Differential contribution of the subthreshold operating currents IT, Ih, and IKir to the resonance of thalamocortical neurons

Membrane potential oscillations of thalamocortical (TC) neurons are believed to be involved in the generation and maintenance of brain rhythms that underlie global physiological and pathological brain states. These membrane potential oscillations depend on the synaptic interactions of TC neurons and their intrinsic electrical properties. These oscillations may be also shaped by increased output responses at a preferred frequency, known as intrinsic neuronal resonance. Here, we combine electrophysiological recordings in mouse brain slices, modern pharmacological tools, dynamic clamp, and computational modeling to study the ionic mechanisms that generate and modulate TC neuron resonance. We confirm findings of pioneering studies showing that most TC neurons display resonance that results from the interaction of the slow inactivation of the low-threshold calcium current I_T with the passive properties of the membrane. We also show that the hyperpolarization-activated cationic current I_h is not involved in the generation of resonance; instead it plays a minor role in the stabilization of TC neuron impedance magnitude due to its large contribution to the steady conductance. More importantly, we also demonstrate that TC neuron resonance is amplified by the inward rectifier potassium current I_Kir by a mechanism that hinges on its strong voltage-dependent inward rectification (i.e., a negative slope conductance region). Accumulating evidence indicate that the ion channels that control the oscillatory behavior of TC neurons participate in pathophysiological processes. Results presented here points to I_Kir as a new potential target for therapeutic intervention.NEW & NOTEWORTHY Our study expands the repertoire of ionic mechanisms known to be involved in the generation and control of resonance and provides the first experimental proof of previous theoretical predictions on resonance amplification mediated by regenerative hyperpolarizing currents. In thalamocortical neurons, we confirmed that the calcium current I_T generates resonance, determined that the large steady conductance of the cationic current I_h curtails resonance, and demonstrated that the inward rectifier potassium current I_Kir amplifies resonance.

Electrophysiological characterization of Müller cells from the ischemic retina of mice deficient in the leukemia inhibitory factor

Leukemia inhibitory factor (LIF) is a cytokine that exerts different effects in the nervous system. It is involved in neuronal injuries and diseases and is assumed to be neuroprotective and to regulate reactive gliosis. In LIF-deficient (LIF^-/-) mice, expression of glial fibrillary acidic protein in retinal Müller glial cells as a hallmark of reactive gliosis is suppressed during retinal degenerations. Here, we detected expression of LIF and its receptors in Müller cells of the murine retina. Moreover, electrophysiological alterations of Müller cells 7 days after transient retinal ischemia were studied by the patch-clamp technique. The amplitude of inward currents in Müller cells from the postischemic retina was reduced to 51% in wild type and to 70% in LIF^-/- mice. This demonstrates that decrease of inward currents takes place in reactive Müller cells even in the absence of LIF.