The three participating research groups share a common interest in understanding the postembryonic development of neurons, the neural systems in which they function, and the muscles they control. Growing collaboration among these groups over the past three years and increasing mutual focus on the mechanisms that control the developmental plasticity of nerve and muscle cells have led to the emergence of this new Program Project. Among the research areas represented by these laboratories are: the roles and mechanisms of short-distance and contact-mediated intercellular influences in neural development; hormonally regulated, postembryonic differentiation and respecification of sensory and motor neurons and interneurons; ultrastructural and physiological aspects of synapse formation in developing neural systems; correlation and coordination of cellular, physiological, and neurochemical events in neurogenesis; the role of glial cells in the development of organized neuropil in the central nervous system; and developmental, physiological, anatomical, and molecular studies of olfactory, visual, mechanosensory, and motor systems. The participants propose to mount multidisciplinary, highly collaborative investigations of mechanisms underlying hormonal and trans- cellular regulation of the survival and development of nerve cells and muscles during postembryonic life. The five component projects in this program project probe for cellular and physiological mechanisms of: (1) influences of primary-sensory neurons, glial cells, and development- regulating hormones and neurotransmitters ont he development of arborizations and voltage- and ligand-gated membrane ion channels in olfactory interneurons in primary cell culture; (2) steroid-hormonal regulation of development of identified motor neurons in primary cell culture; (3) influences of steroid hormones on cellular, neurochemical, and systemic characteristics of the first-order olfactory center in the brain. All of the proposed studies are based on the use of non-vertebrate model systems that are economical, readily available, and experimentally tractable. Because they have been extensively studied by many investigators, including the participants in this program project, the insect preparations to be used in the proposed studies are especially well understood and favorable for these project, the insect preparations to be used in the proposed studies are especially well understood and favorable for these experiments. Taking advantage of this background, the component projects focus on neurons and glial cells that are identifiable as individuals or as specific functional types from animal. The basic mechanisms of development have been conserved during evolution. We expect, therefore, that information obtained in these projects about neural and muscular development in insects will illuminate related phenomena in other animals including human beings.