Three projects are proposed. In the first, single developing rat sympathetic neurons will be cocultured with cardiac myocytes in microcultures. The neurons will be subjected to various concentrations of medium conditioned by non-neuronal cells, and the time course of the transition from adrenergic to dual-function to cholinergic status will be followed by repeated physiological assays. The fine structure of neurons at various stages in the transition will be investigated. In the second project, the changing character of the junctions with cardiac myocytes will be investigated with several fine structural methods. In the third project, the electrophysiological and pharmacological properties of dissociated smooth muscle cells of the developing rat iris will be compared with the properties of sphincter muscle cells in the intact iris of the adult rat.