title: Transgenic mice expressing a fluorescent in vivo label in a distinct subpopulation of neocortical layer 5 pyramidal cells.
abstract: The neuronal components of cortical circuits have been characterized on the basis of their morphological and functional properties, and further refined by correlation of marker proteins with particular cell types. This latter approach has been very fruitful for GABA-containing neurons, but comparable diagnostic markers for subpopulations of excitatory pyramidal cells have been more elusive. An emerging new approach consists of transgenic mice that express fluorescent proteins under the control of promoters that are active in specific cell types. Here, we analyzed a line of transgenic mice that carries a transgene consisting of regulatory sequences of the potassium channel Kv3.1 and enhanced yellow fluorescent protein (EYFP). In these mice, a set of neurons in neocortical layer 5 expresses high levels of the transgenic marker protein. EYFP-expressing, and nonexpressing layer 5 cells were easily identified in living tissue under conditions suitable for patch-clamp electrophysiology. By using immunolabeling, retrograde Fast Blue labeling and electrophysiological recordings with biocytin injections, we identified the fluorescent neurons as a population of pyramidal cells with distinct morphological and electrophysiological properties when compared with nonfluorescent neighboring layer 5 pyramidal cells. The most prominent morphological difference between these two populations was a much smaller number of apical oblique dendrites in EYFP-positive as compared with the EYFP-negative cells. The most prominent electrophysiological feature was a steady spike frequency adaptation in EYFP-positive cells, whereas EYFP-negative cells responded to a depolarizing current injection with a closely spaced spike doublet followed by constant frequency firing. The in vivo labeled transgenic mice provide an experimental tool for further functional differentiation of these populations of layer 5 pyramidal cells.
authors.affiliation: Laboratory for Neuronal Circuit Dynamics, RIKEN Brain Science Institute, Wako-shi, Saitama 351-0198, Japan.
authors.forename: Walther
authors.initials: W
authors.lastname: Akemann
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Zhong
authors.forename: Noritaka
authors.initials: N
authors.lastname: Ichinohe
authors.forename: Kathleen S
authors.initials: KS
authors.lastname: Rockland
authors.forename: Thomas
authors.initials: T
authors.lastname: Knöpfel
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000578:Amidines; D000818:Animals; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D048430:Cell Shape / Q000502:physiology; D003712:Dendrites / Q000502:physiology / Q000648:ultrastructure; D004558:Electric Stimulation; D008164:Luminescent Proteins / Q000096:biosynthesis / Q000235:genetics*; D008239:Lysine / Q000031:analogs & derivatives*; D051379:Mice; D008822:Mice, Transgenic; D019579:Neocortex / Q000166:cytology* / Q000502:physiology; D009479:Neuropeptides / Q000235:genetics*; D018408:Patch-Clamp Techniques; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics*; D017966:Pyramidal Cells / Q000166:cytology* / Q000378:metabolism / Q000502:physiology; D051670:Shaw Potassium Channels; D013194:Staining and Labeling / Q000379:methods*
chemical_list: D000578:Amidines; D001426:Bacterial Proteins; D008164:Luminescent Proteins; D009479:Neuropeptides; D024642:Potassium Channels, Voltage-Gated; D051670:Shaw Potassium Channels; C031455:diamidino compound 253-50; C054562:yellow fluorescent protein, Bacteria; C013411:biocytin; D008239:Lysine