Apical dendritic spines of the visual cortex and light deprivation in the mouse

Summary The effects of light deprivation on the number of apical dendritic spines have been studied in the visual cortex of the mouse. In the portion of the apical dendrites of layer V-pyramidal cells traversing layer IV, dendritic segments of 50 in length from different cells were selected. The number of spines on each of 50 different segments per animal was counted. The countings were done in the areae striata and temporalis prima from mice raised in complete darkness since birth up to 22–25 days old. The observations were compared with the countings obtained in the areae striata and temporalis prima from mice raised under normal conditions. The results indicated that mice raised in darkness had a significant reduction in the number of spines per dendritic segment at the level of layer IV in area striata when compared with control animals. No significant difference was found in the number of spines per dendritic segment in layer IV between both groups of normal and dark raised mice in the area temporalis prima. The mean number of dendritic spines per consecutive segments along complete apical dendrites of layer V-pyramidal cells in area striata has been found to increase exponentially with the distance from the cell body. The same exponential relation, but with somewhat lower values, was obtained in the apical dendrites in area striata in mice raised in darkness. The significance of these findings were discussed. It was concluded that: First, visual sensory deprivation affect the fine structure of the central nervous system. Second, the results observed support the assumption that structural changes in the nerve cells occur as the result of experience.