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This Article Full Text Full Text (PDF) All Versions of this Article: 99/5/2066    most recent 00556.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Endo, T. Articles by Isa, T. Search for Related Content PubMed PubMed Citation Articles by Endo, T. Articles by Isa, T.

Dendritic I_h Ensures High-Fidelity Dendritic Spike Responses of Motion-Sensitive Neurons in Rat Superior Colliculus

¹Division of Behavioral Development, Department of Developmental Physiology, ²Division of Cerebral Structure, Department of Cerebral Research, and ³Section of Mammalian Transgenesis, Center for Genetic Analysis of Behavior, National Institute for Physiological Sciences; and ⁴The Graduate University for Advanced Studies, Okazaki, Japan

Submitted 18 May 2007; accepted in final form 22 January 2008

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels that generate I_h currents are widely distributed in the brain and have been shown to contribute to various neuronal functions. In the present study, we investigated the functions of I_h in the motion-sensitive projection neurons [wide field vertical (WFV) cells] of the superior colliculus, a pivotal visual center for detection of and orientating to salient objects. Combination of whole cell recordings and immunohistochemical investigations suggested that HCN1 channels dominantly contribute to the I_h in WFV cells among HCN isoforms expressed in the superficial superior colliculus and mainly located on their expansive dendritic trees. We found that blocking I_h suppressed the initiation of short- and fixed-latency dendritic spike responses and led instead to long- and fluctuating-latency somatic spike responses to optic fiber stimulations. These results suggest that the dendritic I_h facilitates the dendritic initiation and/or propagation of action potentials and ensures that WFV cells generate spike responses to distal synaptic inputs in a sensitive and robustly time-locked manner, probably by acting as continuous depolarizing drive and fixing dendritic membrane potentials close to the spike threshold. These functions are different from known functions of dendritic I_h revealed in hippocampal and neocortical pyramidal cells, where they spatiotemporally limit the propagations of synaptic inputs along the apical dendrites by reducing dendritic membrane resistance. Thus we have revealed new functional aspects of I_h, and these dendritic properties are likely critical for visual motion processing in these neurons.