Effects of the steroid hormone 20-hydroxyecdysone and prior sensory input on the survival and growth of moth central olfactory neurons in vitro.

Neurons in the developing (antennal) olfactory lobe of the moth Manduca sexta undergo a period of extensive process outgrowth and branching that coincides temporally with both a rising titer of the steroid hormone 20-hydroxyecdysone and the ingrowth of sensory axons from receptors in the antenna. To evaluate the contribution of these two influences to the morphological development of antennal-lobe neurons, we placed the neurons in cell culture. Antennal-lobe neurons were dissociated from normal and chronically unafferented lobes at different stages of development and were exposed to different doses of hormone. Six neuronal cell types with distinctive and stable morphologies appeared in cultures from all stages of pupal development. Morphological changes in these neuronal types were examined quantitatively by comparison of the total length and number of branches. We found that 20-hydroxyecdysone had little direct effect on the morphological development of antennal-lobe neurons, but brief exposure to sensory axons in vivo prior to dissociation significantly enhanced subsequent outgrowth in culture.