Environmental Enrichment Influences Neuronal Stem Cells in the Adult Crayfish Brain

New neurons are incorporated throughout life into the brains of many vertebrate and nonvertebrate species. This process of adult neurogenesis is regulated by a variety of external and endogenous factors, including environmental enrichment, which increases the production of neurons in juvenile mice and crayfish. The primary goal of this study was to exploit the spatial separation of the neuronal precursor cell lineage in crayfish to determine which generation(s) of precursors is altered by environmental conditions. Further, in crayfish, an intimate relationship between the first-generation neuronal precursors (stem cells) and cells circulating in the hemolymph has been proposed (Zhang et al., 2009). Therefore, a second goal was to assess whether environmental enrichment alters the numbers or types of cells circulating in the hemolymph. We find that neurogenesis in the brains of sexually differentiated procambarid crayfish is enhanced by environmental enrichment as previously demonstrated by Sandeman and Sandeman (2000) in young, sexually undifferentiated Cherax destructor. We also show that environmental enrichment increases the cell cycle rate of neuronal stem cells. Although there was no effect of environment on the overall numbers of cells circulating in the hemolymph, enrichment resulted in increased expression of glutamine synthetase (GS), a marker of the neuronal stem cells, in a small percentage of circulating cells; there was little or no GS immunoreactivity in hemolymph cells extracted from deprived animals. Thus, environmental enrichment influences the rate of neuronal stem cell division in adult crayfish, as well as the composition of cells circulating in the hemolymph. (C) 2010 Wiley Periodicals, Inc. Develop Neurobiol 71: 351-361, 2011