The goal of this study is to determine the central regulators of neuronal function using cultured superior cervical ganglion (SCG) neurons as models. The focus of this proposal is to examine the regulatory interrelationship between neuronal peptide and classical transmitter expression, and in particular, the expression of neuropeptide Y (NPY) and catecholamines (CA) in the SCG. Several questions examining the factors and environmental cues that coordinately or independently regulate SCG NPY and catecholamine (CA) expression will be addressed, including (1) What are the regulators of neuronal NPY expression? (2) Are NPY and CA expression altered by the same regulatory factors? (3) How does neuronal phenotype affect NPY expression? (4) Do specific target tissues regulate neuronal NPY expression? (5) What are the cellular mechanisms of altered neuropeptide expression? Several parameters will be used to characterize culture NPY/CA content and biosynthesis including radioimmunoassay, biosynthetic labeling techniques, Northern blot analysis, and HPLC/electrochemical detection techniques. The effects of neuronal input onto SCG cells, that is stimulation of second messenger system, calcium flux, depolarization, and specific receptor- mediated stimulation on SCG NPY production will be examined and correlated to CA production levels. How factors that change SCG neurotransmitter expression from catecholaminergic to cholinergic phenotype alter NPY expression will be examined. In coculture studies, the effects of SCG target cells on neurotransmitter/neuropeptide expression will be determined. These studies will have significant implications in establishing how complex and integrated signals direct normal neuronal development and physiological functions.