourished from the 16th day of gestation until 25 postnatal days of age were raised either in enriched (EC) or isolated (IC) environmental conditions between about 35 and 115 days of age. A parallel set of well‐fed rats was raised in identical environments. At the end of this period all rats were killed by perfusion with 2% phosphate buffered glutaraldehyde. Body and forebrain weights and forebrain lengths and widths were determined for each animal. The left cerebral hemisphere was embedded in paraffin‐wax and serially sectioned. Three of these coronal sections (defined by subcortical landmarks) taken from the occipital cortex region were used for cortical depth measurements. Small pieces of cortical tissue taken from area 17 of the right cerebral hemisphere were embedded in resin and cut to yield 0.5 μm thick sections through the entire depth of the cortex. These sections were used to estimate the nuclear diameters and numerical densities of neurons and oligodendrocytes as well as neuronal perikaryal volumes. Two‐way analysis of variance tests on data combined from both nutritional groups revealed significant main effects of nutrition on body weight, forebrain weight, forebrain width, and forebrain length × width values. Environment had significant main effects on forebrain weight, forebrain length, forebrain length × width values, and on neuronal numerical density. The interaction between nutrition and environment was not significant for any of the measurements carried out. These results suggest that 80 days of environmental diversity beginning at about 35 days of age can produce morphological changes in the brains of both well‐fed rats and rats undernourished during early life. These changes seem to be similar in direction and magnitude in the two nutritional groups.