Depression of synaptic efficacy in high- and low-output Drosophila neuromuscular junctions by the molting hormone (20-HE)

The molt-related steroid hormone, 20-hydroxyecdysone (20-HE), was applied t o muscles 6 and 7 of third instar larval of Drosophila melanogaster neuromu scular junction preparations to examine if rapid, nongenomic responses coul d be observed as was shown recently to occur in crustacean neuromuscular ju nctions. At a dose of 10 mu M, the excitatory junction potentials were redu ced in amplitude within minutes. To elucidate the site of action of the hor mone, focal-macropatch recordings of synaptic currents were obtained over t he neuromuscular junctions. The results showed that the high-output (Is) an d the low-output (Ib) motor nerve terminals, which innervate muscles 6 and 7, released fewer synaptic vesicles for each stimulation while exposed to 2 0-HE. Because the size and shape of synaptic currents from spontaneous rele ases did not change, the effects of the 20-HE are presynaptic. The rapid ef fects of this hormone may account in part for the quiescent behavior associ ated with molts among insects and crustaceans.