Effects of early environment on granule cell morphology in the dentate gyrus of the guinea-pig.

The aim of the present study was to determine whether early environment affects the morphology of the dentate gyrus granule cells in the guinea-pig, a rodent whose brain is at an advanced stage of maturation at birth. Male and female guinea-pigs were assigned at six to seven days of age to either a control (social) or an isolated environment where they remained for 80-90 days. The dendritic tree and somata of the granule cells were quantified in Golgi-Cox-stained brains. The granule cells of isolated males had fewer dendritic branches and a shorter dendritic length than those of control males in the inner two-thirds of the dendritic tree, but a larger number of branches and a larger dendritic length in the distal one-fourth. In contrast, the granule cells of isolated females had a larger number of branches and a larger dendritic length than control females in the inner one-half of the dendritic tree and a reduced number of branches and a shorter dendritic length in the distal one-fourth. The granule cell somata were smaller in isolated than in control males. No such difference was observed in females. Sex differences were found in the granule cell morphology. In the control environment, the granule cells of males had more branches and a greater dendritic length in the inner one-half of the dendritic tree than those of females but fewer dendritic branches and a shorter dendritic length in the distal one-fourth. In the isolated environment, the granule cells of males had fewer branches and a shorter dendritic length in the inner two-thirds of the dendritic tree than females, but more dendritic branches and a greater dendritic length in the distal one-fourth. In the control environment male granule cells had a larger soma than those of females. The opposite occurred in the isolated environment. The results of this study indicate that early isolation induces remarkable structural changes in the granule cells of the dentate gyrus in a rodent whose brain is at an advanced stage of maturation at birth. They also indicate that the effects of environment are different at different levels of the dendritic tree and in the two sexes.