N-methyl-D-aspartate receptor activity and estradiol: separate regulation of cell proliferation in the dentate gyrus of adult female meadow vole B K Ormerod, E M Falconer and L A M Galea Department of Psychology and Graduate Neuroscience Program, 2136 West Mall, The University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 (Requests for offprints should be addressed to L Galea; Email: lgalea@psych.ubc.ca) Abstract We have previously found that estradiol increases (within 4 h) but then decreases (within 48 h) cell proliferation in the dentate gyrus of adult female ovariectomized (OVX) rats and of intact meadow voles and that estradiol partially stimulates adrenal activity to suppress cell proliferation in rats. Estradiol enhances N-methyl-D-aspartate receptor (NMDAr) activity and NMDAr activation suppresses cell proliferation in the adult rodent dentate gyrus. Therefore, we tested whether estradiol alters cell proliferation in the dentate gyrus of adult OVX female meadow voles by stimulating NMDAr activity. In experiment 1, OVX females were injected with estradiol (10 μg) or oil and then with NMDA (30 mg/kg) or vehicle 3 h later and bromo- deoxyuridine 4 h later (BrdU; 50 mg/kg). Voles were perfused 1 h after BrdU injection. Relative to oil vehicle, estradiol increased (P0·001) and NMDA decreased (P0·006) labeled cell number. Coadministration of estradiol/NMDA increased labeled cell numbers relative to NMDA alone (P0·03), suggesting that within 4 h estradiol does not influence the effect of NMDA receptors on cell proliferation. In experiment 2, OVX females were injected with either estradiol or oil and then with either MK-801 (1 mg/kg) or vehicle 47 h later and BrdU 48 h later. The animals were perfused 1 h after BrdU was injected. Relative to oil-treated voles, estradiol-treated voles had fewer (P ,0·006) and MK-801-treated voles had more labeled cells (P0·0001) in the dentate gyrus. However, estradiol did not appear to stimulate NMDA receptors to suppress cell proliferation because estradiol (48 h)/MK-801-treated voles had fewer BrdU-labeled cells than oil (48 h)/MK-801-treated voles (P0·06). The results show that estradiol time-dependently influences cell proliferation but that estradiol does not stimulate NMDAr activity to influence cell proliferation in the dentate gyrus of adult voles. Journal of Endocrinology (2003) 179, 155–163 Introduction New granule neurons are added to the dentate gyrus of all mammalian species that have been studied, including humans, throughout adulthood (Altman & Das 1965, Cameron et al. 1993, Gould et al. 1997, 1998, 1999, Eriksson et al. 1998, Kornack & Rakic 1999). The number of granule neurons added to the mammalian dentate gyrus appears substantial. In rats, approximately 9000 new cells are produced daily and many of these new cells differen- tiate into granule neurons (Cameron & McKay 2001). Altering progenitor cell proliferation, the fate of daughter cells or the survival of new granule neurons could increase or decrease neurogenesis in the dentate gyrus. Under- standing how different components of adulthood neuro- genesis are influenced by a single factor is important because a factor that both increases cell proliferation and decreases the survival of young neurons could produce no net change in new neuron number. Estradiol dynamically influences neurogenesis within the adult rodent dentate gyrus by first increasing and then decreasing cell prolifer- ation (Ormerod & Galea 2001, Ormerod et al. 2003) as well as by enhancing the survival of young neurons (Ormerod et al. 2002). This study was designed to better understand how estradiol dynamically influences cell proliferation in the adult rodent dentate gyrus. Several studies have shown that estradiol influences cell proliferation in the dentate gyrus of adult rodents. For example, short-term exposure to estradiol (2–4 h) stimu- lates cell proliferation in the dentate gyrus of adult ovariectomized (OVX) female rats (Tanapat et al. 1999, Banasr et al. 2001, Ormerod et al. 2003). Interestingly, we have previously shown that estradiol initially enhances cell proliferation (within 4 h) but subsequently suppresses cell proliferation (within 48 h) in the dentate gyrus of OVX adult female rats, suggesting that estradiol time- dependently influences cell proliferation (Ormerod et al. 2003). In fact, estradiol appears to dynamically regulate 155 Journal of Endocrinology (2003) 179, 155–163 0022–0795/03/0179–155  2003 Society for Endocrinology Printed in Great Britain Online version via http://www.endocrinology.org