[Spine density of lamina V pyramidal cells in the visual cortex of laboratory rats after lengthy dark exposure].

1. The spine density was investigated at the apical dendrites of lamina-V-pyramidal cells in the visual cortex of rats following dark rearing for 250 days. 2. There are no significant differences in the average spine density between rats reared in darkness and normal conditions. 3. The results are discussed in view of the significant differences found after dark rearing for 50 days. It is assumed that these present results are caused by a delay in spine development in younger animals, which is compensated in the adult stage.