The pubertal-related decline in cellular proliferation and neurogenesis in the dentate gyrus of male rats is independent of the pubertal rise in gonadal hormones

摘要

Pubertal development is marked by significant decreases in cellular proliferation and neurogenesis in the dentate gyrus of the hippocampal formation. Though it is unclear what mediates these developmental changes in the dentate gyrus, gonadal hormones have been implicated in modulating many neurobiological processes during puberty and various parameters of neurogenesis in adulthood. Thus, it is possible that the gradual and sustained increase in gonadal hormones experienced during puberty plays a role in these changes in neurogenesis. In the present experiments, we first quantified cellular proliferation and neurogenesis using 5-bromo-2′-deoxyuridine (BrdU) and doublecortin (DCX) immunohistochemistry, respectively, in the dentate gyrus of pre-pubertal (30d), mid-pubertal (45d), and adult (90d) male rats. We found the decline in BrdU and DCX cell numbers throughout these ages were coincident with increases in their plasma testosterone levels. We next tested whether exposure to the pubertal rise in gonadal hormones was necessary for this decrease in hippocampal neurogenesis to occur. Thus, we examined cellular proliferation and neurogenesis in intact 30 day (pre-pubertal) and 60 day old (late-pubertal) rats, as well as 60 day old rats that had previously been gonadectomized or sham-gonadectomized at 30 days of age. Although we again found the expected decline in BrdU and DCX cell numbers between 30 and 60 days of age in the intact groups, there were no differences among the 60 day old animals, regardless of gonadal status. These data indicate that the pubertal-related decline in hippocampal cellular proliferation and neurogenesis is independent of the pubertal change in gonadal hormones.