FACTORS THAT INFLUENCE THE DEVELOPMENT OF CULTURED NEURONS FROM THE BRAIN OF THE MOTH MANDUCA-SEXTA

During metamorphic adult development, neurons and glial cells in the d eveloping olfactory (antennal) lobes of the moth undergo characteristi c and extensive changes in shape. These changes depend on an interplay among these two cell types and ingrowing sensory axons. All of the di rect cellular interactions occur against a background of changing ster oid hormone titers. Antennal-lobe (AL) neurons dissociated from stage- 5 (of 18 stages) metamorphosing animals survive at least 3 wk in prima ry cell culture. We describe here the morphological influences on AL n eurons of (1) exposure to the steroid hormone 20-hydroxyecdysone, (2) exposure to sensory axons, and (3) interactions among the AL neurons. Cultured AL neurons respond only weakly, if at all, to 20-hydroxyecdys one. They do, however, show greater total outgrowth and branching when they had been exposed in vivo to sensory axons. Because there is no d irect contact between some of tile neuronal types and the sensory axon s at the time of dissociation, the increase in outgrowth must have bee n mediated via a diffusible factor(s). When AL cells (neurons and glia ) are plated at high density in low volumes of medium, or when the cel ls are plated at low density but in the presence of medium conditioned by high-density cultures, neurite outgrowth and cell survival are inc reased. Nerve growth factor (NGF), epidermal growth factor (EGF), fibr oblast growth factor-basic (bFGF), transforming growth factor-beta (TG F(beta)) and insulin-like growth factor (ILGF) had no obvious effect o n neuronal morphology and thus are unlikely to underlie these effects. Our results suggest that the mature shape of AL neurons depends on de velopmental interactions among a number of diffusible factors.