Electrophysiological and biochemical experiments will be performed on sympathetic neurons dissociated from superior cervical ganglia of newborn rats or chick embryos and grown in: 1) microcultures i.e., cultures consisting of small (less than 300 microns in diameter) islands of a substratum such as collagen, non-neuronal cells, etc. and one or a few (less than 5) neurons; 2) mass cultures containing many thousands of nerve cells either alone or with non-neuronal cells. In electrophysiological experiments microelectrode techniques will be used to investigate synaptic and electrical properties of the neurons developing in culture. The electrophysiological properties of the neurons will include among others: a) the sodium and calcium component of the action potential; b) sodium inactivation potassium permeability mechanisms controlled in calcium and/or voltage; c) the ability of the neurons to fire repetitively to a maintained depolarization (accommodation); d) TTX-sensitive base-line noise; and e) acetylcholine noise fluctuations. Preliminary biochemical experiments will be performed to determine whether transmitter production and certain electrophysiological properties are coordinately expressed. The major objectives of the research are: 1) to characterize as quantitatively as possible the electrophysiological development of sympathetic neurons grown in culture in the absence of other cell types; and 2) to determine in what way and to what extent this development is influenced by the presence in the culture of other cell types such as cardiac muscle (potential target cells), skeletal muscle, spinal cord (presynaptic neurons), fibroblasts, or glia. In this way influences of cellular associations which affect the electrophysiological development of sympathetic neurons and which would otherwise be difficult or impossible to detect in vivo, might be uncovered.