Destruction or dysfunction of the dopaminergic neurons of the mesencephalon is believed to underlie a variety of disorders of movement, motivation and mentation, including Parkinson's disease, and schizophrenia. In those disorders, not accompanied by death of the dopaminergic neurons, it is likely that a disruption of the activity patterns of those neurons is an important component of the pathology. Dopaminergic neurons fire in stereotyped modes, controlled largely by calcium currents and by calcium-dependent potassium currents. We will employ calcium-imaging of single neurons injected intracellularly with calcium indicator during whole cell recording in slices visualized by infra-red DIC microscopy. This will allow simultaneous detection of membrane potential at the cell bodies of the dopaminergic neurons and detection of calcium entry in the cell body and dendritic tree. Current models of firing pattern generation by dopaminergic neurons differ in their predictions of the location of calcium entry, and our experiments allow a critical test of these models. Synaptic excitation and local dendritic excitation by applied glutamate or glutamate agonists will be used to test for the local control of dendritic calcium currents by subthreshold excitatory currents. We will measure how action potentials propagating into dopamine cell dendrites contribute to slow oscillations in dendritic calcium levels and resulting calcium dependent potassium current that ultimately control the output firing pattern. Experiments will examine how the extent of dendritic spike propagation regulates pacemaker firing rate and whether modulation of dendritic spike propagation contributes to irregular and burst firing. Calcium channel blockers will be used in conjunction with calcium imaging to establish the types and distribution of calcium channels that contribute to voltage dependent calcium imaging to establish the types and distribution of calcium channels that contribute to voltage-dependent calcium entry in these cells. Finally, immunocytochemistry using antibodies against clones of channel subtypes will also be used to examine the distribution of calcium and calcium dependent potassium channels in the dendritic arbors of dopamine cells and results from will be compared to those from calcium imaging.
