Effects of the ecdysoneless mutant on synaptic efficacy and structure at the neuromuscular junction in Drosophila larvae during normal and prolonged development

Hormonal regulation in development and maintenance of synaptic transmission involves examination of both the presynaptic and postsynaptic components a nd a system in which the hormones can be controlled. We used the ecdysonele ss heat-sensitive mutation (1(3)ecd(l)11(3)ecd(l)) of Drosophila to provide the ability to regulate endogenous ecdysone production at various larval s tages. In conjunction, we used the neuromuscular junctions of Drosophila si nce they offer the advantage of assessable preparations for both morphologi cal and physiological measures. The growth in the Ib and Is motor nerve ter minals and the corresponding muscle 6 in segment 4 of the larval Drosophila throughout the third instar stage in the presence of normal and a much red uced endogenous ecdysone level was investigated. Muscle 6 and the motor ner ve terminals parallel in growth throughout the third instar. The nerve term inals increase in length and varicosity number, thus providing an increase in the number of synaptic release sites. The ecdysoneless larvae also show an increase in muscle size, however the Is and Ib motor nerve terminals do not mature to the extent of the wild-type ecdysone producing flies. The mot or nerve terminal length is shorter with fewer numbers of varicosities per terminal. In spite of a shorter nerve terminal and fewer varicosities, with an increasing muscle fiber, the compound excitatory junctional potentials of Ib and Is in the ecdysoneless flies are larger, which is suggestive of s ynaptic structural modification. This study demonstrates ecdysone's role in modifying nerve terminal develop ment and neuromuscular junction function. (C) 2001 IBRO. Published by Elsev ier Science Ltd. All rights reserved.