Ultrastructural techniques have been conspicuously under-utilized in studies of neural development in invertebrates, despite their success in a few such studies, particularly on visual systems. The proposed research is an ultrastructural examination of developing antennal lobes in a moth. The lobes are the brain's centers for processing olfactory information from the antennae. Both the antennae and the antennal lobes arise de novo during postembryonic development. A previous study of the histological development of the antennal lobe and of the maturation of lobe synapses during the latter half of a dult development (Tolbert et al., J. Neuroscience, in press) indicated that many important cellular events occur during the first half of development. The proposed study focuses on that early development. One aim is to unravel some of the influences that first-order neurons exert on second-order neurons during development. To this end, I will find out when synapses begin to be laid down in the lobe, and in particular, when the sensory axons from the antenna form synapses, and compare this with the timetable of appearance of morphological, biochemical and electrophysiological traits. I will also compare the fine structure of normal lobes with that of lobes that have been deprived of antennal-nerve input throughout their development. Another aim is to continue to chronicle the series of fine structural steps involved in synaptogenesis in this accessible system. Experiments will involve electron microscopy of normal and uninnervated antennal lobes as well as of material in which individual neurons or clusters of axons have been filled with electron-opaque markers. It is expected that in the long run, elucidation of the mechanisms guiding development of this simple system will aid us to understand the development of more complicated mammalian neural networks.