Neurobiology of Aging 25 (2004) 361–375 Prominent decline of newborn cell proliferation, differentiation, and apoptosis in the aging dentate gyrus, in absence of an age-related hypothalamus–pituitary–adrenal axis activation Vivi M. Heine ∗ , Suharti Maslam, Marian Joëls, Paul J. Lucassen Institute for Neurobiology, Faculty of Science, Swammerdam Institute for Life Sciences, University of Amsterdam, Kruislaan 320, 1098 SM, Amsterdam, The Netherlands Received 5 August 2002; received in revised form 13 March 2003; accepted 25 March 2003 Abstract Neurogenesis and apoptosis in the hippocampal dentate gyrus (DG) occur during development and adulthood. However, little is known about how these two processes relate to each other during aging. In this study, we examined apoptosis, proliferation, migration, and survival of newborn cells in the young (2 weeks), young-adult (6 weeks), middle-aged (12 months), and old (24 months) rat DG. We also measured dentate volume and cell numbers, along with basal corticosterone and stress response parameters. We show that new cell proliferation and apoptosis slow down profoundly over this time period. Moreover, migration and differentiation into a neuronal or glial phenotype was strongly reduced from 6 weeks of age onwards; it was hardly present in middle-aged and old rats as confirmed by confocal analysis. Surprisingly, we found no correlation between cell birth and corticosterone levels or stress response parameters in any age group. © 2003 Elsevier Science Inc. All rights reserved. Keywords: Aging; Neurogenesis; Apoptosis; Migration; Stress; Corticosterone; Rat; Wistar; Hippocampus 1. Introduction Both cell birth and apoptotic cell death are common during central nervous system development. Decades after its initial description [3], it is now widely accepted that neurogenesis continues to occur also in the adult brain in the subventricular zone (SVZ) and the hippocampal dentate gyrus (DG) [2,13,26,29]. Cell birth and cell death appear closely associated in the DG as a continuous cell turnover takes place. Consequently, the DG consists of a diverse and heterogeneous group of mature and developing cells. This turnover is furthermore highly sensitive to various hormonal and environmental stimuli [24,36,39,89,90]. Removal of steroid hormones by adrenalectomy (ADX), e.g. induces apoptosis in the DG, but at the same time increases the division of immature cells [7,11,64]. On the other hand, stress reduces new cell birth [28,33,34,38]. In contrast, an enriched environment or learning tasks stimulate neurogenesis [36,37,49,51]. The influence of age on rates of neurogenesis and apop- tosis has not been studied in detail. Changes in the relative proportion of young DG neurons may have considerable ∗ Corresponding author. Tel.: +31-20-5257719; fax: +31-20-5257709. E-mail address: heine@science.uva.nl (V.M. Heine). consequences for hippocampal function and could possibly contribute to age-dependent structural and functional hip- pocampal deficits [5,6,8,93]. Moreover, relatively little is known about the life span of the individual newborn cells as the organism ages. In the present study, we examined the hypothesis that age of the animal influences (1) the balance between neu- rogenesis and apoptosis, and (2) the process of migration and neuronal maturation of individual newborn cells. To test this, we stereologically assessed birth rate, migration, and survival of the newborn cells, as well as cell death and structural maturation of the DG in young (2 weeks), young-adult (6 weeks), middle-aged (12 months), and old (24 months) rats. Dividing cells were labeled with bromod- eoxyuridine (BrdU) and studied after survival times of 24 h, 1 and 4 weeks. Triple immunocytochemical analysis (BrdU, NeuN, and S100) was used to study age-related changes in the phenotype of adult generated cells. Elevated glucocorticoid (GC) levels are frequently found in aged rats and may contribute to age-related memory and learning deficits [43,58,61,63,69,71]. In addition, stress and corticosterone (a) can reduce adult progenitor proliferation, and (b) may relate to the decline in neurogenesis during aging. Following ADX, neurogenesis indeed increased in old rodents, suggesting that reduced neurogenesis during 0197-4580/$ – see front matter © 2003 Elsevier Science Inc. All rights reserved. doi:10.1016/S0197-4580(03)00090-3