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This Article Full Text Full Text (PDF) All Versions of this Article: 98/4/1953    most recent 00427.2007v1 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 Yang, S. Articles by Feng, A. S. Search for Related Content PubMed PubMed Citation Articles by Yang, S. Articles by Feng, A. S.

Heterogeneous Biophysical Properties of Frog Dorsal Medullary Nucleus (Cochlear Nucleus) Neurons

Department of Molecular and Integrative Physiology and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois

Submitted 15 April 2007; accepted in final form 5 April 2007

The cochlear nucleus (CN) in mammals, or its counterpart in birds, has multiple subdivisions each containing distinct morphological and functional (i.e., temporal discharge patterns and biophysical properties) cell types that project to different auditory nuclei in the brain stem in parallel. The analogous structure in frogs, the dorsal medullary nucleus (DMN), is a single phylogenetically older structure with no subdivision. Similar to the CN, the DMN has complex cytoarchitecture and contains neurons with diverse morphological phenotypes, but whether these cell types possess distinct biophysical characteristics, like their counterparts in mammals and avians, is unclear. Here we show that DMN neurons in young adult northern leopard frogs (Rana pipiens pipiens) possess heterogeneous biophysical properties. There are four major biophysical phenotypes on the basis of the unit's response (i.e., its temporal firing pattern) to depolarizing currents: onset, phasic-burst, sustained-chopper, and adapting. These cells have distinct membrane input resistances and time constants, spike shapes, current-voltage relationships, first-spike latencies, entrainment characteristics, and ionic compositions (i.e., low-threshold potassium current, I_kl, and hyperpolarization-activated current, I_h). Furthermore, these phenotypes correspond to cells' dendritic morphologies, and they bear similarities and differences to those found in the mammalian CN. The similarities are remarkable considering that amphibians are a distinct evolutionary lineage from birds and mammals.