The effects of a 30 day period of environmental diversity on well-fed and previously undernourished rats: Neuronal and synaptic measures in the visual cortex (area 17)

Abstract

Black and white Lister hooded rats were undernourished from the 16th day of gestation until 25 postnatal days of age. These previously undernourished rats and a set of well‐fed rats were later subjected to 30 days of environmental diversity, i.e., environmental enrichment or isolation. Two separate experiments were carried out. In experiment 1, the environmental diversity lasted from 85 to 115 days of age and in experiment 2, from 35 to 65 days of age. At the end of the period of environmental diversity, all rats were killed by perfusion with 2% phosphate‐buffered glutaraldehyde. Small pieces of tissue from the right visual cortex were embedded in Spurr's resin. For each rat two blocks of resin‐embedded tissue were randomly selected, and from these semithin sections (0.5 μm) were cut and stained with toluidine blue. Photomicrographs of cortical layers II and III were taken from these sections and used to estimate the numerical density of neurons. Ultrathin (ca. 70 nm) sections of the same region of the cortex were cut and stained with lead citrate. These sections were used to estimate the synaptic disc diameter and numerical density. Synapse‐to‐neuron ratios were calculated from the estimates of synaptic and neuronal numerical densities. In experiment 1, well‐fed rats raised in enriched environments had a significantly smaller neuronal numerical density and a greater synaptic disc diameter than well‐fed rats raised in an impoverished environment. In experiment 2, neither the well‐fed nor previously undernourished rats showed significant effects of environmental treatment on any of the features studied. The statistical interaction between nutrition and environment was not significant for any of the features in either experiment.