Hyperpolarization-Activated Currents Regulate Excitability in Stellate Cells of the Mammalian Ventral Cochlear Nucleus

Abstract

Rodrigues, Aldo Rogelis A. and Donata Oertel. Hyperpolarizationactivated currents regulate excitability in stellate cells of the mammalian ventral cochlear nucleus. J Neurophysiol 95: 76 -87, 2006. First published September 28, 2005 doi:10.1152/jn.00624.2005. The differing biophysical properties of neurons the axons of which form the different pathways from the ventral cochlear nucleus (VCN) determine what acoustic information they can convey. T stellate cells, excitatory neurons the axons of which project locally and to the inferior colliculus, and D stellate cells, inhibitory neurons the axons of which 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 (I h ) reversed at -40 mV, was activated at voltages negative to Ϫ60 mV, and half-activated at approximately Ϫ88 mV; maximum hyperpolarization-activated conductances (g h max ) were 19.1 Ϯ 2.3 nS in T and 30.3 Ϯ 2.6 nS in D stellate cells (means Ϯ SE). Activation and deactivation were slower in T than in D stellate cells. In both types of stellate cells, 50 M 4(N-ethyl-N-phenylamino)1,2-dimethyl-6-(methylamino) pyridinium chloride (ZD7288) and 2 mM Cs ϩ blocked a 6-to 10-fold greater conductance than the voltage-dependent g h determined from Boltzmann analyses at -62 mV. The voltageinsensitive, ZD7288-sensitive conductance was proportional to g h max and g input . 8-Br-cAMP shifted the voltage dependence of I h 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 g h with a Q 10 of 1.3 and slowed the kinetics with a Q 10 of 3.3.

Activation state of the hyperpolarization-activated current modulates temperature-sensitivity of firing in locus coeruleus neurons from bullfrogs

“…In LC neurons E h was Ϫ40.7 Ϯ 3.2 mV (n ϭ 12). This mean for E h is similar to values obtained for I h /HCN channels in mammalian cells (1,3,43).…”

“…Similar to the methods of others (20,36,43), steady-state voltage dependence of Ih activation and maximal conductance was determined by eliciting tail currents from a series of prepulse steps (Ϫ52 to Ϫ142 mV) for 3 s and then measured immediately following a step to Ϫ92 mV (see Fig. 3).…”

Electrophysiological Properties of Octopus Neurons of the Cat Cochlear Nucleus: an In Vitro Study

“…Resting membrane potentials and action potentials were comparable, but again, input resistances were larger and time constants were longer in stellate and bushy cells in comparison to those of mice (Rodrigues and Oertel 2006;Cao et al 2007;Wu and Oertel 1987). In the present study, in response to depolarizing current pulses, stellate cells of kittens had a similar response pattern to those of mice, firing trains of action potentials with constant interspike intervals.…”

“…In the present study, in response to depolarizing current pulses, stellate cells of kittens had a similar response pattern to those of mice, firing trains of action potentials with constant interspike intervals. Increases in current strength increased the number of action potentials (Wu and Oertel 1984;Rodrigues and Oertel 2006;Ferragamo et al 1998). Similarity between responses of bushy cells of kittens and mice to depolarizing and hyperpolarizing current injections were also striking.…”

Hyperpolarization-Activated Cation Channels: From Genes to Function

“…However, in some neurons, a large I INS lacking timedependent I SS has been reported (12,100,326). Speculations on the nature of I INS reach from models where this current represents a leak conductance or an experimental artifact to models in which I INS is caused by a second pore that is found within the same HCN channel that produces I SS or a second channel population associated with HCN channels (236,237,312).…”