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Mechanisms Underlying Subthreshold and Suprathreshold Responses in Dorsal Cochlear Nucleus Cartwheel Cells
| Title: | Mechanisms Underlying Subthreshold and Suprathreshold Responses in Dorsal Cochlear Nucleus Cartwheel Cells |
| Author: | Tong, Mingjie |
| Description: | Cartwheel cells (CWCs) are a group of interneurons in the dorsal cochlear nucleus (DCN). Unlike other DCN neurons, which respond to stimuli with simple spikes, or trains of individual action potentials, CWCs respond to suprathreshold stimuli with complex spikes, rapid bursts of action potentials superimposed on a slow depolarization, or a combination of simple and complex spikes. In vitro whole-cell current clamp recordings from young rats (P11 – P15) show that CWCs respond to brief suprathreshold stimuli with complex spikes or simple spikes followed by afterdepolarizations (ADPs); and to subthreshold stimuli with subthreshold depolarizations (SDPs). Although complex spikesand ADPs are produced by Ca^2+ currents, SDPs are unaffected by Ca^2+ current antagonists but are substantially depressed by the Na^+ channel antagonist TTX. Voltage clamp recordings reveal that SDPs are produced by a persistent Na^+ current activating below spike threshold in CWCs. A hyperpolarization-activated inward current (Ih) is shown to contribute to the repolarization of SDPs; and voltage-gated K^+ currents, including transient and Ca^2+-activated K^+ currents contribute to the repolarization of suprathreshold responses in CWCs. Computational simulations demonstrated that SDPs are produced by persistent Na^+ currents; furthermore, these currents are required for the activation of high-threshold Ca^2+ channels during suprathreshold responses to produce complex spikes in response to brief suprathreshold stimuli. Delayed-rectifier, transient and Ca^2+-activated K^+ currents contribute to the repolarization of complex spikes and increase of maximal conductances in any of three K^+ currents converts complex spikes into simple spikes. In contrast, removal of the hyperpolarization-activated inward current Ih increases the amplitude and duration of SDPs, but otherwise has little effect on suprathreshold responses of CWCs. These results demonstrate that a combination of voltage-gated conductances that activate over a range of subthreshold and suprathreshold membrane potentials contribute to the unique electrophysiologic responses of CWCs. |
| Permanent Link: |
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1133806721
http://hdl.handle.net/2374.OX/19401 |
| Date: | 2005 |
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