Environmental Enrichment Stimulates Progenitor Cell Proliferation in the Amygdala Hiroaki Okuda, 1 * Kouko Tatsumi, 1 Manabu Makinodan, 2 Takahira Yamauchi, 2 Toshifumi Kishimoto, 2 and Akio Wanaka 1 1 Department of Anatomy and Neuroscience, Faculty of Medicine, Nara Medical University, Kashihara City, Nara, Japan 2 Department of Psychiatry, Faculty of Medicine, Nara Medical University, Kashihara City, Nara, Japan Enriched environments enhance hippocampal neuro- genesis, synaptic efficacy, and learning and memory functions. Recent studies have demonstrated that enriched environments can restore learning behavior and long-term memory after significant brain atrophy and neural loss. Emotional and anxiety-related behav- iors were also improved by enriched stimuli, but the effect of enriched environments on the amygdala, one of the major emotion-related structures in the central nervous system, remains largely unknown. In this study, we have focused on the effects of an enriched environ- ment on cell proliferation and differentiation in the murine amygdala. The enriched environment increased bromodeoxyuridine (BrdU)-positive (newborn) cell numbers in the amygdala, almost all of which, immedi- ately after a 1-week period of enrichment, expressed the oligodendrocyte progenitor marker Olig2. Further- more, enriched stimuli significantly suppressed cell death in the amygdala. Some of the BrdU-positive cells in mice exposed to the enriched environment, but none in animals housed in the standard environment, later differentiated into astrocytes. Our findings, taken together with previous behavioral studies, suggest that progenitor proliferation and differentiation in the amygdala may contribute to the beneficial aspects of environmental enrichment such as anxiolytic effects. V V C 2009 Wiley-Liss, Inc. Key words: enriched environment; amygdala; progeni- tor; BrdU; astrocyte The external environment is known to influence adult neurogenesis. Kempermann et al. (1997a) found that mice housed in an enriched environment had more new granule cells in the dentate gyrus than did control mice. An enriched environment is one that prompts increased exploratory behavior and sensory motor stimu- lation and is provided by housing animals in large cages furnished with toys and exercise wheels. These complex environmental stimuli enhance hippocampal neurogene- sis, synaptic efficacy, and learning and memory functions (van Praag et al., 2000; Cao et al., 2004; Sale et al., 2007; Tashiro et al., 2007; Wright and Conrad, 2008). Hippocampal slices from rodents housed in enriched environments reveal changes in excitatory postsynaptic potentials and also enhancement of long-term potentia- tion (LTP), a function correlated with certain forms of learning and memory (Huang et al., 2006). Furthermore, enriched environments restore learning behavior and long-term memory after brain atrophy and neural loss (Fischer et al., 2007). For brain regions other than the hippocampus, Ehninger and Kempermann (2003) reported that enriched environments enhanced cell genesis and microglia proliferation in the adult murine neocortex. The amygdala, one of the most important struc- tures of the limbic system, is composed of several subnu- clei, including the basolateral and corticomedial regions. These subnuclei each have distinct connections and structural characteristics. The amygdala is considered to play an essential role in emotional, motivational, and social processes as well as in learning and memory (Phelps and LeDoux, 2005). Bernier et al. (2002) reported adult neurogenesis in the rostral temporal lobe, including the amygdala, of squirrel and cynomolgus monkeys. In rodents, however, adult neurogenesis in the amygdala was not observed under normal conditions but could be evoked by pentylenetetrazole-induced epilepsy (Park et al., 2006). The first two authors contributed equally to this work. Additional Supporting Information may be found in the online version of this article. Contract grant sponsor: Daiwa Housing Group (Indoor Environmental Medicine); Contract grant sponsor: Japanese Ministry of Education, Cul- ture, Sports, Science and Technology. *Correspondence to: Hiroaki Okuda, PhD, Department of Anatomy and Neuroscience, Faculty of Medicine, Nara Medical University, Kashihara City, Nara 634-8521, Japan. E-mail: okuda@naramed-u.ac.jp Received 16 February 2009; Revised 28 April 2009; Accepted 6 May 2009 Published online 29 June 2009 in Wiley InterScience (www. interscience.wiley.com). DOI: 10.1002/jnr.22160 Journal of Neuroscience Research 87:3546–3553 (2009) ' 2009 Wiley-Liss, Inc.