Work over the last twenty-five years has identified a remarkable number of proteins that form ion channels in the mammalian brain. In many cases, we now have detailed information about the molecular characteristics of the channels. However, we understand much less about how the many types of ion channels present in a single central neuron work together to produce the firing patterns characteristic of that particular neuron. The goal of the proposed research is to understand how the firing properties of particular central neurons are produced by particular combinations of ion channels. The work will combine current clamp recordings of action potential firing together with voltage-clamp analysis of the ion channels regulating both subthreshold and suprathreshold electrical properties. One project will examine the channels that are important for generating and regulating spontaneous firing of midbrain dopaminergic neurons, including an exploration of differences between dopaminergic neurons in substantia nigra pars compacta and the ventral tegmental area. The role of calcium entry though different types of calcium channels will be evaluated, and we will test the hypothesis that electrogenic current from the sodium-calcium exchanger is important for pacemaking. A second project will determine the ion channels important for enabling very rapid firing in cerebellar Purkinje neurons, a model system for other fast-spiking neurons in the brain. A third project will explore how active subthreshold conductances interact with excitatory and inhibitory synaptic potentials to amplify or dampen their effects. An emerging common theme is that some conductances (e.g. voltage-dependent sodium channels and A-type potassium channels) have dual roles, generating both large transient currents determining spike shape and also very small subthreshold currents between spikes that are important for determining firing patterns. Understanding the channel gating mechanisms that integrate these two functions is a major challenge. Recordings will be made both from intact neurons in brain slices and from acutely dissociated neurons, where high-quality voltage clamp of large currents is possible. Dynamic clamp and action potential clamp techniques will link current clamp and voltage clamp recordings. Understanding the mechanisms involved in regulating the excitability of central neurons will help in understanding the normal function of the nervous system as well as pathophysiological states resulting from epilepsy, Parkinson's disease, and other disorders.
The goal of the research is to understand the basic mechanisms that control electrical activity of neurons in the mammalian brain. The processes being investigated are not only critical for understanding the normal function of the brain but also for understanding pathophysiological states such as epilepsy, where electrical activity is excessive and uncontrolled. A major part of the project will characterize electrical activity in midbrain dopaminergic neurons, whose death is the causative event in Parkinson's disease. Specifically, we will analyze modes of entry of calcium into dopaminergic neurons and determine what specific ion channels are important for calcium entry, which has been hypothesized to be the proximate cause of cell death in Parkinson's disease. Understanding the role of calcium entry in the function of dopaminergic neurons could suggest particular pharmacological targets for slowing or preventing cell death while maintaining electrical function of the neurons.
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