NEUROGENESIS IN ADULT INSECT MUSHROOM BODIES

The occurrence of neurogenesis in mushroom bodies of adult insects bel onging to several orthopteroid and coleopteran families is described. Using injections of 5-bromo, T2'-deoxyuridine, we showed that neurobla sts, which are progenitors of Kenyon cells during preimaginal instars, continue to divide in adult Acheta domesticus. Their progeny constitu te a central column in mushroom body cortices of 3-week-old females. O ther Gryllidae, Gryllus bimaculatus and Gryllomorpha dalmatina, show t he same pattern of neuroblast activity and migration of their progeny. Immunocytochemical staining of glial cells failed to reveal any immun oreactivity, either in proliferating regions or in the resulting cells . In another orthopteran, Locusta migratoria, discrete clusters of cel ls, located dorsolateral to the Kenyon cells, incorporated 5-bromo, al -deoxyuridine, but we could not detect any neuronal progeny migrating to the mushroom body cortices. These cells were strongly labeled with an antiglial antibody, indicating that the replicating cells are gliob lasts rather than neuroblasts. In Periplaneta americana (Dictyoptera), cells replicating their DNA were similarly shown to immunoreact with glial antibodies. In contrast, three coleopterans (Tenebrio molitor, Z ophobas species, Harmonia axyridis) have two large neuroblasts located in the middle of the mushroom body cortices. These produce cells whic h migrate within the group of Kenyon cells, their nuclei having the sa me shape and size as those of surrounding Kenyon cells. In adult insec ts, neurogenesis in mushroom bodies occurs in Gryllidae and several co leopteran families, but could not be demonstrated in Dictyoptera and A crididae. Its occurrence and distribution raise the issue of unexpecte d plasticity in the adult insect brain. (C) 1996 Wiley-Liss, Inc.