DEVELOPMENTAL PLASTICITY OF NEUROPEPTIDE EXPRESSION IN MOTONEURONS OFTHE MOTH, MANDUCA-SEXTA - STEROID-HORMONE REGULATION

Developmental changes in the expression of a FMRFamide-like( Phe-Met-A rg-Phe-NH2) peptide or peptides in motoneurons of the tobacco hornworm , Manduca sexta, were demonstrated using immunohistochemical technique s. The onset of FMRFamide-like immunoreactivity (FLI) was gradual duri ng larval growth but by the final larval stage, immunoreactivity was p resent in the majority of motoneurons. FLI then declined during metamo rphosis and was absent in all identified adult motoneurons. We used a novel in vivo culture system to demonstrate that the steroid hormone, 20-hydroxyecdysone, regulates the loss of FLI in motoneurons during me tamorphosis, The small commitment peak of ecdysteroid appears to shut off the program of neuropeptide accumulation that is characteristic of the larval state of the motoneurons. The prepupal peak of steroid the n causes the rapid loss of stored FLI, This steroid-induced change in the neuropeptide content of motoneurons may reflect major changes in n euromuscular functions between the larval and adult stages. (C) 1996 J ohn Wiley & Sons, Inc.