Estrogen regulation of cell proliferation and distribution of estrogen receptor-alpha in the brains of adult female prairie and meadow voles

Abstract

Adult female prairie (Microtus ochrogaster) and meadow (M. pennsylvanicus) voles were compared to examine neural cell proliferation and the effects of estrogen manipulation on cell proliferation in the amygdala, ventromedial hypothalamus (VMH), and dentate gyrus of the hippocampus (DG). Unlike prior studies, our study focused on the amygdala and VMH, because they are involved in social behaviors and may underlie behavioral differences between the species. Meadow voles had a higher density of cells labeled with the cell proliferation marker 5-bromo-2'-deoxyuridine (BrdU) in the amygdala and DG than did prairie voles. Treatment with estradiol benzoate (EB) for 3 days increased the density of BrdU-labeled cells in the amygdala, particularly in the posterior cortical (pCorA) and medial (pMeA) nuclei, in meadow, but not prairie, voles. Furthermore, the majority of the BrdU-labeled cells in the pCorA and pMeA displayed either a neuronal or a glial progenitor phenotype, but no species or treatment differences were found in the percentage of neuronal or glial progenitor cells. To understand better estrogen's effects on adult neurogenesis, we also examined estrogen receptor-alpha (ERalpha) distribution. Meadow voles had more ERalpha-labeled cells in the pCorA and VMH, but not in the pMeA or DG, than did prairie voles. In addition, more than one-half of the BrdU-labeled cells in the amygdala of both species coexpressed ERalpha labeling. Together, these data indicate that estrogen alters cell proliferation in a species- and region-specific manner, and some of these effects may lie in the specific localization of estrogen receptors in the adult vole brain.

Fig. 1

Photomicrographs displaying BrdU-labeled cells in prairie and meadow voles. For the dentate gyrus of the hippocampus (A), prairie voles (top) had fewer BrdU-labeled cells than did meadow voles (bottom). CA4, CA4 layer of the hippocampus; GrL, granule cell layer; Hil, hilus. For the central nucleus of amygdala (CeA; B), BrdU-labeled cells did not appear to differ between prairie (top) and meadow (bottom) voles. Scale bars = 200 μm.

Fig. 2

Species differences in the densities of BrdU-labeled cells in the dentate gyrus of the hippocampus (DG) and amygdala. For the DG (A), meadow voles displayed a higher density of BrdU-labeled cells than did prairie voles. For the amygdala (AMY; B), meadow voles also had a higher density of BrdU-labeled cells than did prairie voles. This difference was due largely to meadow voles having more BrdU-labeled cells in the posterior cortical subnucleus of the amygdala (pCorA). No species differences were found in other subnuclei of the amygdala, including the anterior cortical (aCorA), anterior medial (aMeA), posterior medial (pMeA), and central (CeA) subnuclei. *P < 0.05; error bars indicate SEM.

Fig. 3

Photomicrographs displaying the species–treatment interaction on BrdU-labeled cells in the posterior cortical (pCorA) and posterior medial (pMeA) nuclei of the amygdala. In both areas, BrdU-labeled cells did not seem to differ between control (A) and estradiol benzoate (EB)-treated (B) prairie voles. However, meadow voles treated with EB (D) appeared to have significantly more BrdU-labeled cells in both the pCorA and the pMeA than controls (C). opt, Optic tract. Scale bar – 200 μm in D (applies to A–D).

Fig. 4

Species–treatment interactions in the density of BrdU-labeled cells in the vole brain. In the dentate gyrus of the hippocampus (DG; A), treatment with estradiol benzoate (EB) did not alter BrdU labeling in either species. In the amygdala (AMY; B), particularly in the posterior cortical (pCorA) and posterior medial (pMeA) subnuclei, EB treatment elicited a significant increase in the density of BrdU-labeled cells only in meadow voles. No species or treatment differences were found in the anterior cortical (aCorA), anterior medial (aMeA), or central (CeA) subnuclei of the amygdala. *P < 0.05; error bars indicate SEM.

Fig. 5

Phenotype of BrdU-labeled cells in the amygdala. Confocal laser microscope images display labeling for BrdU (red; left), TuJ1 (green; center left), NG2 (blue; center right), and all three markers (right) in the posterior cortical nucleus (pCorA) of the amygdala in the vole brain. Some BrdU-labeled cells coexpressed the neuronal (TuJ1; A) or glial progenitor (NG2; B) marker. Scale bar – 5 μm in B (applies to A–B, all panels).

Fig. 6

Photomicrographs displaying ERα labeling in the amyg-dala and ventromedial hypothalamus (VMH) in prairie (left) and meadow (right) voles. In the posterior cortical nucleus of the amyg-dala (A,B) and VMH (E, F), meadow voles (B, F) appeared to have more ERα-labeled cells than did the prairie voles (A, E). However, no species differences were found in the posterior medial nucleus of the amyg-dala (C, D). opt, optic tract. Scale bar – 200 μm in F (applies to A–F).

Fig. 7

Species differences in the densities of ERα-labeled cells. Meadow voles displayed higher densities of ERα-labeled cells in the posterior cortical amygdala (pCorA) and ventromedial hypothalamus (VMH) than did prairie voles. Significant species differences were not found in the posterior medial amygdala (pMeA) or dentate gyrus of the hippocampus (DG). *P < 0.05; error bars indicate SEM.

Fig. 8

Nuclei coexpressing BrdU and ERα labeling in the posterior cortical nucleus of the amygdala in prairie (A) and meadow (B) voles. Confocal laser microscope images display labeling for BrdU (red; left), ERα (green; center), and both markers (right). In the right panels, the BrdU and ERα colocalized cells display a yellow image, and cross marks on the larger image indicate the location of views along the y-z axis (right) and x-z axis (below) to demonstrate 3D colocalization of BrdU and ERα. Scale bar – 5 μm in B (applies to A, B).