Environmental enrichment stimulates progenitor cell proliferation in the amygdala

Enriched environments enhance hippocampal neurogenesis, 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 behaviors 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 environment 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, immediately after a 1-week period of enrichment, expressed the oligodendrocyte progenitor marker Olig2. Furthermore, 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.