Innervation of the ring gland of Drosophila melanogaster

In insects, peptidergic neurons of the central nervous system regulate the synthesis of the main developmental hormones. Neuropeptides involved in thi s neuroendocrine cascade have been identified in lepidopterans and dictyopt erans. Since these organisms are not suitable for genetic research, we iden tified peptidergic brain neurons innervating the ring gland in Drosophila m elanogaster. In larvae of Drosophila, ecdysteroids and juvenile hormones ar e produced by the ring gland, which is composed of the prothoracic gland, t he corpus allatum, and the corpora cardiaca. Using the GAL4 enhancer trap s ystem, we mapped those neurons of the central nervous system that innervate the ring gland. Eleven groups of neurosecretory neurons and their target t issues were identified. Five neurons of the lateral protocerebrum directly innervate the prothoracic gland or corpus allatum cells of the ring gland a nd are believed to regulate ecdysteroid and juvenile hormone titers. Axons of the circadian pacemaker neurons project onto dendritic fields of these f ive neurons. This connection might be the neuronal substrate of the circadi an rhythms of molting and metamorphosis in Drosophila. Most of the neurons presented here have not been described before. The enhancer trap lines labe ling them will be valuable tools for the analysis of neuronal as well as ge netic regulation in insect development. J. Comp. Neurol. 431:481-491, 2001. (C) 2001 Wiley-Liss, Inc.