Influence of environmental stimulation on neurogenesis in the adult insectbrain

Mushroom bodies are the main integrative structures of insect brain. They r eceive sensory information from the eyes, the palps, and the antennae. In t he house cricket, Acheta domesticus, a cluster of mushroom body neuroblasts keeps producing new interneurons during an insect's life span, The aim of the present work is to study the impact of environmental stimuli on mushroo m body neurogenesis during adulthood. Crickets were reared either in an enr iched environment, where they received complex environmental and congeneric stimulations or isolated in small cages and deprived of most visual, audit ory, and olfactory stimuli. They then were injected with a S-phase marker, 5-bromo, 2'-deoxyuridine (BrdU) and sacrificed at different periods of thei r life, Neurogenesis and cell survival were estimated by counting the numbe r of BrdU-labeled cells in the mushroom bodies. Environmentally enriched cr ickets were found to have an increased number of newborn cells in their mus hroom bodies compared with crickets housed in cages with an impoverished en vironment. This effect of external factors on neurogenesis seems to be limi ted to the beginning of imaginal life. Furthermore, no cell loss could be d etected among the newborn neurons in either environmental situation, sugges ting that cell survival was not affected by the quality of the environment. Considering vertebrate studies which showed that enriched environment incr eases hippocampal cell survival and improves animal performances in spatial learning tests, we suggest that the increased number of interneurons produ ced in an integrative brain structure after exposure to enriched environmen t could contribute to adaptive behavioral performances in adult insects, (C ) 2000 John Wiley & Sons, Inc.