The main aim of this project is to provide a clearer understanding of the differentiation process by which cell populations acquire their neurochemical properties. The cell populations to be studied are two components of the sympathoadrenal system, the neurons from the paravertebral sympathetic ganglia and the adrenal gland chromaffin cells. These cells differentiate from common precursors in the neural crest into neurons and chromaffin cells that synthesize neuroactive substances such as dopamine, norepinephrine, epinephrine, enkephalin, somatostatin, vasoactive intestinal polypeptide neuropeptide Y and possibly serotonin. Environmental factors have been shown to determine and modulate the acquisition and expression of several neurotransmitter properties in the mammalian sympathoadrenal system. However, recent results from our group indicate that the process of differentiation and acquisition of biochemical traits by sympathetic neurons differs between birds and mammals. In order to better understand the biochemical differentiation process we will use the avian model. We propose to (1) characterize and quantitate the expression of monoamines in the developing chicken through embryonic to post-hatched stages and compare it to our neuropeptide development data (2) test the effect of several environmental factors in vivo and in vitro on the expression of neuroactive substances, both monoamines and neuropeptides. Radioimmunoassays will be used to quantify the amount of neuropeptides and high performance liquid chromatography together with electrochemical detection will be used to identify and quantify the amount of monoamines in the animal and in cultures. Immunocytochemical and neurochemical techniques will be used to identify and quantify the number of cells showing different phenotypes. The results should lead to a better understanding of how cells from the endocrine or nervous systems differentiate into cells expressing specific neurotransmitters, neuropeptides or peptide hormones.