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 aff ects 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 an d 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 d ays. The dendritic tree and somata of the granule cells were quantified in Golgi-Cox-stained brains. The granule cells of isolated males had fewer den dritic 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 branc hes and a larger dendritic length in the distal one-fourth. In contrast, th e granule cells of isolated females had a larger number of branches and a l arger dendritic length than control females in the inner one-half of the de ndritic tree and a reduced number of branches and a shorter dendritic lengt h in the distal one-fourth. The granule cell somata were smaller in isolate d than in control males. No such difference was observed in females. Sex di fferences were found in the granule cell morphology. In the control environ ment, 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 bu t 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 dend ritic tree than females, but more dendritic branches and a greater dendriti c 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 gyms in a rodent who se brain is at an advanced stage of maturation at birth. They also indicate that the effects of environment are different at different levels of he de ndritic tree and in the two sexes. (C) 2001 IBRO. Published by Elsevier Sci ence Ltd. All rights reserved.