engleski

Effect of environmental enrichment on morphology of dentate granule cells and deep layer III and layer V pyramidal cells of occipital cortex in oldest-old rat.

The hippocampus of aged rats shows marked age-related morphological changes that could cause memory deficits. Experimental evidence has established that environmental enrichment attenuates memory deficits in aged rats. We therefore studied whether environmental enrichment produces morphological changes on the dentate granule cells of aged rats and deep layer III and layer V pyramidal neurons in the associate rat neocortex. Fifteen male Sprague-Dawley rats, 24 months of age, were randomly distributed in two groups that were housed under standard (n=7) or enriched (n=8) environmental conditions for 26 days. Quantitative data of dendritic morphology and spine density were obtained on Golgi-Cox stained sections. The environmental enrichment induced marked increase in the complexity and size of granule cells dendritic tree (total number of segments increased by 61% and length by 116%), and spine density (88% increase). Those values were much lower in both groups than in adult rat. It is possible that the dendrites had started to express regressive changes, a phenomenon that has been observed in the "oldest old" stage. This might imply that the effect of enriched environment is actually in slowing down the speed of regression. In the occipital cortex effects of the enriched environment were less pronounced and the values for total dendritic length and spine density were close to values found in the adult rats. For the layer III pyramidal cells increase of total segment number (37, 5%) and intermediate segments dendritic diameter (20-27%) was observed. Moderate effect were also observed for total dendritic length (19% increase) and spine number (30% increase). For the layer V pyramidal cells significant differences were found for the number of primary dendrites per neuron (30%) and diameter of intermediate segments (26%). There were large interindividual differences within the enriched group, indicating differential individual responses to environmental stimulation. Previous studies have observed changes produced by environmental enrichment in the morphology of dentate gyrus granule cells only in young and adult animals. The results of the present study show that environmental enrichment can also produce marked changes in dentate granule cell morphology in the senescent brain suggesting that hippocampus retains its neuroplastic capacity during aging. Interestingly, in the occipital cortex environmental enrichment induced only moderate changes. Our results suggest that in aging enriched environmental housing conditions are especially beneficial in the regions that undergo age-related degenerative changes, attenuating age-related dendritic regression and synaptic loss, thus preserving memory functions. This demonstrates the importance of cognitive stimulation for arresting regression in the hippocampus during normal aging and, moreover, for diminishing the deleterious effects of neurodegenerative disorders (i.e. Alzheimer’s disease) on the hippocampus.

aging; enriched environment; Golgi staining; dentate gyrus; occipital cortex

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