The goal of this project is the examination of regenerative calcium currents in central nervous system neurons grown in tissue culture and the effects of catecholamines on these currents. Calcium-dependent action potentials have been demonstrated in both central and peripheral vertebrate neurons in the last few years. In molluscan nerve cells, heart tissue, and peripheral nervous systems, some of the catecholamines have been found to act by modifying the voltage dependent properties of the calcium channel. Given the importance of catecholamines to normal brain function and their implication in a variety of neurologic and psychiatric disorders, it is critical to define the mechanism of action of these transmitters. Several laboratories have suggested that in vertebrate neurons calcium action potentials may be preferentially located on dendrites. Recently we have demonstrated the presence of calcium spikes in mitral cells of the olfactory bulb. These cells are a favorable system for the study of calcium currents and their modulation since 1) they can be maintained in dispersed cell tissue culture, 2) they have long dendrites which participate in reciprocal synapses, and 3) the bulb contains many defined populations of monoaminergic cells and terminals. Neurons from the olfactory bulb of young rats will be used in this study. Electrophysiological studies will proceed in two phases. In the first, neurons will be penetrated with a single microeletrode and the presence and characteristics of calcium dependent action potentials will be determined. Catecholamines will then be added to the bath an/or iontophoresed directly on the cells, and effects on the calcium dependent action potential will be noted (e.g. rate of rise, duration, amplitude). In the second phase, the newly developed technique of voltage clamping of excised patches of membranes will be used to study the kinetic properties of the calcium current in detail at a single or multiple channel level. It will then be possible to study the modulation of this current by catecholamines at a more basic level than has so far been possible.
