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1 Physiology, University of Wisconsin, Madison, Madison, WI, USA
* To whom correspondence should be addressed. E-mail: oertel{at}physiology.wisc.edu.
The differing biophysical properties of neurons whose axons form the different pathways from the ventral cochlear nucleus (VCN) determine what acoustic information they can convey. T stellate cells, excitatory neurons whose axons project to locally and to the inferior colliculus, and D stellate cells, inhibitory neurons whose axons project to the ipsi- and contralateral cochlear nuclei, fire tonically when they are depolarized and, unlike other cell types in the VCN, their firing rates are sensitive to small changes in resting currents. In both types of neurons the hyperpolarization-activated current (Ih) reversed at -40 mV, was activated at voltages negative to -60 mV and half-activated at ~-88 mV; maximum hyperpolarization-activated conductances (gh max) were 19.1 ± 2.3 nS in T and 30.3 ± 2.6 nS in D stellate cells. Activation and deactivation were slower in T than in D stellate cells. In both types of stellate cells 50 µM ZD7288 and 2 mM Cs+ blocked a six- to ten-fold greater conductance than the voltage-dependent gh determined from Boltzmann analyses at -62 mV. The voltage-insensitive, ZD7288-sensitive conductance was proportional to gh max and ginput. 8-Br-cAMP shifted the voltage-dependence of Ih in the depolarizing direction, increased the rate of activation and slowed its deactivation in both T and D stellate cells. Reduction in temperature did not change the voltage-dependence but reduced the maximal gh with a Q10 of 1.3 and slowed the kinetics with a Q10 of 3.3.
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